Self-assembled lyotropic liquid crystal interlayer regulated interfacial polymerization for modulating structure and performance of nanofiltration membranes

Domain: chemistry
Published: 2026-01-07
Editorial outcome: major_revision

Abstract
Nanofiltration(NF)isakeymembraneseparationtechnologythatispromising
invariouschemicalandenvironmentalapplications.Theneedforhigh-
performancethin-filmcomposite(TFC)NFmembranes,particularlythosewith
enhancedsaltselectivityandfoulingresistance,necessitateseffectivestrate-
giesforoptimizingtheirfabricationprocesses—interfacialpolymerization(IP).
Inthisstudy,wedemonstrateaneffectivestrategyforfine-tuningofIPprocess
throughintegratinglyotropicliquidcrystals(LLCs),whichself-assembleinto
aninterlayerwithhexagonalstructureonsubstrates.PerformingIPontheLLC-
coatedsubstratesleadstotheformationofpolyamidewithcharacteristic
tubularstructure.ComparedwithconventionalTFCmembranes,theLLC-
modulatedTFCmembranesdisplaydoubledwaterpermeabilitywhilepre-
servingcomparableNa SO selectivity,therebyachievinganenhancedwater/
2 4
saltselectivity.Moreover,thesemembranesdemonstratehighion/ionselec-
tivity(e.g.,Na+/Ca2+andLi+/Mg2+)andenhancedfoulingresistance,rendering
themhighlydesirableforvariousseparationprocesses.Furtherexploration
intointerfacialstructuresandmechanismsrevealsthepivotalroleoftheLLC-
interlayersinaffectingthediffusionofthediaminemonomer(i.e.,piperazine),
therebyresultinginthepolyamidelayerwiththedistinctivetubularstructure
andimprovedseparationproperties.Ourresultshighlightthepromiseand
potentialofutilizinginterlayerswithself-assembledstructuresforcreating
high-performanceNFmembranes.

Introduction
Nanofiltration (NF) represents a cutting-edge technology in various applications,such as water softening,lithiumextraction,
membrane separation1,2. This process utilizes membrane materi- andsolventseparation4–7.
alsfeaturingporesizesof~1nm,enablingeffectiveseparationof The forefront of NF membrane technology relies on the devel-
solutes on a sub-nanometer scale3. As such, NF membranes opmentofthin-filmcomposite(TFC)membranes8.Thesemembranes
exhibit unparalleled selectivity towards both ionic and organic consistofapolyamideactivelayercreatedviainterfacialpolymeriza-
species. Such characteristic renders them practical solutions for tion(IP)ontopofaporoussubstrate9–12.DespitetheadvanceofNF
process,developingNFmembraneswithenhancedselectivityremains bicontinuous cubic structures, leading to the formation of inter-
challengingduetotheselective-permeabilitytrade-off3,13.Thatis,an penetratingnetworks.Thesenetworksexhibitedaneffectiveporesize
increaseinwaterpermeabilityisassociatedwithacorrespondingrise of0.75nm,whichwascapableofhighsaltrejectionwhiledisplaying
in salt permeability, thereby leading to a reduction in membrane comparablewaterpermeabilitytothatofcommercialmembranes36.In
selectivity.Inaddition,theaccumulationoftherejectedsubstances, another study, researchers leveraged LLCs with direct cylindrical
such as organic, inorganic, or biologic compounds, on membrane mesophase (H) to fabricate NF membranes featuring hexagonally
I
surfaces poses another daunting challenge of fouling14–17. Such packedcylinders.Suchstructureenabledwaterpermeancethrough
unprecedented fouling significantly increases operating costs and the gap between cylindrical nanofibers but excluding larger-size
reducesthelifespanoftheNFmembranes.
solutesviasizeexclusion37.Whilethesestudieshighlightthepoten-
Recent studies have highlighted significant enhancement of NF tialofLLCsasaselectivelayerforthedirectfabricationofNFmem-
membraneperformancethroughintegratingnanomaterialinterlayers13,18. branes, substantial efforts are needed to systematically evaluate
These advancements involve the deposition of various nanomaterials, their performance in real-world applications, including fouling pro-
such as nanotubes19,20, nanostrand21, graphene22, or metal-organic pensity, chlorine resistance, and long-term stability39. Given the
frameworks23, onto substrates, followed by IP process to form poly- established scalability and widespread application of the interfacial
amidelayers(Fig.1a)11,24–27.Theintroductionoftheseinterlayersaltered polymerization (IP) process—the gold standard in NF membrane
physiochemicalpropertiesofthesubstrates,includingsurfacetension, manufacturing13—incorporatingLLCsasaninterlayeroffersafacileand
porosity,andmorphology.Consequently,themodifiedsubstratesfur- practical strategy for tailoring polyamide properties. This approach
ther affect IP process to form polyamide layers with high separation willenabletheeffectivemodulationofpolyamideNFmembraneswith
performance or fouling resistance28–30. However, although these inter- well-definedstructuresandenhancedperformance,moreimportantly,
layers have been shown to modulate the IP process, the relationship aligningwithindustrialrequirementsforlarge-scaleimplementation.
betweenthefundamentalpropertiesoftheinterlayerstructureandthe Inthisstudy,wedemonstrateaneffectivestrategyinregulatingIP
resulting polyamide morphology remains unclear. Moreover, the processbyincorporatinginterlayermadeofLLCs.TheLLCmolecules
mechanisticbasisbywhichinterlayerdesigninfluencespolyamideper- self-assembleintohexagonalcolumnarphases,thusgeneratinginter-
formancehasyettobesystematicallyelucidated11.Suchdiscrepancyand layerswithhighly-orderedstructureonsubstratesurface(Fig.1b).In
knowledgegapsarelargelyascribedtothefactthattheexistingstrate- thefollowingIPprocess,thepresenceoftheLLCinterlayerfacilitates
giesforconstructinginterlayersreliedonuncontrolled,freedeposition the formation polyamide layer with tubular structure and internal
processes.Asaconsequence,theresultinginterlayersoftenexhibitdis- nanocavities.EvaluatingperformanceoftheresultingTFCmembranes
ordered, non-tunable features, thereby obscuring the delineation of reveals an enhanced water/salt and ion/ion selectivity, as well as
exactmechanismsoftheinterlayersininfluencingIPprocesses.
enhancedanti-foulingproperties.Wealsocarryoutsystematicchar-
Lyotropicliquidcrystals(LLCs)areaclassofamphiphilicmole- acterization of interfacial structures and elucidate mechanisms and
culesthatcanself-assembleinwatertoformorderedstructures,such effects of the LLC interlayer in regulating IP process. Our results
as columnar, cubic, and lamellar phases. These ordered structures underscore the potential in using self-assembled interlayers in IP
could be maintained through polymerization of LLC monomers in reactionforfabricatinghigh-performanceNFmembranes.

Results
Loadingoflyotropicliquidcrystal(LLC)interlayersonsubstrate
surface
Wesynthesizedapolymerizableamphiphilicsurfactant,MA11-6-11MA,
whose chemical structure is illustrated in Fig. 1b 40. This molecule
consistofahydrophilicheadwithtwoquaternaryammoniumgroups substratealsoexhibitedthefan-liketextureunderPOM(Fig.2cand
andtwohydrophobictails,eachcontaining11carbonatoms(synthe- SupplementaryFig.7),whilethetransmissionintensityofthepristine
sizedprocedureillustratedintheSupplementaryFigs.1).TheMA11-6- PSf was undetectable (Fig. 2b). Moreover, numerous pores were
11MA/waterbinaryphasediagramillustratesthetransitionsthrough observedonthepristinePSfsurface(Fig.2d),consistentwiththepore
micellar solution (L
I
) to hexagonal columnar(H
I
), lamellar(Lα), and size of 42.8nm determined from molecular-weight cut-off (MWCO)
crystal(K)phases,asthesurfactantconcentrationincreasedfrom0to measurements(SupplementaryFig.8).Incontrast,theseporeswere
100wt% at room temperature (Supplementary Fig. 4). When mixed not observable on the surface of the LLC-coated sample (Fig. 2e),
with water at a weight ratio of 3:1, this molecule undergoes self- indicatinguniformcoverageoftheLLClayeronthesubstrate.Notably,
assemblyintoahexagonalcolumnarphaseliquidcrystal,referredas thepresenceoftheLLCinterlayerresultedinaninterfacewithsmaller-
H-LLC. Observation under polarized optical microscopy (POM) sized, uniform pores, as evident from MWCO result (Supplemen-
I
revealedadistinctfan-liketexture(Fig.2a),whichisthecharacteristic taryFig.9).
oftheH mesophasestructure.
I
FTIRspectradisplayedanewpeakat1721cm−1fortheLLC-coated
We then coated the H-LLC mixture onto a microporous poly- sample(Fig.2fandSupplementaryFig.10),attributedtothestretching
I
sulfone(PSf)support,whichwassubsequentlyusedasasubstratefor oftheestergroup(O-C=O).XPSspectraofbothpristine(Fig.2g)and
interfacial polymerization (IP) reaction. During surface coating, we LLC-coated PSf substrates (Fig. 2h) exhibited strong C signals at
1s
addedethanolintotheLLCmixturetoenhanceevenspreadingofthe 284.6eV.Deconvolutionofthispeakrevealedsub-peakscorrespond-
viscousLLCsonthesurface.BydispersingLLCinethanolatdifferent ing to C–O (286.4eV), C–C (284.6eV), and C–S (285.1eV),
concentrations and loading it onto the substrate, we obtained LLC respectively41,42.TheLLC-coatedsampleshowsadecreasedintensityof
layerswithvaryingthicknesses(SupplementaryFig.5).Specifically,the theC–Speak,acharacteristicfingerprintofPSfmaterial,alongwithan
thicknessoftheLLClayeratconcentrations2%and20%was180and emergenceofapeakat288.3eV(characteristicO–C=OofLLC).Taken
500nm,respectively.TheLLC-impregnatedsubstratewasthenshaken together,theseresultsverifythesuccessfulcoatingoftheLLC-layeron
for2mintofacilitatesolventevaporation.Then,a focusedspotUV topofthePSfsubstrate.
beamwasshedonthecoated-surfacetoinitiatethecrosslinkingofthe We further employed small-angle X-ray scattering (SAXS) to
LLCmonomerstoformasolidLLC-filmonthePSfsubstrate.Notably, investigate the assembled structure of the crosslinked LLC on the
thePOM texture remained unchanged before and after UV-induced surface(Fig.2i).X-rayswerepropagatedperpendicularlythroughthe
crosslinking, indicating the phase stability of this H-LLC (Supple- filmplane,asillustratedintheschematic(theupperpanel).Collected
I
mentary Fig. 6). Following the coating process, the LLC-coated PSf crystal plane families are indexed using Miller indices {hk}.

FabricationoftubularpolyamideNFmembranes
PolyamideactivelayerisproducedbyIPreactionbetweenpiperazine apolyamideselectivelayer.Thecross-sectionstructureoftheresult-
(in aqueous phase) and trimesoyl chloride (in hexane phase) on a ing thin-film composite membrane was visualized by SEM images
support.WeaimedtotuneIPreactionbyintroducingtheinterlayerof (Fig. 3b), in which elemental mapping displays a clear interface
theself-assembledH-LLC,asschematicallyillustratedinFig.3a.Sub- betweenthenitrogen-richpolyamideandsulfur-richPSf(Fig.3cand
I
sequently,IPwascarriedoutontopoftheLLC-coatedsupporttoyield SupplementaryFigs.12and13).
Notably,acharacteristictubularstructurewithawidthof~1μm
andalengthof~10μmwasobservedonthepolyamidelayer(Fig.3d).A
closer examination of thistubularstructurerevealedahollowinternal
cavity(Fig.3e).Thepresenceoftubularprotuberancesinpolyamide
was also observed by the cross-sectional image obtained through
transmissionelectronmicroscopy(TEM,Fig.3f).Thistubularstructure
isevenlydistributedacrossthesurface,contributingtoaroughmor-
phology(Fig.3g)ontopofthesmoothPSfsubstrate(Fig.3h).Whilea
similarinternalcavityhasbeenwidelyobservedinthecharacteristic
ridge-and-valleystructureofTFCmembranesmadefromtheIPreac-
tion between m-phenylenediamine (MPD) and trimesoyl chloride
(TMC)44,45,thesizeofthetubularstructure(~1μm)inourmembranesis
significantlylargerthanthatofforthe typicalridges(~100nm).We
surmisedtheemergenceofthistubularstructureislargelyascribedto
the introduction of the LLC interlayer, whose exact role in manip-
ulatingIPthusnecessitatesfurtherinvestigationandelucidation.

Effects of LLC interlayer on polyamide structure
ToinvestigatetheroleoftheLLCinterlayerinaffectingIPreaction,we
firstassessedandcomparedtheimpactsofLLCconcentrations.The
LLCmixturewasdissolvedinethanolatdifferentconcentrationsand
depositedonPSfsubstrate.WethenperformedIPonthesesubstrates
to produce polyamide thin-film nanocomposite (TFN) membranes,
whichwererespectivelydenotedasTFN ,TFN ,andTFN
0%LLC 2%LLC 20%
. The control sample (i.e., TFN ) displayed a smooth surface
LLC 0%LLC
(Fig. 4a), consistent with the typical surface structure of NF mem-
branes made from the PIP-TMC reaction24,46–48. Deposition of low
concentrationLLC(2wt%)leadstotheemergenceofcrescent-shaped
protrusionsonthesurface (Fig.4b). Thisstructuralfeature evolved
intoadistinctiveY-shapetubularshapeusinga20wt%LLCinterlayer
(Fig.4c).FurtherincreasingLLCconcentrationto50wt%and100wt%
maintainthepresenceoftheprotrusionfeaturesacrosstheentireLLC
concentrationrange(SupplementaryFig.14).Ingeneral,anincreasein
LLCconcentrationresultedinprotrusionswithsmallerlateralsizesbut
highersurfacedensities.Asaconsequence,theseprotrusionsleadto
increasedpolyamidethickness(Fig.4d–f,from250nmofTFN to
0%LLC
382nmofTFN )andincreasedsurfaceroughness(Supplemen-
20%LLC
taryFig.15).Notably,theprotrusionstructureremainedunchanged
after operating at5bar—a typical pressure used inNF system (Sup-
plementaryFig.16),demonstratingtheirstructuralstability.
AnalysisofC andO spectrarevealedanotabledecreaseinthe
1s 1s
contentofcarboxylicacidgroups(O–C=O)withtheintroductionof
LLCinterlayers(Fig.4g–i).XPSanalysisoftheelementalcompositionof
the polyamide layer indicated the degrees of crosslinking (DOC) of
40.4%and70.0%forTFN andTFN (Fig.4g–i,Supplementary
0%LLC 20%LLC
Figs.17,andSupplementaryTable1),respectively.Deconvolutionof
thehigh-resolutionC andO spectraofthepristineTFN (Fig.4g)
1s 1s 0%LLC
revealedadistinctpeakat533.51eVcorrespondingtothecarboxylic
acid(–COOH)group.Incontrast,thispeakwasnotobservableinthe
TFN membrane,implyingthedisappearanceof–COOHgroup.
20%LLC
This result aligns with the increased degree of crosslinking for this
membrane,indicatingthepresenceofamoreuniformnetworkforthe
resulting polyamide layer. To further quantify the carboxyl group
content,weemployedasilverionprobemethod49,50.Specifically,an
adsorption–desorptionprocedurewasconductedusingAg⁺ions,and
thedesorbed silver concentration was quantified via inductively
coupled plasma–mass spectrometry (ICP-MS). TFN exhibited a
0%LLC
carboxylgroupdensityof16.6sitesnm−2,whileTFN showeda
20%LLC
reduceddensityof12.8sitesnm−2.Thisresultprovidesfurtherevidence
thattheLLCinterlayerreducestheformationofunreactedorhydro-
lyzedcarboxylgroups(SupplementaryFig.19).WealsotestedtheDOC
ofpolyamideformedaftergraftingahigherconcentrationofLLC,but
the value slightly decreased relative to the TFN membrane
20%LLC
(SupplementaryFig.20andSupplementaryTable1).AstheLLCcon-
centrationfurtherincreases,theviscosityofthedispersionalsorises
duetothereducedethanolcontent,reachingagel-likestateat100%
LLC concentration. This high viscosity leads to poor flowability and
hinders uniform spreading, resulting in visibly uneven coating and
defect formation upon deposition (Supplementary Fig. 21). Conse-
quently,whenLLCwasloadedontothesubstrateathighconcentra-
tions,theformationofdefectsbecamemorelikely.Additionally,AFM
thickness measurements indicate that when the LLC concentration
exceeds50%,thethicknesscanincreasetothemicrometerscale,which
furtherhinderstheefficientreactionbetweenPIPandTMCmonomers
duringinterfacialpolymerization.

Enhancedseparationperformanceandfoulingresistanceof
LLC-modulatedpolyamidemembranes
We further evaluated membranes performance using a lab-scale
crossflow NF system. The presence of LLC interlayer significantly
enhancesthewaterpermeance(Fig.5a),withthe20%LLCmembrane
achieving22.2±0.3Lm−2h−1bar−1,nearlydoubledthatofthepristine
TFN (12.3±0.2Lm−2h−1bar−1). This improvement is primarily
0%LLC
attributedtotheenlargedsurfacearearesultingfromtheformationof
Y-shape structure on the polyamide surface. Notably, the Na SO
2 4
rejection remained statistically comparable between the TFN
0%LLC
control(99.1±0.1%)andtheTFN membrane(98.2±0.2%)atthe
20%LLC
95% confidence level (p=0.08,n=3;seeFig.5aandSupplementary
Table 2),indicatingthation selectivitywaslargelypreserved. Toge-
ther, these results demonstrate enhanced water/salt selectivity
enabledbyLLC-modulatedinterfacialpolymerization.
The antifouling properties of the membranes were evaluated
through three cycles of fouling-rinsing experiments using 50mgL−1
sodium alginate (with 0.5mM CaCl ) as model foulants (Fig. 5b).
2
Duringthefirstcycle,thepristineTFN membranesexhibitedthe
0%LLC
most severe fouling, resulting in a 32% reduction in water flux. In
comparison,thefluxofTFN andTFN decreasedby25%and
2%LLC 20%LLC
23%,respectively.Inthesecondandthirdcycles,waterfluxofTFN
0%
LLC
alsoexperiencedahigherpronounceddropcomparedtothatof
TFN andTFN .Notably,thefluxrecoveryoftheTFN
2%LLC 20%LLC 20%LLC
membranewasover90%afterrinsing,suggestingthatphysicalrinsing
effectivelyremovedmajorityoffoulants.Overthe12-hfoulingrun,the
controlTFN membraneexhibitedthemostseverefouling,with
0%LLC
waterfluxreductionof>60%,whereasTFN andTFN were
2%LLC 20%LLC
muchlessaffected(SupplementaryFig.22).SEMimagesofthefouled
membranesurfacesrevealedthatthefoulingcoverageofTFN and
2%LLC
TFN wassignificantlylesscomparedtotheTFN membrane
20%LLC 0%LLC
(Supplementary Fig. 23). This enhanced fouling resistance is likely
attributedtotwofactors.First,theincorporationoftheLLCinterlayer
resultedinTFNmembraneswithalowerdensityof–COOHgroups.
This reduction minimized Ca2⁺-mediated bridging effect, thereby
mitigatingfoulingcausedbyalginatemolecules.Second,thepresence
of the large tubular protrusions likely induced turbulence near the
membrane surface. Such interfacial turbulence disrupted foulant
depositionandreducedaccumulation,thusenhancingtheantifouling
performanceofthemembranes.
Selective separation of monovalent and divalent ions from a divalentions(Ca2+,Mg2+)fordifferentmembranes,i.e.,theselectivity
mixture represents another major application of NF membranes, of pristine TFN for Na+/Ca2+, Li+/Mg2+ is 0.96, 0.98, and the
0%LLC
aimingatmitigatinginorganicmetalscaling51orextractinglithium selectivityofTFN forNa+/Ca2+,Li+/Mg2+is5.8and11.4.These
20%LLC
fromsaltlakes/brines52.ThehigherDOCandfewercarboxylgroups resultsrevealthepromiseoftheTFN membranes in separating
LLC
onthesurfaceofTFN membraneimplyamoreintegralnetwork monovalent and divalent ions, which hold potential in various
20%LLC
within the polyamide layer, thereby enhancing selectivity toward applications(e.g.,watersofteningandlithiumrecovery).Despitethe
ionic species. At the same time, the reduced negative surface inherent trade-off in NF membranes, the TFN membrane
20%LLC
potential, as confirmed by zeta potential measurements (Supple-
24),weakenstheelectrostaticattractiontopositively
chargedions, further contributing to theimproved ionseparation
performance. Notably, we further evaluate the rejection of the
TFN membranealsoexhibitedahigherrejectiontowarddiva-
20%LLC
lentcation(Ca2+orMg2+)comparedtomonovalentcation(Na+orLi+),
leadingtoafive-foldincreasefortheNa+/Ca2+pair(Fig.5c)andten-
foldincreasefortheLi+/Mg2+pair(Fig.5d).Inparticular,theTFN
0%LLC
membranedisplayslowrejectionofbothmonovalentcations(37%
forNa+and17%forLi+)anddivalentcations(34%forCa2+,and16%for
Mg2+).TheTFN membraneresultedinrejectionof19%forNa+,
2%LLC
51% for Li+, and 42% for Ca2+, 82% for Mg2+, while the TFN
20%LLC
exhibitedhighrejectionofbothdivalentcations(87%forCa2+and
95% for Mg2+) and monovalent cations (28% for Na+, 48% for Li+).
UsingEq.3,wecalculatedtheselectivityformonovalent(Na+,Li+)and

ProposedimpactsofLLCinterlayeroninterfacial
polymerization
WefurthercharacterizetheLLC-coated substratefor elucidating its
regulatedIPreactionmechanism.TheLLCinterlayerisdepositedon
thePSfsubstrate,leadingtotheformationofuniformchannelsforPIP
moleculetransport(Fig.6b).Inbulksolution,ourLLCmoleculesself-
assembledintoahexagonalcolumnarstructure,evidencedbydistinct
{10},{11},and {20} scattering rings inSAXS patterns (Fig. 6c). Upon
loadingontothesubstrate,only{10}scatteringringremains(Fig.6d),
ascribingtothethin-layeroftheLLClayercoatedontothePSfsurface.
The1DSAXSdata,extractedfromthe2DpatternsinFig.6e,showan
unchangedlocationofpeak{10},indicatingthatthehexagonalpacking
structureismaintained.Inaddition,thetwo-dimensionalsignalsare
shownasscattingrings insteadofscattingpoints,indicatingplanar
depositionofthishexagonalcolumnarLLConthePSfsubstrate,and
exposingpositivelychargedhydrophilicgroupstothesurface.Asa
result,weobservedanincreaseofsurfacehydrophilicityonthesur-
facesviawatercontactanglemeasurements(Fig.6fandSupplemen-
taryFig.25and78°forpristinePSfvs.40°forPSf ).Tofurther
20%LLC
investigatethestateofhexanediffusiontothesubstratesurfacedur-
ing the IP process, we measured the underwater contact angle of
hexaneonthePSfandPSf surface(Fig.6f).Theresultsshoweda
20%LLC
contactangleof63°and122°forPSfandPSf ,respectively,indi-
20%LLC
catinggreateroleophobicitytowardhexaneaftertheintroductionof
theLLCinterlayer.TheseresultsindicatedthatthepresenceoftheLLC
layer enhanced the surface’s repulsion toward the organic phase,
thereby increasing resistanceto hexane wetting (Fig. 6a).During IP
reaction, PIP molecules first penetrate the porous PSf and subse-
quently migrate into the homoporous LLC layer. Owing to the
increasedhydrophilicityoftheLLC-modifiedsurface,thesemolecules
tend to spread and flatten, exhibiting enhanced wetting behavior.
Importantly,the LLCinterlayerrestrictstheverticaldiffusionofPIP
towardtheorganicphaseinterfaceduetobothphysicalandchemical
effects.
TofurtherinvestigatetheinfluenceoftheLLCinterlayeronthe
substratesurfaceproperties,wemeasuredthezetapotentialofpris-
tinePSfandLLC-loadedPSfsubstrates.PristinePSfexhibitedanega-
tive surface potential at pH>3.5. In contrast, the zeta potential
increasedsignificantlywithLLCloading,reaching6.2and9.5for2wt%
and20wt%LLC,respectively(SupplementaryFig.26).Theseresults
indicatethattheLLClayerrendersthesubstratesurfacenearlyelec-
tricallyneutralathigherpHvalues.Giventhepositivelychargednature
of PIP molecules, this near-neutral surface weakens electrostatic
attraction,furtherslowingPIPdiffusiontowardthereactioninterface.
Takentogether,thenanoscaleconfinementandreducedelectrostatic
drivingforceconstituteadualhindrancemechanism,whichlowersPIP
fluxattheinterfaceandpromotestheformationofprotruded,wrinkle-
likefeaturesintheresultingPAlayer.
We also performed molecular dynamics (MD) simulations to
determinediffusioncoefficientsofPIPmoleculesinpurewaterand
inwatercontainingLLC53,54.AsshowninFig.6g,h,simulationboxes
wereconstructedforbothsystems,andthemeansquaredisplace-
ment(MSD)ofPIPmoleculeswasanalyzedusingEinstein’srelation.
The diffusion coefficient of PIP was found to decrease from
2.50×10−9m2s-1 in pure water to 1.81×10−9m2s−1 in the LLC-
containingenvironment.Theseresultsconfirmthatthepresenceof
LLCsignificantlyhindersthediffusionofPIPmolecules,whichplaya
criticalrole in regulating the polymerization kinetics and resulting
membranemorphology.
Insummary,weconstructedtheself-assembledLLCinterlayeron
PSf substrates. The presence of the LLC interlayer affected the IP
reactionandthusyieldapolyamidefilmwithacharacteristicY-shaped
tubularstructure.SuchLLC-modulatedpolyamidemembranenotonly
exhibitedenhancedion-ionselectivitybutalsodemonstratedexcep-
tionalresistancetofouling.ThepresenceoftheLLClayersignificantly
hinders the vertical diffusion of the aqueous-phase monomer (PIP)
throughphysicalconfinementandreducedelectrostaticinteractions.
Simultaneously,theincreasedinterfacialhydrophilicitypromoteslat-
eral(in-plane)diffusionofPIPacrossthereactioninterface.Thisani-
sotropicdiffusionbehaviorleadstolocalizedmonomerenrichment,
whichinturnfacilitatestheformationofdistinctiveY-shapedtubular
nanostructureswithinthepolyamidelayer.Ourstudynotonlypresents
aplatformforrevealingtheroleofinterlayerstructureonmanipulating
thestructureandperformanceofpolyamidelayer,butalsooffersa
potentialstrategyusingself-assembleinterlayerswithcontrolledsur-
facepropertiesforfabricatinghigh-performanceNFmembranes.

Methods
Synthesisoflyotropicliquidcrystal(LLC)monomer
LLCmonomerusedinthisstudyisGeminipolymerizablesurfactant
MA11-6-11MA.Synthesisofthissurfactantinvolvestwosteps(Supple-
mentary Fig. 1). First, esterification of 11-bromo-1-undecanol and
methacryloylchloridewascarriedouttoformmethacryloyloxyasthe
polymerizable group. Then, the positively charged quaternary
ammonium salt was covalently bonded through a quaternization
reaction.Theresultingmaterialwasverifiedusing1HNMR,withafinal
yieldwas~60%.(SupplementaryFig.2).Detailedsynthesisprocedure
ofMA11-6-11MAisprovidedintheSupplementaryInformation.

PreparationofLLC-loadedsubstrates
LLCwithhexagonalcolumnarstructurewasformedbymixingMA11-6-
11MAsurfactant(70wt%)andwater(30wt%).TheobtainedLLCmix-
ture was added into ethanol at various mass ratios (2, 20, 50, and
100wt%),anduniformlyspreadonpolysulfone(PSf)supports.These
supports were respectively labeled as PSf , PSf , PSf ,
2%LLC 20%LLC 50%LLC
and PSf . To facilitate ethanol evaporation, the supports were
100%LLC
shaken at 200rpm for 2min on a plate shaker under a nitrogen
atmosphere.Aftercompleteevaporationofethanol,theLLCretained
itsself-assembledmorphology,indicatingthatethanoldidnotdisrupt
the self-assembly process. The LLC structures remained stably
depositedonthePSfsurface(SupplementaryFig.3).Next,theLLC-
coatedPSfsupportswerethenirradiatedunderUV(365nm)for60sto
initiate polymerization of the LLC monomer, forming anisotropic,
solidLLCfilmsonPSfsurface.

Interfacialpolymerization
Tofabricatepolyamideselectivelayer,IPreactionwasconductedon
topoftheLLC-coatedPSfsupports.ThepristinePSf,PSf ,PSf ,
2%LLC 20%LLC
PSf ,andPSf substrateswereinitiallyimmersedina1wt%
50%LLC 100%LLC
PIPaqueoussolutionfor3min.ExcessPIPsolutiononthesurfacewas
removed using an air knife. Next, the PIP-saturated substrate was
immersed in a 0.15wt% TMC hexane solution to initiate poly-
condensation of PIP with TMC, resulting in the formation of cross-
linked polypiperazine film. To enhance water permeability, we also
investigatedalternativemonomerconcentrations—specifically,0.5wt%
PIPand0.1wt%TMC—withtheaimofformingathinnerselectivelayer
with enhanced water transport. The resulting membrane was subse-
quentlywashedwithpurehexaneandcuredinDIwaterat65°Cfor
10min.TheobtainedNFmembraneswerestoredinDIwaterat4°C
beforetesting.

Characterizationofmembranes
Surfaceandcross-sectionmorphologyofNFmembraneswerechar-
acterizedbyscanningelectronmicroscopy(SEM,Gemini450,Zeiss).
Surface roughness and thickness of membrane were measured by
atomic force microscopy (AFM, MultiMode, Veeco). Cross-sectional
images of TFN membranes prepared were obtained using a field-
emissiontransmissionelectronmicroscope(TEM,JEM-2100F,JEOL).
Self-assemblytextureswereobservedusingpolarizedopticalmicro-
scopy (POM, DM750, Leica). Surface hydrophilicity of membranes
weretestedbyatensiometer(ThetaFlex,Biolin).Molecularstructure
and chemical bonding were tested by attenuated total reflection
Fourier transform infrared (ATR-FTIR, Nicolet 8700, Thermo Fisher
Scientific).Surfacezetapotentialofmembranewasevaluatedusinga
solid surface Zeta potential analyzer (SurPASS 3, Anton Paar). Ele-
mentalcontentofmembranessurfaceswasdetectedbyX-rayphoto-
electron spectroscopy (XPS, ESCALAB 250Xi, Thermo Fisher
Scientific).Self-assembledorderedstructuresweretestedon1Dand
2Dsmall-angleX-raydiffraction(SAXS)usingadiffractometercoupled
with synchrotron source atShanghaiSynchrotron Radiation Facility
(BeamlinesBL16B1andBL10U1)andtheNationalFacilityforProtein
ScienceinShanghai(BeamlineBL19U2).

Evaluationofmembranesseparationperformance
TheperformanceofallNFmembraneswasevaluatedusingalab-made
systemwithcross-flowfiltrationcells(effectiveareaof19.5cm2).Prior
tothemeasurements,membranecouponswerecompactedat6bar
for4hourstoobtain astablewaterflux.Purewaterfluxwasdeter-
mined at 5bar and cross-flow velocity of 1.07cms−1 at 25°C. Salt
rejectionwasdeterminedusing1gL−1Na SO or50mMNaClsolution
2 4
asafeedsolution.Saltrejection,R,wascalculatedby:
!
C
R= 1(cid:2) p ×100% ð2Þ
C
f
whereCfandCprepresentconductivityoffeedandthepermeate.
Membrane selectivity was tested with a mixture solution con-
taining 5mM NaCl (LiCl) and 1mM CaCl (MgCl ). Selectivity of
2 2
monovalentcations(Na+/Li+)todivalentcations(Ca2+/Mg2+)wascal-
culatedusing:
Selectivity
X+
=
C
f
(Y2+)
=
C
f
(X+)
=
100(cid:2)R
X+
ð3Þ
Y2+
C
(Y2+)
C
(X+)
100(cid:2)R
P
P
Y2+
where C f and C p represent the ion concentrations in the feed and
permeate,respectively.Averageselectivityforeachmembranetypeis
calculatedbyaveragingtheselectivityofLi+andMg2+obtainedfrom
individualmembranecoupons.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript written by Xu et al. introduces a novel approach for fabricating high-performance nanofiltration (NF) membranes using lyotropic liquid crystals (LLCs). Polymerizable LLC monomers were synthesized to self-assemble into a hexagonal columnar phase, forming highly ordered interlayers on substrate surfaces. Interfacial polymerization (IP) on these interlayers yielded polyamide NF membranes, extensively characterized with state-of-the-art techniques, including synchrotron SAXS. Notably, the membranes featured unique, tunable hollow tubular structures on their surface, controlled by LLC deposition conditions. In separation experiments, they exhibited excellent ion/ion selectivity and enhanced fouling resistance—both are critical properties for NF applications. The study also elucidated how LLC interlayers regulate interfacial polymerization, linking structural changes to performance improvements.\nOver the past decade, the use of interlayers to manipulate IP has been a key focus in fabricating high-performance nanofiltration (NF) membranes. Compared to existing filtration-deposition-based strategies, this study introduces a novel approach for constructing interlayers with controlled, tunable structures. I think both the method and insights in this study will advance the understanding of interlayer-regulated IP processes, and contribute to future innovations in this field. I offer the following comments for the authors’ consideration:\n1. The authors employed a procedure for synthesizing LLC monomers. Could the authors clarify the overall yield of this synthesis process? Such information is critical for evaluating the practical potential and scalability of their approach.\n2. Ethanol was added to prepare the LLC mixture, which was subsequently spread and deposited on polysulfone supports. Could the authors provide additional details on the role of ethanol? For instance, does ethanol act as a solvent to aid dispersion or facilitate the self-assembly of the LLC? Furthermore, does the self-assembly process occur in the aqueous phase or after ethanol evaporation? Additionally, besides the hexagonal columnar phase, did the authors observe other self-assembled structures, such as lamellar or reverse hexagonal phases?\n3. The authors observed tubular structures with micrometer-scale sizes and hollow internal cavities on the membrane surface. Considering the significance of these rough, hollow features for their membrane performance, additional evidence verifying the hollow nature of these structures would be valuable. Furthermore, could the authors discuss whether these large features can withstand high-pressure conditions and maintain stability during NF operation?\n4. As shown in Figure 2e, the LLC layer effectively covers the surface of the pristine polysulfone support, altering its surface charge (Figure 6f) and wettability (Figure 6g). Could the authors also elaborate on how the LLC interlayer affects the pore structure and selectivity of the support? How do these changes influence the subsequent interfacial polymerization process?\n5. Crosslinking of the LLC layer would result in a solid structure on the support. After interfacial polymerization, does this crosslinked LLC layer still exist between the polyamide layer and the polysulfone support, or is it removed during subsequent NF testing through the porous side of the support?", "reviewer_2": "In this paper, the authors demonstrated a new approach for fabricating thin-film composite (TFC) polyamide nanofiltration (NF) membranes using Lyotropic Liquid Crystal (LLC)-regulated interfacial polymerization. The manuscript is generally well-written and includes extensive experimental results. The use of self-assembled LLC interlayers to fabricate TFC-PA membranes is, to the best of my knowledge, under-explored and represents a new contribution.\nHowever, I find it less convincing that LLCs are as effective as nanomaterial interlayers in enhancing NF membrane performance. Furthermore, some aspects of the proposed mechanism underlying the function of LLCs remain unclear. Therefore, the significance of this work’s contribution to the field is not yet fully evident. I do not recommend the publication of the current version.\nPlease see detailed comments below:\n1. The enhancement of NF membrane performance attributed to LLC-regulated interfacial polymerization appears limited:\na. The LLC-modulated membranes exhibited the water permeance of 11 LMH/bar and Na2SO4 rejection rate of 90%. (Page 9, Line 202 – 211)\ni. The commercial NF270 and NF90 membranes achieve water permeance of ~20 LMH/bar and ~10 LMH/bar, and their Na2SO4 rejection rates are approximately 80% to 99% at similar testing condition in the paper.\nii. TFC-PA NF membranes incorporating other nanomaterials (e.g., carbon nanotubes, graphene oxide, metal oxides, etc.) often demonstrate significantly greater enhancements, with water permeance ranging from 20 LMH/bar to over 50 LMH/bar and Na₂SO₄ rejection rates typically above 90%, often exceeding 95%.\niii. Further discussion or evidence is necessary to substantiate the claim that LLCs are a competitive alternative to these nanomaterials in enhancing NF membrane performance.\n2. Page 8, Line 192-195:\na. The statement that the disappearance of the -COOH group indicates a more uniform polyamide network requires further clarification. Can the authors provide additional evidence or a more detailed explanation for this claim?\n3. Page 9, Line 224 – 226:\na. The mechanism by which tubular protrusions inhibit foulant deposition is unclear.\ni. Could the authors elaborate on how these protrusions achieve this effect?\nii. Does the increased surface roughness pose a competing factor, potentially counteracting the antifouling benefits?\n4. Page 10, Line 229 - 246:\na. It reads like that there lacks a clear purpose of a more suitable application of such LLCs-derived TFC-PA membranes.\nb. The selectivity performance for divalent and monovalent ions appears similar to other NF membranes, which diminishes the novelty of this approach.\nc. A more comprehensive comparison of the performance of LLC-derived membranes with existing literature would better contextualize their findings and potential applications.\n5. Page 11, Line 268 – 270: “Considering the positive nature of PIP molecules, the near neural surface thus led to a lower electrostatic attraction to PIP molecules with retarded diffusion”\na. This is the only sentence I found that talks about the mechanism of LLC enhancement of membrane performance.\nb. Without any evidence, it is an bold implication of one possible mechanism of LLC effect.\n6. Mistakes in writing:\na. Based on the data shown in Figure 5d, the author intended to write 82% for Mg2+ at line 239, rather than 82% for Ca2+.\nb. At line 244, the authors want to indicate TFN20%.\n7. Additionally, based on the data provided by the authors and the ion selection formula described in the Methods section, the Li/Mg selectivity for TFN20% should be 7.6. Could the authors explain why the value is 10.6 in the article?", "reviewer_3": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts.", "reviewer_4": "The manuscript NCOMMS-24-72236 describes synthesis and characterization of nanofiltration membranes by including a polymerized lyotropic liquid crystal (LLC) layer (with pore size on the order of 1 nm) on the polysulfone support layer (an ultrafiltrtion membrane with pore size of ~ 43 nm). I rate the work as a comprehensively analytical one with an engineering approach without digging into the fundamental science behind observations (moderate development). In addition, there are some serious questions about some of the observations and reported results. The major concerns are as follows:\n1) The thickness of LLC layer and its effect have not been discussed. The currently provided SEM micrograph does not show the LLC layer. The paper just refers to the LLC as a thin layer.\n2) Authors reported \"a unique tubular structure with a width of ~1 μm and a length of ~10 μm was observed on the polyamide layer\". However, the physics behind formation of these wrinkles has been overlooked. Why and how do they form?\n3) As the concentration of LLC in precursor changes, the surface charge does not changes significantly (especially beyond 20%). Then, why are the morphology, chemistry, and performance of obtained TFC NF membranes affected?\n4) Does the LLC layer (especially beyond 20%) change the rate and mechanism of polymerization? If not, why do the surface morphology, degrees of crosslinking, and concentration of COOH groups of IP layer change? The current discussion mainly refers everything to Figure 6b, which is just a schematic of LLC morphology. In another attempt authors attributed the change in degree of crosslinking to the increase in \"viscosity using the high concentration LLC.\" This is fundamentally wrong.\n5) Authors observed that the flux increases when LLC layer is incorporated between polysulfone support layer and polyamide thin film. At the same time, the rejection of ions have increased, which can be attributed to smaller nominal pore size in active layer. Both of these observations suggest that the hydraulic resistance have been increased. This is in contradiction to reported flux trends by authors when comparing the control sample and samples with LLC. In other words, based on models in literature, each layer can be treated as a resistor. How is it possible that having two resistors in series can provide a lower resistance than a single resistor? If the increase in surface area is a factor, its effect should be quantified and considered in hydraulic resistances. However, I have doubt that adding an LLC layer with 1 nm pore size (and unknown thickness) can eventually decrease the hydraulic resistance (and thus the flux)?\n6) According to Figure 4, 20%LLC sample has ~2x thickness of active layer compared to 0%LLC and 2%LLC. Why does it have higher flux?\n6) Piperazine is probably a good solvent for crosslinked MA11-6-11MA. So, one can argue that during the interfacial polymerization and/or subsequent washing, the LLC structure is collapsed and/or washed away.\n7) Authors mentioned that \"These results reveal the promise of the TFNLLC membranes in separating monovalent and divalent ions, which hold potential in various applications (e.g., water softening and lithium recovery)\". However, their membranes' performance does not seem to be very different compared to currently available NF membranes in the market.\n8) It is mentioned that \"Due to the increased hydrophilicity, these PIP molecules tend to wet the substrate and flatten on the surface.\" Then, why do we observe more wrinkles on the final surface with LLC layer on the support?\nSome minor comments:\n- Authors mentioned that \"While these investigations underscore the potential of LLCs for direct fabrication of NF membranes, scaling-up the proposed strategies into roll-to-roll fabrication processes still presents significant challenges.\" I do not believe their approach (additional step for coating and drying LLC precursor) addresses this criticism.\n- There are concerns related to reported SAXS results for membranes (LLC on polysulfone). SAXS measurement details and accuracy for these results (for thin layer of LLC on membrane) should be evaluated."}, "author_response": "Response to referee comments, manuscript NCOMMS-24-72236\nREVIEWER #1\nBefore our response to the specific comments of the reviewer, we would like to highlight the key\nrevisions made:\n1. Expanded experimental investigations into the role of LLC interlayers in regulating\ninterfacial polymerization process, including the dynamics of PIP diffusion to hexane phase\nand the interfacial wettability of water and hexane for the LLC-coated substrates.\n2. Enhanced data analysis and discussion by incorporating additional experimental evidence,\nparticularly regarding the impact of ethanol dispersion, the presence and role of LLC at\ndifferent stages of interfacial polymerization, and the structural stability of the surface\nprotrusions on the polyamide layer.\n3. Clarified the performance consistency of the LLC-regulated strategy and its potential\nscalability for industrial membrane fabrication, highlighting its applicability in various\nseparation processes.\nGeneral Comment: This manuscript written by Xu et al. introduces a novel approach for\nfabricating high-performance nanofiltration (NF) membranes using lyotropic liquid crystals\n(LLCs). Polymerizable LLC monomers were synthesized to self-assemble into a hexagonal\ncolumnar phase, forming highly ordered interlayers on substrate surfaces. Interfacial\npolymerization (IP) on these interlayers yielded polyamide NF membranes, extensively\ncharacterized with state-of-the-art techniques, including synchrotron SAXS. Notably, the\nmembranes featured unique, tunable hollow tubular structures on their surface, controlled\nby LLC deposition conditions. In separation experiments, they exhibited excellent ion/ion\nselectivity and enhanced fouling resistance—both are critical properties for NF applications.\nThe study also elucidated how LLC interlayers regulate interfacial polymerization, linking\nstructural changes to performance improvements.\nOver the past decade, the use of interlayers to manipulate IP has been a key focus in\nfabricating high-performance nanofiltration (NF) membranes. Compared to existing\nfiltration-deposition-based strategies, this study introduces a novel approach for constructing\ninterlayers with controlled, tunable structures. I think both the method and insights in this\nstudy will advance the understanding of interlayer-regulated IP processes, and contribute to\nfuture innovations in this field. I offer the following comments for the authors’ consideration:\nOur Response: We sincerely appreciate the reviewer’s positive comments on the novelty and\nsignificance of our study. We are also grateful for the reviewer’s constructive feedback, which\nprovides valuable insights in refining our manuscript. Below, we present detailed responses\nto the reviewer’s comments.\nPage R1\nResponse to referee comments, manuscript NCOMMS-24-72236\nComment 1: The authors employed a procedure for synthesizing LLC monomers. Could the\nauthors clarify the overall yield of this synthesis process? Such information is critical for\nevaluating the practical potential and scalability of their approach.\nOur Response: We appreciate the reviewer’s interest in the synthesis procedure for LLC\nmonomers and its implications for scalability. The LLC monomers were synthesized via a\nmulti-step chemical process, followed by purification, yielding of ~60% in the final step. This\nyield highlights the feasibility of our synthesis approach, while also indicating room for\nfurther optimization to enhance its practical applicability and scalability.\nTo ensure clarity, we have incorporated this information into the Methods section as follows:\nLine 333-335: “The resulting material was verified using 1H NMR, with a final yield was ~60%\n(Supplementary Figure 2). Detailed synthesis procedure of MA11-6-11MA is provided in the\nSupplementary Information.”\nComment 2: Ethanol was added to prepare the LLC mixture, which was subsequently spread and\ndeposited on polysulfone supports. Could the authors provide additional details on the role\nof ethanol? For instance, does ethanol act as a solvent to aid dispersion or facilitate the self-\nassembly of the LLC? Furthermore, does the self-assembly process occur in the aqueous\nphase or after ethanol evaporation? Additionally, besides the hexagonal columnar phase, did\nthe authors observe other self-assembled structures, such as lamellar or reverse hexagonal\nphases?\nOur Response: We thank the reviewer for these insightful questions regarding the role of ethanol\nin the self-assembly process. In our approach, the LLC monomer was initially mixed\nthoroughly with water to initiate the self-assembly. Ethanol was then introduced as a\ndispersing agent to ensure the uniform distribution of the LLC self-assembled structures on\nthe surface of the polysulfone substrate.\nThe complete evaporation of ethanol, conducted under a nitrogen atmosphere, allowed the\nself-assembled structures to stabilize on the substrate surface. Under specific compositional\nconditions (molecule with water at a weight ratio of 3:1), LLC self-assembles into a columnar\nstructure, exhibiting a fan-shaped texture under polarized optical microscopy (POM, see\nFigure R1 below). When diluted with ethanol, the LLC self-assembled morphology was not\ninitially observed at low concentrations under POM. However, after ethanol evaporation, the\ncolumnar structure reappeared, indicating that ethanol did not disrupt the LLC self-assembly\nbut rather served as a temporary dispersing medium.\nPage R2\nResponse to referee comments, manuscript NCOMMS-24-72236\nFigure R1. POM micrographs of LLC before and after ethanol evaporation.\nFollowing the reviewer’s comments, we have added the following explanation to the relevant\nsections of the manuscript for clarification. The revised text and figure include:\nLines 340-346: “To facilitate ethanol evaporation, the supports were shaken at 200 rpm for 2\nmin on a plate shaker under a nitrogen atmosphere. After complete evaporation of ethanol, the\nLLC retained its self-assembled morphology, indicating that ethanol did not disrupt the self-\nassembly process. The LLC structures remained stably deposited on the PSf surface\n(Supplementary Figure 3). Then, the LLC-coated PSf supports were irradiated under UV light\n(365 nm) for 60 s to initiate polymerization of the LLC monomer, forming anisotropic, solid LLC\nfilms on PSf surface.”\nWe have added a new figure (Supplementary Figure 3) to the Supplementary\nInformation:\nSupplementary Figure 3. Polarized optical microscope (POM) micrographs of LLC before\nand after ethanol evaporation.\nThe self-assembly of LLC is governed by the mass ratio of monomers to water. As the water\nconcentration decreases, the LLC undergoes a series of phase transitions, progressing through\ndistinct phases, including micellar solution (L ), hexagonal columnar (H ), lamellar (L ), and\n1 1 ɑ\ncrystal (K) phases (Figure R2).\nPage R3\nResponse to referee comments, manuscript NCOMMS-24-72236\nFigure R2. Binary phase diagram of MA11-6-11MA/water system.\nTo enhance clarity, we have included a binary phase diagram of LLC self-assembly in the\nSupplementary Information and revised the corresponding text in the Results section as\nfollows:\nLines 109-117: “This molecule consists of a hydrophilic head with two quaternary ammonium\ngroups and two hydrophobic tails, each containing 11 carbon atoms (synthesis procedure\nillustrated in Supplementary Figure 1). The MA11-6-11MA/water binary phase diagram\nillustrates the transitions through micellar solution (L) to hexagonal columnar (H), lamellar\nI I\n(L ), and crystal (K) phases, as the surfactant concentration increased from 0 to 100 wt.% at\nα\nroom temperature (Supplementary Figure 4). Mixing of this molecule with water at a weight\nratio of 3:1 leads to self-assembly into a hexagonal columnar phase liquid crystal, referred as\nH-LLC. When mixed with water at a weight ratio of 3:1, this molecule undergoes self-assembly\nI\ninto a hexagonal columnar phase liquid crystal, referred as H-LLC.”\nI\nAdditionally, we have added a new figure (Supplementary Figure 4) to the\nSupplementary Information:\nPage R4\nResponse to referee comments, manuscript NCOMMS-24-72236\nSupplementary Figure 4. Binary phase diagram of MA11-6-11MA/water system.\nComment 3: The authors observed tubular structures with micrometer-scale sizes and hollow\ninternal cavities on the membrane surface. Considering the significance of these rough,\nhollow features for their membrane performance, additional evidence verifying the hollow\nnature of these structures would be valuable. Furthermore, could the authors discuss whether\nthese large features can withstand high-pressure conditions and maintain stability during NF\noperation?\nOur Response: We appreciate the reviewer’s suggestion to provide additional evidence regarding\nthe hollow features and stability of the tubular structures on the membrane surface. To assess\ntheir mechanical robustness, we examined the membrane morphology using SEM after\nsubjecting to a pressure of 5 bar for 24 hours. The results confirmed that the tubular structures,\nincluding their hollow cavities, remained intact under these conditions (see Figure R3 below).\nThis finding highlights the structural stability of the wrinkled features on TFC membranes,\ndemonstrating their stability to withstand high-pressure nanofiltration operating conditions.\nPage R5\nResponse to referee comments, manuscript NCOMMS-24-72236\nFigure R3. SEM surface images of membranes after operation at 5 bar for 24 hours: (a)\nTFN , (b) TFN , (c) TFN , (d) TFN , (e) TFN .\n0%LLC 2%LLC 20%LLC 50%LLC 100%LLC\nTo clarify these findings, we have added corresponding data into the manuscript. The revised\ntext include:\nLines 208-210: “Notably, the protrusion structure remained unchanged after operation at 5\nbar—a typical pressure used in NF system (Supplementary Figure 16), demonstrating their\nstructural stability.”\nComment 4: As shown in Figure 2e, the LLC layer effectively covers the surface of the pristine\npolysulfone support, altering its surface charge (Figure 6f) and wettability (Figure 6g). Could\nthe authors also elaborate on how the LLC interlayer affects the pore structure and selectivity\nof the support? How do these changes influence the subsequent interfacial polymerization\nprocess?\nOur Response: We appreciate the reviewer’s insightful question regarding the influence of the\nLLC interlayer on the pore structure, selectivity of the support, as well as its impact on the\nsubsequent interfacial polymerization process. The LLC layer, applied via spin coating,\neffectively covers the surface pores of the underlying PSf support, forming an additional\ninterlayer with distinct structural and physicochemical properties. Compared to the widely\ndistributed and non-uniform pores of the conventional PSf support, the LLC layer introduces\nuniformly sized channels with a consistent pore size of ~1 nm, attributed through its self-\nassembled structure.\nPage R6\nResponse to referee comments, manuscript NCOMMS-24-72236\nTo evaluate the change of surface characteristics, we first performed rejection test using\npolyethylene glycol (PEG) with different molecular weights (see Figure R4 below). The\nresults demonstrated a significant decrease in the molecular weight cutoff (MWCO), from\n300,000 Da of the pristine PSf, to 6000 Da for the LLC-coated PSf (i.e., PSf ), indicating\n20%LLC\na substantial reduction in pore size. The transformation of surface characteristics was also\nreflected in the surface wettability, where the water contact angle decreased from 75° to 40°\n(Figure R5), indicating an increased hydrophilicity. The increased hydrophilicity was\nattributed to the exposure of hydrophilic heads during the self-assembly process.\nThe reduction in pore size and increase in hydrophilicity play a crucial role in modulating the\nsubsequent interfacial polymerization process. Specifically, the presence of isoporous, small-\npore structure, together with the increased hydrophilicity, facilitated the creation of a uniform\ninterface. Consequently, in the following interfacial polymerization, piperazine (PIP)\nmolecules diffuse more evenly from within the pores to the water-hexane interface. This even\ndiffusion thus leads to a denser and more homogeneous polyamide layer formation, ultimately\nimproving membrane performance.\nFigure R4. Rejection of polyethylene glycol (PEG) with different molecular weights by pristine\nPSf and PSf substrates.\n20%LLC\nPage R7\nResponse to referee comments, manuscript NCOMMS-24-72236\nFigure R5. Water contact angle measurements of pristine PSf and PSf supports with varying\nLLC content (PSf , PSf , PSf , and PSf ).\n2%LLC 20%LLC 50%LLC 100%LLC\nWith the reviewer’s comments, we have added the relevant analysis into the manuscript. The\nrevised text now reads:\nLines 134-139: “Moreover, numerous pores were observed on the pristine PSf surface (Figure\n2d), consistent with the pore size of 42.8 nm determined from molecular-weight cut-off (MWCO)\nmeasurements (Supplementary Figure 8). In contrast, these pores were not observable on the\nsurface of the LLC-coated sample (Figure 2e), indicating uniform coverage of the LLC layer on\nthe substrate. Notably, the presence of the LLC interlayer resulted in an interface with smaller-\nsized, uniform pores, as evident from MWCO results (Supplementary Figure 9).”\nWe have also added a new figure (Supplementary Figure 9) to the Supplementary\nInformation:\nPage R8\nResponse to referee comments, manuscript NCOMMS-24-72236\nSupplementary Figure 9. Rejection of polyethylene glycol (PEG) with different molecular\nweights by pristine PSf and PSf substrates.\n20%LLC\nComment 5: Crosslinking of the LLC layer would result in a solid structure on the support. After\ninterfacial polymerization, does this crosslinked LLC layer still exist between the polyamide\nlayer and the polysulfone support, or is it removed during subsequent NF testing through the\nporous side of the support?\nOur Response: We appreciate the reviewer’s question regarding the fate of the crosslinked LLC\nlayer during and after the interfacial polymerization (IP) process. To address this concern, we\nanalyzed the morphology of the LLC layer at different stages of the IP process using 2D\nsmall angle X-ray scattering (SAXS) technique (Figure R6). When the LLC layer was immersed in\nPIP aqueous solution and subsequently soaked in trimesoyl chloride (TMC) solution in\nhexane, distinct scattering rings corresponding to the LLC structure were observed. However,\nafter the final step of IP—where the fabricated TFN membranes were immersed in hot\nwater—these scattering rings of LLC disappeared. These results indicate that the LLC\ninterlayer was effectively removed upon completion of the IP reaction.\nPage R9\nResponse to referee comments, manuscript NCOMMS-24-72236\nFigure R6. 2D SAXS patterns of the LLC interlayer at different stages of the interfacial\npolymerization process.\nFor clarification, we have added corresponding text and analysis to the manuscript. The\nrevised text and figures include:\nLines 162-170: “… demonstrating the effective introduction of the LLC layer onto the PSf\nsubstrate. To further investigate the presence of the LLC interlayer throughout the IP process,\nwe analyzed 2D SAXS patterns at various polymerization stages (Supplementary Figure 11).\nThe results showed that when the LLC interlayer was immersed in the PIP aqueous solution,\nboth the {11} and {10"}]

Decision letter