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User: As a text script expert, please help me to write a short text script with the topic "Microscopic structure and dynamics of shear-thinning suspensions of polydisperse, repulsive vesicles Nikolaos Kolezakisa, Stefano Aimeb, Raffaele Pastorea, Vincenzo Guidac, Gaetano D’Avinoa and Paolo Edera∗b Weinvestigatetherheology,microscopicstructure,anddynamicsofanindustriallyrelevantdispersion made of cationic surfactant vesicles, from dilute to concentrated conditions.This leads us to propose that the observed structural and dynamic transition could arise, as an entropic effect, from the large sample polydispersity coupled to crowding.2 Materials and Methods This approach assumes that the tracers’ motion accurately 2.1 Samplepreparation reflects the behavior of the sample’s local environment, an assumption which turns out to be especially delicate in samples A 13% w/w aqueous dispersion of vesicles made from a double- with heterogeneous microstructures, including many systems of tailedcationicsurfactant(diethylesterdimethylammoniumchlo- practicalinterest.The volume fraction of this starting vesicle dispersion samples, they provide access to the microscopic relaxation time, was characterized according to the method introduced by Seth τ, whichtypicallyincreaseswithpackingfractionproportionally et al.34 and found to correspond to a volume fraction φ of 58% to η011,25,26.In its original formulation, this model describes the volume The primary output of this analysis is a set of image correlation fraction dependence of the zero-shear viscosity, as a function of functions D(Q,∆T), for scattering vectors Q ranging from 2π/L the solvent viscosity, ηs, and a phenomenological threshold vol- to π/lp.To this end, we modelD (Q)astheproductofI(Q)timesthemicroscopetransfer 3.2 Microscopicstructure 0 function, T(Q)24, neglecting the contribution of the static back- Cryo-TEM and particle sizing Asaninitialcharacterizationof ground intensity, which is negligible in the experimental condi- the sample’s microstructure, we examine a concentrated vesicle tionsconsideredinthispaper.BecauseT(Q)dependsuniquelyon suspension(φ≃58%)throughcryo-TEMimaging41.sured samples, we correct for it by normalizing the image static Tobettercharacterizesamplepolydispersity,wesampleitusing structure functions by that measured for the most diluted sam- a commercial particle size analyzer based on static light scatter- ple: I(c,Q)/I(c 0,Q)=D 0(c,Q)/D 0(c 0,Q), where c 0 =0.1%.2b, indicating that vesicles with size between 100nm and independent of concentration, times the structure factor, S(Q), 1µmcontributetoabout90%ofthevolumefraction,withame- which would tend to 1 with decreasing concentration.3.1 Rheology Wemeasuretherate-dependentviscosity,η(γ˙),ofsamplesatdif- Static Light and Small Angle X-ray Scattering Tomoreprop- ferent concentrations, between φ =4.5% and 54%.sample,wecomplementCryo-TEMmeasurementswithSmallAn- gleX-rayscattering(SAXS).Comparingsamplesatdifferentcon- centrations, we find that the scattered intensities, I(Q), almost collapse on a φ-independent mastercurve when normalized by the concentration of surfactant, c, as shown in Fig.More precisely, we obtain a nice collapse for large scattering vectors, while for smaller Q, we identify two distinct families of curves: one for lower concentrations, with c<1%, characterized by an extendedpower-lawregime,I∝Q−3for0.01<Q<0.1nm−1,pre- sumablyarisingfromthelargesamplepolydispersity,andanother for higher concentrations, qualitatively similar to the first one, but shifted towards smaller Q.the multilayer structure of vesicles, the extreme polydispersity of shape and size, and the fluctuations from spherical form that are due to the Microscopy We find that for concentrations above 1%, the membranesoftness.3.3 Microscopicdynamics To mitigate the effect of multiple scattering, we decide to probe the microscopic dynamics of our vesicle suspensions through DDM,followingtheproceduredetailedinSec.2.4.Triangles: Dilute regime For samples in the dilute regime (c < 1%), SALS intensity for the most diluted samples, c≤1%.To confirm this trend, distributionofFig.2b,andcomputetherelativeincreaseintheef- we extend these results by DLS experiments at large scattering fectivevolumefractionthatwouldbeobtainedifthelongrange angles, using the measured correlation functions to extract in- repulsion was forcing the vesicle membranes to stay a distance termediatescatteringfunctionsfullycompatiblewiththosemea- d∗ apart.Concentrated regime To highlight the qualitative features of the dynamics observed in the concentrated regime, we consider thecaseofc=4%,correspondingtoavesiclevolumefractionof φ=18%.Themoststrikingdifferencefromthedilutecase,shown inFig.4a, isthatinanintermediaterangeofscatteringvectors, f(Q,∆T)displaysatwo-stepdecay.Whilethisfeatureisnoteasily detectable from Fig.By contrast, τ1(Q) exhibits a transition between impact at small Q due to the larger depth of focus29, and we diffusive-like dynamics for Q>Q∗, and a small-Q regime where aim at defining a viable Q range where multiple scattering can τ1 depends more weakly on Q, apparently reaching a plateau still be neglected.We fit this model to the data for Q>0.5 µm−1, corresponding to α >0.1, thereby disregard- ing τ1 extracted from correlation functions where the contribu- tion of the fast dynamics accounts for less than 10% of the to- tal decay, as such condition prevents a robust estimation of the fit parameters.We interpret the coexisting fast and slow dynamics, unveiled by DDM, as yet another indication that in this range of concen- trations the sample changes its microstructure, by locally segre- gating vesicles of similar sizes, in microscopic domains of a few microns in size.Open diamonds correspond to α<0.1, open squares correspond to time diffusivity, D fast(φ), with an Arrhenius law49: D fast(φ)= τ2>103 s or to α>0.8.Thisisunexpected,giventhatindependentmea- (black), as estimated from the dependence of the fast decay amplitude surements of interactions between individual vesicles of similar α(Q) (▷), and from the dependence of the fast decay time τ1(Q) (◁).In the single scattering regime, changes in concentration simply scale the in- Fig.To obtain the intermediate scattering function, we fit SmallAngleX-rayScatteringandbackgroundsubtraction D(Q,∆T) with a single stretched exponential decay function, Differencesinthecapillariesthicknessreflectindifferencesinthe D(Q,∆T)= A(Q)(1−exp{−(∆T/τ(Q))0.825}+B(Q), where A(Q) baseline,duetoglassandsolvent(water)scattering.Foreachframerate, DDM measurements can be evaluated by analyzing the his- wecalculateagainthedynamic(D(Q,∆T))andthestatic(D (Q)) 0 tograms of image intensities, P(I˜), obtained for different sam- powerspectrawithoutanybackgroundsubtraction.Forsuchcon- ple concentrations (Fig.Tab.3presentsthe stretching exponents obtained from fitting the ISFs of samples Journal Name, [year], [vol.1 Introduction focus on dispersions of solid particles, with low or moderate Soft glassy materials, like dense colloidal dispersions, gels, and polydispersity,whilethepeculiarbehaviorofdense,polydisperse fibernetworks,aremassivelyexploitedintheproductionofcon- vesiclesuspensionshasnotreceivedmuchattention4–7.AtlowI, system control parameters, such as concentration, temperature, long-range Electrostatic Double Layer (EDL) interactions cause and particle interaction, and strongly depends on the applied thesesuspensionstokineticallyarrest,formingWignerglasses,at shear history1, giving rise to a variety of behaviors that can be volumefractionsassmallasφ =0.2,wellbelowthehard-sphere tailored tothe user needs.Earlier typically formulated at high concentration, and further diluted results suggest that such dense samples display a Newtonian at need.The volume fraction of this starting vesicle dispersion samples, they provide access to the microscopic relaxation time, was characterized according to the method introduced by Seth τ, whichtypicallyincreaseswithpackingfractionproportionally et al.34 and found to correspond to a volume fraction φ of 58% to η011,25,26.2.3 SmallAngleX-rayScattering SmallAngleX-rayScattering(SAXS)experimentshavebeencar- In this paper, we study dense, polydisperse vesicle dis- ried out at the SWING beamline of Soleil synchrotron radiation persions of industrial interest.Datawere Combining optical microscopy, static light scattering and small acquired at two different sample-detector distances to cover the angle X-ray scattering (SAXS), we show that the onset of shear- widestpossiblewavevectorrange,between10and2·104 µm−1.attractive colloidal suspensions, in our repulsive system, we propose the large sample polydispersity as a key ingredient.],1–14 Table1 Samplesconcentration,volumefraction,andapplicableexperimentaltechniques concentration,c[%] volumefraction,φ [%] SAXS SALS SLS/DLS DDM RheologyIn its original formulation, this model describes the volume The primary output of this analysis is a set of image correlation fraction dependence of the zero-shear viscosity, as a function of functions D(Q,∆T), for scattering vectors Q ranging from 2π/L the solvent viscosity, ηs, and a phenomenological threshold vol- to π/lp.sured samples, we correct for it by normalizing the image static Tobettercharacterizesamplepolydispersity,wesampleitusing structure functions by that measured for the most diluted sam- a commercial particle size analyzer based on static light scatter- ple: I(c,Q)/I(c 0,Q)=D 0(c,Q)/D 0(c 0,Q), where c 0 =0.1%.3.1 Rheology Wemeasuretherate-dependentviscosity,η(γ˙),ofsamplesatdif- Static Light and Small Angle X-ray Scattering Tomoreprop- ferent concentrations, between φ =4.5% and 54%.Another mechanism causing structure for- mation in repulsive colloids is depletion: effective attraction be- tween large, repulsive colloids dispersed in a solution of small, non-adsorbingpolymerchains.To confirm this trend, distributionofFig.2b,andcomputetherelativeincreaseintheef- we extend these results by DLS experiments at large scattering fectivevolumefractionthatwouldbeobtainedifthelongrange angles, using the measured correlation functions to extract in- repulsion was forcing the vesicle membranes to stay a distance termediatescatteringfunctionsfullycompatiblewiththosemea- d∗ apart.Dashed line: diffusive fit τ=1/(DQ2) where α is the Q-dependent relative amplitude of the two de- todataatQ<0.6 µm−1,yieldingD≃0.17µm s2 .Assuch, itmaybeattributedeitherto distinct dynamics, reminiscent of glassy systems48: a fast relax- polydispersity, ortoadditionalrelaxationmodesassociatedwith ation process, entailing small-scale displacements that dominate shape fluctuations, that are expected for flexible vesicle mem- thesignalatlargeQ,andaslowrelaxationprocessthatinvolves branesintheregimeQR>1.We fit this model to the data for Q>0.5 µm−1, corresponding to α >0.1, thereby disregard- ing τ1 extracted from correlation functions where the contribu- tion of the fast dynamics accounts for less than 10% of the to- tal decay, as such condition prevents a robust estimation of the fit parameters.We interpret the coexisting fast and slow dynamics, unveiled by DDM, as yet another indication that in this range of concen- trations the sample changes its microstructure, by locally segre- gating vesicles of similar sizes, in microscopic domains of a few microns in size.Open diamonds correspond to α<0.1, open squares correspond to time diffusivity, D fast(φ), with an Arrhenius law49: D fast(φ)= τ2>103 s or to α>0.8.Here, we formulated the assumption that a similar scenario may hold for highly polydisperse suspensions that the assumed linear dependence accounts fairly well for the likeours.Bluecircles: Fig.9showsthecomparisonbetweendifferentrheologicalmod- measured volume fraction values for each c. Red line: linear fitting (φ=5.73c)tothesedata.Rescaled image power spectrum The rescaled image power spectrum, D˜ (Q;c), provides a means to identify the wavevector 0 rangewheremultiplescatteringeffectsmayarise.Foreachframerate, DDM measurements can be evaluated by analyzing the his- wecalculateagainthedynamic(D(Q,∆T))andthestatic(D (Q)) 0 tograms of image intensities, P(I˜), obtained for different sam- powerspectrawithoutanybackgroundsubtraction.Forsuchcon- ple concentrations (Fig.The divergence of the viscosity can be described by different rheological models: Krieger-Dougherty model (blue), Mode Coupling Theory with three free parameters (green), or with two free parameters (red).Tab.3presentsthe stretching exponents obtained from fitting the ISFs of samples Journal Name, [year], [vol.Thedata b b are fitted with stretched exponential decays, with stretching exponent βDLS=0.94.exp(−(∆T/τ)βDLS) d) Average relaxation time τR(Q), fitted with AQ−p, resulting in A=4.25, p=2.45.".Your output should use the following template:\n\n## {Subtitle01}\n- {Bulletpoint01}\n- {Bulletpoint02}\n## {Subtitle02}\n- {Bulletpoint03}\n- {Bulletpoint04}\n\nSummarize the giving topic to generate a mind map (as many subtitles as possible, with a minimum of three subtitles) structure markdown. Do not include anything in the response, that is not the part of mindmap.\n  Most Importantly your output must use language "English" and each point or pointer should include no more than 9 words.
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