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# Tuning the Diameter of Supramolecular Nanocylinders: Balancing Long and Short Polymer Arms for Optimized Self-Assembly

Sandra Kalem, Mingsheng Ji, Antonio Valverde Gonzalez, David Siefker, Jean-michel Guigner, Ralf Schweins, Sandrine Pensec, Jutta Rieger, Laurent Bouteiller, Erwan Nicol, et al.

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Sandra Kalem, Mingsheng Ji, Antonio Valverde Gonzalez, David Siefker, Jean-michel Guigner, et al. Tuning the Diameter of Supramolecular Nanocylinders: Balancing Long and Short Polymer Arms for Optimized Self-Assembly. Journal of Polymer Science, 2025, 46 (1), 10.1002/pol.20250561. hal-05337227

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# Tuning the Diameter of Supramolecular Nanocylinders: Balancing Long and Short Polymer Arms for Optimized Self-Assembly

Sandra Kalem †, Mingsheng Ji ‡, Antonio Valverde Gonzalez ‡, David Siefker †, Jean-Michel Guigner #, Ralf Schweins §, Sandrine Pensec ‡, Jutta Rieger ‡, Laurent Bouteiller ‡, Erwan Nicol* † and Olivier Colombani* †

† Institut des Molécules et Matériaux du Mans (IMMM), UMR 6283 CNRS, Le Mans Université, 72085 Le Mans, Cedex 9, France

erwan.nicol@univ-lemans.fr ; olivier.colombani@univ-lemans.fr

‡ Sorbonne Université, CNRS, Institut Parisien de Chimie Moléculaire, Equipe Chimie des Polymères, 4 Place Jussieu, F-75005 Paris, France

# Sorbonne Université, CNRS UMR 7590, IRD UR 206, MNHN, Institut de Minéralogie, Physique des Matériaux et de Cosmochimie, 4 Place Jussieu, F-75005 Paris, France

§ Institut Max von Laue - Paul Langevin, DS / LSS, 71 Av. des Martyrs, CS 20 156, F-38042 Grenoble, France

**Funding:** This work was supported by the French Agence Nationale de la Recherche in the frame of the ANR project JAROD (ANR-21-CE06-0017).

**Keywords:** Supramolecular Chemistry, Janus particles, Nanocylinders, Hydrogen Bonds, Arm length

## Abstract text.

Nanocylinders find applications in biology, catalysis and material science due to their high aspect ratio and nanometric diameter granting them a high specific area. They can be formed by supramolecular assembly in solution of polymers decorated by stickers promoting directional assembly. Controlling the dimensions of nanocylinders impacts their applicative properties. Many strategies exist to tune their length, much fewer to tune their diameter. We address this point here by synthesizing water-soluble polymers of different lengths end-functionalized by hydrogen
bonding tris(urea) stickers. It is shown through a combination of light/neutron scattering experiments and cryo-transmission electron microscopy, that short polymer arms (DP ≤ 80) produce thin (d = 10 nm) and long (L > 500 nm) nanocylinders, whereas longer polymer arms (DP ≥ 500), required to significantly increase d, inhibit self-assembly due to the strong entropic penalty caused by their stretching. A compromise to control d is to mix a few long arms, which increase d, with a sufficient amount of short arms, which alleviate the entropic penalty and maintain high L. This approach proposes a straightforward way to tune the specific area of nanocylinders; a key parameter for applications in catalysis, emulsion stabilization or interactions with biological materials.

# 1. Introduction

Nanocylindrical particles, which can be metallic, inorganic or organic, exhibit a small diameter ranging from a few to several hundred nanometers, and large lengths from several hundred nanometers to microns. This endows them with high specific surface area and aspect ratio, making them relevant for biomedical[1] or agricultural applications[2] where they can be used to transport and progressively release cargos for example, for composites where they can be used as fillers to improve the mechanical properties or conductivity of the materials[3], for emulsions where they have been shown to be very efficient stabilizers[4], or for catalysis upon their functionalization with catalytically active units[5]. Controlling the length and diameter of nanocylinders is crucial to tune their properties and applicative relevance. For example, transport across biological membranes has been shown to depend on the length and diameter of the nanocylinders[6], thereby affecting the efficiency of drug delivery. The biodistribution and toxicity of nanoparticles has additionally been shown to depend on their shape and size[7, 8]. In the field of catalysis, researchers seek to reduce the diameter of nanocylinders to increase their specific area and thereby improve catalytic efficiency[5].

A versatile approach for creating nanocylindrical particles (or nanorods) relies on supramolecular self-assembly of polymers in solution using directional non covalent interactions such as π-stacking interactions or, mostly, hydrogen bonds between functional groups (stickers) attached to the polymers.[9–13] These directional interactions afford the spontaneous one-dimensional stacking of hundreds to thousands of rather small polymers (a few thousands of g/mol with dimensions of a few nanometers) into supramolecular nanocylinders reaching lengths of several hundred nanometers. Many studies aimed at controlling the dimensions of supramolecular polymer
nanocylinders, both because of the scientific challenge it represents and due to the applicative consequences mentioned above. Most of these studies have focused on controlling the extent of self-assembly, thereby affecting the length of the supramolecular nanocylinders. To this respect, a pioneering theoretical work by Wang *et al.*[14] predicted that the 1D self-assembly of polymers decorated by one sticker per chain resulted in the formation of supramolecular bottle-brush polymers with a very high grafting density. The latter causes steric hindrance, forcing the polymer arms to stretch, which causes a loss of their conformational entropy detrimental to supramolecular assembly. From a thermodynamic point of view, high aggregation numbers, that is long nanocylinders, are formed if the enthalpy gain due to favorable interactions between the 1D-assembling stickers overcomes the entropy loss due to polymer arms stretching.

This can be achieved by using stickers developing very strong interactions, as experimentally achieved in several studies. Perrier, Joliffe and Biesalski,[13, 15, 16] dwelling on initial studies by Ghadiri[17], showed that polymer-decorated cyclic oligopeptides develop strong cooperative hydrogen bonds allowing the formation of several hundred nanometers-long nanocylinders in organic and aqueous medium. Brendel *et al.*[18] demonstrated that benzene tricarboxamide (BTA) stickers initially developed by Meijer *et al.*[19] for small molecules only formed spherical aggregates when decorated with polymer arms, but led to long nanocylinders when the amide hydrogen bonding functions where replaced by urea ones which associate more strongly. Catrouillet *et al.*,[20] in apolar organic solvents, or Han *et al.*,[21] in aqueous medium, observed that increasing the number of urea groups in stickers consisting of several urea units resulted in a transition from small spherical assemblies to nanocylinders of several hundred nanometers. Choisnet *et al.*[22], Obert *et al.*,[23] Mellot *et al.*[12, 24] or Sijbesma *et al.*[25-28] reinforced the hydrogen bonds between bis(urea)s by hydrophobic interactions, whereas Klein *et al.*[29, 30] did the same with benzene trispeptide derivatives, affording the formation of long supramolecular polymer nanocylinders in aqueous medium in spite of the steric hindrance of the polymer arms and of the competing role of water towards hydrogen bonds. Harvey *et al.*[31, 32] or Nicolas *et al.*[33] also demonstrated that the strength of the interactions between bis(urea) stickers can be altered relying on a light or a redox stimulus, respectively, thereby allowing a transition from long nanocylinders to small spheres upon application of the stimulus.
Another thermodynamic approach to tune the length of supramolecular nanocylinders is to control the repulsive interactions between the polymer arms decorating them. Several studies revealed that increasing the degree of polymerization of the polymer arms attached to urea-[³⁴], benzene tripeptide-[³⁵], or cyclic oligopeptide-based[³⁶⁻³⁸] nanocylinders generally reduces the length of the nanocylinders, with some exceptions attributed to subtle effects of hydrogen bond protection by the polymer arms[³⁷]. It was also shown that more sterically hindering polymer units such as styrene[³⁴, ³⁹] or oligoethylene oxide acrylates[⁴⁰] units strongly disfavor self-assembly. Finally, cyclic oligopeptides decorated with pH-sensitive chains were shown to form shorter nanocylinders when the polymer arms became ionized due to repulsive electrostatic interactions[⁴¹, ⁴²]. The length of polymer supramolecular nanocylinders can also be controlled kinetically if the supramolecular nanocylinders are not formed under thermodynamic equilibrium, as is often the case in aqueous medium[²¹, ²², ³², ³³, ⁴³⁻⁴⁷].

Attempts to change the diameter of supramolecular polymer nanocylinders are much rarer. Perrier *et al.*[³⁶] and Biesalski *et al.*[³⁸] both investigated cyclic oligopeptides decorated with polymer arms of different degrees of polymerization in organic medium. The former started by forming the cyclic peptide-decorated polymers and then assembled them, whereas the latter first formed the assemblies and then grew polymer arms by polymerization from the assemblies. In both cases, a progressive increase of the diameter of the nanocylinders was observed (in the 5-15 nm range); albeit with a simultaneous reduction of their length (in the 30-200 nm range) for reasons mentioned above. Perrier *et al.*[³⁶] also mixed 75 mol% of cyclic oligopeptides decorated with poly(*n*-butyl acrylate) arms having a degree of polymerization of 108 (P*n*BA₁₀₈) with 25 mol% of P*n*BA₁₆, leading to nanocylinders with lengths intermediate between the two extreme cases (0 or 100% of P*n*BA₁₆). The impact on the diameter of the nanocylinders was not commented by the authors and seemed weak according to Transmission Electron Microscopy (TEM) images.

To fill this gap, we therefore aimed in this paper at controlling the diameter of supramolecular polymer nanocylinders while keeping their length above the 100 nm range. This study was conducted with a bicomponent system consisting of 48-PDMAcₓ/84-PHEAᵧ where PDMAc = poly(dimethyl acrylamide), PHEA = poly(2-hydroxyethyl acrylate), 48- and 84- are two complementary hydrogen bonding stickers consisting of three urea functions separated respectively by 4 and 8 or 8 and 4 methylene units (Figure 1A).[⁴⁷] These stickers were chosen because they
develop strong hydrogen bonding and hydrophobic interactions, affording the formation of long
supramolecular nanocylinders in water. Additionally, the complementarity of the stickers allows
the formation of Janus nanocylinders decorated with a different polymer arm on each side[45]
without relying on the incompatibility of the polymer arms as required for other strategies in the
literature[44, 48–50]. With short polymer arms (x = 80 and y = 50, **Figure 1B.1**), long (L > 500 nm)
and thin (d = 10 nm) supramolecular nanocylinders[45, 47] were obtained. In order to affect
significantly the diameter of the nanocylinders, stickers decorated with very long polymer arms
were prepared (x = y = 500 or 1300) in the present study. However, based on the literature
summarized above, these long polymer arms should hinder assembly and therefore reduce L,
resulting in thick but short nanocylinders (**Figure 1B.2**). Long and short arms were therefore mixed
according to different strategies (**Figures 1B.3 and 1B.4**) in order to find the right balance of steric
hindrance and optimize supramolecular assembly to tune L and d independently. The assemblies
were studied mainly by light scattering (LS) and cryogenic transmission electron microscopy (cryo-
TEM) and completed by small angle neutron scattering (SANS) experiments for the most relevant
samples.

<figure><img src="image_2.png" /><figcaption>**Figure 1.** **A:** Structure of 48-PDMAcₓ and 84-PHEAᵧ. The polymers are functionalized with a non-symmetrical hydrogen bonding sticker consisting of three urea functions separated first by either 4</figcaption></figure>
or 8 carbons. **B**: Different combinations of arms degrees of polymerization (x and y) to control the length L and diameter d of the JNR (see text).

## 2. Results and Discussion

The synthesis of the polymers used in this study is described in Section 1 of the Supporting Information.

## 1. Impact of the arm length using complementary polymers with similar arm lengths on both sides

First, the impact of the arm length of the polymers on their extent of assembly and on the resulting length (L) and diameter (d) of the objects was investigated by using polymer pairs (48-PDMAcₓ and 84-PHEAᵧ) with increasing degrees of polymerizations (DPn) but with similar DPn on each side for a given pair (x ~ y) as depicted on **Figure 1A-B**. Specifically, the assemblies obtained with a pair of short polymers (48-PDMAc₈₀ + 84-PHEA₅₀) were compared to those formed with medium-sized polymers (48-PDMAc₅₀₀ + 84-PHEA₆₀₀) or long ones (48-PDMAc₁₃₀₀ + 84-PHEA₁₃₀₀). DPn ≥ 500 were intentionally selected, as doubling the DPn from ~ 40 to ~ 80 did not result in any noticeable difference in diameter (**Figure S7**).

It was previously reported that an equimolar mixture of 48-PDMAc₈₀ + 84-PHEA₅₀ formed well defined nanocylinders in aqueous medium; but that the latter were out-of-equilibrium structures with characteristics depending on the preparation process.[45, 47] Long nanocylinders were obtained by following a so-called “DMSO-route”. It consisted in preparing, first, an equimolar mixture of 48-PDMAc₈₀ + 84-PHEA₅₀ in DMSO at a total polymer concentration C₀ = 90 g/L. DMSO was selected because it allows the complete dissolution and dissociation of 48-PDMAc₈₀ and 84-PHEA₅₀ into unassembled chains. Then, water was added under stirring at a constant flow rate of 0.5 mL/h and at 20 °C until a final polymer concentration of 0.9 g/L and a DMSO/water content of 1/99 by volume were reached. The characteristics of the resulting assemblies were already presented in a previous study.[47] Briefly, cryo-TEM revealed rod-shaped structures several hundred nanometers long which exhibited a diameter of approximately 10 nm (almost monodisperse in terms of diameter) (**Figure 2A**). Static Light Scattering (SLS) data showed that the scattered intensity displayed a q⁻¹ dependency, which confirmed the formation of rigid
cylindrical structures with a length exceeding 1000 nm, corresponding to a radius of gyration R_g > 300 nm, in agreement with the cryo-TEM observations (Figure 2A and 2B). The molecular weight M_w exceeded 10^7 g/mol, corresponding to a minimum aggregation number N fen = M_w/M_w[unimers] > 1300 (no plateau was observed at low q values). Dynamic Light Scattering (DLS) yielded a hydrodynamic radius R_h = 70 nm, corresponding to a R_g/R_h ratio > 4, again compatible with anisotropic structures. Finally, SANS confirmed the diameter of 10 nm found by cryoTEM (Figure 2B). Overall, cryo-TEM, SANS and LS confirmed the formation of long, thin and rigid nanorods for 48-PDMAc50 + 84-PHEA50 as previously observed for other polymer arms (48-PDMAc32 + 84-PNAM46). [45] The amount of polymer effectively forming nanocylinders was estimated to be 70% from the absolute value of the scattered intensity in the q⁻¹-dependent region. [47]

On the contrary, increasing the DPn of the complementary polymers to 500 or 1300, leading to mixtures of 48-PDMAc500 + 84-PHEA600 or 48-PDMAc1300 + 84-PHEA1300, respectively, resulted in both cases in the absence of any angular dependency of the scattered intensity in SLS indicating the formation of small particles (R_g < 20 nm). The weight-average molar mass (Mw 48-PDMAc500+84-PHEA600 = 1.15·10^5 g/mol and Mw 48-PDMAc1300+84-PHEA1300 = 1.5·10^5 g/mol) of the particles revealed their very low aggregation number: Nagg = Mw / Mw[unimer] = 1.9 for (48-PDMAc500 + 84-PHEA600) and Nagg = 1.1 for (48-PDMAc1300 + 84-PHEA1300). DLS measurements revealed the existence of a single population of scatterers with an average hydrodynamic radius R_h = 30 nm in the case of 48-PDMAc500 + 84-PHEA600 and R_h = 30 nm for 48-PDMAc1300 + 84-PHEA1300. These results imply that 48-PDMAc1300 and 84-PHEA1300 hardly co-assemble: they remain in the unimer state or close to it. (48-PDMAc500 + 84-PHEA600) have an Nagg slightly above one and a similar R_h = 30 nm compared to (48-PDMAc1300 + 84-PHEA1300) in spite of the comparatively lower DPn of their arms. This can potentially be attributed to the presence of a small amount of aggregates in addition to unimers for the former pair, or to the co-assembly of this polymer pair into short supramolecular oligomers (note that both polymers alone in aqueous solution remain as unimers, with Mw = 6.0·10^4 g/mol corresponding to Nagg = 1.2 for 48-PDMAc500 and Mw = 7.0·10^4 g/mol corresponding to Nagg = 1.0 for 84-PHEA600 see Figure S8). However, the association remains very weak. Overall, SLS and DLS showed that (48-PDMAc500 + 84-PHEA600) and (48-PDMAc1300 + 84-PHEA1300) do not self-assemble (or co-assemble very weakly) and certainly do not form nanocylinders (Figure 2C).
<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /><figcaption>**Figure 2.** Reference conditions to form nanocylinders: (48-PDMAc<sub>x</sub> and 84-PHEA<sub>y</sub>) equimolar mixture (0.9 g L<sup>-1</sup> in DMSO/water (1/99 v/v) obtained starting from C<sub>0</sub> = 90 g.L<sup>-1</sup> in DMSO, with an addition rate of water R = 0.5 mL/h at T = 20 °C until a final polymer concentration C<sub>f</sub> = 0.9 g L<sup>-1</sup>. **A:** cryo-TEM image of 48-PDMAc<sub>80</sub> + 84-PHEA<sub>50</sub>; **B:** SLS data and SANS data of 48-PDMAc<sub>80</sub> + 84-PHEA<sub>50</sub> (blue circles, empty for SLS and filled for SANS). The data were fitted (red curve) by combining a model of cylinders exhibiting a disperse radius r = 5.0 ± 1.2 nm (lognormal distribution, PD = 0.3) with L >1000 nm with a Gaussian coil model (R<sub>g</sub> = 2 ± 1.0 nm nm, i<sub>0</sub> = 0.06 cm<sup>-1</sup>). SLS data for 48-PDMAc<sub>500</sub> + 84-PHEA<sub>600</sub> (pink diamonds) and 48-PDMAc<sub>1300</sub> + 84-PHEA<sub>1300</sub> (green triangles). SANS data were only performed for the system where there is</figcaption></figure>
co-assembly. C: Schematic representation of the targeted morphologies (not obtained) and of the resulting objects.

Increasing the length of the polymer arms while keeping the process parameters constant therefore strongly impacted the extent of assembly. One reason to explain this result may be a change of the urea concentration during the experiments as decreasing C₀ has been observed to lower the extent of assembly.[47] Indeed, all experiments were conducted at the same weight concentration of polymer, which implies a much lower molar concentration of urea functions with increasing DPn of the arms and may prevent assembly. To investigate this issue, the (48-PDMAc₁₃₀₀ + 84-PHEA₁₃₀₀) pair was tested starting from a higher polymer concentration: 180 g/L in DMSO, corresponding to [tris(urea)] = 1.3·10⁻³ mol/L. The results were compared to those obtained for (48-PDMAc₈₀ + 84-PHEA₅₀) starting from a lower polymer concentration: 9 g/L in DMSO, corresponding to nearly the same urea concentration [tris(urea)] = 1.2·10⁻³ mol/L. In these conditions, (48-PDMAc₈₀ + 84-PHEA₅₀) formed fewer and shorter nanocylinders[47] (see Figure S9), but long nanocylinders (L= 400nm) in significant proportions were still observed. On the contrary, despite the increase of the tris(urea) concentration in the (48-PDMAc₁₃₀₀ + 84-PHEA₁₃₀₀) mixture, the polymer still remained as unimers, implying that the change of urea concentration alone cannot explain the absence of assembly for the long polymers.

Another explanation of the observed results may be the increased entropic penalty of stretching for
longer arms as outlined in the introduction.[13, 14] Quantitatively, the distance between two
consecutive arms along the axis of the nanocylinders is about 1 nm, whereas the diameter of
gyration in DMSO of unassembled 48-PDMAc80 or 84-PHEA50 is about 6 nm.[47] These rather
short polymer arms should therefore not have to stretch too much to accommodate within a
nanocylindrical supramolecular assembly. Indeed, considering a dimension of 0.25 nm per vinylic
monomer unit, the theoretical diameter of the nanocylinders formed by 48-PDMAc80+84-PHEA50
should be (80 + 50) x 0.25 ~ 33 nm if the polymer arms were fully stretched within the
nanocylinders and if the dimension of the stickers was neglected. The actual experimental diameter
of the nanocylinders (10 nm) formed by these polymers suggests that the polymers are stretched to
~ 30% of their full length. On the contrary, unassembled chains of 48-PDMAc500 (or 1300) and 84-
PHEA600 (or 1300) exhibit a very large hydrodynamic diameter (Dh = 2.Rh ~ 60 nm) compared to
the distance of 1 nm separating two consecutive chains within a cylindrical supramolecular structure. These long polymer chains would need to stretch strongly to allow the formation of nanocylinders. The high cost of conformational entropy due to stretching thus probably explains the lack of assembly of the average and long (DPn = 500 and 1300) polymers. This hypothesis is supported theoretically by the general model proposed by Wang et al.[14] described in the introduction and experimentally by the behavior of similar 1D-assembling systems.[18, 20, 21, 50]

Finally, the driving force for the assembly of these stickers was previously revealed to be due to a combination of hydrogen bonding between the urea units and hydrophobic effect caused by the alkyl chains separating the urea units. It was actually observed that the extent of assembly increases with increasing water content in DMSO/water mixtures, possibly because the polymers become less soluble with higher water contents, triggering their assembly into nanostructures.[47] It is therefore possible that much longer hydrophilic chains attached to the assembling stickers increase the solubility of the molecules in DMSO/water, disfavoring assembly.

Overall, these results demonstrate a pronounced effect of the DPn on the association. Nanocylinders were not obtained with medium or long arms, preventing any control of their dimensions. To cope with this issue, it was attempted to mix long polymer arms with short ones. It was anticipated that the long arms would govern the diameter of the nanocylinders, whereas the presence of the short ones would favor assembly by reducing the entropic penalty of stretching of the arms or possibly by achieving a favorable hydrophilic/hydrophobic balance. Several different mixing strategies are presented in the following parts.

## 2. Combining short arms on one side with long arms on the other side

Given that a DPn ≥ 500 completely inhibits assembly when long arms are present on both sides, it was attempted to use only one longer arm on one side and a short one on the other side (Figure 1B.3). To that respect, (48-PDMAc500+ 84-PHEA50) was tested in standard conditions (starting from a total concentration of 90 g/L in DMSO and respecting an equimolar ratio of each sticker). Cryo-TEM revealed rod-shaped structures that measure several hundred nanometers in length and exhibit a rather uniform diameter of approximately 7 nm (Figure 3A). The SLS data (Figure 3C)
exhibited a $q^{-1}$ dependency, confirming the formation of rigid cylindrical structures with a length of 400 nm, consistent with the cryo-TEM observation.

One may argue at this stage that our strategy to control the diameter of the nanocylinders was successful. However, co-assembly of 48-PDMAc<sub>500</sub> and 84-PHEA<sub>50</sub> should have led to an increase of the diameter of the cylinders compared to (48-PDMAc<sub>80</sub> + 84-PHEA<sub>50</sub>). On the contrary, the diameter of the nanocylinders formed by (48-PDMAc<sub>500</sub> + 84-PHEA<sub>50</sub>) (d = 7 nm, see **Figure 3A**) was smaller than that of cylinders formed by (48-PDMAc<sub>80</sub> + 84-PHEA<sub>50</sub>) (d = 10 nm, see **Figure 3A**). In order to understand this result, DMSO/water solutions were prepared applying the same elaboration process to each polymer of the mixture separately. It was observed by light scattering that 48-PDMAc<sub>500</sub> remained unassembled as expected (see **Figure S10**). In contrast, 84-PHEA<sub>50</sub> alone self-assembled into nanocylinders with a diameter of 7 nm according to cryoTEM (**Figure 3B**), consistent with the diameter of the nanocylinders formed by (48-PDMAc<sub>500</sub> + 84-PHEA<sub>50</sub>) (**Figure 3A**). This suggests that co-assembly between the two polymers did not occur and that the nanocylinders observed for the solution of (48-PDMAc<sub>500</sub> + 84-PHEA<sub>50</sub>) consisted of 84-PHEA<sub>50</sub> homo-assemblies (**Figure 3D**).
<figure><img src="image_6.png" /><figcaption>**Figure 3.** (48-PDMAc₅₀₀ and 84-PHEA₅₀) equimolar mixture (0.9 g L⁻¹ in DMSO/water (1/99 v/v) obtained starting from C₀ = 90 g/L in DMSO, with an addition rate of water R = 0.5 mL/h at T = 20 °C until a final polymer concentration C_f = 0.9 g L⁻¹. **A:** cryo-TEM image of 48-PDMAc₅₀₀ + 84-PHEA₅₀; **B:** cryo-TEM image of 84-PHEA₅₀ alone (C₀ = 10 g/L in DMSO, with an addition rate of water R = 0.5 mL/h at T = 20 °C until a final polymer concentration C_f = 1 g L⁻¹ at DMSO/water 10/90. The scale is the same for both cryoTEM images and is indicated in image **B**; **C:** SLS data of 48-PDMAc₅₀₀ + 84-PHEA₅₀ in diamond (C₀ = 90 g/L and C_f = 0.9 g L⁻¹). The theoretical curve expected in the absence of co-assembly between 48-PDMAc₅₀₀ and 84-PHEA₅₀</figcaption></figure>
(that is if 48-PDMAc<sub>500</sub> remains as unimers in the mixture, whereas 84-PHEA<sub>50</sub> forms the same nanocylinders as when it is alone in solution) is presented in black dashed line. The theoretical curve expected for a complete co-assembly of 48-PDMAc<sub>500</sub> + 84-PHEA<sub>50</sub> (assuming that 70% by weight of the polymer forms nanocylinders, as observed for 48-PDMAc<sub>80</sub> + 84-PHEA<sub>50</sub>) is presented as green dashed line. **D**: Schematic representation of the targeted morphologies (not obtained, crossed-out) and of the particles effectively formed.

To further validate this hypothesis, SLS was performed. Two extreme scenarios can be postulated. If 48-PDMAc<sub>500</sub> and 84-PHEA<sub>50</sub> polymers do not co-assemble and behave exactly as they do when prepared on their own, with no interaction with each other, the (I/KC) value of the mixture should equal the mass-weighted average values of (I/KC) measured for each polymer separately (Figure 3C and Figure S10). On the contrary, in the case of complete co-assembly, it is possible to predict the expected scattering intensity that co-assembled cylinders would have by assuming 1) that the proportion of formed cylinders is the same as in the most favorable case with small arms on each side (48-PDMAc<sub>80</sub> + 84-PHEA<sub>50</sub>), that is 70 wt%; 2) that the nanocylinders consist of one molecule in the cross-section and; 3) that their length is larger than the whole q<sup>-1</sup> range (Figure 3C, green dashed line). An intermediate situation would indicate the formation of a reduced proportion of nanocylinders, incomplete incorporation of one of the polymer arms, or a combination of both hypotheses. The experimental data for (48-PDMAc<sub>500</sub> + 84-PHEA<sub>50</sub>) actually superimpose with the first extreme scenario corresponding to no interaction in the mixture between 48-PDMAc<sub>500</sub> and 84-PHEA<sub>50</sub> (Figure 3C). In other words, when 48-PDMAc<sub>500</sub> and 84-PHEA<sub>50</sub> are mixed in an equimolar way, 84-PHEA<sub>50</sub> self-assembles to form nanocylinders on its own (d = 7 nm), whereas 48-PDMAc<sub>500</sub> remains as unimers (Figure 3D).

Three other mixtures (48-PDMAc<sub>80</sub> + 84-PHEA<sub>600</sub>), (48-PDMAc<sub>1300</sub> + 84-PHEA<sub>50</sub>) and (48-PDMAc<sub>80</sub> + 84-PHEA<sub>1300</sub>) were also studied, leading to the same conclusion (Figure S11, S12 and S13). Therefore, the strategy consisting in mixing short polymer arms on one side of the nanocylinders and long ones on the other side to alleviate entropic penalty compared to the previous section (long arms on both sides) did not allow co-assembly of the short and longer arms and did not allow tuning d and L of the nanocylinders. To solve this issue, it was attempted to mix short arms with a fraction of medium ones on each side (Figure 1B.4).
### 3. Combining mixture of short/medium arms on both sides

To further alleviate the entropic penalty for assembly caused by longer polymer arms, their amount was decreased. 10 mol% of 48-PDMAc₅₀₀ were mixed with 90 mol% of 48-PDMAc₈₀ on one side and 10 mol% of 84-PHEA₆₀₀ were mixed with 90 mol% of 84-PHEA₅₀ on the other side of the targeted nanocylinders: (48-PDMAc₈₀/500(0.9/0.1) + 84-PHEA₅₀/600(0.9/0.1)). The cryo-TEM analysis revealed the presence of nanocylinders that were slightly shorter than those observed for (48-PDMAc₈₀ + 84-PHEA₅₀), with a diameter of approximately 10 nm (Figure 4A). Polydisperse spheres were also observed with a diameter ranging from 14 nm to 80 nm (Figure 4B). In SLS, the measurement confirms the presence of different types of objects as the data were compatible with a $q^{-1}$ dependency of the scattered intensity only for high q values (Figure 4C), suggesting a different behavior than for (48-PDMAc₈₀ + 84-PHEA₅₀). The experimental data were different from the two extreme scenarios where either 1) (48-PDMAc₈₀ + 84-PHEA₅₀) co-assemble on their own, whereas 48-PDMAc₅₀₀ and 84-PHEA₆₀₀ remain as unimers, or 2) 48-PDMAc₈₀, 48-PDMAc₅₀₀, 84-PHEA₅₀ and 84-PHEA₆₀₀ fully and perfectly co-assemble into nanocylinders. This implies that the presence of the 10 mol% of 48-PDMAc₅₀₀ and 84-PHEA₆₀₀ on each respective side influences the co-assembly of (48-PDMAc₈₀ + 84-PHEA₅₀). However, it remains unclear whether the nanocylinders observed by cryoTEM contain 48-PDMAc₅₀₀ and/or 84-PHEA₆₀₀ arms or if these nanocylinders only consist of (48-PDMAc₈₀ + 84-PHEA₅₀) the assembly of which is hindered to some extent by the presence of longer arms in the solution. Indeed, the experimental curve does not match the theoretical curve predicted for the co-assembly of only short arms. It is not possible either at this stage to determine which type of arms compose the spheres. Additionally, the diameter of the nanocylinders is not significantly increased through this strategy compared to the initial diameter of 10 nm for (48-PDMAc₈₀ + 84-PHEA₅₀) and the presence of the large spheres represents a problematic deviation from our intended objective (Figure 4D). Consequently, we have elected to discontinue this approach.
<figure><img src="image_7.png" /><figcaption>**Figure 4.** (48-PDMAc<sub>80/500(0.9/0.1)</sub> + 84-PHEA<sub>50/600(0.9/0.1)</sub> equimolar mixture (0.9 g L<sup>-1</sup> in DMSO/water (1/99 v/v) obtained starting from C<sub>0</sub> = 90 g/L in DMSO, with an addition rate of water R = 0.5 mL/h at T = 20 °C until a final polymer concentration C<sub>f</sub> = 0.9 g L<sup>-1</sup>). **A** and **B**: cryo-TEM image of 48-PDMAc<sub>80/500(0.9/0.1)</sub> + 84-PHEA<sub>50/600(0.9/0.1)</sub>. The scale is the same for both cryoTEM images and is indicated in image **B**; **C**: SLS data of (48-PDMAc<sub>80/500(0.9/0.1)</sub> + 84-PHEA<sub>50/600(0.9/0.1)</sub>) (purple triangles, △). The theoretical curve expected in the absence of co-assembly between 48-PDMAc<sub>80/500(0.9/0.1)</sub> + 84-PHEA<sub>50/600(0.9/0.1)</sub> (that is if 48-PDMAc<sub>500</sub> and 48-PDMAc<sub>600</sub> remain as unimers in the mixture, whereas 48-PDMAc<sub>80</sub> + 84-PHEA<sub>50</sub> form the same nanocylinders as when they are alone in solution corresponding to 45g/L as a starting concentration</figcaption></figure>
for 48-PDMAc80 + 84-PHEA50) is presented as black dashed line. The theoretical curve expected
for a complete co-assembly of 48-PDMAc80/500(0.9/0.1) + 84- PHEA50/600(0.9/0.1) (assuming that 70%
by weight of the polymer forms nanocylinders, as observed for 48-PDMAc80 + 84-PHEA50) is
presented as green dashed line. D: Schematic representation of the targeted morphologies (not
obtained) and of the particles effectively formed.

The same experiments were performed on 48-PDMAc80/1300(0.9/0.1) + 84-PHEA50/1300(0.9/0.1) and the
results demonstrated that the shorter DPn form assemblies independently, while the longer DPn
remain as unimers (Figure S15 and S16).

4. Combining short and medium arms on one side with short arms on the other side

In order to further decrease steric hindrance to promote the co-assembly of at least a portion of the
long arms and control both L and d, two arms of different lengths were mixed on only the 48-
PDMAc side. Two molar fractions, 10 mol% and 50 mol%, of 48-PDMAc500 were incorporated
with 48-PDMAc80 and mixed with one equivalent of 84-PHEA50.

The (48-PDMAc80/500(0.9/0.1) + 84-PHEA50) mixture formed rod-shaped structures hundreds of
nanometers long and exhibiting a rather uniform diameter of approximately 13 nm according to
cryoTEM (Figure 5A). The change of diameter was confirmed by SANS experiments (Figure 5E).
This suggests that co-assembly occurred between the small and medium arms as the diameter
increased by 30 % compared to (48-PDMAc80+ 84-PHEA50) (d = 10 nm, Figure 2A). This result
was confirmed by SLS (Figure 5B): the total scattering intensity of the mixture (48-
PDMAc80/500(0.9/0.1) + 84-PHEA50) is nearly identical to the theoretical curve predicted for complete
co-assembly. A small curvature at the lowest q for the experimental data suggests that the
nanocylinders are slightly shorter than 1000 nm, in good agreement with cryoTEM, whereas the
model curve was plotted for infinitely long nanocylinders, explaining the perfect q⁻¹ dependency
down to the lowest q for the latter.

Increasing the proportion of medium arms to 50 mol%, corresponding to (48-PDMAc80/500(0.5/0.5) + 84-PHEA50), still leads to long nanocylinders according to cryo-TEM (Figure 5C) and SANS (Figure 5E), without any change in diameter (d = 13 nm) compared to 10 mol% of 48-PDMAc500.
In SLS, the $q^{-1}$ dependency of the scattering intensity at $q > 5.10^6$ m$^{-1}$ confirms the presence of nanocylinders (**Figure 5D and 5E, Table 1**) with a length of 610 nm, that is shorter than with 10 mol% of 48-PDMAc$_{500}$, in agreement with cryoTEM. However, the experimental curve exhibits a lower value than the theoretical prediction for complete co-assembly ($M_{L,exp}/M_{L,theo} = 15.10^3 /26.10^3 = 0.56$). This suggests that 50 mol% of medium arms hinder partly the assembly. Indeed, the decrease of scattered intensity compared to the theoretical prediction for complete co-assembly can be explained either 1) if the 48-PDMAc$_{80}$-to-48-PDMAc$_{500}$ proportion is the same within the nanocylinders as the overall proportion in the solution but with a lower weight concentration of polymers forming nanocylinders in this mixture (< 70 %) as for (48-PDMAc$_{80}$ + 84-PHEA$_{50}$) (70%); 2) if the weight proportion of polymers forming nanocylinders is 70% for (48-PDMAc$_{80/500(0.5/0.5)}$ + 84-PHEA$_{50}$) (that is the same as for (48-PDMAc$_{80}$ + 84-PHEA$_{50}$ **Figure 2B))), but with a lower proportion of 48-PDMAc$_{500}$ incorporated within the nanocylinders than the overall proportion in the mixture; or 3) if both parameters are lower than expected in the model (weight proportion of polymer forming nanocylinders and amount of 48-PDMAc$_{500}$ arms in the nanocylinders).
<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>
**Figure 5.** **A:** cryo-TEM image of 48-PDMAc<sub>80/500(0.9/0.1)</sub> + 84-PHEA<sub>50</sub> (pink triangles, △). **B:** SLS data of 48-PDMAc<sub>80/500(0.9/0.1)</sub> + 84-PHEA<sub>50</sub> (pink triangles, △). The theoretical curve expected in the absence of co-assembly between 48-PDMAc<sub>80/500(0.9/0.1)</sub> + 84-PHEA<sub>50</sub> (that is if 48-PDMAc<sub>500</sub> remains as unimers in the mixture, whereas 48-PDMAc<sub>80</sub> + 84-PHEA<sub>50</sub> forms the same nanocylinders as when it is alone in solution) is presented as black dashed line. **C:** cryo-TEM image of 48-PDMAc<sub>80/500(0.5/0.5)</sub> + 84-PHEA<sub>50</sub>. **D:** SLS data of 48-PDMAc<sub>80/500(0.5/0.5)</sub> + 84-PHEA<sub>50</sub> (orange circles, ○). The theoretical curve expected in the absence of co-assembly between 48-PDMAc<sub>80/500(0.5/0.5)</sub> + 84-PHEA<sub>50</sub> (that is if 48-PDMAc<sub>500</sub> remains as unimers in the mixture, whereas 48-PDMAc<sub>80</sub> + 84-PHEA<sub>50</sub> forms the same nanocylinders as when they are alone in solution) is presented as black dashed line. The theoretical curve expected for a complete co-assembly of 48-PDMAc<sub>80/500(0.5/0.5)</sub> + 84-PHEA<sub>50</sub> (assuming that 70% by weight of the polymer forms nanocylinders, as observed for 48-PDMAc<sub>80</sub> + 84-PHEA<sub>50</sub>) is presented as green dashed line. **E:** SLS (empty symbol) and SANS data (filled symbol) of 48-PDMAc<sub>80</sub> + 84-PHEA<sub>50</sub> (blue circles ○, ●), 48-PDMAc<sub>80/500(0.9/0.1)</sub> + 84-PHEA<sub>50</sub> (pink triangles △, ▲) and 48-PDMAc<sub>80/500(0.5/0.5)</sub> + 84-PHEA<sub>50</sub> (orange diamonds ◇, ♦). The data were fit by combining a model of cylinders exhibiting a disperse radius r (lognormal distribution, PD = 0.3) and monodisperse length L with a Gaussian coil model (R<sub>g</sub> = 2 ± 1.0 nm, nm, i<sub>0</sub> = 0.06 cm<sup>-1</sup>). For 48-PDMAc<sub>80</sub> + 84-PHEA<sub>50</sub>, r = 5.0 ± 1.2 nm and L > 1000 nm. For 48-PDMAc<sub>80/500(0.9/0.1)</sub> + 84-PHEA<sub>50</sub>, r = 6.5 ± 1.3 nm and L = 780 nm. For 48-PDMAc<sub>80/500(0.5/0.5)</sub> + 84-PHEA<sub>50</sub>, r = 6.5 ± 1.3 nm and L = 610 nm for 48-PDMAc<sub>80/500(0.5/0.5)</sub> + 84-PHEA<sub>50</sub>.

Overall, mixing 48-PDMAc<sub>500</sub> medium-sized arms with 48-PDMAc<sub>80</sub> short ones on only one side of the nanocylinders does allow their co-assembly into long (L > 600 nm) nanocylinders with an increased diameter, as confirmed by SANS and cryo-TEM (Figure 5) as long as the amount of medium-sized arms remains low. The higher the amount of longer arms, the shorter the nanocylinders and the more incomplete the co-assembly, until co-assembly does not occur anymore for 100% 48-PDMAc<sub>500</sub> on the PDMAc-side (Table 1). This confirms that the presence of longer arms limits the extent of assembly, either because of steric hindrance (= entropic penalty) and/or because of a decrease of the hydrophobic interactions of the stickers in the presence of long
hydrophilic polymer arms. The impact on the diameter of the nanocylinders seems similar for 10 mol% or 50 mol% of 48-PDMAc500. Considering that fully stretched long arms would have a contour length of 125 nm and that Gaussian coils of PDMAc500 have a hydrodynamic radius of 30 nm (see section 2), the experimental diameter is not solely dictated by the PDMAc500 arms but probably corresponds to an average between the contribution of the PDMAc500 and PDMAc80 arms. The fact that the diameter does not increase above 13 nm no matter whether 10 or 50 mol% of PDMAc500 arms are added in the mixture and the fact that co-assembly is imperfect for 50 mol% of PDMAc500 may then suggest that the amount of PDMAc500 which can effectively co-assemble within the cylinders is limited; preventing d to increase further.

<table><caption>**Table 1.** Characteristics of the nanocylinders formed with the different mixtures of polymers with the following conditions: C₀ = 90 g/L, R = 0.5 mL/h at T = 20 °C, Cₛ = 0.9 g/L.</caption><thead><tr><th rowspan="2"></th><th colspan="2">d<sup>a</sup> [nm]</th><th>L<sup>b</sup> [nm]</th></tr><tr><th>SANS</th><th>Cryo-TEM</th><th>SANS</th></tr></thead><tbody><tr><td>48-PDMAc<sub>80</sub>+84 PHEA<sub>50</sub></td><td>10 ± 2.4 nm</td><td>10 ± 1.9 nm</td><td>&gt;1000</td></tr><tr><td>48-PDMAc<sub>80/500(0.9/0.1)</sub>+84 PHEA<sub>50</sub></td><td>13 ± 2.6 nm</td><td>13 ± 1.7 nm</td><td>780</td></tr><tr><td>48-PDMAc<sub>80/500(0.5/0.5)</sub>+84 PHEA<sub>50</sub></td><td>13 ± 2.6 nm</td><td>13 ± 1.5 nm</td><td>610</td></tr><tr><td>48-PDMAc<sub>500</sub> + 84 PHEA<sub>50</sub></td><td colspan="3">No co-assembly</td></tr></tbody></table>

a) diameter d was determined by cryo-TEM and by SANS (Figure 5), fitting the data using a model of cylinders. b) length L was determined by fitting the SLS+SANS data using a model of cylinders (Figure 5E).

Attempts to co-assemble (48-PDMAc80/1300(0.9/0.1) + 84-PHEA50) resulted in the independent co-assembly of (48-PDMAc80 + 84-PHEA50) into nanocylinders while 48-PDMAc1300 remained as
unimers (Figure S17). This is most probably due to the too strong steric hindrance/entropic penalty caused by 48-PDMAc<sub>1300</sub>.

**Conclusion**

To summarize, different strategies were investigated to try to control independently the length and the diameter of supramolecular nanocylinders formed in aqueous medium by combining 48-PDMAc<sub>x</sub> and 84-PHEA<sub>y</sub> building blocks in order to optimize co-assembly. The assemblies were studied using LS, cryoTEM and SANS. The results showed that medium and long arms, with a DP<sub>n</sub> of 500/600 (Figure 6, box D3) or 1300/1300 respectively, significantly hinder the self-assembly processes. Consequently, it is not feasible to obtain long nanocylinders of large diameters using these arms alone. Having longer arms on only one side or mixing a small amount of longer arms (DP = 500 or 1300) with short ones (DP = 80) on both sides of the nanocylinders was not successful either, probably because the steric hindrance / entropic penalty caused by the longer arms was still too high. It was eventually possible to incorporate medium-sized 48-PDMAc<sub>500</sub> arms on one side of the nanocylinders resulting in a significantly (30%) increased diameter of the nanocylinders while only slightly limiting their length (Figure 6, box B1 and C1), provided that only short 84-PHEA<sub>50</sub> arms were present on the other side and that the proportion of 48-PDMAc<sub>500</sub> arms remained limited.
<figure><img src="image_13.png" /><figcaption>**Figure 6.** Schematic overview of the morphologies obtained with different combinations. With green background, the mixture of short and medium arms on one side resulted in an increased diameter. Boxes with red background show either no co-assembly or, in one case, a mixture of nanocylinders and spheres (represented in purple). In this latter case, co-assembly does occur, but the distribution of the polymers into the spheres and nanocylinders is unknown and the diameter of the nanocylinders remains unaffected.</figcaption></figure>

# 4. Experimental Section/Methods

**4.1. Synthesis of the polymers.** The synthesis of the polymers 48-PDMAcₓ and 84-PHEAᵧ (Figure 1A) was achieved by Radical Addition Fragmentation chain-Transfer (RAFT) polymerization using chain transfer agents (CTA) bearing the 48- or 84- stickers, namely 48-CTA or 84-CTA. The synthesis of the CTA stickers was previously reported, [45] whereas the conditions for the RAFT polymerization and the characteristics of the polymers are described in Supporting Information (Table S1).
Deuterated solvents (toluene-d<sub>8</sub>, CDCl<sub>3</sub>, DMSO-d<sub>6</sub> and D<sub>2</sub>O) and hydrogenated DMSO were purchased from Aldrich. MilliQ (18.2 MΩ.cm) water was used. PTFE filters with 1 µm pore size were purchased from Whatman.

**4.2. Preparation of the solutions.** The preparation of the solutions for light scattering was previously reported<sup>[22, 45]</sup>. Stock polymer solutions of 48-PDMAc<sub>x</sub> and 84-PHEA<sub>y</sub> were independently dissolved in DMSO at a concentration of 90 g/L. After heating them for 30 minutes at 80 °C, the solutions were mixed in a 1/1 molar proportion to prepare 0.3 mL of mixed polymer solution. After stirring overnight, water (filtered with a 0.02 µm filter) was added under stirring at 20 °C using a syringe pump (0.5 mL/h) until a DMSO/water composition of 1/99 (v/v) was reached.

For Small Angle Neutron Scattering experiments (SANS), the same procedure was applied using
deuterated solvents instead of hydrogenated ones

**4.3. cryo-TEM.** Selected solutions analyzed by light scattering or SANS were also analyzed subsequently by cryo-TEM. Unless specified otherwise, the solutions were analyzed without filtration. The cryo-TEM samples were prepared by depositing a drop of the sample solution on a Quantifoil coated carbon grid, removing the excess solution with a filter paper, either manually or using a cryo-plunge 3 system (Gatan), and flash freezing a thin film of the aqueous solution in liquid ethane. We stress that this classical preparation process may change the concentration of particles on the grid surface due to blotting and capillary flow so that the density of particles on the cryoTEM pictures should not be considered representative of the concentration of particles within the polymer solution.

The samples were observed with two different TEM apparatuses. On the first apparatus,
observations were done at -180 °C on a JEOL JEM-2100 LaB6 microscope operating at 200 kV
under low-dose conditions (10 electrons Å<sup>-2</sup> s<sup>-1</sup>). Digital images were recorded on a 2k x 2k CCD
camera, Gatan Ultrascan 1000. On the second apparatus, observations were done at -176 °C using
a 2100 HR microscope (Jeol) operating at 120 kV or 200kV and equipped with a LaB<sub>6</sub> filament.
Images were recorded with a 2048 × 2048 ORIUS SC200D CCD camera (Gatan).

It was verified by observing several sections of the cryoTEM samples at different magnifications
that the pictures and dimensions of the particles presented in the manuscript are representative of
the samples. For the diameter measurements, all the nanorods of a given section of a couple of representative pictures were measured, corresponding to 60-100 nanorods.

**4.4. Static and Dynamic Light Scattering.** Measurements were done at 20 °C on an ALV-CGS3 system operating with a vertically polarized laser with wavelength $\lambda$= 633 nm, to cover a 2.8 × 10⁶ m⁻¹ to 2.6 × 10⁷ m⁻¹ q-range, with q the scattering vector defined as $q = 4\pi n \sin(\theta/2)/\lambda$ with θ the angle of observation and n the refractive index of the solvent.

The solutions were filtered using a 1 µm pore size Whatman filter before analysis.

*Dynamic Light Scattering (DLS).* The normalized electric field auto-correlation function $g_1(q,t)$ was measured by dynamic light scattering from which the relaxation time $\tau$ can be extracted assuming a distribution A($\tau$) of different relaxation times $\tau$. The REPES routine was used to obtain A($\tau$) without assuming a specific shape for the distribution.[51]

$$g_1(t) = \int A(\tau) \exp\left(-\frac{t}{\tau}\right) d\tau \qquad (1)$$

The apparent diffusion coefficient of the particles D can be determined from the average relaxation time $\tau$ of the relaxation mode as $D = \langle\tau^{-1}\rangle/q^2$.

At the investigated concentration (~ 1 g/L) and at sufficiently low q, the apparent diffusion coefficient of the particles D corresponds to the true diffusion coefficient of the particles and relates to their hydrodynamic radius, $R_h$, according to **equation 2**, as determined previously for similar nanocylinders[45].

$$R_h = \frac{kT}{6\pi\eta D} \qquad (2)$$

where k = 1.38 × 10⁻²³ J · K⁻¹ is the Boltzmann constant, T is the absolute temperature and η is the viscosity of the solvent.
*Static Light Scattering (SLS)*. The normalized scattered intensity measured by static light scattering measurements is represented by the Rayleigh ratio determined following **equation 3**:

$$R_{\theta} = \frac{I_{\text{solution}}(\theta) - I_{\text{solvent}}(\theta)}{I_{\text{toluene}}(\theta)} \cdot \left(\frac{n_{\text{solvent}}}{n_{\text{toluene}}}\right)^2 \cdot R_{\text{toluene}} \quad (3)$$

with $I_{\text{solution}}$, $I_{\text{solvent}}$, and $I_{\text{toluene}}$ the average intensities scattered, respectively, by the solution, the solvent, and the reference (toluene) at a given angle $\theta$, $n_{\text{solvent}} = 1.333$ (water) and $n_{\text{toluene}} = 1.496$ the respective refractive indexes of the solvent and of toluene, and $R_{\text{toluene}} = 1.35 \times 10^{-5} \text{ cm}^{-1}$ the Rayleigh ratio of toluene for a wavelength $\lambda = 633$ nm. For water solutions containing small amounts of DMSO, $n_{\text{solvent}}$ was taken equal to that of water.

**4.5. Small Angle Neutron Scattering (SANS).** SANS measurements were performed in 2 mm banjo cells at the Institut Laue-Langevin (ILL, Grenoble, France), on the small angle neutron scattering instrument D22. A circular neutron beam was used (diameter of 13 mm). The D22 instrument uses two detectors: a front detector, at a fixed distance of 1.4 m (relative to the sample), as well as a rear detector. Measurements were achieved using a sample to rear detector distance of 17.6 m (collimation) and a neutron wavelength of $6 \times 10^{-10} \text{ m}$. This setup allowed for probing over a wide q-range: $2.6 \times 10^7 \text{ m}^{-1}$ to $6.4 \times 10^9 \text{ m}^{-1}$. Neutron detection was achieved using two $^3$He detectors (multi-tube detector consisting of vertically aligned Reuter-Stokes tubes, with 128 tubes for the rear and 96 tubes for the front detector, all with a diameter of 8 mm and a pixel size of 8 mm x 8 mm). Acquired detector images were reduced using GRASP software, to correct for the transmission of the direct beam, to scale to absolute intensity, and to azimuthally average. Scattering contribution of the empty cell and solvent were subtracted from the scattering curves. Unless specified otherwise, the solutions were analyzed without filtration.

**4.6. Treatment of the Scattering techniques.** The normalized excess scattered intensity $I$ determined by SLS or SANS is related to the molecular weight $M_w$ of the scatterers in g/mol, their weight concentration $C$ in g.cm$^{-3}$, their contrast $K$, their structure factor $S(q)$, describing the interactions between the particles and to their form factor $P(q)$, describing the dimension and morphology of the particles, see **equation 4**.

$$I = K \cdot C \cdot M_w \cdot S(q) \cdot P(q) \quad (4)$$
In the 1-10 g/L concentration region, it was previously shown on similar nanocylinders [45] that the interactions between the scatterers become negligible, meaning that $S(q) \sim 1$. The estimation of the contrast differs in SLS and SANS and details of the calculations were already reported.[47]

The data were fitted using SASView application (http://www.sasview.org/) to determine $P(q)$. Briefly, the data could be fitted by combining a model of homogeneous cylinders exhibiting a disperse radius and a Gaussian coil model corresponding to unassociated chains or hairs attached to hairy cylinders[47].

For rod-like particles, the number of molecules in the cross-section $n_m$ of 48-PDMAc$_{80}$ and 84-PHEA$_{50}$ was already reported[47] and the amount of polymer effectively forming nanocylinders was estimated to be 70% from the absolute value of the scattered intensity in the $q^{-1}$-dependent region.

## Acknowledgements

This work was supported by the French Agence Nationale de la Recherche in the frame of the ANR project JAROD (ANR-21-CE06-0017). The authors thank Rihab Zguir for fruitful discussions. F. Niepceron is thanked for teaching SK how to prepare the cryoTEM grids, whereas A. Rousseau is thanked for showing SK how to use the TEM microscope from platform "Microscopy" at IMMM and to help her on the imaging of some samples. The authors thank the platform "Matière Molle" at IMMM. SANS beam time allocation from ILL is acknowledged (10.5291/ILL-DATA.9-11-2166). This work benefited from the use of the SasView application, originally developed under NSF award DMR-0520547. SasView contains code developed with funding from the European Union's Horizon 2020 research and innovation program under the SINE2020 project, grant agreement No 654000.

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