Temperature-Controlled Star-Shaped Cellulose Nanocrystal

Letter Cite This: ACS Macro Lett. 2019, 8, 345−351

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Temperature-Controlled Star-Shaped Cellulose Nanocrystal Assemblies Resulting from Asymmetric Polymer Grafting Fangbo Lin,† Fabrice Cousin,‡ Jean-Luc Putaux,† and Bruno Jean*,† †

Université Grenoble Alpes, CNRS, CERMAV, 38000 Grenoble, France Laboratoire Léon Brillouin, Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA) Saclay, F-91191 Gif-sur-Yvette, France

‡

ACS Macro Lett. Downloaded from pubs.acs.org by UNIV OF TEXAS AT DALLAS on 03/11/19. For personal use only.

S Supporting Information *

ABSTRACT: We present here the grafting of thermoresponsive polyetheramines at the reducing ends of cellulose nanocrystals (CNCs) using a two-step protocol involving an end carboxylation followed by a peptide coupling with the primary amine moiety of the polyetheramine. In aqueous suspensions these end-modified CNCs became associated by their derivatized tips when the temperature was raised past a lower critical solution temperature (LCST), above which these polyetheramines are known to collapse and become hydrophobic. The CNC association was reversible when the temperature was lowered and the phenomenon of association/ disassociation was totally reproducible in repeated temperature cycles as followed by dynamic light scattering (DLS). Smallangle neutron scattering (SANS) data revealed the presence of grafted chains with an extended conformation and showed the assembly of modified CNCs into swollen aggregates in suspension at T > LCST. Transmission electron microscopy (TEM) images confirmed that the once dispersed derivatized CNCs at low temperature became associated through their reducing ends above the LCST. At such temperatures, these modified CNCs attached themselves in a remarkable fashion, forming the arms of regular four-, five-, or six-branched stars.

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reducing ends or enzymatic degradation of the nonreducing counterparts.12,13 So far, only a very limited number of works have focused on the asymmetric modification of the CNC tips. As examples of these developments, one can quote the grafting of various polymers (polydimethylsiloxane and polyacrylamide,14 poly(Nisopropylacrylamide), poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride) and polystyrenesulfonate)15 or β-casein nanoparticles16 at the reducing ends of CNCs or the production of cilia-mimetic hairy surfaces, based on endimmobilized nanocellulose at gold surfaces.17,18 In another report, Yang and van de Ven have hooked CNCs to one another, forming one-dimensional nanochains.19 Starting from originally partially oxidized cellulose II CNCs, Risteen and coworkers obtained patchy nanocrystals onto which thermosensitive polymers were grafted not only on both ends but also, to a lesser extent, on the rest of the CNC surface.20 Recently, Villares et al. reported the preparation of CNC complexes following the biotin functionalization of the reducing ends of tunicate CNCs, and the addition of the multivalent streptavidin proteins acting as linking points.21 In previous works, we have successfully covalently grafted the thermosensitive Jeffamine polyetheramine M2005 on the

ellulose nanocrystals (CNCs) consist of crystalline nanorods resulting from the acid hydrolysis of native cellulose. These nanoparticles exhibit a unique combination of valuable properties, which make them highly attractive as building blocks for innovative biosourced materials with high potential in various fields ranging from aeronautical construction, to packaging, oil recovery, cosmetics, biomedical products, etc.1 Typically, CNCs display high and tunable aspect ratios that depend on the cellulose origin, a low density (1600 kg m−3), a high specific surface area ranging from 150 to 300 m2 g−1,2,3 excellent mechanical properties,4−6 and the ability to self-organize into liquid crystalline phases.7,8 As of today, these nontoxic biosourced particles are no longer only produced at the laboratory scale, but pilot-plant quantities are commercially available in North America.9 A special feature of CNCs that is receiving increasing attention is their chemical polarity. Indeed, the two ends of one cellulose chain are not identical since the so-called nonreducing end exhibits a secondary hydroxyl group, while the reducing end displays a hemiacetal cyclic moiety, in equilibrium with a highly reactive aldehyde form. Since each CNC is in fact a cellulose I crystal, where all the chains are crystallized in a parallel arrangement,10,11 the chemical polarity of each chain is transmitted to the nanocrystal which, accordingly, has a nonreducing end rich in secondary hydroxyl groups and a reducing end covered with aldehyde moieties. This property was evidenced by specific staining of the © XXXX American Chemical Society

Received: December 26, 2018 Accepted: March 8, 2019

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DOI: 10.1021/acsmacrolett.8b01005 ACS Macro Lett. 2019, 8, 345−351

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Scheme 1. (a) Two-Step Asymmetric Functionalization of CNCs with Thermosensitive Polyetheramine Chains in Aqueous Mediuma and (b) Thermoreversible Association of Polyetheramine-e-CNCs into Star-Shaped Assemblies

a The first step consists of carboxylating the reducing ends to yield Ox-e-CNCs, which are in a second step grafted with polyetheramine chains via a peptide coupling reaction.

Figure 1. (a) Hydrodynamic diameter as a function of a temperature cycle between 4 and 40 °C for CNCs (red squares), Ox-e-CNCs (blue dots), and M2005-e-CNCs (purple triangles) in 0.5 wt % aqueous suspensions. Heating and cooling are indicated by arrows. (b) Hydrodynamic diameter variations for M2005-e-CNCs in 0.5 wt % aqueous suspensions during multiple cycles of temperature increase and decrease between 4 and 40 °C. The dotted lines are only guides for the eye.

The CNCs used in this study were prepared from cotton linters following the sulfuric acid hydrolysis protocol described by Revol et al. in their seminal work.7 The resulting particles had average dimensions of 150 nm × 22 nm × 6 nm, as revealed by statistical measurements from TEM and AFM images. Conductometric titration gave a sulfur content of 0.69%, which, combined to the CNC dimensions, corresponds to an average surface charge density of 0.48 e− nm−2. A ζ potential of −34 ± 5 mV was measured from a 0.1 wt % suspension. Some CNCs were used as such, whereas others were treated in a nonswelling dilute aqueous solution of Nmethyl morpholine N-oxide (NMMO) to improve the accessibility of the chain ends at the CNC tips (see the Supporting Information for experimental details). The asymmetric functionalization of the reducing ends of CNCs with Jeffamine polyetheramine M2005 and T5000 chains was achieved in aqueous medium, following the two-step protocol

whole surface of CNCs, yielding hairy colloids exhibiting a reversible and reproducible heat-induced aggregation.22,23 This polyetheramine is a linear statistical copolymer comprising 29 propylene oxide and 6 ethylene oxide groups (Mw ∼ 2000 g mol−1) possessing a primary amine end group and exhibiting a lower critical solution temperature (LCST) of ∼16 °C in aqueous solution.24 Another thermosensitive polymer belonging to the same series is Jeffamine polyetheramine T5000, which is a three-branched polymer of PO with a molecular weight of about 5000 g mol−1 possessing amine end groups at each of its branches, showing a LCST of ∼12 °C (Supporting Information Figure S1). Here, we have used these two polyetheramines for the specific functionalization of the reducing tips of CNCs with the goal of producing a thermosensitive reversible association of these nanocrystals through the derivatized ends. 346

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Figure 2. TEM micrographs of negatively stained CNCs at room temperature (a) and of Ox-e-CNCs prepared from aqueous suspensions at 4 (b) and 40 °C (c).

chains at the CNCs ends. Thus, the DLS measurements provided an indirect proof of the successful grafting. When the temperature was increased from below the LCST to 40 °C, a spectacular increase in hydrodynamic diameter was observed as Dh nearly tripled, going from 114 to 326 nm. This Dh increase is consistent with the formation of finite-sized aggregates. When the heated samples were then cooled to 4 °C, the hydrodynamic diameter decreased until it reverted to the initial value of ∼114 nm as soon as the temperature was below 12 °C. This result clearly shows that the temperatureinduced aggregation is fully reversible even though a hysteresis related to association−dissociation kinetics was observed. This behavior is very different from what was observed by Risteen et al. for “patchy” thermosensitive polymer-modified CNCs, since, in their case, a very moderate increase in Dh (29%) was measured.20 The remarkable reversibility and reproducibility of the phenomenon was evidenced when temperature cycles between 4 and 40 °C were repeated (Figure 1b), showing that no degradation or loss of the thermally-induced aggregation occurred when multiple temperature variations were applied and thus evidencing the robustness of the system. As shown in Supporting Information Figures S2 and S3, identical results were obtained for M2005-e-CNCs-NMMO and T5000-e-CNCs-NMMO samples. Additionally, as shown in Supporting Information Figure S4, Dh was unaffected by temperature for a suspension of Ox-e-CNCs that was submitted to the grafting protocol with the M2005 polyetheramines but without the addition of the catalyst, thus preventing the coupling from taking place. Such data show that the effect of temperature results from the covalent grafting of the thermosensitive polymer at the reducing end of the CNCs. In order to further characterize the temperature-triggered aggregation revealed by DLS, TEM was used to observe the samples at 4 and 40 °C (see Supporting Information section for sample preparation). Figure 2a shows TEM micrographs of CNCs prepared by sulfuric acid hydrolysis of cotton linters. Consistent with literature reports, these particles have a length between 100 and 300 nm and a width between 10 and 30 nm.17 The negative staining clearly reveals that most particles are in fact fascicles of a few parallel elementary subunits. The interparticle distance indicates a significant electrostatic repulsion due to the negative charge of sulfate groups at the surface of the CNCs, resulting from the sulfuric acid hydrolysis. The TEM micrograph of Ox-e-CNCs shown in Figure 2b reveals that these nanoparticles are very similar to the initial

described in Scheme 1a. First, the CNCs were endcarboxylated using the chlorite oxidation method where the aldehyde groups at the reducing end were transformed to carboxylate moieties. Since in the corresponding samples, hereafter referred to as Ox-e-CNCs, the reducing ends only represent a few percent of the total CNC surface, attempts to measure the degree of oxidation of Ox-e-CNCs using techniques such as Fourier-transform infrared (FTIR) or 13C solid-state nuclear magnetic resonance (NMR) spectroscopy were unsuccessful. Even in the case of our polyetheramine grafting of the whole surface of the CNCs, the collected signals were weak, leaving no chance to properly identify the chemical modifications in the case of end functionalization. However, both the initial and postoxidation aldehyde contents, i.e., the concentration of reducing ends, could be measured. The initial value was 24.9 ± 0.4 μmol of CHO g−1, in good agreement with the values calculated from the CNC average dimensions, and 5.3 ± 0.8 μmol of CHO g−1 after the oxidation step, which corresponds to an oxidation reaction yield of 78%. In a second step, the polyetheramines were covalently grafted onto Ox-e-CNCs by a peptide coupling reaction between the amino groups of the polymer chain end and the previously generated carboxylate groups. Again, for the aforementioned reason, the degree of substitution and peptide coupling reaction yield could not be measured by FTIR or solid-state NMR. The effect of the presence of Jeffamine polyetheramine M2005 locally grafted at one end of the cellulose rods was investigated by dynamic light scattering (DLS) as a function of temperature, and comparisons with bare as-prepared CNCs and Ox-e-CNCs were made. As shown in Figure 1a, the hydrodynamic diameter (Dh) of bare CNCs and endcarboxylated CNCs remained constant at about 96 nm in the 4−40 °C temperature range. This value, which corresponds to what is usually reported for cotton CNCs prepared under conditions similar to ours, shows that the samples consisted of nonaggregated CNCs irrespective of the temperature within the probed range and the same conclusion can be drawn for Ox-e-CNCs. For the M2005-e-CNCs, when the temperature was below the LCST of the polyetheramine, i.e., 16 °C, the hydrodynamic diameter was constant at about 114 nm, indicating that the sample was also composed of individualized M2005-e-CNCs without any association. The small increase in hydrodynamic diameter when M2005-e-CNCs and Ox-eCNCs are compared is consistent with the occurrence of a lower diffusion coefficient due to the presence of polymer 347

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Figure 3. TEM images of negatively stained M2005-e-CNCs prepared from suspensions at 4 °C (a) and 40 °C (b), M2005-e-CNCs-NMMO prepared from suspensions at 4 °C (c) and 40 °C (d), and T5000-e-CNCs-NMMO prepared from suspensions at 4 °C (e) and 40 °C (f).

CNCs and that the chlorite oxidation reaction had no effect on their morphology. Furthermore, when the temperature was raised from 4 to 40 °C (Figure 2c), no significant difference could be detected, proving the nonsensitivity of these samples to temperature. TEM images at 4 and 40 °C of M2005-eCNCs, M2005-e-CNCs-NMMO, and T5000-e-CNCsNMMO are shown in Figure 3. In Figure 3a,c,e, the samples prepared from suspensions kept at 4 °C showed rodlike nanoobjects that are well-dispersed and similar to the initial CNCs shown in Figure 2a. Thus, at a temperature below the LCST of the polyetheramine, the polymer-e-CNCs behaved as repulsive individual nanoparticles. The grafted chains are too short to be detected by TEM, but the presence of these chains under good solvent conditions should generate entropic repulsion forces between the nano-objects, which add to the electrostatic interactions provided by the inherent ester sulfate groups at the CNC surface.

TEM images of CNCs prepared from the same suspensions at 40 °C clearly showed the spectacular formation of assemblies of CNCs organized in a star-shaped association of four, five, or six nanocrystals hooked by their ends (Figure 3b,d,f). The observation of these CNC stars at 40 °C is fully consistent with the DLS data that reveal the presence of large objects showing a close to 3-fold higher hydrodynamic diameter at this temperature as compared to the samples prepared at 4 °C. No clear effect of the treatment with NMMO was observed. The temperature-induced formation of these star-shaped assemblies can be explained by modifications of the polyetheramine conformation and hydration. Indeed, when the temperature is increased above the LCST, the thermosensitive polymer chains grafted at the reducing end of CNCs collapse due to poor solvent conditions and thus turn from hydrophilic to hydrophobic. Thus, in the aqueous environment, the interactions between these collapsed chains 348

DOI: 10.1021/acsmacrolett.8b01005 ACS Macro Lett. 2019, 8, 345−351

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ACS Macro Letters become attractive, with the result of the association of the polymer-e-CNCs through their reducing ends. In the images shown in Figure 3b,d,f, besides the star structures that are dominant, a small number of individual polymer-e-CNCs is still observed: they can likely be attributed to the dilute conditions required for TEM observations, which limit the probability of CNCs to associate. These individual particles might also correspond to CNCs with a low degree of grafting. It has to be noted that the thermally-induced formation of starlike structures is a proof that the grafting only exclusively occurred at the reducing end of the CNCs since we could not detect any strings of CNCs that would have been formed from associations involving both tips of the nanocrystals. DLS results have shown that the formation of these CNC stars was fully reversible. Indeed, when the temperature was decreased below the LCST of the considered polyetheramine, good solvent conditions were recovered, hydrogen bonds were re-established between the polymer chains and water and polymer−polymer interactions became repulsive, leading to the dissociation of the star-shaped assembly into individual particles. A remarkable characteristic of these star-shaped aggregates is their high degree of symmetry. As shown in Figure 3a,c,f, the arms of the stars are separated by angular sectors of values close to 2π/n, where n is the number of CNCs in a star, i.e., π/ 2, 2π/5, and π/3 for four-, five-, and six-nanocrystal stars, respectively. This structure is the result of opposite interaction forces between the polymer-e-CNCs. Indeed, while at T > LCST the polymer−polymer interactions are attractive and connect the polymer-e-CNCs by their end, electrostatic repulsive forces still persist between the surface length of the noncovered negatively charged sulfated CNCs. To get more insight into the structure of the CNC assemblies in aqueous suspension, small-angle neutron scattering (SANS) experiments were performed on a 1 wt % M2005-e-CNC suspension in D2O at different temperatures. The scattering results are shown in Figure 4, which also presents the data corresponding to as-prepared CNCs. For the two temperatures below the LCST of the polyetheramine, namely, 8 and 12 °C, both SANS spectra of the M2005-e-CNC suspension were identical and corresponded to individual asymmetrically modified CNCs. Both spectra exhibited the typical Q−1 decay of rodlike objects in the low-Q range, as was also the case for bare CNCs. However, in the high-Q range, while the spectrum of bare CNCs followed a Q−4 decay corresponding to the sharp interface between the crystalline rods and the solvent, M2005-e-CNCs exhibited a decay close to Q−1. This scattering behavior in a Q-region where the nanometer length scale is probed is attributed to the presence of the chains grafted at the end of the CNCs, which are expected to scatter as Q−1/ν, where ν is the Flory exponent. From the slope close to −1 at high Q, it can be deduced that the grafted chains are described by a ν ∼ 1 Flory exponent, corresponding to an extended chain conformation. Such a conformation reveals that the grafted chains were in a brushlike regime resulting from a high grafting density allowed by the high density of chain-end carboxylates (about 4 COO− nm−2), which was reached after the oxidation step. At 16 °C, a slight increase in the intensity at low-Q was observed but the SANS curve superimposed with the data at 8 and 12 °C for Q > 1.10−2 Å−1. These features at a temperature close to the LCST may result from the formation of complexes involving no more than two functionalized particles, since the

Figure 4. SANS spectra of a 1 wt % M2005-e-CNC suspension in D2O at 8 °C (blue circles), 12 °C (green squares), 16 °C (orange triangles), and 24 °C (red diamonds) and of a 1 wt % CNC suspension (blue crosses). Solid straight lines show the characteristic decay of the intensity in the high-Q region. A plot where the spectra were arbitrarily shifted is available as Supporting Information Figure S6. The curve corresponding to as-prepared CNCs could be fitted using the form factor of a parallelepiped with a rectangular crosssection, giving average dimensions of 150 nm × 20 nm × 5 nm for the initial nanoparticles (Supporting Information Figure S7).

intensity when Q tends to 0 is only about 1.5 times higher at 16 °C than at 8 °C. However, a further increase of the temperature up to 24 °C (8 °C above the LCST) resulted in a significant change of the scattering signal in the low-Q region. A 10-fold increase of the intensity when Q tends to 0 was observed but at the same time the intensity tended to plateau when Q decreases. Such features suggest the formation of finite-sized assemblies of about 10 individual particles corresponding to star-like aggregates with an increased number of branches due to the higher concentration used for the SANS experiments and/or to the association of five-branch stars. No chain conformation change was observed at 24 °C due to the high grafting density. As shown in Supporting Information Figure S8, a perfect superimposition of the spectra was obtained when the temperature was reverted to 8 °C, evidencing a complete disassembly of the star-shaped complexes when the temperature went below the LCST, which thus confirms the reversibility of the system as already observed with the DLS results. In summary, we have developed a protocol to graft thermosensitive polyetheramines at the reducing ends of CNCs in aqueous suspension. These derivatized nanocrystals became hooked to one another by their reducing end tips when the temperature of the medium was raised above the LCST, corresponding to the heat demixing property of these polyetheramines in water. This association was fully reversible as the CNCs repeatedly redispersed at temperatures below the LCST to reaggregate upon temperature increase above this threshold. The heat-induced aggregation of CNCs remarkably occurred as four-, five-, and six-armed stars radiating from centers where the reducing ends tips of the individual CNCs had coalesced. 349

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(6) Eichhorn, S. J.; Dufresne, A.; Aranguren, M.; Marcovich, N. E.; Capadona, J. R.; Rowan, S. J.; Weder, C.; Thielemans, W.; Roman, M.; Renneckar, S.; Gindl, W.; Veigel, S.; Keckes, J.; Yano, H.; Abe, K.; Nogi, M.; Nakagaito, A. N.; Mangalam, A.; Simonsen, J.; Benight, A. S.; Bismarck, A.; Berglund, L. A.; Peijs, T. Review: Current International Research into Cellulose Nanofibres and Nanocomposites. J. Mater. Sci. 2010, 45, 1−33. (7) Revol, J.-F.; Bradford, H.; Giasson, J.; Marchessault, R. H.; Gray, D. G. Helicoidal Self-Ordering of Cellulose Microfibrils in Aqueous Suspension. Int. J. Biol. Macromol. 1992, 14, 170−172. (8) Lagerwall, J. P. F.; Schütz, C.; Salajkova, M.; Noh, J.; Park, J. H.; Scalia, G.; Bergstrom, L. Cellulose Nanocrystal-Based Materials: From Liquid Crystal Self-Assembly and Glass Formation to Multifunctional Thin Films. NPG Asia Mater. 2014, 6, No. e80. (9) Bras, J.; Chauve, G. Industrial Point of View of Nanocellulose Materials and Their Possible Applications. In Handbook of Green Materials: Processing Technologies, Properties and Applications; Oksman, K., Bismark, A., Rojas, O., Sain, M., Eds.; World Sci. Pub. Co., 2014. (10) Nishiyama, Y.; Langan, P.; Chanzy, H. Crystal Structure and Hydrogen-Bonding System in Cellulose Iβ from Synchrotron X-ray and Neutron Fiber Diffraction. J. Am. Chem. Soc. 2002, 124, 9074− 9082. (11) Koyama, M.; Helbert, W.; Imai, T.; Sugiyama, J.; Henrissat, B. Parallel-Up Structure Evidences the Molecular Directionality During Biosynthesis of Bacterial Cellulose. Proc. Natl. Acad. Sci. U. S. A. 1997, 94, 9091−9095. (12) Chanzy, H.; Henrissat, B. Undirectional Degradation of Valonia Cellulose Microcrystals Subjected to Cellulase Action. FEBS Lett. 1985, 184, 285−288. (13) Hieta, K.; Kuga, S.; Usuda, M. Electron Staining of Reducing Ends Evidences a Parallel-Chain Structure in Valonia Cellulose. Biopolymers 1984, 23, 1807−1810. (14) Sipahi-Sağlam, E.; Gelbrich, M.; Gruber, E. Topochemically Modified Cellulose. Cellulose 2003, 10, 237−250. (15) Zoppe, J. O.; Dupire, A. V. M.; Lachat, T. G. G.; Lemal, P.; Rodriguez-Lorenzo, L.; Petri-Fink, A.; Weder, C.; Klok, H.-A. Cellulose Nanocrystals with Tethered Polymer Chains: Chemically Patchy versus Uniform Decoration. ACS Macro Lett. 2017, 6, 892− 897. (16) Karaaslan, M. A.; Gao, G.; Kadla, J. F. Nanocrystalline Cellulose/β-Casein Conjugated Nanoparticles Prepared by Click Chemistry. Cellulose 2013, 20, 2655−2665. (17) Lokanathan, A. R.; Nykänen, A.; Seitsonen, J.; Johansson, L.-S.; Campbell, J.; Rojas, O. J.; Ikkala, O.; Laine, J. Cilia-Mimetic Hairy Surfaces Based on End-Immobilized Nanocellulose Colloidal Rods. Biomacromolecules 2013, 14, 2807−2813. (18) Arcot, L. R.; Lundahl, M.; Rojas, O. J.; Laine, J. Asymmetric cellulose nanocrystals: thiolation of reducing end groups via NHSEDC coupling. Cellulose 2014, 21, 4209−4218. (19) Yang, H.; van de Ven, T. G. M. A Bottom-up Route to a Chemically End-to-End Assembly of Nanocellulose Fibers. Biomacromolecules 2016, 17, 2240−2247. (20) Risteen, B.; Delepierre, G.; Srinivasarao, M.; Weder, C.; Russo, P.; Reichmanis, E.; Zoppe, J. Thermally Switchable Liquid Crystals Based on Cellulose Nanocrystals with Patchy Polymer Grafts. Small 2018, 14, 1802060. (21) Villares, A.; Moreau, C.; Cathala, B. Star-like Supramolecular Complexes of Reducing-End-Functionalized Cellulose Nanocrystals. ACS Omega 2018, 3, 16203−16211. (22) Azzam, F.; Siqueira, E.; Fort, S.; Hassaini, R.; Pignon, F.; Travelet, C.; Putaux, J.-L.; Jean, B. Tunable Aggregation and Gelation of Thermoresponsive Suspensions of Polymer-Grafted Cellulose Nanocrystals. Biomacromolecules 2016, 17, 2112−2119. (23) Azzam, F.; Heux, L.; Putaux, J.-L.; Jean, B. Preparation By Grafting Onto, Characterization, and Properties of Thermally Responsive Polymer-Decorated Cellulose Nanocrystals. Biomacromolecules 2010, 11, 3652−3659. (24) Belbekhouche, S.; Dulong, V.; Picton, L.; Le Cerf, D. ; Physicochemical, S. A.; Aspects, E. Saccharide Effect on the LCST

The reversibility of the described aggregation of endmodified CNCs during heat cycles should induce dramatic modifications of the rheological properties of such systems, which therefore should find specific applications in a number of fields, in particular in the biomedicals. Other routes would be to see how other external stimuli such as ionic strength or pH could combine with the heat-induced response of the systems, either at the colloidal or at the ultrastructural level. Work is being done to follow these avenues.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsmacrolett.8b01005. Experimental details, descriptions of the polyetheramines including evaluation of the LCST using UV absorbance, chemical structure of Jeffamine, hydrodynamic diameter as a function of temperature, TEM images, additional DLS and SANS data (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Fabrice Cousin: 0000-0001-7523-5160 Jean-Luc Putaux: 0000-0002-9760-5369 Bruno Jean: 0000-0002-4157-7186 Funding

F.L. acknowledges the French Ministry of Higher Education and Research for his Ph.D. grant. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge the Glyco@Alps program (Investissements d’Avenir grant #ANR-15-IDEX-02) and the NanoBio chemistry platform (ICMG FR 2607) for granting access to the electron microscopy facilities and Laboratoire Léon Brillouin for neutron beamtime allocation. Huntsman Corporation is acknowledged for the generous gift of Jeffamine polyetheramine samples. We also thank H. Chanzy for valuable comments during the writing of this manuscript.

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REFERENCES

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