Electroactive Bi-Functional Liquid Crystal Elastomer Actuators.

Liquid crystal elastomers (LCEs) with promising applications in the field of actuators and soft robotics are reported. However, most of them are activated by external heating or light illumination. The examples of electroactive LCEs are still limited; moreover, they are monofunctional with one type of deformation (bending or contraction). Here, the study reports on trilayer electroactive LCE (eLCE) by intimate combination of LCE and ionic electroactive polymer device (i-EAD). This eLCE is bi-functional and can perform either bending or contractile deformations by the control of the low-voltage stimulation. By applying a voltage of ±2 V at 0.1 Hz, the redox behavior and associated ionic motion provide a bending strain difference of 0.80%. Besides, by applying a voltage of ±6 V at 10 Hz, the ionic current-induced Joule heating triggers the muscle-like linear contraction with 20% strain for eLCE without load. With load, eLCE can lift a weight of 270 times of eLCE-actuator weight, while keeping 20% strain and affording 5.38 kJ·m-3 work capacity. This approach of combining two smart polymer technologies (LCE and i-EAD) in a single device is promising for the development of smart materials with multiple degrees of freedom in soft robotics, electronic devices, and sensors.

Self-adhesion of uncrosslinked poly(butadiene-co-acrylonitrile), i.e. nitrile rubber, an inhomogeneous and associative polymer.

Nitrile rubber (i.e., NBR) is a crosslinked copolymer of butadiene and acrylonitrile that finds widespread use in the automotive and aerospace industry as it sustains large, reversible deformations while resisting swelling by petrochemical fuels. We recently demonstrated that this material has a drift in composition due to the difference in reactivity between acrylonitrile and butadiene monomers during emulsion copolymerisation. Thus, although NBR is often thought of as a random copolymer, it does experience thermodynamic driving forces for self-assembly and kinetic barriers for processing like those of block copolymers.1 Here, we illustrate how such drift in composition hinders interdiffusion and prevents self-adhesion. The key result is that contacting uncrosslinked NBR (i) in the melt, (ii) in the presence of tackifiers, or (iii) in the presence of organic solvents promotes interdiffusion and enables self-adhesion. However, the contact times required for self-adhering, tc ∼ O(100 h), are orders of magnitude above those needed for non-polar synthetic rubbers like styrene-butadiene rubber (i.e., SBR) of comparable molecular weights and glass transition temperatures, tc ∼ O(100 s), unveiling the dramatic effect of compositional inhomogeneities and physical associations on polymer interdiffusion and large-strain mechanical properties. For example, when welded with organic solvents, the self-adhesion energy of NBR continues to increase after the solvent has evaporated because of polymer nanostructuring.

Structure of proteins under pressure: Covalent binding effects of biliverdin on ß-lactoglobulin.

High pressure (HP) is a particularly powerful tool to study protein folding/unfolding, revealing subtle structural rearrangements. Bovine ß-lactoglobulin (BLG), a protein of interest in food science, exhibits a strong propensity to bind various bioactive molecules. We probed the effects of the binding of biliverdin (BV), a tetrapyrrole linear chromophore, on the stability of BLG under pressure, by combining in situ HP small-angle neutron scattering (SANS) and HP-UV absorption spectroscopy. Although BV induces a slight destabilization of BLG during HP-induced unfolding, a ligand excess strongly prevents BLG oligomerization. Moreover, at SANS resolution, an excess of BV induces the complete recovery of the protein "native" 3D structure after HP removal, despite the presence of the BV covalently bound adduct. Mass spectrometry highlights the crucial role of cysteine residues in the competitive and protective effects of BV during pressure denaturation of BLG through SH/S-S exchange.

Direct Access to Polysaccharide-Based Vesicles with a Tunable Membrane Thickness in a Large Concentration Window via Polymerization-Induced Self-Assembly.

Polymersomes are multicompartmental vesicular nano-objects obtained by self-assembly of amphiphilic copolymers. When prepared in the aqueous phase, they are composed of a hydrophobic bilayer enclosing water. Although such fascinating polymeric nano-objects have been widely reported with synthetic block copolymers, their formation from polysaccharide-based copolymers remains a significant challenge. In the present study, the powerful platform technology known as polymerization-induced self-assembly was used to prepare in situ pure vesicles from a polysaccharide-grafted copolymer: dextran-g-poly(2-hydroxypropyl methacrylate) (Dex-g-PHPMA). The growth of the PHPMA grafts was performed with a dextran-based macromolecular chain transfer agent in water at 20 °C using photomediated reversible addition fragmentation chain transfer polymerization at 405 nm. Transmission electron microscopy, cryogenic electron microscopy, small-angle X-ray scattering, atomic force microscopy, and dynamic light scattering revealed that amphiphilic Dex-g-PHPMAX = 100-300 (X is the targeted average degree of polymerization, Xn̅, of each graft at full conversion) exhibit remarkable self-assembly behavior. On the one hand, vesicles were obtained over a wide range of solid concentrations (from 2.5% to 13.5% w/w), which can facilitate posterior targeting of such rare morphology. On the other hand, the extension of Xn̅ induces an increase in the vesicle membrane thickness, rather than a morphological evolution (spherical micelles to cylinders to vesicles).

Effect of Ligands on HP-Induced Unfolding and Oligomerization of ß-Lactoglobulin.

To probe intermediate states during unfolding and oligomerization of proteins remains a major challenge. High pressure (HP) is a powerful tool for studying these problems, revealing subtle structural changes in proteins not accessible by other means of denaturation. Bovine ß-lactoglobulin (BLG), the main whey protein, has a strong propensity to bind various bioactive molecules such as retinol and resveratrol, two ligands with different affinity and binding sites. By combining in situ HP-small-angle neutron scattering (SANS) and HP-ultraviolet/visible absorption spectroscopy, we report the specific effects of these ligands on three-dimensional conformational and local changes in BLG induced by HP. Depending on BLG concentration, two different unfolding mechanisms are observed in situ under pressures up to ∼300 MPa: either a complete protein unfolding, from native dimers to Gaussian chains, or a partial unfolding with oligomerization in tetramers mediated by disulfide bridges. Retinol, which has a high affinity for the BLG hydrophobic cavity, significantly stabilizes BLG both in three-dimensional and local environments by shifting the onset of protein unfolding by ∼100 MPa. Increasing temperature from 30 to 37°C enhances the hydrophobic stabilization effects of retinol. In contrast, resveratrol, which has a low binding affinity for site(s) on the surface of the BLG, does not induce any significant effect on the structural changes of BLG due to pressure. HP treatment back and forth up to ∼300 MPa causes irreversible covalent oligomerization of BLG. Ab initio modeling of SANS shows that the oligomers formed from the BLG-retinol complex are smaller and more elongated compared to BLG without ligand or in the presence of resveratrol. By combining HP-SANS and HP-ultraviolet/visible absorption spectroscopy, our strategy highlights the crucial role of BLG hydrophobic cavity and opens up new possibilities for the structural determination of HP-induced protein folding intermediates and irreversible oligomerization.

Self-Assembly of PEG-b-PTMC Copolymers: Micelles and Polymersomes Size Control.

Poly(ethylene glycol)45-b-poly(trimethylene carbonate)n PEG45-b-PTMCn diblock copolymers were synthesized with five different PTMC degrees of polymerization (n = 38, 96, 144, 170, 332) and their self-assembly properties in water were studied using a manual nanoprecipitation procedure. We confirmed that the copolymer's hydrophilic weight fraction (fPEG) is controlling nanoparticles morphology. We determined that the PEG45-b-PTMC96 with fPEG ≈ 17% is the optimal hydrophilic fraction for the stabilization of well-defined unilamellar vesicles with a membrane thickness of δ ≈ 14.6 nm. Maintaining this fraction constant and modulating the overall molar mass of the block copolymers allowed the establishment of a power law of [Formula: see text] which provides a robust correlation between the molar mass of PTMC and vesicles' membrane thickness. Finally, we proved that controlling nanoprecipitation's conditions by microfluidics allowed fine-tuning and control of the nanoparticles size and polydispersity index while maintaining their shape with a perfect batch-to-batch reproducibility.

Self-Assembly of Stimuli-Responsive Biohybrid Synthetic- b-Recombinant Block Copolypeptides.

The synthesis and original thermoresponsive behavior of hybrid diblock copolypeptides composed of synthetic and recombinant polypeptides are herein reported. A thermoresponsive recombinant elastin-like polypeptide was used as a macroinitiator to synthesize a range of poly( l-glutamic acid)- block-elastin-like polypeptide (PGlu- b-ELP) diblock copolypeptides with variable PGlu block lengths. Their temperature-triggered self-assembly in water and in phosphate-buffered saline (PBS) was investigated at the macroscopic scale using complementary techniques such as turbidimetry, dynamic and static light scattering, small-angle neutron scattering, and at the molecular scale by 1H NMR and circular dichroism (CD). In deionized water, PGlu- b-ELP copolypeptides showed one transition from free soluble chains below the transition temperature ( Tt) of the ELP block to macroscopic aggregates above the Tt. In contrast, in PBS, four successive regimes were observed upon increasing temperature: below the Tt, copolypeptides were soluble, above the Tt, large aggregates appeared and fell apart into discrete and defined spherical nanoparticles at a temperature named critical micellization temperature (CMT), before finally reaching an equilibrium. During the last regime, neutron scattering experiments revealed that the micelle-like structures underwent a densification step and expelled water from their core. In addition, 1H NMR and CD experiments revealed, in deionized water, the formation of type II ß-turns into the ELP block upon temperature increase. These ß-turns are known to participate in the intrinsic thermoresponsive behavior of the ELPs. In contrast, in PBS, circular dichroism measurements showed an attenuation of folded structure during the self-assembly phase, leading to less cohesive aggregates able to reorganize into nanoparticles at the CMT.

Comb-Like Fluorophilic-Lipophilic-Hydrophilic Polymers for Nanocapsules as Ultrasound Contrast Agents.

Imaging the enhanced permeation and retention effect by ultrasound is hindered by the large size of commercial ultrasound contrast agents (UCAs). To obtain nanosized UCAs, triblock copolymers of poly(ethylene glycol)-polylactide-poly(1 H,1 H,2 H,2 H-heptadecafluorodecyl methacrylate) (PEG-PLA-PFMA) with distinct numbers of perfluorinated pendant chains (5, 10, or 20) are synthesized by a combination of ring-opening polymerization and atom transfer radical polymerization. Nanocapsules (NCs) containing perfluorooctyl bromide (PFOB) intended as UCAs are obtained with a 2-fold increase in PFOB encapsulation efficiency in fluorinated NCs as compared with plain PEG-PLA NCs thanks to fluorous interactions. NC morphology is strongly influenced by the number of perfluorinated chains and the amount of polymer used for formulation, leading to peculiar capsules with several PFOB cores at high PEG-PLA-PFMA20 amount and single-cored NCs with a thinner shell at low fluorinated polymer amount, as confirmed by small-angle neutron scattering. Finally, fluorinated NCs yield higher in vitro ultrasound signal compared with PEG-PLA NCs, and no in vitro cytotoxicity is induced by fluorinated polymers and their degradation products. Our results highlight the benefit of adding comb-like fluorinated blocks in PEG-PLA polymers to modify the nanostructure and enhance the echogenicity of nanocapsules intended as UCAs.

The role of solvent swelling in the self-assembly of squalene based nanomedicines.

Squalene based nanoparticles obtained via nanoprecipitation are promising candidates as efficient anti-cancer drugs. In order to highlight their preparation process and to facilitate further clinical translation, the present study enlightens the paramount role of the solvent in the formation of these nanomedicines. Three different squalene-based nanoparticles, i.e. squalenic acid, deoxycytidine squalene and gemcitabine squalene, have been investigated before and after organic solvent evaporation. Size and structural analysis by Small Angle Neutron Scattering revealed that droplets' size was uniquely controlled by the solvent composition (ethanol-water), which evolved during their gradual formation. The particles were preferably swollen by water and the swelling increased when less ethanol was present. Either coalescence or fragmentation was observed depending on the increase or decrease of the ethanol content, supporting an equilibrium control of the size. Moreover, a high water swelling was observed for the three local organization of the nanodroplets (hexagonal for gemcitabine squalene, cubic for deoxycytidine and not structured for squalenic acid) and could be the source of the previously reported efficiency of related anti-cancer squalene based nanomedicines.

Polymersomes with PEG corona: structural changes and controlled release induced by temperature variation.

Thermoresponsive behavior of different kinds of polymersomes was studied using small angle neutron scattering (SANS), transmission electron microscopy (TEM), and proton nuclear magnetic resonance ((1)H NMR). The polymersomes were made of block copolymers containing a 2000 Da polyethylene glycol (PEG) as a hydrophilic block and either a liquidlike polymer (e.g., PBA: polybutylacrylate), a solidlike polymer (PS: polystyrene), or a liquid crystalline (LC) polymer as a hydrophobic block. Structural changes in polymersomes are driven in all cases by the critical dehydration temperature of PEG corona, which is closely related to the chemical structure and chain mobility of the hydrophobic block. No structural changes occur upon heating from 25 to 75 °C in the liquidlike polymersomes where the critical dehydration temperature of PEG should be higher than 75 °C. In contrast, glassy PEG-b-PS polymersomes and LC polymersomes show structural changes around 55 °C, which corresponds to the critical dehydration temperature of PEG in those block copolymers. Furthermore, the structural changes depend on the properties of the hydrophobic layer. Glassy PEG-b-PS polymersomes aggregate together above 55 °C, but the bilayer membrane is robust enough to remain intact. This aggregation is reversible, and rather separate polymersomes are recovered upon cooling. However, LC polymersomes display drastic and irreversible structural changes when heated above ∼55 °C. These changes are dependent on the LC structures of the hydrophobic layer. Nematic LC polymersomes turn into thick-walled capsules, whereas smectic LC polymersomes collapse into dense aggregates. As these drastic and irreversible changes decrease or remove the inner compartment volume of the vesicle, LC polymersomes can be used for thermal-responsive controlled release, as shown by a study of calcein release. Finally, toxicity studies proved that LC polymersomes were noncytotoxic and had no effect on cell morphology.

The effects of biliverdin on pressure-induced unfolding of apomyoglobin: The specific role of Zn2+ ions.

Apomyoglobin (apoMb), a model protein in biochemistry, exhibits a strong propensity to bind various ligands, which makes it a good candidate as a carrier of bioactive hydrophobic drugs. The stability of its hydrophobic pocket determines its potential as a carrier of bioactive compounds. High pressure (HP) is a potent tool for studying protein stability, revealing the specific role of hydrophobic cavities in unfolding. We probed the effects of biliverdin (BV) binding and its complex with Zn2+ ions on the structure and HP stability of apoMb. CD spectroscopy and SAXS measurements revealed that BV and BV-Zn2+ complexes make the apoMb structure more compact with higher α-helical content. We performed in situ HP measurements of apoMb intrinsic fluorescence to demonstrate the ability of BV to stabilise apoMb structure at HP conditions. Furthermore, the presence of Zn2+ within the apoMb-BV complex significantly enhances the BV stabilisation effect. In situ visible absorption study of BV chromophore confirmed the ability of Zn2+ to increase the stability of apoMb-BV complex under HP: the onset of complex dissociation is shifted by ∼100 MPa in presence of Zn2+. By combining HP-fluorescence and HP-visible absorption spectroscopy, our strategy highlights the crucial role of tetrapyrrole-metal complexes in stabilising apoMb hydrophobic pocket.

In Situ Monitoring of Block Copolymer Self-Assembly via Solvent Exchange through Controlled Dialysis with Light and Neutron Scattering Detection.

Solution self-assembly of amphiphilic block copolymers (BCs) is typically performed by a solvent-to-water exchange. However, BC assemblies are often trapped in metastable states depending on the mixing conditions such as the magnitude and rate of water addition. BC self-assembly can be performed under near thermodynamic control by dialysis, which accounts for a slow and gradual water addition. In this Letter we report the use of a specifically designed dialysis cell to continuously monitor by dynamic light scattering and small-angle neutron scattering the morphological changes of PDMS-b-PEG BCs self-assemblies during THF-to-water exchange. The complete phase diagrams of near-equilibrium structures can then be established. Spherical micelles first form before evolving to rod-like micelles and vesicles, decreasing the total developed interfacial area of self-assembled structures in response to increasing interfacial energy as the water content increases. The dialysis kinetics can be tailored to the time scale of BC self-assembly by modifying the membrane pore size, which is of interest to study the interplay between thermodynamics and kinetics in self-assembly pathways.

Exploring and strengthening the potential of R-phycocyanin from Nori flakes as a food colourant.

This study aimed to purify, characterise and stabilise the natural food colourant, R-phycocyanin (R-PC), from the red algae Porphyra spp. (Nori). We purified R-PC from dried Nori flakes with a high purity ratio (A618/A280 ≥ 3.4) in native form (α-helix content 53%). SAXS measurements revealed that R-PC is trimeric ((αß)3) in solution. The thermal denaturation of α-helix revealed one transition (Tm at 52 °C), while the pH stability study showed R-PC is stable in the pH range 4-8. The thermal treatment of R-PC at 60 °C has detrimental and irreversible effects on R-PC colour and antioxidant capacity (22 % of residual capacity). However, immobilisation of R-PC within calcium alginate beads completely preserves R-PC colour and mainly retains its antioxidant ability (78 % of residual capacity). Results give new insights into the stability of R-PC and preservation of its purple colour and bioactivity by encapsulation in calcium alginate beads.

Vesicles in ionic liquids.

The formation of vesicles from 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) in several room-temperature ionic liquids, namely, 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF(4)), 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf(2)), and N-benzylpyridinium bis(trifluoromethylsulfonyl)imide (BnPyNTf(2)), as well as in a water/BmimBF(4) mixture, was investigated. In pure ionic liquids, observations by staining transmission electron microscopy demonstrated clearly the formation of spherical structures with diameters of 200-400 nm. The morphological characteristics of these vesicles in ionic liquids, in particular, the membrane thicknesses, were first investigated by small-angle neutron scattering measurements. The mean bilayer thickness was found to be ∼63 ± 1 Å in a deuterated ionic liquid (BnPyNTf(2)-d). This value was similar to that observed in water. The effect of ILs on the modification of the phase physical properties of multilamellar vesicles (MLVs) was then investigated by differential scanning calorimetry. In pure IL as in water, DPPC exhibited an endothermic pretransition followed by the main transition. These transition temperatures and the associated enthalpies in ILs were higher than those in water because of a reduction of the electrostatic repulsion between zwitterionic head groups. To better understand the effect of ionic liquid on the formation of multilamellar vesicles, mixtures of BmimBF(4) and water, which are miscible in all proportions, were analyzed (BmimBF(4)/water ratio from 0% to 100%). SANS and DSC experiments demonstrated that the bilayer structure and stability were strongly modified by the IL content. Moreover, matching SANS experiments showed that BmimBF(4) molecules prefer to be located inside the DPPC membrane rather than in water.

Large hybrid Polymer/Lipid Unilamellar vesicle (LHUV) at the nanoscale: An insight into the lipid distribution in the membrane and permeability control.

Membrane structuration of Large Hybrid Unilamellar Polymer/Lipid Vesicle (LHUV) is an important parameter on the optimization of their properties and thus their valuation in various fields. However, this kind of information is hardly accessible. In this work, we will focus on the development of LHUV obtained from the self-assembly of diblock poly(dimethylsiloxane)-b-poly(ethylene oxide) (PDMS-b-PEO) of different molar masses combined with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at 15% and 25% w/w content. The hybrid character of the resulting vesicles as well as their membrane structure are characterized by the mean of different techniques such as small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM). We show that hybrid vesicles with homogeneous membrane structure are obtained whatever the molar mass of the block copolymer (from 2500 to 4000 g/mol), with of a small number of tubular structures observed with the higher molar mass. We also demonstrate that the permeability of the LHUV, evaluated through controlled release experiments of fluorescein loaded in LHUV, is essentially controlled by the lipid/polymer composition.

Fluorescent polymer cubosomes and hexosomes with aggregation-induced emission.

Fluorescent polymer cubosomes and hexosomes with aggregation-induced emission (AIE) were prepared from amphiphilic block copolymers PEG-b-PTPEMA where the hydrophobic block PTPEMA was a polymethacrylate with tetraphenylethene (TPE) as the AIE side group. Four highly asymmetric block copolymers with hydrophilic block weight ratio f PEG ≤ 20% were synthesized. Cubosomes and hexosomes with strong fluorescence emission were obtained by nanoprecipitation of polymers with f PEG < 9% in dioxane/water and THF/water systems. Their ordered internal structures were studied by electron microscopy (cryo-EM, SEM and TEM) and the X-ray scattering technique (SAXS). To elucidate the formation mechanisms of these inverted colloids, other parameters influencing the morphologies, like the water content during self-assembly and the organic solvent composition, were also investigated. This study not only inspires people to design novel building blocks for the preparation of functional cubosomes and hexosomes, but also presents the first AIE fluorescent polymer cubosome and hexosome with potential applications in bio-related fields.

pH and temperature responsive polymeric micelles and polymersomes by self-assembly of poly[2-(dimethylamino)ethyl methacrylate]-b-poly(glutamic acid) double hydrophilic block copolymers.

The aqueous solution behavior of novel polypeptide-based double hydrophilic block copolymers (DHBCs), namely, poly[2-(dimethylamino)ethyl methacrylate]-b-poly(glutamic acid) (PDMAEMA-b-PGA), exhibiting pH- and temperature-responsiveness is presented using a combination of scattering techniques (light and neutron) and transmission electron microscopy. Close to the isoelectric point (IEP), direct or inverse electrostatic polymersomes are generated by electrostatic interactions developing between the two charged blocks and driving the formation of the hydrophobic membrane of the polymersomes, with the latter being stabilized in water by uncompensated charges. Under basic conditions, that is, when PDMAEMA is uncharged, the thermosensitivity of the DHBCs relates to the lower critical solution temperature (LCST) behavior of PDMAEMA around 40 degrees C. As a consequence, at pH = 11 and below this LCST, free chains of DHBC unimers are evidenced, while above the LCST the hydrophobicity of PDMAEMA drives the self-assembly of the DHBCs in a reversible manner. In this case, spherical polymeric micelles or polymersomes are obtained, depending on the PGA block length. These possibilities of variation in size and shape of morphologies that can be achieved as a function of temperature and/or pH variations open new routes in the development of multiresponsive nanocarriers for biomedical applications.

Biocompatible and biodegradable poly(trimethylene carbonate)-b-poly(L-glutamic acid) polymersomes: size control and stability.

Poly(trimethylene carbonate)-b-poly(L-glutamic acid) (PTMC-b-PGA) diblock copolymers have been synthesized by ring-opening polymerization (ROP) of gamma-benzyl-L-glutamate N-carboxyanhydride (BLG) initiated by amino functionalized PTMC and subsequent hydrogenation. Self-assembly in water gave well-defined vesicles which have been studied combining light and neutron scattering techniques with electron microscopy imaging. The size and dispersity of vesicles have been tuned by varying preparation conditions, direct dissolution, or nanoprecipitation. In addition, PGA conformation could be reversibly manipulated as a function of environmental changes such as pH and ionic strength. Vesicles showed high tolerance and stability toward nonionic surfactant and pH due to a thick membrane and were revealed to be nonpermeable to water. Nevertheless, they can be rapidly degraded by enzymatic hydrolysis of the polycarbonate block. The ability to tune their size through the formation process, their stimuli responsiveness, their high stability, and their biodegradability make them suitable for biomedical applications.

On the Origin of the Anomalous Behavior of Lipid Membrane Properties in the Vicinity of the Chain-Melting Phase Transition.

Biomembranes are key objects of numerous studies in biology and biophysics of great importance to medicine. A few nanometers thin quasi two-dimensional liquid crystalline membranes with bending rigidity of a few kT exhibit unusual properties and they are the focus of theoretical and experimental physics. The first order chain-melting phase transition of lipid membranes is observed to be accompanied by a pseudocritical behavior of membrane physical-chemical properties. However, the investigation of the nature of the anomalous swelling of a stack of lipid membranes in the vicinity of the transition by different groups led to conflicting conclusions about the level of critical density fluctuations and their impact on the membrane softening. Correspondingly, conclusions about the contribution of Helfrich's undulations to the effect of swelling were different. In our work we present a comprehensive complementary neutron small-angle and spin-echo study directly showing the presence of significant critical fluctuations in the vicinity of the transition which induce membrane softening. However, contrary to the existing paradigm, we demonstrate that the increased undulation forces cannot explain the anomalous swelling. We suggest that the observed effect is instead determined by the dominating increase of short-range entropic repulsion.

Effect of the microstructure of n-butyl acrylate/N-isopropylacrylamide copolymers on their thermo-responsiveness, self-organization and gel properties in water.

HYPOTHESIS: Polymer composition, microstructure, molar mass, architecture… critically affect the properties of thermoresponsive polymers in aqueous media. EXPERIMENTS: The behaviour of n-isopropylacrylamide and n-butyl acrylate-based copolymers of variable composition and structure (statistical, diblock or triblock) was studied in solution at different temperatures and concentrations with turbidimetry measurements, differential scanning calorimetry, electronic microscopy, rheology and scattering experiments. FINDINGS: This study illustrates how it is possible through chemical engineering of the microstructure of amphiphilic thermoresponsive polymers to modulate significantly the self-assembly, morphological and mechanical properties of these materials in aqueous media. Statistical structures induced a strong decrease of cloud point temperature compared to block structures with similar composition. Moreover, block structures lead below the transition temperature to the formation of colloidal structures. Above the transition temperature, the formation of colloidal aggregates is observed at low concentrations, and at higher concentrations the formation of gels. Neutron scattering and light scattering measurements show that for a given composition diblock structures lead to smaller colloids and mesoglobules than their triblock counterparts. Moreover, diblock structures, compared to triblock analogs, allow the formation of gels that do not demix with time (no synaeresis) but that are softer than triblock gels.