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Solution self-assembly of amphiphilic block copolymers (BCs) is typically performed by solvent to water exchange. However, BC assemblies are often trapped in metastable states depending on the mixing conditions, such as the magni-tude 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 communication we report the use of a specifically de-signed dialysis cell to continuously monitor by dynamic light scattering and small-angle neutron scattering the mor-phological changes of PDMS-b-PEG BCs 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. more...

Solution self-assembly of amphiphilic block copolymers (BCs) is typically performed by solvent to water exchange. However, BC assemblies are often trapped in metastable states depending on the mixing conditions, such as the magni-tude 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 communication we report the use of a dialysis cell specif-ically designed to continuously monitor by dynamic light scattering and small-angle neutron scattering the morpho-logical changes of PDMS-b-PEG BCs during THF to water exchange. The complete phase diagrams of equilibrium structures can then be established. Spherical micelles first form before evolving to rod-like micelles and vesicles, de-creasing the total interfacial area of aggregates in response to increasing interfacial energy. The dialysis kinetics can be adapted to the time scale of self-assembly by modifying the membrane pore size. The approach described herein should be relevant in polymer self-assembly and in supramolecular chemistry in general to better understand the interplay between thermodynamics and kinetics in aggregate formation. more...

Well-defined diblock copolymers comprising thermosensitive poly(N-isopropyl acrylamide) (PNIPAM) and poly(n-butylacrylate) (PBA) blocks were synthesized by macromolecular design by interchange of xanthates (MADIX)/reversible addition−fragmentation chain transfer polymerization (RAFT) using a xanthate-type mediating agent. Their behavior in aqueous solution as a function of temperature was studied by scattering and microscopy techniques. The cloud point temperature values were strongly correlated to the hydrophobic content of the copolymers. Moreover, above the cloud point, the block copolymer structure led to the formation of large reversible aggregates with well-defined sizes. Those polymers were then used to study the synthesis and stability of gold nanoparticles (AuNPs) dispersions either by coating preformed AuNPs or by in situ preparation. In this latter case, we showed that the appropriate choice of polymer concentration allows one to control the size of the AuNPs. Furthermore, the AuNPs were embedd... more...

International audience; 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. more...

The phase diagram and microstructure of the ternary system ionic, liquid benzylpyridinium bis(trifluoromethanesulfonyl)imide)/nonionic surfactant (octylphenol ethoxylate)/toluene, were studied by using conductivity measurements, dynamic light scattering, pulse field gradient spin-echo NMR, and small-angle neutron scattering. Three microregions were identified by conductivity measurements according to the percolation theory. The sizes of IL-in-oil microemulsions with various IL fractions were then determined by NMR and DLS and were found to be in accordance with the radii of gyration (approximately 2 or 3 nm) determined by SANS. The reverse IL-in-oil microemulsions were used as nanoreactors to perform a Matsuda-Heck reaction between p-methoxyphenyl diazonium salt and 2,3-dihydrofurane in the presence of a palladium catalyst. The reaction yields obtained were greater in microemulsions (67%) than in bulk IL (33%), highlighting a strong effect of confinement. Moreover, a direct correlation between the quantity of IL and the reaction yield was observed. more...

National audience; Double hydrophilic block copolymers (DHBC) consisting of a Jeffamine block, a statistical copolymer based on ethylene oxide and propylene oxide units possessing a lower critical solution temperature (LCST) of 30 degrees C in water, and Poly(L-glutamic acid) as a pH-responsive block were synthesized by ring-opening polymerization of gamma-benzyl-L-glutamate N-carboxyanhydride using an amino-terminated Jeffamine macroinitiator, followed by hydrolysis. This DHBC proved thermoresponsive as evidenced by dynamic light scattering and small-angle neutron scattering experiments. Spherical micelles with a Jeffamine core and a poly(L-glutamic acid) corona were formed above the LCST of Jeffamine. The size. of the core of such micelles decreased with increasing temperature, with complete core dehydration being achieved at 66 degrees C. Such behavior, commonly observed for thermosensitive homopolymers forming mesoglobules, is thus demonstrated here for a DHBC that self-assembles to generate thermoresponsive micelles of high colloidal stability. more...

Self-assembling properties of poly(sodium acrylate) grafted with dodecyl [C12], PAAgC12, or poly(N-isopropylacrylamide) [PNIPA] side chains, PAAgPNIPA, were studied in unentangled semidilute aqueous solution. While PAAgC12 self-associates through hydrophobic interactions, the gelation of PAAgPNIPA is triggered by heating in response to the lower critical solution temperature of PNIPA (LCST ∼ 32 °C). The local structure of the physical networks was investigated by small-angle neutron scattering, and the scattering patterns were described using a polydisperse sphere model taking into account hard-sphere interactions. This model allow us to draw a realistic picture of physical gels with quantitative information concerning the size of hydrophobic cores, the volume fraction of stickers in the aggregates, the fraction of stickers which take part in the aggregation process, the range of repulsive interactions, and the structural modifications induced by temperature. The description of the network is in good agre... more...

The effect of dense grafting on the polymer brush's conformation is studied by small-angle neutron scattering on well-defined branched copolymers. We have determined the persistence length lp of the backbone of poly(chlorovinyl ether) grafted with polystyrene (PCEVE-g-PS) copolymers. In a good solvent, this length lp can be directly obtained from the scattering vector q* at which the polymer chain locally behaves as a rod; i.e., its form factor enters the q-1 variation regime. This method is first applied to a linear PCEVE polymer, as reference. Then, we compare to the branched copolymers by using the matching condition for the PS branches in order to only measure the form factor of the PCEVE backbone. From the flexible linear chain to the bottlebrush-like polymer, the persistence length increases from 12 to 110 A. more...

The backbone conformation of a comblike polymethacrylate, PMA-CH 3 , was studied by small-angle neutron scattering in the nematic phase. The backbone is perpendicular to the mesogenic side chain moieties, corresponding to the oblate ellipsoid of the N 1 phase of Wang and Warner's theory. We have measured the temperature dependence of the conformation of the polymer backbone on five well-defined molecular weights. In the direction perpendicular to the hanging groups, the backbone adopts a weakly confined random walk conformation, compared to that of the isotropic phase. In the direction of the nematic field, the chain conformation is extended: the exponents of the scaling laws vary between 0.60 and 0.50. At low temperature, smectic fluctuations freeze the backbone anisotropy. When increasing the temperature, the nematic order exerts a weaker force on the polymer backbone, which tends to an isotropic Gaussian conformation. The scaling laws for the backbone conformation and their variations with temperature are compared to the theoretical predictions. more...

This article reports a study of the chain conformation in thin films of amorphous polymer prepared by spin coating. Polystyrene chains of two molecular weights Mw, 230 000 and 660 000, are confined in layers of thickness equal to either 1000 A, thus greater than their unperturbed radii of gyration Rg, or 100 A, thus smaller than Rg. The form factor of the chain inside the layer is measured by small-angle neutron scattering. Changes of the scattering are observed as a function of the film thickness in the intermediate scattering vector range. We analyze the data in the frame of the wormlike model. In the 1000 A films, the chain has the same Gaussian conformation as in the bulk. In the films of 100 A, the persistence length of the chain is increased (compared to 9.2 A the value in the bulk) up to 45 A, for both Mw values. However, the corresponding scattering intensity is higher than expected for such an extended chain. more...

The molecular and supramolecular structure of poly(n-hexyl isocyanate) in n-octane has been studied in the sol state and in the gel state by neutron and light scattering. In the sol state the chains appear stiff with dimensional characteristics consistent with the literature on this polymer. The gel consists of a network phase and free chains. The network phase appears to be an array of cross-section polydispersed fibers which can be described with a cross-section radius distribution function of the type w(r) ∼ r-1 with two cut-off radii rmax = 6.7 ± 0.4 nm and rmin = 1.3 ± 0.1 nm. These results are compared to the morphology revealed by electron microscopy. The sol state was also studied by dynamic light scattering as a function of concentration, time, and temperature. This revealed the presence of slow and fast modes which could be correlated respectively with the aggregates leading to gelation and to the individual polymer chains. The sol optical activity properties of the pregels revealed a reduction ... more...

The molecular structure of thermoreversible gels made up of poly(vinyl chloride) (PVC) and chemically-modified PVCs in diethyl oxalate has been investigated by SANS. The chemical modification, which chiefly takes place in the less stereoregular sequences, consists of replacing a few chlorine atoms by either hydrogen or benzothiolate groups. It is shown that small modifications significantly alter the gel structure. At small q vectors the results are analyzed by considering cross-section polydispersed fibers characterized by a distribution function of the type w(r)∼r -1 . Results at larger q vectors, which yield a q -2 behavior, indicate that the fibers are no longer compact at short distances more...

The formation of thermoreversible gels and aggregates of poly(methyl methacrylate) (PMMA) has been investigated as a function of temperature in two different solvents, i.e., bromobenzene and o-xylene. The molecular structure and the thermal behavior have been determined and correlated. It is again shown that the systems are composed of rigid, interconnected cylinders characterized by a two-population distribution as far as the transverse cylinder radius, r H , is concerned: a majority of cylinders with r H =1.5±0.1 nm and a minority of cylinders with r H =3.5-4.0 nm. When the gelation sets in, the proportion of the second population is seen to increase substantially at the expense of the first population more...

The thermoreversible gelation of agarose in different water/DMS0 mixtures has been studied by polarimetry and SANS, and the modulus-concentration relations have been determined. In the sol state it has been found that the chain is fairly rigid, independent of the solvent composition, with a persistence length exceeding 9 nm. Theoretical fits of the scattering patterns are consistent with conformations close to single helices. The mass per unit length, which decreases with increasing DMSO content, is accounted for by considering the formation of an agarose/DMSO complex more...

Etude par SAWS, diffraction neutronique et gonflement, de la structure helicoidale, de l'arrangement chaine-solvant et de la trajectoire de la chaine. Les resultats montrent que la structure en helice 12 1 est absente dans l'etat naissant et que la structure serait proche d'une helice 3 1 solvatee (modele de type echelle) more...