Ref HAL: hal-01942648_v1
Exporter : BibTex | endNote
Résumé:

Upon pH stimulus, double hydrophilic block copolymers form polyion complexes (PIC) in the micellar form. We used PIC micelles as ecofriendly templates for the synthesis of ordered mesoporous materials. The porosity of the final material is revealed by simple inversion of the pH stimulus. Various mesoporous silica materials have been obtained from cubic to lamellar.The control over the structure of the final material is expected to relate to the lyotropic behavior just as observed when micelles of amphiphilic molecules are used as template. However such lyotropic behavior has never been reported for PIC micelles. Moreover the same PIC leads to different structured silica materials depending on the physico-chemical conditions.Using X-rays and light scattering, optical microscopy and osmometry, we establish the equation of state (osmotic pressure vs volume fraction) of a PEO-b-PAA/oligoamine electrostatic complex. Its lyotropic behavior is characterized by a transition of shape at 0.16 w/w and a transition to a lamellar phase at 0.30w/w. The water content of the core of the micelles is addressed from the complete phase diagram of the polyelectrolyte complex in its coacervate form and explains why a single complex leads to porous material of different structure.

Ref HAL: hal-01934881_v1
Exporter : BibTex | endNote
Résumé:

By combining rheology, light scattering, small angle X-ray scattering and simulations we explore the glassy dynamics of soft colloids using microgels and charged particles interacting by steric and screened Coulomb interactions, respectively. In the supercooled regime, the structural relaxation time (SRT) of both systems grows steeply with volume fraction, reminiscent of the behavior of colloidal hard sphere systems [1]. This suggests that softness has no impact on the growth of the SRT on approaching the glass transition, as confirmed by computer simulations. We show that the onset of a finite yield-stress, occurring within the supercooled regime, systematically corresponds to a minimum of the stretching exponent characterizing the decay of the two-time intensity autocorrelation function.Softness becomes relevant only at very large packing fractions, when the system falls out of equilibrium. In this non-equilibrium regime, the SRT depends surprisingly weakly on packing fraction and time correlation functions exhibit compressed exponential decays consistent with internal stress-driven relaxation. The transition to this novel regime coincides with the onset of an anomalous decrease of local order with increasing density, reminiscent of the reentrant glass transition predicted theoretically in ultrasoft systems [2,3], and corresponds to a weakening of the volume fraction dependence of the plateau modulus of the suspensions. We propose that these peculiar dynamics result from a competition between the non-equilibrium aging dynamics of the glassy state and the tendency of soft systems to refluidize at high packing fractions.

Ref HAL: hal-01680368_v1
DOI: 10.1039/c7py01853c
WoS: 000418645100006
Exporter : BibTex | endNote
4 Citations
Résumé:

Control of film structures made from a polystyrene-polystyrene sodium sulfonate-polystyrene (PS-PNaSS-PS) copolymer micellar solution is investigated in a THF/water mixture. Four different copolymers (varying molecular weights) are synthesised via RAFT (Reversible Addition Fragmentation chain Transfer) polymerisation. Depending on parameters such as copolymer molecular weight, solvent composition and copolymer concentration, the PS-PNaSS-PS triblock self-assembles into different morphologies in solution and dry state. The effect of each parameter is investigated using characterization techniques such as AFM, TEM, Cryo-TEM, SEM and SAXS. The morphologies obtained for PS-PNaSS-PS are found to be extremely sensitive when the water content of the micellar solution is low. Among the structures observed, a highly ordered nano-porous film is obtained using a PS10k-PNaSS6k-PS10k triblock copolymer solution containing 3.0 wt% of water. This micellar solution is used to prepare a porous membrane for filtration applications. Pure water filtration data suggest a pore size in the range of ultrafiltration, making these membranes attractive for applications in the food industry, for bacteria, virus and protein removal.

Ref HAL: hal-01896690_v1
DOI: 10.1039/c8sm00911b
WoS: WOS:000442269000021
Exporter : BibTex | endNote
1 Citation
Résumé:

We use space-resolved dynamic light scattering in the highly multiple scattering regime (Photon Correlation Imaging Diffusing Wave Spectroscopy, PCI-DWS) to investigate temperature-induced phase transitions in polymorphic materials. We study paraffin wax as a simple model system and chocolate, a prototypical example of fat-based products exhibiting complex, history-dependent phase transitions. We find that microscopic dynamics measured using PCI-DWS show remarkable, non-monotonic behavior upon heating: they transiently accelerate when crossing phase transition and slow down above the transition temperature. Sub-micron resolution measurements of the local drift of the sample surface reveal that the speed-up of the dynamics is due to the strain field induced by the change in density at transition temperature. The transition temperatures obtained from PCI-DWS are found to be in excellent agreement with those inferred from complementary differential scanning calorimetry and X-ray scattering experiments, thereby validating PCI-DWS as a new, powerful tool for the characterization of phase transitions in complex soft matter. Finally, we demonstrate the unique possibilities afforded by space-resolved DWS by investigating the spatially heterogeneous response of poorly manufactured or composite chocolate samples.

PMID 29758608
DOI: 10.1103/PhysRevE.97.040601
WoS: WOS:000429636700001
30 Citations
Résumé:

We explore the glassy dynamics of soft colloids using microgels and charged particles interacting by steric and screened Coulomb interactions, respectively. In the supercooled regime, the structural relaxation time τα of both systems grows steeply with volume fraction, reminiscent of the behavior of colloidal hard spheres. Computer simulations confirm that the growth of τα on approaching the glass transition is independent of particle softness. By contrast, softness becomes relevant at very large packing fractions when the system falls out of equilibrium. In this nonequilibrium regime, τα depends surprisingly weakly on packing fraction, and time correlation functions exhibit a compressed exponential decay consistent with stress-driven relaxation. The transition to this novel regime coincides with the onset of an anomalous decrease in local order with increasing density typical of ultrasoft systems. We propose that these peculiar dynamics results from the combination of the nonequilibrium aging dynamics expected in the glassy state and the tendency of colloids interacting through soft potentials to refluidize at high packing fractions.

Ref HAL: hal-01804723_v1
WoS: WOS:000429556704623
Exporter : BibTex | endNote
Résumé:

A series of double hydrophilic block copolymers DHBCs has been synthesized by controlled radical polymerization (Figure 1). Poly(ethylene oxide)-b-poly(acrylic acid) PEO-b-PAA was prepared by ATRP in acetone. PEO-b-PAA and PEO-b-Poly(N-isopropyl acrylamide) PEO-b-PNIPAM were prepared by RAFT using a PEO-based dithiobenzoate macro-RAFT agent, in water and dioxane respectively. Poly(poly(ethylene glycol) methyl ether acrylate)-b-PAA PmPEGA-b-PAA was prepared by RAFT in water using a trithiocarbonate RAFT agent. Poly(acrylamide)-b-PAA PAM-b-PAA and PAM-b-poly(3-acrylamidopropyl)trimethylammonium chloride) PAM-b-PAPTAC were prepared by RAFT/MADIX using xanthate as control agent, in water/ethanol for the PAM block and directly in water for the second block. The block copolymers have been characterized by SEC, pH titration, conductimetry, and capillary electrophoresis (CE).The reversible formation of micelles by variation of temperature in the case of PEO-b-PNIPAM, or by the mixing of polyelectrolyte DHBCs with a polyelectrolyte of opposite charge in the right range of pH (e.g. anionic PEO-b-PAA associated with cationic oligochitosan) has been studied. The micelles have been characterized by various scattering techniques and CE.Such stimuli-responsive (T, pH, ionic strength) micellar systems have been involved as structuring agents in the synthesis of nanostructured mesoporous silica by sol-gel process. A relationship between the composition of the DHBCs, the composition of the micelles, the experimental conditions of micelle formation and the final mesostructure of the silica materials is foreseen. This strategy has been applied to the preparation of drug-loaded silica for biomedical applications.

Ref HAL: hal-01627752_v1
Ref Arxiv: 1811.06903
DOI: 10.1039/c7sm00596b
WoS: WOS:000411436600003
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
5 Citations
Résumé:

Vegetable oil based hybrid films were developed thanks to a novel solvent- and heating- free method at the air-water interface using silylated castor oil cross-linked via a sol-gel reaction. To understand the mechanism of the hybrid film formation, the reaction kinetics was studied in detail by using complementary techniques: rheology, thermogravimetric analysis, and infrared spectroscopy. The mechanical properties of the final films were investigated by nano-indentation, whereas their structure was studied using a combination of wide-angle X-ray scattering, electron diffraction, and atomic force microscopy. We found that solid and transparent films form in 24 hours and, by changing the silica precursor to castor oil ratio, their mechanical properties are tunable in the MPa-range by about a factor of twenty. In addition to that, a possible optimization of the cross-linking reaction with different catalysts was explored and finally, cytotoxicity tests were performed on fibroblasts proving the absence of film toxicity. The results of this work pave the way to a straightforward synthesis of castor-oil films with tunable mechanical properties: hybrid films cross-linked at the air-water interface combine an easy and cheap spreading protocol with the features of their thermal history optimized for possible future micro/nano drug loading, thus representing excellent candidates for the replacement of non-environment friendly petroleum-based materials.