Dilational rheology and relaxation properties of the adsorption layers of electrostatic complexes between Eudragit RS and chitosan sulfate at the methylene chloride-water interface.

International audienceThe electrostatic interpolyelectrolyte complex formation between the hydrophobic cationic polyelectrolyte Eudragit RS and the anionic hydrophilic polyelectrolyte chitosan sulfate at the methylene chloride–water interface has been studied by dilational rheometry

Dilational viscoelasticity and relaxation properties of interfacial electrostatic complexes between oppositely charged hydrophobic and hydrophilic polyelectrolytes

Strongly adsorbing hydrophobic cationic polyelectrolyte, Eudragit RS, containing approximately 2.5 mol% of pendent hydrophilic trimethylammonium (TMA) groups irreversibly adsorbs from its methylene chloride (MCl) solution at the MCl/water interface and forms solid-like adsorption layers (ALs). Submitted to periodic dilational deformations with the standard radial frequency omega(0)=0.63 rad/s, these ALs exhibit relatively high dilational storage modulus E\u27 approximately 20 mN/m and practically zero loss modulus E\u27\u27 at the bulk concentration C(Eud)=4 x 10(-3)g/L. The frequency scanning of these ALs in the diapason omega=0.01-0.63rad/s and the approximation of the experimental dependences E\u27(omega) and E\u27\u27(omega) by two relaxation times rheological model makes it possible to estimate the crossing frequency of these ALs determined from the condition E\u27(omega(c))=E\u27\u27(omega(c)) as omega(c) approximately 5 x 10(-4)rad/s. Upon dissolving the hydrophilic anionic polyelectrolyte, chitosan sulfate (ChS), in the water phase (C(ChS)=3 x 10(-2)g/L) the electrostatic interpolyelectrolyte complexes form at the MCl/water interface. The elasticity moduli E\u27 and E\u27\u27 of these mixed AL did not undergo remarkable variations, but the crossing frequency is sharply increased by approximately 10 times becoming equal to omega(c) congruent with 3 x 10(-3)rad/s. The increase of omega(c) certifies for the liquefaction of mixed Eudragit RS/ChS adsorption layers. A remarkable decrease of the storage modulus down to E\u27=8 mN/m and simultaneous increase of the crossing frequency up to omega(c) congruent with 10(-2)rad/s occurs upon increasing the concentrations of both components, Eudragit RS and ChS, up to 0.1g/L. The liquefaction effect in the mixed ALs of oppositely charged polyelectrolytes was explained on the basis of the proposed relaxation mechanism. The effect of the liquefaction of adsorption layers of strongly adsorbing hydrophobic polyelectrolytes by formation of interpolyelectrolyte complexes with hydrophilic polyelectrolytes must be taken into account in the production of nano-capsules and nano-fibers

Interactions of bile salts with a dietary fibre, methylcellulose, and impact on lipolysis

Methylcellulose (MC) has a demonstrated capacity to reduce fat absorption, hypothetically through bile salt (BS) activity inhibition. We investigated MC cholesterol-lowering mechanism, and compared the influence of two BS, sodium taurocholate (NaTC) and sodium taurodeoxycholate (NaTDC), which differ slightly by their architecture and exhibit contrasting functions during lipolysis. BS/MC bulk interactions were investigated by rheology, and BS behaviour at the MC/water interface studied with surface pressure and ellipsometry measurements. In vitro lipolysis studies were performed to evaluate the effect of BS on MC-stabilised emulsion droplets microstructure, with confocal microscopy, and free fatty acids release, with the pH-stat method. Our results demonstrate that BS structure dictates their interactions with MC, which, in turn, impact lipolysis. Compared to NaTC, NaTDC alters MC viscoelasticity more significantly, which may correlate with its weaker ability to promote lipolysis, and desorbs from the interface at lower concentrations, which may explain its higher propensity to destabilise emulsions

Amphiphilic derivatives of chitosan using microwave irradiation. Toward an eco-friendly process to chitosan derivatives

Conventional heating and microwave irradiation have been compared for the synthesis of chitosans grafted with alkyl chains. Reaction time (1–60 min), temperature (25 and 40 °C) and chitosan molar mass have been studied onto the yield of alkylation. The irradiation mode has been scrupulously controlled to highlight the effect of the use of microwaves. The chemical structure of modified polymers (degree of alkylation) is determined from NMR. In relation to the rheological behavior and surface tension measurements, the evolution of hydrophobic interactions is studied as a function of the yield of alkylation. A maximum of intrinsic viscosity and hydrodynamic diameter was observed for a degree of alkylation of around 10%. All the results tend to prove that microwave assisted synthesis is a powerful method to obtain modified chitosan under extremely low reaction time without any degradation and/or property modifications

Thermogelation of methylcellulose in aqueous solutions

Aqueous solutions of methylcellulose (MC) were studied as a function of temperature. It is well known that semi-dilute MC solutions are forming a gel upon heating. The gelation phenomenon is time-dependent and reversible but with a hysteresis. Different cyclic thermal treatments were conducted characterizing the formation of progressive interactions. An aggregation above 35°C is also shown by studies in dilute solution. Moreover, the role of the chemical structure (distribution of substituents and degree of substitution value) on the MC rheological properties was underlined. Gelation is then mainly attributed to hydrophobic interactions

Relation entre le taux de rétention et la distribution de pores dans une membrane d'ultrafiltration

L'étude porte sur les propriétés d'ultrafiltration d'une membrane homogène anionique ; la distribution des rayons de pores a été déterminée par thermoporométrie. Les taux de rétention de solutés neutres et ioniques ont été déterminés et comparés à la fraction de pores accessibles y obtenue par thermoporométrie. En absence d'adsorption, on montre que le taux de rétention d'un soluté donné est égal à (1 — yR) avec yR la fraction de pores de rayon supérieur au rayon R de la molécule considérée ; un modèle de tamis rend alors bien compte du comportement de la membrane. En présence d'adsorption même faible (cas des dextranes dans l'eau), le taux de rétention du soluté déterminé à partir des flux de solvant et de soluté est supérieur à la valeur prévue à partir du volume hydrodynamique du soluté. Avec des solutés ioniques, nous mettons de plus en évidence un effet d'exclusion électrostatique lorsque la force ionique de l'éluant est inférieure à 10— 2 N