Concomitant adsorption of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers and sodium dodecyl sulfate at the silica-water interface.

Upon addition of silica to aqueous solutions of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers (PEO-b-PCL) and sodium dodecyl sulfate (SDS), adsorption of the solutes occurs at the silica-water interface. The amount of the adsorbed constituents has been measured by the total concentration depletion method. Small-angle neutron scattering experiments (SANS) have been carried out to investigate the structure of the adsorbed layer. Although SDS is not spontaneously adsorbed onto hydrophilic silica, adsorption is observed in the presence of PEO-b-PCL diblocks, in relation to the relative concentration of the two compounds. Conversely, SDS has a depressive effect on the adsorption of the copolymer, whose structure at the interface is modified. Copolymer desorption is however never complete at high SDS content. These observations have been rationalized by the associative behavior of PEO-b-PCL and SDS in water.

Adsorption of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers at the silica-water interface.

The adsorption of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) and poly(ethylene oxide)-b-poly(gamma-methyl-epsilon-caprolactone) copolymers in aqueous solution on silica and glass surfaces has been investigated by flow microcalorimetry, small-angle neutron scattering (SANS), surface forces, and complementary techniques. The studied copolymers consist of a poly(ethylene oxide) (PEO) block of M(n) = 5000 and a hydrophobic polyester block of poly(epsilon-caprolactone) (PCL) or poly(gamma-methyl-epsilon-caprolactone) (PMCL) of M(n) in the 950-2200 range. Compared to homoPEO, the adsorption of the copolymers is significantly increased by the connection of PEO to an aliphatic polyester block. According to calorimetric experiments, the copolymers interact with the surface mainly through the hydrophilic block. At low surface coverage, the PEO block interacts with the surface such that both PEO and PCL chains are exposed to the aqueous solution. At high surface coverage, a dense copolymer layer is observed with the PEO blocks oriented toward the solution. The structure of the copolymer layer has been analyzed by neutron scattering using the contrast matching technique and by tapping mode atomic force microscopy. The experimental observations agree with the coadsorption of micelles and free copolymer chains at the interface.

Mixed self-assembly of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers and sodium dodecyl sulfate in aqueous solution.

Interaction of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers with anionic sodium dodecyl sulfate (SDS) has been investigated in aqueous solution. Formation of mixed micelles has been confirmed by surface tension measurements, whereas the influence of the surfactant on the copolymer self-assembling has been studied by measurement of the 1H NMR self-diffusion coefficients and by small-angle neutron scattering. As a rule, the surfactant decreases the heterogeneity of the micellar structures formed by the copolymer in water. Moreover, increasing the content of SDS results in the increasingly more important extension of the poly(ethylene oxide) (PEO) corona chains and the copolymer micelle deaggregation. The stability of the micelles against SDS increases with the length of the hydrophobic block. Preliminary two-dimensional NMR measurements with nuclear Overhauser enhancement have confirmed the spatial vicinity between SDS and the constitutive blocks of the copolymer.

Self-assembly of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers in aqueous solution.

The associative behavior of monodisperse diblock copolymers consisting of a hydrophilic poly(ethylene oxide) block and a hydrophobic poly(epsilon-caprolactone) or poly(gamma-methyl-epsilon-caprolactone) block has been studied in aqueous solution. Copolymers have been directly dissolved in water. The solution properties have been studied by surface tension, in relation to mesoscopic analyses by NMR (self-diffusion coefficients), transmission electron microscopy, and small-angle neutron and X-ray scattering. The experimental results suggest that micellization occurs at low concentration (approximately 0.002 wt %) and results in a mixture of unimers and spherical micelles that exchange slowly. The radius of the micelles has been measured (ca. 11 nm), and the micellar substructure has been extracted from the fitting of the SANS data with two analytical models. The core radius and the aggregation number change with the hydrophobic block length according to scaling laws as reported in the scientific literature. The poly(ethylene oxide) blocks are in a moderately extended conformation in the corona, which corresponds to about 25% of the completely extended chain. No significant modification is observed when poly(gamma-methyl-epsilon-caprolactone) replaces poly(epsilon-caprolactone) in the diblocks.