Surface properties swelling

AB diblock copolymers in the presence of a selective surface can form an adsorbed layer, which is a planar form of aggregation or self-assembly. This is very useful in the manipulation of the surface properties of solid surfaces, especially those that are employed in liquid media. Several situations have been studied both theoretically and experimentally, among them the case of a selective surface but a nonselective solvent [75] which results in swelling of both the anchor and the buoy layers. However, we concentrate on the situation most closely related to the micelle conditions just discussed, namely, adsorption from a selective solvent. Our theoretical discussion is adapted and abbreviated from that of Marques et al. [76], who considered many features not discussed here. They began their analysis from the grand canonical free energy of a block copolymer layer in equilibrium with a reservoir containing soluble block copolymer at chemical potential peK. They also considered the possible effects of micellization in solution on the adsorption process [61]. We assume in this presentation that the anchor layer is in a solvent-free, melt state above Tg. The anchor layer is assumed to be thin and smooth, with a sharp interface between it and the solvent swollen buoy layer. 

Similar molecular weight poly(DMA-co-EPl), 1750 daltons, ca. 13 repeat units, and poly(TMDAB-co-DCB), 1500 daltons, ca. 11 repeat units were compared. The two condensation polymers appeared to be about equally effective in preventing the swelling of Wyoming bento-nite. Any small differences are probably due to repeat unit chemical structure differences rather than the small variations in polymer molecular weight. The presence of the hydroxyl group and the smaller N - N distance in poly(DMA-co-EPl) could affect polymer conforma-tion in solution, geometry of the polymer - clay complex, and surface properties of the polymer - clay complex as compared to poly(TMDAB-co-DCB). 

For moderate reduction the changes are completely reversible but they are progressively less so with more thorough reduction (Stucki et al 1984 Komadel et al 1995 Gates et al 1996). There are concomitant changes in the clay s physical and chemical properties, including its surface area, swelling behaviour, and capacity to sorb cations. 

In spite of the fact that stratum corneum cells are metabolically inert, changes in keratin structure and organization occur as each cell transits through the stratum corneum prior to desquamation (28). This suggests some asymmetry in physical and chemical properties through the thickness of the corneum. One demonstration of this is the swelling of fresh frozen transverse sections of corneum in dilute acid or base. The most mature surface cells swell considerably more slowly and to a lesser extent than the lower layers of the corneum (18). Such asymmetry is of particular importance in studying the diflFusion and mechanical properties of this membrane. 

All films prepared for contact angle studies were cast from an excess of dry polymer swollen and fluidized by a small quantity of added liquid (usually triple-distilled water, the last two distillations being in an allquartz apparatus). The pH of these weak gels at the initiation of film formation was always 5. All our surface films were gel-dried rather than sol-dried. Although swelling may not have reached equilibrium prior to film drying, the films were only about 1 mm thick and their surface properties, as determined by contact angle measurements, were always reproducible within 5°. 

GC methods have been used to measure the adsorption of non-swelling vapours on the surface of dry (. -8.) and moist (9.-12.) cellulose. Adsorption isotherms, surface areas, isosteric heats and entropies of adsorption have been measured for a range of hydrocarbons and organic vapours. Perhaps the most useful aspect of the method is that the effect of relative humidity on surface properties may be investigated. The validity of the method as applied to surface area measurements is described in some detail below. Other applications of GC to cellulose surfaces are then summarized briefly. 

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