Self-adsorption process

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. 

The activated Ba(OH)2 was used as a basic catalyst for the Claisen-Schmidt (CS) condensation of a variety of ketones and aromatic aldehydes (288). The reactions were performed in ethanol as solvent at reflux temperature. Excellent yields of the condensation products were obtained (80-100%) within 1 h in a batch reactor. Reaction rates and yields were generally higher than those reported for alkali metal hydroxides as catalysts. Neither the Cannizaro reaction nor self-aldol condensation of the ketone was observed, a result that was attributed to the catalyst s being more nucleophilic than basic. Thus, better selectivity to the condensation product was observed than in homogeneous catalysis under similar conditions. It was found that the reaction takes place on the catalyst surface, and when the reactants were small ketones, the rate-determining step was found to be the surface reaction, whereas with sterically hindered ketones the adsorption process was rate determining. 

Decher G, Hong JD. Buildup of ultrathin multilayer films by a self-assembly process. 1. Consecutive adsorption of anionic and cationic bipolar amphiphiles on charged surfaces. Makromolekulare Chemie-Macromolecular Symposia 1991a 46 321-327. 

G. Decher, J.D. Hong, J. Schmitt, Build-Up of Ultrathin Multilayer Films by a Self-Assembly Process 3. Consecutively Alternating Adsorption of Anionic and Cationic Polyelectrolytes on Charged Surfaces , Thin Solid Films, 210,831 (1992)... 

Fig. 25. Schematic representation of molecular adsorption processes at a nanocapsule membrane. A certain fraction Pads of the triglyceride molecules (hexagons) as well as of surfactant molecules in aqueous solution (circles) is adsorbed by tbe inner and outer membrane surface. They undergo a continuous exchange process with another fraction Pdes of the molecules in the bulk medium. This exchange is characterized by average residence times in the adsorbed and the desorbed state Tads and Tdes- A third fraction P ee of the bulk phase is excluded from this exchange process within the experimental time frame by the Umited self-diffusion. All numbers are discussed in Section 4.4.

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