Flat surface measurements, polymer adsorption

Metallic nanopartides were deposited on ceramic and polymeric partides using ultrasound radiation. A few papers report also on the deposition of nanomaterials produced sonochemically on flat surfaces. Our attention will be devoted to spheres. In a typical reaction, commerdally available spheres of ceramic materials or polymers were introduced into a sonication bath and sonicated with the precursor of the metallic nanopartides. In the first report Ramesh et al. [43] employed the Sto-ber method [44] for the preparation of 250 nm silica spheres. These spheres were introduced into a sonication bath containing a decalin solution of Ni(CO)4. The as-deposited amorphous clusters transform to polyciystalline, nanophasic, fee nickel on heating in an inert atmosphere of argon at a temperature of 400 °C. Nitrogen adsorption measurements showed that the amorphous nickel with a high surface area undergoes a loss in surface area on crystallization. 

In principle every method suited for measuring some property of an adsorbed polymer as a function of time can be used for studying one or more aspects of the dynamics of polymer adsorption. Some methods can only be used for polymer adsorption on flat (oxidic) siufaces, others require higher amounts of adsorbed polymers and therefore can only be applied in dispersions with sufficient surface area. Recently some reviews on experimental methods have been published [1, 35]. In this section we will discuss some frequently applied methods applicable for oxidic surfaces. 

Measurements on Flat Surfaces. Using planar substrates, polymer adsorption can be studied under well-defined conditions of surface eneigies and known surface area. These measurements provide important insists into the structure and dynamics of adsorbed pol3rmers, which are often not experimentally achievable using dispersed particles. 

Fig. 3 a-c. Summary of data from different laboratories, obtained by surface force measurement, on the average layer thickness L as a function of tethered chain length for flat, tethered layers constructed by adsorption of amphiphilic polymers on mica. Adapted from Ref. 21. (a) Data of reference 20 on poly-tert-butylstyrene chains anchored by adsorbing blocks of poly-2-vinylpyridine. (b) Data of references 11 and 12 on polystyrene chains anchored by adsorbing blocks of poly-2-vinylpyridine. (c) Data of references 13 and 14 on polystyrene chains anchored by adsorbing zwitterionic groups [13] or by small adsorbing blocks of polyethyleneoxide [14]... 

The first, though not necessarily the most important, piece of information needed for understanding the adsorption of polymers is the adsorption isotherm. This is almost always determined by difference in polymer concentration before and after adsorption, though Stromberg" has directly measured adsorption to flat metal surfaces of radiolabelled polystyrene. Problems in isotherm determination can come from fractionation of the polymer, degradation by shear or biodegradation of water-soluble polymers. ... 

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