Monolayers adsorbed polymers

It is the increase in surface viscosity produced by adsorbed films (insoluble and Gibbs monolayers, adsorbed polymers, etc.) that leads to the production of persistent foams, helps stabilize emulsions, and explains the role of spread monolayers in dampening surface waves, among other important interfacial phenomena. 

The acid monolayers adsorb via physical forces [30] however, the interactions between the head group and the surface are very strong [29]. While chemisorption controls the SAMs created from alkylthiols or silanes, it is often preceded by a physical adsorption step [42]. This has been shown quantitatively by FTIR for siloxane polymers chemisorbing to alumina illustrated in Fig. XI-2. The fact that irreversible chemisorption is preceded by physical adsorption explains the utility of equilibrium adsorption models for these processes. 

Ruths and Granick [95] have studied the self-adhesion of several monolayers and adsorbed polymers onto mica. For loose-packed monolayers, the adhesion, in excess of a constant value observed at low rate, increased as a power law with the square root of the separation rate. In the case of adsorbed diblocks, the excess adhesion increased linearly with logarithmic separation rate. The time effects were ascribed to interdigitation and interdiffusion between the contacting layers. 

The following may be concluded. The reaction process for modification in aqueous solvent is affected by the pH of the solution. Maximal loading is obtained at natural pH. The modification layer is composed of a chemically bonded monolayer and an overlying physically adsorbed polymer network. 

In sec. 3.6 it was shown that, to a first approximation, C does not depend on the salt concentration, whereas does. At salt concentrations of about 0.1 mol dm C becomes so large that C= C . Under these conditions any change in C upon adsorption of polymer must reflect the presence of train segments. The amount adsorbed in trains is then obtained by comparing the Stern capacitance in the absence (C °) and in the presence (C ) of adsorbed polymer, provided the capacitance for a surface fully covered with a monolayer of segments (denoted by C ) is known. Then... 

In adsorption from solution, physisorption is far more common than chemisorption, although the latter is sometimes possible. Solute adsorption is usually restricted to a monomolecular layer, since the solid-solute interactions, although strong enough to compete successfully with solid-solvent interactions in the first adsorbed monolayer, do not do so in subsequent monolayers, because the interaction is screened by the solvent molecules. Thus, multilayer adsorption has only rarely been observed in a number of cases, and identified, when the number of adsorbate molecules exceeds the number of mono-layer molecules possible on the total adsorbent surface area. However, this analysis cannot be applied to polymer adsorption, because it is generally impossible to determine the surface area of a monomolecular layer of a polymer adsorbed flat on the solid surface. This is because the adsorbed polymer can only be anchored to the surface at a few points, with the remainder of the polymer in the form of loops and ends moving more or less freely in the liquid phase. 

Reiter G, Sommer JU (1998) Crystallization of adsorbed polymer monolayers. Pbys Rev Lett 80(17) 3771-3774... 

The mechanism of adsorption of polymers containing quaternary ammonium ions on silica at low pH is by no means clear. The point of zero charge of silica is about pH 2, yet Derevyanko et al. (318) report that the adsorption of poly(2-methyl-5-vinylpyridinium choride) is at a maximum at pH 2.9 and that a monolayer of polymer was adsorbed on silica at pH 0.5 or 2.9. 

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