Transition, first-order conformational motion

The two examples of adsorbed side chain substituted macromolecules, i.e., the poly(n-butyl acrylate) brush and the tris(p-undecyloxybenzyloxo) benzoate jacketed polystyrene, demonstrate two rather complementary aspects of the interaction of such molecules with a planar surface. In the first case the two-dimension to three-dimension transition results in a cooperative collapse of an extended coil conformation to a globule. The second case shows a rather high degree ordering with a distinct orientation of the backbone in the substrate plane. Combination of both effects and partial desorption can lead to a repta-tion-hke directed motion as depicted schematically in Fig. 36. 

Nano-Confinement. There are limited, but interesting studies, regarding the confinement in ordered mesoporous materials. First observations were made on nematic liquids within mesoporous SBA-15 host materials which showed a change in the phase transition, when confined within the mesoporous cavities. To evidence also that there are many studies of confinement in mesoporous materials in the polymer diffusion and membrane literature, but they refer essentially to entropic effects due to restricted motion of these materials inside the ordered mesoporous materials which in enhanced by more hydrophobic and less polar surfaces. This is especially true as the molecules become larger, because the number of conformations the molecule can adopt in a confined space is limited. We refer here, on the contrary, to aspects relevant for catalysis and in which thus the dimensions of the molecules (of the order of 0.1 nm) is far below the dimensions of the cavities (around 5 nm for SBA-15, for example). 

First, it is necessary to find the configuration conditional probability p(i,t /,0) = Piioit) in Eq. (8.30) in order to obtain the internal correlation functions. This is achieved by following the master equation method of Wittebort and Szabo [8.4]. Conformational transitions between N distinct configurations occur via one-bond, two-bond, or three-bond motion [8.24] in the chain. These bond motions are characterized by phenomenological rate constants and fcs, respectively. In general, there is more than... 

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