We have measured the force-distance profiles between two curved mica sheets immersed in toluene and in xylene, both in the pure solvents and following addition of polystyrene (PS), end-functionalized polystyrene of different molecular weights Af, PS-X(AÍ), and polystyrene-poly (ethylene oxide) diblock copolymers (PS-PEO) with a short PEO block. Our results show that PS does not adsorb from the (good solvents) toluene and xylene but that once PS-X or PS-PEO are added to the solution the surface is rapidly covered, showing that the nonadsorbing PS tails are anchored at one end only. The force profiles following surface coverage are monotonically repulsive, and the range 2L0 for onset of interaction is roughly twice that of the corresponding adsorbed chains. There is no evidence of bridging attraction at low surface coverage or of finite relaxation times following strong compression, both of which are characteristic of adsorbed chains. The qualitative behavior with both PS-X and PS-PEO is very similar. For the PS-X(ilf), we find La Af0•6, and we are also able to estimate the mean interanchor spacing s and find it to increase markedly with M. These features are in accord with equilibrium expectations for a fixed anchoring energy of the polystyrene on the mica. We find that our data are well fitted quantitatively both by scaling and by mean-field models.

Herein we report the photocontrol of cucurbit[8]uril (CB[8])-mediated supramolecular polymerization of azobenzene-containing monomers. The CB[8] polymers were characterized both in solution and in the solid state. These host-guest complexes can be reversibly switched between highly thermostable photostationary states. Moreover, a remarkable stabilization of Z-azobenzene was achieved by CB[8] complexation, allowing for structural characterization in the solid state.

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Specular neutron reflection was used to investigate the density profile of polystyrene-poly-(ethylene oxide) (PS-PEO) block copolymers adsorbed from d-toluene onto quartz. The neutron beam passed through the quartz substrate and was reflected from the quartz/d-toluene interface. The PEO block, which comprises a small fraction of the total polymer molecular weight, strongly adsorbs onto the quartz substrate, while the PS block remains in solution. Thus, the chains form a terminally attached polymer "brush". The reflectivity profiles are well described by a parabolic or error function polymer density profile normal to the interface, but the data cannot be fitted to exponential or power law decay profiles. The layer thickness values are in good agreement with the results of interlayer force measurements for the same polymersolvent system adsorbing onto mica. The molecular weight dependence of the layer thickness and adsorbance obtained from the data obey scaling laws in accord with the theory of semidilute polymer brushes.

The adsorption kinetics and adsorption isotherm of a polystyrene (PS)-poly(ethy1ene oxide) (PEO) diblock copolymer onto a silicon wafer from toluene solution was measured in situ by ellipsometry. Both blocks are in good solvent conditions but the small PEO block is adsorbed while the much larger PS block dangles in solution. Thus, PS-PEO behaves like an end-adsorbed chain. The adsorption kinetics shows two processes on a clearly seperated time scale. In the beginning, the time behavior of the adsorbed amount can be described as a diffusion-controlled process leading to a surface coverage with small interaction between molecules. A still denser surface coverage is achieved by the penetration of chains through the existing monolayer combined with the conformational rearrangement to a more brushy conformation. Experiments with different molecular weights indicate that the repulsion between the nonadsorbing PS blocks determines the maximal adsorbed amount. The adsorbed monolayer can be rapidly and completely displaced by PEO oligomer with a length comparable to the PEO block in the block copolymer. Models of the adsorption process are discussed in detail.