Geometry problems polymers

If concentrated polymer solutions confined in thin film geometry are considered, it turns out that the static properties readily match the theoretic expectations (Fig. 17) whereas the problem with dynamics is more complex [16,17] writing Zgff = -f-1, one expects a corresponding decrease in the... 

The problems associated with the in situ approaches can be avoided by using a discrete catalyst. The presumed structure of the monometallic palladium catalyst contains the sulfonated phosphine ligand chelated to the palladium and a palladium-carbon bond (polymer), most probably in cis geometry with respect to the phosphorous (Fig. 8). 

The coaxial cylinder geometry has the advantage of low heat loss from the ends by having a large length to diameter ratio. However, there is a problem of error due to it being very difficult to make the test piece fit accurately. This is not the case with a molten polymer and such apparatus has allowed measurements on polymers under pressure40. 

The polymer must be able to accommodate geometric changes demanded by the metal ion as the oxidation state changes. Actually, since much work is done with Fen/Fein, Run/Ruin and Osn/OsnI, where in all cases octahedral geometry is dominant, this presents little problem for PVP. Mobility of polymer chains could, however, be an important factor in bringing two redox sites into juxtaposition. Some sophistication is often seen in biological redox polymers where the redox sites are held in favourable spatial relationship and the metal is located in sites which represent a compromise between the geometrical requirements of the oxidized and reduced forms. 

The outlined problems correspond to the most typical system where three phases, e.g. liquid, gas and solid, are brought in contact. Additional wetting geometries can occur when the liquid phase consists of two subphases, e.g. mixture of incompatible polymer liquids, and/or the substrate surface exhibits variations in chemical composition. In these cases, the interfacial interactions will strongly interfere with the phase separation inside the film. Laterally ordered polymer films might be formed due to the preferential wetting of the patterned substrate by one of the liquid phases. 

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