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Deuterium NMR has been employed to determine the average orientation of chain segments in poly(butadiene) networks. It is shown that the free induction decay separates the contribution to the orientation arising from the network constraint to that from chain interactions. The NMR spectrum line shape reveals the orientational distribution of network vectors due to the cross-links, whereas the observed splitting gives information about the orientation due to segmental interactions. Both the line shape and splitting have been fitted simultaneously for a range of deformed poly(butadiene) networks. From the fitting parameters, the separate contributions to the average orientation of the chain segments arising from the network constraint and from the interactions are calculated. These in turn are used to determine the molecular weight between cross-links and the size of the segmental interactions, which we choose to express in terms of the Edwards' screening length. This work is also important to computer modeling of the stress−optical coefficient where the interchain interactions are ignored.

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Abstract. A Peclet number, Pe, for the drying of colloidal films can be used as a predictor of the uniformity of water concentration in the direction normal to the film. Uniform drying is predicted to occur when Pe < 1, whereas with Pe > 1, a layer of packed particles is expected to develop above a more dilute layer. Routh and Zimmerman have more recently proposed that the particle concentration gradient between the packed and dilute layers, dφp/dz , will scale as Pe 1/2 . Here, this scaling relation is tested experimentally with magnetic resonance profiling data obtained from waterborne colloidal films dried under conditions to yield a range of Pe. It is found that dφp/dz increases with Pe but scales as Pe 0.8 . This disagreement with the prediction can be attributed to an underestimate of Pe when there are greater non-uniformities of drying, because of an unquantified slowing down of the evaporation rate.

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