Theory of an electric field induced periodic phase in a nematic film

The elastic theory of nemtatic liquid crystals is used to determine whether it gives support for recent experimental observations of a novel periodic phase occurring in homeotropically aligned films when an electric field is applied in the plane of the film. The director remains in the plane defined by the film normal and the field, and the wavevector of the periodicity is parallel to the field. It is found that the theory is consistent with experiment.     

Synthesis and novel reactivity of halomethyldimethylsulfonium salts

Iodomethyl-, chloromethyl-, and fluoromethyldimethylsulfonium salts, 4b-d, have been synthesized and are observed to be highly reactive molecules that exhibit extraordinary diversity with respect to the nature of their reactivity, undergoing facile direct substitution (S(N)2) reactions, but also being highly susceptible to electron-transfer reactions. Cyclic voltametry experiments indicated that the iodomethyldimethylsulfonium compound, 4b, is a potent electron acceptor, even surpassing the reactivity of perfluoro-n-alkyl iodides in that capacity. The iodo- and chloromethyldimethylsulfonium salts, 4b,c, as well as the analogous iodomethyltrimethylammonium salt, 3a, are shown to be reactive SET acceptors.     

Scaling and mesostructure of Carbopol dispersions

Rheological measurements were performed on aqueous dispersions of two commercial crosslinked polymer microgels, Carbopol Ultrez 10 and Carbopol ETD 2050, prepared over a wide range of concentration and pH. For all concentrations studied, both the yield stress and the elastic modulus initially increased dramatically with pH and displayed broad peaks at intermediate pH. This is consistent with the onset of jamming of the Carbopol particles due to a rapid increase in particle size caused by osmotic swelling in the presence of NaOH. Scaling of both yield stress and elasticity with concentration was observed only at higher concentrations, which we believe indicates a change from a percolated structure at low volume fractions to a space filling network of compressed particles at high volume fractions. This model is supported by confocal microscopy of fluorescently dyed Carbopol dispersions.