We have derived a generalization of Poisson's equation, a fourth-order partial differential equation, to describe the electrostatic behavior of polarizable, quadrupolar fluids. Our theory is in accord with the approach of Evangelista and Barbero. This equation was solved for the case of multipoles of arbitrary order placed at the center of a spherical cavity in a quadrupolar fluid. Our solution indicates that the quadrupolar portion of the disturbance created by an electrostatic probe in a polarizable quadrupolar fluid is localized to a distance of about a bohr, while asymptotically the fluid behaves as a polarizable medium. Internal field corrections as well as internal field gradient corrections have been computed. Fairly good agreement is found between our theory and the experimentally determined dielectric constant for carbon dioxide. The cavity model solution has been applied toward understanding the solvation of ions and dipolar molecules in supercritical carbon dioxide. We have used our theory to show that ions do not dissolve in supercritical carbon dioxide. Our theory displays improving agreement with data on the solubility of water molecules in supercritical carbon dioxide as pressure and temperature are increased. Ways to enhance agreement with experiments are suggested. We speculate on generalizations of our approach to fluids composed of higher-order multipoles, e.g., methane, whose first nonvanishing moment is an octupole.

Microwave radiation resonant with the natural phonon frequencies of double-stranded DNA (dsDNA) is shown to couple strongly to the breather modes of dsDNA under certain conditions. The excitation of the disruptive breather modes is controlled to a great extent by energy dissipation to its aqueous environment. For sufficiently high power-much higher than expected under ambient conditions-the breather solutions become unstable. Our analysis discounts the disruptive effect of low frequency, low power radiation on dsDNA. The authors hope to stimulate experiments via their analysis. The resulting data will dictate the future evolution of their models.

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We have developed a theory of polymer entanglement using an extended Cahn-Hilliard functional, with two extra terms. One is a nonlocal attractive term, operating over mesoscales, which is interpreted as giving rise to entanglement, and the other a local repulsive term indicative of excluded volume interactions. This functional can be derived using notions from gauge theory. We go beyond the Gaussian approximation, to the one-loop level, to show that the system exhibits a crossover to a state of entanglement as the average chain length between points of entanglement decreases. This crossover is marked by critical slowing down, as the effective diffusion constant goes to zero. We have also computed the tensile modulus of the system, and we find a corresponding crossover to a regime of high modulus. The single parameter in our theory is obtained by fitting to available experimental data on polystyrene melts of various chain lengths. Extrapolation of this fit yields a model for the cross-over to entanglement. The need for additional experiments detailing the cross-over to the entangled state is pointed out.Comment: Accepted for publication by Phys. Rev. E. Replaces previous version. Includes comparison with experimental dat