The thermodynamics of the A–B transition in superfluid He as a probe of the A-phase gap node geometry

We have used a magnetic field gradient to stabilise the phase boundary between the A- and B-phases of superfluid ³He inside a quasiparticle black body radiator down to 146 μK. The radiator technique enables us to measure very accurately the density of quasiparticle excitations and therefore the temperature of the B-phase inside the radiator. As we ramp the field through the transition we can observe the cooling (warming) effect when the volume of A-phase is increased (decreased). From these measurements we deduce the temperature dependence of the latent heat, which provides the lowest temperature verification yet of the existence of nodes in the A-phase order parameter.     

The molecular weight distribution for chain polymerization plus side reaction

The kinetics of chain polymerization is investigated for the case of a complicating side reaction. In addition to the polymerization reaction, A_i + M → A_i+1, there is a reversible side reaction, A_i + Q ↔ B_i. Initiation is assumed to be instantaneous. The monomer concentration M, and the concentration of the reacting species Q, are assumed to be constant. The reaction kinetics are solved exactly, yielding the distribution of living and dormant polymer, as well as the molecular weight distribution, as explicit functions of the reaction rate constants and the time. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1711–1725, 1997     

Review and kinetic analysis of the photodegradation of UV absorbers

Ultraviolet absorbers (UVA's) undergo photodegradation with quantum yields on the order of 10⁻⁶ even in glassy, unreactive matrices such as poly(methyl methacrylate) (PMMA). The kinetics of UVA loss in a film or coating can be described by the equation: A = log₁₀[(1-T_o)10 + 1] where A is the absorbance at time t, T_o is the initial transmission, A_o is the initial absorbance, and k is an “infinite absorption” zero order rate constant. The derivation and implications of this equation and a general review of UVA degradation chemistry are discussed.     

Interactions between surfaces coated with solvophobic and solvophilic homopolymers

Using scaling theory, we investigate the interaction between two planar surfaces that are coated with both A and B homopolymers. The polymers are tethered by one end and grafted at relatively low densities. The B chains are chosen to be solvophobic, while the A polymers are solvophilic. Calculating the energy of interaction versus distance profile, we find that the curve shows a wide attractive region as the surfaces are compressed. The features of this profile can be tailored by varying the length and grafting densities of the different chains. Our results provide guidelines for controlling the interaction between polymer-coated colloidal particles.