J. V. Maher

Partitioning of polystyrene latex spheres in immiscible critical liquid mixtures

We have made a systematic survey of the behavior of colloidal polystyrene latex spheres (PLSs) in critical mixtures of 2,6-lutidine plus water at temperatures where the liquid mixture separates into two immiscible phases. By varying the particle size, particle-surface charge density, and global PLSs concentration, we observe a robust and reversible set of phenomena that include the partitioning of the particles into a preferred phase at temperatures close to {ital T}{sub {ital c}} with a subsequent population of the interface between the liquid phases as the temperature is quenched deeper into the two-phase region. These results are shown to be in good qualitative agreement with thermodynamic models if the models are extended to include the singular temperature dependence of the particle-liquid and liquid-liquid interactions near the critical point. We also observe crystalline ordering of particles on the interface when the population of PLSs on the liquid-liquid interface is high.

PROTON HOLE STATES IN THE SHAPE TRANSITIONAL REGION VIA THE SM(D,HE-3)PM REACTION AT ED=50MEV

Abstract Angular distributions have been measured for the 148,150,152,154 Sm(d, 3 He) 147,149,151,153 Pm reactions at a deuteron energy of 50MeV. Summed spectroscopic strengths are in reasonable agreement with the expected 12 protons outside the closed Z = 50 core. For 154 Sm sizeable ( f 7 2 ) 2 admixtures, probably from the next higher shell, are found. The fragmentation of the single-hole strength increases with mass number for 148,150,154 Sm, whereas 152 Sm shows a very different spectrum with only a few strong transitions and a presumbably strongly fragmented remaining strength. The results for 152,154 Sm are compared with Nilsson-model calculations including band mixing.

A coupled-channels born-approximation analysis of rare-earth (d, t) transitions

Abstract A CCBA (coupled-channels Born approximation) analysis has been performed on a very large set of rare-earth (d, t) transitions. Calculations were performed for states in 159 Gd, 161, 163 Dy and 165, 167 Er which have been identified as members of rotational bands built on the Nilsson single- hole states 11 2 − [505], 1 2 − [521], 3 2 − [521], 5 2 − [523], 5 2 + [642], 5 2 + [633] and 7 2 + [404]. In the cases where the DWBA works well, the CCBA gives results similar to those of DWBA. For the anomalous transitions the CCBA calculations tend to fit better than do the DWBA calculations — but the overall agreement is still rather poor.

Observation of the relaxation of composition fluctuations in a binary liquid mixture

Light scattering was used to study the decay of concentration fluctuations in a critical mixture of isobutyric acid and water. The aim of the experiment was to study the dynamic interaction between composition and velocity in the mixture. At large wavenumber, the structure factor S(k, t) is observed to decay exponentially, with a relaxation rate somewhat smaller than the equilibrium value. At small k, however, there is a marked departure from the exponential relaxation one expects in the absence of coupling between composition and velocity. Also measured was the spinodal ring diameter, km, as a function of the total scattered intensity, Ctot(t) = (2π)−2 ∫ S(k, t)k2dk. A calculation of Ruiz, based on the above coupling effect, predicts a linear variation of Inkm(t) with Ctot(t) and such a linear variation is observed.

Adsorption and wetting on moveable walls

Polystyrene latex spheres, colloidally suspended at very low volume fraction in critical and nearcritical mixtures of 2,6-lutidine and water (LW), have been observed to segregate strongly into a complete wetting phase when the LW mixture is placed in its two-phase region near Tc. The wetting temperature, Tw, is observable as that at which colloidal particles abruptly begin to migrate to the meniscus. In the one-phase region near the coexistence temperature, the particles aggregate reversibly through a process which appears to be interpretable as a form of capillary condensation.