Emulsion copolymerisation, process strategies

\u3cp\u3eEmulsion copolymerisation allows the production of materials with properties which cannot be obtained by latex products consisting of one monomer, that is, homopolymer latexes, or by blending homopolymers. This chapter focuses on key features to understand the emulsion copolymerisation kinetics and on the influence of the mode of operation on the copolymer composition of the final latex products. The focus is on batch and semi-batch or semi-continuous operation. The chapter first addresses monomer partitioning and operational strategies. Next, it presents different alternatives to produce copolymers with a desired composition in semi-continuous operation. This edition first published 2013\u3c/p\u3

Dipoles in solid solutions Sr1-xGdxF2+x

In this paper we present new results on the dielectric relaxation behavior of solid solutions of the type Sr1-xGdxF2+x. Attention will be paid to dipole relaxation peaks associated with two different complexes: (a) the nearest-neighbor (NN) Gd3+-Fi- dipole and (b) the next-nearest-neighbor (NNN) Gd3+-Fi- center. The experiments have been carried out in the frequency range from 100 to 3×104 Hz. From the behavior of the NN and NNN dipole relaxation bands as a function of the excitation frequency, we have determined the energy difference between the two different dipole configurations to be about 0.050 eV. In addition, we have studied the intensity of the dipole bands as a function of the concentration (x) of Gd3+ ions. It is possible to explain the observed behavior of the intensity of the dipole relaxation peaks as a function of x without the need of assuming that there is extensive clustering of Gd3+ impurities. We propose to divide the dipoles into two different groups: The first one contains dipoles that are not disturbed severely by extremely close dipoles, contributing to the dipole relaxation peak; the second group of dipoles, which are at close distances from at least a second dipole, contributes significantly to the dc-ionic-conduction process