D. F. Hinman

Space-charge effects of semiconductive coatings on triboelectric charge exchange

Abstract Triboelectric charge exchange studies have revealed a previously unreported “semiconductive” effect. A semiconductive film on a metal substrate acquires the opposite sign of charge when contacted with another body than that expected on the basis of energy level considerations for the two contacting materials. The effect is explained in terms of a space-charge region (depletion or accumulation layer) caused by charge exchange of the semiconductor film with the substance onto which it is coated. It is estimated from our measurements that the space-charge depth for poly(N-vinylcarbazole) is between 3 and 8 μm.

Effects of solvent and thermal annealing on the dielectric properties and morphology of dimethyl siloxane/α-methylstyrene block copolymers

Abstract The dielectric and morphological properties of a series of 9/1 poly(dimethyl siloxane) PDMS)/poly(α-methylstyrene) (PαMS) block copolymers and a 6/4 PDMS/PαMS block copolymer have been determined as a function of solvent casting and thermal treatment. Transmission electron microscope (TEM) results show better phase separation as a function of thermal annealing and casting from cyclohexane, a PDMS preferential solvent. Dielectric studies in the temperature region of the PDMS glass transition are consistent with the TEM results and are interpreted in terms of a most probable distribution of PDMS/PαMS mixed states. When the PDMS segment molecular weight is less than the critical molecular weight, thermal annealing of the solvent cast samples produces a phase separated sample exhibiting the Tg of PDMS as well as a mixed phase. Thermal annealing of samples with the PDMS segment molecular weight greater than the critical molecular weight produces little change in the mixed structure and the dielectric data. All samples have PαMS segment molecular weights less than the critical molecular weight. The observed changes are interpreted in terms of kinetic effects associated with polymer melt viscosity (critical molecular weight) and expected mixing of the two components.

A dynamic characterization via relaxation techniques of the shell membranes of the domesticated fowl (gallus/gallus (L.))

Abstract The shell membrane is made up of a unique three-layered structure which consists of outer, inner and limiting membranes. The structure is capable of adsorbing water in excess of 2.5 times its weight. The water containing species give rise to dielectric and n.m.r. relaxations associated with tightly bound and loosely bound water. An additional relaxation which appears to be intrinsic to the biomolecule is observed at low temperatures. The intensity and effectiveness of this relaxation is governed by the amount of water present. The facility of the membrane to interact with water enables the molecular reorientational process of the membrane itself to take place with a greater ease, with the result that the structure changes its deformation characteristics from that of a brittle to a low modulus elastomeric material. Thermal treatment of the membrane alters its relaxation properties. The membranes ability to adsorb water is drastically reduced and the molecular reorientational processes do not occur as readily. As a result, the change from brittle fracture to low modulus yield that is observed for a saturated, non-heat treated material is not found, and the water-saturated, heat treated material fails in a brittle manner. It appears that the irreversible changes that take place on heat treatment do so gradually above room temperature reaching an appreciable rate above 410K. No changes corresponding to those found in the relaxation, differential scanning calorimetry (d.s.c.) and mechanical measurements are observed in the scanning electron microscopy (s.e.m.) data of the heat treated material.