Jacques R. Emery

Dielectric, ultrasonic and carbon-13 nuclear magnetic resonance relaxation measurements of t-butyl alcohol–water mixtures

Dielectric, ultrasonic and 13C nuclear magnetic resonance relaxation measurements are reported on mixtures of t-butyl alcohol and water over the temperature range 278–308 K. Supporting measurements of the refractive index, density and viscosity are also presented. Deviations from ideal mixing behaviour are observed in the volumes of mixing, permittivities and adiabatic compressibilities of the mixtures. The location of the minima in the excess occurring at different compositions depend upon the method of measurement. Similarly the relaxation behaviour, as observed using different techniques, reveals different aspects of the motion of the molecules in the fluid. The various effects observed are rationalized in terms of a model in which it is assumed that t-butyl alcohol dimers and trimers and various hydrated forms play an important role in determining the structure of these mixtures.

Real-time dielectric studies of network formation in thermally activated epoxy-amine and isocyanate-triol systems

Abstract Dielectric measurements are reported on the changes that occur in the nature of the dipole relaxation processes during cure of an epoxy-amine and a diisocyanate-triol system. The epoxy resin forms a vitrified solid in the final cured state, whereas the urethane retains its elastomeric properties. The initial behaviour for the epoxy resin is dominated by ionic conduction processes. Subtraction of the conductivity contribution reveals a dipolar relaxation process, which is analysed using the Havriliak-Negami (HN) equation. The characteristic exponent 1 - n of the HN equation changes in a similar manner to that found with other epoxy-amine systems. However, the dipolar process in the urethane occurs at very high frequency and a different form of the 1 - n dependence is observed. Sensitivity of the dielectric method for the detection of vitrification and gelation is critically assessed. If the vitrification is allowed to occur, then detection of a gel point may not necessarily be inferred from the dielectric data.

Dielectric relaxation properties of the polymer coating during its exposition to water

Abstract Dielectric relaxation spectroscopy is applied for the study of α- and Maxwell–Wagner (MW) relaxations of polyurethane (PU) coating on steel and gold substrates during a water exposition. The evolution of the α-relaxation time of the PU coating in contact with water can be characterized by four stages: (1) Relaxation time increases with starting of the water penetration. The presence of water molecules in the coating leads to an increase in charge carriers at the metal/polymer double layer which influences the cooperative molecular motions in the polymer coating. (2) Relaxation time decreases because of the plasticizing effect of the water in the polymer. (3) Decreasing of the relaxation time and ionic conductivity associated with formation and growing of blisters. Appearance of blisters gives way to an interfacial dielectric relaxation (MW) in the low frequency region. (4) Overlapping of the α-relaxation peak by MW effect when the coating is completely displaced with water. The role of the metal/polymer interaction on these stages is discussed.

Ultrasonic studies of polyurethane network formation

Abstract The formation of polyurethane networks has been followed by measuring ultrasonic absorption and velocity as a function of time for discrete frequencies. In order to determine the relaxation spectra in the pre-gel phase, ultrasonic measurements were performed on quenched samples over the frequency range 5–1000 MHz. The data observed are discussed in terms of molecular motions and interactions.

Application of dielectric relaxation spectroscopy to study metal/polymer interfacial interaction

Abstract Dielectric Relaxation Spectroscopy (DRS) has been applied for the investigation of the influence of the metal/polymer interfacial interaction on the dielectric relaxation properties of polyurethane (PU), in the frequency range from 0,1 Hz to 10 MHz at temperatures from 223 to 423 K in the dependence of thickness of the PU layer (from 10 to 150 μm) and electrode material (gold and steel). Strong electrostatic interaction between steel substrate and the PU results in changing the dielectric relaxation properties of the latter, comparatively with gold substrate. The influence of metal/polymer electric double layer becomes significant at thickness less than 60 μm for the steel substrate. For the gold electrodes, the relaxation characteristics of the PU hardly depend on thickness.