The bulk electrical conductivities of a series of monocarboxylic and polycarboxylic aromatic acids and some derivatives of these acids have been measured in order to study the effect of hydrogen bonding on conductivity. Electrical measurements were made on carefully purified, polycrystalline samples, compressed to remove voids, using a guarded direct-current method. The measurements were characterized by time-dependent currents which decreased to equilibrium values in times ranging from seconds to hours. The temperature dependence of the conductivity followed the usual exponential law for all the compounds. The activation energy for conduction, Ea, was independent of the polarization effects and sample purity and served as a reliable parameter for comparison among the compounds. A definite relationship existed between Ea and the position and number of carboxyl groups on an aromatic system. This relationship was interpreted in terms of the hydrogen bonding and electron withdrawing properties of the carboxyl groups on the assumption that the aromatic pi electrons were involved in the generation of charge carriers. Those substituents which tended to reduce the electron density of the aromatic system produced a rather substantial increase in the activation energy. Extended intermolecular overlap resulting from the hydrogen bonding of polycarboxylic acids produced a decrease in Ea.
Slit smearing effects have been experimentally investigated for a typical Bonse-Hart small-angle diffractometer. This instrument was found to satisfy the cl iteria for infinite slit-height configuration for a wide range of angular divergence-limiting schemes. Standard mathematical desmearing methods applied to the data show excellent agreement with scattering data obtained from an essentially slit-correctionless instrument.* Note added in proof :-Fedorov et al. (1969) have employed such a method to check slit-correction procedures in the Kratky camera.
In an investigation of the effect of electric fields on the critical opalescence, time-dependent phenomena have been observed which are related to theoretical relaxation times of concentration fluctuations for a binary mixture. Rectangular dc pulses of 25 to 60 kV/cm and 10–200-μsec duration have been applied to a critical mixture nitrobenzene and 2,2,4-trimethylpentane at a series of temperatures above the critical solution temperature. Relaxation times associated with the change in the transmitted light intensity were found to be independent of the pulse width and the field strength. The relaxation times are proportional to (T—Tc)−0.9 and have magnitudes comparable with relaxation times determined from the frequency broadening of light scattered from similar binary systems. It has also been possible to extend the agreement between the Debye theory of the electric field effect on critical opalescence and the experimental results to within 0.1°C of the critical temperature.
Light scattering provides information concerning the size, shape, number, and time dependence of the physical nonuniformities of a system. Measurements of the scattered intensity as a function of both scattering angle and wavelength describe static properties, whereas the spectral distribution of the scattered radiation is related to time dependent phenomena. The applications of light scattering are discussed, including critical phenomena, molecular weight determination, air pollution analysis, and diffusion phenomena.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.