Dielectric relaxation and infrared studies of hydrogen bonding
Siddiqui, Mohammad Arshad
Master of Science
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Dielectric relaxation and infrared study of a number of associating (H-bonding) compounds in glassy media, mainly polystyrene, have been carried out. The dielectric measurements by a General Radio 1621 Precision Capacitance bridge and infrared measurements by a Beckman spectrophotometer IR4250 have been described. The experimental dielectric data as a function of frequency at different temperatures were subjected to analysis by a series of computer programs written in APL and BASIC languages. The activation energy barriers opposing the dielectric relaxation processes were obtained by the application of the Eyring rate equation. An infrared study of various sterically hindered alcohols in polystyrene have been carried out. It is shown that a decrease in temperature leads to an increase in the degree of polymerization. The effect of steric factors on the degree of polymerization at a given temperature has also been discussed. Dielectric studies of sterically hindered alcohols, mainly in polystyrene matrix, have yielded, in some cases, completely separated molecular and intramolecular processes due to the H-bonded species. All alcohols gave a process owing to the H-bonded species with the exception of the most sterically hindered di-tert-butyl carbinol, tricyclohexyl carbinol and diphenyl methyl carbinol. The presence of Hbonded species was indentified by the infrared spectrum of the sample. In addition to sterically hindered alcohols, some simple small alcohols and water were also studied in a polystyrene matrix and in some other glassy media. The process owing to the H-bonded species was found to occur in the similar temperature region as was observed for sterically hindered alcohols. The energy barriers of the process related with H-bonded species for all the alcohols and water in a polystyrene were of a similar order of magnitude. A possible mechanism for the process related to H-bonded species was discussed. Dielectric studies on alcohol and amine systems in a polystyrene matrix have been carried out. It has been discussed that alcohols interact with amines, thus increase the dipole moment of the complexes which leads to an increase in the dielectric loss factor of the system. However, in many cases the dielectric process due to the complex, formed by alcoholamine interaction, was overlapped with the absorption owing to the H-bonded species of the alcohol and/or to the molecular process of amine.