Relaxation of hexaaquochromium(3+) and hexaaquomanganese(2+) ions in polyacrylonitrile in the glassy and rubber-like states studied by electron spin resonance

Abstract

X-Band and Q-band esr line widths and intensities of [Cr(H20)e]3+ and [ ( 2 )ß] + in acrylonitrile and polyacrylonitrile were measured as functions of the concentrations of Zn(C104)2-6H20 or Li(C104) added to the monomer and polymer systems. The line width of [Cr(H20)e]3+ incorporated in the polymer was studied as a function of temperature and concentration both in the glassy and rubber-like states. The zero-field splitting parameter was evaluated for [Cr(H20)e]3+ and for [ ( 20)ß]2+ in the polymeric system both above and below the glass transition temperature. It is shown that the electronic relaxation in the polymeric matrix is due to modulation of the zero-field splitting interaction, probably via rotational tumbling of the [Cr(H20)6]3+ ion. A correlation time of ~2 X 10"11 sec at 300°K for the hydrated chromium ion is found both in the glassy and the rubber-like states. In view of the short correlation time scale found and the possibility that ligand exchange mechanisms may operate in the rubberlike state, the similarities of the polymeric system to true liquid solutions are discussed. Evidence from esr and magnetic susceptibility measurements for strong Cr-Cr interaction in the glassy state at low temperature is presented.

Fluorine-19 NMR relaxation and water penetration in surfactant micelles

“…Firstly, one needs to have a good theoretical understanding of the spectroscopic parameter monitored (and not only use empirical correlations such as polarity scales obtained in studies of the probe in simple solvents), and, secondly, one needs precise information on the distribution of the probe over the micelle. 12 The difficulties in the former respect were amply demonstrated by Muller13"19 in studies of fluorinated surfactants by 19F NMR chemical shifts. Although using a probe intrinsic to these surfactants, he could demonstrate that reliable information on hydration could not be obtained since the spectroscopic parameter has a very complex relation to the nature of the molecular environment.20…”

Electron spin relaxation as a tool for studying the dynamics in the outer solvation sphere of6S spin state ions

“…No wonder, therefore, that the system has received increasing attention as a paramagnetic probe for structural and dynamic studies. Among the main fields of investigation one could cite studies of solute-solvent interactions and complex formation [2][3][4][5][6][7][8][9][10], binding sites on macromolecules and biopolymers [11][12][13], molecular dynamics [14][15][16][17][18][19] and structure [20] in liquids, selective solvation [21,22], nature of intracrystalline fluids in oxides [23,24], zeolites [25], polymers [26,27], etc.…”