On the simulation of inhomogeneous ESR lineshape of a spin probe in a liquid crystalline polymer

Abstract

A procedure for the analysis of the electron spin resonance (ESR) lineshape of a cholestane paramagnetic tracer dissolved in a liquid crystalline polymer is described. Due to its rodlike geometry, the cholestane probe is subjected to an anisotropic reorientational motion in the polymer matrix. On the basis of the generalized MorŸ theory, sirnulation approaches to the lineshape have been developed. The ESR lineshape has been calculated fora molecule reorienting in a homogeneous molecular site according to diffusion or jump motion. Moreover, the case of inhomogeneous sites with continuous or discrete distribution functions was also accounted for. Systematic compa¡ with experimental spectra has been carried out, and a two-~ distribution function of the molecular sites has been singled out as best description of the experiment. The temperature dependence of the two species has been fully investigated and the spatial character of the heterogeneity has been proved.

Heterogeneity in the dynamics of a molecular tracer dissolved in liquid crystal homopolymer and copolymer

“…Careful simulations proved that the inhomogeneous character of the ESR lineshapes was well taken into account by a two d-like distribution function of the molecular tracer sites, in agreement with previous results [14].…”

Heterogeneity and Dynamics in Azobenzene Methacrylate Random and Block Copolymers: A Nanometer–Nanosecond Study by Electron Spin Resonance Spectroscopy

“…7,51 In particular, a two δ-like distribution function, with a fast and a slow dynamic components, was shown to provide the best simulation of the ESR spectra. 51…”

Fractionary couplings of spin probe to backbone and side group dynamics of a liquid crystal polymer

“…In fact, a two‐ δ distribution function of the correlation times with fast and slow reorienting sites was shown to reproduce the experimental line‐shape better than log‐Gauss and square distributions. Moreover, we proved that assuming a bimodal log‐Gauss distribution did not improve the result obtained with the two‐ δ distribution 16…”

“…Many efforts were made to carefully take account of the inhomogeneous nature of the experimental line‐shape. The details of the study are reported elsewhere 16. The analysis led us to recognize the bimodal character of the distribution function of the spin‐probe sites.…”

“…The principal components of the magnetic tensors of the spin probe were drawn by the powder lineshape15 of the linear ESR recorded at T = 143 K, according to the procedure detailed elsewhere 16. The values of the Zeeman and hyperfine tensors in the molecular frame are listed in Table 2.…”