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

Abstract

The cholestane spin probe dynamics in a nematic polymeric matrix after annealing at a temperature value slightly above the TNI was investigated by ESR spectroscopy in a wide temperature interval. Careful lineshape analysis showed that a two δ‐like distribution better represented the experimental spectra. The dependence on temperature of the population in the different sites was evaluated and compared with the analogous one previously found for the same polymer/spin probe system that had been annealed at a temperature well above the TNI.1 The temperature dependence of the spinning correlation time of the spin probe rearranging in slow and fast sites led us to locate them in the backbone and side groups of the polymer. The cooperativity degree in dynamics was quantified. A signature in temperature scale at the onset of cooperativity in backbone dynamics was recognized.

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

“…The value is consistent with that of R70 (ξ HT(F) = 0.52), 60 and shows a possible similarity with the homopolymer PMA4 (ξ HT(F) = 0.61) after the thermal annealing at 358 K. 61 The relatively high value of ξ HT(F) , together with the clear sensitivity of the probe dynamics to the nematic-to-isotropic transition, located near 1.2T g , strengthens the hypothesis that the sites experienced by the molecular tracer in these liquid crystalline polymers may be located among the mesogenic side groups. This appears also in agreement with previous observations on a closely related nematic polyacrylate.…”

A calorimetric study of structural relaxation in the glassy state of a liquid-crystal polymer

“…½ eq …T † has been evaluated through the TH model (T fˆT in equation (9)). In ®gure 8 the temperature dependence of ½ eq …T † for enthalpy relaxation is reported for two diOE erent T 2 and compared with its shear viscosity, suitably rescaled (Andreozzi et al 2002).…”

On the Dynamics of the Cholestane Spin Probe in a Nematic Azobenzene Side Group Oligomer

“…As one can see, equilibrium spectra were quickly reached, whereas very different behaviors were observed in PMA4 homopolymers [8,10] and copolymers [25,26], where the setting up of complex competitive molecular processes led to very slow evolution of molecular peculiarities on the nanometer and nanosecond scales experienced by the cholestane probe.…”

“…Nonetheless, precise analysis of the ESR lineshapes can provide information on dynamics heterogeneity, when the lifetime of heterogeneity becomes larger than the measuring observation time, and on space heterogeneity, due to the distribution of sites available to the rotating molecule. To cite a few examples, very different molecular sites can be populated depending on the polymer polydispersity index [9], thermal treatment [8,10], and presence of plasticizing impurities [11]. ESR investigations on azobenzene methacrylate polymers and co-polymers pointed out that molecular sites available to the probe rotation exhibited a discrete distribution depending on the thermal treatment [12].…”