Dielectric Spectroscopy of PVAc at Different Isobaric-Isothermal Paths

Soheil Sharifi

doi:10.4236/msa.2012.33026

Abstract

We studied broadband dielectric spectroscopy of a glass from systems that the dynamics of the primary α- and the Johari-Goldstein (JG) β-processes are strongly correlated in Poly(vinyl acetate) over a wide temperature T and pressure P range. Analysing the temperature and pressure behaviour of the α- and (Non-JG) β-processes, a correlation hasnot been found between the structural relaxation time, the (Non-JG) β-processes relaxation time and the dispersion of the structural relaxation. These results support the idea that the (JG)-processes relaxation acts as a precursor of the structural relaxation and therefore of the glass transition phenomenon but it isnot clear relation in the (Non-JG) β-processes and structural relaxation at PVAc.

Highlights

In the Glass former materials we can find complex relaxation pattern, which evolves over several time decades
We studied broadband dielectric spectroscopy of a glass from systems that the dynamics of the primary - and the Johari-Goldstein (JG) -processes are strongly correlated in Poly(vinyl acetate) over a wide temperature T and pressure P range
The origin of the structural -relaxation is ascribed to cooperative motions that involve an increasing number of molecules and slow down dramatically when the glass transition is approached, for example either by decreasing temperature T or increasing pressure P [1,2,3]

Summary

Introduction

In the Glass former materials we can find complex relaxation pattern, which evolves over several time decades. In non polymeric materials the slowest process is usually called main, structural or αrelaxation [2,3,4,5,6]. It reflects the cooperative motion of the molecules and its characteristic time can be related to the overall viscosity of the material. The origin of the structural -relaxation is ascribed to cooperative motions that involve an increasing number of molecules and slow down dramatically when the glass transition is approached, for example either by decreasing temperature T or increasing pressure P (i.e., density) [1,2,3]. The main goal is to find relation between alpha and secondary relaxation in PVAc and compare this system with relation of alpha and secondary relaxation in the mixture of the rigid polar molecule quinaldine (QN) and tristyrene

Experiment and Materials

Results

Discussion

Conclusion