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An Effective Temperature Theory for the Nonequilibrium Behavior of Amorphous Polymers

Rui Xiao's picture

Freely available until Aug. 8th: http://authors.elsevier.com/a/1RDyK57Zjcoxj

Amorphous polymers lack an organized microstructure, yet they exhibit  structural evolution, where physical properties change with time, temperature, and inelastic deformation.  To describe the influence of structural evolution on the mechanical behavior of  amorphous polymers, we developed a thermomechanical theory that introduces the effective temperature as a thermodynamic state variable representing the nonequilibrium  configurational structure.  The theory couples the evolution of the effective temperature and internal state variables  to describe the temperature-dependent and rate-dependent inelastic response through the glass transition.   We applied the  theory to model the effect of temperature, strain rate, aging time, and plastic pre-deformation on the uniaxial compression response and enthalpy change with temperature of an acrylate network.  The results showed excellent agreement with experiments and demonstrate the ability of the effective temperature theory to explain the complex thermomechanical behavior of amorphous polymers.  

 

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Pu Zhang's picture

Hi Rui,

I am delighted to read this paper, although not quite carefully. It reminds me about the time-temperature correspondence principle, which indicates that some slow evolution processes can be modeled by lowering the temperature, and vice versa. Therefore, the theory in your work is, in some sense, related to this principle. Not sure if I got your point or not.  

Rui Xiao's picture

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Hi Pu,

Thanks for interest in our paper. The point you mentioned is definitely one part we addressed in the paper, which is time-temperature superposition. In this work we adopted effective temperature to represent the nonequilibrium polymer structure. You can see from the results, even at the same temperature, due to different thermal history, the mechanical response is quite different.  Thus the time-temperature superposition is extended to time-temperature-structure superposition. The viscosity or relaxation time has a shift factor depends on the temperature and effective temperature. A lower effective temperature resulted in a more sluggish polymer structure ( a larger viscosity). The central concept in this paper is we showed that the effective temperature also evolves with mechanical deformation, which results in a more mobile polymer structure and strain softening. 

Rui

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