[Paper Review] Dimensional crossover of heat conduction in amorphous Polyimide nanofibers

Lan Dong, Qing Xi+8 more|arXiv (Cornell University)|Feb 26, 2018

Thermal properties of materials3 citations

TL;DR

This study reveals a dimensional crossover in heat conduction—from three-dimensional (3D) to quasi-one-dimensional (1D) behavior—in amorphous polyimide (PI) nanofibers at a fixed temperature. A random walk-based theoretical model quantitatively explains the interplay between inter-chain and intra-chain hopping, successfully predicting the diameter-dependent thermal conductivity and estimating the upper limit of thermal conductivity in the quasi-1D regime for amorphous polymers.

ABSTRACT

The mechanism of thermal conductivity in amorphous polymers, especially polymer fibers, is unclear in comparison with that in inorganic materials. Here, we report the observation of across over of heat conduction behavior from three dimensions (3D) to quasi-one dimension (1D) in Polyimide(PI) nanofibers at a given temperature. A theoretical model based on the random walk theory has been proposed to quantitatively describe the interplay between the inter-chain hopping and the intra-chain hopping in nanofibers. This model explains well the diameter dependence of thermal conductivity and also speculates the upper limit of thermal conductivity of amorphous polymers in the quasi-1D limit.

Motivation & Objective

• To understand the thermal conduction mechanism in amorphous polymer nanofibers, which remains poorly understood compared to inorganic materials.
• To investigate how heat conduction behavior transitions from 3D to quasi-1D as the nanofiber diameter decreases.
• To develop a theoretical model that captures the interplay between intra-chain and inter-chain phonon hopping in disordered polymer systems.
• To quantitatively explain the observed diameter dependence of thermal conductivity in PI nanofibers.
• To estimate the theoretical upper limit of thermal conductivity for amorphous polymers under quasi-1D confinement.

Proposed method

• A theoretical model based on random walk theory is developed to describe phonon transport in amorphous PI nanofibers.
• The model distinguishes between intra-chain hopping (along polymer chains) and inter-chain hopping (between chains) as distinct thermal transport pathways.
• The interplay between intra- and inter-chain hopping is mathematically formulated to predict effective thermal conductivity as a function of nanofiber diameter.
• The model is calibrated and validated against experimental observations of thermal conductivity variation with diameter.
• The model is extended to predict the theoretical upper limit of thermal conductivity in the quasi-1D regime for amorphous polymers.

Experimental results

Research questions

• RQ1 How does the dimensionality of heat conduction change in amorphous PI nanofibers as their diameter is reduced?
• RQ2 What is the relative contribution of intra-chain versus inter-chain hopping to thermal conductivity in disordered polymer nanofibers?
• RQ3 Can a random walk-based model quantitatively describe the diameter-dependent thermal conductivity in amorphous polymer nanofibers?
• RQ4 What is the theoretical upper limit of thermal conductivity achievable in amorphous polymers under quasi-one-dimensional confinement?
• RQ5 How does the transition from 3D to quasi-1D behavior affect the thermal transport properties of amorphous polymers?

Key findings

• A clear dimensional crossover from 3D to quasi-1D heat conduction is observed in amorphous polyimide nanofibers at a fixed temperature as the diameter decreases.
• The proposed random walk-based model successfully explains the experimentally observed diameter dependence of thermal conductivity in PI nanofibers.
• The model identifies inter-chain hopping as a dominant but limiting factor in thermal transport, especially in narrow nanofibers.
• The model predicts that thermal conductivity in amorphous polymers approaches an upper limit under quasi-1D conditions, suggesting a fundamental constraint on thermal transport in disordered systems.
• The theoretical framework provides a quantitative basis for understanding and engineering thermal transport in amorphous polymer nanostructures.