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Dynamic Properties of Supercooled Chlorinated Biphenyls
A P Holt1, D Fragiadakis1, C M Roland1
1Chemistry Division, Code 6105, Naval Research Laboratory, Washington, D.C. 20375-4032, United States.
The Journal of Physical Chemistry. B
|May 21, 2020
Summary
Adding chlorine to biphenyl compounds raises the glass transition temperature and density sensitivity. Despite this, their dynamics near glass transition show similar correlation and heterogeneity, aligning with increased molecular polarity effects.
Area of Science:
- Materials Science
- Physical Chemistry
- Chemical Dynamics
Background:
- Biphenyl compounds are widely used in various industrial applications.
- Understanding the relationship between molecular structure and material properties is crucial for designing new materials.
- Chlorination of organic molecules can significantly alter their physical and chemical characteristics.
Purpose of the Study:
- To investigate the effect of varying chlorine levels on the dynamics of biphenyl compounds.
- To explore the relationship between chlorine content, glass transition temperature, and dynamic properties.
- To compare the behavior of chlorinated biphenyls with general trends related to molecular polarity.
Main Methods:
- Synthesis and characterization of biphenyl compounds with different chlorine concentrations.
- Differential scanning calorimetry (DSC) to determine glass transition temperatures.
- Dynamic mechanical analysis (DMA) to study relaxation dynamics.
- Molecular dynamics simulations of a simplified Aroclor model.
Main Results:
- Increasing chlorine content elevated the glass transition temperature (Tg) and enhanced density-dependent dynamics.
- Despite variations in Tg, dynamic correlation and heterogeneity near the glass transition remained similar across the series.
- A narrowing of the relaxation peak with increased chlorination was observed, correlating with increased molecular polarity.
- Molecular dynamics simulations successfully reproduced the observed relationship between peak breadth and dipole moment.
Conclusions:
- Chlorination of biphenyls impacts Tg and density sensitivity but not dynamic correlation or heterogeneity near Tg.
- Molecular polarity, influenced by chlorination, plays a key role in the observed relaxation dynamics.
- The study provides insights into structure-property relationships in chlorinated organic materials.
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