Date Approved

4-24-2024

Embargo Period

4-24-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Physics & Astronomy

College

College of Science & Mathematics

Advisor

Samuel Lofland, Ph.D.

Committee Member 1

Joseph F. Stanzione, III Ph.D.

Committee Member 2

Vince Z. Beachley, Ph.D.

Keywords

Chemical Kinetics; Glass Transition; Material Kinetics; Phonons; Polymer Physics; Raman Spectroscopy

Subject(s)

Polymers; Glass; Raman spectroscopy

Disciplines

Materials Science and Engineering | Physics

Abstract

Unlike liquids and crystalline solids, glassy materials exist in a constant state of structural nonequilibrium. Therefore, a comprehensive understanding of material kinetics is critical for understanding the structure-property-processing relationships of polymeric materials. Amorphous materials universally display low-frequency Raman features related to the phonon density of states resulting in a broad disorder band for Raman shifts below 100 cm-1, which is related to the conformational entropy and the modulus. This disorder band is dominated by the Boson peak, a feature due to phonon scattering because of disorder and can be related to the transverse sound velocity of the material, and a well-defined shoulder due to a van Hove singularity. Quasi-elastic Rayleigh scattering also contributes to the signal, particularly in liquid-phase materials. We have demonstrated that we can measure both glass transition and polymerization kinetics by normalizing the disorder band to its shoulder and monitoring its evolution as a function of time and temperature. We also demonstrate a relationship between the chemical and structural kinetics, which appears to relate to the softness of the material, which we verify via rheological analysis. Low-frequency Raman spectroscopy is, therefore, a promising technique for thermo-structural analysis of polymers. Not only is it chemically agnostic and contactless, but it requires neither intensity calibration nor multivariate analysis.

Download

Share

COinS