Tuning Polymer Glass Formation Behavior and Understanding Time-temperature Superposition Breakdown with Oligomeric Additives

Graduation Year

2024

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Chemical, Biological and Materials Engineering

Major Professor

David S. Simmons, Ph.D.

Committee Member

Nathan D. Gallant, Ph.D.

Committee Member

Robert S. Hoy, Ph.D.

Committee Member

Ryan G. Toomey, Ph.D.

Committee Member

Weizhong Zou, Ph.D.

Keywords

Dynamic Heterogeneity, Polymer Formulation, Rheology, Simulations

Abstract

The glass transition of polymer melts has been investigated for over a century. Even so, there are still many unanswered questions about the underlying physics. Countless theories were proposed to explain and define glass transition temperatures. More specifically, both the origins of the glass transition and underlying classification of glass as a state of matter remain unresolved. Time-temperature superposition (TTS) is one of the most widely used techniques to characterize the viscoelastic behavior of a material and the mechanical behavior and is employed to reduce the measuring time during characterization. Despite the widespread use of TTS, many authors have reported a breakdown of TTS near the glass transition. Even though, the underlying physics of TTS breakdown near the glass transition regime remains unexplained. These diluents, also known as plasticizers and antiplasticizers in most cases, are now already widely used in industries. In brief, diluents are simply classified as plasticizers or antiplasticizers based on their effect on the glassy moduli.

This work probes the fundamental connection between segmental dynamics and chain dynamics near glass transition temperature Tg and how the small numbers of the diluents affect the polymer dynamics in both low-frequency regimes and high-frequency regimes. This work includes wet lab experiments like rheological tests and broadband dielectric spectroscopy as well as differential scanning calorimetry and computational simulation. These projects will validate the heterogeneous Rouse model (HRM) in the TTS breakdown regime, allowing the prediction of linear viscoelastic response by HRM. Work also was performed in studying the effects of diluents regarding their size, interaction energy as well as the design of formulation.

Work was done on the characterization of a series of polymers and all-atom simulations with different chemical components. Comprehensively, this work aims to bridge theory and application to build a protocol that can help to screen and select the correct additives regarding the chemical structure of the polymer itself and the desirable properties.

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