Leveraging Acoustic Modeling to Reveal Long-Range Coupling of Local Modulus Across Glass-Liquid Polymer Interfaces Restricted; Files Only

Abstract

In this dissertation, I investigate features of glass-liquid polymer bilayer films that

have a mechanistic influence on long-range local coupling of material properties across

the interface. One way in which I studied this was using pyrene fluorescence to measure

a local gradient in the glass transition temperature Tg(z) when one of the polymer

domains had its thickness constrained. That work focused on bilayers of polystyrene

(PS) and poly(n-butyl methacrylate) (PnBMA), which previously exhibited a Tg(z)

gradient spanning ≈250 nm. Limiting the PS thickness to only 75 nm, the Tg(z) gradient

in the PS interestingly shrunk to a length-scale of only ≈30 nm. The magnitude

of the local Tg perturbation at the PS/PnBMA interface was also greatly weakened.

This work highlighted that domain size can fundamentally alter the behavior of interfacial

perturbations to local material property gradients.

I also developed an acoustic transfer-matrix modeling method that enabled the

identification of local gradients in the complex shear modulus G(z) given quartz crystal

microbalance (QCM) data. For this work, I took QCM measurements on bilayers

of PS and polybutadiene (PB). Analyzing the data using my transfer-matrix model, I

found that there is a ≈230 nm gradient in G(z) corresponding to previously identified

Tg(z) gradients across such polymer-polymer interfaces. Notably, the gradient was

symmetric about the PS/PB interface on a logarithmic modulus scale, corresponding

to an interface with a local modulus that was the geometric mean of the PS and

PB bulk modulus values. As that is the optimal condition for acoustic impedance

matching, this finding was consistent with the idea that impedance matching is an

important mechanistic feature of local property coupling across interfaces.

Finally, I tested the impedance matching picture of local property coupling by

applying the QCM method to films with an impedance matching layer at the PS/PB

interface. This layer was made up of 5 nm of styrene-butadiene random copolymer

P(S-r-B), meant to emulate the ≈5 nm interfacial region of annealed PS/PB bilayers.

I found that without even needing to anneal the system above the bulk Tg value

of PS, the P(S-r-B) impedance matching layer significantly reduced the dissipation

measured in the films. Transfer-matrix analysis demonstrated that changes in the

data were caused by the formation of a 122 nm log G(z) gradient across the interface.

The presence of the P(S-r-B) also accelerated the broadening of the G(z) gradient

with subsequent annealing. Collectively, my work significantly illuminates new perspectives

for better understanding how long-range local property gradients emerge

across glassy-rubbery interfaces.

Table of Contents

1 Introduction 1

1.1 The Glass Transition of Bulk Polymer Systems . . . . . . . . . . . . . 2

1.2 Confinement Effects on the Glass Transition . . . . . . . . . . . . . . 6

1.3 The Modulus of Bulk Polymer Systems . . . . . . . . . . . . . . . . . 9

1.4 Confinement Effects on Modulus . . . . . . . . . . . . . . . . . . . . . 11

1.5 Understanding Relevant Parameters for Confinement Effects . . . . . 15

1.6 Interfaces Between Distinct Neighboring Polymer Domains . . . . . . 19

1.7 Fluorescence Spectroscopy for Measuring the Glass Transition . . . . 24

1.8 Quartz Crystal Microbalance for Measuring Modulus . . . . . . . . . 28

1.9 Outline of Dissertation . . . . . . . . . . . . . . . . . . . . . . . . . . 32

2 Impact of Domain Size on the Length Scale of Local Glass Transition

Perturbations Caused by an Immiscible Glassy-Rubbery Interface 35

2.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

2.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

2.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 39

2.4 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

3 Analyzing QCM Data Using a New Transfer-Matrix Model: Long-

Ranged Asymmetric Gradient in Shear Modulus Identified Across

Immiscible Glassy-Rubbery Polymer Interface 52

3.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

3.3 Experimental Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 59

3.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 62

3.4.1 New Acoustic Transfer-Matrix Model for QCM Data . . . . . 65

3.4.2 Analysis of Experimental QCM Data from PS/PB Bilayer Films 73

3.4.3 Analysis of the Annealed Bilayer Data . . . . . . . . . . . . . 80

3.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

4 Narrow Impedance Matching Layer Accelerates Long-Range Coupling

of Local Modulus Between Glassy and Rubbery Polymer Domains

95

4.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

4.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

4.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 99

4.4 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

4.4.1 Sample Preparation and Multilayer Assembly . . . . . . . . . 112

4.4.2 Interfacial Composition Profile . . . . . . . . . . . . . . . . . . 116

4.4.3 QCM Measurements . . . . . . . . . . . . . . . . . . . . . . . 119

4.4.4 QCM Continuum Mechanics Shear-Wave Model with Transfer-

Matrix Math . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

4.4.5 Extended Discussion of QCM Data and Fitting Approaches . 125

4.4.6 Characterizing the Modulus of the P(S-r-B) Random Copolymer130

5 Summary and Conclusions 133

Bibliography 139

About this Dissertation

Rights statement

• Permission granted by the author to include this thesis or dissertation in this repository. All rights reserved by the author. Please contact the author for information regarding the reproduction and use of this thesis or dissertation.

School	Laney Graduate School
Department	Physics
Degree	Ph.D.
Submission	Dissertation
Language	English
Research Field	Physics, Condensed Matter Physics, Molecular Physics, Acoustics
Keyword	Polymer Fluorescence Tg Film Modulus QCM
Committee Chair / Thesis Advisor	Roth, Connie, Emory University
Committee Members	Sussman, Daniel, Emory University Burton, Justin, Emory University Shekhar, Shashank, Emory University Kindt, James, Emory University

Last modified

Primary PDF

Thumbnail	Title	Date Uploaded	Actions
	File download under embargo until 12 January 2027	2025-11-26 13:59:45 -0500	File download under embargo until 12 January 2027

Supplemental Files

Thumbnail	Title	Date Uploaded	Actions