Uncovering the Role of Neighboring Domain Modulus on the Local Glass Transition and Shear Wave Propagation in Nanostructured Polymeric Materials Pubblico

Abstract

In this dissertation, I use a modified fluorescence method to measure the local glass transition temperature Tg(z) of multilayer polymer films, and I develop a quartz crystal microbalance (QCM) method to measure the modulus of single layer and bilayer films. My fluorescence measurements demonstrate that the local Tg(z) in a glassy polystyrene (PS) film is strongly dependent on the Young’s modulus of a neighboring polydimethylsiloxane (PDMS) domain. Specifically, by varying the Young’s modulus from 0.9 to 2.6 MPa I find that the local Tg(z) in PS at a distance of z = 50 nm away from the PS/PDMS interface increases by 40 K. In addition, I find that the length scale of perturbation to bulk Tg in PS near the interface is z ≈ 65–90 nm. Although this length scale is large compared to the interfacial width for this system of wI ≈ 1.5 nm, it is considerably shorter than what would be expected from other systems studied previously by our group. We attribute this difference in length scale to a smaller interfacial width in our system compared to those studied previously. Gathering these results and others from the literature, we propose that acoustic impedance matching might be the control parameter influencing perturbations to local Tg(z) near dissimilar polymer-polymer interfaces. In acoustic impedance matching, acoustic waves are maximally transmitted across a boundary if the product of the density and shear moduli are similar between the layers, and if the width of the transition in the shear moduli or the density between the layers is large. In the rest of the dissertation, I develop an experimental method using a quartz crystal microbalance (QCM) and a continuum physics model to study the influence of annealing a polybutadiene (PB) / polystyrene interface on the MHz-frequency shear wave propagation through the interface. Along the way, I measure the shear modulus of PB, polydimethylsiloxane, and PS films at MHz frequencies. I find that annealing a PB/PS bilayer at 120 ◦C for 100 min results in a pronounced change in the QCM experimental signal associated with changes in viscoelasticity, and by applying a continuum physics layer model show that the width of the modulus profile near the PB/PS interface extends to approximately 150 nm. This broad length scale of the modulus profile across dissimilar polymer domains developed by annealing suggests an increase in the transmission of vibrational modes across the interface. This increased transmission of vibrational modes may then perturb the local vibrational modes in the polymer domains, which have been shown to be predictors of structural relaxations associated with the glass transition. These results suggest that this increased transmission of vibrational modes across the well-annealed polymer-polymer interface may be the source of dynamical coupling causing the broad, extended Tg(z) profiles that are observed to develop with interface annealing. 

Table of Contents

1. Introduction 1

1.1 The Glass Transition in Polymers in the Bulk 2

1.2 Modulus of Bulk Polymer Systems 4

1.3 The Glass Transition in Polymer Thin Films 7

1.4 Current Theoretical Understanding of the Glass Transition in Confined Polymer Systems 10

1.5 Modulus of Thin Polymer Films 11

1.6 Influence of Polymer-Polymer Interfaces on the Glass Transition 15

1.7 Experimental Methods 20

1.8 Outline of Dissertation 22

2 Local Glass Transition Temperature Tg(z) Within Polystyrene Is Strongly Impacted by the Modulus of the Neighboring PDMS Domain 25

2.1 Synopsis 25

2.2 Introduction 26

2.3 Experimental Methods 28

2.4 Results and Discussion 29

2.5 Conclusions 37

2.6 Appendix 38

3 Physically Intuitive Continuum Mechanics Model for Quartz Crystal Microbalance: Viscoelasticity of Rubbery Polymers at MHz Frequencies 47

3.1 Synopsis 47

3.2 Introduction 48

3.3 Experimental Methods 51

3.4 Results and Discussion 56

3.4.1 Continuum physics model and numerical fitting 56

3.4.2 Continuum physics model applied to glassy polystyrene films 62

3.4.3 Continuum physics model applied to rubbery polybutadiene films 65

3.4.4 Continuum physics model applied to rubbery PDMS films 72

3.5 Conclusions 76

3.6 Appendix 78

4 Annealing Matters: Modulus Profile Developed on Annealing a Dissimilar Polymer-Polymer Interface Measured by QCM 84

4.1 Synopsis 84

4.2 Introduction 85

4.3 Experimental Methods 88

4.4 Results and Discussion 88

4.4.1 Continuum Physics Model 94

4.5 Conclusions 102

5 Summary and Conclusions 104

Bibliography 112 

About this Dissertation

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School	Laney Graduate School
Department	Physics
Degree	Ph.D.
Submission	Dissertation
Language	English
Research Field	Physics, Molecular Physics, Condensed Matter Physics, Acoustics
Parola chiave	Polymer Physics Soft Matter
Committee Chair / Thesis Advisor	Connie B. Roth, Emory University
Committee Members	Justin C. Burton, Emory University James T. Kindt, Emory University Eric R. Weeks, Emory University Daniel M. Sussman, Emory University

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