Local Glass Transition Gradients near Dissimilar Polymer-Polymer Interfaces in Nanostructured Polymeric Materials Öffentlichkeit
Baglay, Roman R. (Fall 2017)
Abstract
In this dissertation, I show how perturbations arising from dissimilar polymer-polymer interfaces locally affect the glass transition temperature (Tg) within nanostructured polymeric materials, an issue of critical importance to understanding polymeric blends with sub 100 nm domain sizes. Using a 10-15 nm polymer layer chemically labeled with trace amounts of a fluorescent Tg sensitive pyrene dye inserted at positions z away from dissimilar polymer-polymer interfaces in semi-infinite polymer bilayer films, I measured local Tg(z) profiles for a variety of polymer pairs. I demonstrate that the local Tg(z) profile across a polystyrene (PS) / poly(n-butyl methacrylate) (PnBMA) interface in a PS/PnBMA semi-infinite bilayer with a Tg difference of 80 K between the high Tg glassy-PS (Tgbulk, PS = 101 oC) side and low Tg rubbery-PnBMA (Tgbulk, PnBMA = 21 oC) side of the bilayer is highly asymmetric towards the high Tg PS component. The Tg(z) profile surprisingly extends 350-400 nm across the PS/PnBMA interface before bulk Tgs of each component are recovered. I then extend the semi-infinite bilayer geometry to a variety of dissimilar polymer pairs, and show that the local Tg(z) length scales seem to be universally grouped by if the measured polymer component is the high Tg or low Tg component of the semi-infinite bilayer, so called hard vs. soft confinement. I find that the Tg(z) profiles are not strongly affected by the bulk Tg difference between the polymer pairs, chemical structure, interaction parameter (equilibrium interfacial width of the interface) or fragility.
I then further show how local Tg profiles are affected by the presence of two PS/PnBMA interfaces and the effect of increased cooling rates in a fixed 300 nm thick PS domain sandwiched between two thick PnBMA domains, mimicking the periodic boundary condition geometry and extended cooling rates (faster timescales) commonly employed by computer simulations. Finally, I introduce a PS polymer chemically labeled with a photomechanical dye capable of generating stresses within polymer films.
The results presented in my dissertation challenge the theoretical textbook understanding of polymer blends, specifically how material properties are affected in nanostructured materials that are dominated by polymer-polymer interfaces with domain sizes reaching below 100 nm.
Table of Contents
Chapter 1: Introduction to the Glass Transition, Physical Aging, and Modulus in Polymer Thin Films 1
1.1 Synopsis 1
1.2 Introduction to Polymeric Glasses 2
1.2.1 General Glassy Behavior 2
1.2.2 Polymer Tg upon Confinement 10
1.3 Polymer Glassy and Rubbery Modulus Behavior 15
1.4 Experimental Goals and Overview of Dissertation 18
1.4.1 Experimental Summary 18
1.4.2 Dissertation Outline 23
1.5 References 26
Chapter 2: Effect of Adjacent Rubbery poly(n-butyl methacrylate) Layer on the Glass Transition and Physical Aging of Glassy Polystyrene 30
2.1 Synopsis 30
2.2 Tg by Fluorescence: Original Method Developed by the Torkelson Group 32
2.3 Sample Preparation 36
2.3.1 Polymerization and Sample Build 36
2.3.2 Fluorescence Measurements 37
2.4 Modification to the Fluorescence Method Originally Developed by the Torkelson Group 38
2.5 Comparison and Verification of the Modified Fluorescence Method to Literature: Single Layer PS Films 42
2.6 Fluorescence Tg of Supported Single Layer PnBMA Films 45
2.7 PS/PnBMA Bilayer: Average Tg(z) of PS 46
2.8 Physical Aging of PS/PnBMA Bilayer 50
2.8.1 Experimentally Determining Aging: Ellipsometry of PS/PnBMA Bilayer 50
2.8.2 Comparison of Fluorescence Tg to Physical Aging of PS in PS/PnBMA Bilayers 53
2.8.3 Open Questions 57
2.9 References 59
Chapter 3: Experimentally Determined Profile of Local Glass Transition Temperature Across a Glassy-Rubbery Polymer Interface with a Tg Difference of 80 K 62
3.1 Synopsis 62
3.2 Introduction 63
3.3 Experimental Methods 66
3.4 Results and Discussion 72
3.5 Conclusions 84
3.6 References 86
Chapter 4: Local Glass Transition Temperature Tg(z) of Polystyrene Next to Different Polymers: Hard vs. Soft Confinement 89
4.1 Synopsis 89
4.2 Introduction 90
4.3 Experimental Methods 96
4.4 Results and Discussion 100
4.4.1Comparing PS/PSF to PS/PnBMA: Hard vs. Soft Confinement 100
4.4.2 Universal Behavior: Local Tg(z) of PS Next to Different Polymers 111
4.4.3 Varying Annealing Time of PS/PSF Interface: Importance of Reaching Equilibrium 119
4.5 Conclusions 125
4.6 References 128
Chapter 5: Experimental Study of the Influence of Periodic Boundary Conditions: Effects of Finite Size and Faster Cooling Rates on Dissimilar Polymer-Polymer Interfaces 133
5.1 Synopsis 133
5.2 Introduction 135
5.3 Introduction of a Second PS/PnBMA Interface 138
5.4 Cooling Rate Effects on Finite Size Domains of PS Between Two PnBMA Layers 144
5.5 Conclusions 149
5.6 References 151
Chapter 6: Characterization of Polystyrene Chemically Labeled with a Photomechanical Azo Dye using Ellipsometry 153
6.1 Synopsis 153
6.2 Introduction 155
6.2.1 Modulus of Polymer Films in Confined Thin Film Geometries 155
6.2.2 Introduction to Photomechanical Azos and DR1 161
6.3 Characterization of PS Labeled with DR1 165
6.3.1 Polymerization and Characterization of PS Labeled with DR1 and PS-DR1 Thin Film Sample Preparation 165
6.3.2 Calibration of the Laser System 169
6.3.3 Ellipsometry Film Thickness Measurements of PS Labeled with Photomechanical DR1 Excited by a 532 nm 50 mW Laser 172
6.3.4 Ellipsometry Film Thickness Measurements of PS Labeled with Photomechanical DR1 Excited by a 532 nm Variable Power Laser 179
6.4 References 187
Chapter 7: Summary and Conclusions 189
References 197
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