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The Disorder-To-Order Phase Transition in Poly(Styrene-Block-N-Butyl Methacrylate) : the Effect of Pressure." (2001)

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The Disorder-To-Order Phase Transition in Poly(Styrene-Block-N-Butyl Methacrylate) : the Effect of Pressure. University of Massachusetts Amherst ScholarWorks@UMass Amherst Doctoral Dissertations 1896 - February 2014 1-1-2001 The disorder-to-order phase transition in poly(styrene-block-N- butyl methacrylate) : the effect of pressure. Michael Anthony Pollard University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/dissertations_1 Recommended Citation Pollard, Michael Anthony, "The disorder-to-order phase transition in poly(styrene-block-N-butyl methacrylate) : the effect of pressure." (2001). Doctoral Dissertations 1896 - February 2014. 1023. https://scholarworks.umass.edu/dissertations_1/1023 This Open Access Dissertation is brought to you for free and open access by ScholarWorks@UMass Amherst. It has been accepted for inclusion in Doctoral Dissertations 1896 - February 2014 by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. THE DISORDER-TO-ORDER PHASE TRANSITION IN POLY(STYRENE-BLOOC-N-BUTYL METHACRYLATE): THE EFFECT OF PRESSURE A Dissertation Presented by MICHAEL ANTHONY POLLARD Submitted to the Graduate School of the University of Massachusetts Amherst in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY September 2001 Polymer Science and Engineering THE DISORDER-TO-ORDER PHASE TRANSITION IN POLY(STYRENE-BLOCK-N-BUTYL METHACRYLATE): THE EFFECT OF PRESSURE A Dissertation Presented by MICHAEL ANTHONY POLLARD Approved as to style and content by: T. Russell, Chair M. Muthukumar, Member . Watkins, Member XMa/^— T. McCarthy, Department Head Polymer Science and Engineering © Copyright by Michael Anthony Pollard 2001 All Rights Reserved ACKNOWLEDGEMENTS A number of people were instrumental building up the foundation for the work presented in thesis. They provided technical expertise, a stimulating research atmosphere, and a collegiate working environment. I am indebted to the following people, in particular, for their role in shaping my professional and personal growth over the course of five years: Prof. T. Russell, Prof. M. Muthukumar, Prof. J. Watkins, and Prof. D. Hoagland; Dr. P. Mansky, Dr. O. K. C. Tsui, Dr. T. Thurn-Albrecht, and Dr. T. Kerle; A.-V. Ruzette, and Prof. A. Mayes; Dr. A. Waddon, and L. Raboin; J. DeRouchey, G. Brown, D. Flanagan, and G. Menges. iv ABSTRACT THE DISORDER-TO-ORDER PHASE TRANSITION IN POLY(STYRENE-BLOCK-N-BUTYL METHACRYLATE): THE EFFECT OF PRESSURE SEPTEMBER 2001 MICHAEL A. POLLARD, B. S., UNIVERSITY OF SOUTHERN MISSISSIPPI M. S., UNIVERSITY OF MASSACHUSETTS AMHERST Ph. D., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Thomas P. Russell The effect of hydrostatic pressure on the lower disorder-to-order transition (LDOT) in poly(d-styrene-Woc/c-n-butyl methacrylate) having symmetric and asymmetric block lengths was investigated by in situ small-angle neutron scattering (SANS). Currently, linear diblock copolymers having styrenic and methacrylic monomers are the only systems that display a thermally accessible phase transition from the disordered homogeneous melt to the ordered microphase-separated state upon heating. The location of this phase transition was mapped as a function of temperature and pressure by analyzing one-dimensional SANS intensities, where discontinuities in the width and height of the scattering peak indicated the traversal of the transition isothermally or isobarically. The T-P phase diagram of p(d-S-b-nBMA) built using this method shows an expansion of the disordered, homogenous region with increasing pressure. For the v diblock copolymer with a 4 lamellar morphology and = 8.5 Mw x 10 , the slope of the phase transition line was ~ 150 K/kbar, and was approximately linear over a range of 1 kbar. Increasing the molecular weight of p(rf-S-k-nBMA) resulted in a vertical shift of the phase transition line in the phase diagram and no detectable change in slope. Similar effects were observed for diblock copolymers with a cylindrical morphology. The bulk enthalpy and volume changes at the phase transition, which dictate the pressure coefficient for a one component system, were either at the limit of experimental resolution or unobservable due to kinetic factors. In-situ X-ray reflectivity experiments, however, showed a significantly reduced thermal expansion coefficient in the disordered phase and a discontinuous increase in film thickness as a function of temperature at the bulk LDOT. The pressure coefficient, dTLDOT /dP, for these materials is greater by a factor of five than currently observed in diblock copolymers with conventional UODT phase behavior, i.e. ordering upon cooling. This dramatic phase behavior allows rapid and convenient access to the order-disorder phase transition, isothermally, and suggests that LDOT block copolymers could be employed in blend and multi-component systems as minor components to impart pressure-induced compatibiHzation, surface activity, or flow properties. vi TABLE OF CONTENTS ACKNOWLEDGEMENTS iv ABSTRACT v LIST OF FIGURES Vlll CHAPTER 1. INTRODUCTION x A. Background 2 B. Methods and Materials 4 C. References 5 2. PRESSURE DEPENDENCE OF LDOT 8 A. Initial SANS Experiments 8 B. Further SANS Experiments 13 C Phase Diagram 15 D. Summary 16 E. References 17 F. Figures 18 3. VOLUME AND HEAT EFFECTS 28 A. X-Ray Reflectivity 28 B. Differential Scanning Calorimetry 31 C. Polarized Light Microscopy 35 D. Discussion 36 E. References 37 F. Figures 39 4. PHASE DIAGRAM OF p(d-S-k-nBMA) 43 A. Schematic Phase Diagrams 43 B. Experimental Studies 46 C. Discussion 48 D. References 58 E. Figures 61 5. CONCLUSIONS 67 BIBLIOGRAPHY 71 vn LIST OF FIGURES Fi ure 8 Page 2.1 SANS profiles, 85k 18 2.2 Peak parameters, 85k 19 2.3 SANS profiles, 85k 20 2.4 Peak parameters, 85k 21 2.5 Peak parameters, summary 22 2.6 SANS profiles, 134k 23 2.7 Temperature-pressure superposition, 85k 24 2.8 Pressure coefficient, 85k 25 2.9 Phase diagram, 96k 26 2.10 Phase diagram, summary 27 3.1 Reflectivity profiles, 85k 39 3.2 Film thickness discontinuity, 85k 40 3.3 DSC, 75k 41 3.4 Ordering kinetics, 75k & 78k 42 4.1 Schematic block copolymer phase diagrams 61 4.2 Transition temperatures, UODT and LDOT 62 4.3 Best fit of transition temperatures 63 4.4 Flory-Huggins parameters in LCST blends 64 4.5 Deuteration effect in p(S-b-nBMA) 65 viii CHAPTER 1 INTRODUCTION A. Background Block copolymers are created by joining two homopolymer chains, (-A-), and (-B-) together covalently to form (-A-B-) . N The presence of the junction point restricts phase separation when there are strong repulsions between A and B blocks. As a result, the size of the phase-separated domains is determined only by the chain length, typically tens of nanometers. A variety of periodic structures will then spontaneously form as a result of the packing between A and B domains. Classically, these equilibrium morphologies consist of either spheres, cylinders, or lamellae, depending on the fraction, f A , of A monomers relative to B monomers. Due to the complexity of this 'self- assembling' process, and the variety of solution- and melt-based structures that develop naturally out of this simple linear chain architecture, block copolymers have been of keen interest in the scientific and industrial communities for many decades. An extensive literature covering phase behavior and properties is summarized in " several excellent reviews. 1 1 A theme which is of continuing interest in the study of linear diblock copolymers is their phase behavior. Guided by theory, the phase behavior is usually characterized in terms of the product (xN), where Xab is the Flory-Huggins interaction parameter, and N is the chain length. This parametrization reflects the thermodynamic forces that are compering for dominance of the free energy. Microphase separation is driven by the chemical incompatibility between A and B monomers, but the chain-stretching and 1 loss of translational freedom that accompanies microphase separation is entropically unfavored. By selecting highly incompatible monomers, the strong repulsions between A and B will dominate the free energy for all but the shortest chains. This is the strong-segregation regime which is described by the condition (%N) » 10. Here, the microphase-separated (ordered) state is most stable. Alternatively, by selecting compatible monomers, so that the condition (%N) « 10 is met, the entropy will dominate since the interaction energy is too weak to force microphase separation. In this situation, the phase-mixed (disordered) state is the most stable. fine balance A exists between the energetic and entropic forces when (%N) ~ 10. In this regime, the phase transition separating the ordered and disordered states can be accessed thermally. This allows the state of the block copolymer to be controlled simply by adjusting the temperature. Since the interaction energy assumes form, X~ 1/T, a block copolymer with properly chosen molecular weight and interaction energies will undergo this transition from the homogeneous state to the microphase separated state when cooled. This phase transition is denoted the microphase separation transition (MST) or the order-disorder transition (ODT). When a diblock copolymer is cooled into the ordered state, the A blocks will locally segregate from the B blocks and subsequently form an extendend lattice as these domains pack together. These anisotropic structures will develop during an experimentally relevant time scale, and give rise to rapid and discontinuous changes in the mechanical and optical properties. Dynamical mechanical spectroscopy and depolarized light scattering are currently widely employed to study these property changes at the order-disorder transition." Since a block copolymer in the ordered phase can be melted by raising its temperature, we denote this phase transition the upper order-disorder transition 2 (UODT) by analagy with the UCST phase behavior observed in two-component mixtures. In a striking deviation from this classical behavior, block copolymers composed of poly(styrene) and poly(n-butyl methacrylate) were shown to possess an inverted temperature 7 dependence of this transition.
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