University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Doctoral Dissertations Graduate School 8-2005 Factors Affecting the Phase Separation of Liquid Crystals from Acrylate-based Polymer Matrices Nathan Joseph Crawford University of Tennessee, Knoxville Follow this and additional works at: https://trace.tennessee.edu/utk_graddiss Part of the Chemistry Commons Recommended Citation Crawford, Nathan Joseph, "Factors Affecting the Phase Separation of Liquid Crystals from Acrylate-based Polymer Matrices. " PhD diss., University of Tennessee, 2005. https://trace.tennessee.edu/utk_graddiss/4312 This Dissertation is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a dissertation written by Nathan Joseph Crawford entitled "Factors Affecting the Phase Separation of Liquid Crystals from Acrylate-based Polymer Matrices." I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Doctor of Philosophy, with a major in Chemistry. Mark D. Dadmun, Major Professor We have read this dissertation and recommend its acceptance: Bin Zhao, Bin Hu, Peter Zhang Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) To the Graduate Council: I amsubmitting herewith a dissertation written by NathanJoseph Crawfordentitled "Factors Affectingthe Phase Separationof Liquid Crystals fromAcrylate-based Polymer Matrices." I have examinedthe final paper copy of this dissertation forform and content and recommend that it be accepted in partial fulfillmentof the requirements forthe Doctor of Philosophy, with a major in Chemistry. MarkD. Dadmun, Major Professor We have read this dissertation andrecommend its acceptance: Bin Zhao Bin Huls1icz c::, 1k Peterh�- Zhang Accepted forthe Council: Vice Chancellor an Graduate Studies 'fh�- -,s , rJ5 • 1 13 FACTORS AFFECTING THE PHASE SEPARATION OF LIQUID CRYSTALS FROM ACRYLATE-BASED POLYMER MATRICES A Dissertation Presented forthe Doctor of Philosophy Degree University of Tennessee,Knoxville Nathan Joseph Crawford August 2005 ACKNOWLEDGEMENTS I wish to thank ProfessorMark D. Dadmun for affordingme the opportunity to work on a project that has broadened and deepened my understanding of science and technology. I also thank my committee members, Professors Bin Zhao, Bin Hu, and Peter Zhang, fortheir patience and input. I would also like to thankmy colleagues, Charles O'Brien, Michael Arlen, Eric Eastwood, Gary Lynn, Kevin Rice, Steve Wargacki, Scott Fontana, Asif Rasheed, and Sudesh Karnath, for their advice and friendship. Special thanksare also given to my familyand friendswho have given me financialas well as moral support. Above all, I must thankmy wife, Katrina. Without her steadfastlove, emotional and financialsupport, I could never have accomplished this work. 11 ABSTRACT The work presented in this dissertation covers the study of phase separation of small-molecule liquid crystals (LC's) fromacrylate-based polymer matrices. These materials are used in the construction of polymer dispersed liquid crystals, or PDLC's, an emerging technology with applications ranging fromprivacy windows to photonic materials. The firstpart of this study involves the determinationof the effectof increasing polymer molecularweight on the solubility of the LC 4'-octyl- 4-biphenyl carbonitrile, or 8CB, in poly(methyl methacrylate), or PMMA. Optical microscopy is used to determine the equilibrium phase diagrams for blends of 8CB and PMMA with weight-average polymer molecularweights ranging from 23,000-600,000 g/mol, anddifferential scanning calorimetry, DSC, is used to determine the fractionof 8CB that remains trapped in the polymer matrix, or the solubility limit of 8CB. Phase diagramsshow what appears to be anupper limit to the effectof polymer molecularweight. The effect of polymer molecularweight on the phase behavior is quantified by extraction of the Flory-Huggins interaction parameterfrom fits of the microscopy data to the Flory-Huggins theory for polymer solutions. The solubility limit data also show a limit to the effect of polymer molecular weight, and when comparedto solubility limit data from previous studies that use different polymer matrices, the data supports the independence of the solubility limit frompol ymer composition. The second partof this work changes the emphasis of the study fromthe effect of polymer molecularweight to fluorinationof the polymer matrix. Monomers of 2,2,2- 111 trifluoroethyl methacrylate, TFEMA, and methyl methacrylate , MMA, are polymerized by atom transferradical polymerization, or ATRP, to form copolymers with 8, 19, 25, 44, and 70% TFEMA content. The copolymers are blended with 8CB, and phase diagrams of the blends are determined by optical microscopy. As the TFEMA content of the copolymer increases, a correspondingincrease in the region of immiscibility of 8CB is observed. In order to quantify the effectof increasing TFEMA content, the Flory­ Huggins interaction parametersfor each blend aredetermined fromthe fittingprocedure used in the previous section. The final part of this thesis employs time-resolved light scattering to study the phase separation kinetics of the LC blend E7 from a polymer matrix formedby polymerization-induced phase separation, or PIPS. The light scattering experiments start with syrups that consist of two differentE7 fractions, 40 and50% by mass. The syrups are cured by a greendiode laser under four differentcure beam intensities. The scattering profilesfor the lowest cure beam intensity exhibit behavior that supports phase separation by a spinodal decomposition mechanism. lV TABLE OF CONTENTS Chapter Page 1 Polymer Dispersed Liquid Crystals: Introduction and Experimental Strategies ........................................................................... 1 1.1 Introduction ................................................................. 1 1.2 Liquid Crystal Primer ......................................................4 1.3 Matrix Construction Techniques ........................................10 1.4 Description of PDLC Phase Behavior ..................................14 1.5 Goals andExperimental Strategies ......................................3 4 2 Experimental Techniques .........................................................38 2.1 Microscopy .................................................................. 38 2.2 Differential ScanningCalorimetry .......................................4 3 2.3 Time-resolved Light Scattering ......................................... .48 2.4 Polymerizations............................... ............................. 54 3 Polymer MolecularWeight Effectson the Solubility of 8CB in PMMA Matrices ............................................................................. 62 3.1 Introduction .................................................................62 3.2 Experimental ...............................................................64 3.3 Results ....................................................................... 75 3 .4 Discussion.................................................................. 86 3.5 Conclusions ..................................................................88 4 The Consequence of Matrix Fluorination on Liquid Crystal Solubility in PolymerDispersed Liquid Crystals ............................................. 90 V 4.1 Introduction ...............................................................90 4.2 Experimental .............................................................. 92 4.3 Results and Discussion .................................................. 99 4.4 Conclusions .............................................................. 107 5 Time-resolved Light Scattering of Phase Separation in PDLC's Formed by Photo-polymerization Induced Phase Separation...................... ..... 108 5.1 Introduction ............................................................... 108 5.2 Experimental .............................................................11 0 5.3 Results and Discussion................................................. 114 5.4 Conclusions ............................................................... 148 6 Conclusions andFuture Work .................................................150 Bibliography.................................................................... ...... 154 Vita.......................................................... .......................... 161 Vl LIST OF TABLES Table Page 2. 1 ATRP results forP(MMA-co-TFEMA ) synthesis, * copolymer synthesized by C. P. O'Brien ......................................................................... ...........61 3. 1 List of sources, the number and weight average molecularweights and polydispersities (PDI) for the poly(methyl methacrylate) polymers used in this study ........................................................................................... 65 3. 2 Values forthe polymer segmentlengths, N2, critical fraction,<l> c, and the critical interaction parameter,X e, extracted fromthe microscopy data; Effectivesegment size forN 2 determination ca. 10,000 g/mol. .................