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Three Facets of Modern Liquid Crystal Science

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Three Facets of Modern Liquid Crystal Science Three facets of modern liquid crystal science The complex phase behavior of chiral thermotropic smectics Electrospinning of nano-/microfibers with liquid crystals Dispersing and aligning carbon nanotubes in lyotropic liquid crystals Jan Lagerwall January 27, 2011 2 Curiosity is one of the permanent and certain characteristics of a vigorous intellect. Samuel Johnson 3 Three facets of modern liquid crystal science Habilitationsschrift zur Erlangung des akademischen Grades doctor rerum naturalium habilitatus (Dr. rer. nat. habil.) vorgelegt der Naturwissenschaftlichen Fakult¨atII der Martin-Luther-Universit¨atHalle-Wittenberg von Herrn Tekn. Dr. Jan P. F. Lagerwall geb. am 28.05.1970 in G¨oteborg, Schweden Gutachter: 1. Herr Prof. Dr. H. Kitzerow (Universit¨atPaderborn) 2. Herr Prof. Dr. E. Samulski (University of North Carolina at Chapel Hill) 3. Herr Prof. Dr. C. Tschierske (Martin-Luther-Universit¨atHalle-Wittenberg) Halle (Saale), verteidigt am 23.11.2010. 4 Preface This habilitation thesis summarizes my research during the almost eight years that have passed since I gained my Ph.D. The common denominator of this work is liquid crystals, which have played a central role in almost all my research work. During the last five-six years I have however combined liquid crystal research with aspects, materials and techniques from quite different research areas. Therefore, of the three main chapters of this thesis only the first deals purely with liquid crystals. The two latter are devoted to polymer fibers containing liquid crystals| produced by the technique of coaxial electrospinning|and composites of liquid crystals and carbon nanotubes, respectively. Considering this quite broad scope I hope that a readership comprising also non-liquid crystal researchers can find the thesis interesting. In order to render the thesis understandable also for these readers, working perhaps mainly with electrospinning or carbon nanotube research, I have included an introductory chapter that is relatively comprehensive, aiming to introduce also scientists with little or no background in liquid crystals into this fascinating materials class and its study. While liquid crystal researchers often focus strongly on one of the two main liquid crystal classes, thermotropics or lyotropics, both of them actually play very important roles in my research and I therefore discuss the two classes on equal par in the introduction. This approach is quite rare, hence I believe that the introductory chapter may in fact have some novelty value even for many a liquid crystal expert. I hope that the comparison of the two classes, highlighting their similarities as well as their differences, can stimulate interesting new research ideas. The topics that are specific to the three main chapters of the thesis|spontaneous polarization in chiral smectics, electrospinning and carbon nanotubes|are introduced concisely at the beginning of each respective chapter. My research would not have been possible without the input and help from many other scientists. In particular, my entrance into the fields of carbon nanotube and electrospinning research would have been very much more difficult without the generous and open attitudes of the friends and colleagues from these communities that I have come to know in the last few years. Giusy Scalia was the one who got me interested in carbon nanotubes and initiated me into their study together with liquid crystals. I owe a great deal of my understanding about these particles to her. Giusy's support has however reached well beyond the field of carbon nanotubes. Via Giusy I was also fortunate enough to come to know the carbon nanotube research group of Siegmar Roth at the Max-Planck-Institut f¨urFestk¨orperforschung in Stuttgart. Through him and his colleagues, foremost Ursula Dettlaff-Weglikowska, Viera Skakalova, Miro Haluska, Monica Jung de Andrade and Marcio Dias Lima, I learnt invaluable things not just about carbon nanotubes, but the spectrum ranged from Slovak cooking via etymology to other scientific fields. For my achievements in the field of electrospinning I am much indebted to Jesse McCann, Eric Formo and Younan Xia. It was Jesse's inspiring talk at a one-day conference on electrospinning, that I attended more or less by coincidence, that attracted me to this field and gave me the basic ideas for my research on the topic. I then got my first practical experience with electrospinning during a three week visit to the Xia group at the University of Washington in Seattle in May 2007. i ii PREFACE Not only did Jesse and Eric help me with the practical work of conducting the first experiments on electrospinning of fibers with liquid crystalline cores during this visit, but with their open and enthusiastic attitude they also shared many vital tips and tricks with me on how to succeed with the preparation and characterization of the fibers. My interest in liquid crystals is much older, in fact introduced to me by my father, Sven Lagerwall, when I was a child by showing the colorful and dynamic textures of liquid crystals between crossed polarizers. My fascination for liquid crystal polarizing microscopy textures has never ended, and neither has the support of Sven throughout my journey to explore the secrets of liquid crystals. Although he is now officially retired, he is still active in liquid crystal research and his input on any idea of mine has always been extremely valuable. My advisors from my doctoral time at Chalmers, Bengt Stebler and Per Rudquist, have also been very important for my continued scientific career. Still today, although it is now some eight years since we lived in the same country, the interaction with Per and Bengt is both inspiring and joyful. Bengt has also always been very helpful in many practical issues, even when I gave him extremely little time to prepare. The most important person in teaching me the physical chemistry of liquid crystals has been Frank Gießelmann. My stay as a post-doc in his group at the University of Stuttgart from 2003 to 2007 was a period of fascinating research and at the same time, great fun. Frank is generous not only in sharing scientific understanding, but also good wines and food were often enjoyed in the company of him and his family. I first met Frank when he stayed as visiting professor in the Chalmers group when I did my doctoral studies. In the group at that time was also his previous fellow doctoral student from the Technical University of Clausthal, Ingo Dierking, then conducting a post-doc at Chalmers. The interaction with Ingo, since a couple of years at the University of Manchester, has been very inspiring, his broad approach to liquid crystal research being a good model to follow. While it was Giusy who in practice introduced me to carbon nanotubes, it was the team of Ingo and Giusy that did some of the seminal work on CNT liquid crystal composites. Between my Ph.D. and my post-doctoral stay in Germany I spent a brief time as a post-doc at the University of Colorado at Boulder, working together with the groups of Noel Clark and Dave Walba in the physics and chemistry departments, respectively. Although very short, this was a fantastically intense stay from which I learnt a lot and got plenty of inspiration for how to develop my own independent research. Still today, I learn something new every time I meet Dave and Noel at conferences or other occasions and their approach to liquid crystal research certainly demonstrates how rich this research field is. When starting in Germany I did not go to Frank right away but I first spent a few months in the group of Gerd Heppke at the Technical University of Berlin. Although again very short, also this stay was most rewarding, the pleasant atmosphere in this lab inspiring to many new ideas. In fact, I had come to know the Heppke group during a shorter stay in Berlin a few years earlier, where a long-lasting friendship with several students in the group started. In particular I wish to mention Daniel Kr¨uerke, Hans Sawade and Mario M¨uller,with whom I am still interacting actively. Since 2007 I have been working at the Martin-Luther-Universit¨atHalle-Wittenberg, sur- rounded by many scientists who have helped me very much in developing my research these years. Wolfgang Weissflog and Carsten Tschierske were my first contacts here, already prior to moving to Halle, and their support and enthusiasm set the stage for a very pleasant working environment. I have also learnt a great deal about thermotropic liquid crystal chemistry from them and Carsten's enthusiasm and active involvement in our current joint project on developing a new class of materials for aiding nanotube dispersion in thermotropic liquid crystals has been instrumental for its success. Another greatly enthusiastic person in Halle is Ute Baumeister, whose expertise in x-ray scattering and willingness to collaborate with my group have been of iii great value for our research. While I had acquired good experience in surfactant-based lyotropic liquid crystals during my time in Stuttgart, my knowledge in this field was greatly improved thanks to the discussions with Annette Meister and Alfred Blume, in particular regarding the lamellar phases formed by phospholipids. Prof. Blume as well as Prof. J¨orgKressler are both thanked also for their kind welcome to me at the institute. Many questions about DNA and biophysical chemistry were clarified by Andreas Kerth who has also been of great help in setting up various lab equipment. Invaluable practical support was also provided during my time in Halle by Andreas Lonitz, always available when a computer needs to be convinced about something or when a particular cable arrangement is needed. Equally important is the incredibly professional help of Herr Reese in the mechanical workshop of the chemistry institute.
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