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Coffee-Rings and Glasses: Colloids out of Equilibrium COFFEE-RINGS AND GLASSES: COLLOIDS OUT OF EQUILIBRIUM Peter Joseph Yunker A DISSERTATION in Physics and Astronomy Presented to the Faculties of the University of Pennsylvania in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy 2012 Arjun G. Yodh, James M. Skinner Professor of Science Supervisor of Dissertation A.T. Charlie Johnson, Associate Professor of Physics Graduate Group Chairperson Dedication To my family ii Acknowledgements No man is an island, and even if a graduate student lives alone on an island, no thesis is written alone. I owe a great debt of gratitude to a large number of people. I’ll start with those who were with me from the beginning, my parents and siblings. Their love and support is an integral part of who I am today. My parents nurtured my interest in science and technology from a young age, taught me to figure things out on my own, and encouraged me to find a vocation that is also my avocation. Next, I must thank my fiance e´ and best friend, Erin Buckley. Erin is always there for me, and there’s no one in the world I would rather spend time with. From our marathon-first-date in New York, to our engagement to in Paris, I’ll always treasure the time we spent together in grad school. I am tremendously grateful to my advisor, Arjun Yodh. Arjun has been my ideal mentor. He encourages creativity, and allows students to invent and pursue their own ideas - with the under- standing that you explain and justify these ideas and experiments in gory detail. Additionally, Arjun taught me a great deal about communication in science, from writing papers to giving talks. I’m embarrassed to think of the first paper I wrote and the first talk I gave in grad school. Thanks to Arjun’s direct style of criticism and encouragement, I (hopefully) have progressed significantly from that point. During my time at Penn, I have been privileged to collaborate with many experts in soft matter. I am especially grateful to Andrea Liu and Tom Lubensky, who inspired many of my experiments, and then helped me to understand them. Randy Kamien consistently would “look- in” on us experimentalists from time-to-time. Doug Durian gave me key advice on a number of occasions. I have also been fortunate to know and work with Kevin Aptowicz, from West Chester iii University, and Piotr Habdas, from St. Joseph’s University. They both aided me considerably, especially when I was first learning the ropes in research, and it has been especially rewarding to continue working with them. I don’t know that I can thank all of my wonderful labmates enough. I must start by ac- knowledging Dan Chen and Ahmed Alsayeed, who taught me the basics when I first joined the group, from Kohler¨ illumination to sample preparation. I distinctly remember Ahmed scanning through samples so fast I couldn’t even tell what we were looking at and Dan making pristine microscope slides that made the ones I prepared look like my dog made them. But Dan and Ahmed were patient, and they made joining the Yodh group a pleasurable experience. I was also fortunate to work with Yilong Han early in my graduate career. Yilong taught me a great deal about programming in IDL, and crafting a research project in general. One of the great pleasures I had in my time at Penn was working with my labmate Zexin Zhang. Zexin was a great collaborator, and a better friend. His friendly-optimism was infectious, and his knowledge of chemistry was invaluable. Tim Still was a great source of knowledge about chemistry, discussions about physics, and debates about esoteric subjects. Ke Chen was a valuable collaborator and challenger, who invigorated the lab with his density of states work. Enormous thanks go to my fellow graduate students, Oni Basu, Matt Lohr, and Matt Gratale. The four of us had a lot of fun together, in and out of physics. Matt Lohr entertained the lab with his unique sense of humor and enthusiasm. As I recall, Gratale and I may have engaged in one or two discussions about sports. Oni proved invaluable as a dog-sitter, making it much easier to leave town. I couldn’t have asked for a better set of graduate students to to work and learn with me. I should also thank my classmate and good friend Wesley Baker, who was a great friend to iv me during my time here at Penn. Finally, I should thank my dog, Betty. You may think it is silly to acknowledge an animal in a thesis, but Betty has been an invaluable friend who freely gives her love and happiness to others. v ABSTRACT COFFEE-RINGS AND GLASSES: COLLOIDS OUT OF EQUILIBRIUM Peter Joseph Yunker Arjun G. Yodh This thesis describes experiments that utilize colloids to explore nonequilibrium phenomena. Specifically, the deposition of particles during evaporation and the glass transition are explored. In the first set of experiments, we found that particle shape has a profound effect on particle deposition. We evaporated drops of colloidal suspensions containing micron-sized particles that range in shape from isotropic spheres to very anisotropic ellipsoids. For sessile drops, i.e., drops sitting on a solid surface, spheres are deposited in a ring-like stain, while ellipsoids are deposited uniformly. We also confined drops between glass plates and allowed them to evaporate. During evaporation, colloidal particles coat the air-water interface, forming colloidal monolayer mem- branes (CMMs). As particle anisotropy increases, CMM bending rigidity was found to increase. This increase in bending rigidity provides a new mechanism that produces a uniform deposition of ellipsoids and a heterogeneous deposition of spheres. In the second set of experiments, we employed colloidal suspensions to investigate the char- acter of glassy materials. “Anisotropic glasses” were investigated with ellipsoidal particles con- fined to two-dimensional chambers at high packing fractions; this system enabled the study of the effects of particle shape on the vibrational properties of colloidal glasses. Low frequency vi modes in glasses composed of slightly anisotropic particles are found to have predominantly rotational character. Conversely, low frequency modes in glasses of highly anisotropic particles exhibit a mix of rotational and translational character. Aging effects in glasses were explored using suspensions of temperature-sensitive microgel spheres. We devised a method to rapidly quench from liquid to glass states, and then observed the resultant colloidal glasses as they aged. Particle rearrangements in glasses occur collectively, i.e., many particles move in a correlated manner. During aging, we observed that the size of these collective rearrangements increases. Thus, the slowing dynamics of aging appear governed by growing correlated domains of particles required for relaxation. Using the same microgel particles, the transformation of a crystal into a glass due to added disorder was investigated by adding smaller particles into a quasi-two-dimensional colloidal crystal. The crystal-glass transition bears structural signatures similar to those of the crystal- fluid transition, but also exhibits a sharp change in dynamic heterogeneity which “turns-on” abruptly as a function of increasing disorder. Finally, we investigated the influence of morphology and size on the vibrational properties of disordered clusters of colloidal particles. Spectral features of cluster vibrational modes are found to depend strongly on the average number of nearest neighbors but only weakly on the number of particles in each glassy cluster. The scaling of the median phonon frequency with nearest neighbor number is reminiscent of athermal simulations of the jamming transition. vii Contents Dedication ii Acknowledgements iii Abstract vi List of Figures xxx 1 Introduction 1 1.1 Coffee-Ring Effect . 3 1.2 Glasses . 6 1.2.1 Aging in Glasses . 9 1.2.2 The Crystal-to-Glass Transition . 12 1.2.3 Particle Shape affects Glass Properties . 13 1.3 Disordered Clusters . 15 1.4 Technical Advances . 16 1.4.1 Rapid Quenching of Microgel Particle Liquids . 18 1.4.2 Measurement of Phonon Modes for Anisotropic Particles . 19 viii 1.4.3 Theory of Buckled Quasi-2D Membranes . 20 1.5 Organization . 21 2 Coffee Ring Effect Undone by Shape Dependent Capillary Interactions 23 2.1 Introduction . 23 2.2 Method and Materials . 26 2.3 Capillary Interactions . 28 2.4 Evaporation of Colloidal Suspensions . 31 2.4.1 Characterization of Particle Deposition . 33 2.4.2 Characterization of Evaporation Process . 34 2.4.3 Particle Behavior during Evaporation . 37 2.4.4 Adsorption Position . 43 2.4.5 Single Particle Trajectories . 43 2.5 Final Distribution of Other Anisotropic Particles . 44 2.6 Mixtures of Spheres and Ellipsoids . 46 2.7 Future Directions . 47 3 Influence of particle shape on bending rigidity of colloidal monolayer membranes and particle deposition during droplet evaporation in confined geometries 48 3.1 Introduction . 48 3.2 Method and Materials . 50 3.3 Theory of Buckled Quasi-2D Membranes . 54 3.4 Dependence of Bending Rigidity on Particle Shape . 59 3.5 Particle Deposition in Confined Geometries . 61 ix 3.6 Mixtures of Spheres and Ellipsoids . 63 3.7 Summary . 65 4 Irreversible Rearrangements, Correlated Domains and Local Structure in Aging Glasses 66 4.1 Introduction . 66 4.2 Methods and Materials . 68 4.3 Rapid Quenching via Optical Heating . 69 4.4 Aging Dynamics . 71 4.5 Irreversible Rearrangements . 74 4.6 Aging Structure . 78 4.7 Packing Fraction Dependence . 84 4.8 Summary . 86 4.9 Future Directions . 88 5 Observation of the Disorder-Induced Crystal-to-Glass Transition 89 5.1 Introduction . 89 5.2 Methods and Materials . 90 5.3 Structural Quantities .
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