Clemson University TigerPrints All Dissertations Dissertations 8-2018 Wetting of Bio-Inspired Complexly-Shaped Fibers and Channels Chengqi Zhang Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_dissertations Recommended Citation Zhang, Chengqi, "Wetting of Bio-Inspired Complexly-Shaped Fibers and Channels" (2018). All Dissertations. 2172. https://tigerprints.clemson.edu/all_dissertations/2172 This Dissertation is brought to you for free and open access by the Dissertations at TigerPrints. It has been accepted for inclusion in All Dissertations by an authorized administrator of TigerPrints. For more information, please contact [email protected]. TITLE WETTING OF BIO-INSPIRED COMPLEXLY-SHAPED FIBERS AND CHANNELS A Dissertation Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Materials Science and Engineering by Chengqi Zhang August 2018 Accepted by: Dr. Konstantin G. Kornev, Committee Chair Dr. Igor Luzinov Dr. Olga Kuksenok Dr. Ulf D. Schiller i ABSTRACT This Dissertation is centered on studying the wetting of complexly-shaped fibers and channels which is inspired by the Lepidopteran proboscis. From materials science and engineering standpoint, the Lepidopteran proboscis is a multifunctional microfluidic device. The unique materials organization, morphology, structure, and surface properties of the proboscis allows the Lepidopterans to feed on various food sources from highly viscous to very thin liquids while keeping its surface clean. Thus, the study on the proboscis wetting phenomena has drawn great interests of materials scientists and engineers. The shape of the Lepidopteran proboscis has a very special design combining complexly- shaped fibers and channels. However, it remains unknown how this unique shape benefits the multiple functions of the proboscis. In this Dissertation, we investigate the effect of shape on the wetting properties of proboscis by separately studying the wetting of complexly-shaped fibers and channels, and then, applying the gained knowledge to explain various wetting phenomena observed on the Lepidopteran proboscis. In Chapter I, the definition of wetting is introduced and the fundamental studies on wetting of fibers and channels are reviewed. Then the structure and function of Lepidopteran proboscis is introduced, and the motivation for conducting the research in this Dissertation is explained. In Chapter II, several wetting phenomena on the ribbon-like fiber, e.g. the morphological transitions of droplet configurations, stability of coating films, capillary rise ii of menisci on ribbon-like fiber, and wetting of the ribbon rail are studied experimentally and theoretically. This study sets up the foundation for investigating the wetting phenomena of other complexly-shaped fibers and channels. The developed experimental and theoretical methods are actively used throughout this Dissertation. In Chapter III, the instability of a thin coating film on the internal and external walls of a straight hollow elliptical fiber is studied, and the mechanisms of drop formation from the coating films and the droplet morphology is briefly discussed. Then the study is expanded to the ring made of a curved elliptical tube to cover a broad range of wetting phenomena associated with such complexly-shaped fibers by discussing the effect of ring radius of curvature and the cross-sectional ellipticity. In Chapter IV, a new method for studying the wetting of complexly-shaped channels is developed based on the Princen theory, and examined with the V-shaped channel. Then, the wetting/dewetting of C-shaped channel is systematically studied both experimentally and theoretically. In Chapter V, several wetting phenomena associated with the Lepidopteran proboscises, e.g. the food uptake from a pool of liquid or from a limited volume of liquid, the stability of liquid films deposited on proboscis after dipping it into a nectar source, and self-assembly of proboscis after the insect emerges from the pupa, are discussed based on the study of wetting of complexly-shaped fibers and channels. All the results are summarized in Chapter VI. iii DEDICATION This Dissertation is dedicated to my family for their support and encouragement throughout my PhD study. iv ACKNOWLEDGMENTS First of all, I would like to thank my advisor, Dr. Konstantin Kornev, for his guidance, patience and encouragement during my PhD study at Clemson University. His passion about science, broad knowledge in multiple disciplines, ingenious insights on research, and hard work certainly inspired and helped me grow as a scientist. I would also like to express my gratitude to my committee members, Dr. Igor Luzinov, Dr. Olga Kuksenok, and Dr. Ulf Schiller for their valuable comments, suggestions and time. I want to thank all the past and current group members, in particular, Dr. Vladislav Vekselman, Pavel Aprelev, Golnaz Tomaraei, Salahuddin Kabir, Luke Sande, Dr. Arthur Salamatin, Tatiana Stepanova, Vaibhav Palkar, Yueming Sun, Bochuan Sun for their help and support during this journey. I also very thankful to Mykhailo Savchak for the help on silanization, and Dr. Peter Adler and his group members, Dr. Charles Beard and Ms. Suellen Pometto for their help with research on butterflies and moths. I would also like to thank Dr. Gary Lickfield, Kimberly Ivey, James Lowe, Stanley Justice, Diane Swope and all other faculty and staff members of MS&E department for their continuous support. I would like to thank all my close friends especially Liying Wei and her husband Yuqi Zeng, Ying Yang, Yawei Wei, Zhaoxi Chen, Yuzhe Hong for making my life enjoyable and memorable at Clemson. Last but certainly not least, I would like to thank my parents. No words can ever describe my gratefulness for your unwavering support and encouragements. You are the greatest parents in the World. v TABLE OF CONTENTS Page TITLE ............................................................................................................................... i ABSTRACT ..................................................................................................................... ii DEDICATION ................................................................................................................ iv ACKNOWLEDGMENTS ............................................................................................... v LIST OF TABLES ........................................................................................................ viii LIST OF FIGURES ......................................................................................................... x CHAPTER 1 Introduction ............................................................................................................... 1 1.1 Definition of wetting ..................................................................................... 1 1.2 Wetting of fibers ........................................................................................... 2 1.3 Wetting of channels ...................................................................................... 5 1.4 Lepidopteran proboscis as a microfluidic device consisting of complexly-shaped fibers and channels ......................................................... 7 1.5 Motivation ................................................................................................... 11 1.6 References ................................................................................................... 12 2 Wetting of ribbon-like fibers .................................................................................. 18 2.1 Introduction ................................................................................................. 18 2.2 Morphological transitions of droplet configurations on the ribbon-like fibers ........................................................................................................... 19 2.3 Capillary rise of menisci on ribbon-like fibers ........................................... 40 vi 2.4 Wetting of the ribbon rail ........................................................................... 47 2.5 References ................................................................................................... 57 3 Wetting of elliptical fibers ...................................................................................... 59 3.1 Introduction ................................................................................................. 59 3.2 Mathematical description of a thin film on an elliptical hollow fiber coiled in a circular ring ............................................................................... 60 3.3 Behavior of liquid films on straight elliptical hollow fiber ........................ 66 3.4 Behavior of liquid films on a ring coiled with elliptical hollow fiber ........ 79 3.5 Conclusions ................................................................................................. 92 3.6 References ................................................................................................... 93 4 Wetting of complexly-shaped channels .................................................................. 94 4.1 Introduction ................................................................................................. 94 4.2 Liquid column in the V-shaped channel ..................................................... 95 4.3 Liquid droplet morphology in the