Two dimensional colloidal assembly under an alternating electric field from introduction to structure

Two Dimensional Colloidal Assembly under an Alternating Electric Field: from Introduction to Structure LIU YU (B.Sc., Xiamen University) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF PHYSICS NATIONAL UNIVERSITY OF SINGAPORE 2008 Acknowledgements I would like to express my gratitude to my supervisors, Prof Liu Xiang-Yang, and A/P Janaky Narayanan for their instructive and patient supervision throughout this project I am also grateful to Dr Zhang Ke-Qin for the enlightening instructions I take this opportunity to express my gratitude to Dr Christina Strom who has contributed a lot through my PhD study I owe much to her for helping me throughout the period of my research by providing advice, support and editing the papers I gratefully acknowledge the financial supports from the National University of Singapore I also gratefully acknowledge the help and support of all my fellow lab mates, past and present, who have spent countless hours of insightful discussion I am pleased to thank all of you, Yanwei, Huaidong, Huiping, Dawei, Junying, Junxue, Jingliang, Perry, Junfeng, Du Ning, Rongyao, Yanhua, Tianhui, Zhou Kun, Gangqin, Xiaodan, Yang Zheng, Tingting, Wang Lei, Xiuzhong, Rongguo, Dai Liang, and Li Yang Special thanks are due to Mr Teo, Eric, and Michael for their support and i help throughout my research work, as well as many other close friends that could not fit in the available space I would like to thank those closest to me, especially Sun Han, Zhuang Ying, Xiaoju, Liu Yan, Guowen, Wang Peng, and aunt Zhang, whose presence helped me to complete my graduate work and made me feel at home, I extend them my deepest appreciation Last but not least, I would like to express my deepest gratefulness to my family, in particular, my mother Zhang Zhi-Min, my father Liu He-Ping, and my husband Xie Rong-Guo for their endless support and encouragement ii Table of Contents Acknowledgements Summary Publications i vi viii List of Tables ix List of Figures x Introduction 1.1 Colloidal System 1.2 Implications and Applications 1.3 Self-Assembly Strategies for Colloid Arrays 1.4 Review on 2D Colloidal Assembly under an Alternating Current Electric Field 13 1.5 Objectives 22 1.6 Scope and Summary 23 Techniques, Materials and Data Analysis 2.1 Experimental Techniques 25 25 iii 2.1.1 25 2.1.2 Zetasizer 28 2.1.3 Temperature Control System 31 2.1.4 Scanning Electron Microscope 31 Data Analysis 32 2.2.1 Radial Pair Correlation Function g 2D (r) 35 2.2.2 2.2 Experimental Setup Bond-orientational Correlation Function g6 (r) 35 Mechanism of 2D Colloidal Assembly under an AC Field 37 3.1 Introduction 37 3.2 Experiments and Data Analysis 39 3.3 Colloidal Assembly under an AC Field 41 3.3.1 Phase Behaviors of Colloidal Particles at different Zeta Potentials, Field Strengths and Frequencies 41 3.3.2 Effects of Ionic Strength and Salt Specificity 45 3.3.3 The Role Played by the Particle Size on Colloidal Assembly 48 3.4 Discussions 49 3.5 Summary 61 Colloidal Phase Transition Driven by Alternating Electric Field 62 4.1 Introduction 62 4.2 KTHNY Theory 63 4.3 A Frequency-driven KTHNY Phase Transition 64 4.4 Summary 69 iv Kinetics, Equilibrium Distribution, and Degree of Assembly Perfection 71 5.1 Introduction 71 5.2 Degree of Perfection of Colloidal Assembly and Equilibrium Distance 73 5.3 Kinetics and Equilibrium Distribution 75 5.3.1 Method to Perform Kinetics Measurements 75 5.3.2 5.4 Kinetics and Analysis 80 Investigation of the Effect of Field Strength and Particle Size on Colloidal Assembly 5.5 85 Summary 86 Fine Tuning of Equilibrium Distance of 2D Colloidal Assembly 6.1 Introduction 6.2 89 89 Non-Close Packed Arrays by the Combination of Frequency, Field Strength, and Temperature 91 6.2.1 Effect of Temperature on Colloidal Assembly 91 6.2.2 Non-Close Packed Arrays by the Combination of Frequency, Field Strength, and Temperature and Formation of Permanent Template 6.3 96 Summary 99 Conclusions and Future Work 101 7.1 Conclusions 101 7.2 Future work 104 References 108 v Summary The lateral assembly of charged, monodispersed colloidal particles into two dimensional (2D) ordered structures in the presence of an alternating current (AC) electric field has evoked much interest in the past two decades both experimentally and theoretically In this work, the transverse two-dimensional assembly of colloidal particles is studied by varying the frequency and field strength, in the absence and presence of an added electrolytes The variation of the translational and bond-orientational correlation functions with frequency suggests the existence of a hexatic phase in which the particles retain the remnants of the crystalline long-range orientational order, but has a liquidlike translational order The electrohydrodynamic (EHD) flow is analyzed in the light of the existing theoretical models put forward by Trau [16,43], and Sides [48, 81] et al It follows that the equilibrium distribution req of particles is considered to be the resultant of mainly two opposing forces-Stoke’s attractive force due to EHD flow, the repulsive screened Coulomb interaction, and dipoledipole repulsions between the colloidal particles The EHD flow is found to affect directly the particle aggregation, the equilibrium interparticle separation req , which was also considered as functions of ionic strength and ζ-potential vi In this aspect, the kinetics and equilibrium distribution (req ) of colloidal particles under an AC electric field are investigated by varying the frequency, field strength, and salt concentration The variation of the aggregation rate constant as well as the order/crystallinity of the lattice can be correlated to the variation of the equilibrium interparticle separation req within the frequency window for the 2D assembly Particle size, ionic concentration, and field strength also affect the mean equilibrium distance between neighboring particles, thus establishing that req can be used as a new criterion to examine the degree of perfection of a 2D colloidal assembly and the self-assembly process of colloidal particles The understanding gained may be found useful in the design of self-assembled templates using colloidal particles The effect of temperature on the transverse 2D colloidal assembly was also examined The dependence on temperature of the phase diagram of the equilibrium distance (req ) of the particles as a function of frequency was investigated which could be explained with the existing theoretical models based on electrohydrodynamic (EHD) flow Furthermore, a facile method was developed to reversibly modulate the lattice space of 2D colloidal assembly over a wide range of temperature and the frequency and strength of AC electric field Once the desired colloidal assembly formed, it could be permanently fixed by simply switching to a direct current (DC) electric filed The technique presented may find important applications in the field of photonic devices, chemical and biological sensors vii Publications [1] Yanwei Jia, Janaky Narayanan, Xiang-Yang Liu, and Yu Liu, “Investigation on the Mechanism of Crystallization of Soluble Protein in the Presence of Nonionic Surfactant” Biophysical Journal 89, 4245 (2005) [2] Yu Liu, Janaky Narayanan and Xiang-Yang Liu, “Colloidal Phase Transition Driven by Alternating Electric Field” J.Chem.Phys 124, 124906 (2006) [3] Yu Liu, Xiang-Yang Liu and Janaky Narayanan, “Kinetics and Equilibrium Distribution of Colloidal Assembly under an Alternating Electric Field and Correlation to Degree of Perfection of Colloidal Crystals” J.Phys.Chem.C 111, 995 (2007) [4] Yu Liu, Rong-Guo Xie and Xiang-Yang Liu, “Fine Tuning of Equilibrium Distribution Two Dimensional Colloidal Assembly under an Alternating Electric Field” Appl Phys Lett 111, 91, 063105 (2007) viii List of Tables 1.1 Classification of Colloids ix References [36] J Visser, Surface and Colloid Science 8, Wiley, New York (1976) [37] S M Yang, S G Jang, D G Choi, S 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Liu, Janaky Narayanan and Xiang-Yang Liu, ? ?Colloidal Phase Transition Driven by Alternating Electric Field? ?? J.Chem.Phys 124, 124906 (2006) [3] Yu Liu, Xiang-Yang Liu and Janaky Narayanan, “Kinetics... Mechanism of 2D Colloidal Assembly under an AC Field 3.1 Introduction The lateral assembly of charged, monodispersed colloidal particles into two dimensional (2D) ordered structures under an alternating. .. Yanhua, Tianhui, Zhou Kun, Gangqin, Xiaodan, Yang Zheng, Tingting, Wang Lei, Xiuzhong, Rongguo, Dai Liang, and Li Yang Special thanks are due to Mr Teo, Eric, and Michael for their support and