Table Of Content

Colloidal Active Matter What do bird flocks, bacterial swarms, cell tissues, and cytoskeletal fluids have in common? They are all examples of active matter. This book ex- plores how scientists in various disciplines, from physics to biology, have collated a solid corpus of experimental designs and theories during the last two decades to decipher active systems. The book addresses, from a multidisciplinary viewpoint, the field of active matter at a colloidal scale. Concepts, experiments, and theoretical models are put side by side to fully illuminate the subtilities of active systems. A large variety of subjects, from microswimmers or driven colloids to self-organized active fluids, are analysed within a unified perspective. Generic collective effects of self-propelled or driven colloids, such as motility-induced flocking, and new paradigms, such as the celebrated concept of active nematics in reconstituted protein-based fluids, are discussed using well-known experimental scenarios and recognized theories. Topics are covered with rigor and in a self-consistent way, reaching both practitioners and newcomers to the field. The diversity of topics and conceptual challenges in active matter have long hampered the chance to explore the field with a general perspective. This monograph, the first single-authored title on active matter, is intended to fill this gap by bridging disparate experimental and theoretical interests from colloidal soft matter to cell biophysics. Francesc Sagués Mestre, Universitat de Barcelona. Advances in Biochemistry and Biophysics This monograph series offers expert summaries of cutting edge topics across all areas of biological physics. Individual titles address such topics as molecular biophysics, statistical biophysics, molecular modeling, single-molecule biophysics, and chemical biophysics. The goal of the series is to facilitate interdisciplinary research by training biologists and biochemists in quantitative aspects of modern biomedical research and to teach key biological principles to advanced students in physical sciences and engineering. Pulling Rabbits Out of Hats Using Mathematical Modeling in the Material, Biophysical, Fluid Mechanical, and Chemical Sciences David Wollkind, Bonni J. Dichone Colloidal active matter Concepts, experimental realizations and models Francesc Sagués Mestre Colloidal Active Matter Concepts, Experimental Realizations, and Models Francesc Sagués Mestre First edition published 2023 by CRC Press 6000 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487-2742 and by CRC Press 4 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN CRC Press is an imprint of Taylor & Francis Group, LLC © 2023 Francesc Sagués Mestre Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information stor- age or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, access www.copyright. com or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. For works that are not available on CCC please contact mpkbookspermis- [email protected] Trademark notice: Product or corporate names may be trademarks or registered trademarks and are used only for identification and explanation without intent to infringe. ISBN: 978-1-032-28894-9 (hbk) ISBN: 978-1-032-29840-5 (pbk) ISBN: 978-1-003-30229-2 (ebk) DOI: 10.1201/9781003302292 Typeset in font CMR10 by KnowledgeWorks Global Ltd. Publisher’s note: This book has been prepared from camera-ready copy provided by the authors. To my dog and my cat. Contents Preface xi List of Figures xv Symbols xix 1 Introduction 1 2 Fundamental Concepts: Isotropic and Anisotropic Colloidal Suspensions 3 2.1 Isotropic Dilute Suspensions . . . . . . . . . . . . . . . . . . 5 2.1.1 Microscopic Colloidal Behavior: Diffusion, Sedimentation and Random Walk Models . . . . . . . 5 2.1.2 The Boundary Layer Concept: Electrically Charged Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.3 Effects of Polymers on Colloidal Stability . . . . . . . 10 2.2 Anisotropic Dense Suspensions: Colloidal Liquid Crystals . . 12 2.2.1 The Role of Colloid Shape and Concentration . . . . . 12 2.2.2 Basic Concepts of Liquid Crystals: Phases and Order Parameter . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.2.3 Long- and Short-Range Order: Orientational Distortions and Defects . . . . . . . . . . . . . . . . . 16 2.3 A Composite System: Nematic Colloids . . . . . . . . . . . . 18 3 Particle-based Active Systems 23 3.1 Self-propelled Swimmers . . . . . . . . . . . . . . . . . . . . 25 3.1.1 Self-phoretic Swimmers and their Active Brownian Particle (ABP) Models. . . . . . . . . . . . . . . . . . 26 3.1.1.1 General Concepts . . . . . . . . . . . . . . . 26 3.1.1.2 Experimental Realizations of Phoretic Swimmers. . . . . . . . . . . . . . . . . . . . 29 3.1.1.3 Basic Statistical Properties of Self-phoretic Swimmers: Diffusion and Sedimentation . . . 32 3.1.1.4 The Active Brownian Model . . . . . . . . . 34 3.1.2 Swimmers Based on Marangoni Flows . . . . . . . . . 38 3.1.3 Biological Microswimmers . . . . . . . . . . . . . . . . 40 3.1.3.1 Flagellated Bacteria . . . . . . . . . . . . . . 40 vii viii Contents 3.1.3.2 Other Biological Microswimmers . . . . . . . 41 3.2 Colloids Driven to Swim . . . . . . . . . . . . . . . . . . . . 42 3.2.1 Magnetic Forcing . . . . . . . . . . . . . . . . . . . . . 42 3.2.1.1 A Doublet Roller. . . . . . . . . . . . . . . . 43 3.2.1.2 A Magnetically Driven Magnetic Snake . . . 46 3.2.1.3 Magnetic Spinners . . . . . . . . . . . . . . . 47 3.2.2 Electric Forcing: Quincke Rollers under DC Driving . 50 3.2.3 ElectricForcing:ClassicalFixed-ChargeElectroosmotic Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3.2.4 Induced-Charge Electrophoresis under AC Driving . . 55 3.2.4.1 Induced-Charge Electrophoresis . . . . . . . 55 3.2.4.2 Liquid Crystal-Enabled Electrophoresis . . . 57 3.2.4.3 AnomalousStatisticalCharacteristicsofDriven Nematic Colloids . . . . . . . . . . . . . . . . 61 3.3 Brief Commented List of Selected Review Papers . . . . . . 67 4 Protein-based Active Fluids 71 4.1 Active Gels Based on Filamentary Proteins . . . . . . . . . . 72 4.1.1 Active Gels Based on Actin Filaments . . . . . . . . . 72 4.1.2 Active Gels Based on Microtubules . . . . . . . . . . . 73 4.1.2.1 Historic Antecedents . . . . . . . . . . . . . . 73 4.1.2.2 The Brandeis Approach . . . . . . . . . . . . 74 4.2 Two-dimensional Active Nematics . . . . . . . . . . . . . . . 77 4.2.1 Active Nematics Based on Microtubules . . . . . . . . 77 4.2.2 Active Nematics Based on Actin Filaments . . . . . . 83 4.3 The Effect of the Interface on Two-Dimensional Active Nematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.3.1 Aqueous Active Nematics Interfaced with Isotropic Oils 84 4.3.2 Aqueous Active Nematics Interfaced with Anisotropic Oils . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 4.4 Effects of Spatial Confinement . . . . . . . . . . . . . . . . . 93 4.4.1 Encapsulated Active Nematics . . . . . . . . . . . . . 93 4.4.2 Geometric Confinement of Active Nematics . . . . . . 99 4.4.3 A New Concept: Active Boundary Layers . . . . . . . 103 4.4.4 Geometric Confinement of Active Gels . . . . . . . . . 106 4.5 Recent Advances in the Preparation of Active Gels and Active Nematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5 Emerging Concepts in Active Matter 115 5.1 Dynamic Clustering and Swarming Behavior . . . . . . . . . 116 5.1.1 Experimental Observations of Dynamic Clustering . . 117 5.1.2 Modeling Approaches to Clustering of Microswimmers 121 5.2 Motility-Induced Phase Separation . . . . . . . . . . . . . . . 122 5.3 Active Turbulence . . . . . . . . . . . . . . . . . . . . . . . . 128 5.4 Thermodynamic Concepts in Active Matter . . . . . . . . . . 132 Contents ix 5.4.1 Active Temperature . . . . . . . . . . . . . . . . . . . 132 5.4.2 Active Pressure . . . . . . . . . . . . . . . . . . . . . . 133 6 Modeling Active Fluids 139 6.1 Linearized Leslie-Ericksen Theories for Active Polar Fluids . 140 6.1.1 General Scheme of Equations . . . . . . . . . . . . . . 141 6.1.2 Analysis of +1 Defects: Asters, Vortices, and Spirals . 146 6.1.3 Activity-Induced Flows from Aligned States . . . . . . 148 6.1.4 MinimalVersionforaTwo-DimensionalActiveNematic in Absence of Flow-Alignment . . . . . . . . . . . . . 151 6.2 A Beris-Edwards Approach to Model Active Nematics . . . . 155 6.2.1 General Scheme of Equations . . . . . . . . . . . . . . 155 6.2.2 A Simplified Analysis of Defect Dynamics . . . . . . . 157 6.2.3 Theoretical Description of Active Nematic Turbulence 160 6.3 Modeling Interfaced Active Fluids . . . . . . . . . . . . . . . 163 6.4 Modeling Confined Active Fluids . . . . . . . . . . . . . . . . 171 6.4.1 Modeling Active Flows in Thin Films and Droplets . . 171 6.4.1.1 Thin Active Films . . . . . . . . . . . . . . . 171 6.4.1.2 Active Droplets . . . . . . . . . . . . . . . . 174 6.4.2 Modeling Active Flows under Geometric Confinement 179 6.5 Brief Commented List of Selected Review Papers . . . . . . 183 7 Concepts and Models for Dry Active Matter 187 7.1 Hydrodynamic-like Theories . . . . . . . . . . . . . . . . . . 189 7.1.1 Flocking of Active Polar Particles. . . . . . . . . . . . 189 7.1.1.1 Giant Number Fluctuations . . . . . . . . . . 192 7.1.2 Particles Interacting Nematically on a Substrate . . . 194 7.1.3 Self-Propelled Rods with Nematic Alignment . . . . . 197 7.2 Microscopic-like Theories . . . . . . . . . . . . . . . . . . . . 199 7.2.1 Particle-Based Models for Dry Systems . . . . . . . . 199 7.2.2 Common Rationale: Phase-Separated Regimes . . . . 202 7.2.3 Specific Class-Dependent Features . . . . . . . . . . . 203 7.2.3.1 Traveling Bands in Polar Class . . . . . . . . 203 7.2.3.2 Unstable Nematic Bands . . . . . . . . . . . 204 7.2.4 Properties of the Liquid Ordered Phase . . . . . . . . 205 8 Appendix 1: Microswimming in Constrained and Disordered Environments 207 8.1 Microswimming under Constrained Motion . . . . . . . . . . 207 8.2 Microswimming under the Effects of Noise and Disorder . . . 211 9 Appendix 2: Microswimming in Complex Fluids 217 9.1 Motion of Microorganisms in Complex Fluids . . . . . . . . . 217 9.2 Artificial Microswimmers Performing in Complex Fluids . . . 219 9.3 Theoretical Approaches to Microswimming in Complex Fluids 222