Table Of Content

H i r s t Fundamentals of F Physical sciences u n d Soft a Soft materials such as liquid crystals, polymers, biomaterials, and colloidal m systems touch every aspect of our lives. Not surprisingly, the rapid growth e n of these fields over the past few decades has resulted in an explosion of soft t a matter research groups worldwide. Fundamentals of Soft Matter Science l Matter s introduces and explores the scientific study of soft matter and molecular self- o assembly, covering the major classifications of materials, their structure and f characteristics, and everyday applications. S o Designed for beginners to the field with a basic scientific background, this f Science t readable book emphasizes conceptual understanding, minimizing detailed M mathematical derivations. Each chapter is dedicated to a different group of soft materials, including liquid crystals, surfactants, polymers, colloids, and a soft biomaterials. Each subject is broken down into the essential concepts: t t material structures and physical characteristics, some simple theoretical ideas, e and important experimental methods. The book emphasizes commonly used r experimental techniques and practical applications. Full color illustrations and S photographs are incorporated throughout to help describe the systems and c key concepts. i e n c e Linda S. Hirst K11369 ISBN: 978-1-4398-2775-8 90000 www.crcpress.com 9 781439 827758 w w w. c r c p r e s s . c o m K11369_COVER_final_revised.indd 1 10/19/12 12:52 PM Fundamentals of Soft Matter Science Fundamentals of Soft Matter Science Linda S. Hirst With photography and illustrations by Trevor P. Hirst CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2013 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Version Date: 20130103 International Standard Book Number-13: 978-1-4665-9092-2 (eBook - PDF) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the valid- ity 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. 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Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com This book is dedicated my Dad, Bill Matkin, who inspired my love of books Contents Preface ............................................................................................................................................................................................................xiii Acknowledgments ..................................................................................................................................................................................xv About the Author ...................................................................................................................................................................................xvii About the Illustrator ...............................................................................................................................................................................xix Chapter 1 Introduction ....................................................................................................................................................................1 Learning Objectives ...................................................................................................................................................1 1.1 What Is Soft Matter? ....................................................................................................................................2 1.2 Basic Thermal Physics ................................................................................................................................3 1.2.1 Thermal Equilibrium ................................................................................................................3 1.2.2 Phase Transitions .......................................................................................................................4 1.2.3 Solids, Liquids, and Gases .....................................................................................................6 1.2.4 The Ideal Gas ................................................................................................................................7 1.3 Intermolecular Forces ................................................................................................................................9 1.3.1 The van der Waals Attraction ............................................................................................9 1.3.2 Hard Sphere Repulsion ........................................................................................................10 1.3.3 Electrostatic Forces ................................................................................................................11 1.3.4 The van der Waals Equation of State (for a Nonideal Gas) .............................11 1.3.5 Hydrophobic Effects and the Hydrogen Bond .....................................................11 1.4 Diffusion and Random Walks .............................................................................................................14 1.5 Self-Assembly ...............................................................................................................................................16 1.6 The Phase Diagram ...................................................................................................................................18 1.6.1 The Clausius–Clapeyron Equation ................................................................................20 1.7 Aggregation and Assembly .................................................................................................................21 1.7.1 Power Laws and Fractals.....................................................................................................22 1.8 Mechanical Properties of Soft Matter ............................................................................................25 1.8.1 Stress and Strain .......................................................................................................................26 Questions .......................................................................................................................................................................29 The Concept of Soft Materials and Their Characteristics ...................................................29 Review of Thermal Physics ...................................................................................................................30 Review the Mechanical Properties of Materials ......................................................................30 References ......................................................................................................................................................................31 Further Reading ..........................................................................................................................................................31 Chapter 2 Liquid Crystals ..............................................................................................................................................................33 Learning Objectives .................................................................................................................................................33 2.1 Introduction to Liquid Crystals ..........................................................................................................34 2.1.1 What Is a Liquid Crystal? .....................................................................................................34 2.2 Anisotropy in Liquid Crystals ...............................................................................................................34 2.3 The Order Parameter ...............................................................................................................................36 vii viii Contents 2.4 Thermotropic and Lyotropic Liquid Crystals .............................................................................36 2.5 Birefringence in Liquid Crystals .........................................................................................................36 2.6 Defect Textures ...........................................................................................................................................38 2.7 Thermotropic Liquid Crystal Phases ...............................................................................................39 2.7.1 The Nematic Phase ...............................................................................................................40 2.7.2 The Smectic Phases ...............................................................................................................41 2.7.3 Chirality in Liquid Crystals ..................................................................................................43 2.7.4 The Cholesteric Phase .........................................................................................................44 2.7.5 The Chiral Smectic Phases ................................................................................................46 2.7.6 Other Chiral Smectic Phases ............................................................................................47 2.7.7 The Bent-Core (Banana) Phases ......................................................................................49 2.7.8 Discotic Phases .........................................................................................................................50 2.8 Experimental Techniques ......................................................................................................................51 2.8.1 Deforming Liquid Crystals .................................................................................................51 2.8.2 Polarized Optical Microscopy ..........................................................................................52 2.8.3 Electro-optical Measurements ........................................................................................55 2.8.4 The Dielectric Properties of Liquid Crystals ............................................................55 2.8.5 The Fréedericksz Transition and Measurement of the Elastic Constants ......................................................................................................................56 2.8.6 X-ray Diffraction .......................................................................................................................58 2.8.7 Differential Scanning Calorimetry .................................................................................60 2.9 Applications of Liquid Crystals ...........................................................................................................62 2.9.1 Liquid Crystal Displays .........................................................................................................62 2.9.2 The Twisted Nematic Display ..........................................................................................64 2.9.3 Spatial Light Modulators .....................................................................................................65 2.9.4 Liquid Crystal Temperature Sensors ............................................................................65 Questions .......................................................................................................................................................................67 The Characteristics of Liquid Crystal Materials ........................................................................67 Anisotropy and Birefringence ............................................................................................................67 The Structure of Liquid Crystal Phases .........................................................................................68 Experimental Techniques and Liquid Crystal Technologies ............................................68 References ......................................................................................................................................................................69 Further Reading ..........................................................................................................................................................69 Chapter 3 Surfactants .....................................................................................................................................................................71 Learning Objectives .................................................................................................................................................71 3.1 Introduction ..................................................................................................................................................72 3.2 Types of Surfactants .................................................................................................................................72 3.3 Surface Tension and Surfactants ......................................................................................................74 3.4 Self-Assembly and Phase Behavior..................................................................................................77 3.4.1 The Micellar Phase and the Critical Micelle Concentration ...........................78 3.4.2 Other Surfactant Phases .....................................................................................................79 3.4.3 The Packing Parameter ........................................................................................................81 3.5 Membrane Elasticity and Curvature ...............................................................................................82 3.5.1 Bicontinuous Phases.............................................................................................................84 3.6 Applications of Surfactants ..................................................................................................................85 3.6.1 Detergents ...................................................................................................................................85 Contents ix 3.6.2 Detergent Foams.....................................................................................................................87 3.6.3 Emulsifiers and Emulsions ..................................................................................................88 3.6.4 Commercial Paints and Inks.............................................................................................90 3.6.5 Surfactants and Gel Electrophoresis ...........................................................................91 3.6.6 Lung Surfactant ........................................................................................................................91 3.7 Experimental Methods ...........................................................................................................................92 3.7.1 The Langmuir Trough ...........................................................................................................92 3.7.2 Measuring Surface Tension ..............................................................................................94 Questions .......................................................................................................................................................................95 Physical and Chemical Properties of Surfactants ...................................................................95 The Hydrophobic Effect .........................................................................................................................95 The Importance of Molecular Shape on Phase Structure and Membrane Curvature ...........................................................................................................95 References ......................................................................................................................................................................96 Further Reading ..........................................................................................................................................................96 Chapter 4 Polymers ..........................................................................................................................................................................97 Learning Objectives .................................................................................................................................................97 4.1 Introduction ..................................................................................................................................................98 4.2 Early Polymers ..............................................................................................................................................98 4.3 Polymer Structure ......................................................................................................................................99 4.4 Liquid Crystal Polymers .......................................................................................................................103 4.5 Polymer Solutions ...................................................................................................................................104 4.5.1 The Ideal Chain ......................................................................................................................105 4.5.2 Excluded Volume and Solvent Effects ....................................................................107 4.5.3 The Radius of Gyration ......................................................................................................108 4.5.4 Increasing the Concentration of a Polymer Solution .....................................108 4.5.5 Stretching a Polymer Chain: The Entropic Spring .............................................110 4.5.6 Polyelectrolytes ......................................................................................................................112 4.5.7 Polymer Gels ............................................................................................................................113 4.5.8 Hydrogels ...................................................................................................................................114 4.6 The Glassy and Polymer Melt Phases ...........................................................................................115 4.7 The Mechanical Properties of Polymers.....................................................................................117 4.8 Experimental Techniques ...................................................................................................................120 4.8.1 Scattering Techniques.......................................................................................................120 4.8.2 Polymer Spectroscopy ......................................................................................................122 4.8.2.1 Fourier Transform Infrared Spectroscopy .......................................123 4.8.2.2 Raman Spectroscopy ..................................................................................123 4.8.2.3 Nuclear Magnetic Resonance ................................................................124 Questions ....................................................................................................................................................................127 Polymer Architecture ............................................................................................................................127 Polymers in Solution .............................................................................................................................127 Experimental Methods ........................................................................................................................128 References ...................................................................................................................................................................128 Further Reading .......................................................................................................................................................128