Ivan I. Smalyukh

Soft Condensed Matter Physics

Department of Physics &

Liquid Crystals Materials Research Center

University of Colorado at Boulder

http://www.colorado.edu/physics/SmalyukhLab/SoftMatter/

Soft Condensed Matter Physics "Soft Condensed Matter Physics " is a course about

the science of liquid crystals, polymers, plastic crystals, biological membranes, biopolymers, block copolymers, molecular monolayers, colloids, nanoparicle suspensions, emulsions, foams, gels, elastomers, ferrofluids, granular materials, cells, tissues, filamentous networks, electro-rheological fluids, paints, foods, inks, cosmetics and other soft materials.

Is there something in common between these very different soft matter systems? 2

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Pierre-Gilles de Gennes (Nobel prize in physics 1991): ”All physicochemical systems that have large response functions.”(i.e., a mild external influence has a big effect) Helmut Möhwald (Editorial board member, Soft Matter): ”Materials that are held together by non-covalent interactions. These interactions are typically weak, often on the order of kT and thus comparable to entropic forces.”

Richard A. L. Jones, in Soft Condensed Matter: ”Materials in states of matter that are neither simple liquids nor crystalline solids of the type studied in other branches of solid state physics.”

Before tackling actual complex soft matter systems, we need to understand (amongst other things) these response functions, non-covalent interactions and entropic forces.

What do we mean by Soft Condensed Matter?

•  The term usually refers to states of matter which are neither simple liquids nor crystalline solids.

•  Includes many familiar types of matter – soap, yoghurt, paint, liquid crystals, putty….but also much of our bodies including cell membranes and the cytoplasm inside.

•  In general we will be dealing with lengthscales intermediate between atomic and macroscopic; these are often known as mesoscopic.

•  Quantum mechanics will not therefore be very useful; the predominant techniques we will use will be statistical.

•  Mean field theories will be found to be useful, as you have seen before, to describe the behaviour of large numbers of molecules.

•  Although dealing with ensembles of molecules, we will find that thermal energy is comparable with the energies giving rise to distortion and interaction energies, so Brownian motion and fluctuations are important.

•  This is a key difference with 'hard condensed matter' for which thermal fluctuations are not important.

What do we mean by Soft Condensed Matter?

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Liquid Crystals (LCs)

n̂

Average local molecular orientations in liquid crystals are described by the director with head-tail symmetry nn ˆˆ −≡

Crystal liquid crystal Isotropic fluid

→ Flow like liquids; → Anisotropic like solid crystals; CN

Nematic liquid crystal

n

director

n

director

Only orientational order (crystal), no positional order (liquid)

center of mass locations

Nematic liquid crystal

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Very useful soft materials → Response to tiny external fields

J. Hwang et al., Nature materials 4, 383 (2005)

→ Periodic structure of molecular orientations with a defect layer.

→ Learning from nature: soft materials are useful for a variety of applications;

Fujicake, Sato, & Murashige, Tokyo, Japan.

→ Flexible displays

~E

kHzf 1~

Vvoltage 1~

Flat Panel LCD TVs – just an example

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Plastic Crystals – no orientational order

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Colloids •  Colloids are systems in which one of the systems (at least) has dimensions

of ~1µm or less. •  Thus many aspects of nanotechnology are essentially colloidal.

•  Examples: Solid in liquid such as Indian

Ink or sunscreen Suspension Liquid in Liquid such as

mayonnaise or salad dressing Emulsion Gas in Liquid such as beer or

soap foam Foam

Gas in Solid such as bath sponge or ice cream

Sponge

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Semi-flexible biopolymers

2 – 30 micron length 7-8 nm in diameter

~ 16 micron persistence length

Actin Wormlike Micelle ( polybutadiene-polyethyleneoxide )

10 – 50 micron length ~ 15 nm in diameter

~ 500 nm persistence length

DNA

16 micron length 2 nm in diameter

40 nm persistence length

Neurofilament

5 - 20 micron length 12 nm in diameter

~ 220 nm persistence length

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(1) Interactions / Forces • What are the interactions between constituents? • How do these interactions arise? • How do these interactions affect self-assembly, structure, dynamics, rheology, transport properties? (2) Self-Assembly / Collective Properties • Novel Phases (Equilibrium Statistical Physics) • Role of shape, charge, concentration, conformation, size, ... • Structure, Dynamics, Rheology, Optical Properties, ... • Beyond Equilibrium: Metastable phases, glasses, …

We are interested in understanding

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•  Soft Matter is susceptible to small external influences (”large response functions”) •  Has a complex microscopic structure, composition and internal dynamics •  Means such systems as colloids, polymers, liquid crystals,

surfactants, and biological matter

•  Exhibits a huge range of different time and length scales

•  Usually Entropy Dominates! (But not quantum mechanics!)

Unifying properties of soft matter

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Useful Books (1) P.M. Chaikin & T.C. Lubensky, Principles of Condensed Matter Physics (Cambridge Univ.

Press, 2000); (2) R.G. Larson, The Structure and Rheology of Complex Fluids (Oxford Univ. Press, 1999); (3) P-G de Gennes and J. Prost, The Physics of Liquid Crystals (Clarendon, Oxford, 1993),

2nd Ed. (4) R.A.L. Jones, Soft Condensed Matter (Oxford Univ. Press, 2003); (5) I. W. Hamley, Introduction to Soft Matter (Wiley, 2000); (6) M. Kleman and O. Lavrentovich, Soft Matter Physics: an introduction (Springer, 2003); (7) M. Daound and C.E. Williams (eds.), Soft Matter Physics (Springer, 1999); (8) P. Oswald and P. Pieranski, Nematic and Cholesteric Liquid Crystals (Taylor & Francis,

2005); (9) P. Oswald and P. Pieranski, Smectic and Columnar Liquid Crystals (Taylor & Francis,

2006).

Additional Texts 1.  RAL Jones Soft Condensed Matter OUP 2002 2.  D Tabor Gases, Liquids and Solids, 3rd ed CUP 1991 3.  M Daoud and CE Williams, Soft Matter Physics, Springer 1999 4.  IW Hamley, Introduction to Soft Matter, Wiley 2000 5.  P Nelson, Biological Physics, Freeman 2003 6.  KW Dill and S Bromberg, Molecular Driving Forces, Garland Science 2003 7.  SA Safran, Statistical Thermodynamics of Surfaces, Interfaces and Membranes, Addison Wesley 1994 8.  M Daune, Molecular Biophysics, OUP 1999 9.  JN Israelachvili Intermolecular and Surface Forces, Academic 1985 10.  M Rubenstein and R Colby Polymer Physics,OUP 2003 11.  PG de Gennes, F Brochard-Wyart and D Quéré, Capillarity and Wetting Phenomena Springer 2002 12.  ME Cates and MR Evans, Soft and Fragile Matter, IoP 2000 13.  IM Ward Mechanical Properties of Solid Polymers, Wiley 1983 14.  IM Ward and J Sweeney, An Introduction to the Mechanical Properties of Solid Polymers, Wiley 2004 15.  S Vogel Life in Moving Fluids Princeton 1994 16.  RAL Jones Soft Machines OUP 2004 17.  J Goodwin Colloids and Interfaces with Surfactants and Polymers Wiley 2004 18.  M Doi Introduction to Polymer Physics OUP 1992 19.  R Balescu Statistical Dynamics, Imperial College Press 1997 20.  D Boal Mechanics of the Cell, CUP 2002 21.  DC Bassett Principles of Polymer Morphology CUP 1981 22.  AM Donald, AH Windle and S Hanna, Liquid Crystalline Polymers, CUP 2006 23.  JR Waldram, The theory of thermodynamics 24.  WCK Poon and D Andelman, eds, Soft Condensed Matter Physics in Molecular and Cell Biology, Taylor and

Francis 2006