Soft Matter PhysicsMohamed Daoud, Claudine E. Williams In a liquid crystal watch, the molecules contained within a thin film of the screen are reorientated each second by extremely weak electrical signals. Here is a fine example of soft matter: molecular systems giving a strong response to a very weak command signal. They can be found almost everywhere. Soft magnetic materials used in transformers exhibit a strong magnetic moment under the action of a weak magnetic field. Take a completely different domain: gelatin, formed from col lagen fibres dissolved in hot water. When we cool below 37°C, gelation occurs, the chains joining up at various points to form a loose and highly deformable network. This is a natural example of soft matter. Going further, rather than consider a whole network, we could take a single chain of flexible polymer, such as polyoxyethylene [POE = (CH CH O)N, 2 2 5 where N rv 10 ], for example, in water. Such a chain is fragile and may break under flow. Even though hydrodynamic forces are very weak on the molecular scale, their cumulated effect may be significant. Think of a rope pulled from both ends by two groups of children. Even if each girl and boy cannot pull very hard, the rope can be broken when there are enough children pulling. |
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2-dimensional acrylamide adsorbed adsorption aggregates alkane amphiphilic amphiphilic molecules behaviour bicontinuous bilayer bonds capillary characteristic chemical colloidal concentration constant contact angle contact line cosurfactant crystal curve deformation density dewetting diameter diffusion dilute dispersed distance droplet effect emulsion energy example fibre flocculation fluid forces fractal dimension function Gaussian curvature giant micelles glass transition hydrophobic increase interactions interface interfacial tension lamellar phase latexes layer length liquid macromolecules mean curvature medium membrane micellar micelles microemulsions microlatexes microscopic modulus molecular weight molecules monomer nucleation object observed obtained osmotic parameters percolation persistence length plane polymer polymerisation pressure properties radius random walk reaction region repulsive scale invariance shape shown in Fig smectic solid solubility solution solvent speed sphere spherical sponge phase spontaneous curvature stabilise stability structure surface tension surfactant suspension temperature thermal thickness threshold vesicles viscosity volume fraction wave vector wetting zero