Mechanical Properties of Soft Matter

When we introduced the concept of soft matter at the beginning of this chapter, different types of household materials were given as examples. It is impossible to classify common materials like Jell-O, toothpaste, or soap as a simples solid or liquid since they fall somewhere between the two. These and other soft materials are easily deformable—their mechanical properties are different from a solid, but neither are they exactly liquids. If we want to describe different types of soft matter in terms of their mechanical properties, then we need to review our definition of softness. The ability of a material to deform when subjected to an applied force can be described in terms of measurable physical parameters such as stress and strain. 

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Di Michele L, Varrato F, Fiocco D, Sastry S, Eiser E, Eoffi G. Aggregation dynamics, structure, and mechanical properties of bigels. Soft Matter. 2014 10(20) 3633-3648. 

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Kumachev A, Tumarkin E, Walker GC, Kumacheva E (2013) Characterization of the mechanical properties of microgels acting as cellular microenvironments. Soft Matter 9 2959-2965... 

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Porter, D., Vollrath, F. and Shao, Z., Predicting the mechanical properties of spider silk as a model nanostructured polymer. Eur. Phys. J. E. Soft Matter, February 2005,16(2) ... 

The continuum theories of mechanical properties of orientationally ordered soft matter, such as liquid crystals, can be developed in close analogy to solid crystals, but it is necessary to extend the usual formalism. In addition to the usual translational displacements, which describe deformation in solids, one also has to consider the displacements that correspond to rotations of alignment axes. The situation is schematically illustrated in Figure 4.1. 

Review basic physical concepts relevant to the study of soft matter, including basic thermal physics, intermolecular forces, and the mechanical properties of materials. 

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Choi J, Hui CM, Pietrasik J, Dong H, Matyjaszewski K, Bockstaller MR (2012) Toughening fragile matter mechanical properties of particle solids assembled from polymer-grafted hybrid particles synthesized by ATRP. Soft Matter 8(15) 4072-4082... 

Indeed, one matter of concern in the development of new polymer ionic membranes lies in the fact that their high conductivity is often associated with amorphous, low-viscosity phases. Therefore, in their conductive form, these membranes behave like soft solids with poor mechanical stability their direct use in LPBs may give rise to those problems commonly met in conventional liquid electrolyte systems, such as leakage, loss of interfacial contacts and short circuits. Under these circumstances, one of the most useful feature of LPBs, namely the solid-state configuration, would then be lost. Consequently, it is of key importance to assure that the polymer electrolyte membrane maintains good mechanical properties even in its conductive state. 

To mimic the mechanical behavior of the native tissue is a basic assumption to facilitate the biointegration and function of the substitute. Incorporation of fibers to the biomaterial matrix opens the way to inhomogeneity, anisotropy, nonlinearity, and viscoelasticity features. Provided that interfacial binding between matrix and fibers in the composite goes on, mechanical properties could be tailored by varying the amount and orientation of fibers embedded, to suit the purpose applications, whether it s related to hard or soft tissue substimtes. Individual fibers, no matter how small and isolated compared to fibrous structure, could affect mechanical properties. To be effective, fibers principal direction should be considered and controlled. 

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