Soft matter
[2] Pierre-Gilles de Gennes, who has been called the "founding father of soft matter,"[3] received the Nobel Prize in Physics in 1991 for discovering that methods developed for studying order phenomena in simple systems can be generalized to the more complex cases found in soft matter, in particular, to the behaviors of liquid crystals and polymers.
[10] In 1920, Hermann Staudinger, recipient of the 1953 Nobel Prize in Chemistry,[11] was the first person to suggest that polymers are formed through covalent bonds that link smaller molecules together.
[12] The idea of a macromolecule was unheard of at the time, with the scientific consensus being that the recorded high molecular weights of compounds like natural rubber were instead due to particle aggregation.
[14] Together, they postulated that the chemical stability, ease of deformation, and permeability of certain polymer networks in aqueous environments would have a significant impact on medicine, and were the inventors of the soft contact lens.
[18] By way of contrast, in hard condensed matter physics it is often possible to predict the overall behavior of a material because the molecules are organized into a crystalline lattice with no changes in the pattern at any mesoscopic scale.
Unlike hard materials, where only small distortions occur from thermal or mechanical agitation, soft matter can undergo local rearrangements of the microscopic building blocks.
[20] The ease of deformation and influence of low energy interactions regularly result in slow dynamics of the mesoscopic structures which allows some systems to remain out of equilibrium in metastable states.
[20] Self-assembly can be classified as static when the resulting structure is due to a free energy minimum, or dynamic when the system is caught in a metastable state.
[18][27] Soft materials often exhibit both elasticity and viscous responses to external stimuli[22] such as shear induced flow or phase transitions.
[1][28] Soft matter becomes highly deformed before crack propagation, which differs significantly from the general fracture mechanics formulation.
[23][32] Foams have found applications in insulation and textiles,[32] and are undergoing active research in the biomedical field of drug delivery and tissue engineering.
[33][34] Research into functionalizing gels that are sensitive to mechanical and thermal stress, as well as solvent choice, has given rise to diverse structures with characteristics such as shape-memory,[35] or the ability to bind guest molecules selectively and reversibly.
[37] Liquid crystals can consist of proteins, small molecules, or polymers, that can be manipulated to form cohesive order in a specific direction.
[22] Biological systems, such as protein crystallization, are often investigated through X-ray and neutron crystallography,[41] while nuclear magnetic resonance spectroscopy can be used in understanding the average structure and lipid mobility of membranes.
[42] Computational methods are often employed to model and understand soft matter systems, as they have the ability to strictly control the composition and environment of the structures being investigated, as well as span from microscopic to macroscopic length scales.
[42] Liquid crystals are often probed using polarized light microscopy to determine the ordering of the material under various conditions, such as temperature or electric field.
Liquid crystals, for example, were originally discovered in the biological sciences when the botanist and chemist Friedrich Reinitzer was investigating cholesterols.
[27] Due to their stimuli responsive behavior, 3D printing of hydrogels has found applications in a diverse range of fields, such as soft robotics, tissue engineering, and flexible electronics.
