Physica A 249 (1998) 262–265 Gels under strong deformation Ken Sekimoto Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto, 606-01, Japan Abstract Polymer gel serves as a model system which represents many aspects of static and dynamic processes in solids in an amplied manner both spatially and temporaly. We will give a brief overview of those aspects and refer to the recent topics on the subjects. c  1998 Elsevier Science B.V. All rights reserved. PACS: 62.20.Mk; 82.70.Gg; 77.80.Dj; 02.40.Pc Keywords: Fracture; Gel; Hysteresis; Topology 1. Strong deformation in one-dimensional space Polymer gel is an ideal system in which we can observe a variety of physical and chemical phenomena in an exaggerated manner. Phase transition occurs with an enor- mous change of sample volume at around room temperature and at ambient pressure [1]. Such enhanced response of gels can be attributed to the property of a single polymer chain of high degree of polymerization N 1; i.e., the coil–globule transition. Strong static heterogeneity of swollen gel and the related inverse buttery scattering anisotropy upon deformation of the gel, observed through small angle neutron scatter- ing [2,3], was explained by the enhanced response of the local volume of gels upon swelling or anisotropic loading [4,5]. These are the phenomena which one can basically understand by considering a one-dimensional caricature of gel, using a density function of gel as a function of only, say x-coordinate. 2. Strong deformation in two-dimensional space Among the phenomena caused by large deformation of gels, there are certainly a group which can be understood only in higher spatial dimensionalities. Buckling of the surface region of gels upon strong swelling [6,7] is a typical example: Since the gel can only swell from its surface, absorbing the surrounding solvent, the lateral deformation 0378-4371/98/$19.00 Copyright c  1998 Elsevier Science B.V. All rights reserved PII S0378-4371(97)00474-3