Physica A 249 (1998) 245–252 Static inhomogeneities and dynamic uctuations of temperature sensitive polymer gels Mitsuhiro Shibayama ∗ , Shin-ichi Takata, Tomohisa Norisuye Department of Polymer Science and Engineering, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606, Japan Abstract The static inhomogeneities and dynamic uctuations in polymer gels have been studied by light scattering as a function of the gel preparation temperature, T prep, and the cross-link density. The light scattered intensity of polymer gels was decomposed to two parts; the intensities due to the thermal uctuations, I F, and the frozen inhomogeneities, IC. The analysis employing ensemble (〈··〉 E ) and time averaging (〈··〉 T ) of light scattered intensity disclosed that 〈IF〉 T (the thermal uctuations) depends neither on the cross-link density nor the temperature of gel preparation, but on the temperature of observation. On the other hand, 〈I C〉 E (the frozen inhomogeneities) is a function of both temperatures at preparation and at observation. This clearly shows that gel is matter with dynamic uctuations superimposed on the static frozen inhomogeneities. The latter are built-in inhomogeneities due to topological constraints of the gel by cross-linking formation. c  1998 Elsevier Science B.V. All rights reserved. 1. Introduction A polymer gel is a three-dimensional polymer chain network immersed in a sol- vent. Thus, the gel has both liquid-like and solid-like properties. The most distinguish- able properties of gels are the presence of shear modulus which allows the gel to be self-sustainable [1]. The shear modulus is generated by permanent cross-links which result in a frozen structure in the gel superimposed on the dynamic concentration uc- tuations. The cross-link inhomogeneities due to the frozen concentration uctuations have been studied more than two decades [ 2 – 4]. Scattering methods, such as light scattering, small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS), have been mainly employed, and several methods were proposed to decom- pose the liquid-like and solid-like components of the scattered intensity. The liquid-like component is subtracted by (i) assuming that the liquid-like component is the same * Corresponding author. 0378-4371/98/$19.00 Copyright c  1998 Elsevier Science B.V. All rights reserved PII S0378-4371(97)00472-X