Premium
Characterization of thermo‐reversible gels by means of sedimentation equilibria
Author(s) -
Borchard Werner,
Cölfen Helmut
Publication year - 1992
Publication title -
makromolekulare chemie. macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 0258-0322
DOI - 10.1002/masy.19920610112
Subject(s) - swelling , polymer , thermodynamics , isotropy , materials science , flory–huggins solution theory , polymer chemistry , composite material , physics , quantum mechanics
Abstract This paper describes the deformation of gels in a centrifugal field leading to a continuous equilibrium. A gel is considered to be a binary mixture of cross‐linked polymer and solvent and is assumed to remain isotropic during the deformation. From the equation for the osmotically effective pressure, called swelling pressure, the thermodynamic properties of a gel can be calculated. For highly swollen gels the expression of Svedberg and Pedersen is obtained. It is shown that the complete concentration dependence of the swelling pressure in the concentration range of the maximally swollen gel up to that at the cell bottom can be measured in a single equilibrium experiment. The homogeneity of weakly cross‐linked gels can be examined by means of the method described. Soluble parts which are not incorporated into the polymer network can also be detected if they are present. From the swelling pressure‐concentration curves it is possible to derive the thermodynamic properties of the physically crosslinked gelatin/water gels that were investigated. These gels can be described by means of a slightly modified Flory‐Huggins equation with an interaction parameter χw in the weight fraction scale, which depends linearly on concentration. The interaction parameters show a dependence on concentration which is explained by an increased branching and crosslinking of the polymer with increasing initial polymer concentration of the gels. At low initial polymer concentration, the primary chains have to aggregate to build up relatively long chains between the network junctions. The static shear modulus G which can be calculated from the network term has the same order of magnitude as the real part of the complex shear modulus which is measured at low frequency.