Structure and thermodynamics of flexible polymer gels

Abstract

Unlike the situation for polymer solutions, for swollen polymer networks, there is no generally accepted relation between the macroscopic osmotic properties and the scattering behavior. Complementary measurements involving osmotic and elastic observations, small angle neutron and x-ray scattering, as well as quasielastic light scattering, can, however, yield detailed information on the relationship between the structure and the thermodynamics in polymer gels. Here, we apply such a complementary investigation to two types of networks, differing in the mechanism of cross linking. The neutron scattering spectra of the gels contain two components, dynamic and static. The former is governed by the macroscopic osmotic and elastic moduli of the swollen network, and is associated with the thermodynamic concentration fluctuations. The static component of the scattered intensity is generated by local variations of the cross-link density. The amplitude of the static concentration fluctuations 〈δφ2〉/φ2 is determined by the detailed mechanism of the cross-linking procedure. Its concentration dependence can be expressed in terms of the same macroscopic osmotic and elastic variables as govern the thermodynamic properties of the gel.

Structure and swelling behaviour of hydrophilic epoxy networks investigated by SANS

“…We think that unlike the rest of the samples, this system is more homogeneous exhibiting dynamic and static fluctuations in density reflected in scattering profile which might be described by formulas given in Refs. [4,5].…”

“…SANS results obtained from neutral polymer networks swollen in good solvents [3][4][5][6][7][8][9][10] have shown that SANS intensity decays monotonously with increasing magnitude of scattering vector. In principle, the decay consists of two parts characterized by two correlation lengths.…”

Small angle x-ray scattering study on role of trapped entanglements in structure of swollen end-linked poly(dimethylsiloxane) networks

“…It is found that the gel 184F04 exhibits excess scattering in small q region relative to the solution of the uncross-linked precursor polymer, which implies the existence of a spatial long-range structure specific to the gel, as in the case of various gels reported earlier. [1][2][3][4][5][6][7][8][9][10] In comparison of the scattering profiles of each gel, a striking difference is observed between the two groups, the gels of M p у23 800 and M p р12 800, where M p is the number-average molecular mass of precursor PDMS. The M p dependence of the scattering curves among each group is much weaker relative to the large difference between the gels of M p ϭ12 800 and 23 800.…”

Small-angle neutron scattering study of nanophase separated epoxy hydrogels

“…At high q-region, this function behaves like q À2 due to random coil nature of polymer chains in blobs. Cross-linking of polymer chains into a network leads to the appearance of another, also monotonously decaying, contribution to the scattering intensity caused by fluctuations induced by network junctions [2][3][4][5][6][7][8][9] characterized by another correlation length, n s, n s > n d . Since both correlation lengths obtain values of 10-100 Å, the swollen polymer networks appear homogeneous on larger length scales.…”