Small-Angle Neutron Scattering Study of Swollen Elongated Gels:  Butterfly Patterns

Abstract

Polymer gels swollen in a good solvent and subjected to a uniaxial deformation have been studied by small-angle neutron scattering (SANS). In all the experiments, the solvent is deuterated; this is equivalent to deuteration of the entire network. The gels were studied at two degrees of swelling, Q: Q ) 11, which is very close to the preparation conditions (Qprep ) 10), and Q ) 23, which is very close to the equilibrium degree of swelling in pure solvent, Qe ) 24. For each degree of swelling several elongation ratios ranging from 1.0 to 1.8 are investigated. For a fixed polymer concentration, it is shown that the scattered intensity at small angles in the direction parallel to the elongation axis increases with increasing deformation while it decreases in the perpendicular direction. Consequently, the isointensity curves mapped on a bidimensional detector are 8-shaped with a major axis parallel to the elongation direction. Such anomalous scattering contours, which cannot be explained by the classical theories of network deformation, are called "butterfly patterns". The experimental results are compared with the predictions of three recent models that account for butterfly isointensity curves in a SANS experiment of swollen elongated gels.

Small-angle neutron scattering on polymer gels: phase behavior, inhomogeneities and deformation mechanisms

“…35 Deformation mechanisms of polymeric systems have been studied by SANS. [47][48][49][50] Although SANS is a suitable means to study the deformation mechanisms of polymeric systems, chucking a polymer gel onto a stretching device is difficult in most cases because of its fragility. Geissler et al 51 used a mold with an elliptical hole and allowed a shrunken gel to swell anisotropically.…”

Concentration fluctuations in polymer gel investigated by neutron scattering: Static inhomogeneity in swollen gel

“…15,24,[29][30][31][32] This is due to the static inhomogeneity, originating from the heterogeneous crosslink density.…”

Deformation Studies on Polymer‐Clay Nanocomposite Gels

“…These lobe patterns are commonly observed in chemically cross-linked gels (chemical gels, OR gels) and are called ''abnormalbutterfly pattern''. [7] These patterns are ascribed to an increase of inhomogeneities due to non-random cross-linking in gels that become explicit by deformation.…”

“…Both of these findings indicate that the structure of NC gels is very different from chemical gels. Since frozen inhomogeneities are amplified by deformation, [7] such as stretching and swelling, it is advantageous to investigate NC gels in a deformed state.…”