Probe-SAXS on hydrogels under elongation

Abstract

We have investigated the effect of polymer/filler interaction on the displacements of silica nanoparticles in gels by introducing them into poly(N,N-dimethylacrylamide) gel (PDAM-NP gel) and polyacrylamide gel (PAM-NP gel). It is well known that PDAM chains are strongly adsorbed onto silica nanoparticles, while PAM chains are not. We carried out SAXS measurements on these gels under uniaxial elongation. Interestingly, we found that the SAXS scattering profiles of PDAM-NP and PAM-NP gels were totally different. A four-spot pattern was observed in the 2D structure factors of the PDAM-NP gel and was assigned to the movement of the nanoparticles in an affine way. On the other hand, as for the PAM-NP gel, a sharp peak was observed in the much lower q region than the prediction of affine deformation, indicating that the peak corresponds to the correlation peak of the high cross-linking region. These experimental findings may lead to the development of “probe-SAXS”, which is a new technology for detecting nano-order inhomogeneity in hydrogels.