SANS Studies on Spatial Inhomogeneities of Slide-Ring Gels

Slide-ring gels (SR gel) [previously termed as topological or polyrotaxane gels: Okumura, Y.; Ito, K. Adv. Mater . 2001, 13, 485] have remarkable physical properties, such as large extensibility and mechanical strength. The SR gels are cross-linked polyrotaxane (PR) consisting of poly(ethylene glycol) (PEG) chains and α-cyclodextrin (CD), in which the cross-linkers are made of CD dimers and capable of sliding along the PEG chains. To elucidate the physical picture and properties, the scattering functions, I ( q )s, of SR gel in NaOD aqueous solutions (NaOD aq ) and in deuterated dimethyl sulfoxide (d-DMSO) were investigated by small-angle neutron scattering (SANS) and were compared with those of pregel solutions, where q is the magnitude of the scattering vector. The following facts were disclosed: (1) The polyrotaxane chains take a rodlike conformation in d-DMSO, whereas a Gaussian chain in NaOD aq . (2) The degree of inhomogeneities of SR gel in NaOD aq has a minimum around the sol−gel transition, whereas that in d-DMSO increases monotonically with increasing cross-linker concentration. (3) I ( q ) of SR gel in NaOD aq can be described by a Lorentz function, while that in d-DMSO is given by the sum of a squared Lorentz function and a scattering function for a rod. These differences in I ( q ) are ascribed to the difference in the stacking behavior of CD molecules on PEG chains in PR.