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.