SANS Studies on Deformation Mechanism of Slide-Ring Gel

Abstract

The deformation mechanism of “slide-ring” (SR) gels was investigated with small-angle neutron scattering (SANS). The SR gels were prepared by coupling α-cyclodextrin (CD) molecules on polyrotaxane chains consisting of poly(ethylene glycol) and CD. Because of a hollow structure of CD molecules, the cross-links made of CD molecules in a figure-of-eight shape can slide along the polymer chain. A normal butterfly pattern was observed for the first time in two-dimensional SANS isointensity profiles for the SR gels under uniaxial deformation, where the normal butterfly pattern means a prolate isointensity pattern in the direction perpendicular to the stretching direction. However, by either increasing the cross-link density or increasing the stretching ratio, the normal butterfly patterns changed to abnormal butterfly patterns as are commonly observed in conventional covalent-bonded chemical gels. The difference in the deformation mechanism as well as the cross-linking inhomogeneities between the SR gels and the covalent-bonded chemical gels is discussed by focusing on the unique architecture of the SR gels.

Novel Cross-Linking Concept of Polymer Network: Synthesis, Structure, and Properties of Slide-Ring Gels with Freely Movable Junctions

“…89,90 However, the slide-ring gel shows a normal butterfly pattern, i.e., prolate patterns perpendicular to the stretching direction as shown in Figure 4. 80 To the best of our knowledge, this is the first study to report that cross-linked polymer gels exhibit the normal butterfly pattern. The normal butterfly pattern is also observed in homogeneous polymeric materials such as polymer films and solutions due to the orientation of the polymer chains along the elongation or flow direction.…”

“…79 Shibayama et al also revealed a significant difference between the behavior of chemical gels and that of slide-ring gels by subjecting them to SANS on uniaxial deformation. 80 It is well known that the chemical polymer gels have inherently large inhomogeneous structures due to the non-random distribution of the cross-links. 17 These inhomogeneities usually increase with the swelling or deformation since the cross-linking junctions are permanently fixed on the polymer chains and the gel cannot adjust its cross-link distribution or polymer length in the network when its environment changes.…”

Universality and Specificity of Polymer Gels Viewed by Scattering Methods

“…The sliding motion was verified by DLS, 112 and it was determined by using SANS to have only a small amount of inhomogeneities. 113 Haraguchi and Takeshita developed nanocomposite gels, to which we will refer as NC gels, made of inorganic clay and polymer chains as schematically shown in Fig. 26b.…”

Recent advances in hydrogels in terms of fast stimuli responsiveness and superior mechanical performance

“…SR gels are considered an intermediate between physical gels and chemical gels, as the polymer network is not formed by either covalent crosslinks, as in chemical gels, or attractive interactions, as in physical gels. This pulley effect has been confirmed through analysis of the static structure of SR gels under uniaxial deformation using smallangle neutron scattering 34,35 and small-angle X-ray scattering. 36 A prolate pattern perpendicular to the deformation direction, which is known as a normal butterfly pattern or an almost isotropic pattern, has been reported for SR gels.…”