Direct Evidence for Structural Transition Promoting Shear Thinning in Cylindrical Colloid Assemblies

Abstract

In this paper, we describe stimuli-responsive hydrogels prepared from a rigid rod-like polyelectrolyte 'imogolite' and a dicarboxylic acid. The hydrogel exhibited thixotropy in response to mechanical shock within the order of seconds or sub-seconds. Here, using the latest structural/rheological characterisation techniques, the relationship between the structural transition processes and the shear thinning was estimated. The evidence obtained by the experiments revealed for the first time the direct relationship between the microscopic structural change and the macroscopic thixotropic behavior that have been extensively discussed. The thixotropic hydrogel has the hierarchical architecture in the combination of imogolite and dicarboxylic acid, i.e., sheathed nanotubes/hydroclusters of cross-bridged nanotubes/frameworks. The formation and disintegration of the network structure upon resting and agitating, respectively, were the origin of gel/sol transition (thixotropy), although the hydroclusters of cross-bridged nanotubes were maintained throughout the transition.

Synthesis of Anisotropic Hydrogels and Their Applications

“…[22][23][24][25][26][27][28][29][30][31][32][33][34] Forstructural fixation by hydrogelation, physical aggregation of gelators is also applicable. [19][20][21][35][36][37][38][39][40][41] Owing to its simplicity and easiness,shear-force orientation has been widely used for the synthesis of anisotropic hydrogels containing various types of 1D-or 2D-shaped nanofillers,i ncluding natural [21][22][23] or synthetic [19,20,38,39] peptide nanofibers,c ellulose nanofibers, [24,40,41] surfactant bilayers, [25][26][27][28][29][30][31] and inorganic nanofillers. [32][33][34][35][36][37] As al imitation of this method, shear forces cannot be homogeneously applied to thick samples,and the processing occasionally suffers from low reproducibility,particularly when the shear forces are applied ...…”

Nanomaterials From Imogolite: Structure, Properties, and Functional Materials

“…Successful grafting of organic moieties can be evidenced by dispersing unmodified and modified nanotubes in organic solvents ( Figure 5.8) [131,135,137]. Grafting of carboxylates [128,138,139] and sulfonates [140] groups have also been reported with similar results as with phosphonates. Otherwise, the use of silane as coupling agent appears to be controversial because the moieties remain hydrolytically labile and are totally removed after several days of dialysis [141,142].…”

“…However, incorporation of PMMA grafted INT into poly(vinyl chloride) (PVC) films reveal that the reinforcement is strongly dependent on the interfacial adhesion between the functionalized nanotubes and the polymer matrix [159]. In addition to reinforcement in solid materials, the combination of imogolite with various polymers also yields homogeneous hydrogels exhibiting thixotropic behaviour, hierarchical ordering as well as reversible isotropicanisotropic structural transitions in response to strain [138,139,161,163,[167][168][169]. Imogolite hydrogels can also be prepared with biomacromolecules [170,171] for encapsulation and/or for sustained release of enzymes or model drugs [172,173].…”

Ordered structurization of imogolite clay nanotubes by the spatiotemporal regulation of their assemblies

“…Herein, the assembly of IG with PAA was performed, as reported previously, via hydrogen bonding and ionic interactions between carboxylic groups of PAA and aluminol groups of IG [19,20]. The experimental system is described in Fig.…”