In Situ Polymorphic Alteration of Filler Structures for Biomimetic Mechanically Adaptive Elastomer Nanocomposites

Abstract

A mechanically adaptable elastomer composite is prepared with reversible soft-stiff properties that can be easily controlled. By the exploitation of different morphological structures of calcium sulfate, which acts as the active filler in a soft elastomer matrix, the magnitude of filler reinforcement can be reversibly altered, which will be reflected in changes of the final stiffness of the material. The higher stiffness, in other words, the higher modulus of the composites, is realized by the in situ development of fine nanostructured calcium sulfate dihydrate crystals, which are formed during exposure to water and, further, these highly reinforcing crystals can be transformed to a nonreinforcing hemihydrate mesocrystalline structure by simply heating the system in a controlled way. The Young's modulus of the developed material can be reversibly altered from ∼6 to ∼17 MPa, and the dynamic stiffness (storage modulus at room temperature and 10 Hz frequency) alters its value in the order of 1000%. As the transformation is related to the presence of water molecules in the crystallites, a hydrophilic elastomer matrix was selected, which is a blend of two hydrophilic polymers, namely, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer and a terpolymer of ethylene oxide-propylene oxide-allyl glycidyl ether. For the first time, this method also provides a route to regulate the morphology and structure of calcium sulfate nanocrystals in a confined ambient of cross-linked polymer chains.

Temperature scanning stress relaxation behavior of water responsive and mechanically adaptive elastomer nanocomposites

“…The hydrophilic elastomer matrix GECO, epichlorohydrin−ethylene oxide−allyl glycidyl ether terpolymer (Hydrin T3108) and hydrophilic polymer resin GEPO, ethylene oxide−propylene oxide−allyl glycidyl ether terpolymer (Zeospan 8030) were kindly provided by Zeon Chemicals. The chemical structures and other details can be found in our previous article . Other compounding ingredients like zinc oxide (ZnO), stearic acid, tetramethylthiuram disulfide (TMTD), mercaptobenzothiazole (MBT), sulfur (S) used were of rubber grade.…”

“…In this work, the focus was given for understanding the morphological changes occurring during the water treatment process. The conditions of water treatment and the compounding ingredients were optimized based on the mechanical properties as discussed in our previous article . In this work, the prepared sample was immersed in water for 3 h and then dried at room temperature (23 °C) for 72 h and was named as “water treated”.…”

“…A more detailed characterization of the mechanically adaptive elastomer nanocomposites including in‐depth mechanical properties, X‐ray crystallographic, and Raman spectroscopy studies can be found in our previous communication …”

“…In one of our previous studies, we exploited the possibility of altering the morphology of calcium sulfate (CaSO 4 ) in situ and developed corresponding mechanoadaptive rubber composites. CaSO 4 exhibit polymorphic characteristics in response to water/heat.…”

“…Only GEPO was not used because of its thermoplastic in nature (have crystalline tendency) whereas GECO is an amorphous elastomer. A small amount of GEPO in the blend does not impart any crystalline character of the blend rather it enhances the water absorption capacity . In this approach, the unique ability of CaSO 4 in exhibiting several crystal structures (when exposed to moisture/temperature) had been exploited by dispersing it as filler in a hydrophilic elastomer blend system, GECO/GEPO.…”