Uniaxial and plane orientations of clay platelets in nanocomposite gels with different compositions during stretching and recovery

- Changes in birefringence (ΔnNC) of nanocomposite (NC) gels upon stretching were investigated.
- The variations of ΔnNCs indicate unidirectional and plane-orientations of clay platelets in NC gels.
- The percentage plane-orientation was evaluated for NC gels with different clay content.
- The effects of water content and recovery process on the ΔnNC-strain curves were also clarified.

Changes in the birefringence (ΔnNC) of nanocomposite (NC) gels upon stretching and recovery were investigated for gels comprising a poly(N-isopropylacrylamide)−clay network structure. Irrespective of the composition of the NC gels, a change in the birefringence appeared upon stretching; ΔnNC varied greatly depending on the clay and water contents (Cclay and Cw, respectively) of the gels and the stretching ratio. The NC gels with low Cclay gave rise to unique ΔnNC vs. strain curves with a maximum ΔnNC. For samples with higher Cclay, the variation of ΔnNCs observed in the edge- and through-directions, which is attributed to plane-orientation of the clay platelets, increased with increasing Cclay. This was confirmed by scanning electron microscopy observation, and the percentage plane-orientation was evaluated from the ΔnNC data. On recovery of the strain, the plane-oriented clay platelets underwent minimal reversion to the original state, although most of the PNIPA chains reverted to the random conformation. The effects of Cw on the ΔnNC-strain curves were also clarified.

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