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The porous poly(vinyl alcohol) (PVA)–poly(vinyl acetate) (PVAc) composite film prepared by acetone extraction from a PVAc latex film containing PVA was colored in organic solvents for PVAc having a refractive index close to that of PVA. The scattered color changed from yellow to green through orange, red, purple, and blue with an increase in the refractive index of the solvents. The coloration phenomena were based on the intersection between the dispersive curve of PVA and that of the solvents for PVAc in the visible region. If a mixed organic solvent of a solvent and a nonsolvent for PVAc was used, the porous film easily exhibited a color change when it was placed between two glass plates which were pressed together using paper clips. When the refractive index of the solvent was higher than that of the nonsolvent, the scattered color changed from yellow to blue with increasing pressure, and when the refractive index of the solvent was lower than that of the nonsolvent, the scattered color conversely changed from blue to yellow. This mechanism was found to involve a very simple phenomenon in which PVAc grafted on the surfaces of the spherical PVA cells selectively absorbs the solvent from the mixed solvent, and the nonsolvent remaining in the PVA cells is forced out of the porous film with increasing pressure. This piezochromism can be controlled by the refractive index of the mixed solvent, the selection of the solvent and the nonsolvent for PVAc, and the pressure gradient.

The coloration phenomena of porous poly(vinyl alcohol) (PVA)-poly(vinyl acetate) (PVAc) composite films in organic solvents, which were prepared from dried PVAc latex films containing PVA as a protective colloid with acetone extraction, have been investigated from the standpoint of light dispersive power. When the white opaque porous films were dipped in organic solvents having a refractive index near that of PVA, they became so transparent that one could read letters under the films. If solvents having a high light dispersive power such as aromatic compounds were used, the porous films became markedly colored. The color of the scattered light, which was complementary to that of the transmitted light, did not change with the observing direction vs the irradiating direction of the white light and shifted from yellow to green through orange, red, violet, and blue as the refractive index of the solvents increased. This was evident from the fact that the intersection of the dispersion curves of PVA had a low light dispersive power and solvents had a high light dispersive power. The coloration of the porous PVA-PVAc composite films in the solvents showed reversible thermochromism. The residual grafted or highly branched PVAc in the spherical cells of PVA after acetone extraction played an important role in the penetration of solvents into the inner parts of the porous films and in the refractive index of the PVAc swollen by the solutions in the porous films.