Polymer–Clay Nanocomposite Microspheres and their Thermosensitive Characteristics

Polymer–clay nanocomposite (P‐NC) microspheres are synthesized through in situ free‐radical polymerization in aqueous media without the use of surfactants. Uniform aqueous dispersions of P‐NC microspheres without flocculation/precipitation are obtained for five types of (co)polymers with different hydrophilic/hydrophobic natures, in which the exfoliated clay platelets play an important role as crosslinkers and stabilizers in water. The sol–gel boundary, transparency of the aqueous dispersion, microsphere particle size, etc. vary depending on the compositions and polymerization methods. Aqueous dispersions of P‐NC microspheres with a well‐defined lower critical solution temperature (LCST)‐type thermosensitive transition are obtained by using N‐isopropylacrylamide (NIPA), 2‐methoxyethylacrylate (MEA), and N,N‐dimethylacrylamide (DMAA) as the (co)monomers. In the case of P‐NC microspheres consisting of inorganic clay and NIPA‐DMAA or MEA‐DMAA copolymers, the LCST is controlled over a wide range, particularly depending on the DMAA content. The P‐NC microspheres applied within double‐layer glass plates are examined as reversible and efficient thermosensitive optical shutters.