Colloidal suspensions are fascinating soft materials that exhibit a wide range of structures and dynamics which derive from a unique interplay of physical, chemical and hydrodynamic mechanisms. Furthermore, the use of colloidal particles as 'big' atoms continues to drive new understanding about atomic scale matter. In this talk I will review experiments [1-3] that employ temperature-sensitive polymers to induce novel phase behavior in suspension. The key ingredient for these studies is NIPA polymer (poly(/N/-isopropylacrylamide)). Typical experiments mix NIPA polymer or NIPA-polymer-based microgel particles into a suspension or gel, and then exploit the temperature-sensitive solubility of the polymer to drive phase transitions. This scheme offers a fantastic new variable for control of lyotropic suspensions. Recent experiments, for example, have enabled us to directly observe premelting of three-dimensional crystals near grain boundaries [1], to directly observe melting of lamellar phases into nematic phases [2], and to create novel lyotropic, carbon-nanotube based liquid crystalline gels [3].
References1. Alsayed, A.M., Islam, M.F., Zhang, J., Collings, P.J., Yodh, A.G., Premelting at defects within bulk colloidal crystals. Science 309, 1112399 (2005).
2. Alsayed, A.M., Dogic, Z., and Yodh, A.G., Melting of lamellar phases in temperature sensitive colloid-polymer suspensions. Physical Review Letters 93, 057801 (2004).
3. Islam, M.F., Alsayed, A.M., Dogic, Z., Zhang, J., Lubensky, T.C., and Yodh, A.G., Nematic nanotube gels. Physical Review Letters 92, 088303 (2004).