(699a) [Invited Talk] Confined Water within Soft Materials

The assembly of amphiphilic copolymers provides the opportunity to manipulate the local environment for water through both interactions with the hydrophilic monomer and the mesoscale structure associated with the assembly of the hydrophobic monomer. Here we will discuss how the selection of the hydrophilic and hydrophobic comonomers influences the properties of water, in particular supercooling. With a hydroxylated monomer, water crystallization can be almost completely suppressed when the average number of water molecules confined between the hydrophobic aggregates is less than 300. These results are consistent with spectroscopic measurements of water clusters at supercooled conditions, where a similar number of water molecules are necessary to nucleate ice. The amphiphilic copolymer can contain move than 50 wt% water and be cooled into "no man's land" without significant crystallization as determined by both x-ray diffraction and differential scanning calorimetry. The glass transition temperature (T_g) of water within these polymers is found to be 136 K and 151 K. The lower T_g is attributed to bulk-like water, when the high T_g is attributed to interfacial water with reduced dynamics. The structure of these soft materials can be manipulated by processing to produce subtle differences in the nanoscale structure that can dramatically influence the thermodynamics of the water confined within these polymers. These simple amphiphilic copolymers provide a simple route to use bulk systems to study the thermodynamics of water at the nanoscale.