Thermo-responsive polymers structure and design of smart materials

Indian Institute ofTechnology Kanpur, Kanpur, India 

Switchable and Responsive Sur ces and Materiais for Biomedical Applications. http //dx.doi.or l0.1016/B978-0-85709-713 2.00001  

For a polymer in aqueous solution, LCST is the point in the phase diagram at which entropy of the water in the system increases due to less ordered arrangement of water molecules and becomes more than enthalpy of water hydrogen bonded to the polymer (Kumar, Srivastava, Galaev, Mattiasson, 2007), therefore entropy of system governs LCST, and enthalpy of system governs UCST (Southall, Dill, Haymet, 2002). 

When temperature of an aqueous solution of thermo-responsive polymer exhibiting LCST behavior is increased, the polymer chains show coil-to-globule-to-aggregate 

For a process to be thermodynamically feasible, it is required that Gibbs free energy (AG) ((AG) = AH-T AS, where T = reaction temperature) for the process be negative at the reaction conditions. Dissolution of polymer in solvent involves a variety of interactions between the polymer and solvent. Thus, the overall outcome of all of these interactions should result in negative values for enthalpy (AH) and entropy (AS) for spontaneous dissolution of the polymer in solvent, resulting in a homogeneous system. If the value for (AG) turns out to be positive for a polymer solvent system at certain temperature, the polymer will not be miscible with that solvent at those conditions, and two different phases of polymer and solvent will separately co-exist. 

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Thermo-responsive polymers structure and design of smart materials... 

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