Analyzing the Effects of Silica Nanospheres on the Sol-Gel Transition Profile of Thermosensitive Hydrogels

The insertion of nanoparticles into smart hydrogels can diversify their functionalities by a synergistic combination of the components properties within the hydrogels. While these hybrid systems are attractive to the biomaterials field, careful design and control of their properties are required since the new interactions between the polymer and the nanoparticles can result in changes or the loss of hydrogels stimuli response. In order to understand the physicochemical aspects of the thermoresponsive systems, nanocomposites of poly(N-vinylcaprolactam) (PNVCL) and silica nanoparticles with different sizes and concentrations were synthesized. The UV-vis and DLS techniques showed that the PNVCL has a sharp phase transition at 34 °C, while the nanocomposites have a diffuse transition. The nanocomposites showed an initial coil-globule transition before the phase transition takes place. This was identified by the evolution of the hydrodynamic diameter of the nanocomposite globules before the cloud point temperature (T_cp), which remained constant for PNVCL. This new transition profile can be described by two stages in which microscopic volume transitions occur first, followed by the macroscopic transition that forms the hydrogel. These results show that the proposed nanocomposites can be designed to have tunable stimuli response to smaller temperature variations with the formation of intermediate globule states.