Thermoshrinking behavior of poly(vinylcaprolactam) gels in aqueous solution

The swelling of newly synthesized slightly crosslinked gels of polyvinylcaprolactam (PVCa) was studied as a function of temperature. In water, PVCa gels undergo a sharp volume transition from a swollen to a collapsed state on heating. In water/alcohol mixtures, the gel first shrinks and then expands as the temperature is raised. The swelling behavior of the thermosensitive PVCa gel in surfactant solution depends on kind and concentration of the surfactant. Normally, an additional swelling of the gel is observed in the presence of ionic surfactants. Addition of the surfactant raises the collapse transition temperature of the gel. Absorption of the surfactant by the PVCa gel as a function of temperature and surfactant concentration is analysed in detail.