Characterization of thermo and pH responsive NIPAM based microgels and their membrane blocking potential

This work aims to study the behavior of temperature-responsive p(NIPAM) and temperature/pH-responsive p(NIPAM)/acrylic acid (AA) microgels. Three microgels were synthesized using surfactant free emulsion polymerization technique, these are p(NIPAM), p(NIPAM)-co-AA 95:5% (w/w) and p(NIPAM)-co-AA 90:10% (w/w). Dynamic light scattering was used to study the behavior of diluted microgel dispersions (0.5%, w/w p(NIPAM)), while rheology was used to study the viscosity of 2% (w/w) p(NIPAM) dispersions. The characterization data indicate the swelling/deswelling and flocculation/deflocculation behavior of the microgels. The conditions required for flocculation were used to test the ability of the microgel dispersions to block a membrane of pore size 5 μm. In 3 h, p(NIPAM), p(NIPAM) 5% AA (w/w) and p(NIPAM)10% AA (w/w) blocked the membrane (decrease the flow rate) by 96.16, 59.44 and 59.8% respectively. Thus, the controlled flocculation of microgels may be used in applications where pore blocking is important such as the treatment of dentinal hypersensitivity, given that the VPTT of p(NIPAM) is ≈34 °C, which is very close to the human body temperature.