A pH-responsive Poly(Acrylic Acid) nanoscale actuator

In this report, we present the development of a nanoscale actuator that takes advantage of the properties of poly(acrylic acid) |PAA| hydrogels as well as an aqueous fluid environment to realize control of height change. We used spatially-resolved and focused low-energy electron beams to irradiate dry 40 nm thick PAA films. After developing in high pH buffer, non-irradiated films dissolved and irradiated polymer remained bonded to the substrate. We show that these gels translate to actuators that undergo height changes as a function of pH. Since the carboxyl groups are deprotonated at high pH, we studied the amount and activity of carboxyl groups in the hydrogels using infrared spectroscopy. Using atomic force microscopy we then studied how these hydrogels respond to aqueous environment, where change was photo-triggered using a photoacid generator.