Preparation of organogel beads for smart valve components: kinetic study of their chemoresponsiveness

Chemoresponsive P(NiPAAm- co -AA) beads (approximately 3 mm radius) were synthesized via UV-light-induced copolymerization of N -isopropylacrylamide (NiPAAm) and acrylic acid (AA) in aqueous droplets suspended in silicone oil. SEM analysis revealed a closed surface for beads with a 3-fold excess of AA; macroporous morphologies appeared for NiPAAm:AA ratios of 1:1 and 3:1. Swelling behavior was mapped across linear alcohols, acids, esters, and their mixtures, revealing a cononsolvency related to ethanol presence. Beads with a 1:1 monomer ratio exhibited the largest swelling difference between ethanol and ethyl acetate or with mixtures of ethyl acetate and ethanol. Their reversible swelling–shrinkage was fitted to two exponential functions. The time constant of the first fast part is on the order of minutes. The extent of shrinkage is negatively correlated with the logarithmic ethanol fraction in ethyl acetate. Beads in a casing were used to halt the flow of ethyl acetate after a switch to ethanol.