Chemoresponsive P(NiPAAm-co-AA) beads with a radius of approximately 3 millimetres were synthesised by UV light induced copolymerisation of N-isopropylacrylamide (NiPAAm) and acrylic acid (AA) in aqueous droplets suspended in silicone oil. Scanning electron microscopy revealed a closed surface for beads prepared with a three-fold excess of acrylic acid, while macroporous morphologies appeared for NiPAAm to AA ratios of 1:1 and 3:1.
The swelling behaviour was mapped across linear alcohols, acids, esters and their mixtures, revealing a cononsolvency effect related to the presence of ethanol. Beads with a 1:1 monomer ratio showed the largest difference in swelling between ethanol and ethyl acetate and in mixtures of the two solvents. Their reversible swelling and shrinking was described by two exponential functions, with the time constant of the first fast part on the order of minutes. The extent of shrinkage is negatively correlated with the logarithmic ethanol fraction in ethyl acetate.
To demonstrate the practical potential of the material, beads placed in a casing were used to halt the flow of ethyl acetate after a switch to ethanol. This fast and reversible response shows how the composition of the beads and the surrounding solvent can be used to adjust the response kinetics, bringing chemically controlled flow regulation in smart valve components a step closer.
The study is a collaboration between the Institute of Technical and Macromolecular Chemistry at the University of Hamburg and the Institute of Thermal Separation Processes at Hamburg University of Technology, carried out within project A01 of the Collaborative Research Centre CRC 1615 (SMART Reactors).
Johannes Gmeiner, Jonah Hasse, Gerrit A. Luinstra, Kathrin M. Eckert, Irina Smirnova (2026). Preparation of Organogel Beads for Smart Valve Components: Kinetic Study of Their Chemoresponsiveness. Macromolecules 59 (14), 8403-8419.
