|dc.description.abstract||The aim of this work is to improve the swelling response of redox active hydrogel actuators. At the moment, complete swelling of our quinone based actuators takes about 150 minutes and that of our 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) based actuators takes about 60 minutes. The aim is to reduce the response time to a few minutes or seconds. To do this, hydrogels are microstructured in order to enhance the solvent and ion diffusion into the hydrogel network and in this way to increase the swelling response rate of the hydrogels.
Four methods will be investigated: an emulsion templating method that employs poly(methyl methacrylate)-b-poly(lauryl methacrylate) (PMMA-b-PLMA) block copolymers that were synthesized under atom transfer radical polymerization conditions, a poly(ethylene glycol) (PEG) templating method, a novel nylon 6,6 templating method, as well as freeze-drying using water or dimethyl sulfoxide (DMSO) as the porogen. All four methods will be tested on simple poly(2-hydroxyethyl acrylate) (PHEA) hydrogels first, and if found to be suitable subsequently applied to the redox-responsive actuators.
It was found that all four methods are suitable to create porous PHEA hydrogels and all but the PEG templating methods can be used to prepare hydrogels with a swelling rate that is increased compared to nonporous PHEA hydrogels. For the PHEA hydrogels, the very good effect of freeze-drying with DMSO as the solvent should be pointed out, which leads to PHEA hydrogels that swell to equilibrium in only 6 minutes compared to 50 hours for the nonporous reference. For the quinone actuator device it was found that both, the emulsion templating method with PMMA-b-PLMA block copolymers as the surfactant as well as freeze-drying with DMSO, can decrease the time until equilibrium swelling is reached to 60 minutes, with almost complete swelling after already 20 minutes, compared to 150 minutes for the nonporous quinone actuator. For the TEMPO actuator device first results indicate a similar efficiency of freeze-drying with DMSO, with almost complete swelling after 10 to 20 minutes, however those results should be verified with further experiments.||