Elucidating the role of the ionic liquid in the actuation behavior of thermo-responsive ionogels

• Published in: Sensors and actuators. B, Chemical Vol. 260; pp. 380 - 387
• Main Authors: Gil-González, Nerea, Akyazi, T., Castaño, E., Benito-Lopez, F., Morant-Miñana, Maria C.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01-05-2018; Elsevier Science Ltd
• Subjects: Actuation; Charge transfer; Chemical synthesis; Correlation analysis; Dependence; Electrochemical impedance spectroscopy; Electrochemical impedance spectroscopy (EIS); Electrodes; Gold; Interdigitated electrodes (IDEs); Ionic liquid (IL); Ionic liquids; Ionogel (IO); Isopropylacrylamide; Lower critical solution temperature (LCST); Organic chemistry; Photopolymerization; Polymerization; Porosity; Smart materials; Sulfate resistance; Ionogel (IO); Interdigitated electrodes (IDEs); Electrochemical impedance spectroscopy (EIS); Ionic liquid (IL); Smart materials; Lower critical solution temperature (LCST)
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2017.12.153

•Charge transfer resistance depends on the porosity and chemical structure of the ionogel.•Ionogels with polar ionic liquids are excellent for fast response applications.•Nonpolar ionic liquids result in ionogels with more robust actuator behavior.
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The characterization of thermo-responsive ionogels with electrochemical impedance spectroscopy using gold interdigitated electrodes is described. The ionogels are synthesized using poly(N-isopropylacrylamide) as thermo-responsive gel and polymerized in the presence of two ionic liquids: ethyl-3-methylimidazolium ethyl sulfate or trihexyltetradecyl-phosphonium dicyanamide. The changes on the charge-transfer resistance show a clear dependence on the porosity and on the chemical structure of the ionogel. Moreover, the charge-transfer resistance parameter can be used to track in real time the photopolymerization and the hydration process of the ionogels. After exposing them to several drying/rehydration cycles the switching performance is fully understood. The results show that the ionogel with 1-ethyl-3-methylimidazolium ethyl sulfate requires less time to absorb and release water and is excellent for fast response applications. On the contrary, the one with the trihexyltetradecyl-phosphonium dicyanamide ionic liquid presents a more robust actuator behavior and a huge potential to be included in long-term applications. Finally, the observed microstructures have been correlated with the measured charge-transfer resistance providing a better understanding of the actuator behavior of these smart materials.