Investigations of Ionic Functional Soft Matter

Electrostatic interactions play an important role in functional self-assembled structures of both natural and synthetic origin. Such processes are complex and reflect the importance of balancing competing interactions which is crucial in the development of materials for new technological advancements. This thesis presents studies on electrostatic forces in different environments and how they can be harvested in functional and motile materials. The first part of the thesis presents new liquid-crystalline materials based on ionic surfactants and their complexation. Publication I studied the thermotropic liquid crystallinity of zwitterionic amphiphilic molecules. The observed melting points were high and thus the compounds were plasticized using a low-melting ionic liquid, which led to decreased transition temperatures, ionic liquid-crystalline complex formation, and ion-conduction. In Publication II, the complexation of cellulose nanocrystals (CNCs) by a nonionic-anionic surfactant led to nematic liquid-crystalline phase formation both in organic solvent toluene and in the bulk state. The suppression of the chirality of CNCs is of high technological relevance as it would widen the applicability of CNCs as, e.g., reinforcements and optical polarizers. The electrostatic interactions were accounted as the driving force for the material properties and structural characteristics in both publications. In the second part of the thesis, electrostatic interactions were used to integrate functional responsiveness in materials. In Publication III, a hydrogel consisting of zwitterionic and nonionic units was demonstrated as a taste-recognizing material. The sensing was based on the interactions between the hydrogel's repeating units and the small-molecular tastant molecules, leading to volumetric and electrical responses depending on the (non)ionic nature of the tastant. In Publication IV, a polyampholyte was used as a ligand to prepare fluorescent gold nanoclusters with pH-responsive photoluminescence, where the protonation of the tertiary amine groups led to enhanced photoluminescence in acidic medium. This feature was further used in the bioimaging of lysosomes. Finally, Publication V demonstrated that a low-magnitude electric field can lead to a controlled locomotion of surfactant-stabilized aqueous droplets. The results suggest that the droplet propulsion occurs through non-equilibrium mechanisms at the zwitterion-covered droplet interface. The results of this thesis contribute to the understanding of ionic interactions and how they can be used in the development of functional responsive materials through equilibrium and nonequilibrium mechanisms.