Date

2022-8-19

Author

Dinç, Ramazan Umut

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Microcargo release systems have been reported including liposome vesicles, micro- capsules, and micro/nanospheres. Liquid crystal (LC) based systems offer an alterna- tive to these release systems since they are easily fabricated and easy to use. Recently, a new method using an LC-based system for microcargo delivery has been reported that releases microcargo via the applied shear by the motile bacteria near LC/Aqueous interface. In our study, we investigated two potential systems to release microcargo on-demand by the application of interfacial shear applied with active particles. In the first part of the study, we used Janus particles formed by anisotopic coating of TiO2 particles with gold, that possess diffusiophoretic motion upon UV light exposure. We characterised Au-coated TiO2 Janus particles and their active motion in different Newtonian media. After these characterisations, we found that the active motions of these Janus particles to cease significantly when positioned at the LC/Aqueous in- terface because of the existing ionic medium. With calculations, we found that the electric double layer thickness at LC/Aqueous interface is comparable with the size of our Janus particles at zero salt concentration. In the second part of the study, we used paramagnetic iron oxide particles to form magnetic microstirrer assemblies at the LC/Aqueous interface upon magnetic field exposure that applies shear to release microcargo within the water-in-LC emulsion. After characterising the paramagnetic particles, we performed release studies using aqueous emulsion droplets loaded with methylene blue (MB) formed in nematic LC. In this system, the external stimuli that induced the internal flow were the shear forces caused by the rotational motion of the microstirrers at the interface. We analysed the effects of the rotational speed of the magnetic flux director and the interfacial concentration of the paramagnetic particles on the release rate of the microcargo. Our experiments at different rotation speeds revealed that the release rate of MB decreases from 100 ng/min to 25 ng/min as the rotation speed decreases in one hour of microcargo release. In addition, we found an intermediate interfacial concentration of the paramagnetic microparticles for the maximum release rate is around 20000 particles/mm2. We also showed the micro- scopic evidence that the rotation of the microstirrers changed the nematic director of LC locally on the interface.

Subject Keywords

Liquid crystal, Active particle, Microcargo release, Electric double layer

URI

https://hdl.handle.net/11511/98690

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Graduate School of Natural and Applied Sciences, Thesis