The shape of the particles is an important factor that can control the characteristics of the particles (rheology, optical properties, and interaction with the cells). Particularly, non-spherical non-spherical particles have been applied to various fields such as photocrystalline materials for displays, photochemical sensors, coating films and cosmetics because of their unique properties. Furthermore, smart particles whose shape changes in response to external stimuli can be applied to various fields such as drug therapy, smart coating, and the like. However, the implementation of smart particles is very limited and the applications are narrow because the shape changes of particles are irreversible. To solve these problems, there is a growing need to develop smart particles that can be reversibly shaped while being fabricated through a simple process. In this thesis, I developed a novel platform for a next generation smart particle in response to external stimuli, which can be summarized as follow.
First, I developed a new methodology to selectively control the shape of particles in the nanoscale through a poly-N isopropylacrylamide (PNIPAM)-based thermosensitive surfactant capable of changing the interface characteristics in response to temperature. Especially, the effect of the structure of thermosensitive surfactants on the temperature range of particle shape transition was systematically investigated. And also reversible particle shape according to temperature change was achieved. The development of a surfactant capable of simultaneously responding to temperature and pH resulted in smart particles that were simultaneously sensitive to various stimuli. Particularly, particles showing deformation to convex lens and ellipsoid shape near pH 7 and body temperature suggested a new range of clinical, biomedical and environmental application. Furthermore, the shape of block copolymer particles can be controlled through a surfactant capable of changing the characteristics of the interface in response to light. Particularly, the effects of light wavelength, intensity and irradiation time on the particle shape were elucidated.
This thesis provides an in-depth understanding of preparation of stimuli-responsive shape-transforming particles. The smart particles that we have demonstrated in this thesis will have a significant impact on the development of practical applications in the field of colloid-based technologies.