Light-Driven Self-Propelled Colloidal Systems Based On Spiropyran

Self-propelled colloid systems can use chemical energy or light/heat energy in the environment for self-propelled motion.Many self-propelled colloidal systems have been studied,but most of them realize the net interface driving force through the asymmetry of the colloidal particle shape.These self-propelled colloidal systems hold potential applications in areas such as drug delivery,fixed-point release,adaptive pollution control and treatment.When spiropyran is irradiated with light of a suitable wavelength,the chemical structure will undergo a reversible isomerization transformation.Based on the photo-induced chemical isomerization of spiropyran,this paper constructs a phototaxis self-propelled colloid system.The biggest feature of this system is that it does not require the shape of colloidal particles to be controlled,and the preparation is relatively simple.This paper mainly completed the following work:1.The concentration gradient of the spiropyran solution under the irradiation of UV light initiates the phototaxis motion,aggregation and long-distance migration of colloidal particles.The prepared self-propelled colloidal systems are introduced in Chapter 2.By dispersing the untreated silica microspheres in the spiropyran solution,a simple and efficient light-induced self-propelled colloidal particle system is prepared.The silica microspheres will move towards the light spot and gather under the irradiation of UV light.The velocity of phototaxis motion is controlled by adjusting the intensity of UV light and the concentration of the solution.Then the aggregates formed at the spot under long-term UV illumination is studied and the model of the aggregates is obtained by software processing.By covering different shapes of masks on the light source,different patterns of light spots are observed by inverted fluorescence microscope.Under the irradiation of different light spots,the planar pattern of the aggregate formed by the silica microspheres also changes accordingly.The long-distance collective migration of silica aggregates under light irradiated,which is similar to the chasing of aggregates by a moving light source is studied.Finally,the mechanism of movement of the self-propelled colloid systems is analyzed.2.Study on the light driven motion of wider range of colloidal particles by the concentration gradient of spiropyran solution.In Chapter 3 the silica microspheres in previous experiments are replaced with silicon microspheres of different particle sizes,polystyrene(PS)microspheres and chlorella cells.The self-propelled behavior of these particles in the solution is studied,proving that the mechanism of photo-induced concentration gradient propulsion can be applied to a wider range of colloidal systems.3.Photoresponsive poly(N-isopropylacrylamide)(PNIPAM)microgels grafted with spiropyran groups is prepared and their phototaxis self-propelled motion are studied.In Chapter 4 acrylate monomers with spiropyran groups were modified to the surface of PNIPAM microgels by copolymerization.By controlling the reaction conditions,the particle size of the prepared microgel is about 2 μm,so that the microgels can be directly observed under an optical microscope.In Chapter 4 the structure,particle size,morphology,hydrophilicity/hydrophobicity,solution color and stimuli responsiveness of the prepared microgels are analyzed.The properties of the microgel such as particle size,hydrophilicity/hydrophobicity,solution color and volume phase transition temperature are changed when the solution of microgel is exposed to the UV light.Finally,the phototaxis motion of the microgel particles under UV light is studied.The work described here can provide a new idea for the preparation of photoresponsive materials,help researchers understand the aggregation and migration behaviors in the field of ecology better,and provide a certain experimental basis for the fluid mechanics-related models.