Research On Fabrication Of The Environmental Response Photonic Crystal Beads From Microfluidic Chip

Photonic crystals are periodic dielectric structures that have a band-gap, enabling it to control light with amazing facility that is similar to the electrical properties of semi-conductors. Due to the unique properties, photonic crystals have potential applications in integrated optics, microwave communication and electronics fields. In the past decade, sensors with photonic crystals have attracted much attention for their rapid response and high sensitivity to external stimuli. As the response could be detected by optical spectrum instrument or read by naked-eyes directly, photonic crystals are expected to be applied in visual sensing filed.In this thesis, size-controlled and monodisperse SiO2 particles were fabricated by the improved sol-gel seed growth method, which is the basis to fabricate photonic crystals. The size of the monodisperse particles could be controlled through the quantity of ammonia and tetrathoxysilane(TEOS) or the temperature of reaction system. The diameter of the particles increases, and the trend become weaker, as the quantity of ammonia and TEOS increases. When the reaction temperature increases, the dimension of the spheres decreases and shows better monodispersity. Photonic crystals films from 10% w/v solution with different sizes of SiO2 particles were prepared by using the horizontal deposition method. The films show different structural colors and their band-gap exhibits red shift with the increasing size of the SiO2 particles. At the same time, monodisperse polystyrene(PS) nanoparticles with diameter of 260 nm were prepared using the emulsion polymerization method and the photonic crystals films with these PS particles show brilliant color.In order to achieve photonic crystal beads(PCBs), the size controlled droplets that generate from the microfluidic chip were used as templates. After water evaporating, the nanoparticles in the droplets self-assembled into PCBs. The size of the droplets was controlled by the flow rate of the oil phase and the water phase. In a certain range, the diameter of the droplets increases as the flow rate of the water phase increasing and decreases as the flow rate of the oil phase increasing. The effects of the concentration of water phase and the heating method on the size, structure and the optical quality of the PCBs were also investigated in this thesis. The PCBs have isotropic band-gaps and structural colors for its spherical structure.To prepare pH sensors with fast response and high sensitivity, the PCBs and the acrylic acid(AA) were used as templates and hydrogel precursor, respectively. The hydrogel beads with inverse opal structure were obtained after UV induced polymerization and hydrofluoric acid(HF) etching. The hydrogel beads are sensitive to pH value change for their small volume and ordered porous network. The hydrogel beads swell as the pH value of the buffer increases with resultant red shift of the band-gap. The composition of the hydrogel precursor greatly affects the sensitivity of the hydrogel beads. The hydrogel beads with 3wt % AA, 31 wt % H2 O have wider pH response range and reach equilibrium in less than 30 s when pH value changes from 5 to 6. In addition, the pH-temperature dual-responsive hydrogel beads with inverse opal structures were produced by using the poly(N-isopropylacrylamide)-arcylic acid(PNIPAm-AA) as hydrogel precursor. When the temperature is above the lower critical solution temperature(LCST), the beads de-swell greatly with decreased lattice size. The structural color of the hydrogel beads also changes with the pH value.With the development of sensors, the quick, highly sensitive and stable testing methods become popular and attractive to meet people’s high requirements for testing. The hydrogel beads in this thesis not only exhibit fast response to external stimuli, but also show good mechanical properties. Moreover, the fast response can still be maintained after several repeated tests. The hydrogel beads have isotropic band-gap and structural color as the PCBs. The structural color of the beads changes with external stimuli and can be easily read by naked-eyes. Therefore, the hydrogel beads have great potential in advanced optical sensitive instruments.