Microfluidics. Recent researches have been focused on developing novel functional soft materials by exploiting a cutting-edge technique, microfluidics, which is the science and technology of systems that process or manipulate small amounts of fluids ranging from 10-9 to 10-18 liters. We have demonstrated that by changing both flow properties and dimensions of the microfluidic channel, the transition from a stable co-flow to drop break-up can be precisely controlled. Using this technique enables generation of new types of smart soft materials, including high-order multiple phase colloids, novel colloid sensors, and high performance diagnostic devices. We use quantum dots, carbon, catalytic metal nanoparticles and nanowires, and biomacromolecules as examples of the materials that can be hybridized to provide specific chemical, physical, or mechanical responsiveness to the soft materials. More recently, we have extended this study to the area of colloid crystals; we have fabricated novel spherical colloidal crystals by using this microfluidic technique. The robustness and versatility of this microfluidic approach are expected to generate more complex systems and create new possibilities to obtain novel functional smart materials.
Colloid science. We study on developing a straightforward technique that can synthesize anisotropic colloidal building blocks. When these unit blocks are allowed to have anisotropies in shape and chemistry, they self-assemble to form an ordered supra-structure with well-defined configurations. For this, we have synthesized a series of uniform anisotropic colloidal building blocks, of which shapes are dumbbells, triangles, cones, and diamonds. Fine-tuning of their shapes in micrometer length scales is achieved by precisely manipulating the directionality of phase separations in seeded polymerizations. By using these anisotropic particles, we have shown that they can more jam and pack in a given space, which is truly important in determining the volume fraction of suspending materials. Chemical anisotropy can be achieved by selectively treating their surface, thus imparting amphiphilicity to them. This study has demonstrated the feasibility of arraying the anisotropic particles at interfaces. Actually, we have directly visualized the packing of anisotropic particles at the water-in-oil interface, indicating they behave just like a surfactant molecule. This shows well that fine control over the geometry of colloidal particles allows us to fabricate a new type of building blocks that are essential in the area of soft matter.
Smart nanofluids. We are also truly interested in developing a robust means of fabricating smart nanofluids. They include vesicles, nanoemulsions, associative nanoparticles, and nanocapsules. The key to this research is to use long ranged molecular interactions between active materials and matrix, creating a material system with controllable length scales as well as interactive surface properties. For example, we have developed nanocarriers, whose periphery is covered by positive surface charges. They are indeed advantageous for transdermal delivery, since they have an ability to disturb the tight lamellar layer of stratum corneum, which eventually enables better diffusion of encapsulated active molecules through the skin. The advantages of using these types of nanofluids are that we cannot only engineer interactive nanospecies, but also impart unique rheological properties to the solution system. These characteristics highlight the robustness and versatility of our approach, which could be used to develop novel smart nanofluids that are truly useful for controlling association of nanoscale materials through any specific media.