Preparation And Performance For Stimuli-responsive Polymer Colloid Spheres Self-assembled Structure

Colloidal crystals and colloidosomes can be accomplished by bottom-up methods based on self-assembly of monodisperse colloidal particles. Colloidal crystals have some important potential applications, such as photonic crystals, sensors, templates, and even paints. The building blocks of colloidal particles are generally "hard" beads, typically silica, polystyrene or poly(methyl methacrylate) spheres. As a result, the obtained crystal film has little mechanical strength. By now, film-forming polymer latex spheres are seldom used as building blocks in colloidal crystal films, since they are likely to deform and merge into a continuous matrix. However, films based on film-forming polymer latex are widely used for their flexibility, robustness and thermomechanical properties. The combination of optical property of colloidal crystal and flexibility of soft latex film can greatly expand the application of colloidal crystal film. Here, monodisperse polymer latexes containing hydrophilic shell were used to prepared solvatochromic-responsive crystal film. When polymer latex co-assemble with the silica nanoparticles, mechanochromic-responsive crystal films can be directly obtained. Colloidosomes can be used in encapsulation and controlled release. However, the driving forces for release of the encapsulated materials are only from osmotic pressure and rupture of outer shell. The limitations highlight the need for fabrication of colloidosomes with new properties, which can response to the changes of environmental stimuli. Therefore, temperature-responsive composite colloidosomes were prepared in this dissertation. The detail contents and results are summarized as follows:(1) A reversible solvatochromic-responsive crystal film based on the film-formation of "soft" monodisperse polymer latex. In this approach, a monodisperse polymer latex containing hydrophilic monomers was first synthesized using one-pot emulsion polymerization method and then cast on substrates, followed by dried at certain temperatures, a colorless and transparent crystal film was directly obtained. When this film meets water or some other polar solvents, brilliant colors appear; when this wetted film is completely dried again, the colors disappear and the film revert to the original colorless and transparent state. This reversible solvatochromic-responsive behavior is attributed to both the periodic structure of polymer film and the contrast of refractive index between core and shell due to the interaction between solvents and hydrophilic shell. However, if the film was obtained by too high drying temperature, e. g.,100℃, or too low content of hydrophilic monomers, e. g.,0.5% or less, no color appeared.(2) A reversible mechanochromic-responsive crystal film based on the room-temperature film-formation of monodisperse polymer latex by the aid of nanosilica particles. In this approach, when the "soft" colloidal polymer spheres were blended with colloidal silica particles and then cast on a substrate, followed by drying at room temperature for self-assembly, an elastic crystal film was directly obtained. These "soft" polymer spheres can self-assemble into three-dimensional ordered crystal film since nanosilica particles can effectively obstruct the coalescence and highly deformation of these "soft" polymer spheres during film formation. This crystal film has not only reversible and repeatable mechanochromic-responsive property, but also tunable color and peak position covering almost entire visible spectral region, depending upon the sizes of polymer spheres and strains. This optical response is attributed to the variation of lattice spacing during deformation.(3) Thermal-responsive poly (N-isopropylacrylamide)/silica composite colloidosomes were synthesized via inverse Pickering suspension polymerization using various sizes of silica particles as stabilizers. The droplets of N-isopropylacrylamide aqueous solution were first emulsified in toluene and stabilized by modified silica particles, and then polymerized to obtain PNIPAm/silica composite colloidosomes. Preliminary studies showed that these PNIPAm/silica composite colloidsomes had similar thermal-responsive behavior as pure microgel with the LCST of 32℃. The colloidosomes prepared by MPS modified silica and DCMS modified silica showed different thermal-responsive behavior and dye release rate. The release experiments showed that release rate of the microspheres increased with increasing silica size and the temperature, indicating that the releasing property can be either controlled by the particle size of silica or the temperature.