Preparation Of Different Morphology Particles Via Miniemulsion Technology And Their Properties

Miniemulsion polymerization technology has been developed for more than thirty years, it would be deeply exploited in many areas, due to the droplet nucleation mechanism, fast polymerization rate, uniformly formed latex and so on the characteristics. So, expanding the applied areas of miniemulsion polymerization technology is of important reality and scientific foreground. Based on the miniemulsion polymerization technology and aimed at expanding its applied areas, we have done some works in latest research areas of preparing the CdS nanocrystalline hollow spheres templated with miniemulsion droplets, synthesising thiol-functionalized PSt particles using miniemulsion polymerization and obtaining organic-inorganic composite particles further, and producing PSt-SiO₂ hybrid asymmetric particles in one step via miniemulsion polymerization. The detailed research content and experimental results are as following:(1) CdS hollow spheres with well-controlled morphology and uniform size were successfully prepared using a miniemulsion technique, in which miniemulsion droplets of isooctane prepared with dodecylmercaptane as a co-stabilizer were employed as templates. Dodecylmercaptane was adopted based on two reasons. First, it could act as a hydrophobe for retarding Ostwald ripening to allow production of a stable miniemulsion. Additionally, its -SH groups could generate S^- ions under alkaline conditions, which is beneficial for the formation of cadmium thiolate with Cd²⁺ ions around the droplets. The cadmium thiolate further reacted with S^2- ions fromNa₂S·9H₂O, directly forming CdS hollow spheres due to the evaporation of isooctane during the reaction and/or the subsequent drying process. No additional surface modification, additional dissolution or calcination of the templates was needed to fabricate the hollow spheres. The size of the hollow spheres could be tuned by altering the molar ratio of the anionic and non-ionic surfactants, while their shell thickness could be adjusted by changing the amount of costabilizer. EDX, XRD, HRTEM and the SA-ED patterns indicated that the shell of the hollow spheres was composed of CdS nanocrystals, which made these hollow spheres exhibit the quantum-confined effect, confirmed by UV-vis absorption and PL spectra.(2) Thiol-functionalized PSt particles were synthesised through miniemulsion polymerization technology, providing a new approach to producing organic-inorganic composite particles. In this system, DDM, CA-897 and KPS/NaHSO₃ were employed as co-stabilizer, surfactant and redox initiator separately. The polymerization kinetics was investigated in detail by varying the concentration of surfactant, type of initiator, polymerization style, adding style of DDM and whether the incorporation of alkali and so on. In addition, taking advantage of the strong interaction between thiol group and inorganic particles, the organic-inorganic composite particles were prepared. Moreover, the relationships between different functional groups and inorganic particles have been studied. It is demonstrated that -S^- and -SH groups could absorb inorganic particle into the surface of organic latex, but other groups appeared in our system could not, which is also proved by the results of TGA.(3) Organic-inorganic polystyrene (PSt)-silica (SiO₂) hybrid asymmetric particles were prepared in one step via a miniemulsion polymerization technique. The organic monomer (St) and inorganic precursor (TEOS) were confined in miniemulsion microreactor droplets. Phase separation of the organic moiety and the inorganic moiety resulted from temperature elevation and polymerization and was enhanced after the formation of PSt and SiO₂ due to the hydrophobicity of PSt and the hydrophilicity of SiO₂. Between each pair of asymmetric particles, silane couplers act as bridges connecting the PSt and SiO₂ particles and PSt-SiO₂ hybrid asymmetric particles could be synthesized in one step. In comparison with other strategies for preparing asymmetric product, the preparation of template particles was not needed in advance, and thus the relatively complicated modification of the templates was not needed. This approach is relatively facile and creative, and the yield of asymmetric particles exceeds 40%. The size of PSt particles in these asymmetric particles was easily tuned either by changing the weight ratio of St/TEOS or by varying the sonication power during the miniemulsion preparation. A possible formation mechanism of asymmetric particles is suggested and proved by the control experiments and the silane couplers play very important role during the formation of asymmetric particles. After functionalization of the as-prepared asymmetric dimers by surface decoration with Ag particles, enhanced surface-enhanced Raman scattering (SERS) properties were observed due to electromagnetic enhancement of the added Ag colloids. In addition, this method is also the application development of the Swelling-phase separation theory.