Design And Synthesis Of Carbon Black (or Silver)-Polymer Core-Shell Hybrid Materials

In recent years, considerable efforts have been devoted to the design and synthesis of core-shell hybrid materials, due to the fact that their properties (optical, electrical, magnetic, catalytic, etc.) are a function of their size, composition and structural order. Encapsulation technologies not only improve the stability of the encapsulated product, protect the particles from interaction with surrounding medium, reduce the toxicity and facilitate storage or transport, but also endow the core optical, electrical, magnetic and catalytic properties. Such core-shell hybrid materials have been widely used in components of electronic and photonic devices, biology, medical fields, catalysis, plastics, coatings, inks and composites.1. Encapsulation of carbon black into polymer latexesCarbon black (CB) is widely used as a remforcing filler to improve dimensional stability, a conductive filler, an ultraviolet light stabilizer, an antioxidant to prolong the lifetime of rubber and a pigment or colorant. Compared with other nanoparticles to be embedded, the primary particle size of carbon black is rather small, the interparticular forces are very high, so that aggregates and agglomerates are easily formed, which inturn weakens the application properties. Therefore, it is of. great importance to prepare the carbon black dispersion with a high dispersion stability, either for pigments purposes or waterborne black ink for int-jet printer or coating. Carbon black modified with various polymers by polymerization produces not only the superior dispersion and stability, but also better wetting of carbon black by the polymer and possibly interaction between carbon black and polymer. So we investigate emulsion copolymerization of styrene with acrylic acid in the presence of aqueous carbon black dispersion. A relatively stable dispersion of carbon black encapsulated with Poly(styrene-acrylic acid) can be obtained. Various polymerization parameters such as the kinds of initiators, polymerization temperature, the ratios of carbon black/monomer were discussed and optimized. In contrast to the behaviors of KPS and AIBN, KPS/NaHSO₃ readily produced good yield of black product. To achieve less aggregates and agglomerates, reasonable rate of polymerization and high yield, polymerization temperature should keep at 40-60 ℃. In order to effectively achieve core-shell hybrid particles, encapsulation of polyacrylonitrile latexes has been designed and synthesized. The successful incorporation of carbon black into the polyacrylonitrile latexes was verified by TEM, FTIR, XPS measurements. The mechanism of the polymerization and encapsulation was discussed. Such toners that have a very small particle size within a narrow size distribution contribute to theenhancement of image quality with higher resolution and less edge roughness.2. Fabrication of Silver/silver oxides-coated carboxylated polystyrene latexesInterest in the design and controlled fabrication of metal-polymer nanocomposites continues to increase, due to their great potential in the areas of electronics, photonics, magnetics, and catalysis. It is well known that silver is superior to other nanostructured metal materials for many reasons such as electrical conductivity, antimicrobial effects, optical properties and oxidative catalysis. Therefore, fabrication of silver-coated latex particles is of special interest, and several routes have been reported in the literature, including surface precipitation reaction, thermal evaporation techniques or sputtering onto latex particles and self-assembly. However, in most cases, irregular thickness, a large number of non-coated particles, merely metal islands and incomplete surface coverage were usually obtained by these methods. Particles coated with silver nanoshells are generally difficult to synthesize because the reduction reaction is too fast to be controlled. Thus, we attempted to slow the rate of the silver reduction and coated carboxylated polystyrene latex particles with silver by the decomposition of the silver complex. It should be possible to control the thermal and hydrolytic decomposition byvarying the experimental conditions such as the amount and concentration of NaOH and temperature.Carboxylated polystyrene latexes were prepared by means of polymerization of styrene with acrylic acid or using oleate as a surfactant. Due to electrostatic attraction between the negatively charged -COO" on the surface of carboxylated polystyrene latex particles and positively charged Ag(NH3)2+ in the solution, Ag(NH3)2+ will be quickly attracted around the surface of carboxylated polystyrene latex particles under a basic condition to ensure the complete encapsulation. Then this silver complex undergoes a thermal and hydrolytic decomposition, Ag/AgO were deposited onto the surface of carboxylated polystyrene latex particles. It is assumed that it is quite critical to use acrylic acid as a comonomer to give a negative charge under a basic condition such that the positively charged silver complex will be quickly attracted around the surface of carboxylated polystyrene latex particles to ensure the complete encapsulation. Furthermore, the interaction between carboxyl group and newly formed Ag/AgO nanoparticles will promote locating Ag/AgO nanoparticles on the surface of carboxylated polystyrene latex particles. The core-shell hybrid materials were characterized with FTIR, TEM, SEM and XRD measurements. The results indicate that reducing agents, the amount of 40% NaOH solution and temperature plays a key role in the morphologies of hybrid particles. Furthermore, the amount of 40% NaOH...