Design, Sysnthesis And Characterization Of Organic(Polymer)/Inorganic Composite Materials

In recent years, nanocomposites as novel materials with unique functions have been researched widely. They have vast range of application prospects in many fields, especially for the fields of photics, conductor materials, magnetic materials and sensing materials for sensor. Because organic/inorganic nanocomposites exhibit the advantages of both organic and inorganic materials, nanocomposites with unique functions which contain workability, flexibility, rigidity and electromagnetic property can be obtained by tuning constitution, structure and size of organic phase and inorganic phase. During numerous composites, core-shell materials attract great interest of researchers due to their special structure and composition. The shell can greatly improve the stability of the core-shell materials and protect the materials from reacting with the outside surroundings. In addition, the shell can endow the materials with optical, electric, and magnetic properties.Silica has many advantages. For example, it is chemical inert and can improve stability of particles. Silica was optically transparent, biocompatible and could protect the surface of the nanoparticles from oxidation. The silanol groups on the silica shell can offer versatile possibilities for further surface modification. Silica can also be easily doped with fluorophores and dyes.Octylmethoxycinamate (OMC) was a commonly used organic UV absorber. It had high UV absorptivity. However, free radical which was produced during photodegradation would damage organism macromolecule and many varied cells, and cause skin troubles and deteriorate quality of cosmetics. In this paper, core-shell nanoparticles with OMC as core and with nanosilica particles as shell were prepared to remedy the defect of OMC and improve compatibility of UV absorber and the skin. First, SiO2 colloid was prepared with Sol-gel method and the optimal H2O/Si and the amount of hydrochloric acid were obtained. Then OMC/SiO2 core-shell nanoparticles were synthesized with the self-templating technique. The resulting nanoparticles are perfectly spherical with smooth particle surfaces, and represent clear core-shell structures.1,4-bis(o-cyanostyryl)benzene (CSB) was a commonly used fluorescent agent. In this paper, core-shell CSB-SiO2 nanoparticles were prepared via an O/W emulsion system using the self-templating technique. The stability of nanoparticles in aqueous solutions was investigated. Agglomeration of particles in aqueous solutions didn't occur until two months, and it was not obvious. In addition, effects of reaction conditions (amount of deionized water, ammonia concentration and solidification time) on their structure and morphologies were researched. Based on our experiment results, we concluded that the particle size and shell thickness could be readily controlled by altering reaction conditions. The UV absorption peaks of core-shell nanoparticles were blue-shifted from 222 nm and 302 nm to 207 nm and 289 nm respectively and the fluorescence emission maximum was also blue-shifted from 496 nm to 485 nm compared to those of CSB. The reason for the blue-shift could mainly be attributed to the different environments of CSB.Poly(p-phenylene vinylene)(PPV) and its derivatives have been widely investigated in electronics and photonics because of their excellent electrical and optical properties. First, Poly(2-methoxy,5-(2'-ethyl-hexoxy)-1,4-phenylenevinylene) (MEH-PPV) was synthesized with Gilch method. Then nanospheres with MEH-PPV cores coated by silica-based shells were prepared with the self-templating method. The resulting nanoparticles have clear core-shell structure and narrow size distribution. In addition, the glass transformation temperature (Tg) of core-shell nanaparticles increased compared to that of MEH-PPV. Afterwards, AIBN was used to regulate the conjugated length of MEH-PPV (MEH-PPVm) by the radical addition onto the double bonds of conjugated polymer, and MEH-PPVm was coated by silica-based shells with the self-templating technique. With the increase of reaction time the fluorescence emission peak of MEH-PPVm/SiO2 core-shell nanospheres was blue-shifted.Then, the mechanism of the self-templating method was discussed. One of the key techniques in preparing core-shell nanoparticles with the self-templating method is keeping the stability of the emulsion system. The whole process requires neither surface treatment for nanosilica particles nor additional surfactant or stabilizer but appropriate reaction parameters (amount of deionized water, ammonia concentration, stirring rate, etc.) to keep the stability of the emulsion system. The mechanism may be described as follows. The mixture of SiO2 nanoparticles and the core compounds in an appropriate amount of aqueous solutions forms an O/W emulsion system under the stirring of a homogenizer with high stirring rate, which prevents the agglomeration between emulsion droplets. After the outer surfaces of the emulsion droplets are solidified by the condensation reactions between the surface silanols, they may serve as self-templates. Subsequently, the un-reacted precursor within the emulsion droplets becomes solidified onto the templates as shell, while the core compounds stay inside as core, producing core-shell nanoparticles.There has been increasing interest in synthesis and development of poly (lactic acid) (PLA), because it was a nontoxic and biodegradable polymer. Here, poly (L-lactic acid) (PLLA) was prepared with L-lactic acid (LLA) as the raw material. First, L-lactide was synthesized with LA, and then PLLA was obtained through ring-opening polymerization of L-lactide. However, PLA also had many disadvantages. For example, it belonged to the polyester and had bad hydrophilic property, which reduced its biocompatibility. PLLA had low mechanical strength and couldn't meet many demands for applying in the filed of biomedicine. In order to broaden their applications, PLLA was modified in this paper. PLLA/SiO2 composites were prepared using 3-aminopropyltriethoxysilane (APS) as the coupling agent of PLLA and silica. The variations of PLLA/SiO2 composites water absorption rate as a function of different reaction conditions (the amount of APS, the amount of stannous octanoate (Sn(Oct)2), pH and the temperature) were researched. Compared to PLLA,the water absorption rate of PLLA/SiO2 composites had a great improvement. The optimal reaction conditions were obtained via orthogonal experiments: VTEOS=0.5 mL,pH=3,Sn(Oct)2=3d,T=50 oC。In addition, the weight loss temperature of PLLA/SiO2 increased obviously, which demonstrated the thermal stability of materials increased. Therefore, the preparation of PLLA/SiO2 composites was an effective means for improving the thermal stability of PLLA. Besides, the effect on transmittance was not obvious after modification.In summary, a series of core-shell composites and doped composites were prepared with self-templating method and Sol-gel method in this paper. The morphology, structure, particle size and shell thickness of nanoparticles obtained with self-templating method could be readily controlled by altering reaction conditions. In addition, the water absorption rate and thermal stability of PLLA/SiO2 composites had great improvements.