Synthesis Mechanism, Properties And Applications Of Silica Nanoparticles Templated With Individual Micelles

Silica nanoparticles templated with individual micelles have shown a very attractive prospect especially in bio-medicine area, because they not only combine the structure characteristic of micelle and the advantage of silica such as easy modification and bio-compatibility,but also overcome the disadventage of instability of micelle and poor loading capacity of silica particles. The use of individual micelles as template is a novel pathway to ynthesis monodisperse silica nanoparticles. The study on the synthesis of silica nanoparticles is meaningful for their applications in many fields such as drug release, adsorption, catalysis and so on.. In this dissertation, the mechanism of synthesis, properties, assembly and function are the main work. First the basic concept of surfactant and micelle has been presented, their application in the drug delivery system is briefly reviewed. Then the synthesis method of monodisperse silica nanoparticles has been concisely introduced, and their application in the drug delivery system is briefly reviewed. Based on these background, we propose the importance of the search project. Main research results obtained during my Ph. D. study are described as follows:1. We investigated the effects of organosilane termination agent in the formation of SCMCSNs. Experimental data (synthesis results, 29Si MAS NMR, molecule probe fluorescence spectra, etc.) from a synthesis system with Pluronic F127 as templates indicate that organosilane covers the surface Si-OH groups of nanoparticles. The reduction of surface Si-OH groups helps the stabilization of the nanoparticles by avoiding aggregation. The terminating behavior of organosilane is determined by its molecular structure including (1) the value of n: agent with larger number of methyls has stronger steric hindrance, which improves the terminating effect. The effective order of termination agent is TMES > DEDMS > MTES. (2) the length of hydrocarbon chain R: agent with longer hydrocarbon chain better blocks the attack from other nanoparticles. Accordingly the terminating effect of PTMS is better than VTES and MTES. (3) the charges of R: agent with charges makes silica nanoparticle well dispersed. (4) The effective organosilane termination agents are also applicable to other synthesis mixtures such as the systems using Si(OC2H4OH)4 as the silica source, or F108 or Brij 700 as the template.2. We have successfully prepared stable, monodisperse silica nanoparticles with tunable sizes from <20 nm to ~90 nm (base on DLS results) which is the most useful size range for the applications of nanoparticles in biomedical area. When 1,3,5-trimethylbenzene (TMB) as swelling agent, the size of nanoparticles can increased to 33 nm, the size increased with the increased amount of TMB and decreased temperature, the reason has been disscussd. When fatty acid as swelling agent, the size of nanoparticles can increase to 90 nm, and the effect of the length of fatty acid on the nanoparticles size has been studied. Among the fatty acid, the best swelling agent is octanoic acid. we use pyrene as a probe to investigate the hydrophobic environment of the core of nanoparticles. The ratios of I1/I3 are between 1.31 and 1.18 for the SCMCSNs functionalized with octanoic acid, which means the polarity of the core of nanoparticles is very low and the microenvironment is hydrophobic. The quick decrease of excimer pyrene is due to the decrease of the pyrene concentration in the hydrophobic region, which results from the hydrophobic core of nanoparticle being enlarged by addition of octanoic acid. It is obvious that the C153 emission shifts from 502 to 522 nm with the addition of more octanoic acid. The red shift of 20 nm is attributed to an increase in polarity of microenvironments, which confirms that the carboxyl group of octanoic acid in the nanoparticle locates at the PPO-PEO interface or PEO region. In summary the fluorescent spectrum behaviors of probe molecules indicate that the carboxylic acid groups of fatty acid locate at the PPO-PEO interface region of silica cross-linked F127 micelles (SCMCSNs).3.We studied the assembly behavior of the monodisperse silica nanoparticles. We investageted the effect of temperature, electrolyte. To increase the acting force among the nanoparticles, we added TEOS to the system, and obtain mesocellular silica foam (MCF).4 We can obtain monodisperse nanoparticles by using the trisodium salt of the triacetic acid N-(trimethoxysilylpropyl) ethylenediamine (TANED) which acts not only as termination agent for the successful synthesis of SCMCSNs but also acts as functional group to improve the performance of SCMCSNs for potential applications.The nanoparticles functional by octanoic acid can be used to load and release drug. The drug loading capacity of nanoparticles increases with the increase of the content of the octanoic acid in the block copolymers, because there is interaction between octanoic acid and drug. The release feature is also enhanced by the interaction. When more drug molecules are loaded, the SCMCSN sample can still release drug at a reasonable rate in long time.