Microemulsions for the Encapsulation of Drugs and Recovery of Metal Nanoparticles

Abstract

The work reported in the present thesis covers various investigations carried out under microemulsion conditions. More specifically it includes the encapsulation of nonsteroid anti- inflammatory drug (piroxicam) and the preparation and recovery of cetyltrimethylammonium chloride (CTACl) capped metal nanoparticles (Au, Pd, SiO2). Microemulsions are colloidal self-assembly fluids, function as nanoreactors and are suitable replacement for enhancing the loading capacity of drugs and recovery of nanoparticles. It was found that high loading capacity of piroxicam (1 wt%) and paramount recovery of nanoparticles (upto 98%) highlight the proficiency of the microemulsions in pharmaceuticals and in separation science. Microemulsion in this thesis has been used for encapsulation of anti-inflammatory drug (piroxicam). The results have demonstrated the absolute stability of microemulsion formulation after the incorporation of piroxicam. The main objective of this study was the development of rapid oil-in-water microemulsion to improve the loading capability of pharmaceutical compound in highly hydrophobic formulation. Tween-80 based microemulsion was successfully utilized to encapsulate and to enhance the solubility of piroxicam. In the present work various rheological and the spectroscopic analyses were employed to explore the gradual changes occurring in the microstructure of microemulsion. In addition, the consequence of piroxicam incorporation on the stability, optical consistency and microstructure of microemulsion formulation was also accomplished. Investigations into the stability of microemulsion under milder conditions showed that it remained clear and transparent over 10 months. During the project a special type of microemulsion was also developed that may make the recovery, recycling and reuse of nanoparticles easier for the manufacturers. The synthesis of nanoparticles in microemulsion systems has recently become an important focus of research. The inverse microemulsion (water-in-oil) technique has been successfully utilized to synthesize colloidal nanoparticles of inorganic materials. In the project a new approach towards the synthesis of gold nanoparticles (Au-NPs) in a reverse microemulsion was established and ‘at the flick of a switch’ water-induced separation route was employed for their recovery. Water-in-oil microemulsions (w/o MEs) stabilized by the cationic surfactant CTACl have been used as reaction media to generate Au-NPs. In addition the pure MEs have also been used as dispersion media for those Au and Pd-NPs, which have been pre- synthesized in aqueous phases and stabilized by sodium 2-mercaptoethanesulfonate (MES) ligands, and commercially available SiO2-NPs. A general method for recovery and separation of the nanoparticles from these mixed NP-ME systems has been demonstrated by tuning phase behavior of the background microemulsions. Addition of appropriate aliquots of water drives a clean liquid-liquid phase transition, resulting in two macroscopic layers, the NPs preferentially partition into an upper oil-rich phase and are separated from excess surfactant which resides in a lower aqueous portion. In order to assemble the detailed quantitative and qualitative outcomes of nanoparticles, UV-vis spectroscopy and transmission electron microscopy (TEM) were developed respectively. For instance, ~90% of the microemulsion prepared Au-NPs can be recovered; with even greater separation efficiencies attainable for pre-synthesized MES stabilized Au-MES-NPs (~98%) and Pd-MES-NPs (92%). For the silica NP-ME dispersions gravimetry indicates ~ 84% recovery of the NPs. TEM images of all systems showed that NP shapes and size distributions were generally preserved after these phase transfer processes. This low-energy and cost-effective purification route appears to be a quite general approach for processing inorganic NPs, having advantages of being isothermal, using only commercially available inexpensive components and requiring no additional organic solvents.