Formulation of novel microemulsions from biodegradable surfactants for their potential applications

Abstract

Microemulsions (ME) are isotropic thermodynamically stable solutions of two immiscible liquids (i.e water and oil) stabilized by surfactant or surfactant mixtures. These are macroscopically homogenous but microscopically heterogenous with distinct oil and water phase. Properties such as ultralow interfacial tension, high interfacial area and spontaneous formation, capacity to solubilize both water and oil soluble compounds make these systems unique for various potential applications such as in food industry, pharmaceutical industry, enhanced oil recovery (EOR), personal care industry, cosmetics and agrochemical formulations. These are also applied in the field of nanotechnology for the synthesis of various nanoparticles where ME is used as a template. Even though MEs have huge number of applications in various fields, but there are several challenges in the formulation of these systems. The main component in the development of microemulsion formulation is surfactant playing a key role in the production of MEs. Conventional surfactants that are widely used in the ME are chemically synthesized and petroleum-derived. The sulfate group present in these surfactants is mainly responsible for their poor biodegradability. There is a growing interest among the researchers from both the academia as well as from the industry to replace the petroleum-based surfactants in the products with biodegradable surfactants which directly influence the human health in pharmaceutical, cosmetic and personal care industry. This forms the primary motivation for current work to develop the microemulsions based on biodegradable surfactants for their potential applications in various fields. Owing to the advantages of sulfate-free surfactants, the work in this thesis is mainly based on the two sulfate-free, biodegradable surfactants for the formulation of microemulsions using combination of biocompatible oils and cosurfactants. The first surfactant used is N-Lauroyl Sarcosinate (SNLS) which is anionic in nature. It is a sodium salt of N-acyl amino acids with long chain hydrophobic acyl radical and hydrophilic carboxylic acid (-COOH) group present in it. The presence of N-methyl amido group [–CON(CH3)–] in the carbon chain strongly influence its physiochemical properties. Also, it is derived from sarcosine which is naturally available in plants and animals. Therefore, this is biodegradable surfactant. The second surfactant is non-ionic polyoxyethelene based surfactant: Igepal CO 520. It is pentaoxyethylene (5) nonylphenyl ether with oxyethylene chain as hydrophilic and branched alkyl chain as hydrophobic moieties in its structure. The polyoxyethylene group present in the surfactant renders superior properties such as solubility, absence of charge easy biodegradability of the surfactant. In this thesis, microemulsions are prepared and characterized using SNLS and Igepal CO 520 with different oils like caprylic acid, oleic acid, isoamyl acetate and isopropyl acetate. Short chain alcohols such as propanol and butanol are used as cosurfactants. Ternary/pseudoternary phase diagrams are prepared to obtain optimized microemulsion area. Effect of oils, cosurfactants, surfactant/cosurfactant ratios were studied in phase diagrams. Conductivity, viscosity, DLS, zeta potential, contact angle, dynamic surface tension, HRTEM, FTIR, UV-spectroscopy, foaming behaviour and stability studies are characterization techniques that are utilized in this research. Further, microemulsions prepared from SNLS are further utilized as nanocarrier for encapsulation of Vitamin E (α-tocopherol) which has application in controlled drug delivery. Encapsulation studies, DPPH antioxidant radical scavenging activity are performed to explain the antioxidant activity of SNLS based microemulsions. This work has applications in pharmaceutical, cosmetic, food and agricultural formulations. Thus, this thesis is mainly based on formulation and characterization microemulsions from biodegradable surfactants and their applications. This thesis consists of total seven chapters.