Formation Mechanism Of Surfactant-Free Microemulsions And Their Applications In Material Synthesis,Drug Solubilization,and Gel Preparation

The application of traditional microemulsions is limited due to the large amount of surfactants,which are costly and prone to harm individual organisms and environment.Surfactant-free microemulsions（SFMEs）overcome the above-mentioned disadvantages of traditional microemulsions and have certain advantages in terms of cost,environmental protection,and biocompatibility.However,there are still many problems that need to be solved for SFMEs.For example,what are the matching conditions between the three components to form SFMEs,what is the stabilization mechanism of SFMEs,what are the practical application prospects of SFMEs?In this thesis,the parameter"?"is defined for the first time to explain the relationship between the three components in SFMEs system.The theory and experiment are combined to provide a reasonable explanation for the formation and stabilization mechanism of SFMEs.In addition,several novel and green SFMEs systems were constructed and their applications were expanded in the field of nanomaterial synthesis,drug solubilization and disinfection gel.Part â…  Study on the formation and stabilization mechanism of SFMEsThe work in this part is based on the Flory-Huggins theory and defines the parameter"?",which establishes the connection of amphi-solvent,water and oil phases.The relationship between?and the proportion of single-phase area in the ternary phase diagram（S）is as follows:S=67.8-97.2?.According to this relationship,the requirement for one ternary system forming SFME can be put forward:when the?value is less than 0.7,SFME can be formed.The ternary system that can form SFME has the largest single-phase area of 70%.The universality and applicability of the proposed regulation was proved by 45 ternary systems.In addition,based on the dissipative particle dynamics（DPD）theory,a new coarse-grained simulation model was proposed from the perspective of molecular volume.Taking the new green SFME system of methyl salicylate/ethanol/water as a representative,the energy changes of the interactions among three different components,the density distribution,and the structural composition of three different sub-regions of oil-in-water（O/W）,bicontinuous（B.C.）and water-in-oil（W/O）in the SFMEs system were obtained.The charge distribution of O/W and W/O droplets was simulated using density functional theory（DFT）.The analysis of the theoretical and experimental results show that the dynamic equilibrium process between the components in the ternary system leads to the decrease of the free energy of the system and promotes the formation of SFME.The directional distribution of the amphi-solvent,which leads to the charge of the droplets,can promote the dispersion of the droplets and enhance the stability of the SFME system.In addition,the water molecules distributed around the hydroxyl groups of ethanol molecules can form"electron traps"when the O/W droplets collide,leading to charges transfer.This work deepens the understanding of the formation mechanism of SFMEs system and provides theoretical guidance for the design of new green SFMEs.It is expected to promote wide applications of SFMEs system in different fields.Part â…¡ Template synthesis of metal oxide nanoparticles by SFME and its catalytic mechanismA new SFME system（decanol/ethanol/water）was constructed,andα-Fe₂O₃was synthesized and characterized using the W/O SFME as a template.The formation mechanism ofα-Fe₂O₃in W/O droplets and its performance in catalytic degradation of Rhodamine B（Rh B）and the degradation mechanism were investigated.It was found that the template role of W/O SFME could be optimized by regulating the reaction temperature and reaction time,avoiding Oswald ripening and obtainingα-Fe₂O₃nanospheres with smooth surface and good dispersion.The surface of the synthesizedα-Fe₂O₃contains a large amount of free Fe,which helps to catalyze the generation of?OH and O₂·^-radicals from H₂O₂.DFT simulations show that the process of generating?OH and O₂·^-radicals can proceed spontaneously under daylight conditions.Therefore,α-Fe₂O₃synthesized in the W/O SFME system has better catalytic properties as well as better catalytic stability and reusability compared toα-Fe₂O₃synthesized in other medium.Hope this work provides important guidance for the synthesis of materials in SFME systems.Part â…¢ Study of solubilization and transdermal release properties of SFME system as drug carrierBased on the conclusions that the SFME systems obtained in the above study have different sub-regional intermolecular interactions,SFME systems can be used as drug carriers to carry lipid-soluble drugs and increase the solubility,stability and bioavailability of drugs.A novel,green SFME drug carrier containing eucalyptus oil,n-propanol and water was constructed.All-trans retinoic acid（ATRA）,a metabolic intermediate product of vitamin A commonly used in clinical practice,was selected as a representative lipid-soluble drug.The solubilization of lipid-soluble drug in the O/W SFME system and its mechanism were investigated for the first time.The transdermal release properties and release kinetics were determined.The results show that the solubilization of ATRA in the SFME system is much higher than that in water and other microemulsion systems.The light stablity,thermal stability,centrifugal stability and oxidation resistance of the solubilized ATRA in the SFME system are greatly improves.The release process of ATRA is in accordance with the Korsmeyer-Peppas kinetic model.The present work demonstrates the advantages of SFME systems in drug design and provides guidance to develop the application of SFME systems in the field of drug carriers.Part â…£ Preparation of SFME-Gel for skin disinfectionBased on the in-depth understanding of the O/W structure and solubilization properties of SFME systems in the above,this part of work considers that the incorporation of large molecular hydrophilic substances in the aqueous phase of the system can construct a new type of SFME-Gel.It has the advantages of both SFME and Gel and is more suitable for use as a skin disinfection preparation.Therefore,a colorless and transparent SFME-Gel with good adhesion,easy to apply and comfortable skin feel was developed for the first time based on methyl salicylate/ethanol/water SFME system combined with natural hydrophilic macromolecular polymer hyaluronic acid（HA）.Experiments show that HA is uniformly distributed in the aqueous phase of the O/W structure of the SFME systems,which plays the role of skeleton support and water absorption and moisturization.Methyl salicylate and ethanol are present in the interstices of the skeletal network structure.Such microstructure makes SFME-Gel heat and cold resistant and has good stability in long-term storage.The closed human skin patch test confirmed that SFME-Gel could reduce the strong irritation of ethanol to human skin and significantly reduce the occurrence of adverse reactions.In addition,the results of skin surface sterilization experiments showed that SFME-Gel had good killing effects on Staphylococcus aureus,Escherichia coli,and Candida albicans,which met the disinfection effect requirements for disinfection products in the Disinfection Technical Specification.The new SFME-Gel system has important practical application value.