| Microemulsion is a dispersion system spontaneously formed by a certain proportion of surfactant,cosurfantant,oil and water,which is transparent or translucent,isotropic and thermodynamically stable,and the droplet size of microemulsion is about 1-100 nm.Microemulsion has the advantages of low interfacial tension,thermodynamic stability and large solubilization capacity,which is widely used in food,pharmaceutical,cosmetic,chemical reaction,and oil exploitation.In this thesis,microemulsion was prepared,and its phase behavior and properties were studied.The thermodynamic and structural parameters of W/O microemulsion were calculated from the physicochemical aspects.Moreover,the curcumin was encapsulated by microemulsion and the related properties were also explored.The Gemini surfactant(14-3-14,14-4-14,14-5-14,14-6-14)were synthesized in our laboratory as a surfactant in microemulsion phase,with short chain fatty alcohol as cosurfactant,with medium chain length fatty hydrocarbon as oil phase.The phase behavior of microemulsion prepared by these four components was systematically studied.The effect of Km value,the number of intermediate linker in Gemini surfactants,the type of alcohol,the type of oil phase and temperature on the area of microemulsion was investigated.(1)The Km of microemulsion is one of the important factors affecting the microemulsion area.The microemulsion area decreases with the increase of Km,thus the reasonable control of Km is important.(2)The length of the intermediate carbon chain of Gemini surfactant has an important effect on the properties.The results show that with the increase connecting group,microemulsion area is decreased with fixed Km value,alcohol and oil.(3)The different length of carbon chain alcohols as cosurfactant added to microemulsion has an important effect on the pseudo three component phase diagrams of 14-n-14/alcohol/water/oil microemulsion.With the increase of carbon chain length,the microemulsion phase area decreases.(4)With the increase of carbon chain of oil phase(aliphatic)of 14-n-14/alcohol/oil/water microemulsion,the phase area is firstly increased and then decreased.(5)In the 14-4-14/alcohol/aliphatic hydrocarbon/water system,the temperature has little effect on the microemulsion phase area,indicating that this microemulsion has good thermodynamic stability.Due to the larger area of single-phase microemulsion formed by 14-4-14/propanol/heptane/water system,so the properties of microemulsion was investigated by means of conductivity,cyclic voltammetry,DLS,DSC,TEM,UV and fluorescence.(1)The microemulsion phase can be divided through conductivity experiments.When the mass fraction of oil is low,the system will appear three kinds of microstructures.With the increase of water content,the W/O,B.C.and O/W structures appear in the single phase region.When the mass fraction of oil increases,the O/W region disappears,and only the first two structures exist in the system and the value of ?c is increased with the increase of mass fraction of oil.Continue to increase the mass fraction of oil,bicontinuous structure(B.C.)system has not yet appeared,and the phase separation has occurred in the system and only W/O structure exists.(2)The cyclic voltammetry used ferricyanide as electrochemical probe.Only when ferricyanide completely dissolved in droplets,the probe will diffuse as the droplets move,then the calculated diffusion coefficient is equal to the diffusion coefficient of microemulsion droplets.The microscopic structure of microemulsion can be determined by plotting the water content and diffusion coefficient.The experimental results show that it is very close to the results of the conductivity,indicating that cyclic voltammetry can also be used to detect the changes of microstructural of microemulsion.(3)The particle size of microemulsion on 7/1 dilution line was measured by DLS,and the relationship between the radius of microemulsion and R value was discussed when the system was in the W/O structure.With the increase of water content,the particle size of microemulsion is also increased.There is a good linear relationship between the microemulsion radius and R value in the W/O structure which is in accord with micellar solubilization theory and proved that the W/O microemulsion is spherical in shape.(4)Methyl orange and methylene blue were used as probes in UV experiment.The results of spectral experiments showed that the polarity of the core in W/O microemulsion is increased with the increase of water content.Fluorescence experiments used pyrene as fluorescent probe,it has shown that with the increase of water content,the ratio of pyrene I1/I3 is increased,indicating that the W/O microemulsion polarity is increased with the increase of water content.The results are consistent with the experimental observations of UV.(5)The results of transmission electron microscopy showed that the shape of the microemulsion is spherical and the particle size is between 1-100 nm.(6)Differential scanning calorimetry can detect the state of water in different structures of microemulsion and indirectly reflect the structure of microemulsion.By measuring the DSC heating curve of a series of microemulsions with different water content on the 7/1 dilution line,the corresponding water structure ratio can be calculated.In 0-10%,the water mainly exists in the form of non freezing water,and the structure of microemulsion is W/O type.As the water content increased to 10-40%,the water in the system has two different kinds of bound water,which indicates that the microemulsion at this point is in the bicontinuous structure.When the water content increased to 50-70%,the water in microemulsion mainly exists in the form of free water,demonstrated that the structure of microemulsion at this time is O/W.The results of DSC are close to the experimental results of cyclic voltammetry which confirmed the reliability of this method.Research on thermodynamic and structural parameters of W/O microemulsion showed that the Gibbs free energy of 14-4-14/alcohol/oil/water system is negative during the formation of microemulsion at 25 ?,indicating the formation of microemulsion is spontaneous behavior.The longer the carbon chain of alcohol,the more formation of W/O microemulsion.When the carbon chain length of oil phase increases,the absolute value of Gibbs free energy increases first and then decreases,which indicates that for the microemulsion,the carbon chain length of oil phase has a maximum value.The increase of the intermediate linker in Gemini surfactant increases the amount of alcohol required in the interfacial layer,which leads to the difficulty of the movement of alcohol from the continuous phase to the interface layer.Therefore,with the increase of n(the number of intermediate linker in Gemini surfactants),the absolute value of Gibbs free energy of alcohol moving from the continuous phase to the interfacial layer decreases,indicating that the decrease of n is beneficial to the stability of microemulsion.When ? is 15(? is water and surfactant molar ratio),with the increase of n,the micelles of the 14-n-14(n = 3,4,5,6)W/O microemulsion become small,and the water core radius Rw,the radius of the dispersed phase Re and the average aggregation number of each dispersed the surface activity of particles in agent molecules ns are decreased.For the 14-4-14/alcohol/oil/water system,with the increase of?,the total dispersed phase Ad and the dispersed Nd decrease,while the Rw,Re,ns and the interfacial layer thickness l increase.With the increase of the number of carbon chains of alcohols,Rw,Re,n,and l increase,while Ad and Nd decrease.With the increase of the number of alkane carbon chains,Rw,Re,n,and l increase firstly and then decrease,while Ad and Nd decrease firstly and then increase.Microemulsion was used to encapsulate curcumin,and the properties of curcumin microemulsion were studied.The following conclusions were drawn:(1)The absorbance at 423 nm with different concentrations of curcumin was measured,and the corresponding standard curve was drawn.Then,the dissolution of curcumin by different aliphatic hydrocarbons was studied,and it was found that heptane dissolved most of curcumin,and the next experiment was done with heptane as oil phase.(2)The size of curcumin microemulsion in different concentrations was studied by DLS experiment.The results showed that(S+A)/O = 7/1,the mass fraction of<0.15%curcumin when curcumin concentration is increased,the particle size is increased.When the mass fraction is more than 0.25%,the increase of curcumin leads to the rupture of the microemulsion,and the particle size is more than the definition of particle size of microemulsion.(3)The results of acid base experiments showed that the curcumin microemulsion system has certain acid and alkali resistance.Studies based on the water content and(surfactant+cosurfactant)/quality of oil phase ratio showed that with the increase of water content,the drug loading(DLR)and entrapment efficiency(EE)increased.With the increase of mass ratio of(surfactant+cosurfactant)/oil phase,the DLR and EE decrease.(4)The results of DPPH antioxidant test showed that the antioxidant capacity decreases with the increase of surfactant/oil phase mass ratio.The results of vitro release experiment of curcumin microemulsion showed that compared with the curcumin ethanol solution,microemulsion have obviously sustained effect of curcumin on PBS medium at pH = 7.2.With(Surfactant+cosurfactant)/oil mass ratio decreases,the sustained release effect continues to increase. |
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