Research On Aggregation Behavior Of Perfluorocarbon Carboxylic Acid Mixed With Different Hydrocarbon Surfactants

Molecular self-assembly is similar to chemical synthesis,which is an important method to produce new substances and new functions.The mixture of surfactants has rich aggregation behavior,which can form a variety of aggregates by self-assembly,including micelles,lamellar structures,vesicles,and cubic structures.Therefore,this article explores the aggregation behavior of fluorocarbon-hydrocarbon surfactant systems by changing the size and geometry of surfactant molecules,the type of surfactant mixing system,and the mixing concentration and ratio,in order to achieve the controllable construction of different aggregation structures.In this paper,the anionic surfactant perfluoroundecanoic acid(C₁₀F₂₁COOH)and the nonionic surfactant tetraethylene glycol monododecyl ether(C₁₂EO₄)are mixed in aqueous solution to study the aggregation behavior of the system by controlling the total concentration of the two surfactants and changing the mixting concentration.It is found that with the increase of C₁₀F₂₁COOH concentration,the mixed system can form the lamellar phase?L_?phase?,gel phase?Gel phase?,L_?'phase and Gel'phase.The rheological results show that the viscoelasticity of the vesicles gels is significantly higher than that of the lamellar phase.The freeze fracture transmission electron microscopy?FF-TEM?images show that there are densely packed vesicles in the two gel phases,and planar lamellar structures in the L_?'phase.Differential scanning calorimetry?DSC?results show that layers of different aggregates are crystal structures at room temperature.Small and wide angle X-ray diffraction?XRD?measurements show that vesicles are arranged more closely than planar lamellar structures.The aggregation behavior of nonadecafluorodecanoic acid(C₉F₁₉COOH)and perfluorononan-1-oic acid(C₈F₁₇COOH)with C₁₂EO₄ in aqueous solution is further investigated in order to investigate the effect of the length of fluorocarbon chain on the aggregation behavior of the mixture of the negative and nonionic surfactant.It has been found that the length of fluorocarbon chain has a significant effect on the aggregation behavior of this type of mixed system.Different from the C₁₀F₂₁COOH/C₁₂EO₄/H₂O system,with the increase of the concentration of C₉F₁₉COOH,there are L_?phase,Gel phase,L?'phase and L₁/P mixed phase in the system of C₉F₁₉COOH/C₁₂EO₄/H₂O.And L_?phase,L₁/L_?mixed phase,L₁/P mixed phase,L₁/L_?'mixed phase and L_?'phase are observed in the system of C₈F₁₇COOH/C₁₂EO₄/H₂O.At the same concentration of fluorocarbon surfactants and C₁₂EO₄,with the increase of the length of the fluorocarbon chain,the size of the vesicles increases obviously,and the viscoelasticity increases obviously as well.The DSC results show that the bilayer of the vesicles formed by the C₈F₁₇COOH/C₁₂EO₄/H₂O system is liquid at normal temperature,while the layer of the vesicles formed by C₉F₁₉COOH/C₁₂EO₄/H₂O and C₁₀F₂₁COOH/C₁₂EO₄/H₂O is crystalline at room temperature.The results of XRD show that the vesicles formed in the C₁₀F₂₁COOH/C₁₂EO₄/H₂O system are more closely arranged.In order to study the aggregation behavior in the mixed system of anionic and cationic surfactant,C₈F₁₇COOH has been mixed with the cationic surfactant dodecyl trimethyl ammonium hydroxide?DTAOH?.It turns out to be that the system has rich aggregation behavior.With the concentration of C₈F₁₇COOH increasing,there are L₁phase,L₁/L_?mixed phase,L_?phase and Gel phase in the system of C₈F₁₇COOH/DTAOH/H₂O.The viscoelasticity of the mixed system increases with the increase of C₈F₁₇COOH concentration,and the viscoelasticity of the sample increases with the increase of the total concentration of the surface active agent without changing the proportion of the two surfactants.The results of cryogenic transmission electron microscopy and FF-TEM show that the L_?phase has multilayer vesicle structure with dense monolayer vesicles in the gel phase.The results of DSC show that the layers of the vesicles in the L_?phase and the Gel phase are crystal structures at room temperature,and XRD further indicates that the vesicles in the Gel phase are more closely arranged.The results of ¹⁹F nuclear magnetic resonance show that the interaction between fluorocarbon chains and hydrocarbon chains in Gel phase is stronger than that in L_?phase.