Study On Aggregates In Aqueous Solution Of CH/CF And CH/Silicone Surfactant Mixtures

Surfactants can self-assemble to form many kinds of aggregates in aqueous solutions such as sphere,rod-like,disk-like or worm-like micelles,vesicles,lamellas.It is the structure and property of the aggregates that determine the performance of surfactants. For example the function of volatilization,emulsion and micro-reactor is connected with the architecture of the aggregates of surfactants in solution.The aggregates in mixed surfactants are much more fascinating.For only by changing the composition or the ratio between surfactants,we can adjust the morphology and property,of aggregates,acquiring idea performance which has more meaning for technical application.Several surfactant systems in aqueous solutions are studied in this paper and the results are summarized as following:1.Different length hydrogenated surfactant/fluorinated surfactant system1.1 C₁₂DMAO/C₇F₁₅CF=CHCOOH system(T=25.0±0.1℃)C₇F₁₅CF=CHCOOH is almost insoluble in water at room temperature and has a Krafft point higher than room temperature.Mixing it into 100mM C₁₂DMAO (dodecyldimethylamine oxide)solution we obtained CH/CF cationic/anionic (catanionic)surfactant system.The phase behavior,structure and property of the aggregates in the mixed surfactant solution were investigated.The results showed that the mixed solution has complex phase behavior.Unilamellar vesicles with a broad distribution formed when the concentration of fluorinated surfactant is at 50 mM. Below this concentration the mixed surfactant system experienced the transformation between worm-like micelle and unilamellar vesicle.Study by phase behavior, rheology measurement,DLS,Cryo-TEM,¹H,¹⁹FNMR and IR shows that the fluorinated surfactant C₇F₁₅CF=CHCOOH and hydrogenated surfactant C₁₂DMAO forms anionic/cationic ionic C₁₂DMAOH⁺-^-OOCCH=CFC₇F₁₅through the hydrophilical heads.The combined structure is helpful to understand the mechanism, structure and properties for the self-assembly aggregation of the salt-free CH/CF catanionic surfactant systems.1.2 C₁₄DMAO/C₇F₁₅CF=CHCOOH systems(T=25.0±0.1℃) The size and size distribution of the aggregates in 100mM C₁₄DMAO (tetradecyldimethylamine oxide)solution changed dramatically when a small quantity of fluorinated surfactant C₇F₁₅CF=CHCOOH was put into it.When the concentration of fluorinated surfactant was at 10 mM,two modules of size distribution of micelles were obtained.When the concentration of fluorinated surfactant was at 50 mM two modules of size distribution of vesicles were observed.The results demonstrate that although the elecstatic combines the hydrophilic heads of the two kinds of surfactants together,the weak interaction of the hydrophobic parts of hydrogenated and fluorinated surfactants leads aggregates with two kinds of compositions formed in mixed CH/CF surfactant system:one of aggregate is rich in hydrogenated surfactant, and another is rich in fluorinated surfactant.It can be concluded that the demixing phenomenon between hydrogenated and fluorinated surfactants will be enhanced when the length of hydrogenated surfactant tail increases or the concentration of the surfactants increases.1.3 C₁₆DMAO/C₇F₁₅CF=CHCOOH systems(T=60.0℃±0.1℃)Vesicle phase formed when 10 mM C₇F₁₅CF=CHCOOH mixed with 100 mM C₁₆DMAO(hexadecyldimethylamine oxide).Since molecular packing parameter (p=V/al)for the mixed surfactants increases,mixed hydrogenated and fluorinated surfactants have more tendency to form Lα-phase.2 Non-ionic surfactant/amino modified polysiloxane system(T=25.0±0.1℃) When 10wt%iso-C₁₃E₅(isotridecylalkohol-5EO)solution(multilamellar vesicle phase) or 10 wt%iso-C₁₃E₅/C₄E₂(wt%/wt%,1:1)(diethylenglykolmonobutylether)solution (disk-like micelle phase)mixed with up to 20%amino modified polydimethylsiloxane (silicone surfactant),transparent microemulsion of amino silicone oil formed at some concentration domain.The droplet dispersed in the microemulsion is actually the aggregates of nonionic surfactants and positive charged amino modified polysiloxane. The structure and properties of self-assembled aggregates were observed through phase behavior,Cryo-TEM,and rheological measurements.It is suggested that the conformation of amino modified polysiloxane changes with its concentration in the mixed surfactant system.And the conformation of amino modified polysiloxane is influenced by its concentration and co-existed surfactants.It is concluded that the key to form transparent microemulsion of amino silicone oil is to control the conformation of amino modified polysiloxane so that the aggregates of amino silicone oil and other surfactants is no bigger than 50 nm.