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Research on Properties of Self-Assembled Structures in Mixtures of Anionic and Cationic Surfactants

Author: WangJingJing
Tutor: ZuoHongNi
School: Shandong University of Science and Technology
Course: Chemical processes
Keywords: mixture of cationic and anionic surfactant system cyclic voltammetry self-assembles diffusion coefficient lyotropic liquid crystal
CLC: O647.2
Type: Master's thesis
Year: 2009
Downloads: 46
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Abstract


Cyclic voltammetry of ferrocene(Fc) was applied to indicate self-assembled structures formed in mixtures of cetyl trimethyl ammonium bromide(CTAB) and sodium dodecyl sulfate(SDS) in order to reaveal the solution properties and formation mechanic.Salt additions and concentration were also studied in this article which effect the formation and properties of self-assembles.Cyclic voltammetry measurement in the mixture of cationic and anionic surfactants was proved not to be a electron reversible process.Ferrocene was performed as electroactive probe in order to detect electronic properties of mixed suractant system.Our observations suggest that electrochemical reaction of ferrocene was diffusion controlled electron reversible process within a range of surfactant concentration in SDS/CTAB system.Randels-Sevick equation was adopted to calculate the self-diffusion coefficient(D).The above research offers a new way in detecting properties of self-assembles in cationic and anionic surfactants system. A diffusion method theory of ferrocene was proposed based on volume of experiments.There exit two different diffusion method,one through moving with the whole self-assembles in short-ordered system and the other is moving through channels in hydrophobic area when long-ordered structures formed.Cyclic voltammetry measurements on relations between diffusion properties and content in SDS/CTAB system shows that the D value of Fc varies regularly with the content of CTAB. There occurred two symmetrical turning point when the mole ratio is about 2:1and 1:2 which indicate the formation of long-ordered structures.The position where occurred turning point was related to concentration and salt additive.The D value of electro active probe decrease with the increase of solution concentration which indicate the increase of long-ordered structures.The process of structure transition as a function of the salt additive was monitored by probing D value of ferrocene probe particles incorporated in these surfactant solutions. Result shows that D value of Fc probe in system with sodium sulphate(Na2SO4) increased compared to those salt-free surfactant system which means the formation of more densely self-assembles.Varying in salt type lead to different diffusion coefficient.Surfactant systems with sodium salicylate(NaSal) possess lower D value than with Na2SO4.The result above supplied with experimental evidence to application of self-assembles in mixed surfactants system.A novel cholestevic-like liquid crystal which shows beautiful iridescent color was observed in SDS/CTAB mixed surfactants system under certain content.We conclude that cholestevic-like liquid crystal maybe a transition form between lamellar and cubic liquid crystal.Self-diffusion coefficient curves of Fc changed wavely with peak in the conversion process of the above liquid crystal structures and reach the bottom when aqueous two phase system formed.The D value of electro active probe depends on its’ own diffusion method and the structure of self-assembles.Enhancing the role of electrostatic repulsion between surfactant molecular will benefit the transformation between lamellar to cholestevic-like and cubic liquid crystals.Property improvement and self-organized nano-particle process could be controlled by adjusting the electrostatic repulsion between surfactant molecular properly.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > The physical chemistry of surface phenomena > Surfactant chemical
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