Electrochemical Characterization Of Supramolecular Gel

Self-assembly of small molecules is an important way of preparing new functional materials. Low molecular weight gelator and surfactant are good self-assembly units. Recently, the characterization of self-assembly and disassembly of supramolecular gel is a subject of increasing attention. Electrochemical method is simple, rapid and has high sensitivity and no requirement on the macro-morphology of gel. So it has a great potential on characterization of the structure of supramolecular gel. In this paper, the self-assembly and disassembly of the supramolecular gels formed by N,N-dibenzoyl-L-cystine (DBC) and the balance of hydrophobic/hydrophilic within the gemini surfactant micellar-hybridized DBC supramolecular gels were studied by electrochemical method. Then, the diffusion of micelle in gemini surfactant micellar-hybridized supramolecular gels formed by N-fluorenyl methoxycarbonyl-L-phenylalanine(Fmoc-Phe-OH) and the diffusion of ferrocene in organogels formed by1,3:2,4-di-O-benzylidene-D-sorbitol(DBS) were investigated. The results were as follows:1. The reduction behavior of electrochemical probes(Europium(Ⅲ) ions, potassium ferricyanide and tris(1,10-phenanthroline)cobalt (Ⅲ) perchlorate trihydrate) in gels formed by self-assembly of DBC and solution formed by disassembly of DBC were studied by differential pulse voltammetry. It was found that the reduction peak currents of electrochemical probes in gels were significantly less than in solutions. Thus the assembly and disassembly of DBC supramolecular hydrogels can be monitored by the change of the peak current of the electrochemical probes.2. The micellar-hybridized systems consisted of micelles formed from gemini surfactants and supramolecular gels formed by DBC. The SEM image indicated that the network structure of the micellar-hybridized gel was denser than that of a non-hybridized gel. It was found that the redox formal potential E0’ in hydrid gel is positive shift compared to that in non-hybrid gel, indicating that the hydrophobicity of the microdomians in hybrid gel was stronger. The hydrophobicity of microdomians in hybrid gel became stronger with the increase of surfactant concentration, leading to gradual positive shift of E0’. It was also found that△E0’ between hybrid gel and non-hybrid gel rapidly decrease with the increase of spacer length of the gemini surfactant and the decrease of alkyl chain length, indicating that the balance between hydrophobic/hydrophilic microdomains in micellar-hybridized systems can be modulated by spacer length and alkyl chain length of gemini surfactant. The results showed that the hydrophobicity of hydrid systems can be estimated by the variation of△E0’.3. SEM image showed three dimensional network structure of the gemini surfactant micellar-hybridized gel formed by Fmoc-Phe-OH. The critical micelle concentration of gemini surfactant16-6-16in gel was0.6times of that in aqueous solution. ESR revealed that electrochemical probe(TEMPO) was completely allocated in the gemini surfactant micelles, indicating that the diffusion of micelle in gemini surfactant micellar-hybridized gels can be monitored with TEMPO by electrochemical method. It was found that the diffusion coefficient of micelle increased first and then decreased with the increase of spacer length of the gemini surfactant, and deceased with the increase of alkyl chain length and concentration of gemini surfactant. The increase of the temperature of the system can accelerate the diffusion of micelle.4. The diffusion of ferrocene in DBS organogels formed in acetonitrile, propene carbonate, and cyclopropanone was studied by cyclic voltammetry. Increasing the viscosity of organic solution, the diffusion coefficient of ferrocene deceased. With the concentration of DBS increased, the network of organogels were denser, resulting in limit diffusion of ferrocene.