Capacity And Computer Simulation Of Gemini Surfactants

The surfactants are readily to adsorb at the surface for its special structure and reduce the surface tension. So they can change the character of the surface and put up a lot of applications. As the head groups in Gemini surfactant are connected by chemical bond and strengthen the hydrophobic effect between hydrocarbon chains, it has much higher surface activity than conventional ionic surfactant. In this paper, some basic characters including cmc, surface tension and aggregation number of a series of anionic Gemini surfactants have been investigated. The relationship between critical micelle concentration and molecular structure has been studied by Quantum Structure–Active Relationship (QSAR) method. And Dissipative Particle Dynamics (DPD) has been employed to study the microstructures of aggregates of Gemini surfactant in aqueous solutions.The overall results are shown below:1 The critical micelle concentration of Gemini surfactants has been studied by electrical conductivity method. Results showed that Gemini surfactants have much higher surface activity than traditional ionic surfactants. Cmc decreases with the increase of the spacer chain length for the spacer having almost the same nature. For the spacer has almost the same length but different nature, the surfactant with the flexible, hydrophilic spacer has the lowest cmc value. Calculation of the standard free energy (ΔG_mic ) of micellization is consistent with their tendency to form micelles in solution and negativeΔG_mic values suggested that the Gemini surfactants have great ability to form micelles in solution. C20 values show that it is more efficient in declining surface tension of the water.2 The steady fluorescence quenching method has been used to study the aggregation numbers (N) of Gemini surfactants in aqueous solutions. Results showed that the longer the spacer chain, the smaller the aggregation number for the same spacer nature and the Gemini with the flexible, hydrophilic spacer has the largest N for almost the same spacer length. The Gemini surfactant with hydrophilic, flexible spacer can form a well-packed micelle. Therefore, it offers us the probability to obtain Gemini surfactants with different aggregation properties by changing the nature of the spacer to need our different uses.3 The micellar growth of Gemini surfactants containing oxyethyl group spacer in aqueous solutions has been studied using dynamic light scattering. The size of the micelles increases with decreasing the length of the spacer chain, which suggested that long spacer chain prevents the growth of micelle. Transmission electron microscopy at cryogenic temperature (cryo-TEM) was extensively used to investigate the microstructure of Gemini surfactant in aqueous solutions. The cryo-TEM studies showed that with increasing the concentration, spherical micelle could be seen and it can exist in a very broad concentration range.4 The relationship between cmc and surfactant structure has been studied using QSAR models and regression models were built up by principle component analysis-partial least squares (PCR-PLS) and genetic function approximation (GFA) respectively. Results showed that the GFA models has much higher precision and predictive capacity and it suggests that QSAR methods can give us probability to predict the character of aqueous solutions of Gemini surfactants with almost the same structure and give guidance to the synthesis of newly Gemini surfactants with higher activity.5 The microstructure of aggregates of Gemini surfactants in aqueous solutions was investigated by dissipative particle dynamics (DPD) simulation. We found that DPD simulation can look into the assemble process. With increasing the concentration of Gemini surfactant, the aggregates can form different structures: spherical micelle, peanut micelle, mixed micelle of sphere and rod, rod-like micelle and lamellar phase. As predigested DPD particles (beads) are employed in DPD simulation, it can hold up the main structure characteristic of these amphiphile and compare with the results of experiments and give advices to the design of the experiments.