Investigation Into Properties And Behaviors Of 3-(N, N-Dimethyldodecylammonio)-2-Hydroxypropanesulfonate

Surfactants are amphiphilic substances which have their hydrophilic and hydrophobic structural parts. A surfactant can be classified by the presence of charged groups. A nonionic surfactant has no charge groups in its head. The head of an ionic surfactant carries a net charge. If the charge is negative, the surfactant is more specifically called anionic; if the charge is positive, it is called cationic. If a surfactant contains a head with two oppositely charged groups, it is termed zwitterionic.Solution of surfactants exhibit unusual physical properties. Adsorption of surfactants as an orientated monolayer at air-water and oil-water interfaces is one way of avoiding the entropically unfavourable contact between water and the hydrophobic part (generally one or two alkyl chains) while retaining the aqueous hydrophilic part contact. Self-association into structures with marked hydrophobe-hydrophile separation is another way of achieving this. Therefore, Surfactants reduce the surface (interfacial) tension by adsorbing at the interface, and. can also assemble in the bulk solution into a variety of aggregates. Indeed, spherical micelles, rod-like micelles, bilayers, reverse micelles, vesicles and others have all been observed. The property of these aggregates is essential in many biological processes and is used in many industrial and domestic applications.3-(N,N-dimethyldodecylammonio)-2-hydroxy-propanesulfonate (abbreviated as DSB) is classified as internal quaternary zwitterionic surfactant, which has been prepared from the reaction of 1-chloro-2-hydroxypropanesulfonate (ECHS) with N.N-Dimethyldodecylamine (ADA). DSB molecule contains a head with two oppositely charged groups: a quaternary ammonium cation and a strongly sulfonate anion. They have exhibited anomalous behavior, such as those of outstanding solubility in strong electrolyte aqueous solution and stability in strong acid and alkaline. DSB is now commercial and used in oil recovery and cosmetic manufacture and so on. The critical micelle concentration (CMC) is defined as the concentration of surfactants in free solution in equilibrium with surfactants in aggregated form. Surface tension has historically provided one of the more popular means for determining CMC. Computer simulations have proved a useful tool to explicitly understand the structure of micelles. The interfacial tension (IFT) at the oil-water interface must be ultralow if the residual crude oil is to be mobilized through the injection of surfactant solutions. Ultralow IFT is necessary for surfactant system to be applied in enhanced oil recovery.This thesis reports an investigation of the properties of aqueous surfactant systems that involved DSB by means of experimental and molecular simulation techniques. Our interest in the properties of DSB aqueous solution stems from our previous work with enhanced oil recovery where the surfactant flooding generally cannot be used to effectively recover oil from reservoirs of high salinity or hardness because of the precipitation of ionic surfactants. It is the fact that the mixed DSB-carboxylates flooding system has a higher salinity and multivalent ions tolerances.Firstly, we have prepared zwitterionic DSB surfactant that had been purified by recrystallization and characterized by ¹H NMR. The rates of change in the concentration of reactants have been examined in different mediums of isopropanol/water. These quaternization reactions have been confirmd to fit second-order kinetics. Therefore, the rate of reaction depends on the effective collisions of 1-chloro-2-hydroxypropanesulfonate (ECHS) and N,N-Dimethyl-dodecylamine (ADA) of per unit time, which leads to an increasing reaction rate.Secondly, the surface tension of aqueous solutions of the systems of DSB and sodium dodecanoate have been measured as a function of the total molality of surfactants. Surface area calculations were based upon the Gibbs adsorption equation for DSB and sodium dodecanoate. Critical micelle concentrations have been determined by means of surface tension measurements. Plots of surface tension vs log concentration for the systems of DSB and sodium dodecanoate at 35℃gave sharp breaks corresponding to values of CMC respectively. Comparison of sodium dodecanoate with DSB shows that the latter is somewhat more surface active. However, the critical micelle concentration of any mixture is lower than that of either pure surfactant. The synergism in this respect is present. The value of the interaction parameterβ^m between sodium dodecanoate and DSB in mixed micelle formation can be calculated by particular expression based on the Rubingh model of nonideal multicomponent mixed micelle. The results indicated that the mixed micelle of DSB-sodium dodecanoate is about equimolarly composition. Thirdly, In order to obtain more details on the characters of DSB micelles and ion distributions at the interface of DSB micelles, we have performed molecular dynamics simulations on a Marrink coarse grained model of water-sodium chloride-surfactant system. We aim to perform a simulation of the spontaneous form DSB and DSB/sodium dodecane sulfonate (SAS) mixed micelles in electrolyte solution. The results, reported in this thesis, show the process of spontaneous aggregation into a roughly spherical micelle from a random solution of surfactant monomers in electrolyte solution.The dynamics of self-assembly process (growth and fragmentation of micelles, surfactant monomer insertion or removal) of DSB/SAS mixed micelle appears to follow that of stepwise addition or removal of surfactant monomers process. As for the pure DSB surfactant micelle, we can observe the process of spontaneous aggregation into a roughly spherical micelle from a random distribution of DSB monomers in NaCl solution undergoes two stages: initial flock together small clusters, subsequently formation of micelle with cluster-cluster coalescence manner. This appears to be due to the formation of premicellar aggregates, which need to be further verified by experiments.By evaluating the properties of DSB micellar structure, such as the radius of gyration, eccentricity, micelle size, NaCl ions and water distribution, radial distribution and probability distributions function of DSB micelle with respect to the center of micellar mass, we can obtain the results that the zwitterionic polar groups (SO3 and NC2 particles) in the DSB molecular structure are unfolding on the surface of the micelle forming a dipolar layer. The Na⁺,Cl^- ions and water can penetrate into the micelle. Some Na⁺,Cl^- ions have been restricted in the dipolar layer of zwitterionic micelle, and the concentration of NaCl ions in the dipolar region is greater than that in the bulk.Finally, the solubility product (K_sp) of fatty acid salt has been analysised to view the hardness tolerance of mixed carboxylates-DSB flooding system. The precipitation of the anionic surfactant by association with counterion can be represented by a solubility product relationship between the anionic surfactant monomer and the total unbound counterion. The concentration of free anionic surfactant monomeror is the CMC of alklycarboxylate-DSB mixture multiply the mole fractions of alkylcarboxylate in mixed solution. Therefore, we can deduce the salinity tolerance (namely counterion concentration necessary to cause precipitation) increases because of that mixed micelle formation reduces the anionic surfactant monomer concentration. On the other hand, the structure of DSB micelles has been studied by the molecular dynamics simulation. The DSB micelle was found to have a dipolar layer on surface of micelle. Some ions of NaCl have been restricted inside the dipolar layer, and the concentration of NaCl ions in the dipolar region is greater than that in the bulk. Since the ions of Na⁺ have been bound in the dipolar region of micelles of zwitterionic DSB, then by inference so have multivalent ions of Ca²⁺ and Mg²⁺. By density functional theory of Gaussian programs, we have calculated the minimum energy for model compound of DSB/dodecyl acid/Ca²⁺, and obtained the charge of dominating atom in this model compound. These results indicate there are probably many "negative-charge holes" in the dipolar layer of micelle, and the ions of Ca²⁺ and Mg²⁺ in solution can be bound in the micelles. Therefore, the research in this thesis has shed new light on the causes of the Ca²⁺ and Mg²⁺ ions tolerance enhancement gained by addition of zwitterionic DSB surfactant to the alkyl carboxylates flooding system.