Average Molecular Weight And Its Distribution Of AAS Effect On The Phase Behavior

In this paper, eight kinds of alkyl aryl sulfonates(AAS) which have definite structurewere finely synthesized from methylbenzene, m-xylene, p-xylene, decanoyl, undecanoyl,dodecanoyl,tridecanoyl chloride,-bromoalkaneand heptyl bromide, the symbols aretC12-3S,mC12-3S,tC14-3S,mC14-3S,tC16-3S,pC16-3S, mC17-8S and mC18-8S,respectively.The content of surfactant in the products were all more than95.5%. Compounded the eightalkyl aryl sulfonates, we got complex systems of average molecular weight which were390,404,418,432. And designed five kinds of molecular weight distribution systems for eachcomplex system, they were incremental distribution, descending distribution, reverse normaldistribution, normal distribution and uniform distribution.The structural parameters and thermodynamic functions (transfered from the continuousoil phase to the interfacial region) of complex systems of AAS/alcohol/n-decane/inorganicsalts microemulsions were obtained by means of dilution method, the effects of the averagemolecular weight and its distribution of AAS on the structural parameters and thermodynamicfunctions were investigated. And the influences of temperature, salinity, content of water,kind of co-surfactants were also investigated.The results showed:(1) the values of Rw, Re, n,di,-â–³G_o⁰â†'i,â–³S_o⁰â†'ipresented: normal distribution﹤descending distribution﹤uniformdistribution﹤incremental distribution﹤everse normal distribution; the values of Nd, Ad,changed to contrary.(2) with the increasing of average molecular weight, the values of Rw,Re, n, di,-â–³G_o⁰â†'i,â–³H_o⁰â†'i,â–³S_o⁰â†'iincreased; the values of Nd, Addecreased; and thevalues of structural parameters changed as a linear function of the average molecular weightof the AAS,generally.(3) increasing the content of water was not advantageous to theformation of the microemulsion and its stability; but increasing the hydrocarbon chain lenghtof alcohols, the salinity and the temperature were advantageous;the process of transfer fromthe continuous oil phase to the interfacial region was endothermic process and it wasentropy-driven.The complex system of AAS/alcohol/n-decane/inorganic salts microemulsions wereobtained by means of Winsor phase diagram.We investigated the effects of the averagemolecular weight and its distribution of AAS on the characteristic parameters of middle phasemicroemulsion. And the influences of temperature, concentration of surfactant andco-surfactant, kind of salts and co-surfactants and content of water were also investigated.Theresults showed:(1) the values of S1, S2, S, S^*presented: normal distribution>descending distribution>uniform distribution>incremental distribution>everse normal distribution; thevalues of V^*and S.P changed to contrary.(2) with the increasing of average molecularweight, the solubilization capacities increased; the electrolyte tolerances decreased; and thevalues of logS^*, V^*, S.P changed as a linear function of the average molecular weight ofAAS.(3) with the increasing concentration of AAS,the solubilization capacities increased;and with the increasing the concentration of n-butanol, the hydrocarbon chain lenght ofalcohols, the temperature, the electrolyte tolerances were worse, the solubilization capacitieswere stronger; the electrolyte tolerance of system which contains K⁺was the strongest, andthe solubilization capacity of system which contains Mg²⁺ was the strongest in thisexperiment.