Aggregation Properties Of Inorganic Electrolyte/SDS/PEG Ternary System

The mixture of macromolecules and surfactants in aqueous solution is widely applied inpetroleum industry, pharmaceutics, chemicals manufacture and biology. Many kinds ofsystems of surfactants and macromolecules can form soft matter cluster self-motivationally.The soft matter cluster can be used as template to prepare metal nanoparticles. With thepurpose to investigate the template function of soft matter cluster in the formation of metalnanoparticle, it is necessary to study the supramolecular interaction between the soft mattercluster and metal ion and the effect of the metal ion on the structure, shape and size of the softmatter cluster.In this paper, the system of inorganic electrolyte/Sodium Dodecyl Sulfate (SDS)/Polyethyleneglycol (PEG) was studied by using surface tension measurement, fluorescenceprobe method, ultra-filtration, atomic absorption spectrometry, laser light scattering andtransmission electron microscope (TEM). The inorganic electrolytes used are Li2SO4, Na2SO4,K2SO4, AgNO3, CuSO4, Ni(NO3)2 and Cd(NO3)2. The main work and results are as follows:① The properties of the γ-lgc curves of system of inorganic electrolyte/SDS/PEG werestudied by using surface tension method. The results showed: for the system of SDS/PEG,the addition of monovalent metal salt was benefit to the formation of SDS bound micelle.The interaction between SDS bound micelle and PEG resulted in the decrease of c1 andthe slight increase of c2;therefore, the clusterization boundary of SDS/PEG extended, andthe saturation capacity of clusterization (Γ∞) and the specific saturation capacity ofclusterization ([Γ∞]) increased. The clusterization became more intense with the increaseof concentration of monovalent metal salt (ce). [Γ∞] of system of Li2SO4(50mmol·L-1)/SDS/PEG was a constant (12.58 mmol·g-1), which indicated that thesupramolecular interaction between SDS and PEG with the addition of monovalent metalsalt also complied with the quantitative rule. Different kinds of monovalent metal saltshad similar effect on c1 and c2, but because the radius of hydrated alkali metal ionincreases in order as follows: K+ (0.232 nm) < Na+ (0.276 nm) < Li+ (0.34 nm), thecapability of reducing surface tension of the hydrated ions decreased in the same order: K+> Na+ > Li+. When bivalent metal salt was added in the system of SDS/PEG, theinteraction between the SDS and PEG changed, which resulted in only one breakpoint onthe γ-lgc curve,② The aggregation number of bound micelle (Nb) in the aqueous solution of SDS/PEG withthe addition of the alkali metal sulfate salt was measured with steady-state fluorescencetechnique. Nb increased with the concentration of SDS(c) linearly when c was between c1and c2 – (cmc – c1), and increased monotonously with ce, while decreased with theconcentration of PEG (cp) because the number of combination points increased with cp.The relationship between Nb and c, ce, cp in alkali metal sulfate salt/ SDS/PEG system canbe expressed in the same equation:p843ep7643ep501243eln()ln()ln()caaaccacaacaccNb = a+ac+aa+ac+a+++++The polarity of the microenvironment of bound micelle, reflected by the pyrene probe,decreased with c and ce, but increased with cp. The value of c1 obtained by steady-statefluorescence technique was in consistent with that derived from surface tension method.③ Two critical concentrations occurred on the ultra-filtration curves of alkali metalsulfate/SDS/PEG system, while only one critical concentration (cmc) appeared on theultra-filtration curves of the systems containing bivalent metal salts, which confirmed theresults from the surface tension measurement. The adsorption number of the alkali metalion on the cluster increased with ce. The interaction between cluster and hydratedpotassium ion was more intense than that of hydrated lithium ion since the radius ofhydrated potassium ion is smaller than that of hydrated lithium ion.④ The result from the laser light scattering demonstrated that the hydrodynamic radius(Rh)of PEG20000 molecule is about 4.5 nm. Rh changed little with different cp, and theaddition of Na2SO4 decreased Rh. In the unitary system of SDS, Rh of SDS micelleincreased with increasing c. The Rh of SDS micelle increased with increasing c at first andthen decreased when Na2SO4 was added. There were two kinds of particles in theSDS/PEG solution. The smaller one was PEG and bound micelle. The relevant Rh was theaverage value of those two and decreased with increasing c at first, then increased. Whenc reached a certain value, the increasing aggregation number of the bound micelletightened the alignment of SDS molecules in the bound micelle and Rh kept stableafterward. The greater one was the cluster formed by PEG and bound micelle, the Rh ofwhich increased with increasing c. The Rh of bound micelle in the SDS/PEG solution withthe addition of Na2SO4 was smaller than that in the system without Na2SO4 and changedslightly with different c.⑤ The aggregation number and bound metal ions of bound micelle were less than those ofmicelle at the same concentration of SDS. The TEM graph demonstrated that the silverparticle prepared in the SDS/PEG system is smaller than that prepared in either SDS orPEG unitary system. It was concluded that the SDS/PEG cluster could be a kind oftemplate to control the size of nanoparticles in the preparing process.