Capillary Electrophoresis Investigation On Complex Interaction Between Poly (Ethylene Glycol) And Sodium Dodecylsulfate

The solution behaviors of polymer-surfactant systems have been more sufficiently revealed,driven by their increasingly widespread applications in the areas of daily chemicals,food,pharmaceuticals,oil drilling,advanced material preparing and so on.As a concern among all the polymer-surfactant systems,the interaction between nonionic polymers and anionic surfactants,including associated concentration range（c₁^c₂）,complex structure and solution property,has been systematically,closely described and identified.What a pity is that few researchers have reported the type of charge of the resulting complex.Beyond that,the importance and role played by the surfactant counterion have not been given consistent picture as well.In addition,although the adsorption at interface and micellization in bulk phase for surfactant have been generally accepted within the scientific community.There is still a lack of direct experimental evidence,limited by micelle size and its characterization technology,for the shape transitions of micelles induced by surfactant concentration,salts or other factors.Capillary electrophoresis,as an efficient,rapid and traceable method to separate and detect species with different charge density and types of charge,has been recently applied to study the interaction between neutral polymer and anionic surfactant as well as the types of charge of the forming complexes.However,because of the weak ultraviolet absorption,poly（ethylene glycol）（PEG）,sodium dodecylsulfate（SDS）and lithium dodecylsulfate（LDS）could not be detected by capillary electrophoresis equipped with UV detector and this method has not been used to study PEG-SDS and PEG-LDS complexes so far.In this paper,with the assistance of micellar solubilization of UV molecular probe or UV labeling reagent capping polymer,capillary electrophoresis makes it possible to solve the above problems.Based on above two auxiliary means,capillary electrophoresis is adopted as major tool of investigation and the experimental details are as follows:1.Identification of complexes without ultraviolet absorption as pseudo-polyanionsPEG-SDS and PEG-LDS were chosen as polymer-surfactant models with association but without ultraviolet absorption.Their electrophoretic behaviors were sucessfully obtained by dint of micellar solubilization of benzophenone or benzoic anhydride（BA）,o-phthalic anhydride（PA）capping PEG.The migration times and effective electrophoretic mobilities（μ_e）of the complexes demonstrated that the resulting complexes between PEG and SDS or LDS are actually pseudo-polyanions.Therefore,it could be concluded that the complexes without ultraviolet absorption,forming between neutral polymers and anionic surfactants,are also pseudo-polyanions.2.Effect of counterion on association interactionThe bridging and effect of counterion for PEG-dodecyl sulfate surfactants were distinctly determined according to the difference in aspect of complex effectiveness and efficiency,or ionization degree(α₁₂)of the PEG bound micelles,or K⁺tolerance,or effective electrophoretic mobility（μ_e）under conditions of various counterions,or inorganic salts,or pH.It was found that counterion with smaller hydrated ionic leads to a broader c₁^c₂,a smallerα₁₂and a more negetive value ofμ_e,which means a stronger interaction as well as pseudo-polyanion for the system.3.Association interaction sites and contribution of the interaction to emulsifiabilityIn order to determine the association interaction sites between nonionic polymers and anionic surfactants and the contribution of interaction to the system emulsifying property,sodium conjugated linoleate（SCL）was skillfully used due to its self-crosslinking activity,and the emulsifying abilities of PEG-SCL under various conditons were compared.It was obtained that the better emulsifying ability for polymer-surfactant compared with surfactant mainly comes from association interaction and the interaction sites are not on hydrophilic surface.of polymer bound micelle.Consequently,some evidence for“association is the key of certain outstanding properties for neutral polymer-anionic surfactant system”was provided.4.Shape transitions of anionic surfactant micellesAs an extension of capillary electrophoresis investigation,this method was applied to anionic surfactant solutions further.Sodium dodecyl benzene sulfonate（SDBS）and SDS were chosen as models to investigated the shape evolution of anionic surfactant micelle,and SDS micelles were endowed with UV response by the introduction of benzophenone.Results of micellar electrophoretic mobility,micellar aggregation number and the solution viscosity as the function of surfactant concentration,obtained by capillary electrophoresis,steady-state fluorescence quenching and capillary viscosimetry respectively,were consistent and reflected a transition process of micellar shape in the range of surfactant concentration,from aspects of driven force,micellar size and solution behavior.