The Interaction Of Poly (Ethylene Glycol) And Sodium Dodecyl Sulfate

The interaction between polyethylene glycol (PEG) and sodium dodecyl sulfate (SDS) was investigated in this paper. The association between nonionic polymer (PEG) with anionic surfactant (SDS) has been verified by a variety of techniques. With increasing surfactant concentration, no interaction between the polymer and the surfactant is detected until a critical aggregation concentration, known as the CAC (Critical Association Concentration) is reached. It has to be noted that the CAC can be detected by a variety of techniques such as surface tension, conductivity and viscosity. The CAC is usually lower than the normal CMC in the absence of polymer. This is a clear indication of interaction between polymer and surfactant. Above the CAC, surfactant form aggregates bound to polymer. The polymer chains become saturated with surfactant aggregates at a concentration C2, above which polymer-surfactant complexes coexist with free micelles. The exact nature of the interaction between PEG and SDS is concluded that the PEG chain is wrapped around the SDS micelle with some of the segments of PEO adsorbed at the hydrocarbon/water interface, while most of them form loops in the surrounding water. The PEG residues interact with the hydrated methylene group and with polar groups of the SDS but do not penetrate the hydrocarbon core.The surface tension method was applied to a mixture of a highly surface active species, the surfactant, and a feebly surface of active species, the polymer, because of the simplicity of this method. We can see from the surface tension data that at lowpolymer concentration, SDS may interact with PEG, which leads to a decrease in surfactant monomer concentration; however, at high PEG concentration, the surface tension remained unchanged, so the surfactant monomer concentration remains constant, and the polymer does no absorb significantly on the surface. There are two possible causes for the disappearance of PEG: either it is forced off the surface by the high surface pressure of the surfactant and/or it is lost by the complexation with the surfactant.The effect of SDS on the molecular size of PEG in aqueous solutions has been studied experimentally by determining their viscosity and conductivity. The plots of conductivity vs. concentration for SDS-PEG aqueous solutions show two transition points, which correspond to the beginning of the complex formation (CAC) and the beginning of the surfactant micelles formation (CMC), respectively. It was found that before CAC, the unperturbed mean square end-to-end distance of the PEG in SDS aqueous solutions was the same as that of in water. In the range between CAC and CMC, an increase of end-to-end distance was observed with increasing the concentration of SDS. When concentration of SDS was larger than its CMC, the expansion of PEG chain reached a maximum. The conclusion from the experimental part is that molecular complexes are formed form PEG chains and charged SDS micelles, which make the chains expand and increase the viscosity of solution.At last, the PEG monolayer was studied. Surface pressure data lead to the conclusion that the spread polymer is in a thermodynamically favorable environment on pure water and with NaCl was added which becomes worse as DMF was added the aqueous sub-phase.