Isothermal Titration Calorimetry Studies of Binding Interactions between Polyethylene Glycol and Ionic Surfactants

Abstract

The binding behaviors between poly(ethylene glycol) (PEG) and sodium dodecyl sulfate (SDS) were examined by isothermal titration calorimetry (ITC) technique. The binding interactions between PEG and SDS are dependent on the molecular weights of PEG. At low molecular weight (MW < 400 Daltons), SDS does not bind to PEG chains. As PEG molecular weight increases from 900 to 1450 Daltons, an endothermic peak, which is attributed to the formation of SDS/PEG aggregation complex by the polymer-induced surfactant micellization process is observed. SDS micelles of lower aggregation number adsorb on the PEG backbones and the PEG segments are solubilized in the hydrophobic core of SDS micelles. When the molecular weight exceeds 3350 Daltons, an endothermic peak followed by an exothermic peak is observed. The exothermic curve is associated with the re-hydration of PEG segments from the SDS micellar core to form SDS/PEG aggregation complexes through ion−dipole association, where the re-hydrated PEG backbones are bound to the outer surface of the SDS hydrophilic headgroups. The binding behaviors are controlled by the equilibrium between polymer-induced micellization at low SDS concentrations and ion−dipole association at high SDS concentrations. After the polymer saturation concentration, C 2, free SDS micelles are formed at C m. Increasing the polymer concentrations causes C 2 and C m to increase, however, the critical aggregation concentration (CAC) is independent of polymer concentrations. Polymer molecular weights strongly influence C m and C 2, but only marginally on the CAC.

Photoluminescent Detection of Nitrite with Carbon Nanodots Prepared by Microwave-assisted Synthesis

“…With a molecular weight cutoff membrane (Amicon Ultra-4, Millipore), CND stock solutions were obtained as equivalent to < 10 kDa. In the PL measurements, as samples were diluted from the crude product by a factor of 10000, PEG concentrations were kept less than 0.01 wt% 17 to avoid the micellar formation.…”

Thermodynamics of micellisation: Sodium dodecyl sulfate/sodium deoxycholate with polyethylene glycol and model drugs

“…Previous work has implied that the interaction between SDS and PEG is dependent upon the molecular weight of the PEG and known to be thermodynamically 'peculiar' exhibiting both endothermic and exothermic effects [15]. Our titration calorimetry results appeared to follow this expectation, as exemplified in Figure 1 for the micellisation of SDS in the presence of PEG whereby the first derivative of the titration curve corresponds to the CMC of SDS whilst the second broad inflection can be attributed to the PEG-SDS interaction (Figure 1).…”

“…Furthermore, increasing the polymeric concentrations can cause the polymer saturation concentration, C 2 , and CMC to increase although the concentration of those bound to polymer does not vary [15].…”

Effect of Acetonitrile and N,N-Dimethylformamide on the Formation of Poly(ethylene oxide)-Sodium Alkyl Sulfate Aggregates

“…This stabilization was mainly due to the solubilization of ethylene oxide groups on the micelle surface, 36 with a concomitant decrease in electrostatic repulsion among the SDS headgroups. 18 As the AN content increased, the ΔΔG agg values remained negative and increased slightly, indicating that the cosolvent decreased the stability of the SDS aggregates formed on the PEO chain, compared to the SDS aggregates formed in AN/water mixtures without polymer, but only to a low degree. Hence, the addition of AN affected the enthalpic/entropic balance associated with the PEO-SDS interaction.…”

“…Among a variety of polymeric structures, poly(ethylene oxide) (PEO) has received great attention for the formation of complexes with surfactants, especially sodium dodecyl sulfate (SDS). [17][18][19][20][21] A delicate balance of interactions governs the process of SDS aggregation with PEO, which occurs in different stages. 22 At the critical aggregation concentration (cac), which is lower than the critical micellar concentration (cmc) of the surfactant, SDS aggregates consisting of a small number of SDS monomers are formed on the polymer chain.…”