Interactions between Poly(acrylic acid) and Sodium Dodecyl Sulfate:  Isothermal Titration Calorimetric and Surfactant Ion-Selective Electrode Studies

• Published in: The journal of physical chemistry. B Vol. 109; no. 11; pp. 5156 - 5161
• Main Authors: Wang, C, Tam, K. C
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 24.03.2005
• Subjects: Acrylic Resins - chemistry; Calorimetry - methods; Ion-Selective Electrodes; Light; Scattering, Radiation; Sodium Dodecyl Sulfate - chemistry
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp045468t

Interaction between a monodispersed poly(acrylic acid) (PAA) (M W = 5670 g/mol, M w/M n = 1.02) with sodium dodecyl sulfate (SDS) was investigated using isothermal titration calorimetry (ITC), ion-selective electrode (ISE), and dynamic light scattering measurements. Contrary to previous studies, we report for the first time evidence of interaction between SDS and PAA when the degree of neutralization (α) of PAA is lower than 0.2. Hydrocarbon chains of SDS cooperatively bind to apolar segments of PAA driven by hydrophobic interaction. The interaction is both enthalpy and entropy favored (ΔH is negative but ΔS is positive). In 0.05 wt % PAA solution, the SDS concentration corresponding to the onset of binding (i.e., CAC) is ∼2.4 mM and the saturation concentration (i.e., C S) is ∼13.3 mM when α = 0. When PAA was neutralized and ionized, the binding was hindered by the enhanced electrostatic repulsion between negatively charged SDS and PAA chains and improved solubility of the polymer. With increasing α to 0.2, CAC increases to ∼6.2 mM, C S drops to 8.6 mM, and the interaction is significantly weakened where the amount of bound SDS on PAA is reduced considerably. The values of CAC and C S derived from different techniques are in good agreement. The binding results in the formation of mixed micelles on apolar PAA coils, which then expands and dissociates into single PAA chains. The majority of unneutralized PAA molecules exist as single polymer chains stabilized by bound SDS micelles in solution after the saturation concentration.