Interactions between Gemini Surfactants and Polymers: Thermodynamic Studies

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• 作者：Rita Muzzalupo ; Maria Rosa Infante ; Lourdes Pé ; rez ; Aurora Pinazo ; Eduardo F. Marques ; Marta Letizia Antonelli ; Chiara Strinati ; Camillo La Mesa
• 刊名：Langmuir
• 出版年：2007
• 出版时间：May 22, 2007
• 年：2007
• 卷：23
• 期：11
• 页码：5963 - 5970
• 全文大小：116K
• 年卷期：v.23,no.11(May 22, 2007)
• ISSN：1520-5827

文摘

Aqueous mixtures containing a homopolymer, poly(vinylpyrrolidone) (PVP), or a hydrophobically modified graftcopolymer, HM-pullulan, (PULAU₉, where 9 stands for the nominal substitution degree), and different Gemini surfactantshave been investigated at 25.0 C. A wide variety of experimental conditions were addressed by changing the amountof polymer and of surfactant. The Gemini surfactants were synthesized, purified, and characterized by routine methods.They differ from each other in polar head groups (two sulfonate-, two quaternary ammonium-, or two arginine-basedgroups), in alkyl chain length (11 or 12 carbon atoms), and in the distance between the polar head groups. The spacersconsist of 2, 3, and 6 methylene units or 3 oxyethylene units. Surface activity and solution calorimetry measurementsyield some physicochemical features inherent to micelle formation and polymer-surfactant interactions. The data aresupported by ionic conductivity, detecting the critical thresholds and quantifying the modifications in binding associatedwith critical association (CAC) and micelle formation (CMC^*). The Gibbs energy of transfer from the micelles to apolymer-binding site, G_trans, was evaluated from the CAC/CMC^* ratios versus the amount of added polymer. Asimilar procedure determined the enthalpy of transfer, H_trans. G_trans decreases with added polymer, whereas H_transbecomes more negative on increasing the amount of polymer in the medium. According to the selected data presentedhere, cationic Geminis do not interact with PVP, while significant interactions have been observed in other surfactants.In mixtures with PULAU₉, the interaction is significant for all Geminis. This effect is due to interactions betweenthe surfactants and the hydrophobic alkyl groups on the main polymer chain. The pendent groups facing away fromthe polysaccharide chain act as binding sites for aggregates onto such polymers.