pH-dependent polyampholyte SDS interactions.
Aqueous solutions of sodium dodecylsulfate (SDS) and poly(N,N'-diallyl-N,N'-dimethyl-alt-maleamic carboxylate) (PalH), a synthetic pH-tuneable polyelectrolyte (PEL), have been investigated by various techniques at different pH-values in absence and presence of NaCl. Potentiometric measurements using a surfactant-selective electrode indicate a quite complex interaction mechanism, which can be subdivided into different regions, where non-cooperative, electrostatic and cooperative hydrophobic interactions are of relevance. It was concluded, that in dependence on pH, conformational changes are responsible for the different interaction behavior in the NaCl-free system. Isothermal titration calorimetry (ITC) suggests that early stage hydrophobic binding is an exothermic process followed by electrostatic interactions, which are endothermic in nature and entropy driven. After NaCl addition the interaction mechanism becomes independent of pH due to a screening of (i) attractive interactions between the surfactant head groups and oppositely charged binding sites and (ii) repulsive forces between the surfactant head groups. Furthermore, the ITC investigations have revealed that after salt-addition surfactant micelles interact with the polymer instead of separated SDS molecules due to a depression of the CMC.
Fechner
Mabya
M
Universität Potsdam, Institut für Chemie, Karl-Liebknecht-Straße 24-25, Haus 25, D-14476 Potsdam (Golm), Germany.
Kosmella
Sabine
S
Koetz
Joachim
J
D004573:Electrolytes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D011108:Polymers / Q000737:chemistry*; D012965:Sodium Chloride; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D055672:Static Electricity
D004573:Electrolytes; D011108:Polymers; D012967:Sodium Dodecyl Sulfate; D012965:Sodium Chloride