Electrochemical and isothermal titration calorimetry studies associated with polymer-micelle complexes and surfactant/cyclodextrin inclusion complexes
The effective degree of micellar dissociation of cetyltrimethylammonium bromide (CTAB) micelles has been determined from electrochemical (EMF) measurements using a CTAB selective electrode. Thermodynamic parameters have been determined using the `Ion binding model' and show dominance of hydrophobic interactions in free CTAB micellization. The enthalpy contribution is insignificant. The binding of the surfactant CTAB onto the neutral watersoluble hydrophobic polymers: poly(propylene oxide) (PPO), poly(vinylmethylether) (PVME) and ethyl(hydroxyethyl) cellulose (EHEC) has also been investigated by the EMF technique. In all cases it has been shown that the surfactant binds to the polymer and the bound surfactant exists in the form of small aggregates. The EMF data has been used to investigate the characterization of the binding process. The formation of inclusion complexes between alkylpyridinium bromide (CPyBr) and alkyltrimethylammonium bromide (CIITAB) with a- and ß-cyclodextrins (CDs) have also been investigated by the EMF technique. In addition the thermodynamics of the inclusion on a- and ß-CDs by the surfactants : CTAB, CPyBr, alkylsulfates (COSO3Na) , and alkanesulfonates (CnSO3Na) have been carried out using an Omega isothermal titration calorimeter (ITC). Whereas ß-CD systems form predominantly 1: 1 complexes, a-CD form 1: 1 and a 2: 1 complexes with surfactants having long hydrophobic tails. For both a- and ß-CD the complexation constants increase as the chain length of the surfactant increases, showing that the driving force dominating the formation of these complexes is the hydrophobic effect. The 1: 1 ß- CD/surfactant complexation is accompanied by large increase in entropy. The 1: 1 a-CD/surfactant complexation and all 2: 1 complexation are accompanied by a large increase in enthalpy.