Electrochemical and isothermal titration calorimetry studies associated with polymer-micelle complexes and surfactant/cyclodextrin inclusion complexes

Mwakibete, HKO

Abstract

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.

Citation

Mwakibete, H. Electrochemical and isothermal titration calorimetry studies associated with polymer-micelle complexes and surfactant/cyclodextrin inclusion complexes. (Thesis). University of Salford, UK

• Thesis Type: Thesis
• Deposit Date: Jun 25, 2009
• Publicly Available Date: Jun 25, 2009
• Additional Information: Additional Information : PhD supervisor: Professor Evan Wyn-Jones
• Award Date: Nov 1, 1994