Nilesh Dharaiya

Spectral and hydrodynamic studies on p-toluidine induced growth in cationic micelle

The effect of p-toluidine (PTD) on the growth of cationic surfactant micelles in aqueous solutions was examined by viscosity, UV-visible spectroscopy, dynamic light scattering (DLS), (1)H NMR and nuclear Overhauser effect spectroscopy (NOESY). Viscosity and scattering results are used to follow the growth of the aggregates and examine the structural transitions that occur. The reduction of electrostatic repulsions between the surfactant headgroups in combination with the hydrophobicity of the additive caused micellar growth and viscoelasticity at high PTD concentration; the micellar growth was found to be more pronounced in the presence of salt. (1)H NMR chemical shift changes reflect the interaction of PTD molecules with surfactant micelles while 2D NOESY experiments reveal that PTD molecules insert themselves in micelles such that its -CH(3) group is in contact with the core region and the benzene ring resides near the palisade layer of micelle.

Microstructural morphologies of CTAB micelles modulated by aromatic acids

The morphological changes in cetyltrimethylammonium bromide (CTAB) micelles caused by the presence of three phenylalkanoic acid analogues viz. 3-phenylpropanoic acid (PPA), 3-phenylprop-2-enoic acid (PPE) and 3-phenylprop-2-ynoic acid (PPY) have been examined by 1H NMR, light and neutron scattering and rheology. Spheroidal CTAB micelles transform into vesicles in the presence of PPY and elongated ellipsoidal micelles with PPE and PPA. The CTAB/PPY system showed an interesting phase transition from vesicles to long rod-like micelles at a temperature of ∼45 °C or at pH ∼9 while CTAB/PPE and CTAB/PPA systems even in alkaline pH (∼9) showed little effect. pH- and temperature-dependent self-assembly of CTAB with analogous aromatic acids behaves differently and may have applications in microfluidics, drag reduction, and encapsulation processes.

Different pH triggered aggregate morphologies in sodium oleate–cationic surfactants mixed systems

The aggregate morphologies in aqueous solutions of sodium oleate (NaOl) + dodecyldimethylamine oxide (DMDAO, zwitterionic) or dodecyltrimethylammonium bromide (DTAB, cationic) were investigated over a wide pH range (3 to 13) by tensiometry, rheology, scattering and spectral measurements. NaOl and DMDAO show interesting micellar behavior with pH changes. NaOl forms worm-like micelles at higher pH (∼12) and ellipsoidal micelles in the pH range ca. 9–11, which transform into vesicles at pH ca. 7 to 8. Due to hydrolysis, NaOl cannot be used in acidic pH, but this deficiency can be conquered by the mixed system of NaOl with DTAB and DMDAO. NaOl strongly interacts with DTAB to form vesicles in a wide pH range. The DMDAO/NaOl mixed system forms ellipsoidal micelles on mixing, which turn into vesicles at pH below 9 and short rods at higher alkaline pH without undergoing any precipitation. The effect of salt on the transition of NaOl as well as mixed micelles has also been described. These studies provide an alternative to the restriction of the use of fatty acid soaps in acidic pH, and are worthwhile for industrial and domestic purposes.