Ishpinder Kaur

Aggregates of cationic surfactants and anionic polyelectrolytes influenced by bulky head group modifications

The conductivity (κ), viscosity (η), turbidity (τ), and 1H NMR measurements of benzylhexadecyldimethyl ammonium chloride (BHDACl)+hexadecylpyridinium bromide (HPyBr) and BHDACl+hexadecylpyridinium chloride (HPyCl) mixtures in aqueous dextran sulfate (DX) and polyacrylic acid (PAA) sodium salts have been carried out. κ, η, and τ showed that HPyBr interacts more strongly with anionic polyelectrolytes and that too with PAA. 1H NMR measurements indicated that intercalation of pyridinium head group of HPyBr and HPyCl in BHDACl micelles produced deshielding to all head group protons of BHDACl, whereas vice versa produced shielding to those of pyridinium head groups. The magnitude of shielding was much stronger on HPyBr rather than HPyCl head group protons. In the presence of polyelectrolytes, the shielding of pyridinium head group by the incorporation of benzylic ones reduced in comparison to that in pure water. The results suggested that pyridinium head group interacted more strongly with DX and PAA rather than with benzylic and which had been attributed to the steric hindrances created by the latter in the course of cationic micelle–anionic polyelectrolyte interactions.

Surfactant-polymer aggregates of mixed cationic micelles and anionic polyelectrolytes: a surfactant head group contribution

Single and mixed-micelle formation by benzyldimethylhexad-ecylammonium chloride (BHDACl), hexadecyltrimethylammonium bromide (HTAB), and their mixtures in aqueous anionic polyelectyrolytes, viz. carboxymethylcellulose sodium salt, dextran sulfate sodium salt, polystyrene sulfonate sodium salt, and polyacrylic acid sodium salt, were studied with the help of conductivity, κ, viscosity, η, turbidity, τ, and NMR studies. κ showed a single aggregation process for pure and mixed surfactants and the concentration at which it took place was slightly higher than the actual critical micelle concentration in pure water. Hence, it was termed the critical aggregation concentration (cac). Application of the Clint equation revealed that the attractive interactions between BHDACl and HTAB even in the presence of polyelectrolytes were responsible for the large deviation from ideal behavior. Both ηr and τ did not indicate the presence of a cac but instead they showed another aggregation process at much lower concentration than the cac, which was termed the pre-cac. They also demonstrated strong electrostriction effects in the case of BHDACl—polyelectrolyte systems, whereas weak electrostriction effects were observed for HTAB—polyelectrolyte. The former was explained on the basis of weak electrostatic interactions due to the steric hindrances created by an aromatic ring in the BHDACl head group. NMR results showed that the proton resonance of head groups and hydrophobic tails of both surfactants underwent deshielding and shielding effects, respectively. The former was more significant in the case of BHDACl, whereas the latter one was more significant in the case of HTAB. Both factors indicated the formation of compact mixed-micelle-polyelectrolyte aggregates.

Triphenyl- and tributyl-phosphonium head groups contributions in mixed cationic surfactants and anionic polyelectrolytes aggregates

Abstract Cationic micelle-anionic polyelectrolyte interactions of hexadecyltrimethyl ammonium bromide (HTAB), hexadecyltriphenylphosphonium bromide (HTPB), hexadecyltributylphosphonium bromide (HTBB), and their mixtures with carboxymethylcellulose (CMC) sodium salt, dextran (DX) sulfate sodium salt, polystyrene sulfonate (PSS) sodium salt, and polyacrylic acid (PAA) sodium salt were studied with the help of conductivity (κ), viscosity (η), turbidity (τ), and NMR studies. The results showed that among the phosphonium surfactants, HTPB interacts more strongly with polyelectrolytes than HTBB since the butyl chains of the latter screen the electropositive centre which has to interact with the active sites of anionic polyelectrolytes. This was explained on the basis of folding of butyl chains in the head group region of the micelle. 1 H NMR results further concluded that HTAB+HTPB produced compact mixed micelles, which interacted more strongly with polyelectrolytes in comparison to HTAB+HTBB mixed micelles.