The self-assembly in aqueous solutions of three quaternary salt-based C 16 -type cationic surfactants with different polar head groups and identical carbon alkyl chain viz. , cetylpyridinium bromide (CPB), cetyltrimethylammonium tosylate (CTAT), and cetyltriphenylphosphonium bromide (CTPPB) in the presence of 1-butanol (BuOH) and 1,4-butanediol (BTD) was investigated using tensiometry, 2D-nuclear Overhauser enhancement spectroscopy (2D-NOESY) and small angle neutron scattering (SANS) techniques. The adsorption parameters and micellar characteristics evaluated at 303.15 K distinctly showed that BuOH promotes the mixed micelle formation while BTD interfered with the micellization phenomenon. The SANS data fitted using an ellipsoid (as derived by Hayter and Penfold using the Ornstein-Zernike equation and the mean spherical approximation) and wormlike micellar models offered an insight into the micelle size/shape and aggregation number ( N agg ) in the examined systems. The evaluated descriptors presented a clear indication of the morphology transition in cationic micelles as induced by the addition of the two alcohols. We also offer an investigation into the acceptable molecular interactions governing the differences in micelle morphologies, using the non-invasive 2D-NOESY technique and molecular modeling. The experimental observations elucidated from computational simulation add novelty to this work. Giving an account to the structural complexity in the three cationic surfactants, the molecular dynamics (MD) simulation was performed for CPB micelles in an aqueous solution of alcohols that highlighted the micelle solvation and structural transition, which is further complemented in terms of critical packing parameter (PP) for the examined systems.
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Vibrational Raman optical activity of diacetyl L‐tartaric acid and corresponding surfactants: Sodium salts and shorter analogs of surfactants simplify the interpretations
Experimental vibrational Raman and Raman optical activity (ROA) spectra for diacetyl L‐tartaric acid (DAT), two of its esters, namely, monomethyl and lauryl esters (T1OH and T12OH), and corresponding sodium salts (DATNa, T1ONa, and T12ONa), are measured. T12OH and T12ONa represent the first chiral surfactants investigated using ROA spectroscopy. The quantum chemical (QC) predictions using B3LYP functional and 6‐311++G(2d,2p) basis set are used to interpret the ROA spectra for DAT, DATNa, T1OH, and T1ONa. It is found that the use of implicit solvation, as represented in polarizable continuum model (PCM), for predicting the experimental ROA spectra in aqueous solutions is inadequate for DAT and T1OH. However, the same PCM predicts the experimental ROA spectra satisfactorily for the DATNa and T1ONa. This favorable observation for the latter is attributed to the absence of intra‐ and inter‐molecular hydrogen bonding interactions for sodium salts in aqueous solutions. The overwhelming number of conformations resulting from 12‐carbon alkyl chain, in T12OH and T12ONa, makes it impractical to undertake QC predictions for them. Nevertheless, it is found that the predictions made for shorter alkyl chain analogs, namely, T1OH and T1ONa, may be used to explain the experimental ROA spectra of T12OH and T12ONa. The current work highlights the importance of converting carboxylic acids to corresponding sodium salts and of QC predictions for shorter achiral alkyl chain analogs to interpret the ROA spectra of chiral surfactants that contain long achiral alkyl chains.
more » « less- NSF-PAR ID:
- 10445137
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Raman Spectroscopy
- Volume:
- 53
- Issue:
- 6
- ISSN:
- 0377-0486
- Page Range / eLocation ID:
- p. 1102-1114
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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