Tensiometry and FTIR study of the synergy in mixed SDS:DDAO surfactant solutions at varying pH
File(s)
Accepted version
Author(s)
Type
Journal Article
Abstract
The interactions between a model anionic and amphoteric surfactant pair in aqueous solution are examined as a function of composition, at floating and fixed pH, employing a combination of tensiometry, regular solution theory analysis, and FTIR spectroscopy. An extensive series of pure and mixed ratios of sodium dodecyl sulfate (SDS) and N,N-dimethyldodecylamine N-oxide (DDAO), ranging from 0.0016 to 100 mM, yielding 77 data points below and above the critical micelle concentrations (CMC), is investigated. Compared to either pure surfactant solutions, the CMC of mixed SDS:DDAO solutions is found to decrease by up to 20-fold, and the surface tension (γ) at CMC down to ≃ 23 mN/m. At all concentrations, the most prominent effects are observed at equimolar SDS:DDAO ratios. Further, the pH of mixed micellar solutions is found to increase with respect to the pure surfactant solutions (from ≃ 7 up to ≃ 9.5), which is attributed to the enhanced protonation of DDAO in the presence of SDS, and supported by FTIR frequency shifts of isolated O‒H stretching vibrations. Vibrational responses from CH2 stretching of the methylene tails, and the S‒O stretching modes for the sulfate headgroups indicate strong lateral interaction and enhanced packing between SDS and DDAO. From regular solution theory analysis of tensiometry data, the molecular interaction parameters are found to have a larger magnitude (i.e., more negative) at the interface as compared to within micelles. At fixed solution pH, a decrease from pH 9.5 to 7.5 results in minimal changes in both interfacial and micellar parameters, indicating the intrinsic origin of these pairwise interactions. Overall, our findings demonstrate a pronounced synergistic interaction between SDS and DDAO, arising from diminished electrostatic and steric repulsions in, respectively, SDS and DDAO, accompanied by enhanced lateral surfactant packing.
Date Issued
2021-03-24
Date Acceptance
2021-03-03
Citation
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2021, 618
ISSN
0927-7757
Publisher
Elsevier
Journal / Book Title
Colloids and Surfaces A: Physicochemical and Engineering Aspects
Volume
618
Copyright Statement
© 2021 Elsevier B.V. All rights reserved
Sponsor
Centre for Process Innovation Ltd
Procter & Gamble Technical Centres Ltd
Engineering & Physical Science Research Council (E
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000642467400004&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Grant Number
PO. 31992
G4P-8003071631
WT377338
Subjects
Science & Technology
Physical Sciences
Chemistry, Physical
Chemistry
Mixed surfactants
Surface tension
Sodium dodecyl sulfate
Dimethyldodecylamine oxide
Synergism
pH
ATR-FTIR
SODIUM DODECYL-SULFATE
BINARY-MIXTURES
DODECYLDIMETHYLAMINE OXIDE
MICELLAR-SOLUTIONS
WATER
SPECTROSCOPY
AIR/WATER
BEHAVIOR
PRECIPITATION
OPTIMIZATION
Publication Status
Published
Article Number
ARTN 126414