Article

Monolayers of gemini surfactants and their catanionic mixtures with sodium dodecyl sulfate at the air–water interface: Chain length and composition effects

Centro de Investigação em Química, Department of Chemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, 687, P-4169-007 Porto, Portugal
Thin Solid Films (Impact Factor: 1.87). 09/2008; 516(21):7458-7466. DOI: 10.1016/j.tsf.2008.03.029

ABSTRACT Monolayers of cationic gemini surfactants and their catanionic mixtures with sodium dodecyl sulfate (SDS), have been investigated with the Langmuir trough technique, at the air–water interface. The gemini surfactants are of the alkanediyl-α,ω-bis(alkyldimethylammonium) type, here designated as m-2-m, where m and 2 are the alkyl chain and spacer lengths, respectively. For the neat geminis, the stability of the monolayer increases as the chain length increases, starting from soluble films of 12-2-12 to stable films of 18-2-18. For the equicharged m-2-m/SDS mixtures (with m = 12, 14, 16 and 18), stable monolayers are obtained. The effect of the gemini chain length on the phase behavior and molecular organization of the films is discussed on the basis of pressure–area isotherms for compression or compression–expansion cycles. The pressure–temperature plots, at constant trough area, yield the desorption temperature and suggest the desorption mechanism of the film molecules. Furthermore, the effect of the mixing molar ratio between m-2-m and SDS on the isotherms, for m = 12 and 14, has also been investigated. It is concluded from the mean area per molecule that the gemini molecules when in excess with respect to equicharged composition desorb from the film, so that the electroneutral composition is maintained.

0 Followers
 · 
80 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study investigates the effects of various cationic surfactants on the cloud point (CP) of the nonionic surfactant Triton X-100 (TX-100) in aqueous solutions. Instead of visual observation, a spectrophotometer was used for measurement of the cloud point temperatures. The values of CPs for Triton X-100 can be measured directly because TX-100 has an average number of oxyethylene units per molecule of p approximately 9.5 and a CP=66.0 degrees C. Quaternary ammonium dimeric surfactants (m-s-m, m=10, 12, and 16, and s=2, 6, and 10) were synthesized and used. The melting temperature T(M) and the Krafft temperature T(K) were measured for 1 wt% aqueous solutions of these synthesized surfactants. The melting temperature of the solid gemini surfactants increased with the carbon number of the alkyl chain. The results showed that additions of the gemini surfactants (which are infinitely miscible with water) to Triton X-100 increased the cloud point of the TX-100 solutions. All salts tested in these studies had a large effect on the CPs of nonionic surfactants due to their effect on water structure and their hydrophilicity. The effect of the alkyl chain length of the gemini surfactant on the CP of Triton X-100 is therefore more important than the spacer chain length.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 02/2010; 75(2):671-7. DOI:10.1016/j.saa.2009.11.038 · 2.13 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The thermal behavior for three homologous series of cationic geminis surfactants of the type n-2-n, alkanediyl-α,ω-bis(alkyldimethylammonium bromide), with n=12, 14, 16, and 18, and sodium alkyl sulfates, SC m S, with m=12, 14, and 16, is reported here. The cationic/anionic molar ratio is kept at 1:2 (equicharged mixtures), and salt is also present. Polarizing light microscopy and differential scanning calorimetry show a stepwise fusion for the mixtures with appearance of several mesophases between the crystalline structures and the isotropic liquid. A main endothermic transition is observed, associated with partial chain melting and consequent loss of crystalline order, followed by a transition to a smectic liquid crystal. The phase transition thermodynamics is interpreted in terms of an interplay between van der Waals chain–chain interactions and ionic head group interactions. KeywordsCatanionic mixture-Mesophase-Soft crystal-Smectic liquid crystal-Van der Waals interactions-Electrostatic interactions-Birefringence
    Journal of Thermal Analysis and Calorimetry 05/2010; 100(2):501-508. DOI:10.1007/s10973-009-0653-8 · 2.21 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: BACKGROUND: Microemulsion is the easiest and cleanest of the popular methods of synthesizing nanomaterial. This work investigated the possibility of forming a single-phase microemulsion using ethanediyl-α,β-bis (cetyldimethylammonium bromide), termed EbCDAB, in a n-hexanol/water system, and looked for the best scale of microemulsion to synthesize TiO2 to give the best cleaning of organic pollution.RESULTS: Results confirm that EbCDAB, n-hexanol and water form a microemulsion system, and this system is an effective way to synthesize nanoparticles of TiO2. Photo catalysis experiments showed sample E6−3 to be the best catalyst, and it decomposed 82% of Methyl Orange (10 mg L−1) in 60 min under UV-light irradiation. E6−3 had 1.4 times higher activity than the commercial P25. Analyses using transmission electron microscopy (TEM), X-ray diffraction (XRD), thermographic differential scanning calorimetry (TG-DSC) and Fourier transform infrared microscopy (FT-IR), showed that particles of E6−3 were of size around 11 nm and of anatase phase.CONCLUSION: The best microemulsion was found to have weight ratio n-hexanol:EbCDAB:water of 6:3:1. At this ratio, TiO2 nanoparticles were easily produced. Copyright © 2010 Society of Chemical Industry
    Journal of Chemical Technology & Biotechnology 06/2010; 85(6):860 - 865. DOI:10.1002/jctb.2379 · 2.49 Impact Factor