Amino acid-based surfactants are
used in academics and industry.
Sodium
N
-dodecanoyl sarcosinate (SDDS) is such an
amino acid-based surfactant having applications in pharmaceutical,
food, and cosmetic formulations. Although the surface properties of
this surfactant have been studied in the presence of univalent cationic
and anionic salts, there is no report on such solution in the presence
of higher valencies. In this experiment, critical micelle concentration
(CMC) of SDDS from tensiometry, conductometry, and fluorimetry has
been determined. In each case, CMC decreases with increasing salt
concentration. Counterion binding of micelles (β), diffusion
coefficient (
D
0
), and surface properties,
e.g., Gibbs free energy for micellization (Δ
G
m
0
), Gibbs
surface excess (Γ
max
), area of exclusion per surfactant
monomer (
A
min
), surface pressure at CMC
(π
cmc
), etc., have been evaluated using methods such
as tensiometry, conductometry, and fluorimetry. The hydrodynamic radius
of SDDS in the presence of different salts was measured by the light
scattering method. Aggregation number and shape of micelle have been
determined by small-angle neutron scattering experiment. The nature
of amphiphilic packing and the aggregation numbers of the assemblies
have also been explored. The results from different experiments have
been rationalized and represented systematically.
The interaction of both cationic dye Safranine T (ST) and anionic dye Congo red (CR) with anionic and cationic surface active ionic liquid 1-butyl-3-methyl imidazolium octyl sulfate ([BMIM][OS]) and 1-decyl-3-methyl imidazolium chloride ([DMIM][Cl]) was investigated by absorbance and emission spectroscopy, time-resolved fluorescence study, and anisotropy methods at premicellar and postmicellar regions. The interaction of dye with both of the ionic liquids occurred electrostatically as well as hydrophobically. In the case of ST, initially absorbance decreases up to a certain concentration without any shift of λ max , and then it increases with red shift of λ max . Absorption spectra of CR gave red-shifted wavelength with addition of [BMIM][OS], but at a higher concentration of surface active ionic liquid (SAIL), no shifting was observed. Again, blue-shifted λ max was found in lower range of [DMIM][Cl]; but at higher concentration, it was further red-shifted. Emission intensity increases in both dye−SAIL systems; for ST in both SAIL media, blue-shifted spectra were observed, but there was no shift of emission maxima in case of CR in those media. Dye−IL binding ratio, binding sites, and binding constants were also calculated from fluorescence measurements. Anisotropy measurement showed that movement of dye in pre-and postmicellar regions was different in different SAIL systems. Time-resolved fluorescence lifetime confirmed microenvironment of dye−SAIL systems.
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