Contamination in Sodium Dodecyl Sulfate Solutions: Insights from the Measurements of Surface Tension and Surface Rheology

Abstract

The presence of contamination in sodium dodecyl sulfate (SDS) solutions in the form of dodecanol (LOH) is known to drastically affect the resulting interfacial properties such as surface tension (SFT) and rheology. Dodecanol molecules, which are the product of SDS hydrolysis and are inherently present in SDS solutions, have higher surface activity compared to SDS because they are less soluble in water. A characteristic dip in the SFT isotherm is an indicator of the dodecanol contamination in the sample. The presence of an electrolyte in the solution impacts the surface activity of SDS and its critical micelle concentration, and could yield SFT isotherms that closely match those obtained for pure SDS samples. The interpretation of the isotherms in such cases could thus lead to misinterpretation of the surface purity. In this work, we have examined the SFT isotherms for SDS solutions in both the absence and presence of electrolyte. We have fitted the isotherms to three different thermodynamic adsorption models to estimate the amount of dodecanol present in the sample. We have applied the estimated values for the LOH content in a two-component rheological model to predict the viscoelasticity of such surfactant-laden surfaces. We have compared these results with the experimentally measured interfacial rheological properties. Our findings demonstrate that the presence of impurities can be captured under dynamic expansion and contractions, even for solutions containing background electrolyte.

Effect of long chain fatty acids on the memory switching behavior of tetraindolyl derivatives

“…We have also calculated compressibility modulus, C s −1 from the pressure-area isotherm curves. 74 Values of C s −1 as well as peaks present in the C s −1 versus p curve gives idea about physical state of the lm associated with molecular packing and phase/ordering of molecules. 74,75 Corresponding plot of C s curves for Indole2 mole fraction up to 0.5 almost resembles the curves for pure SA in terms of peaks present.…”

“…74 Values of C s −1 as well as peaks present in the C s −1 versus p curve gives idea about physical state of the lm associated with molecular packing and phase/ordering of molecules. 74,75 Corresponding plot of C s curves for Indole2 mole fraction up to 0.5 almost resembles the curves for pure SA in terms of peaks present. This indicates existence of similar phases in these lms like that of SA lms, where at higher surface pressure an ordered condensed lm is formed.…”

“…74,75,77 According to Davies and Rideal description liquid-expanded (LE) state of the lm is associated with the modulus values within the range 12.5-50 mN m −1 , whereas, the range 100-250 mN m −1 is related with liquid condensed (LC) state. 74,75,77 Considering maximum value of C s −1 it may be noted that mixed lm up to 0.4 mole fraction possess LC phase, whereas, higher mole fractions the lms possess only LE phase. 74,75,77 I-V studies also revealed that device with Indole2 mole fraction 0.5 or higher showed threshold switching.…”

Paddlebots: Translation of Rotating Colloidal Assemblies near an Air/Water Interface

“…Supporting this, we observe no evidence of capillary interactions under normal experimental conditions. , Without added surfactant, however, beads do become pinned at the interface. − Once bound, surface tension forces dominate any magnetic forces preventing paddlebots from reorienting out of the interfacial plane and translating. The system can be further characterized by the Bond number Bo = Δ ρgL 2 /γ where Δρ is the density difference between the water and the beads, g is the acceleration due to gravity, L is the diameter of an individual bead, and γ is the surface tension of water at experimental surfactant concentrations . When beads are near the interface and not pinned, we note that such a balance of buoyancy forces against those required to deform the interface due to surface tension (Bo = 3.6 × 10 –6 ) suggests that any deviation from a flat interface is minimal.…”

“…The system can be further characterized by the Bond number Bo = ΔρgL 2 /γ where Δρ is the density difference between the water and the beads, g is the acceleration due to gravity, L is the diameter of an individual bead, and γ is the surface tension of water at experimental surfactant concentrations. 34 When beads are near the interface and not pinned, we note that such a balance of buoyancy forces against those required to deform the interface due to surface tension (Bo = 3.6 × 10 −6 ) suggests that any deviation from a flat interface is minimal.…”