Layer Of Sodium Dodecyl Sulfate Research Articles

Influence of detergent builders on surface properties of sodium dodecyl sulfate solutions under dynamic and static conditions

The effects of various detergent builders on surface properties of sodium dodecyl sulfate (SDS) solutions have been investigated by measuring the equilibrium surface tension and hysteresis curves of surface pressure vs surface area under dynamic conditions. While the adsorbed layer of SDS under static conditions is in the liquid‐expanded state, a two‐dimensional phase transition of the adsorbed layer from liquid‐expanded to condensed‐film can be observed on compression at higher rates beyond the saturated adsorption. For the SDS solution containing excess NaCl (1×10−1 M), the adsorbed layer of SDS is already in the condensed state under static condition due to a depression in the dissociation of SDS.It has been found that some polyelectrolytes, as well as conventional ionic builders, contribute to increasing the surface excess concentration of SDS together with promoting micelle formation and also to stabilizing the adsorbed layer of SDS. On the other hand, poly(vinyl alcohol) (PVA) as a nonionic polymer is adsorbed at the air‐water interface in preference to SDS. In this case, the hysteresis of the dynamic surface behavior of the mixed solution can be attributed to the structural change of the adsorbed layer of PVA rather than SDS, which is different from the other ionic builders.

Fluorescence probe studies on the structure of the adsorbed layer of dodecyl sulfate at the alumina—water interface

Pyrene and dinaphthylpropane (DNP) fluorescence probes were used to investigate the structure of the adsorbed layer of sodium dodecyl sulfate at the alumina-water interface. The fluorescence fine structure of pyrene yielded information on the polarity of the microenvironment in the adsorbed layer. Intramolecular excimer formation of DNP was used to measure the microviscosity of this environment. The results indicate the presence of highly organized surfactant aggregates at the solid—liquid interface, formed by the association of hydrocarbon chains. Fluorescence decay methods enabled the determination of the size of these aggregates and their evolution as a function of surface coverage. The overall spectroscopic investigation reveals a molecular model that is in agreement with the concept of hemimicellization.

THE 1‐CYANONAPHTHALENE EXCIMER IN HOMOGENEOUS AND MICELLAR SOLUTIONS

Abstract— An excimer of 1‐cyanonaphthalene is produced in homogeneous organic solvents and in micelle containing detergent solutions. From solvent effects in homogeneous solution it is concluded that the excimer is relatively polar (dipole moment ∼ 4D). From a comparison with emission from that observed in homogeneous solvents, it is concluded that 1‐cyanonaphthalene is solubilized mainly in the Stern Layer of sodium dodecyl sulfate (SDS) and hexadecyltrimethyl ammonium bromide (HDTBr) micelles. The influence of variation of detergent concentration on the excimer to monomer emission ratio and the influence of NaCl concentration on the excimer to monomer emission ratio have been determined. Excimer formation is shown to be a convenient method for determination of the Kraft point of SDS solutions.

Adsorption of Surface Active Substance at Aqueous Surface Using Tritium Labeled Compounds: Adsorption from Mixed Aqueous Solution of Sodium Dodecylsulfate and Dodecanol

Abstract Adsorbed amount of sodium dodecylsulfate (SDS) and n-dodecanol (DOH) at the gas-solution interface of their mixed aqueous solution was directly measured as a function of bulk concentration of DOH by the radiotracer method. For this purpose the surface radioactivity of the mixed solution in which either SDS or DOH was labeled with tritium, was counted by using a 2π window-less gas-flow counter. It was found that the adsorbed amount of DOH rapidly increases with increasing bulk concentration of DOH, while that of SDS gradually decreases. The adsorption of DOH and desorption of SDS are not a simple 1 : 1 replacement. A maximum total adsorption of about 13×10−10 mol/cm2, which exceeds the amount of close-packed monolayer adsorption extends over a wide range of concentration studied. It was suggested that the adsorbed film consists of mixed monolayer or double layers. The latter film is composed of mixed monolyaer of SDS and DOH with adsorbed layer of SDS beneath. The molar ratio of adsorbed amount of DOH to SDS in the surface became unity, when the ratio of the bulk concentration of DOH to SDS was about one hundredth, which shows a stronger adsorption tendency of DOH than that of SDS.