Adsorption Of Surface-active Substances Research Articles

Radiotracer Studies on Adsorption of Surface Active Substance at Aqueous Surface. II. The Effect of Excess Salt on the Adsorption of Sodium Dodecylsulfate

Abstract The adsorbed amount and the surface tension at the air-solution interface of the solution of tritiated sodium dodecylsulfate in the presence of excess common inorganic salt have been accurately measured at 25°C. The radioactivity of tritium β-rays over the solution was counted with a sheet scintillation counter and the surface tension of the solution was measured by a drop volume method. In the sodium dodecylsulfate solution containing sodium chloride of 0.115 mol/l, the adsorbed amount of dodecylsulfate ions was saturated to give 4.33×10−10 mol/cm2 when the bulk concentration was higher than 5.0×10−4 mol/1000 g solution. In the presence of the excess inorganic salt common to the ionic surfactant in solution the Gibbs adsorption isotherm has been experimentally proved to be valid for n=1. Moreover, it was confirmed that the equation of state for the ionic adsorbed film on the salt-free solution proposed previously is also applicable to the ionic surfactant solution with the excess salt.

Polarography of Uranyl‐Diethylenetriaminepentaacetate Complexes and Adsorption Kinetics at the Dropping Mercury Electrode

The chelation of uranium(VI) with diethylenetriaminepentaacetate was investigated polarographically over the pH range 3.7–8.4 and ligand concentration range 0.005–0.1M. The predominant chelate species was found to be with the logarithmic formation constant of 2.96 at pH 6.4–7.5 and ionic strength 0.25. In the presence of Triton , a single irreversible and diffusion‐controlled wave was obtained. The kinetic parameters were determined ( is the order of ). When the concentration of Triton X‐100 is greater than 0.003%, the single wave splits into two irreversible waves, due to the adsorption of surface active substance.

Radiotracer Studies on Adsorption of Surface Active Substance at Aqueous Surface. I. Accurate Measurement of Adsorption of Tritiated Sodium Dodecylsulfate

Abstract We carried out direct measurement of adsorbed amount at the air-solution interface to confirm the validity of the Gibbs adsorption equation by using radiochemically and surface chemically pure tritiated sodium dodecylsulfate (TSDS) and a sheet scintillation counter, which was developed for the purpose of counting β-rays of tritium in air. The adsorbed amount increased with increasing SDS concentration and showed the saturation values of 3.19×10−10 mol/cm2 in the concentration region from 3.2×10−3 to 14.4×10−3 mol/1000 g solution at 25°C. For the salt-free solution of ionic surfactant the Gibbs adsorption equation is confirmed to be valid for n=2 when activity in place of concentration is used. The equation of state for the ionic adsorbed film is further proposed. The cohesive pressure due to the attraction between hydrocarbon chains was given as a function of inverse molecular area.

Mass transfer from a pulsating drop

The primary difficulty in solving the problem of mass transport through an isolated drop (or bubble) moving in a fluid medium at high Reynolds numbers lies in the extreme complexity of the hydrodynamic pattern of the phenomenon. For sufficiently high velocities a separation of the external flow will occur in the rear portion of the drops and bubbles, which leads to the appearance of a turbulent wake and a sharp increase of the hydrodynamic resistance. Beginning with those dimensions for which the resistance force acting per unit surface of the drop or bubble from the external medium becomes greater than the capillary pressure, the surface of the drops and bubbles begins to deform and pulsate. The local variations of the surface tension, resulting either from the process of convective diffusion or from adsorption of surface-active substances, have a large effect on the hydrodynamics of drops and bubbles (particularly on the deformation of their surface) [1, 2], The presence of vortical, and possibly even turbulent, motion within the drops and bubbles may, under certain conditions [1], lead to their fractionation. Naturally, at the present time such complex hydrodynamics cannot be described by exact quantitative relations. Several authors have attempted to solve this problem approximately within the framework of certain assumptions. In particular [3–6], a theory was developed for the boundary layer on the surface of spherical and ellipsoidal gaseous bubbles moving in a liquid, studies were made [7, 8] of the hydrodynamics of drops located in a gas flow and the conditions were found for which fractionation of such drops takes place. Of considerable practical interest is the development of the theory of mass transfer in pulsating drops and bubbles and finding in explicit form the dependence of the mass transfer coefficients on the hydrodynamic characteristics of these systems. Until this relationship is established, every theory which ignores the effect of hydrodynamics on the mass transfer rate from an individual drop or bubble cannot be considered in any way well-founded. This relates particularly to the theories [9, 10] which consider mass transfer in systems with concentrated streams of drops and bubbles. The present paper is devoted to the study of mass transport through the surface of an isolated drop in an irrotational gas or liquid stream for large Peclet numbers P.

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.

Adsorption Modification of Fillers and Structure Formation in Solutions of Polymers

Abstract On addition of a solid disperse phase to a polymer one requisite for its effectiveness as an active filler is close similarity of the molecular properties of the surface of the particles and the polymer. This along with high “dispersity” (specific surface area) is mainly responsible for the high effectiveness of various types of carbon black—a hydrophobic filler of organic origin. For the same reason the majority of mineral fillers, which are usually of hydrophilic character, have relatively low capacity for the active filling of polymers, which is made evident in improvement in the mechanical and other properties of the filled material. As a consequence particular importance attaches to processes of adsorption modification, i.e., the alteration of the molecular properties of the surface of particles of hydrophilic fillers by orientated adsorption of surface-active substances (SAS). The hydrophobicization of the surface of the particles of filler which takes place here increases their “wettability” by the polymer phase and enhances the strength of its bond to the polymer, as has been investigated in detail in the work of P. A. Rebinder et al.. In this case modification leads to activation of the filler; in a number of cases however activation does not take place. As models for filled systems we may take concentrated suspensions of particles of the fillers in solutions of polymers containing additions of surface-active substances, which depending upon the concentration in the solution and proportionally to its increase, at first peptize the particles, lyophilizing them, and then stabilize them as a result of lyophobicization. This causes in sequence coagulation structure-formation in the system and then destruction of the resulting structures. A number of investigations have been devoted to the influence of fillers and pigments on the properties of polymers in the presence of surface active substances —in rubbers, and in lacquers and paints based on drying oils, but the laws of adsorption modification of mineral disperse phases and its influence on the filling effect in connection with the composition and molecular properties of the complex system: polymer-solvent/filler (or pigment)/surface-active substance have not been systematically studied. The present paper aims to investigate this question.

The velocity of air bubble ascending in aqueous solution of surface active substance and inorganic electrolyte

A series of measurements of falling velocities of glass sphere in an aqueous solution of sodium dodecyl sulfate and in pure water were carried out to elucidate the decrease in ascending velocity of air bubble in water due to the presence of surface active substance. From this, it was confirmed experimentally that the air bubble rises as a sphere and the air circulation inside the bubble is the sole factor in increasing rising velocity in the region of bubble radius from 0.03 to 0.07 cm, and that the circulation is actually suppressed by the adsorption of surface active substance.

Adsorption of surface-active substances on an iron electrode in an alkaline solution

1. The effects of various surface-active additives on the electrochemical behavior of an iron electrode in 2 N NaOH were investigated with the aid of measurements of capacity in an alternating current and of determinations of polarization curves. 2. Octyl alcohol molecules and tetrabutylammonium, naphthalenesulfonate, and hexanoate ions do not reduce the capacity of an iron electrode and have little effect on the hydrogen overvoltage; these species, therefore, are not adsorbed appreciably on the iron surface. 3. Compounds that are able to react chemically with ions or oxides of iron (tannin, alizarin, arsenious oxide, and to a lesser extent phenol) greatly reduce the capacity of an iron electrode at potentials more negative than the stationary potential, and they also raise the hydrogen overvoltage to some extent; this indicates that these compounds are adsorbed at the slightly oxidized iron surface. At potentials that are more positive than the stationary potential, these additives (with the exception of arsenic) have no effect on the capacity and are. probably desorbed from the iron surface.

Behaviour of surface-active substances at the dropping mercury electrode

It is found that the differential capacity of the dropping mercury electrode is affected mainly in two ways by added surface-active substances. At about the electrocapillary zero there is a strong lowering of the capacity due to adsorption of surface-active substances. At some higher cathodic potential there is enormous increase in differential capacity leading to a maximum and is followed by a sharp fall in the capacity; the latter is due to the desorption taking place more or less sharply at the higher cathodic potentials. The theory of the phenomenon has been formulated.

Effect of surface active substances on the capacity of the electric double layer

WHILE studying the effect of surface active substances on the kinetics of discharge of cadmium ion at the dropping mercury electrode in pulsating fields I it was observed that the xelocity of discharge was ~ea t ly brought do~vn by the presence of such substances as gelatin. Randles 2 has used an elegant technique based on measurement of phase difference and has reported that the rate of discharge of cadmium ions is brought down a thousand-fold by the addition of gelatine. Similar results have been reported by Keilin 3 who has found that the limiting current in polarography is lowered markedly by the presence of surface act;.ve substances; this has been attributed to the surface active substance getting adsorbed at the mercury surface and preventing electrode processes in the covered areas. The adsorption of surface active substances is known to lower the capacity of the electric double layer and is often responsible for low values of the capacity reported in literature) The present xvork relates to a detailed study of the effect of adsorption of a few surface active substances on the capacity of the electric double layer at the dropping mercury electrode.

The Kinetics of Wool Dyeing

The kinetic curves for the adsorption on textile fibers of a dye having a long hydrocarbon chain (Carbolan Crimson BS) indicate that there is an initial rapid, but limited, reaction which is followed by a much slower reaction. The influence of electrolytes, dye concentration, and temperature was studied, and the magnitude of the initial adsorption was correlated with the surface activity of the solution. The dye thus taken up was shown to be located on the fiber surface which, being largely nonpolar, is an interface for adsorption of surface-active substances. It is suggested that the surface activity of the dye contributes substantially to its high anion affinity.

The Determination of Adsorption in Ternary Solutions

A NUMBER of attempts have been made to determine the adsorption of surface-active substances from solutions containing salts, by the use of the Gibbs' equation, in the form where dρ is the variation of the surface tension caused by a change dμb(= RTd log αB) in the potential of the substance B.1 The complete equation of Gibbs as applied to a ternary system A-B-S is but if the dividing surface up to which the solution is supposed to be perfectly homogeneous is defined so that T = 0, this becomes. This equation reduces to (1) when the variation of μs is negligible in comparison with that of μB. This will be the case when the concentration of B is very small, but will cease to hold at greater concentrations.