P. Joos

Dynamic surface properties of adsorbed protein solutions: BSA, casein and buttermilk

Abstract The dynamic surface properties of three widely different protein systems are investigated using different experimental techniques. These techniques are (i) static drop experiments which allow description of the adsorption of proteins at a clean surface, (ii) experiments at a constant rate of dilatation where the area is continuously expanded and a steady state surface tension is obtained, (iii) modulus experiments where a surface in equilibrium is subjected to small periodic disturbances, (iv) stress relaxation experiments which are theoretically similar to moduli experiments, and (v) to a lesser degree, aspiration and sweeping experiments. The results are described by a process involving two steps: (i) diffusion of proteins to the surface and (ii) unfolding of adsorbed protein molecules at the surface. Only native protein molecules are exchangeable, while the unfolded protein molecules are not. From these results the diffusion relaxation times and reaction relaxation times are obtained.

The principle of Braun—Le Châtelier at surfaces

Abstract The purpose of this note is to show that the principle of Braun-Le Châtelier also has repercussions on equilibria at the surface. Two examples are given to illustrate this principle. One deals with adsorption of surfactants from a mixed solution, the other is applied to a reaction at the surface and is illustrated for protein solutions.

Adsorption kinetics of lower alkanols at the air/water interface: Effect of structure makers and structure breakers

Abstract The dynamic surface tensions of n-propanol, n-butanol, n-pentanol, and n-hexanol were measured by the oscillating jet method. It was found that propanol, butanol, and pentanol show transfer-controlled kinetics. For hexanol and heptanol both the transfer from the subsurface to the surface and the diffusion from the bulk to the subsurface are rate controlling. The adsorption and desorption rate constants are in agreement with the data of V. B. Fainerman and S. V. Lylyk (Kolloidn. Zh.44, 598 (1982), and also with our previous data on bolaform surfactants. The effects of the additives urea (structure breaker) and fructose (structure maker) on the dynamic surface tension are investigated, and these effects are discussed on the basis of the hydrophobic effect.

Comments on some dynamic surface tension measurements by the dynamic bubble pressure method

Abstract Experiments described in recent papers of M. Rosen and co-workers using the dynamic bubble pressure method for different surfactants are reevaluated using diffusion theory. It is concluded that the results can be described by a diffusion-controlled mechanism except in the case of DESS and that the dynamic bubble pressure method gives reliable data.

Study of the dynamic interfacial tension at the oil/water interface

A review is given on three recently developed methods to measure the dynamic interfacial tension at the oil/water interface. These are respectively the dynamic drop volume method, the dynamic capillary method, and the (reversed) funnel method. For each method presented the basic principles are described and a few experimental results are given.

Adsorption kinetics at the oil/water interface

Abstract The dynamic capillary method is introduced as a method for measuring dynamic surface and interfacial tension in a time range below 1 s. The method at the air/water interface is compared with other methods, e.g. strip, inclined plate and dynamic drop volume method. Close agreement between these methods is found. Measurements were performed at the hexane/water interface for aqueous solutions of Triton X-100 and Triton X-405. For Triton X-100 solutions adsorption kinetics are diffusion controlled, whereas for Triton X-405 an adsorption barrier is present (mixed adsorption kinetics.) These results are treated analytically and it follows that the desorption rate constant k 2 ≈ 60 s −1 , a value somewhat lower as observed for other surfactants at the air/water interface ( k 2 ≈ 100 s −1 ).

Dynamic surface properties of aqueous sodium dioctyl sulfosuccinate solutions

Abstract To investigate the very slow surface equilibration of submicellar solutions of straight-chain soidum dioctyl sulfosuccinate (Na-DOSS), different techniques covering a large time domain are used. An adsorption model for Na-DOSS is introduced and the compatibility of the different experiments with this model is explained. Therefore, for longitudinal wave experiments as well as for stress—relaxation experiments, theoretical equations are calculated and interpreted in light of this model.

Adsorption kinetics of micellar Brij 58 solutions

Abstract Because the CMC of Brij 58 is very low, the dynamic interfacial tension at both the air/water and the n-hexane/water interface is affected by the micellisation—demicellisation process even up to a time scale of 1 s (dynamic drop-volume method), where local equilibrium is established between monomers and micelles. The experimental results, however, cannot be described adequately by the equation of Lucassen [J. Lucassen, Faraday Discuss. Chem. Soc., 59 (1975) 76], when considering micellisation as a stepwise reaction process. A new but analogue equation is therefore derived which is compatible with consideration of micelles as a separate (micro)phase and it turns out that good agreement is found now between theory and experiment.

The dynamic surface tension of SDS— dodecanol mixtures: 1. The submicellarsystems

Abstract Samples of sodium dodecyl sulfarte (SDS) are commonly contaminated by dodecanol, as a minor component, which is very suface active and nt easily removed. The desappearance of the minimum in the suface tension concentration curve at the dritical micelle condentration (CMC) gives no definite criterion about the purity of the sample. The question arises as to what the effect pf dodecanol is on the dynamic properties of the surface, having repercussions on the pracrical behavior of the system. Therefore, we investigated the dynamic surface behavior of SDS solution having a known dodecanol content. First, SDS and dodecanol mixtures were considered at concentrations definitely below the CMC. giving mixed adsorbtion of SDS and dodecanol. Subsequently, SDS and dodecanol mixtures at SDS concentrations above the CMC were studied; at these concentrations, a part of the dodecanol is solubilized in the micelles of SDS.

The kinetics of wetting: The motion of a three phase contactline in a capillary

Abstract The movement of the three phase contact line (liquid—air—solid) is studied under complete wetting conditions by means of silicon oils in glass capillaries. It is found that the Washburn, Rideal, and Lucas equation is followed for a receding meniscus but not for an advancing one. In the latter case the dynamic contact angle depends on the capillary number, a phenomenon we account for by the empirical equation cos θ d = cos θ o −2(1+ cos θ o ) ηυ σ 1 2 . The radii of the capillaries and the viscosities of the silicon oils are varied and experiments are performed in different set-ups: capillary rise and withdrawing in vertical capillaries, spontaneous imhibition in horizontal capillaries, and the movement of a liquid column in a vertical capillary, for which the thickness of the film behind the receding meniscus can be predicted by the Carroll-Lucassen equation. At high velocities (wide capillaries) air entrainment is predicted.