Dear Alexander,

Surface active agents drastically modify the surface tension of the water and viscosity. However, contact angle not only dependents on the surface tension of the water but also affected by the surface energy of the substrate.

Some useful references in this line...

Article The debate on the dependence of apparent contact angles on d...

Article Measurement of Lateral Adhesion Forces at the Interface betw...

Article Experimental studies of contact angle hysteresis phenomena o...

hope these will help you in understanding the behavior of liquids at different interfaces.

good luck

Isothermal compressibility and viscosity are the bulk properties of surfactant solutions. Surface tension and contact angle are surface properties. They are difficult to compare. They have different units of measurement. With an increase in the surfactant concentration, they change as follows. The isothermal compressibility of solutions initially decreases, and then increases. The viscosity increases. Surface tension decreases and when CMС reaches a constant value.Contact angle decreases and reaches zero at CMС.

Wetting and surface tension of a solution of dodecyltrimethyl ammonium bromide on a quartz plate.

Elton G.H. Proc. 2nd Intern. Congr. Surface Activity. London.1957.

Dear Yuri and Chandam,

Thank you for your answers!

I understand that the bulk and surface properties are difficult to compare, but at least I need to know the relative effect in %.

I am considering the effect of chemical contamination on seismic velocities and attenuation. In this publication, for example: “Waite et al. (1997). Seismic attenuation in a partially saturated, artificial crack due to restricted contact line motion.” The effect of chemical contamination was attributed to the change of surface energies between water-air and solid interfaces. While, at the same time, chemical contamination changes the bulk viscosity and compressibility, which was assumed to be nearly the same in Waite et al. publication. I wonder, if this assumption is correct? If this assumption is not correct, then one may argue that the alteration of seismic properties is related to the change of water compressibility and viscosity.

Best regards,

Alexander

Your processes occur at high temperature. Organic molecules play a small role there. You need to get acquainted with the effect of P. Rebinder (adsorption reduction in the strength of materials, адсорбционное понижение прочности материалов). You do not forget the Russian language? I think that Wait et. al. rights.

Dear Yuri,

I do not think that Rehbinder effect is relevant here to explaining the stiffening effect of the seismic wave (increase of velocity). Rehbinder effect would explain rather the decrease of velocity.

Wave-induced fluid flow between immiscible fluids inside the crack is restricted by the presence of interface meniscus and the contact line pinning effect, which does not allow the relative motion of fluids, which is limited only by the bending effects of the interface meniscus, which is small.

Any more arguments, why do you think the effect of chemicals on the fluid viscosity and compressibility is small, comparing to its effect on surface tensions?

Thank you and best regards,

Alexander

I'm not an expert on the problem of seismic waves.

Yuri.

Regars.

Surfactants only have a noticeable effect the density of aqueous solutions at fairly high concentrations. For example a 20% sodium dodecyl sulfate (SDS) soln. is quoted by the suppliers as having a density of 1.01 g/cm2 (i.e. about 1 % more than water).

The amounts required to change the surface tension are much smaller. Typically, adding surfactant to water lowers the surface tension from around 70 mN/m to between 25 and 45 mN/m when the critical micelle concentration (cmc) is reached. For SDS the cmc is about 0.24 %.

It’s a similar story with nonionic surfactants. Usually their cmcs are lower. You can find some density information (including temperature effects) on solutions of nonionics in this publication:

https://doi.org/10.1016/j.colsurfa.2004.11.037

(There's probably other, freely available, density data elsewhere on the internet too)

Hello Denis,

Thank you for your reply. In fact, I am more interested in the effect of surfactants on water compressibility, viscosity, surface tension and contact angles (with air on solids) at small concentrations. The effect of surfactants on water density is rather trivial.

Small concentrations of surfactants have large effect (in percentage) on surface tension and advancing and receding contact angles. Will it have also large effect (in %) on water compressibility and viscosity? Simple question – no answer so far. Thank you anyway for all answers.

Best regards,

Alexander

Dear Alexander,

I have a couple of remarks on viscosity and compressibility.

Viscosity effects will depend very much on the type of aggregates the surfactant forms.

Spherical micelles: small effects. The magnitude will depend on the surfactant, but typical behaviour might be to increase the viscosity by a factor of about 2 or 3 at 10 % concentration.

Rod or wormlike micelles: these give a dramatic thickening. Many shampoos are thickened by adjusting the formulation so that rod-like micelles are formed. Often surfactant concentrations of several percent are needed, but some systems form rodlike micelles at quite low concentrations.

Liquid crystals: Surfactants form liquid crystalline phases at high concentations (typically around 20%) - these are often very viscous, sometimes almost solid.

Some work on compressibility has been published by Bloor et al.

( see http://pubs.rsc.org/en/content/articlelanding/1984/f1/f19848001915#!divAbstract ) It was done in order to elucidate micelle structure, in particular the role of the head groups. Generally they found a decrease of compressibility with surfactant concentration. The magnitude varied considerably with surfactant. Decreases of up to about 4% were observed at a concentration of 0.3 M.

Best regards

Dennis

Dear Alexander,

I can offer you some data on the properties that you are interested in (you can easily recalculate them to the compressibility values) from our investigation of the binary system of nonionic surfactant Brij35 (C12E23) in water.

I am attaching the Figure with these data that was published in my PHD theses, that is unfourtunately in Slovene – the legend: experimental data on (a) density, (b) sound velocity, and (c) viscosity dependence on the mass fraction of the surfactant in the system. From the values of the density and sound velocity, you can easily calculate the values of the adiabatic sound velocity according to the equation:

(Adiabatic compressibility) = 1 / (density * (sound velocity)2 )

For the details on the structures in this system (sizes and shapes of the miceles) please refer to the paper:

· M. Tomšič, M. Bešter-Rogač, A. Jamnik, W. Kunz, D. Touraud, A. Bergmann, O. Glatter, Nonionic surfactant Brij 35 in water and in various simple alcohols: Structural investigations by small-angle X-ray scattering and dynamic light scattering, J. Phys. Chem. B 108 (2004) 7021-7032.

With kind regards,

Matija

Thank you very much for all good answers!

Best regards,

Alexander