Contact Angle of Immiscible Liquids in a Tube

[AqibH]

I'm having trouble finding any sources which describe how to accurately measure the contact angle between immiscible liquids in a tube. Any help would be appreciated.

 

[Andy Resnick]

I'm having trouble finding any sources which describe how to accurately measure the contact angle between immiscible liquids in a tube.

There is a lot of information out there, but it may appear confusing for a variety of reasons. Are you actually interested in the contact angle, or are you actually trying to measure the interfacial energy? What information have you found so far?

What do you mean by 'accurately'? In many situations, the contact angle is not a unique angle (advancing/retreating angles and canthotaxis, for example). Additionally, the contact angle at microscopic length scales is not necessarily the same as the contact angle at macroscopic length scales (among others, E. B. Dussan V.'s work is the gold-standard on this question). Finally, is this a static or dynamic (wetting) measurement?

Is your tube cylindrical? optical measurements are then subject to lensing and related difficulties.

 

[AqibH]

I am interested in the contact angle itself as I already have measured the interfacial tension (but not in the same cylindrical tube). I have not been able to find any information on measuring the contact angle of immiscible liquids inside a tube. It seems all the focus of measuring contact angles has been for liquid-vapor-solid interfaces on a flat plane or in a tube.

By 'accurately', I meant a method which was reliable and not some kind of homemade method which I have seen some papers use. I am only interested in the static contact angle as I understand that measuring dynamic contact angles can be difficult. I also understand that the more you zoom on an image the contact angle will change. Basically, I was hoping that there existed some method which is used to measure the angle and it was a method which could be consistently repeatable.

The tube is cylindrical. I understand the issues of optical measurements but this is what I am leaning towards. We don't really have the equipment to measure contact angle of even one liquid in a tube (there are published methods for this liquid-vapor-solid interface).

 

[Andy Resnick]

I am interested in the contact angle itself as I already have measured the interfacial tension (but not in the same cylindrical tube). I have not been able to find any information on measuring the contact angle of immiscible liquids inside a tube. It seems all the focus of measuring contact angles has been for liquid-vapor-solid interfaces on a flat plane or in a tube.

By 'accurately', I meant a method which was reliable and not some kind of homemade method which I have seen some papers use. I am only interested in the static contact angle as I understand that measuring dynamic contact angles can be difficult. I also understand that the more you zoom on an image the contact angle will change. Basically, I was hoping that there existed some method which is used to measure the angle and it was a method which could be consistently repeatable.

The tube is cylindrical. I understand the issues of optical measurements but this is what I am leaning towards. We don't really have the equipment to measure contact angle of even one liquid in a tube (there are published methods for this liquid-vapor-solid interface).

I see. You are correct that the apparent contact angle will vary with 'magnification', that is the essence of Dussan's series of papers. One approach is to place the two fluids in a square/rectangular cuvette (with flat windows for sides), and immerse/withdraw a solid glass rod; this 'inside-out' version obviates many of the imaging difficulties.

Adamson's Physical Chemistry of Surfaces lists a variety of measurement methods. Papers by Slattery, Dussan, and Scriven are another good source of ideas.