This is the so-called phenomenon of "adsorption," which is another cause for the production of a physical membrane covering the surface of a liquid.
"The Mechanism of Life"
Stéphane Leduc
Its basic nature seems to be well established by its behavior with phosphotungstic acid and its ready adsorption by carbons activated to take up basic substances.
"The Vitamine Manual"
Walter H. Eddy
They make the colon's wall rigid and interfere with peristalsis thus leading to further problems with constipation, and interfere with adsorption of nutrients.
"How and When to Be Your Own Doctor"
Dr. Isabelle A. Moser with Steve Solomon