MadSci Network: Chemistry |
Rene, Your question is directed to liquid absorption, so the answer is: a)contact angle b)pore volume c)hydration etc Let me explain... a)For the liquid to be drawn into pores or spaces within the absorber the liquid must like the solid more than itself. That is the "adhesive forces" exceed the "cohesive forces". This results in a contact angle of less than 90 degrees. This defines a "wetting" liquid. The lower the contact angle the better for an absorber. Note that the contact angle is always measured through the liquid. b)The amount of liquid which can be absorbed is a function of the total pore volume or space within the solid. c)The above two parameters explain the physical nature of absorption. Of course there are many absorbers which start off dehydrated in a chemical sense, the ANHYDROUS form. These materials react with water molecules to form the HYDRATE. You must know of white copper sulphate turning blue when water is added. I'm sure you know why. Try to find out what works so well in a modern diaper (nappy). Now, if you want to know what makes a good ADsorber, as in GAS adsorption, then surface area controls the adsorption CAPACITY, at least in the absence of the gas condensing to the liquid phase inside the pores (in which case pore volume is critical). For gases to adsorb the force of interaction with the surface must overcome the thermal energy. When the pore become really small, approaching the size of gas molecules (just a few angstroms, a nanometer or less)then the surface area can become huge. One gram of activated carbon can, for example, exhibit the surface area equivalent to that of a football field - and it doesn't matter which football; American, Association(soccer), Rugby, not even Australian Rules! Thanks for your question!
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