[Spm] Re:(quantify repulsive force in water) (Filby, Andre)

[Yang Gan]

Hi André,

You need to fit the force curves (to derive surface potential, or diffuse layer potential more appropriatley) using a model based on the DLVO theory if the repulsion is caused by the electric double layer interaction. There are enormous literature on this topic, certainly including your latex-mica system.

Roughly, the parameters you need to fit the curve is the concentration of the solution, the diameter of your latex particle, the pH dependent surface potential of your mica substrate, and the Hamaker constant. Then you can fit the curve to derive the latex surface potential (then surface charge with some assumptions) in certain pH and electrolyte concentration condition.

Please contact me offline if you need further information.

Regards,
Yang
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Yang Gan
Professor, PhD
Department of Applied Chemistry
Harbin Institute of Technology
No.92, West Da-Zhi Street, Harbin
Heilongjiang 150001
P. R. China
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Hi all,
I´m using the AFM in order to obtain force-distance curves in water. I´m using colloid probe technique (with a latex particle) and mica as substrate. In certain conditions I see repulsive forces (the curve "bends" until it gets into contact). What I´d like to know, how does one exactly quantify these repulsive forces? I know how the point of contact is extrapolated (through the 2 linear regimes) but I don´t know if there is any special procedure in order to quantify the repulsive force. Could it be that one has to drop a perpendicular of these 2 linear regimes?
 
Thanks in advance for your help.
 
André