ABSTRACT
The force given by both the CDA and the measurements becomes relatively linear on the log plot at negative nominal separations. (Recall that a negative nominal separation would correspond to interpenetration of the bodies or particles if they did not deform; the actual separation is always positive.) Effectively, the Debye length has been renormalized due to the elasticity of the substrate. It is straightforward to obtain from equation (18) an expression for the CDA decay length in this regime. The limiting force is given by
F{ho) = 2nRK^P^-Kh\ (19)
where the decay length is
K = - p - , (20) 1 +(OKD
and the renormalized pressure coefficient is
P^ = Poe"™ (21)
The amount of deformation is substantial, being of the order of 100 nm at the largest applied loads, compared with a particle diameter of 1200 nm. It is possible that the turn up in the force just prior to the van der Waals jump could be due to the contribution from the underlying rigid substrate at these large deformations. Alternatively, there is some evidence that this is instead due to a steric repulsion due to extended polymer chains (see above and below).
