ABSTRACT
An additional consideration is that close to contact other forces will start to contribute, as discussed in connection with the CDA prediction of contact in Fig. 14. In particular, the kink in the data in Fig. 15 at a load of 1.5 -2 nN is evidence of such a non-electrical double-layer force. This and the subsequent steeper gradient in the measured data likely indicate actual steric contact of polymer tails that extend out from the surface of the particle into the solution. (Miklavcic and Marcelja have used a mean-field theory to model the interaction of polyelectrolytes and obtained a similar initial softening of the double-layer repulsion followed by a steeper steric interaction [95].) That this kink occurs at a substantially lower load than the putative van der Waals jump identified in Fig. 14, and is of different character, supports a model of the PDMS droplet as a dense core surrounded by a diffuse corona of polymer tails.
