Measurements of interaction forces between polycations, between clay nanoplatelets, and between polycations and clay nanoplatelets by atomic force microscopy

Interaction forces have been measured between (i) apposing layers of 2.0 +/ - 0.05 nm thick polydiallyl-dimethylammonium. chloride, PDDA, self-assemble d onto a silicon wafer, silicon-substrate/PDDA, and onto a silicon micropar ticle, attached to a tipless AMF catilever, SMP-AFM-tip/PDDA; (ii) apposing layers of 2.0 +/- 0.05 nm thick montmorillonite, M, platelets, self-assemb led onto the silicon-substrate/PDDA (silicon-substrate/PDDA/M) and onto the SMP-AFM-tip/PDDA (SMP-AFM-tip/PDDA/M); (iii) apposing layers of silicon-su bstrate/PDDA and SMP-AFM-tip/PDDA/M, and (iv) apposing layers of silicon-su bstrate/PDDA/M and SMP-AFM-tip/PDDA by scanning force microscopy. Interacti ons between the bare silicon substrate and the bare SMP-AFM-tip and those b etween the silicon-substrate/PDDA and the bare SNIP-AFM-tip have also been measured. The experimentally obtained force/radius vs probe-sample separati on distance plots have been fitted to a simple exponential, taking advantag e of the Derjaguin approximation for assessing the double-layer force betwe en a charged sphere and a flat surface, and to the DLVO theory using the co nstant potential numerical approximation (with the exception of ii, where c onstant charge numerical approximation was used). Values for the adhesion ( the pull back) force, Debye-length, and surface potential have also been ev aluated.