Instead, a repulsive force arose within a short separation distance of 3 nm. Although there was a slight decrease in
the repulsion force with the tip further approaching, the addition
of 1 mg/L lignosulfonate successfully produced repulsions between
the tip and graphite surfaces, resulting in a repulsive barrier to
their approach. Since the adsorption density with the corresponding lignosulfonate is low in deionised water, this repulsive force
should be generated by the enhanced electrostatic repulsion as discussed in the adsorption measurement section. As a result, the
attractive van der Waals force at the close contact was overcome
and the initial easy approach of tip to graphite surface was disabled
in deionised water in the presence of lignosulfonate