Autonomous Motion of Small Particles through Surface Interaction Gradients

A theoretical design by Balazs et al (ACS Nano, 2008), in which two particles are propelled forward by changing their interaction with a compliant surface by releasing nanoparticles, was attempted to be implemented.
Initial studies showed that the design needed to be altered slightly to overcome the friction encountered between the particles and the surface, and to alter the surface by a way other than by the adsorption of nanoparticles. These alterations to the design included changing the interactions present from totally adhesive, to partially or completely repulsive to overcome friction, and substituted a catalytic chemical reaction for the release of nanoparticles used in theoretical design.
An implementation of the theoretical design which used repulsive van der Waals forces to change the particle-surface interaction from adhesive to repulsive, by the catalytic conversion of benzene and bromine to bromobenzene, was investigated. It was found that although the particle-surface interaction could be converted from attractive to repulsive, the rate of the catalytic reaction was too slow to surround the catalytic particles with enough bromobenzene to propel particles forward.
Electrostatic repulsions between a particle and surface were investigated and found to be unable to significantly change the particle-surface interaction, so were of no use in implementing the theoretical design.
Another implementation of the theoretical design which used the steric forces exerted between a particle and surface to alter the particle-surface interaction was investigated. It was found that these steric interactions could significantly influence particles and were able to control their position on a surface. Ways to change the steric interactions from repulsive to more repulsive by a chemical reaction were found and catalytic particles which could release the required reagent created. In all cases it was found that the rate of catalytic reaction was too slow to modify the surface in the correct way to produce propulsion.
It was concluded that substituting a catalytic chemical reaction for the release of nanoparticles in the theoretical design is not a viable alternative which can be used to alter a surface and thus change the particle-surface interaction to create propulsion.