Structuring of Nanoparticles Between Modified Solid Surfaces

Abstract

In order to investigate the effect of confining surfaces on the structuring of nanoparticles in between, confining surface is modified by either attaching a mica sheet on the silica substrate or physically adsorbing polyelectrolytes on silica surfaces with layer-by-layer technique. In the first case, only the surface potential (or surface charge) is tuned. AFM force measurements show an enhanced amplitude in oscillatory forces while the wavelength and correlation length remain constant with increasing confining surface potential. This is an outcome of reduced particle-wall interaction range, due to the fact that the charged walls release additional counterions accumulated in a thin layer at the wall surfaces and contributed to the Debye length of particle-wall interaction. As a consequence, more particles can be accumulated inside the slit. In the second case, the effect of layer-by-layer modification on the surface potential and the surface roughness are also studied. Experimental findings reveal that the layer-by-layer technique modifies the surface roughness without changing the surface potential of a multilayer with the same outermost layer, by increasing number of constituent layers, ionic strength of the polyelectrolyte solutions, and by selecting an appropriate pair of polyelectrolytes. Wavelength and decay length are not affected by the surface roughness. The corresponding reduction in the oscillatory amplitude and the shift in the phase correlate with the increase in surface roughness. Increasing surface roughness further induces a vanishing of the oscillations and both confining surfaces contribute to the effect of surface roughness on the force reduction. In order to show an oscillatory force, the particles have to show positional correlation over a reasonably long range perpendicular to the surface and the correlation function should be the same over a larger lateral area. This requires that both the particles and the surfaces have a high degree of order or symmetry, otherwise the oscillation does not occur. A roughness of a few nanometers on a single surface, which corresponds to about 10 % of the nanoparticle diameter, is sufficient to eliminate the oscillatory force.KeywordsSilicon WaferSurface PotentialForce CurveOscillatory ForceForce ProfileThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.