Geometric Model Describing the Banded Morphology of Particle Films Formed by Convective Assembly

Abstract

Nanoparticle films coated on smooth substrates by convective assembly from dilute suspensions in dip-coating configuration are known to have discrete film morphologies. Specifically, the film morphology is characterized by alternating bands of densely packed particles and bands of bare substrate. Convective assembly is a frontal film-growth process that occurs at the three-phase contact line formed by the substrate, the suspension in which it is submersed, and the surrounding air. The bands are parallel to this contact line and can be either monolayered or multilayered. Monolayered bands result whenever the substrate is withdrawn from the suspension at a rate too high for particles to assemble into a continuous film. We report a new insight to the mechanism behind this banding phenomenon, namely, that inter-band spacing is strongly influenced by the constituent particle size. We therefore propose a geometric model relating the inter-band spacing to the particle size. By making banded films with systematically varied particle sizes (silica/zeolite, 20 to 500 nm), we are able to quantitatively validate our model. Furthermore, the model correctly predicts that multilayered banded films have higher inter-band spacings than monolayered banded films comprising the same particles.

Reliable plasmonic substrates for bioanalytical SERS applications easily prepared by convective assembly of gold nanocolloids

“…As observed in the AFM cross-section the NP strips are thinner on one side. This shape asymmetry was already observed previously, 29,30 on NP assemblies obtained by CSA, and is related to the meniscus shape and its direction of translation during the stick-slip deposition process. Thus our results point out that the thinner side of the NP strips, which is a monolayer of NPs, provides a higher enhancement than the rest of the strip, where the NP assembly adopts a thick multilayer morphology.…”

Structural transitions in a ring stain created at the contact line of evaporating nanosuspension sessile drops

“…Particle structuring effects have also been related to other experimental parameters, i.e., geometry and controlled evaporation. In forced dewetting (substrate retracting from a nanofluid pool), striped deposits with some degree of ordering occurred due to a combination of capillary forces and fluid evaporation [21][22][23][24][25]. When the colloidal fluid was confined in well-defined wedges (glass slides in a triangular configuration), particle crystallites with square and triangular ordered regions formed.…”

Microarrays of gold nanoparticle clusters fabricated by Stop&Go convective self-assembly for SERS-based sensor chips

“…15,23 Under certain experimental conditions, and especially with small colloids (<100 nm), discontinuous lms, with a banded morphology, consisting of periodic stripes or wire-like patterns parallel to the meniscus can be obtained through the so-called stick-slip mechanism. 27,28 We have previously shown that the substrate temperature can have a dramatic effect on the orientation of such wires relative to the meniscus: decreasing the temperature of the substrate changes the NP wire orientation from parallel to perpendicular with respect to the meniscus, passing through an intermediary regime in which island-like assemblies are obtained. 16 In another report, we have proposed a new variant of CSA, called Stop&Go-CSA (SG-CSA) in which, instead of continuously translating the meniscus, a translation for a distance d at speed v s and resting time dt is imposed periodically.…”