Dynamics of Dielectrophoretic-Force-Directed Assembly of NaYF₄ Colloidal Nanocrystals into Tunable Multilayered Micropatterns

The dynamics of dielectrophoretic-force-directed assembly of polarizable colloidal upconverting β-NaYF₄ nanocrystals into tunable multilayers on charge micropatterns written by atomic force microscopy is investigated. Multilayered nanocrystal assembly by this nanoxerography process occurs in two phases. During the first phase typically lasting a few minutes, the nanocrystal assemblies grow up to a maximum thickness under the influence of strong dielectrophoretic forces exerted by the charge patterns. Subsequently, the nanocrystals start to diffuse back into the solvent, leaving a single layer attached to the charge patterns. A theoretical model based on the Fokker–Planck equation is formulated to describe this dynamics involving an interplay of diffusive and dielectrophoretic forces. Being in good agreement with the experimental results, this approach may be reliably extended to simulate the directed assembly of other types of polarizable colloids from liquid phase by nanoxerography

Single-Step Binary Electrostatic Directed Assembly of Active Nanogels for Smart Concentration-Dependent Encryption

Anionic and cationic (<i>N</i>-isopropylacrylamide derivatives) active colloidal hydrogel nanoparticles, i.e., nanogels, are electrostatically assembled on surfaces to form microscale patterns with complex geometries. While using mixed dispersions of these two kinds of nanogels, we demonstrate the capability of sorting the nanogels in one step to form binary nanogel patterns on a surface. These patterns appear independently or simultaneously depending on the relative proportion of each nanogel type in the mixture. Hence, the resulting nanogel patterns provide quantitative information regarding the dispersion composition and can be used to achieve smart concentration-dependent nanogel encryption. Moreover, atomic force microscopy characterization measurements performed in liquid prove that the assembled nanogels maintain their swelling/deswelling properties once attached to the surface. Consequently, this method paves the way for applying such active nanogel patterns to produce smart coatings and sensors