Nanoparticle self-assembly using patterns formed by dewetting / Auto-organização de nanoparticulas utilizando padrões formados por transição de molhabilidade
AUTOR(ES)
Camila Alves de Rezende
DATA DE PUBLICAÇÃO
2007
RESUMO
In this work, we study an original method to promote self-assembly of gold and silica nanoparticles using patterns formed by dewetting of aqueous solutions of poly (N-isopropylacrylamide) (PNIPAM) and sodium dodecylsulfate (SDS). Dewetting is a process where the free surface of an initially stable thin liquid film becomes unstable and deforms to engender rupture and formation of micro or nanostructures on the substrate. We show in this study that these dewetting morphologies can be applied as template to induce complex pattern formation of nanoparticles on a solid substrate. Dispersions containing the nanoparticles and polymer solutions are spread on a solid substrate. Microscopy teehniques, transmission and scanning electron microscopy (TEM &SEM) and scanning probe microscopy (SPM), are used to characterize the morphologies of the dry samples. Neutron reflectivity is used to obtain quantitative information on nanoparticle adsorption at the interface, thus allowing an evaluation of the effects of nanoparticle-substrate interactions. Two major factors are found to influence pattern formation: substrate hydrophilicity and particle-substrate interactions. On a hydrophilic substrate (mica), the aqueous films spread spontaneously and form dewetting and nanoparticle patterns that depend on polymer charge density and drying temperature. At reduced charge density and low temperature, a polygonal network is formed. At increased charge density and temperature, elongated structures are favored. On hydrophobic substrates (nanocrystalline silicon and graphite), the liquid does not spread eompletely and nanoparticle patterns do not reflect characteristic dewetting morphologies. In addition, TEM and neutron reflectivity results indicate particle-substrate adhesion on hydrophobic substrates that is mediated by the polymer-substrate adsorption. Dewetting of thin films of charged polymer solutions on a hydrophilic solid substrate provides an alternative method to template nanoparticle organization. For gold and silica nanoparticles, complex bidimensional patterns, including polygonal network, aligned elongated chains and nanoparticle yarns, are obtained. Under well-controlled drying conditions, these reproducible patterns are formed over large areas eovering hundreds of microns in size. This simple and effective method does not require chemical modifications or prepatterned surfaces and represent a promising method to nano and micro fabrication.
ASSUNTO(S)
filme nanoparticle dewetting transição de molhabilidade nanoparticula sistemas auto-organizadores self-assembly film
