Evaporative Self-assembly Research Articles

Evaporative self-assembly of nanowires on superhydrophobic surfaces of nanotip latching structures

In this letter, we report a site-specific self-assembly of nanowires during the evaporation of a colloid droplet of nanowires on nanoengineered superhydrophobic surfaces. The self-assembly of nanowires is achieved by the interactions between nanowires and the superhydrophobic surface engineered with sharp-tip latching nanostructures of micropillars, provided by the convective hydrodynamic flow and the receding three-phase contact line of the evaporating droplet. The experimental results show that the spatial density of surface structures, the relative dimension of surface patterns to nanowires, and the morphology of tip surface influence the self-assembly and alignment of nanowires on the evaporative superhydrophobic surface.

Controlled evaporative self-assembly of hierarchically structured bottlebrush block copolymer with nanochannels

The toluene solution of a bottlebrush block copolymer, polystyrene–polylactide (PS–PLA), was confined in a cylinder-on-flat geometry, from which the consecutive “stick-slip” motion of the three-phase contact line of the PS–PLA solution was effectively regulated as toluene evaporated, thereby yielding gradient stripes at the microscopic scale. Subsequent selective solvent vapor annealing led to the formation of hierarchically structured PS–PLA in which the lamellar nanodomains of PS–PLA normal to the substrate were obtained within the microscopic stripes. After the selective removal of the PLA block by enzymatic degradation, nanochannels were yielded within the stripes. This facile approach of combining the controlled evaporative self-assembly with subsequent solvent vapor annealing opens up a new avenue to rationally organize and engineer self-assembling building blocks into functional materials and devices in a simple, cost-effective and controllable manner.

Micro-patterns of reduced graphene oxide (RG-O) platelets crafted by a self-assembled template

Highly ordered reduced graphene oxide (RG-O) micro-patterns were crafted by an efficient method capitalizing on the self-assembled polymer template. Central to this strategy is to fabricate the polymer template over a large area via controlled evaporative self-assembly (CESA), and treat the templated glass substrate with the O2 plasma to render the favorable interaction between the RG-O platelets and the substrate, thereby yielding well-defined microscopic RG-O patterns on the large scale.

A simple route of ordered high quality mesoscale stripe polymer patterns

Fine ordered stripe patterns are developed through the evaporative self-assembly of a PMMA-toluene solution and O2 plasma for applications to optical waveguide devices. The stripe patterns were formed by repeating the “stick-slip” motion of the contact line in a restricted geometry. High-quality patterned lines were obtained by removing the residue of the pattern’s sidewall using an O2 plasma asher.

Three-Dimensional Patterning of Micro/Nanoparticle Assembly with a Single Droplet of Suspension

ABSTRACTWe develop a novel patterning technique to create 3D patterns of micro, nanoparticle assembly via evaporative self-assembly based on confinement/release of micro/nano particles assembly based on the coffee-ring effect of evaporating suspension. Based on the presented technique, we demonstrate that the patterns of 3D assembly of various sizes of microparticles (Silica), metal oxide nanoparticles (TiO2, ZnO) and metallic nanoparticles (Ag) can be successfully generated by low-concentrated particle suspension (1.25 wt % ~ 5 wt %) without additional sintering steps and we also show the geometries of the patterns can be finely controlled by adjusting the parameters of the process.

Assembling and positioning latex nanoparticles via controlled evaporative self-assembly

By capitalizing on a simple, robust, and fast approach based on controlled evaporative self-assembly in a cylinder-on-flat geometry, two kinds of polystyrene (PS) latex nanoparticles with different diameters (i.e., D = 50 nm and 500 nm, respectively) were deposited on the Si substrate, forming ordered “coffee rings” composed of PS nanoparticles. Within a “coffee ring”, the packing of PS nanoparticles was found to be dependent upon the particle diameter. More intriguingly, when the aqueous solution of mixed two PS nanoparticles was used, “coffee rings” of small particles were positioned at the edge of three-phase contact line (D = 50 nm), followed by the adjacent deposition of large particles (D = 500 nm). These assembled deposits consisting of monolayer- or multilayer-thick latex nanoparticles over large areas may offer potential for applications in electronic devices, photonic bandgap materials, biosensors, particle sorting, and disease diagnosis.

Simple route to ridge optical waveguide fabricated via controlled evaporative self-assembly

A simple route to intriguing patterns for optical waveguides was demonstrated by controlled evaporative self-assembly (CESA) of confined microfluid. Silica ridge waveguides were fabricated by applying wet and dry etching based on stripe patterns formed by CESA. The optical mode of the resulting waveguides was confirmed by exposing them to the 1064 nm transmission light.

Polyelectrolytes: Influence on Evaporative Self-Assembly of Particles and Assembly of Multilayers with Polymers, Nanoparticles and Carbon Nanotubes

Assembling polyelectrolyte multilayers in a bottom-up approach is reported for polymers, particles, nanoparticles, and carbon nanotubes. Effects of polyelectrolyte multilayers on evaporative self-assembly of particles, which are of interest to a number of applications including photonic crystals, films and substrates, are investigated. Polyelectrolyte multilayer coatings bring multifunctionality to spherical particles and planar films. Studying the construction of polyelectrolyte assemblies is convenient in the planar layout: it is reported here for incorporation of gold and magnetic nanoparticles as well as of carbon nanotubes. Gold nanoparticles concentration is controlled within the films. Potential applications of both spherical structures and planar films are highlighted.

Self‐assembly: Hierarchically Ordered Structures Enabled by Controlled Evaporative Self‐Assembly (Small 20/2010)

Self‐assembly: Hierarchically Ordered Structures Enabled by Controlled Evaporative Self‐Assembly (Small 20/2010)

Hierarchically Ordered Structures Enabled by Controlled Evaporative Self‐Assembly

Hierarchically ordered comb block copolymer (CBCP) stripes are produced by combining top-down, controlled evaporative self-assembly of capillary-held CBCP solution. In the wedge-on-Si geometry, bottom-up, spontaneous self-assembly of CBCP nanodomains is promoted by subsequent solvent vapor annealing.

Hierarchically Organized Structures Engineered from Controlled Evaporative Self-Assembly

By constraining an asymmetric comb block copolymer (CBCP) toluene solution to evaporate in a wedge-on-Si geometry composed of a wedge lens situated on a Si substrate, gradient concentric stripelike surface patterns of CBCP at the microscopic scale were yielded as a direct consequence of controlled evaporative self-assembly of CBCP. The formation of either straight stripes or jagged stripes was dictated by the height of the wedge. Upon subsequent solvent vapor annealing, hierarchically organized structures of CBCP were produced, resulting from the interplay of solvent vapor assisted, unfavorable interfacial interaction driven destabilization of CBCP from the Si substrate at the microscopic scale and the solvent vapor promoted reconstruction of CBCP nanodomains within the stripes at the nanometer scale. This facile approach of combining controlled evaporative self-assembly with subsequent solvent vapor annealing offers a new platform to rationally design and engineer self-assembling building blocks into functional materials and devices in a simple, cost-effective manner.

Coffee-Ring Effect-Based Three Dimensional Patterning of Micro/Nanoparticle Assembly with a Single Droplet

We develop a novel patterning technique to create 3D patterns of micro and nanoparticle assembly via evaporative self-assembly based on the coffee-ring effect of an evaporating suspension. The principle of the technique is analyzed theoretically by the scaling analysis of main parameters of the process and the scaling effect, the effect of the volume, the concentration of the suspension, and the effect of surface treatment on the patterning are studied. On the basis of the presented technique, we demonstrate that the patterns of 3D assembly of various sizes of microparticles (Silica), metal oxide nanoparticles (TiO(2), ZnO), and metallic nanoparticles (Ag) can be successfully generated by low-concentrated particle suspension (1.25-5 wt %) without additional sintering steps, and we also show the geometries of the patterns can be finely controlled by adjusting the parameters of the process.

Nonintrusive measurements of mixture concentration fields by analyzing diffraction image patterns (point spread function) of nanoparticles

The diffraction image patterns of small particles are referred to as their point spread function (PSF); these patterns vary distinctively with the refractive index (RI) of a transparent test medium when the particles are imaged through the medium. The RI correlates directly with the mixture concentration, so proper inversion of measured PSFs can provide full-field information on the mixture concentration field. In this study, fluorescent nanoparticles of 500 nm diameter are fixed on a glass surface by means of evaporative self-assembly, and the time-varying test mixture is placed in front of the glass surface. The time-varying and full-field PSF distributions are imaged and digitally analyzed to determine the local RI values as well as the local mixture concentrations. Both immiscible water/oil mixture and miscible water/glycerol mixture are imaged. The present method shows an RI measurement to have an uncertainty of ±5 × 10−3 RIU and the mixture concentration measurements to have uncertainty of approximately 4%.

Controlled evaporative self-assembly of hierarchically structured regioregular conjugated polymers

A toluene solution of the semiconducting conjugated polymer regioregular poly(3-hexylthiophene) (rr-P3HT) was confined in a sphere-on-flat geometry, forming an axially symmetric, capillary-held microfluid, from which the consecutive “stick–slip” motion of the contact line of the solution viasolvent evaporation was effectively regulated. As a result, hierarchical “snake-skin” like structures of high regularity were obtained where each microscopic ellipsoid within the “snake-skin” was composed of bundles of rr-P3HT nanofibers. This facile, one-step deposition technique based on controlled evaporative self-assembly opens up a new avenue for organizing semicrystalline conjugated polymers into two-dimensional ordered patterns in a simple, cost-effective, and controllable manner.

Evaporative Self-Assembly from Complex DNA−Colloid Suspensions

Evaporation-induced pattern formation has attracted considerable attention as a simple yet versatile method for generating self-assembled structures that have broad applications from photonic devices to biomacromolecular recognition. Previous study of evaporative self-assembly has mainly focused on single nonvolatile component systems, and the driving mechanisms have been extensively investigated. In contrast, pattern formation from evaporating multicomponent systems, despite its wide existence in nature and numerous engineering applications, has been rarely explored. In this work, we examine a DNA-colloid binary suspension as a model system to understand the evaporation-induced interfacial hydrodynamics and self-assembled morphology in multicomponent systems involving complex competing intermolecular and interfacial interactions. Direct microscopic observations show that the composition of the binary system plays a critical role in the multiple-ring formation upon evaporation: (1) suspensions with high DNA concentrations and low colloidal concentrations favor the formation of the multiple-ring pattern; (2) the size of colloidal particles added into DNA aqueous droplets can significantly disrupt smooth multiple rings to form rippled rings and curtain-like periodic patterns with a curious spoke-like structure as the size of colloidal particles increases; and (3) the enhancement of DNA-colloid interaction by oppositely charged colloidal particles results in considerably high irregularity of DNA stain ring spacing. We examine the disruption of the multiring morphology under varied conditions and attribute it to local hydrodynamics governed by colloid aggregation and sedimentation. Our results demonstrate the feasibility of fabricating periodic self-assembled hybrid structures via one-step evaporation of droplets consisting of multiple components.