Diffusiophoretically Mediated Nanopatterning by Solvent Nanodroplets on Polystyrene Surfaces

Dissolution is a ubiquitous process in nature and industry. However, due to technical difficulties, the detailed dissolution process at the nanoscale has seldom been captured experimentally. In this study, we investigated the dissolution dynamics in the confinement of toluene surface nanodroplets on polystyrene (PS) thin films in oversaturated toluene/water mixture solutions. This was achieved by adjusting the immersion durations from several minutes to 9 h. Dissolution takes place upon the deposition of nanodroplets on the PS surfaces, leading to the formation of surface nanostructures. Interestingly, we found that the induced nanostructures underwent complex morphological changes, from complex nanocraters with central bulges and/or multiple rims to simple nanocraters. We speculate that diffusiophoresis plays a key role in the formation of the complex nanocraters, as it facilitates the transportation of dissolved PS molecules inside the nanodroplets. We believe this finding not only enhances our understanding of dissolution dynamics at the nanoscale but also holds promise for applications in dissolution-based nanopatterning.

Photoinitiated Marangoni flow morphing in a liquid crystalline polymer film directed by super-inkjet printing patterns

Slight contaminations existing in a material lead to substantial defects in applied paint. Herein, we propose a strategy to convert this nuisance to a technologically useful process by using an azobenzene-containing side chain liquid crystalline (SCLCP) polymer. This method allows for a developer-free phototriggered surface fabrication. The mass migration is initiated by UV-light irradiation and directed by super-inkjet printed patterns using another polymer on the SCLCP film surface. UV irradiation results in a liquid crystal-to-isotropic phase transition, and this phase change immediately initiates a mass migration to form crater or trench structures due to the surface tension instability known as Marangoni flow. The transferred volume of the film reaches approximately 440-fold that of the polymer ink, and therefore, the printed ink pattern acts as a latent image towards the amplification of surface morphing. This printing-aided photoprocess for surface inscription is expected to provide a new platform of polymer microfabrication.

Hierarchically structured multifunctional porous interfaces through water templated self-assembly of ternary systems

Herein, a facile water-assisted templating approach, the so-called breath figures method, has been employed to prepare multifunctional and hierarchically structured porous patterned films with order at different length scales (nano- and micrometer). Tetrahydrofuran solutions of ternary blends consisting on high molecular weight polystyrene, an amphiphilic block copolymer, polystyrene-b-poly[poly(ethylene glycol) methyl ether methacrylate] (PS(40)-b-P(PEGMA300)(48)), and a fluorinated copolymer, polystyrene-b-poly(2,3,4,5,6-pentafluorostyrene) (P5FS(21)-b-PS(31)), have been used to obtain films varying the proportion of the three components. Confocal micro-Raman spectroscopy and atomic force microscopy demonstrated the preferential location of the different functionalities in the films. Because of the breath figures mechanism, the amphiphilic copolymer yield pores enriched in hydrophilic functionality while the fluorinated copolymer remained mixed with the PS matrix and eventually also forming self-assembled nanostructures at the surface. As a consequence, two levels of order can be observed, i.e., micrometer size pores with nanostructured domains due to the block copolymer self-assembly. In addition, the distribution of the amphiphilic copolymer within the holes is not regular being located principally on the edges of the cavities. This can be attributed to the coffee stain phenomenon occurring in the water droplets as a consequence of the segregation of the block copolymers to the droplets and their self-assembly.

Temperature distribution inside an evaporating two-dimensional droplet lying on curved or flat substrates

The temperature field inside an evaporating two-dimensional droplet resting on curved or flat isothermal substrates is studied under various evaporation conditions. An analytical solution for the temperature is derived, which can be directly used in the cases of pinned and depinned contact lines as well as in stick-slip evaporation modes. It is found that the temperature drop at the free surface of a droplet on a convex, hydrophobic substrate is far greater than that for flat or concave substrates of the same hydrophobicity. The analytical solution for the temperature field allows the direct estimate of the local temperature gradient and, hence, of the local surface tension gradient that gives rise to Marangoni flow directed from the contact lines to the top of the droplet.

Formation of nanodents by deposition of nanodroplets at the polymer-liquid interface

Recent work has shown that it is easy to form nanoscale droplets of fluid phase at interfaces. Here we demonstrate the use of these small droplets as templates for facile modification of a polymer surface. Small dents with the depth of less than 20 nm were created at the interface between polystyrene and water by the deposition of toluene droplets. Polystyrene is much more soluble in the toluene than in the water, so modification of the polystyrene occurs within the droplet but not under the water. The modification is seen to be permanent because the surface pattern remains on the polystyrene after removal from the liquids. Two mechanisms for surface modification are discussed: plastic deformation of the polystyrene due to interfacial tension and transport of dissolved polystyrene to the three-phase line during dissolution of the droplet (the coffee stain effect).

Evaporation dynamics of microdroplets on self-assembled monolayers of dialkyl disulfides

We present a study of the static wettability and evaporation dynamics of sessile microdroplets of water on self-assembled monolayers (SAMs) prepared with unsymmetric dialkyl disulfides CH(3)-(CH(2))(11+m)-S-S-(CH(2))(11)-OH (m = 0, +/- 2, +/- 4, +/- 6) on gold-covered mica. The advancing and receding contact angles decrease linearly with increasing hydrophilicity of the SAM. The latter was changed either via the molar ratio or via the chain length of the hydroxyl-terminated alkyl chains in the monolayer. In contrast to SAMs made of thiols, the contact angle hysteresis was 10 degrees for all disulfides, irrespective of their chain lengths. During evaporation of single droplets, a transition from pinning to constant contact angle mode was observed. The transition time between the modes increases with the surface hydrophilicity, leading to longer pinning. This way, the time for complete droplet evaporation decreases by approximately 30% owing to the fact that during pinning the overall droplet area stays large for a longer time. For single droplets the measured total evaporation times agree well with the calculated ones, showing the validity of the standard evaporation model for both evaporation modes. In contrast to the results for single droplets, many droplets with different initial volumes show a power-law dependence on the total evaporation time with an exponent different from 1.5 as expected from the standard model. For disulfides with m not equal 0, the exponent is in the range of 1.40-1.47 increasing with the surface hydrophilicity. For the SAMs with m = 0 the exponent increases up to 1.61 for the most hydrophilic surface. We explain this deviation from the standard evaporation model with the presence of a liquid precursor film around the droplet, which either enhances or decelerates evaporation. Our results suggest that SAMs of dialkyl disulfides offer the possibility to tune the wettability of gold surfaces in a more controlled way than thiols do.

Interfacial and solvent effects govern the formation of tris(dibenzylidenacetone)dipalladium(0) microstructures

Organometallic palladium adducts have application as catalysts and as precursors for nanoparticle synthesis. Herein, we study the spontaneous formation of molecular crystals of the organometallic reagent tris(dibenzylidenacetone)dipalladium(0) (Pd(2)(DBA)(3)) in THF/H(2)O binary solvent systems. We report structural and chemical characterization of the resulting diverse structures with shapes including hexagonal platelets, rods, cubes, and stars. Optical microscopy, transmission electron microscopy, scanning electron microscopy, and energy-dispersive spectroscopy were used to determine representative structures and corresponding compositions when formed either in a binary solution or upon evaporation on a surface. The difference in Pd(2)(DBA)(3) particle morphology was attributed to differences in the surface tension of growing crystalline faces. The formation of a majority of rods or hexagonal platelets in solution was shown to be determined by the ratio of THF to H(2)O in the solvent, whereas supersaturation effects and interfacial surface tension played a major role in creating the shape of particles formed upon evaporation of Pd(2)(DBA)(3) droplets on a surface.