Cleaning of patterned porous low-k dielectrics with water, carbon dioxide and ambidextrous surfactants

In Situ Contact Angle Tuning of Silver Nanostructures by Laser Heating in Different Fluid Ambient

It has been theoretically suggested by Yan et al. (Colloids Surf., A 2013, 429, 142-148) that the contact angle θ_c of a liquid droplet on any given surface can be controlled by immersing it in an appropriate surrounding environment. Here, we report the first experimental demonstration of such an in situ contact angle tuning of silver (Ag) nanoparticles on quartz substrates via nanosecond pulsed laser heating under various fluid ambients, like air, water, and glycerol. Nanosphere lithography (NSL) was used to deposit Ag nanopyramids on quartz substrates. This system was subsequently melted by laser heating inside the various fluids to form nanoparticles. By using a combination of top and side view scanning electron microscopy (SEM) imaging, we show that the contact angle of Ag nanoparticles could be increased by going from heating in air to heating under fluids, with a near hemispherical shape (θ_c ∼ 99°) under air irradiation to nearly spherical (θ_c ∼ 167°) under glycerol irradiation. The mechanism of this contact angle change could be explained qualitatively by the changing interfacial energies of the substrate and metal in the various fluids. Similar contact angle control was also achieved for nanoparticles created by dewetting of Ag thin films in the various fluids. One practical implication of this contact angle tunability is the ability to change the intensity ratio of the quadrupolar to dipolar localized surface plasmon resonances in the Ag nanoparticles. This work also has implications to those applications in which nanoparticles on a substrate are heated in various gas or fluid ambients, such as in catalysis, as the ensuing shape change can modify properties.

Compressed CO2 mediated synthesis of bifunctional periodic mesoporous organosilicas with tunable porosity

A facile and green method is proposed for the fabrication of bifunctional periodic mesoporous organosilicas (PMOs) using compressed CO2.

CO2: a wild solvent, tamed

This article reviews approaches for modification of solvent properties of supercritical carbon dioxide (scCO(2)), with particular reference to self-assembly of oligomeric and polymeric solute additives. Of special interest are viscosity modifiers for scCO(2) based on molecular self-assembly. Background on polymers and surfactants with CO(2)-compatible functionalities is covered, leading on to the attempts made so far to increase the scCO(2) viscosity, which are described in detail. The significance of this field, and the implications a breakthrough could bring environmentally and economically will be addressed.

Adsorption and self-assembly of surfactant/supercritical CO2 systems in confined pores: a molecular dynamics simulation

A coarse-grained molecular dynamics simulation has been carried out to study the adsorption and self-organization for a model surfactant/supercritical CO2 system confined in the slit-shape nanopores with amorphous silica-like surfaces. The solid surfaces were designed to be CO2-philic and CO2-phobic, respectively. For the CO2-philic surface, obviously surface adsorption is observed for the surfactant molecules. The various energy profiles were used to monitor the lengthy dynamics process of the adsorption and self-assembly for surfactant micelles or monomers in the confined spaces. The equilibrium properties, including the morphologies and micelle-size distributions of absorbed surfactants, were evaluated based on the equilibrium trajectory data. The interaction between the surfactant and the surface produces an obvious effect on the dynamics rate of surfactant adsorption and aggregation, as well as the final self-assembly equilibrium structures of the adsorbed surfactants. However, for the CO2-phobic surfaces, there are scarcely adsorption layers of surfactant molecules, meaning that the CO2-phobic surface repels the surfactant molecules. It seems to conclude that the CO2 solvent depletion near the interfaces determines the surface repellence to the surfactant molecules. The effect of the CO2-phobic surface confinement on the surfactant micelle structure in the supercritical CO2 has also been discussed. In summary, this study on the microscopic behaviors of surfactant/Sc-CO2 in confined pores will help to shed light on the surfactant self-assembly from the Sc-CO2 fluid phase onto solid surfaces and nanoporous media.