Akanksha Singh

Rapidly switched wettability of titania films deposited by dc magnetron sputtering

Rapid switching (5–15 minutes) in the wettability of titania (TiO2) thin films in the anatase phase has been observed after UV irradiation. The film surface becomes superhydrophilic when exposed to UV radiation. The relationship between wettability, thickness and crystallinity of TiO2 films has been investigated. Amorphous and anatase TiO2 thin films have been deposited by varying the argon to oxygen gas ratio, using the reactive dc magnetron sputtering technique. It was found that the gas ratio primarily affects thickness, crystallinity, morphology and wettability of the films. The highest contact angle that has been reported so far, namely, 170°–176°, has been observed for film thickness varying from 112–500 nm in the case of pristine anatase TiO2 films. On the other hand, amorphous films show a variation in the contact angle from 120° to 140° as the thickness varied from 70 to 145 nm. The deposition is extremely robust and has an ultralow hysteresis in the contact angle. The films exhibit a morphology similar to the lotus leaf and the water hyacinth.

Room temperature, water-based, microreactor synthesis of gold and silver nanoparticles

Synthesis of gold and silver nanoparticles at room temperature using a polydimethylsiloxane (PDMS) microreactor has been reported. The reactions have been performed using aqueous metal salt solutions and borohydride reducing agent with tri-sodium citrate as the capping agent. Effect of concentration of reducing agent on the optical properties of the nanoparticles has been investigated. The nanoparticles were characterised by UV-Vis absorption spectroscopy and transmission electron microscopy. The UV-Vis absorption spectra show a blue shift in the spectra with increasing concentration of the reducing agent, which indicates reduction in the size with increased amount of the reducing agent. The sizes of the nanoparticles are uniformly smaller in the microreactor synthesis as compared to those in the conventional batch synthesis, under similar reaction conditions. The microreactor synthesis is very fast and improves the monodispersity with excellent reproducibility.

The effect of concentration in the patterning of silica particles by the soft lithographic technique

Soft lithography provides remarkable surface patterning techniques to organize colloidal particles for a wide variety of applications. In particular, micromolding in capillaries (MIMIC) has emerged as a patterning method in the nanometer to micrometer scale in a single step by using templating and directing nanoparticles via capillary forces in the channel. The present work reports the results of the micropatterning of monodispersed silica particles of ~338 ± 2 nm size in ethanol medium, using MIMIC on silicon substrates. The effect of the concentration of silica particles on the patterning has been investigated. The patterns are well aligned and completely filled at 2 wt% concentration of silica particles.

Microfluidic biochip injection moulded using a patterned SU-8/Si mould insert

Abstract This paper presents the adaptation of a conventional injection moulding process to manufacture microfluidic components in thermoplastic polymers using alternative, exchangeable microstructured silicon-based mould inserts. The mould inserts consist of thick silicon wafers with microfeatures patterned in SU-8 epoxy photo-resist. This process allows changing the mould inserts according to the design, very easily and cost-effectively. The SU-8/Si mould inserts were robust enough to manufacture small series for laboratory purpose. More than a hundred replicas in thin polypropylene (PP) were produced successfully for a biochip designed for protein crystallisation and analysis.