V.K. Parashar

Plastic micropump with ferrofluidic actuation

We present the realization and characterization of a new type of plastic micropump based on the magnetic actuation of a magnetic liquid. The pump consists of two serial check-valves that convert the periodic motion of a ferrofluidic plug into a pulsed quasi-continuous flow. The ferrofluid is actuated by the mechanical motion of an external NdFeB permanent magnet. The water-based ferrofluid is synthesized in-house using a coprecipitation method and has a saturation magnetization of 32 mT. The micropump consists of various layers of polymethylmethacrylate (PMMA), which are microstructured by powder blasting or by standard mechanical micromachining techniques, and are assembled in a single plastic structure using a monomer gluing solution. Two soft silicone membranes are integrated in the microfluidic structure to form two check-valves. Water has been successfully pumped at flow rates of up to 30 /spl mu/L/min and pumping is achieved at backpressures of up to 25 mbar.

Internal Modification of Poly(dimethylsiloxane) Microchannels with a Borosilicate Glass Coating

We report on an original technique for the in situ coating of poly(dimethylsiloxane) (PDMS) microchannels with borosilicate glass, starting from an active nonaqueous and alkali-free precursor solution. By chemical reaction of this active solution inside the microchannel and subsequent thermal annealing, a protective and chemically inert glass borosilicate coating is bonded to the PDMS. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and nuclear magnetic resonance spectroscopy of the active solution show that it is composed of a silicon oxide network with boron connectivity. Thermal gravimetric analysis demonstrates the absence of organic content when curing is done above 150 degrees C. The borosilicate nature of the glass coating covalently bonded to the PDMS is demonstrated using ATR-FTIR spectroscopy and X-ray photoelectron spectroscopy. Atomic force microscopy and scanning electron microscopy show a smooth and crack-free coating. The latter is used as an efficient protective barrier against diffusion in PDMS of fluorescent rhodamine B dye that is dissolved either in water or in toluene. Moreover, the coating prevents swelling and consequent structural damage of the PDMS when the latter is exposed to harsh chemicals such as toluene.

Thermal evolution of sol-gel derived zirconia and binary oxides of zirconia-silica

This study is centred around the evolution of the zirconia polymorph in zirconia and in binary oxides of zirconia-silica derived by the sol-gel technique that can help alter the microstructure by changing the experimental parameters

Borosilicate nanoparticles prepared by exothermic phase separation

Nanoparticles play an important role in chemical and biological sciences due to their ability to bind and concentrate many molecules on their surface. Polymers and silica are widely used to make nanoparticles, but efforts to make nanoparticles from borosilicate glass--which exhibits high tolerance to chemicals and solvents, combined with excellent mechanical and thermal stability--have proved unsuccessful. Here we show that borosilicate nanoparticles (100-500 nm in size) can be synthesized by simply mixing a silicon-boron binary oxide solution, prepared using non-aqueous organic solvents, with water. This induces a vigorous exothermic phase separation in which borosilicate nanoparticles burst out of a silica phase. In addition to potential applications in the life sciences, monodisperse borosilicate particles could also have applications in the production of photonic bandgap devices with high optical contrast, contrast agents for ultrasonic microscopy or chemical filtration membranes.

Two dimensional magnetic manipulation of microdroplets on a chip

In this paper we describe the two-dimensional (2D) magnetic manipulation of aqueous droplets suspended in silicone oil over the chip surface. The magnetic actuation is based on the force imposed on superparamagnetic microparticles inside the droplets. These can be displaced, merged, mixed and separated by changing the topology of the magnetic field created by a multilayer set of coils. The magnetic manipulation forces are generated on our chip without the use of external moving magnets. Our results demonstrate the potential of the proposed system in droplet-based biomedical analysis methods on a chip.

Influence of boric acid on the synthesis of silicon carbide whiskers from rice husks and polyacrylonitrile

Abstracts are not published in this journal

Fabrication and Characterization of Three-Dimensional Microlens Arrays in Sol-Gel Glass

We propose a new replication process for the realization of thick microlenses in SiO2 glass with low organic content. We start by replicating an array of cylindrical micropillars made in SU-8 negative photoresist (Microchem) into poly-dimethylsiloxane (PDMS). The PDMS replica is filled with a photoresist (Clariant AZ 9260), applied to a glass substrate and soft-baked. After demoulding, we obtain cylindrical pillars that are given a dome-like shape by a thermal softening. This structure is used as a master in a second PDMS replication step. An in-house developed sol-gel glass material with low organic content is then poured in the second PDMS replica and subsequently thermally treated to obtain an array of thick, dense and crack-free microlenses. We characterize the shrinkage and the surface roughness of the microlenses. Using imaging of millimeter-size objects in an optical microscope setup, we characterize basic optical properties of the lenses, like focal length, magnification, and distribution of the light intensity around the focal plane

Fabrication of microfluidic mixers with varying topography in glass using the powder-blasting process

The powder-blasting method is used to fabricate structures with a three-dimensional topography in glass using elastomeric masks. The relation between the mask opening width and the erosion depth is exploited to fabricate microstructures with varying depth in a single micropatterning step. As an application, planar three-dimensional micro-mixers were fabricated, which consist of a repeating convergent microfluidic nozzle structure. Three different designs of the micro-mixers were considered. The mixing of co-flowing laminar streams results from the generation of multiple vortices at the exit of the different convergent nozzles.

Micro-replication of optical lenses in glass using a novel sol gel technology

A new method to realize arrays of microlenses using a sol gel glass replication technology is presented. Polydimethyl-siloxane (PDMS) master structures are used for the replication of thin glass membranes, which, by an appropriate annealing procedure, result in converging lenses with positive meniscus. Hereby, we exploit PDMS - sol gel surface interactions and thickness dependent changes in composition of the sol gel solution. The lenses are realized on a circular and square like basis. We characterize the micro-lenses by an optical imaging system and measure their focal length as a function of lens thickness and size. Also lens interference effects are measured.

Anisotropic Magnetic Porous Assemblies of Oxide Nanoparticles Interconnected Via Silica Bridges for Catalytic Application

We report the microfluidic chip-based assembly of colloidal silanol-functionalized silica nanoparticles using monodisperse water-in-oil droplets as templates. The nanoparticles are linked via silica bridges, thereby forming superstructures that range from doublets to porous spherical or rod-like micro-objects. Adding magnetite nanoparticles to the colloid generates micro-objects that can be magnetically manipulated. We functionalized such magnetic porous assemblies with horseradish peroxidase and demonstrate the catalytic binding of fluorescent dye-labeled tyramide over the complete effective surface of the superstructure. Such nanoparticle assemblies permit easy manipulation and recovery after a heterogeneous catalytic process while providing a large surface similar to that of the individual nanoparticles.