On the two-dimensional patterning of inorganic particles in resin using ultrasound

Abstract

The ultrasonic manipulation technique is applicable to opaque particle suspensions and has merits in comparison with the other methods such as radiation force by a laser that needs media transparency and electrostatic force that requires attention to be paid to electrolysis [A. Ashkin: Phys. Rev. Lett. 24 (1970) 156]. Goddard and Kaduchak [G. Goddard and G. Kaduchak: J. Acoust. Soc. Am. 117 (2005) 3440] demonstrated the concentration of polystyrene particles using a line-driven cylindrical glass tube. Oberti et al. [S. Oberti, A. Neild and J. Dual: J. Acoust. Soc. Am. 121 (2007) 778] directly excited ultrasonic transducers attached to a glass plate on a fluidic system to cause propagation of surface wave emitting a sound wave into an adjacent fluid. They achieved particle concentration in parallel lines in the case of one transducer while in the case of two transducers an oval-shaped two-dimensional pattern of particle concentration was obtained. The present study deals with for the first time the formation of a two-dimensional pattern of concentrated particles with indirect irradiation of ultrasound from one transducer. A two-dimensional millimeter-sized pattern of micrometer-sized titanium dioxide particles in UV-reactive acrylic resin using 1.93 MHz ultrasound is fabricated. A mixture of particles and resin is set in a thin layer between square glass plates of which one plate is irradiated with ultrasound. Both vibration normal to the plate and the wave propagating in the mixture form standing waves to provide a two-dimensional pattern of the particles. The twodimensional pattern was hardened with UV irradiation. It is confirmed that the two-dimensional pattern keeps a similar structure before and after UV hardening. The present technique will be promising for novel material fabrication by controlling the boundary condition for the mixture of the particle and resin or vibration mode of the glass.