Visualization of a Standing Lattice of Scattered Light on Spherical Water Droplets under an Acoustic Field Using Biogenic Microparticles

Micromanipulation using acoustic sound is a promising technique for drug delivery, cell manipulation, biosensors, and microfluidic devices. Additionally, the visualization of acoustic fields by advanced optical measurement techniques can be combined with this micromanipulation technique. The present study reveals that a lattice pattern of reflected light appears on the surface of water droplets containing microparticles when the droplets are exposed to audible sound in the range of 1900 to 10000 Hz. A piezoelectric membrane providing an audible acoustic field induced a stream of microparticles on which the lattice pattern overlapped, with the appearance of a standing wave. The effects of microparticles, including BaSO4, TiO2, and guanine platelets derived from fish scales, on the formation of the lattice pattern were investigated. These three types of microparticles in water enabled a visualization of the vortex streams and generated a lattice pattern of reflected light. The guanine platelets exhibited the most precise lattice pattern over the droplet surface, with a lattice width of 100 to 200 μm. This phenomenon may provide a new tool for detecting and manipulating micro vortex flows in the aqueous chamber of a microfluidic device combined with an acoustic transducer.

Investigating the Phase-Morphology of PLLA-PCL Multiblock Copolymer / PDLA Blends Cross-linked Using Stereocomplexation

ABSTRACTThe macroscale function of multicomponent polymeric materials is dependent on their phase-morphology. Here, we investigate the morphological structure of a multiblock copolymer consisting of poly(L-lactide) and poly(ε-caprolactone) segments (PLLA-PCL), physically cross-linked by stereocomplexation with a low molecular weight poly(D-lactide) oligomer (PDLA). The effects of blend composition and PLLA-PCL molecular structure on the morphology are elucidated by AFM, TEM and SAXS. We identify the formation of a lattice pattern, composed of PLA domains within a PCL matrix, with an average domain spacing d0 = 12 – 19 nm. The size of the PLA domains were found to be proportional to the block length of the PCL segment of the copolymer and inversely proportional to the PDLA content of the blend. Changing the PLLA-PCL / PDLA ratio caused a shift in the melt transition Tm attributed to the PLA stereocomplex crystallites, indicating partial amorphous phase dilution of the PLA and PCL components within the semicrystalline material. By elucidating the phase structure and thermal character of multifunctional PLLA-PCL / PDLA blends, we illustrate how composition affects the internal structure and thermal properties of multicomponent polymeric materials. This study should facilitate the more effective incorporation of a variety of polymeric structural units capable of stimuli responsive phase transitions, where an understanding the phase-morphology of each component will enable the production of multifunctional soft-actuators with enhanced performance.