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Shear Distortion and Failure of Capillary Bridges. Wetting Information Beyond Contact Angle Analysis
No full textWater capillary bridges are prepared that span hydrophilic pinning features on parallel opposing smooth, flat, and hydrophobic surfaces. These bridges are distorted by shearing the parallel plates at a low rate. The capillary bridges lengthen and distort to balance Laplace pressure (equilibrate mean curvature) as the features are separated and eventually rupture at a distance that is a function of the liquid volume, the advancing and receding contact angles of the surfaces, the separation between the parallel surfaces, and in particular, the shape and orientation of the hydrophilic pinning features. Two modes of capillary bridge failure are observed: (1) tensile, in which the capillary bridge breaks to form sessile drops on both the upper and lower surfaces, and (2) sessile, in which sessile capillary bridge rupture occurs on one surface to form a puddle (contact-line-distorted sessile drop) on the feature and a retained capillary bridge spanning the hydrophobic surface and the hydrophilic feature on the opposing surface. The shape and orientation of the features control the mode of capillary bridge failure as well as the distribution of water between the two separate sessile drops or the retained capillary bridge and the puddle
An inkjet-printed electrowetting valve for paper-fluidic sensors
No full textPaper-fluidic devices have become an emerging trend for micro total analysis systems (microTAS) in the bioengineering field due to their ability to maintain the rapid, sensitive and specific attributes of microfluidic devices. Subsequently, paper-fluidic devices are also more portable, have a lower production cost and are easier to use. However, one of the obstacles in developing paper fluidic devices is the limited ability to control the rate of fluid flow during an assay. In our project, we use electrowetting on dielectrics where a dielectric, which is normally hydrophobic, is polarized and becomes hydrophilic. We have fabricated paper-fluidic devices by inkjet printing and spraying conductive hydrophobic electrodes/valves in conjunction with conductive hydrophilic electrodes which are able to stop the fluid front of phosphate buffered saline (PBS). The hydrophobic valves were then actuated by an applied potential which altered the fluorinated monolayer on the electrode. As the applied potential between the electrodes was increased, the amount of time for the fluid front to pass the valve decreased because the monolayer was altered faster. However, we did not observe significant differences in time as we increased the distance between the electrodes. The valves were also incorporated in a lateral flow assay where the device was used to detect Saccharomyces cerevisiae rRNA sequences. With the ability to control the fluid flow in a paper-fluidic device, more complex and intricate assays can be developed, which not only can be applied in the biomedical, food and environmental fields, but also can be used in low resource settings for the detection of diseases
Fabrication of Stable Nanoparticle-Based Colloidal Microcapsules
No full textColloidal Microcapsules (MCs) are hollow micron/sub-micron size spherical constructs composed of nanoparticle-based shells. Recent years have witnessed various strategies towards the fabrication of stable colloidal MCs since they find applications in many areas of material and biological sciences e. g. drug delivery, encapsulation and microreactors. The inherent instability of nanoparticles (NPs) at the interface due to thermal disorder makes it difficult to obtain stable colloidal MCs composed of nanoparticles. Stable microcapsules can be obtained by stitching together the nanoparticles at the liquid-liquid interface by either covalent or non-covalent interactions. This review article highlights the critical role of the organic ligand shell on the surface of nanoparticles in fabricating stable colloidal MCs
