Regression Analysis of Wetting Characteristics for Different Random Surface Roughness of Polydimethylsiloxane Using Sandpapers

This is the author accepted manuscript. The final version is available on open access from Elsevier via the DOI in this recordData Availability Statement: The data that support the findings of this study are available from the corresponding author upon reasonable request.This paper studies various wetting characteristics on different surfaces of Polydimethylsiloxane (PDMS) polymer. The random roughness of the surface is engineered by using sandpapers to introduce different order of hydrophobic properties to understand the temporal evolution of drying droplets. We develop statistical models to predict temporal evolution of the base diameter, height, surface, and contact angle of drying droplets with varying grit size or surface roughness. Five different robust polynomial regression models have been compared for the prediction of three dependent variables - base diameter, height, and surface of drying droplets for random rough surfaces. In a nutshell, we here identify the best statistical model to capture the dynamics of drying droplets on hydrophobic surfaces of random roughness characteristics.SERB, IndiaEuropean Regional Development Fund (ERDF

Microdevices for extensional rheometry of low viscosity elastic liquids : a review

Extensional flows and the underlying stability/instability mechanisms are of extreme relevance to the efficient operation of inkjet printing, coating processes and drug delivery systems, as well as for the generation of micro droplets. The development of an extensional rheometer to characterize the extensional properties of low viscosity fluids has therefore stimulated great interest of researchers, particularly in the last decade. Microfluidics has proven to be an extraordinary working platform and different configurations of potential extensional microrheometers have been proposed. In this review, we present an overview of several successful designs, together with a critical assessment of their capabilities and limitations

Electrowetting Force and Velocity Dependence on Fluid Surface Energy

Electrowetting on dielectric is a phenomenon in which the shape and apparent contact angle of a droplet changes when an electric field is applied across the droplet interface. If the field is asymmetric with respect to the droplet, then a net force can be applied to the droplet. In this work, we have measured the electrowetting force by confining the droplet shape beneath a glass plate and measuring the force on the plate. The force was measured as a function of voltage for a range of fluids with different surface energy. Measured forces show excellent agreement with predictions based on the Young–Lippmann equation with measured contact angles. Results also show that the electrowetting force is independent of fluid surface energy below saturation but that the peak force is proportional to the surface tension. This work shows that lowering the surface energy of the fluid can induce larger contact angle change under the same voltage, but it has no beneficial impact on the actuation force in droplet-based actuators. In contrast, velocity tests with deformable droplets show higher speeds for lower surface energy fluids, even above their saturation voltage. However, when the droplet’s shape is restrained, the highest velocity is achieved with high surface energy fluids due to the larger electrowetting actuation forces applied