Resonantly-driven drop contact-line mobility measurement

A method for measuring contact-line mobility of a liquid on a solid substrate, said method comprising the steps of:

• (a) subjecting test droplets of the liquid on the solid substrate to periodic forcing to induce measurable contact-line displacement;
• (b) acquiring image data of the test droplets comprising contact-line displacement, contact-line speed, and contact angle at or near contact-line thereof;
• and
• (c) determining Contact-Line Drag Coefficient M from the image data by generating a contact-line cyclic diagram comprising a plot of ηΔα versus ηη, wherein η=contact line displacement, {dot over (η)}=contact-line speed, and Δα=contact angle deviation, said contact-line cyclic diagram including an advancing loop A having a linear region A and a receding loop R having a linear region R simultaneously, wherein the Contact-Line Drag Coefficient M is a reciprocal slope of a best fit line through linear region A and linear region R.

A method for measuring contact-line mobility of a liquid on a solid substrate, said method comprising the steps of:

• (a) providing a system comprising:
• (i) a motion-generation component comprising an actuator and a controller, wherein said actuator is adapted to mount a solid substrate thereon, and effective to impart periodic forcing to the solid substrate when a test droplet of the liquid is deposited thereon;
• and said controller is adapted to tune frequency and amplitude of the forcing to induce measurable contact-line displacement of the test droplet on the solid substrate;
• (ii) a motion-measurement component comprising an image acquisition device adapted for capturing images of the test droplet deposited on the solid substrate before, during, or after the forcing imparted by the actuator, said image acquisition device having requisite spatial and temporal resolution to enable acquisition of image data of the test droplet comprising contact-line displacement, contact-line speed, and contact angle at or near contact-line;
• and
• (iii) a computer component adapted to receive and analyze the image data from the motion-measurement component, and configured to determine a dimensionless parameter of contact-line mobility of the liquid from the image data, wherein said dimensionless contact-line mobility parameter is Contact-Line Drag Coefficient M, wherein the Contact-Line Drag Coefficient M is determined from the image data by generating a contact-line cyclic diagram comprising a plot of ηΔα versus ηη;
• wherein η=contact line displacement, η′=contact-line speed, and Δα=contact angle deviation, said contact-line cyclic diagram including an advancing loop A having a linear region A and a receding loop R having a linear region R simultaneously, wherein the Contact-Line Drag Coefficient M is a reciprocal slope of a best fit line through linear region A and linear region R;
• (b) depositing one or more test droplet of the liquid onto the solid substrate;
• and
• (c) operating the system in a manner effective to determine the Contact-Line Drag Coefficient M of the liquid.