Instrument and method for accurate measurement of surface viscosity of viscous liquid

A method for determining a surface viscosity of a liquid, the method comprising:

• providing, with a drop ejection system, a drop of a liquid, the drop being provided by introducing the liquid between ends of two rods to form the drop at the ends of the two rods;
• forming, with the drop ejection system, a thread from the drop that increases in length from a start time until the thread pinches off at an end time;
• determining, at the start time, an initial radius h0 of the thread;
• at discrete time intervals between the start time and the end time, (i) determining a minimum radius hmin of the thread and (ii) storing, in a memory, the minimum radius hmin and the discrete time intervals;
• after the end time, determining a linear relationship between the minimum radius hmin and time, using the stored minimum radius and time values of the discrete time intervals;
• determining the surface viscosity μs for the liquid based on the linear relationship between the minimum radius hmin and time;
• and
• determining and setting an operational parameter for drop ejection in the drop ejection system based on the surface viscosity μs.

A method for operating a drop ejection system configured to expel a liquid therefrom, the method comprising:

• operating the drop ejection system to provide a drop of the liquid;
• operating the drop ejection system to form a thread from the drop that increases in length from a start time until the thread pinches off at an end time;
• determining, at the start time, an initial radius h0 of the thread;
• at discrete time intervals between the start time and the end time, (i) determining a minimum radius hmin of the thread and (ii) storing, in a memory, the minimum radius hmin and time values of the discrete time intervals;
• after the end time, determining a linear relationship between the minimum radius hmin and time, using the stored minimum radius and time values of the discrete time intervals;
• determining the surface viscosity μs for the liquid based on the linear relationship between the minimum radius hmin and time;
• and
• determining and setting an operational parameter for drop ejection in the drop ejection system based on the surface viscosity μs.