March 2008

Automated Tilting Base 100-25-A

The Automated Tilting Base option is fully software-driven. We've made significant changes to our DROPimage Advanced software (v2.3) to accommodate this new option. 

The device is easy to setup. Plug in the power and serial cable, turn it on, and it's ready to go. To control the tilt, we've added a new Tilting Base Control dialog box in DROPimage Advanced as shown below. The high-ratio precision gearhead (in the black box) and flexible stepper motor allow for very slow and precise movement with zero backlash. The user can specify an angle between 0° and 90° or 0° and -90°, select the speed (e.g., 1° per second), then click go to proceed to that tilt angle. Additionally, the user can also specify an angle step, e.g., 1°, and then click on step+ or step- to move one degree at a time. Home will bring the tilt back to 0°. There is a "Set as Home" button which will allow the user to reset the resting position and thus synchronize the hardware with the software. Angles can be specified in resolutions of 0.1°.

Automated Tilting Base Control Dialog in DROPimage Advanced v2.3

Additionally we've added tilt angle to the method and experiment wizard allowing the user to design an experiment and include tilt control as one of the variables. You could, for example, setup an experiment that would take 60 measurements starting with a tilt of 0° and then tilting 1° every second while also taking a measurement every second. If the drop rolls off, the experiment would stop and you could capture the roll-off angle. 

A small knob on the rear of the control box is used to calibrate and setup the home position; but the unit can be turned of and fully controlled manually via the knob and in this mode will operate like our new Manual Tilting Base option 100-25-M.

We also have an upgrade kit for the Manual Tilting Base 100-25-M which will upgrade it to an Automated Tilting Base 100-25-A. In essence, a stepper motor and the electrical and communications interfaces are added. The p/n for the upgrade it is 100-25-U.

This past week we shipped our first Automated Tilting Base unit and have another one in the works which will be ready in a few weeks.

The primary purpose of the tilting base option is to measure advancing, receding, and roll-off angles. When a sessile drop is formed on a sample and the instrument is then tilted, gravity will increase the contact angle on the downside (the advancing angle) and the upside contact angle (receding angle) will decrease. The point at which the drop detaches is referred to as the roll-off (or tilt) angle. The difference between the advancing and the receding angle is called the contact angle hysteresis. Superhydrophobic surfaces, for instance, tend to have small hystereses and low roll-off angles. Surface roughness and heterogeneity can be quantified by evaluating the contact angle hysteresis and roll-off angle.

Surface scientists can also measure advancing and receding angles by increasing and decreasing the volume in a level sessile drop - for example with our Automated Dispensing System. But researchers who do a lot of measurements prefer the tilting base method for ease of use and also, since the needle is not required to stay in the drop as it is with the add and remove volume method, the data collected is more accurate.