October 2010

Few sophisticated high-tech products today can trace their lineage back to the 1960's. The ramé-hart Model 500 is one that can. As we prepare to celebrate our 50th anniversary next year (1961-2011), the original NRL goniometer invented by Dr. William Zisman¹ at the Naval Research Lab and manufactured by ramé-hart has undergone an amazing metamorphosis.² The original optical Model A100 contact angle goniometer required a steady hand and a keen eye. In the time it would take to capture a single contact angle measurement back then, we can today with our Model 500 capture and measure several thousand frames. We can even replay and recalculate using different parameters (more on that in the section below). While contact angle is still our tagline, we can now measure surface tension, interfacial tension, surface dilatational elasticity and viscosity, as well as contact angle on pendant drops, captive bubbles, and sessile drops.

ramé-hart Model 500 with Optional Environmental Chamber 100-07

The Model 500 ships with our DROPimage Advanced software, a powerful software tool which includes a methods-based experiment design tool making complex experiments easy to setup and easy to run. The 500 is a complete turn-key tool including PC and LCD, backlighting illuminator with a fiber optic bundle to an adjustable halogen light source, manual drop dispensing with an easy-to-use microsyringe fixture, a flexible 3-axis stage with tilt on two axes, and our high-speed F1 Series digital camera.

What puts Model 500 at the front of the pack is the widest array of optional accessories available. The most popular option with Model 500 is our Automated Dispensing System (100-22) for increasing drop volume precision and making dynamic studies easy to run and highly repeatable. The Automated Dispensing System is followed in popularity by the Automated Tilting Base (100-25-A) for measuring advancing and receding contact angles using the tilt method. (Model 590 includes both the Automated Dispensing System and the Automated Tilting Base.) We also offer for Model 500 the Environmental Chamber (100-07, shown above), Environmental Fixture (100-14), Oscillator (100-28), Advanced Chamber (100-26), Lead Frame Support (100-23), Vacuum Chucks (100-21-VC), Rotating Wafer Supports in (6) standard sizes (100-21), an Immersible Film Stage (100-16), Film Clamps (100-15), an Elevated Temperature Syringe (100-11), and more. In short, Model 500 supports every modular accessory we offer.³

¹ For more on Dr. Zisman, see http://www.ramehart.com/newsletters/2009-09_news.htm.
² For more on the original ramé-hart Model A100 and the history of ramé-hart, see: http://www.ramehart.com/newsletters/2007-12_news.htm. 
³ For more detail on the accessories available for the Model 500, see: http://www.ramehart.com/accessories.htm.
 

DROPimage Advanced is a powerful tool for measuring, among other things, surface tension over time. If you already own a ramé-hart instrument with DROPimage Advanced, you may find this article interesting as we will show how to use one of the most powerful but underutilized commands. If you are not yet a DROPimage Advanced user, the video below illustrates an important competitive advantage: the ability replay and recalculate based on a series of saved frames from an earlier experiment.

In the video below, we walk through the steps of creating a new experiment using the Experiment Wizard. In this example, we are measuring the surface tension of a pendant drop over time while volume is added. To keep things simple, we are taking a series of 10 pictures over a 10 second period. Note that with our F1 or F2 Series camera, it's possible to capture frames at a rate of up to 60 per second. The length of your experiment is only limited by memory - which means you could have thousands of frames depending on the length of the experiment and the capture rate.

Next, before running the experiment, we edit the Method file and change the Data storage setting from None to BMP. This causes each frame to be saved to an individual BMP file. We then run the experiment the first time on a live image. The drop phase is water. The solid phase (needle) is stainless steel, and the external phase is air. As the experiment runs, ten BMP image files are generated.

We now use the Recalculate... command (on the Measure pull-down menu or use the Ctrl-R keyboard shortcut). The current dataset, ST10, shows up in the Bitmap data list since there are a series of files saved from the prior step. We click on ST10 and then Load File. We click the green play button to watch the video. And then click on the "Calculate" button to recalculate the surface tension values. We could also step through the series of frames one at time and calculate them individually or we could identify a series of frames by number.

In this example, we are using the same method file for the live and replayed experiments, but it's possible to use a different method by clicking Get new under the Calculation Method in the Recalculating Control Windows.

In short, the Recalculate... command provides a powerful tool for studying high-speed dynamic experiments and allows the user to look at individual frames or series of frames from different vantage points in order to better understand the change in surface tension (or contact angle) over time or in dynamic conditions.