Development of a low-cost automated micro dispense digital goniometric device with drop shape analysis

Abstract

Accurate measurement of contact angles can define fluid dynamics, surface material properties and contribute to the development of micro/nanofluidic devices. The drop shape analysis technique was developed to accurately determine the contact angle and surface tension of a liquid drop on a solid surface. The technique involves capturing a reflected image of the drop profile, acquiring coordinate points along the contour and finding the mathematical best-fit accordingly. Many conventional equipment utilizes this method through manual acquisition and analysis of data. This is an arduous, time consuming task which can introduce inaccuracies. Nevertheless, partially automated equipment can be prohibitively expensive. Here its shown that by utilizing embedded system development techniques, both the imaging and profile analyzing tasks as well as the liquid dispenser can be automated and precisely controlled by a computer application at a fraction of the cost of a commercial unit. The developed system also facilitates sample stage tilting which can provide information on dynamic liquid profiles to determine advancing and receding contact angles. Importantly the device is capable of dispensing and analyzing less than 5 nl volumes of liquid. Such measurements are becoming increasingly important in the understanding of areas such as superhydrophobicity and microfluidic devices.