How many times have you wondered if the tap water in the hotel you just checked into is safe to drink? Have you ever wanted to check the amount of alcohol concentration in a drink served by a kind bartender? If you have, you might be able to find the answers right from your mobile phone using the new technique recently introduced by a group of MIT computer scientists to measure surface tension of a liquid. This technology can potentially not only confirm any water contamination and measure alcohol concentration, but also identify the presence of substances in liquid for diagnosis in healthcare or detect counterfeit luxury goods such as brandy or perfume.
Existing liquid testing methods are often based on a liquid's measurable properties such as electric permittivity, optical absorption, and so on. Surface tension is another property of liquids, representing the tendency of liquid surfaces to shrink into the minimum surface area possible, resulting from the greater attraction of liquid molecules to each other. However, it is one of the most difficult properties to measure and requires high-cost and sophisticated instruments, called tensiometers. Examples of these tensiometers include Du Noüy ring, Wilhelmy plate, spinning drop, pendant drop, bubble pressure, and acoustic levitation. Although such tensiometers can achieve high accuracy, their measurements are often performed in-lab due to the complexity of hardware, preparation, and manual procedures. To address these drawbacks, recent efforts on measuring surface tension using mobile devices have shown some promising results. However, its current poor performance and complexity are the two main reasons for its low adoption.