The capacitive drop tensiometer - a novel multianalysing technique for measuring the properties of liquids

A new instrumental method for measuring the physical properties of a liquid has been developed. The instrument, called a capacitive drop tensiometer ( CDT), is based on the drop volume principle in combination with a capacitiv e transducer. A delivery head with a specialized wetting design was constru cted for forming drops. The capacitive transducer uses the delivery head as one of its plates and a cylindrical ring plate, which surrounds the delive ry head and the space occupied by the drop that is formed, as another. Exce llent linearity is achieved by optimizing the design, with an accuracy of d rop volume measurement of approximately 2 mu l. The system is suitable for measuring both drops in equilibrium and those in the process of growing. It s capability of real-time measurement makes it particularly useful for vola tile liquids, in which instance the measurement of drop volume using a flow meter or a pump is no longer reliable. The CDT can also be used to determin e concentration. It was found that the concentration curve is linear for aq ueous glycerol solutions although not so for aqueous ethanol solutions. The CDT's ability to measure surface tension was also explored and experimenta l results are presented here.