Development of microfluidic device for on-chip measurement of surface tension

• Main Author: Nang, Thazin Phway
• Other Authors: Nguyen Nam-Trung
• Format: Final Year Project
• Language: English
• Published: 2010
• Subjects: DRNTU::Engineering::Aeronautical engineering
• Online Access: http://hdl.handle.net/10356/20713
• Institution: Nanyang Technological University

This report relates the experiments conducted using a microfluidic surface tension sensor made from Polydimethylsiloxane (PDMS). The sensor is able to measure both surface tension (liquid/air interface) and interfacial tension (liquid/liquid interface). The sensor prototype contains a microchannel network for droplet formation and an optical system for bubble detection. The optical system consists of an optical fibre from a laser source which is inserted into a channel normal to the outlet channel. Another optical fibre inserted into a channel on the other side of the outlet channel receives the light signal. For the surface tension measurement, the liquid sample is introduced into a main channel, while air is introduced into a T-junction. For the interfacial tension measurement, the immiscible liquid such as oil is introduced into a main channel, while the sample liquid is introduced into a T-junction. The formation frequency of the micro bubbles is a function of the surface tension between the two phases. The frequency can be measured by optical detection. Bubble formation experiments were carried out using Distilled water with various TWEEN20 surfactant concentrations as the continuous phase and Nitrogen gas as the dispersed phase. Droplet experiments were carried out using pure Mineral Oil and Mineral Oil with various Span 80 surfactant concentrations as the continuous phase and Distilled water as the dispersed phase.The effect of varying the pressure, flow rate, type of fluid and the surfactant concentration on the bubble size, shape and formation frequency were collected.