Measurement of the Sol–Gel Transition Temperature in Agar

Abstract

Aqueous solutions of agar show a sol–gel transition temperature in the range from 32°C to 47°C depending on colloid concentration; however, the width of the transition and the subsequent process occurring after it, are not well understood. In this work the sol–gel transition of agar is studied by a simple optical method. It consists of the illumination of the sample using a non-coherent light source and the monitoring of transmitted light using a photodiode. It is shown that during the sol–gel transition, the transmitted light decays over a broad range of temperature. Simultaneously, it is possible to observe that fluctuations in the transmitted light decrease along the sol–gel transition, and at a specific temperature, they become very small. Based on these observations, the sol–gel transition temperature for three different concentrations of agar (0.5, 1.5, and 2.5% w/v) is determined. These results are compared with the sol–gel transition temperature values provided by the conventional rheological method.