Optical Microscopy inside a Heating Capillary

This paper presents a heating-capillary video-microscopy system that allows visual observation and quantification of phenomena involving biphasic dispersions with interfaces at high temperatures. The cylindrical capillaries were made to have inside diameters of ~200 (mu)m, while their exterior was coated with a transparent tin-doped indium oxide film that acted as an electrically heating jacket. The produced capillaries achieved temperatures ranging from ambient to at least 287 (degree)C, the boiling temperature of n-hexadecane, a high boiling point hydrocarbon used in the temperature-calibration experiments. The generated temperatures may oscillate, with maximum deviations of about 3 (degree)C from ambient to 80 (degree)C, 9 (degree)C from 80 to 170 (degree)C, and 45 (degree)C from 170 to 265 (degree)C. In the range of 100-265 (degree)C, the desired temperatures were attained at a rate from 75 to 198 (degree)C/s and could be easily adjusted by changing the applied ac voltage with a variable transformer. Two examples of using the heating-capillary technique for interfacial studies at high temperatures are illustrated.