Photopyroelectric Techniques for Thermal Diffusivity and Optical Absorption Coefficient Measurements of SiO2 Colloids

In this work Photopyroelectric Techniques for thermal and optical characterization are introduced for measuring thermal diffusivity and optical absorption coefficient of colloidal suspensions of SiO₂. Thermal diffusivity and Optical absorption coefficients at 904 nm, 940 nm, 980 nm and 1550 nm were measured for spherical SiO₂ colloidal suspensions of 61 and 673 nm average size, in a range of 1 mg/mL to 26 mg/mL. It was found a linear increment of this optical property with SiO₂ nano-spheres concentration, which was not possible to obtain by means of absorbance measurements with conventional UV-Vis spectroscopy; in relation with thermal diffusivity it was found a slightly increment of this thermal property with increasing concentration, however this increment was not as large as the one reported for similar samples but using experimental techniques involving the optical properties of the samples. The direct measurement of optical absorption coefficients of colloidal suspensions allowed the knowledge of their absorptivity at the selected wavelengths. The presented methodology could be useful for measuring this optical property for colloidal suspensions in general at other wavelengths and as a function of other variables of interest, such as size particle.