Temperature Dependence of the Rayleigh Ratio for Toluene: Thermoresponsive Polymers Characterization

摘要

Benzene and toluene are commonly used reference substances for static light scattering (SLS) measurements. However, due to the appearance and wide availability of solid-state lasers with various wavelengths, there is a need for data on the Rayleigh ratios for references at various wavelengths. Thermoresponsive polymers, which are widely researched now, can have lower critical solution temperature (LCST) values very close to the human body temperature (30-36 °C). Such polymers can be used to develop efficient means for targeted drug delivery. In this paper, we report how to accurately determine the absolute molecular weights of thermoresponsive polymers by the SLS method. This is especially important when the LCST value of a polymer is close to the room temperature (at which SLS measurements are usually taken), which can lead to over- estimated results due to the aggregation of macromolecules. So, it is necessary to carefully select the measurement temper- ature and, accordingly, data are needed on the temperature dependence of the Rayleigh ratios for a reference sample. The Rayleigh ratios and depolarization factors, 1u and 1v, were first determined for toluene within a wide temperature range (10- 50 °C). The temperature dependencies of these parameters were shown to be linear in the whole range investigated. Temperature coefficients for the calculation of the Rayleigh ratios at different scattering geometries were obtained. The particular importance of choosing the optimal measurement temperature when determining the molecular weights of thermoresponsive polymers with low values of LCST using the static light scattering method was demonstrated.