Thermo-gravimetric analysis of a single microcapsule by using a microcantilever

MasterMicrocapsules containing functionally active materials have been widely used in various fields such as drug release, smart material systems, preservation and protection of products. It is very important to understand their mechanical and physical properties to control release or sustentation of core materials. The measurement of the mechanical and physical properties of microcapsules is generally performed using well-established methods such as thermo gravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). However, these methods are not sensitive enough to measure properties of a single microcapsule. Recently, several studies have investigated the mechanical deformation and rupture of a single capsule using stain gauges and atomic force microscopy. However, to our best of knowledge, no study has shown the thermo-mechanical property of a single capsule, which is an important factor for successful release and sustentation of a single capsule. Here, we describe a novel method to measure thermo-mechanical properties of a single capsule using a microcantilever in TGA. A microcantilever is well known for its high sensitivity and can typically detect pico-gram mass changes while the commercial TGA has minimum detectable mass changes in microgram level. The microcapsules containing chlorobenzene solvents were synthesized using in situ interfacial polymerization. Each of the synthesized microcapsules was then mounted on the free end of the microcantilever by using glass tube. The microcantilever resonating at 8 kHz was placed on a heater and the resonant frequency was measured at varying temperature to analyze the thermal characteristics. Each capsule exhibits two kinds of weight lossa primary weight loss due to vaporization of core material and a secondary weight loss due to thermal degradation of polyurethane shell. The microcantilever-based TGA successfully demonstrated the ability of differentiating the microcapsules containing various solvents by measuring the mass change with temperature.Knowing that the masses of core and shell materials are approximately 80% and 20% of the total mass, we will further investigate the wall thickness and polymerized density of capsule shell. These properties may provide important information about releasing properties and stability of a single capsule