Thermal properties of nanocapsules measured by scanning force microscopy methods

Heated micromechanical cantilevers were used to probe the thermal properties of nanogram samples in two ways: (i) as a micromechanical thermogravimetric balance and (ii) as a local nano-heater for heating individual objects. For micromechanical thermogravimetry, 6 ng of polyurethane nanocapsules containing silverazide were freeze dried and attached to the micromechanical cantilever apex. The resonant frequency of the micromechanical cantilever upon heating was recorded. After heating to 250 °C, 25% mass was found remaining on the micromechanical cantilever. In order to image structural changes, the tip of the heatable micromechanical cantilever was positioned on individual nanocapsules weighing less than 6 fg, and the capsule was imaged using a scanning force microscope. Then the cantilever was heated and temperature–deflection curves were recorded. Both methods revealed a decomposition temperature of 180 °C for silverazide encapsulated in a polyurethane nanocapsule. Topographic images of individual capsules after decomposition showed a rupture of the shell at one position.

Figure optionsDownload as PowerPoint slideHighlights
► Analysis of thermal properties of polymeric nanocapsules containing gas generators.
► Comparison of two different SPM based techniques using heatable cantilevers.
► Cantilevers as ultrasensitive balance for nano-thermal gravimetric analysis.
► Analysis and imaging of single capsules.
► Analysis of decomposition temperature and shell rupture.