Thermomechanical analysis of picograms of polymers using a suspended microchannel cantilever

Abstract

Microchannel cantilevers are an emerging platform for physical characterization of materials at the picogram level. Here we report on detecting multiple thermal transitions in picogram amounts of two well-known polymers, semicrystalline poly(L-lactide) (PLA) and amorphous poly(methylmethacrylate) (PMMA), using this platform. The polymer samples, when loaded inside the cantilever, affect its resonance frequency due to changes in its total mass and stiffness. When taken through a thermal cycle, the resonance response of the cantilever further changes due to multiple thermal transitions of the samples. Continuous monitoring of the resonance frequency provides information about β-transition (T_β), glass transition (T_g), crystallization (T_c), and melting (T_m) of the confined polymer samples. The measured T_g, T_c, and T_m for PLA were ∼60, 78, and 154 °C, respectively, while the T_g and T_β for PMMA were 48 and 100 °C, respectively. These results are in an agreement with the data obtained from differential scanning calorimetry (DSC). Because of its high sensitivity, this technique is capable of detecting the weaker β-transitions that cannot be observed with conventional DSC.