High-sensitivity differential scanning calorimetry using a MEMS thermopile chip for analyzing polymer crystallization†

This paper introduces a high-sensitivity differential scanning calorimetry (DSC) technique based on a MEMS single-crystalline silicon thermopile chip and its application for analyzing the crystallization process of polyamide 6 (PA6) under various thermal processing conditions. The chip integrates 54 pairs of single-crystalline silicon thermocouples beneath a SiN_x-suspended film, achieving a temperature responsivity of 31.5 mV per °C and a power responsivity of 147 V W⁻¹. Additionally, the chip's cooling time constant is only 2.4 ms. The non-isothermal experimental results of PA6 suggest that melt-crystallization is suppressed at cooling rates exceeding the critical rate of 50 °C s⁻¹, and cold-crystallization is suppressed at heating rates above the critical rate of 300 °C s⁻¹. Thanks to its high sensitivity, this chip can detect subtle exothermic signals associated with the γ–α phase transition in PA6. The critical heating rate for this phase transition is determined to be 25 °C s⁻¹. Isothermal experimental results show that PA6 undergoes crystallization within 70 °C to 170 °C, with the shortest half-crystallization time of ∼1.1 s at 120 °C. The high-sensitivity DSC technique proposed in this work holds great promise for studying the thermal behaviour of various materials at high heating and cooling rates.