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_<i>x</i>-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.