Volatile Organic Compound Sensing Properties of Parylene E: Thermal Transition and Sorption Kinetics

The material properties of parylene E from chemical vapor deposition (CVD) have been characterized in the pursuit of gas sensing applications. First, the glass transition behavior and viscoelastic nature of amorphous parylene E have been detailed based on temperature-modulated differential scanning calorimetry (TMDSC) and a quartz crystal microbalance with dissipation (QCM-D). It is found that as-deposited parylene E experiences glass transition with an endothermic step below 40 degrees C and that Young's modulus of parylene E is 2 orders of magnitude smaller than that of semicrystalline parylene C and 40 times larger than that of poly(dimethylsiloxane) (PDMS). Then, the gas sensing performance of parylene E has been benchmarked using capacitive detectors with interdigitated electrodes. In the toluene-parylene E system, the equilibrium and dynamic responses have been quantified in the form of the partition coefficient and diffusivity, respectively. Temperature-dependent diffusivity follows the Arrhenius-type relation, and the partition coefficient of the toluene-parylene E system becomes as large as 2500 at room temperature. It is supported by diffusion modeling in swollen parylene E that heat-treated parylene E has PDMS-like nature of sorption affinity to nonpolar volatile organic compound (VOC) vapor. The excellent sensitivity of parylene E would provide leverage in future VOC gas sensors.