Abstract
It is generally accepted that inducing molecular alignment in a polymer precursor via mechanical stresses influences its graphitization during pyrolysis. However, our understanding of how variations of the imposed mechanics can influence pyrolytic carbon microstructure and functionality is inadequate. Developing such insight is consequential for different aspects of carbon MEMS manufacturing and applicability, as pyrolytic carbons are the main building blocks of MEMS devices. Herein, we study the outcomes of contrasting routes of stress-induced graphitization by providing a comparative analysis of the effects of compressive stress versus standard tensile treatment of PAN-based carbon precursors. The results of different materials characterizations (including scanning electron microscopy, Raman and X-ray photoelectron spectroscopies, as well as high-resolution transmission electron microscopy) reveal that while subjecting precursor molecules to both types of mechanical stresses will induce graphitization in the resulting pyrolytic carbon, this effect is more pronounced in the case of compressive stress. We also evaluated the mechanical behavior of three carbon types, namely compression-induced (CIPC), tension-induced (TIPC), and untreated pyrolytic carbon (PC) by Dynamic Mechanical Analysis (DMA) of carbon samples in their as-synthesized mat format. Using DMA, the elastic modulus, ultimate tensile strength, and ductility of CIPC and TIPC films are determined and compared with untreated pyrolytic carbon. Both stress-induced carbons exhibit enhanced stiffness and strength properties over untreated carbons. The compression-induced films reveal remarkably larger mechanical enhancement with the elastic modulus 26 times higher and tensile strength 2.85 times higher for CIPC compared to untreated pyrolytic carbon. However, these improvements come at the expense of lowered ductility for compression-treated carbon, while tension-treated carbon does not show any loss of ductility. The results provided by this report point to the ways that the carbon MEMS industry can improve and revise the current standard strategies for manufacturing and implementing carbon-based micro-devices.
Highlights
The carbon precursors solution is electrospun into polymer nanofibers mats in a process that is described in detail in our previous reports [4,10,11,12,13]
Some of the polymer nanofiber mats are mechanically rolled and treated under approximately 5.88 MPa compressive stress, while another portion of polymer fibers are treated with a tensile load of 52 kPa
In a previous of tension-induced pyrolytic carbon nanofibers (TIPC) fibers could be caused by the lower tension threshold of the carbon fibers, which study, we reported that a sizable amount of graphitic and pyridinic nitrogen atoms is leads to microtears and the disruption of PAN fibers prior to pyrolysis
Summary
The effects of molecular alignment of carbon precursors on the microstructural, mechanical, and electrical properties of carbon nanofibers have been studied previously in a number of reports [1,2,3,4,5,6,7,8]. The majority of the reported studies are focused on the more recognized method of air stabilization and carbonization under tensile stress. A standard example of the current trend is the hot-drawing method, where the manufacturing process includes mild heat treatment of stretched polymer fibers prior to or during stabilization.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
