Salzberg Chemistry Seminar Series

Subramanian Ramakrishnan Department of Chemical and Biomedical Engineering FAMU-FSU College of Engineering presents "Insights into Preceramic Polymer-Based Additive Manufacturing Inks via Rheological and Scattering Studies of Preceramic Polymer-Grafted Nanoparticles Suspended in Polycarbosilane"

Abstract:Preceramic polymers (PCPs) offer advantages in producing ceramics due to their processability and ability to tailor the final chemistry of the produced material. However, challenges such as volumetric shrinkage and mass loss during pyrolysis often result in polymer-derived ceramics containing pores and cracks. PCP-grafted ceramic nanoparticles (PCPGNPs) have been proposed and studied as a route to mitigate the shrinkage issues associated with neat PCPs. Prior studies on PCPGNPs have principally focused on the synthesis and characterization of neat materials. Dispersing PCPGNPs in commercial preceramic polymer is another attractive, but underexplored, route to control the rheological and char yield properties of PCP systems. In this work, a systematic rheological study of commercial PCP (SMP-877) and PCPGNP (silica with poly(1,1-dimethylpropylsilane corona) mixtures was executed to develop design rules for the processing of such systems. A rheological study demonstrated the effect of increasing particle concentration on network formation with percolation occurring between 50 and 60 wt%. Samples above the percolation threshold exhibited higher viscosities and rapid shear thinning thus demonstrating their direct-write printability. X-ray photon correlation spectroscopy (XPCS) corroborated the rheology and showed two diffusive modes when the material was above percolation. Mixtures of PCPGNPs and SMP-877 had synergistically higher char yields upon thermal treatment and pyrolysis. XPCS and rheological measurements during thermal treatment identified thermal jamming of the polymer grafts as a key factor in improving the char yield. With the insights gained here, we expect these mixed systems to provide attractive feedstocks for polymer-derived ceramics, with proof-of-principal application as feedstocks for direct ink write (DIW) additive manufacturing. Extension of this technology to 2D materials (MXenes) will also be discussed for high temperature applications. A brief overview of the recently funded NSF Center on Additive Manufacturing at Florida A&M University will also be given.

Biography: S. Ramakrishnan is a Professor of Chemical and Biomedical Engineering at Florida A&M – Florida State University College of Engineering in Tallahassee, Florida. After earning a B. Tech degree in Chemical Engineering from the Indian Institute of Technology he proceeded to earn MS and PhD in Chemical Engineering from the University of Illinois at Urbana-Champaign. He conducted post-doctoral work at Princeton University from 2001-2002 and at the Nanoscience Center at University of Illinois from 2002-2005. In August 2005 he joined the Chemical Engineering department in Tallahassee and was promoted to full professor in August 2018. During 2016-2017 he was a visiting
Associate Professor at Harvard University on an NSF funded sabbatical. Research in his group focuses on understanding the physics, chemistry and processing of complex fluids (colloids, proteins, polymers and other “soft materials”) with an aim of producing useful materials for engineering applications. In the process, fundamental questions that arise in assembling them into useful structures will also be answered. He is currently the director of two centers – NASA InSpace Manufacturing Center and the interdisciplinary NSF funded Center on Additive Manufacturing with three thrust areas 1) High throughput discovery and integration of programmable functional polymer nanocomposite devices, 2) Bioderived, recyclable, printable polymer matrices for advanced composites and 3) Stimuli responsive biohybrid soft material
processing for 4D fabrication a micro actuation. He is also working with the Army and the Air Force in developing ceramic materials for defense applications.