Ajay Vallabh
PhD Thesis title:
"DEFORMATION-INDUCED BONDING OF GLASSY POLYMERIC FILMS & THE IMPACT OF BIDISPERSE BLENDS"
Bio
Ajay grew up in Agra, India (the same city where the Taj Mahal resides), where he enjoyed playing cricket and basketball.
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His Bachelor of Technology degree was from Gla University in Mathura, India in 2015, after which he pursued his MS in Mechanical Engineering in 2019 from the Indian Institute of Technology Kanpur (India). Ajay joined UNH straight afterwards to pursue his PhD in Mechanical Engineering. Ajay started his journey under the supervision of Dr. Nikhil Padye, yet transitioned to the supervision of Prof. John Tsavalas in 2022. Ajay's area of expertise was at first only tangentially related to the focus of the Tsavalas group, yet it quickly became apparent that there were many areas of overlapping expertise, phenomena, and areas for mutual developmental benefit. In particular, Ajay's focus has been on the interdiffusion of polymer films under compression for short time scales and while fully in the glassy state. Plastic deformation, relevant in Ajay's work, afford an alternate pathway to polymer rearrangement and interdiffusion across interfaces, yet not by the classic reptation model which accounts for diffusion in rubbery polymer systems. Here, dilatation (or densification) allows for slippage of chains under force and rearrangement and importantly also the ability for new entanglements to be produced across the newly bonded interface. This in fact has direct relationship to the fundamental principles at hand in the Tsavalas group Spherocylinder project and also has elements important to polymer particle morphology development with regard to the impact of molecular weight distributions.
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Ajay's work is predominantly on the theoretical side, yet he also has experience with hands on experimentation and mechanical testing.
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Ajay is imminent to defend his PhD thesis and is in search of either a postdoctoral appointment or an industrial role focused on in-silico research.
Project 1: The Role of a Diluent in Deformation-Induced Bonding of Glassy Polymer Bidisperse Blends
Bonding between polymers below the glass transition temperature through molecular-scale dilatation (or densification)-based interdiffusion of macromolecules has recently been introduced. In this mechanism, short timeframe plastic deformation enables polymer chains to interdiffuse and form entanglements at the interface, facilitating rapid bonding below the glass transition temperature (Tg ). Here, we are addressing the role of a lower molecular weight diluent in bonding polymer interfaces of bidisperse blends through deformation-induced bonding (DIB) at temperatures well below both the surface and bulk glass transition temperatures, Tg,surface and Tg,bulk, respectively, by using molecular simulations. These simulations reveal that addition of the diluent (φ < 20%) drastically enhances the number of chain-ends at the interfacial region compared to a pure glass sample (φ = 0%) during deformation below Tg,surface , which improves the possibility of opposite side entanglement formation. The changes in stress-strain response of debonded samples correlate with the normalized entanglement density. Likewise, the maximum interfacial fracture energy G_I,max of debonded samples is correlated with the diluent concentration (φ), below Tg,surface. Furthermore, the optimization of material and process conditions for DIB has yielded a notable advancement for the conditions tested here: achieving a higher bonding strength, approximately one-third of the bulk, all while remaining below Tg .
REVISIONS SUBMITTED (Macromolecules, ma-2024-011856)
Vallabh, A., Padhye, N. Dilatational-plasticity opens a new mechanistic pathway for macromolecular transport across glassy interfaces. Sci Rep 14, 18552 (2024).
Project 2: blah blah blah - Coming Soon
This space will be used to describe Ajay's second project.
Contact
I'm always looking for new and exciting opportunities. Let's connect.