Subhadeep Pal

Subhadeep Pal

PhD Candidate, Northwestern University

Research Projects

Micro-Ballistic Performance of PGN Thin-Film Monolayers

Advisor: Dr. Sinan Keten
2022 – 2024

  • Performed micro-ballistic LIPIT simulations on coarse-grained SiO₂–PMMA polymer-grafted nanoparticle (PGN) films to study how graft chain length and NP core density affect ballistic performance, leveraging PGNs’ remarkable mechanical properties.
  • Identified a positive relation between cohesive energy density and specific penetration energy (E_p^*), and a failure-mode shift from segment pull-out to fragmentation for shorter grafts due to lower cohesion.
  • Proposed a new ballistic metric, average deceleration rate of the bullet (A_b). Found intermediate graft lengths ((N \approx 40–100)) optimize both (E_p^*) and (A_b), suggesting designs for impact-resistant coatings where backface deformation must stay low.

Characterizing the Shear Response of PGNs

Advisors/Collaborators: Dr. Sinan Keten; Arman Moussavi; Dr. Zhenghao Wu (Xi’an Jiaotong University)
2022 – 2023

  • Built PGN models with Kremer–Grest beads and FENE bonds to probe shear response across NP core radius, grafting density, and chain length; observed a linear relation between NP volume fraction and modulus.
  • Showed PGNs with short grafts have higher stiffness than linear polymer melts due to NP reinforcement, indicating routes to stronger polymer composites (helpful for reducing reliance on single-use plastics).

Predicting Mechanical and Fracture Properties of Mixed-Hardener Epoxies

Advisors/Collaborators: Dr. Sinan Keten; Dr. Timothy Sirk (ARL); Dr. Kerim Dansuk (Boğaziçi University); Dr. Andrea Giuntoli (University of Groningen)
2022 – 2023

  • Used a chemistry-specific coarse-grained model to study how mixed hardeners tune epoxy failure mechanisms and the strength–toughness trade-off.
  • Estimated fracture toughness via a continuum fracture model informed by simulations that captured experimental trends.
  • Found intermediate-length Jeffamine chains enhance toughness while maintaining modulus, yielding a predictive framework for less-brittle epoxy design.

A Catch-Bond Mechanism with Looped Adhesive Tethers

Advisors/Collaborators: Dr. Sinan Keten; Dr. Kerim Dansuk (Boğaziçi University)
2021 – 2023

  • Designed a molecular NP system that mimics catch-bond behavior using looped and straight tethers for load sharing under force; simulations showed a force-enhanced lifetime curve.
  • Derived an analytical relation (validated by molecular and Monte-Carlo simulations) to tune loop/adhesion interactions, enabling customizable catch-bond lifetimes for self-strengthening materials.

Development of a Many-Body Potential for a Particle-Based PGN Model

Advisors/Collaborators: Dr. Sinan Keten; Dr. Wei Chen; Dr. Sanat K. Kumar (Columbia); Dr. Zhenghao Wu (Xi’an Jiaotong University)
2024 – Present

  • Advanced the Implicit Chain Particle Model (ICPM) representing each PGN as a single bead, achieving ~10⁷× speed-up over all-atom models while accurately predicting bulk modulus and toughness.
  • Built two- and three-body interaction forms from strain-energy functions, complemented by an ML model trained on simulation data, enabling micron-scale simulations beyond traditional MD length-scale limits.

Understanding Cement Paste Rheology for 3D-Printing Applications

Advisors/Collaborators: Dr. Sinan Keten; Dr. Faramarz Joodaki; Dr. Gianluca Cusatis
2023 – Present

  • Created a nanoscale C3S–water model and computed potential of mean force (PMF) between cement surfaces across water contents to inform a micron-scale rheology model.
  • Simulated nozzle flow in 3D printing and found viscosity decreases with increasing shear rate and water-to-cement ratio, matching rheological expectations.

Real-Time Super-Resolution Imaging of Polymer-Chain Conformational Changes

Advisors/Collaborators: Dr. Sinan Keten; Ruiqi Xiao; Dr. Muzhou Wang
2023 – 2024

  • Built finite-element models of bottlebrush-polymer thin films with rigid indentation and frictional contact to mirror experiments (scaling to ~10⁷ DOF in ABAQUS).
  • Quantified single-chain orientation changes by mapping vector fields through the simulated strain field; simulations validated experimental observations, giving molecular-level insight into chain motion.

Engineering the Mechanics of Nanocomposites via Polymer-Conformation Programming

Advisors/Collaborators: Dr. Sinan Keten; Tiffany Chen; Dr. Ting Xu (UC Berkeley)
2023 – 2024

  • Devised a particle-based, micron-scale simulation using Lennard-Jones interactions to replicate nano-indentation and compare moduli across systems.
  • Matched the experimental modulus trend vs NP volume fraction and traced the higher stiffness in a specific system to increased cohesion from optimal grafting density and greater activated polymer volume—a mechanism not directly visible in experiments alone.

Network Topology and Percolation in Model Covalent Adaptable Networks

Advisors/Collaborators: Dr. Sinan Keten; Benjamin Hafner; Dr. Kenneth Shull
2023 – 2024

  • Developed coarse-grained models of recyclable, disulfide-based epoxies (LAMMPS + in-house MATLAB) to complement experimental network-analysis.
  • Explored a large design space to locate the percolation threshold, finding strong agreement with Flory’s mean-field theory.