Research
Dr. Padmanabhan's research group works on a bottom-up approach to synthesizing materials with novel structure and novel properties using self-assembly
In other words, we design the molecular building blocks and their chemical interactions, which lead to the complex organization of thousands or millions of molecules into complex structures. Our approach leverages thermodynamics to predict the phase diagram of several workhorse model systems ranging from polymers to colloids to liquid crystals.
Block copolymers contain two distinct types of repeating units connected end-to-end. When one of the blocks has chiral building blocks, the entire conformation (shape of a single molecule) can become chiral. These molecules can in turn self-assemble into chiral or achiral mesoscopic structures with unique properties. Our group probes the conformational level and studies the thermodynamics of these materials. We employ a variety of tools and study several really interesting self-assembly phenomena including chirality transfer, the sergeant-soldier for chiral amplification, and sequence-dependent conformational structures. Top image below illustrates the phenomenon of chirality transfer. Lower image below shows simulation snapshots from sample conformations of different models used.
The gyroid morphology is characterized by a network, where each network comprises of three-fold junctions. Single and double (two interweaving networks) gyroids can be formed from block copolymers but are challenging to study due to (i) narrow thermodynamic stability, and (ii) complexity of structure. Our group utilizes particle-based simulations and characterizes the network topology in great detail. This provides insights into how the molecules are arranged, and enables us to quantify chain stretching.
Two-dimensional macromolecules or covalent organic frameworks have shown promise as candidates for next-generation extreme strength materials as they combine the advantages of traditional Kevlar, and more recent graphene-like materials. The in-plan pi-pi interactions and hydrogen bonding across planes are key to providing superior strength. Recent work by a team at DEVCOM Army Research Laboratory have demonstrated that the mechanical strength of a model COF is comparable, or even greater than Kevlar or graphene nanotubes. Solution processing also shows that these materials can have abnormal properties. Our simulations using ReaxFF force field shows binding mechanisms of bulk solvents. DFT calculations and the simulation below illustrates hydrogen-bonding of the nitrogen in the COF with the hydrogen in the water molecule as the energetically preferred binding mechanism.
Acknowledgements
We gratefully acknowledge the staff and high-performance computing resources provided by RIT Research Computing that enables to do our work.
The Kate Gleason College fund has provided funding from 2017 - 2024 for graduate and undergraduate student researchers.
We acknowledge National Science Foundation for awarding he PI with a CAREER award in 2022 (DMR 2144511) and continued support.
We received funding from the Army Research Labs (DOD Army Materiel Command) from 2020 - 2021 to investigate solvation of 2D polymers.