"The roles of entropy and chirality during self-assembly of block copolymers" by Poornima Padmanabhan

Poornima Padmanabhan

Linear block copolymers are amphiphilic molecules comprised of two dissimilar and repelling polymers joined end-to-end. They are capable of assembling hierarchically at multiple length scales. In typical block copolymers, self-assembly is governed by the enthalpic repulsion between the blocks and entropic considerations related to translation, mixing, and polymer conformations. A variety of microstructures can be obtained by self-assembly, each useful in disparate applications ranging from lithography to catalysis to solar cells to photonic devices.

Recently, novel block copolymers can be synthesized where the chirality of one of the blocks can be precisely controlled. This results in the manifestation of chirality at several length scales (monomer to conformation to microstructure), referred to as chirality transfer. Using particle-based simulations and free energy calculations, we can decouple the underlying thermodynamic contributions of this phenomenon.

In one half of the talk, I will discuss thermodynamic strategies to stabilize the three-dimensional single gyroid, which exhibits chirality at the longest length scale but does not require chiral building blocks. In the other half of the talk, chirality is introduced at the conformational length scale, and its impact on self-assembly is assessed. Conformational measurements combined with microstructural metrics provide evidence of the frustration of chirality transfer in the lamellar structure suggest a novel type of thermodynamic frustration.


Poornima Padmanabhan is an Assistant Professor at Rochester Institute of Technology in the Department of Chemical Engineering, with an affiliation in the Department of Chemistry and Materials Science.

She received her B. Tech in Chemical Engineering from the Indian Institute of Technology Madras and Ph.D. from Cornell University. Her research interests are in the areas of the thermodynamics and rheology of soft materials comprised of polymers and colloids. Her group develops rational design approaches using computational methods to understand the interplay between competing thermodynamic driving forces to design materials of desired composition and length scales.

She recently received an NSF CAREER award to study the interplay between chirality and thermodynamics, and to improve engineering pedagogy by designing activities targeted at improving spatial thinking skills in first year engineering students. In addition to research, she is actively involved in increasing the presence of women in STEM through outreach and engagement.

Seminar sponsored by the Department of Chemical and Biomolecular Engineering.