(3ew) Biomimetic Crystal Growth for Programmable Separations and Chiroptical Properties

Non-classical growth mechanisms are a hallmark of biomimetic crystal growth and colloidal self-assembly. However, these growth mechanisms are often investigated as an after-thought, rather than a set of rules which can be broken at will to create the desired structures/properties. This lack of understanding translates into our inability to synthetically recreate the complexity of nature and, understand seemingly simple observations such as the origin of homochirality on Earth.

Here, I will describe two studies where informed intervention at the early stages of crystal growth lead to (i) record-breaking membrane performance and, (ii) hierarchically complex chiral micro-particles. Firstly, I will describe the engineering of one-dimensional defects in two-dimensional zeolite nanosheets as an extendable model system [1]. This study demonstrates the impact of atomic scale defects on enhanced macro-scale separation performance for xylene mixtures [2,3]. Secondly, I will demonstrate the art of navigating the free-energy landscape during the self-assembly of gold-cysteine colloids with programmable chiroptical properties [4]. Both these studies leverage the synergistic application of state-of-the-art characterization, computational and mathematical tools across multiple length scales towards a unified understanding of non-classical growth.

Moving forward, I want to pose the following challenges – Can we push the limits of characterization techniques (such as TEM) to study active nucleation events? Can we discern and control the driving forces that guide the disorder to order transitions? Can we create systems that combine optical, mechanical and separation properties within a single package? I will further describe the strategies to tackle these challenges and resolve nanometer to micron scale events in a hierarchical order towards programmable platforms with far reaching advances in climate science, pharmaceutical industry, and data transmission technologies.

Selected Publications (* equal contribution, ± corresponding author)

[1] Prashant Kumar, Kumar Varoon Agrawal, Michael Tsapatsis, K Andre Mkhoyan. Quantification of thickness and wrinkling of exfoliated two-dimensional zeolite nanosheets. Nature Communications, 6, 7128 (2015).

[2] Prashant Kumar ^±, Dae Woo Kim, Neel Rangnekar, Hao Xu, Evgenii Fetisov et. al. One-dimensional intergrowths in two-dimensional zeolite nanosheets and their effect on ultra-selective transport. Nature Materials, 19, 443–449 (2020).

[3] Mi Young Jeon*, Donghun Kim*, Prashant Kumar*, Pyung Soo Lee*, Neel Rangnekar, Peng Bai et. al. Ultra-selective high-flux membranes from directly synthesized high aspect ratio zeolite nanosheets. Nature, 543, 690-694 (2017).

[4] Wenfeng Jiang, Zhibei Zhu, Prashant Kumar et.al. Emergence of complexity in Hierarchically Organized Chiral Particles. Science, 368, 6491, 642-648 (2020).

[5] Xiaoli Ma*, Prashant Kumar*, Nitish Mittal*, P. Douditis, K. Andre Mkhoyan, Michael Tsapatsis. Zeolitic imidazolate framework membranes made by ligand-induced permselectivation. Science, 361, 6406, 1008-1011 (2018).

Teaching interests

Like every other kid, I was fascinated with rainbows after a storm, motorcyclists riding in the ‘wall of death’, and ‘super-bouncy’ balls. When basics of reflection, refraction, and reaction forces explained these fascinating events to me, high-school physics became my favorite subject. In retrospect, such events have been imprinted in my memory, due to the ability of a subject taught in school, to explain a daily life phenomena. I firmly believe that learning is accelerated when curiosity is ignited, and this can be achieved by developing a correlation between fundamental concepts of materials science with typical events in a student’s life, through classroom teaching as well as hands-on experiments.

As an instructor for an undergraduate laboratory course, I designed experiments which taught students the methods to study the mechanical properties of materials (metals, ceramics and polymers). During the course, I worked closely with a group of twelve students to evaluate their progress as they conducted experiments to estimate the elastic modulus, ductility and hardness of standard material specimens like 6061-T6 Aluminum and, 304 stainless steel. To encourage critical thinking, statistical error analysis along with a comprehensive description about sources of errors in their measurements was stressed upon. Furthermore, to pique their curiosity, I initiated a discussion with them on the impact of ductility, hardness, creep and crack propagation on failure of materials by showing them TEM and SEM images of fracture surfaces, grain boundaries and elemental distribution. It was particularly reinvigorating and satisfying for me to feel their excitement and awe upon seeing real atomic-resolution images of edge and screw-dislocations in different materials.

I look forward to building the foundations for next-generation of researchers and engineers by instilling the curiosity within them through term papers/presentations on real world problems and empowering them with fundamentals of materials science to tackle such problems. My background in Metallurgy, Materials Science and Chemistry, gives me confidence to teach a broad selection of classes, ranging from introductory level courses for undergraduates (nano-scale materials and applications, mechanical behavior and design principles) to specialized courses for graduate students (grain boundaries & interfaces in nanocrystalline materials, transmission electron microscopy).