Rowan engineering collaboration shapes nanoparticle fingerprints for potential uses in solar cells

Rowan engineering collaboration shapes nanoparticle fingerprints for potential uses in solar cells

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Read the article at http://advances.sciencemag.org/content/4/10/eaat8597.

A team of engineers and researchers at the Henry M. Rowan College of Engineering (HMRCOE) at Rowan University – in collaboration with the University of Pennsylvania – discovered a new method to assemble nanoparticles into periodic patterns using cholesteric liquid crystals, resembling the textures of fingerprints, with future plans to potentially design solar cells, batteries or microelectronics.

“While our fundamental study is still far away from real applications, I would be happy if we can use our technique in the future to improve solar cells by enhancing the energy harvesting efficiency or if we manage to use the resulting structures as conductive pathways for the transport of electricity so we can design new capacitors, batteries or microelectronics,” said Dr. Martin Haase, an assistant professor in the Department of Chemical Engineering. “In our research, we discovered a new method to assemble nanoparticles into periodic patterns that resemble the textures of fingerprints, and we employed liquid crystals as templates for nanoparticle organization.”

Haase noted that everyday applications such as cell phones and TV displays contain liquid crystals. These technologies are based on the reorientation of a liquid-crystal material in response to applied fields, which then results in a change in its observed properties.

Take nanoparticles and cholesteric liquid crystals, for example. When these two intertwine, they generate patterns of fingerprint-like textures. This discovery made at Rowan University provides chemists and engineers with structures for potential uses in a range of products and materials.

Liquid crystal is a term referring to substances that are neither crystalline (solid) nor isotropic (liquid) but somewhere between the two. The main types of liquid crystals (Nematic, Smectic Cholesteric) are identified by their varying amounts of molecular order and positioning. The cholesteric phase is characterized by the molecules being aligned, at slight angles to one another, stacked within very thin layers; cholesteric is the last phase before a substance becomes solid or liquid. The cholesteric liquid crystal often is found in common household items such as thermometers. Nanoparticles, on the other hand, are ultra-small solid objects and can be made from a variety of materials, such as ceramics, metals and plastics. They can be assembled into useful materials such as filters, solar cells, batteries and microelectronics.

However, such nano-assembly processes are not straightforward and require specialized chemical and physical techniques. Thanks to the collaborative research by Rowan University’s Department of Chemical Engineering and three departments (Physics, Material Science and Engineering, and Chemical and Biomolecular Engineering) at the University of Pennsylvania, a new assembly technique has now been introduced. 

The team comprises Haase and Lisa Tran, a graduate student in the Department of Physics at the University of Pennsylvania. A multidisciplinary group of scientists from the University of Pennsylvania supported Haase and Tran, including Dr. Randall Kamien, professor of physics; Dr. Shu Yang, professor of material science and engineering; Dr. Kathleen Stebe, professor of chemical and biomolecular engineering; and Ningwei Li and Hye-Na Kim, engineering graduate students.

This research was conducted in the Nanoscale Interfacial Engineering Lab at Rowan University and recently was published in the journal Science Advances.

“Think of nanoparticles as building blocks for functional materials such as sensors or solar cells. To obtain these functions, the particles need to be combined with each other like you would combine different Lego bricks to build a toy car,” Haase said. “But unlike Legos, their tiny size prevents them from being picked up and assembled. Our research has introduced a novel technique for self-assembling such nanoparticles into complex structures based on their interaction with liquid crystals.”

Liquid crystals are ubiquitous in modern TV displays (LCDs), Tran noted. “We discovered that liquid crystals can be used to self-assemble nanoparticles into periodic patterns. They are ordered liquids, and we manipulated them to transfer their ordering to nanoparticles.”

The surface of a so-called cholesteric liquid crystal generates intricate patterns that resemble those of a fingerprint. The researchers found that nanoparticles organize themselves into these patterns to generate unique structures with potential uses in solar cells, batteries or optical materials. Discovering a new approach of self-assembling nanoparticle organized patterns will allow Haase and the team to conduct further research and apply this system to develop new, advanced materials.

This research was supported by Haase’s CAREER award for developing green alternatives to replace costly, chemical processes from the National Science Foundation (NSF); NSF Materials Research Science, Engineering Centers’ grant; the Simons Foundation; and the American Fellowship grant from the American Association of University Women.