Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

Home > Press > Penn Researchers Show New Level of Control Over Liquid Crystals

Manipulating the surface of liquid crystals. (Art courtesy of Felice Macera, Daniel Beller, Apiradee Honglawan and Simon Čopar)
Manipulating the surface of liquid crystals.

(Art courtesy of Felice Macera, Daniel Beller, Apiradee Honglawan and Simon Čopar)

Abstract:
Directed assembly is a growing field of research in nanotechnology in which scientists and engineers aim to manufacture structures on the smallest scales without having to individually manipulate each component. Rather, they set out precisely defined starting conditions and let the physics and chemistry that govern those components do the rest.

Penn Researchers Show New Level of Control Over Liquid Crystals

Philadelphia, PA | Posted on January 7th, 2013

An interdisciplinary team of researchers from the University of Pennsylvania has shown a new way to direct the assembly of liquid crystals, generating small features that spontaneously arrange in arrays based on much larger templates.

The study was led by Shu Yang, associate professor in the School of Engineering and Applied Science's departments of Materials Science and Engineering and Chemical and Biomolecular Engineering; Kathleen Stebe, Engineering's vice dean for research and professor in Chemical and Biomolecular Engineering; and Randall Kamien, professor in the School of Arts and Sciences' Department of Physics and Astronomy. Apiradee Honglawan of Yang's lab, Daniel Beller of Kamien's group and Marcello Cavallaro Jr. of Stebe's lab also contributed to the research.

They came together through Penn's Materials Research Science and Engineering Center, which recently received a $21.7 million National Science Foundation grant to support this kind of interdisciplinary research. Stebe and Kamien are leaders of the Center's sub-group focused on elasticity in soft materials and knew they had the expertise on hand to do groundbreaking work with liquid crystals.

Their work was published in the Proceedings of the National Academies of Science.

Crystals are materials that have molecules arrayed in regular three-dimensional patterns; liquid crystals contain some, but not all, of these patterns, and their molecules can flow around one another and change the direction they face. This behavior allows defects, places on the surface where the molecular orientation of the liquid crystals is disrupted.

Despite their name, such defects are highly desirable. If the location of the defects can be controlled, the change in pattern or orientation can be put to use. In a liquid crystal display, for example, the crystals' orientation in different regions determines which parts of the screen are illuminated.

"Liquid crystals naturally produce a pattern of close-packed defects on their surfaces," Yang said, "but it turns out that this pattern is often not that interesting for device applications. We want to arbitrarily manipulate that pattern on demand."

Electrical fields are often used to change the crystals' orientation, as in the case with liquid crystal displays, but the Penn research team was interested in manipulating defects by using a physical template. Employing a class of liquid crystals that forms stacks of layers spaced in nanometers — known as "smectic" liquid crystals — the researchers set out to show that, by altering the geometry of the molecules on the bottommost layer, they could produce changes in the patterns of defects on the topmost.

"The molecules can feel the geometry of the template, which creates a sort of elastic cue," Stebe said. "That cue is transmitted layer by layer, and the whole system responds."

The researchers' template was a series of microscopic posts arrayed like a bed of nails. By altering the size, shape, symmetry and spacing of these posts, as well as the thickness of the liquid crystal film, the researchers discovered they could make subtle changes in the patterns of the defects.

For example, a smectic liquid crystal that would naturally form a hexagonal array of dimple-like defects on its surface could be templated to form a square pattern or to have dimples that were more closely or loosely packed.

Critically, these induced defect patterns weren't one-to-one reproductions of the pattern of posts on the template layer. The researchers were able to generate more complex relationships, such as getting four defects to sit atop each circular post or defects that formed over the points of a triangular post. They were also able to deduce the rules that govern these relationships and predict what defect patterns a given set of post parameters would produce.

"The first layer's molecules tend to be pinned to the edges of the posts," Kamien said, "so changing a post's size and shape will change how many defects can sit on its edges at the same time."

The size discrepancy between the posts and individual molecules of the liquid crystal is also a key feature for using this class of liquid crystal in directed assembly. The posts are each a few microns wide and tall, still microscopically small, but large enough to be easily and economically made to specification. This is much more attractive than trying to directly control the size and arrangement of the liquid crystals' defects.

"The liquid crystal layers are very thin, so the defects are on the order of several nanometers across" Kamien said. "Those defects would normally be very hard to control, especially compared to the posts, which are more like a few thousand nanometers across."

Beyond sensors and displays, these defects can be used in nanomanufacturing.

"If you make defects like dimples, you could put ink in them and use them like a stamp," Kamien said. "Or you could make the inverse of the dimples and make points, which could be used as localized surface plasmon resonance hot spots for chemical and biological sensing or as a topographic protrusion for creating a superhydrophobic surface."

And because the layers of liquid crystals transmit elastic energy, they can also be used to do mechanical work. This means that the top layer could be used as a template to assemble even larger molecules.

"You could put nanoparticles, quantum dots or carbon nanotubes in the liquid crystal layers and they would be expelled into to the defects," Yang said.

A template consisting of circular posts could even be dynamically altered with heat and an electric field, for example, making the posts in a certain region elliptical. This microscopic geometric cue would travel up the layers of liquid crystal and produce micrometer-scale changes on the surface.

By establishing the mathematical relationships between the post parameters and the surface-layer defects, the researchers are laying the foundation of a directed assembly technique that can be used with any smectic liquid crystal.

"We are providing a very crude cue and getting exquisite molecular level organization," Stebe said. "Any liquid crystal that makes layers can now be used to make rather beautiful control over textures on the surface.

The research was supported by the National Science Foundation.

####

For more information, please click here

Contacts:
Evan Lerner

215-573-6604

Copyright © University of Pennsylvania

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Pulses of electrons manipulate nanomagnets and store information: Scientists use electron pulses to create and manipulate nanoscale magnetic excitations that can store data July 21st, 2017

The first light atomic nucleus with a second face July 20th, 2017

Semiliquid chains pulled out of a sea of microparticles July 20th, 2017

Harnessing light to drive chemical reactions July 19th, 2017

Nanoparticles could spur better LEDs, invisibility cloaks July 19th, 2017

Physics

The first light atomic nucleus with a second face July 20th, 2017

Chemistry

Tokyo Institute of Technology research: Antiaromatic molecule displays record electrical conductance July 19th, 2017

Harnessing light to drive chemical reactions July 19th, 2017

Studying Argon Gas Trapped in Two-Dimensional Array of Tiny "Cages": Understanding how individual atoms enter and exit the nanoporous frameworks could help scientists design new materials for gas separation and nuclear waste remediation July 17th, 2017

Carbon displays quantum effects July 13th, 2017

Display technology/LEDs/SS Lighting/OLEDs

Nanoparticles could spur better LEDs, invisibility cloaks July 19th, 2017

Govt.-Legislation/Regulation/Funding/Policy

The first light atomic nucleus with a second face July 20th, 2017

Semiliquid chains pulled out of a sea of microparticles July 20th, 2017

Here's a tip: Indented cement shows unique properties: Rice University models reveal nanoindentation can benefit crystals in concrete July 20th, 2017

Harnessing light to drive chemical reactions July 19th, 2017

Self Assembly

Oddball enzyme provides easy path to synthetic biomaterials May 17th, 2017

Nanotubes that build themselves April 14th, 2017

Nanocages for gold particles: what is happening inside? March 16th, 2017

Most Complex Nanoparticle Crystal Ever Made by Design: Possible applications include controlling light, capturing pollutants, delivering therapeutics March 2nd, 2017

Nanotubes/Buckyballs/Fullerenes/Nanorods

Killing cancer in the heat of the moment: A new method efficiently transfers genes into cells, then activates them with light. This could lead to gene therapies for cancers July 9th, 2017

Tests show no nanotubes released during utilisation of nanoaugmented materials June 9th, 2017

Ag/ZnO-Nanorods Schottky diodes based UV-PDs are fabricated and tested May 26th, 2017

Fed grant backs nanofiber development: Rice University joins Department of Energy 'Next Generation Machines' initiative May 10th, 2017

Discoveries

Pulses of electrons manipulate nanomagnets and store information: Scientists use electron pulses to create and manipulate nanoscale magnetic excitations that can store data July 21st, 2017

The first light atomic nucleus with a second face July 20th, 2017

Semiliquid chains pulled out of a sea of microparticles July 20th, 2017

Here's a tip: Indented cement shows unique properties: Rice University models reveal nanoindentation can benefit crystals in concrete July 20th, 2017

Announcements

Pulses of electrons manipulate nanomagnets and store information: Scientists use electron pulses to create and manipulate nanoscale magnetic excitations that can store data July 21st, 2017

Probiotics: Novel biosynthetic tool to develop metallic nanoparticles: This research article by Dr. Nida Akhtar et al has been published in Recent Patents on Drug Delivery & Formulation, Volume 11, Issue 1, 2017 July 20th, 2017

The first light atomic nucleus with a second face July 20th, 2017

Semiliquid chains pulled out of a sea of microparticles July 20th, 2017

Quantum Dots/Rods

Coupling a nano-trumpet with a quantum dot enables precise position determination July 14th, 2017

Graphene and quantum dots put in motion a CMOS-integrated camera that can see the invisible May 29th, 2017

The brighter side of twisted polymers: Conjugated polymers designed with a twist produce tiny, brightly fluorescent particles with broad applications May 16th, 2017

Nanoparticles open new window for biological imaging: “Quantum dots” that emit infrared light enable highly detailed images of internal body structures April 10th, 2017

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project