Showing posts sorted by relevance for query liquid crystal. Sort by date Show all posts
Showing posts sorted by relevance for query liquid crystal. Sort by date Show all posts

Monday, June 28, 2010

Liquid Crystals - A New Way to Better Data Storage ?

In continuation of my update on liquid crystals (after a long gap)....

As cell phones and computers continue to shrink, many companies are seeking better ways to store hundreds of gigabytes of data in small, low-power devices. A special type of liquid crystal (similar to those used in computer displays and televisions) offers a solution  and lasers can encode data throughout a liquid crystal known as holographic storage, the technique makes it possible to pack much more information in a tiny space.   

But attempts to use liquid crystals for data storage have had limited success. In order to reliably record and rewrite data, researchers must figure out a way to uniformly control the orientation of liquid crystal molecules as the most liquid crystal technologies currently rely on physical or chemical manipulation, such as rubbing in one direction, to align molecules in a preferred direction. 

In an important advance, scientists at the Tokyo Institute of Technology have created a stable, rewritable memory device that exploits a liquid crystal property called the "anchoring transition". Researchers  demonstrated memory and rewritable bistable devices based on an anchoring transition of a nematic liquid crystal on a perfluoropolymer surface. Spontaneous orientation changes between planar and homeotropic occur on cooling and heating with a large temperature hysteresis. Orientation switching also occurs by applying an electric field with a response time of several milliseconds depending on the field strength claims the researchers.

Using either a laser beam or an electric field, the researchers can align rod-like liquid crystal molecules in a polymer. Their tests show that the liquid crystal created by the team can store data, be erased and used again...
"This is the first rewritable memory device utilizing anchoring transition," said Hideo Takezoe, who led the research. And because the device is bi-stable -- the liquid crystals retain their orientation in one of two directions -- it needs no power to keep images, adds Takezoe.

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Tuesday, June 27, 2017

Liquid crystal technique could be new way to control drug delivery process

In continuation of my update on liquid crystals..

Liquid crystals are strange substances, both fish and fowl. They can flow like a liquid, but have the orderly molecular structure of a crystalline solid. And that internal structure can be changed by small cues from outside.

A group of scientists at the University of Chicago's Institute for Molecular Engineering has found a way to exploit this property to turn liquid crystals into a tool to manipulate the shape of synthetic cell membranes. The technique has potential for use in biology, medicine, and advanced materials development. The team reported its findings in the Aug. 10, 2016 edition of Science Advances.

"What we've done is reproduced the beginnings of cell division in a synthetic system," said Juan de Pablo, Liew Family Professor in Molecular Engineering, who headed the group. When a cell divides, the spherical cell membrane stretches into an elliptical form, develops a waist in the middle, and then splits into two spherical cells. The scientists built sophisticated models that produced this behavior on the computer and then reproduced it in the real world, testing the model's predictions.

"It's the first time that this has been done," said de Pablo. "It's a system that has been engineered at the molecular level using computer models."

Cellular stand-ins

Standing in for cells in the experiments were capsules, or "vesicles," a few microns in diameter (a fraction the width of a human hair) made of some of the same phospholipids that make up real cell membranes. These were immersed in a bath of liquid crystal oil whose molecules are slightly elongated rather than round. At temperatures above about 97 degrees Fahrenheit the oil behaves like any other oil. But when the temperature is lowered slightly, the molecules of the oil pack tightly against one another like cigarettes and align along a single direction.

"When that happens, the liquid crystal presses on the vesicle more in one direction than in the other, so the vesicle becomes elongated," de Pablo said. "If you squash it more and more, it becomes an ellipsoid and the two ends become pointier and pointier. There is a point when the molecules around those points separate from one another and create a little gap in the membrane through which things could be squeezed out."

Lipid vesicles are in current use for drug delivery. De Pablo envisions using the liquid crystal technique as a cunning way to control that process.

"What we find intriguing is that we have a mechanism that will allow us to take vesicles loaded with something interesting, and by changing the temperature a little bit, we could deform the vesicle and have it squeeze out whatever it has inside without our ever touching the vesicle. And then as we restore the temperature to the original value, the vesicle becomes spherical again."

Calculations indicate that squeezing more or less would alter the size of the gap, allowing for the release of contents of varying sizes. "But that's something that we still have to demonstrate," said de Pablo.

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Sunday, January 25, 2009

Use of Liquid crystals in high-resolution digital X-rays !

We have seen many applications of liquid crystals, but now something interesting like "X-ray light valve" (a term coined by Dr.John Rowlands). This finds importance because the use of liquid crystals reduces the cost of high-resolution digital X-rays by many folds. As the use of digital X rays is becoming essential (because its simple to analyse, manipulate and store-in comparison with the presently used ones). Most of them work by using a layer of amorphous selenium to convert the X-rays into electric charge. This charge image is then recorded using an array of transistors and other electronic components, akin to those used in some digital cameras.

X-rays cannot be easily focused, so X-ray machines work by recording the shadow of an object rather than a focused image. That means the recording medium, be it an electronic imager or conventional X-ray film, must be at least the same size as the object being scanned and this add to the cost of digitally imaging. Thanks to Dr.Rowland and his group for X-ray light valve-consisting of a layer of liquid crystal - which is opaque or transparent depending on whether an electric charge is present - covered with a layer of amorphous selenium. These layers are sandwiched between a pair of electrodes which generate an electric field across them. When an X-ray is taken, the rays that hit the selenium layer generate a charge which is drawn towards the liquid crystal by the electric field. This makes the liquid crystal transparent at those locations. The overall pattern of transparency and opacity can be read off the liquid crystal layer using a light-based digital scanner and presented as a digital image. This research is of significance because of the fact that it separates the read-out system from the X-ray mechanism.

As pulmonary tuberculosis is becoming an epidemic in the developing countries, development of this technique is a boon to the people.

When I was working for my Ph.D., my guide (Dr. Shankar C. Bennur  (now retired) Professor of Organic Chemistry, Karnatak University Dharwad, Karnatak, India) used to tell me that the liquid crystals will have many fold uses in the days to come. He did work (UFSC, Florianopolis, SC, Brazil) on the synthesis of many liquid crystals and used to tell me about his experience with this interesting field (which was at nascent stage). Whenever we used to get products (in my case, the compounds had methylene aminoxy methyl moiety) with low melting points, he  used to elaborate about  smectic point./long chain compounds.....Hope,  he will be happy about this innovative idea. Congrats Dr.Rowland......

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