Attracted to mayonaisse

Aug 18, 2002
Public release date: 29-Mar-2004

Contact: Jade Boyd
[email protected]
Rice University

Bizarre attractive force found in mayonnaise

Rice engineers find evidence of little-understood force in everyday emulsions

HOUSTON, March 29, 2004 -- Scientists at Rice University have discovered that a little-understood tensile force, which was previously thought to be an oddity found only in the types of plastics used to make bulletproof vests, occurs in everyday emulsions like mayonnaise and salad dressing.

First identified about 25 years ago, the phenomenon known as "negative first normal stress difference" refers to an attractive force that is created within fluids under certain conditions.

For example, imagine two glass plates that are stacked like a sandwich, with a thin layer of liquid between. If the bottom plate is held still and the top plate is moved quickly to one side, it sets the fluid in motion, and creates forces within the fluid that, in turn, act upon the glass.

In simple fluids like water, this sliding motion creates complementary forces that tend to push the plate along in the direction that it was sliding. In more complex fluids like polymers, tension develops, creating forces that tend to push the plates apart. Around 1980, it was discovered that liquid crystalline polymers --the chief ingredients in ultrastrong fibers like Kevlar® and Zylon® -- created forces that tugged the plates together. This force is referred to as "negative normal stress," as opposed to the more common positive forces that push plates apart.

Last year, Matteo Pasquali, assistant professor of chemical engineering, and colleague professors and graduate students at Rice were trying to create a strong fiber of pure carbon nanotubes. The researchers were attempting to adapt the methods DuPont had pioneered in the creation of Kevlar, and they ended up with a solution of nanotubes that behaved like a liquid crystalline polymer. The solution exhibited negative normal stress, which was a confirmation that the nanotubes had made a liquid crystal.

At about the same time, Pasquali and graduate students Alberto Montesi and Alejandro Peña were testing emulsions of oil and water. Emulsions are combinations of two or more liquids that do not mix, and they are common in industrial settings like oil fields as well as in everyday foodstuffs like mayonnaise or vinaigrette salad dressing. In oil and water, an emulsion is created when tiny droplets of water become dispersed throughout the oil.

Pasquali, Montesi and Peña found that negative normal stress was present in their oil and water emulsions when the concentration of water droplets was in a specific range. The research was published last month in the academic journal Physical Review Letters.

"When I first saw the data, I thought we had made a mistake," said Pasquali. "My students and I joked that we must be the only lab that had ever had negative normal stresses on two systems. However, we double- and triple-checked, and the effect was still there.

"Then, we heard that Erik Hobbie's group at the National Institute for Standards and Technology was getting similar results with suspensions of carbon nanotubes. A collaboration ensued and we all began to feel more certain that the findings -- though unusual -- were correct."

The startling results led Pasquali's group to expand its experiments to some commonplace emulsions.

"I went to the store, bought a jar of mayonnaise and tested it," said Montesi. "I was curious to see if it showed the same negative normal stress, and it did."

The findings clearly open the door to future studies about the underlying phenomena behind negative normal stress.

"This finding opens interesting research and development opportunities," said Peña, now a senior research engineer at Schlumberger. "A better understanding of the phenomena that underlay the onset of negative normal stresses -- the interplay between the tendency of droplets to form collective structures at the microscopic level and the macroscopic behavior of emulsions in flow -- will lead to novel developments in the formulation of emulsions and other dispersed systems of practical relevance such as suspensions of solids and foams."

Pasquali added that more study is needed before practical applications will become apparent.

"It's really too early to foresee the full range of useful applications that might arise from this new understanding of negative normal stress," said Pasquali. "Obviously, any application where there are mixtures of oil and water -- like petroleum production, food processing and the like -- could be candidates."

I quite like the idea of rice engineers too ;)



Justified & Ancient
Dec 31, 2003
Hate to burst your bubble, Your Imperial Highness, but that's Rice as in Rice University, MIT of the Southwest. If you're incredibly smart in a science-nerdish way and don't want to go to California or the northeast, you go to Rice.


Abominable Snowman
Jan 4, 2002
Whereas these really are Californian rice engineers :D

Waiter, There's a Drug in My Rice

By Kristen Philipkoski | Also by this reporter Page 1 of 1

02:00 AM Mar. 30, 2004 PT

The California Rice Commission on Monday approved a biotech company's request to grow the state's first crop genetically modified to contain a drug.

The rice commission narrowly passed the proposal by a 6-5 vote. The commission advises the California Department of Food and Agriculture, which has the final decision on whether Ventria Bioscience of Sacramento can plant its pharmaceutical crop. If the agency approves, the company could be the first to commercialize such a product.

The rice is genetically modified to produce two human proteins that fight infection: lactoferrin and lysozyme. Some rice growers and environmental groups oppose the project, saying the rice could contaminate regular crops and damage the export market.

"Consumers in Japan will not accept (genetically engineered) contamination of any crop," said rice farmer Greg Massa in a statement. "The decision to approve Ventria's guidelines is bad news for farmers and California's rice industry."

But Ventria's proteins could be a big step forward in preventing infections in infants. Lactoferrin and lysozyme are present in breast milk, and protect babies from ear infections, diarrhea, respiratory tract infections, meningitis and other infections. But these protective proteins disappear when a baby stops breast feeding or doesn't receive breast milk at all. Researchers at Ventria were first to develop a human form of these proteins that could become therapies.

Ventria believes growing rice that produce proteins like lactoferrin and lysozyme in rice could be a cheaper way to develop drugs than building and maintaining expensive manufacturing plants.

But environmental groups and consumer advocates sued the U.S. Department of Agriculture in November 2003 for inadequate oversight of pharmaceutical crops. Companies like Dow Chemical and Monsanto are experimenting with corn, soybeans, tobacco, rice and sugar crops to find a cheaper way to mass-produce drugs.

Opponents say growing the crops in open fields endangers organic and conventional crops, as well as human health. And it's not just an issue environmentalists and consumer advocates are worried about, said Paul Achitoff, managing attorney of Earthjustice in Hawaii.

"Even food-processing corporations are very upset about this as well, because they know all you need is one shipment of corn flakes that has a contraceptive in it and there's a real problem, obviously," Achitoff said.

In 2002, federal officials ordered ProdiGene, of College Station, Texas, to burn 155 acres of corn and 500,000 bushels of soybeans because the crops had been contaminated by the company's pharmaceutical corn, which had been genetically engineered to produce an experimental diarrhea vaccine for pigs.

"Contamination is inevitable under this protocol, and the CRC did not act in the best interests of California rice farmers or consumers," said Renata Brillinger of Californians for GE-Free Agriculture.

"Instead of the normal 30-day public comment period that would exist with any other regulation, this fast tracking allows a 10-day review by CDFA," said Rebecca Spector of the Center for Food Safety. "The CDFA level is really the time where we depend on the public to be able to submit comments. We hope that the secretary of agriculture will review the proposal under the normal public review process."

"This is kind of a big mess," she said. "We requested that they wait to see how FDA and USDA are going to regulate this before approving this planting protocol. Ventria is taking advantage of this regulatory vacuum and in the meantime has gone through the regulatory bodies in California."

Ventria executives were not immediately available for comment.

Ventria's proposal restricts the production to counties that do not currently grow rice: San Luis Obispo, Kern, Santa Barbara, Ventura, Los Angeles, Orange, San Bernardino, Riverside, San Diego and Imperial.
Original story