When most people look at a window they see solid panes of glass but to physicists it isn't so simple. Window glass has always been a puzzle but an Emory University research team led by physicist Eric Weeks has found another clue.
Weeks has devoted his career to probing the mysteries of "squishy" substances that cannot be pinned down as a solid or liquid. Referred to as "soft condensed materials," they include everyday substances such as toothpaste, peanut butter, shaving cream, plastic and glass.
Scientists fully understand the process of water turning to ice.
As the temperature cools, the movement of the water molecules slows. At 32 F, the molecules form crystal lattices, solidifying into ice. In contrast, the molecules of glasses do not crystallize. The movement of the glass molecules slows as temperature cools, but they never lock into crystal patterns. Instead, they jumble up and gradually become glassier, or more viscous. No one understands exactly why.
"One idea for why glass gets so viscous is that there might be some hidden structure," says Weeks, associate professor of physics. "If so, one question is what size is that structure".
The Emory Physics lab began zeroing in on this question two years ago when Hetal Patel, an undergraduate who was majoring in chemistry and history, designed a wedge-shaped chamber, using glue and glass microscope slides that allowed observation of single samples of glassy materials confined at decreasing diameters.
For samples, the Emory lab used mixtures of water and tiny plastic balls - each about the size of the nucleus of a cell. This model system acts like a glass when the particle concentration is increased.
The samples were packed into the wedge-shaped chambers, then placed in a confocal microscope, which digitally scanned cross-sections of the samples, creating up to 480 images per second.
The result was three-dimensional digital movies, showing the movement and behavior of the particles over time, within different regions of the chamber.
"The ability to take microscopy movies has greatly improved during the past five to 10 years," Weeks says. "Back in the mid-90s, the raw data from one two-hour data set would be four gigabytes. It would have completely filled up your hard drive. Now, it's just a tiny part of your hard drive, like a single DVD."
Two students collected and analyzed the data: Carolyn "Carrie" Nugent, an undergraduate from Bucknell University who worked in the Emory Physics Lab during two summers, and Kazem Edmond, currently an Emory graduate student in the Department of Physics.
The data showed that the narrower the sample chamber, the slower the particles moved and the closer they came to being glass-like. When the researchers increased the particle concentration in the samples, the confinement-induced slowing occurred at larger plate separations. The dimension between the plates at which the particles consistently slowed their movement was 20 particles across.
"It's like cars and traffic jams," Weeks says. "If you're on the highway and a few more cars get on, you don't really care because you can still move at the same speed. At 3 p.m., traffic gets worse and you may slow down a little bit. But at some point, your speed has to go from 40 mph to 5 mph. That's kind of what's happening with glass."
Previous research has shown groups of particles in dense suspensions move cooperatively. "Our work suggests glasses are solid-like because these groups can't move when the sample chamber is thinner than the typical size of these groups," Weeks says. "These experiments help us understand earlier work done with thin polymer films and other glassy materials, but as we use particles rather than atoms, we get to directly see how confinement influences the glass transition."
Nanotechnology is one example of a field that can benefit from research into the behavior of colloidal glass and plastics in tight spaces.
"When making machines as small as a cell, people have found that they're even more fragile than you might expect," Weeks said. "One interesting thing is that small plastic structures become more fragile because, when they are really tiny, they're less glassy."
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- Researchers Created A Laser Bullet To See What It Would Look Like - And Here It Is
- Will Holding Thermal Printer Paper Really Send Your BPA Levels Soaring?
- The Quote Of The Week - Shocked And Disappointed
- As The Weather Changes, So Do Beliefs About Climate Change
- ECFA Workshop: Planning For The High Luminosity LHC
- Great Earthquakes Doubled In The Most Recent 10 Year Period - What That Means
- Limiting Global Warming To 2°C: The Philosophy And The Science
- "I have no time for you. Either learn how to have a decent, mature conversation without resorting..."
- "The past 12 months—October 2013–September 2014—was the warmest 12-month period among all..."
- "Do you really think science20 readers are all so stupid that they are going to fall for Climate..."
- "'Mememine' is a well known astro-turfer for the denial industry. He spams the same identical gish..."
- "I have heard (from someone who worked there) of a laboratory in a country far, far away where they..."
- National Wildlife Refuge System bans on GMOs and neonics lack transparency, scientific rationale
- Want better sperm? Eat more pesticides
- Beyond universal donors, some people are programed with no blood type at all
- Anti-conventional ag movement spurs Big Ag to look to organic pesticides
- Can people really inherit memories?
- An end to fat shaming? The 50 year DNA mystery of metabolic dysfunction may soon be solved
- New policymaking tool for shift to renewable energy
- Teens whose parents exert more psychological control have trouble with closeness, independence
- Two days later: Adolescents' conflicts with family spill over to school, vice versa
- Children in high-quality early childhood education are buffered from changes in family income
- 'Breath test' shows promise for diagnosing fungal pneumonia