Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Sandia researchers solve mystery of attractive surfaces

07.08.2006
When smooth surfaces that hate water approach each other underwater, scientists have observed that they snap into contact. This is apparently due to attractive forces that extend for tens to hundreds of nanometers.

But action over these distances -- though small to us -- are unexplainable by conventional theories, which find no standard force sufficiently long-ranged to accomplish this task.

The action is of considerable possible importance. Long-range attractions between hydrophobic surfaces might help guide the complex folding of proteins, for example, from their initial passive clothesline-like shape into the active fist-like formations upon which life depends.

In a paper published this Thursday in the journal Nature, Sandia National Laboratories researchers were able to increase the long-ranged attraction from nanometers to microns by inserting rough hydrophobic surfaces in place of smooth ones. They also were able to slow the reaction down, enabling them to measure the attraction and visually observe its origin -- a cavitation called a vapor bubble that bridges the gap between the submerged surfaces.

These experiments offer new insight into the long-range attractions that encourage hydrophobic surfaces to snap together under water. The improved observation led the group to conclude that cavitation may be responsible in general for the hydrophobic interactions that exceed the known range of van der Waals or electrostatic forces.

The new test conditions were effected, first, by using rough, so-called superhydrophobic surfaces rather than conventional smooth hydrophobic surfaces.

Superhydrophobic surfaces, on which water droplets roll like marbles, can be formed simply by evaporating liquid from a silica solution in an assembly process developed by Sandia Fellow Jeff Brinker.

The interactions of superhydrophobic materials underwater have not been studied.

"Previous experimentalists had always used smooth materials -- but the common materials of nature are rough, and roughness greatly influences the interaction with water," says Brinker.

In addition, a microscope that resists the 'snap-together' effect enabled the Sandia team to measure the forces involved as the surfaces closed upon each other.

The microscope, called an Interfacial Force Microscope, is similar to an Atomic Force Microscope, but a teeter-totter end piece allows the tip to maintain its distance and measure the forces acting on it rather than succumbing to them. The IFM was developed and patented under the direction of Sandia researcher Jack Houston and is now available at some universities.

Through IFM resistance, the group slowed the 'snap' into a longer time frame that allowed step-by-step observation of what exactly was happening in the formerly indecipherable moment.

"When force becomes overwhelming for an AFM, surfaces snap together uncontrollably," says Houston. "The IFM just measures the force without caving in to it. We can move in as slowly as we want until we reach the point of contact."

"There's no other instrument that can do that," says first author Seema Singh, who did the experimental work under direction of Brinker and Houston.

The group observed that two superhydrophobic surfaces approaching each other force the water between them to change state to a vapor, creating a cavity. This cavitation has less internal pressure, so external water pressure forces the two hydrophobic surfaces at each end of the cavity closer.

This very long-range attractive interaction may be a longer scale version of the unexplained interactions seen to-date for smooth surfaces.

The superhydrophobic material was self-assembled by simply drying a slurry of hydrophobically modified silica in a technique originally developed to create super low-density silica aerogels. During drying, the silica gel shrinks and re-expands to create a rough, rather than smooth, surface. The roughness creates a spike-like effect, causing a water drop to adopt an almost spherical shape.

"This greater hydrophobicity apparently increased the distance over which cavitation could occur, allowing it to be visually imaged for the first time," says Sandia researcher Frank Van Swol, who calculated the theoretical cavitation distance and the energy and forces associated with cavitation.

Asked whether the observed reaction might offer some insight into the mechanisms by which proteins fold, Brinker said, "The only evidence so far for things snapping together comes from the measurements of interactions between flat smooth hydrophobic surfaces underwater. The longer-range interactions for rough surfaces may more closely represent how proteins fold, since proteins are certainly not flat surfaces."

Rough superhydrophobic surfaces have been of much recent interest for their self-cleaning properties -- the so-called Lotus effect, where rolling drops of water cleanse such surfaces of particles and parasites.

Neal Singer | EurekAlert!
Further information:
http://www.sandia.gov
http://www.sandia.gov/news/resources/releases/2006/snap.html

More articles from Materials Sciences:

nachricht Graphene origami as a mechanically tunable plasmonic structure for infrared detection
25.04.2018 | University of Illinois College of Engineering

nachricht Scientists create innovative new 'green' concrete using graphene
24.04.2018 | University of Exeter

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: BAM@Hannover Messe: innovative 3D printing method for space flight

At the Hannover Messe 2018, the Bundesanstalt für Materialforschung und-prüfung (BAM) will show how, in the future, astronauts could produce their own tools or spare parts in zero gravity using 3D printing. This will reduce, weight and transport costs for space missions. Visitors can experience the innovative additive manufacturing process live at the fair.

Powder-based additive manufacturing in zero gravity is the name of the project in which a component is produced by applying metallic powder layers and then...

Im Focus: Molecules Brilliantly Illuminated

Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.

Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...

Im Focus: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Getting electrons to move in a semiconductor

25.04.2018 | Physics and Astronomy

Reconstructing what makes us tick

25.04.2018 | Physics and Astronomy

Cheap 3-D printer can produce self-folding materials

25.04.2018 | Information Technology

VideoLinks
Science & Research
Overview of more VideoLinks >>>