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!
From ancient fossils to future cars
21.10.2016 | University of California - Riverside
Study explains strength gap between graphene, carbon fiber
20.10.2016 | Rice University
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.
In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...
'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.
Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
24.10.2016 | Power and Electrical Engineering
24.10.2016 | Life Sciences
24.10.2016 | Life Sciences