Skeletal joints must provide lubrication under considerable load. Lubrication between two sliding surfaces in aqueous environments can be greatly enhanced by polyelectrolyte brushes ( 1 ): Long macromolecular chains that bear charges at each repeating unit are grafted densely to a planar or curved surface. In the so-called osmotic limit (low salt concentrations), a large fraction of the counterions are confined within the brush layer, thus creating an enormous osmotic pressure (see the figure, left). Surface forces apparatus (SFA) ( 2 ) studies revealed a marked repulsion between such surfaces ( 3 ), and Klein and co-workers ( 4 ) showed that this effect very efficiently lubricates polyelectrolyte brush interfaces. It is now generally believed that lubrication in many biological systems works according to the same principle. On page 1434 of this issue, Yu et al. ( 5 ) add a twist to this story by studying the same problem in a SFA and finding that traces of di- and trivalent ions can increase the frictional force between two polyelectrolyte brush layers, dramatically so for Y3+ ions.
On 10 July, researchers in Chile will unveil an online public random number service. Later in July, the U.S. National Institute of Standards and Technology (NIST) will launch its Randomness Beacon as a permanent service, upgrading a pilot program that began in 2013. Brazil, too, is planning ... more
The Convention on Biological Diversity (CBD) commits its 196 nation parties to conserve biological diversity, use its components sustainably, and share fairly and equitably the benefits from the utilization of genetic resources. The last of these objectives was further codified in the Conve ... more
Solar windows turn some of the light shining through into electricity. They've been on the market for years. But many of these windows absorb some visible light, leaving them with a reddish or brownish hue, a trait frowned on by architects. Now, new versions are on the way that absorb invis ... more
Researchers have developed a compound that can transform near-infrared light into broadband white-light, offering a cheap, efficient means to produce visible light. The emitted light is also exceedingly directional, a desirable quality for devices like microscopes that require high spatial ... more