January 22, 2014
Spider Silk Not Great Heat Conductor, Despite 2012 Study’s Findings
[ Watch the Video: Science Showdown Over Spider Silk ]
Lee Rannals for redOrbit.com - Your Universe Online
Two years ago Iowa State University scientists found that spider silk was not only a great heat conductor, but that the silk was just as good of a heat conductor as metal. However, the team from Spain repeated the experiment and are bringing the 2012 discovery into question.
The Iowa State University team announced at the time that spider silk was an excellent thermal conductor. The team measured thermal diffusivity at 70 mm2/s, which is as high as some of the best metals.
"Our discoveries will revolutionize the conventional thought on the low thermal conductivity of biological materials," the main author of the paper, Xinwei Wang, said in a statement at the time they announced the study.
Physicists from the University of the Basque Country decided to conduct their own experiment to validate the strange findings by the Iowa team. They proceeded to repeat the experiment in their laboratory at the Higher Technical School of Engineering in Bilbao, which has equipment capable of analyzing how heat is transferred in very thin filaments.
"We took web strings from the garden spider (Araneus diadematus), one of the most common in Europe, and analyzed how temperature declined with distance to the point where a laser beam hits," said Agustín Salazar, lecturer at the UPV/EHU and main author of the study published in the journal Materials Letters.
The team found that the thermal diffusivity of the spider was just 0.2 mm2/s, which is about 300 times smaller than what the Iowa team reported two years ago. They said spider silk is formed from chains of amino acids, which are poor conductors of heat.
Salazar said he disregards the possibility that the discrepancy in the results is due to their having worked with two different species of spider.
"It is unlikely that this could be the cause of such enormous differences in thermal diffusivity,” he said. “In fact, I would not be surprised if this silk was a thermal insulator rather than a good conductor, because over millions of years evolution has favored the physical properties of materials that represent some benefit for the spider and its web, such as resistance, elasticity and thermal insulation."
The researchers said they used a simple method based on infrared thermography, but the method applied by their counterparts was “not very reliable.”
“The American team used extremely complex processing to eliminate heat losses from their experimental data, as well as the influence of coatings and the effect of filament length: they worked with 1 mm-long strings while ours were a centimeter long or more,” said Salazar.
The team says the implications of these kinds of studies should remind scientists all over the world how important it is to reproduce experiments.
"It is an aspect often forgotten by mainstream press, who announce attention-grabbing discoveries with striking headlines as if they were incontrovertible truths, before they can be corroborated by other researchers,” the team wrote in the journal.