FOM-researcher Wim de Jeu and his fellow researchers from the United States of America and from Chile will announce this in Science, on August 3rd, 2007. The wrinkles arise, being influenced by the surface tension of the drop of water. Consequently, such a floating polymer sheet is a fine model for studying the behaviour of thin films in fluids. This combination is generally found in biological and synthetic soft materials.
The researchers used thin sheets (in academic jargon ‘films’) of polystyrene for their measurements, which they attached to a glass substratum. The thickness of the thin sheets, defined by means of x-ray reflectivity, varied from 31 to 233 nanometers. Then, they cut a circle 22.8 millimetres in diameter in each of the sheets and after that they dipped it into a Petri dish in distilled de-ionized water. In the Petri dish the surrounded part of the thin sheets came off and was floating on the water. As polystyrene is so-called ‘hydrophobic’, the surface tension flattens the polystyrene at the edge of the sheet. Thus, floating flat discs of polystyrene came into being. If the researchers then placed a droplet of water in the centre or pressed a needle, as a consequence of this disruption regular patterns of wrinkles arose that were facing outwards.
The wrinkled pattern appears to correspond nicely to the prognosis of a recently developed theory. This theory converts the surface tension of the drop of water in capillary forces that are affecting the polymer film. The researchers now combined the scaling relations that were developed for the length of the wrinkles with those for the number of wrinkles that will arise. This will produce a measuring standard to define the elasticity and thickness of very thin polymer sheets. In order to accomplish this, it appears that in actual practice, all that is necessary is a Petri scale with water, a plain microscope and a digital camera, because the patterns are extremely well visible at a small magnification. Next, they tested their method on polymer films that they had provided with plasticiser in order to vary the elasticity of the films. Even then the method produces reliable results to the thickness of the films.
The method that the researchers have been developing, just provides another large advantage. When they disrupt the film by placing a drop of water or pressing a needle, wrinkles will arise. In time the wrinkles will disappear, because the disruptions are spreading out all over the film. The film is ‘relaxing’ so to speak. Other research methods are applying the films to a firm substratum, which may lead to mechanical tensions in the sheets. These are disrupting the ‘relaxation’ of the film, which influences the measuring results. When the films are floating in or on a fluid, similar tensions may then ebb to the underlying fluid, after which the measurements will solely reproduce the process of the wrinkling.
Huub Eggen | alfa
'Frequency combs' ID chemicals within the mid-infrared spectral region
16.03.2018 | American Institute of Physics
Fraunhofer HHI have developed a novel single-polarization Kramers-Kronig receiver scheme
16.03.2018 | Fraunhofer-Institut für Nachrichtentechnik, Heinrich-Hertz-Institut, HHI
Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...
On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...
The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...
At the 2018 ILA Berlin Air Show from April 25–29, the Fraunhofer Institute for Laser Technology ILT is showcasing extreme high-speed Laser Material Deposition (EHLA): A video documents how for metal components that are highly loaded, EHLA has already proved itself as an alternative to hard chrome plating, which is now allowed only under special conditions.
When the EU restricted the use of hexavalent chromium compounds to special applications requiring authorization, the move prompted a rethink in the surface...
At the ILA Berlin, hall 4, booth 202, Fraunhofer FHR will present two radar sensors for navigation support of drones. The sensors are valuable components in the implementation of autonomous flying drones: they function as obstacle detectors to prevent collisions. Radar sensors also operate reliably in restricted visibility, e.g. in foggy or dusty conditions. Due to their ability to measure distances with high precision, the radar sensors can also be used as altimeters when other sources of information such as barometers or GPS are not available or cannot operate optimally.
Drones play an increasingly important role in the area of logistics and services. Well-known logistic companies place great hope in these compact, aerial...
16.03.2018 | Event News
13.03.2018 | Event News
08.03.2018 | Event News
16.03.2018 | Earth Sciences
16.03.2018 | Physics and Astronomy
16.03.2018 | Life Sciences