2020年9月1日

聚合物納米纖維,小於一百人的頭發的大小,安裝在MEMS機械測試裝置。插圖顯示了兩個設備定位垂直地粘附和摩擦力量可以同時測量相交點的接觸。信貸:伊利諾伊大學香檳分校使用設備,小到可以裝在一根大頭針的針頭,伊利諾伊大學香檳分校的研究人員獲得了新知識在nanoscale-knowledge聚合物纖維的性質,可以告訴產品的設計和製造的隨機網絡絲,如強大的過濾器旨在阻止外國粒子進入我們的肺。“網絡的互聯細絲到處都是在生物學和生物工程係統中,如結締組織,蜘蛛網,和組織生長的支架,以及消費產品,如空氣過濾器,“說Debashish Das,博士後學者在航空航天工程係U的我。“這項研究提供了直接的實驗洞察粘附和摩擦的方式耦合納米長度尺度。納米纖維的材料相互強烈堅持使分離困難。即使他們強行分開,他們自發地粘在一起。獲得實驗洞察這些現象可以直接影響強烈的設計,彈性,艱難的軟納米纖維網絡。”Das explained as we examine fibers and other surfaces at micro and nanoscales, the landscape changes. "As we go smaller and smaller from the macro length scale, which are visible to unaided eye, to the micro and nanometer length scales, the surface area of particles and fibers decreases slower compared to the volume and everything becomes stickier." In a network of crisscrossing nanofibers with millions of junctions, Das conducted experiments to find out what happens at one of the overlapping junctions and to measure the force required to pull or slide two fibers apart. The diameter of just one of his nanofibers is more than one hundred times smaller than a human hair. "To understand what happens in the network at the macro scale, which is potentially comprised of billions of nanofibers, first we need to understand the mechanical phenomena at the junction where two nanofibers cross," he said. Experimenting with nanoscale fibers requires specialized micro-sized devices. Das designed and fabricated tiny machines—Micro-Electro-Mechanical Systems, or MEMS—that are smaller than one millimeter in size. "In a previous study, we used a MEMS device to stretch a single collagen fiber," he said. "In this study, we coupled two MEMS devices oriented orthogonally to push two fibers together and then separated them by sliding. While doing so we were able to simultaneously measure the force due to adhesion and due to friction. This was the first time such complete measurements were made possible for nanoscale fibers. "From our experimental measurements, we calculated the size of the contact area that is formed between the two nanofiber surfaces at their junction. As we applied a sliding force, the contact started peeling until the sliding force suddenly dropped and an instability occurred, which shows how strong adhesive properties can be at the nanoscale." Das said, "A key finding from our experiments was that the critical sliding force divided by the contact area was equal to the shear yield stress of the polymer . As we pull or stretch a polymer, at a particular stress, it will start deforming plastically and won't go back to its initial configuration. The stress at which the plastic deformation sets in is known as the yield stress of the polymer." According to Das, this is the first study to identify what is happening during the sliding of polymer nanofibers. "We tested fibers with different diameters. Each time, we found that the sliding instability occurred at a particular value of the shear stress—the tangential force divided by the contact size—that is equal to the shear strength of the polymer. This was something we didn't know before, although such a response had been reported before for metals." The study, "Sliding of adhesive nanoscale polymer contacts," was written by Debashish Das and Ioannis Chasiotis. It is published in the Journal of the Mechanics and Physics. Explore further