Lokesh Muruga, Vaippully Rahul, Nalupurackal Gokul, Roy Srestha, Bhallamudi Vidya P, Prabhakar Anil, Roy Basudev
Department of Physics, Indian Institute of Technology Madras, Chennai, 600036, India.
Department of Electrical Engineering, Indian Institute of Technology Madras, Chennai, 600036, India.
RSC Adv. 2021;11(55):34636-34642. doi: 10.1039/D1RA06960H. Epub 2021 Oct 26.
Conventionally, the work of adhesion at the nanoscale is estimated using an atomic force microscope with a tip of the size of 10 nm. It is pressed into a surface with nano-Newton forces and then retracted to ascertain when the tip breaks away from the surface. Thus this ensures "hard probing" of a surface. However there can be another configuration where the particle is barely placed into the surface when the work of adhesion attaches the particle to the surface and this can be called "soft probing". In this configuration, if a birefringent particle is confined in linearly polarized optical tweezers, and then the surface is moved in the direction tangential to the plane, a rolling motion can be induced. Study of this rolling motion can also show the work of adhesion. We use this configuration to find the rolling work of adhesion of a 3 μm diameter birefringent particle on a glass surface. We go on to study the effects of changing the surface to a hydrophobic slippery surface like polydimethyl siloxane (PDMS). Then we go on to show that even 500 nm diameter diamonds bearing nitrogen vacancy (NV) centers which are birefringent due to the stresses on the crystal could also be trapped and rolled to generate pitch (out-of-plane rotation) motion with 50 nm contact diameters. We find that this mode of soft probing yields a work of adhesion of about 1 mJ m while the conventional nanoscale probing with atomic force microscopes (AFM) yields about 50 mJ m.
传统上，纳米尺度的粘附功是使用尖端尺寸为10纳米的原子力显微镜来估计的。它以纳牛顿力压入表面，然后缩回以确定尖端何时从表面脱离。因此，这确保了对表面的“硬探测”。然而，可能存在另一种配置，即当粘附功将粒子附着到表面时，粒子几乎没有放置到表面中，这可以称为“软探测”。在这种配置中，如果一个双折射粒子被限制在线性偏振光镊中，然后表面在与平面相切的方向上移动，就可以诱导出滚动运动。对这种滚动运动的研究也可以显示粘附功。我们使用这种配置来找到直径为3μm的双折射粒子在玻璃表面上的滚动粘附功。我们接着研究将表面换成疏水性光滑表面（如聚二甲基硅氧烷（PDMS））的效果。然后我们接着表明，即使是直径为500nm且带有氮空位（NV）中心的钻石，由于晶体上的应力而具有双折射，也可以被捕获并滚动以产生接触直径为50nm的俯仰（平面外旋转）运动。我们发现这种软探测模式产生的粘附功约为1mJ/m²，而使用原子力显微镜（AFM）进行的传统纳米尺度探测产生的粘附功约为50mJ/m²。
