Liquid dispensing and writing by a nano-grooved pin
  Liquid dispensing and writing in the extremely small size regime are important for applications in many current technologies, such as micro/nano fabrication, biological/chemical patterning and analysis, and drug discovery. Most of current dispensing/writing methods can be sorted into a category of liquid flowing through tiny tubes or nozzles that requires inputting an impulse energy, which leads to complex procedures, expensive equipment and narrow material applicability, especially for biomaterials. Here, we report a method that may lead to a new category: liquid flows over the tapered surface of a pin with longitudinal nano grooves on the surface to uninterruptedly perform droplet dispensing and direct writing. The dispensed droplet diameters were controllable from several microns down to 150 nm, and the written line heights were as low as 5 nm. The mechanism underlying automatic liquid storage on conical surface and spontaneous liquid transport through nano grooves is revealed and well modeled by a simple relationship. Furthermore, the nano-grooved pins are much simpler and cheaper in fabrication than nanoscale tubes and nozzles, and pins have much depressed clogging problems that are typically troublesome for tubes and nozzles. Our new strategy may constitute a basis for creating liquid dispensing/writing technologies that are simultaneously smaller, simpler, faster and applicable for more types of materials. 
Hualai Dong, Xing Yang, Cunjing Lv, Quanshui Zheng
cond-mat.soft physics.flu-dyn physics.optics