Eichelsdoerfer Daniel J, Brown Keith A, Mirkin Chad A
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA.
Soft Matter. 2014 Aug 14;10(30):5603-8. doi: 10.1039/c4sm00997e.
Here, we explore fluid transfer from a nanoscale tip to a surface and elucidate the role of fluid flows in dip-pen nanolithography (DPN) of liquid inks. We find that while fluid transfer in this context is affected by dwell time and tip retraction speed from the substrate, their specific roles are dictated by the contact angle of the ink on the surface. This is shown by two observations: (1) the power law scaling of transferred fluid with dwell time depends on contact angle, and (2) slower retraction speeds result in more transfer on hydrophilic surfaces, but less transfer on hydrophobic surfaces. These trends, coupled with the observation of a transition from quasi-static to dynamic capillary rupture at a capillary number of 6 × 10(-6), show that the transfer process is a competition between surface energy and viscosity. Based on this, we introduce retraction speed as an important parameter in DPN and show that it is possible to print polymer features as small as 14 nm. Further explorations of this kind may provide a useful platform for studying capillary phenomena at the nanoscale.
在此，我们探究了从纳米级针尖到表面的流体转移，并阐明了流体流动在液体墨水的蘸笔纳米光刻（DPN）中的作用。我们发现，虽然在这种情况下流体转移受驻留时间和针尖从基底缩回速度的影响，但其具体作用由墨水在表面的接触角决定。这通过两个观察结果得以证明：（1）转移流体与驻留时间的幂律缩放关系取决于接触角，以及（2）较慢的缩回速度在亲水性表面上导致更多的转移，但在疏水性表面上导致的转移较少。这些趋势，再加上在毛细管数为6×10⁻⁶时观察到从准静态到动态毛细管破裂的转变，表明转移过程是表面能和粘度之间的竞争。基于此，我们将缩回速度引入DPN作为一个重要参数，并表明可以打印出小至14纳米的聚合物特征。此类进一步的探索可能为研究纳米尺度的毛细管现象提供一个有用的平台。
