O'Connell Cathal D, Higgins Michael J, Marusic David, Moulton Simon E, Wallace Gordon G
ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, AIIM Facility, Innovation Campus, University of Wollongong , Wollongong, NSW 2522, Australia.
Langmuir. 2014 Mar 18;30(10):2712-21. doi: 10.1021/la402936z. Epub 2014 Mar 3.
The controlled deposition of attoliter volumes of liquid inks may engender novel applications such as targeted drug delivery to single cells and localized delivery of chemical reagents at nanoscale dimensions. Although the deposition of small organic molecules from an atomic force microscope tip, known as dip-pen nanolithography (DPN), has been extensively studied, the deposition of liquid inks is little understood. In this work, we have used a set of model ink-substrate systems to develop an understanding of the deposition of viscous liquids using an unmodified AFM tip. First, the growth of dot size with increasing dwell time is characterized. The dynamics of deposition are found to vary for different ink-substrate systems, and the change in deposition rate over the course of an experiment limits our ability to quantify the ink-transfer dynamics in terms of liquid properties and substrate wettability. We find that the most critical parameter affecting the deposition rate is the volume of ink on the cantilever, an effect resulting in a 10-fold decrease in deposition rate (aL/s) over 2 h of printing time. We suggest that a driving force for deposition arises from the gradient in Laplace pressure set up when the tip touches the substrate. Second, the forces acting upon the AFM cantilever during ink deposition were measured in order to gain insight into the underlying ink-transfer mechanism. The force curve data and simple geometrical arguments were used to elucidate the shape of the ink meniscus at the instant of deposition, a methodology that may be used as an accurate and real-time means of monitoring the volume of deposited dots. Taken together, our results illustrate that liquid deposition involves a very different transfer mechanism than traditionally ascribed to DPN molecular transport.
阿托升体积的液体油墨的可控沉积可能会催生新的应用，如将药物靶向递送至单个细胞以及在纳米尺度上局部递送化学试剂。尽管通过原子力显微镜针尖沉积小有机分子（即蘸笔纳米光刻技术，DPN）已得到广泛研究，但液体油墨的沉积却鲜为人知。在这项工作中，我们使用了一组模型油墨 - 基底系统，以了解使用未修饰的原子力显微镜针尖沉积粘性液体的情况。首先，表征了点尺寸随停留时间增加的生长情况。发现不同油墨 - 基底系统的沉积动力学各不相同，并且在实验过程中沉积速率的变化限制了我们根据液体性质和基底润湿性来量化油墨转移动力学的能力。我们发现影响沉积速率的最关键参数是悬臂上的油墨体积，这一效应导致在2小时的打印时间内沉积速率（阿托升/秒）下降了10倍。我们认为沉积的驱动力源于针尖接触基底时所建立的拉普拉斯压力梯度。其次，测量了油墨沉积过程中作用在原子力显微镜悬臂上的力，以便深入了解潜在的油墨转移机制。力曲线数据和简单的几何论证被用于阐明沉积瞬间油墨弯月面的形状，这种方法可作为一种准确且实时监测沉积点体积的手段。综上所述，我们的结果表明，液体沉积涉及的转移机制与传统上归因于DPN分子传输的机制截然不同。
