MRI: Developing Instrumentation for Measuring Lateral Drop Adhesion

技术摘要拉马尔大学将建造第一台此类仪器，用于测量液滴与表面之间的横向附着力。该仪器将利用离心力驱动液滴通过接触表面。离心臂可以倾斜，使其相对于重力水平或垂直。水平对准将允许测量任何实际作用力的滴面侧向粘附力，而不是当前倾斜阶段方法的非常弱的粘附力限制。然而，在垂直对准中，离心机将修改法向力，直到由于重力而使液滴向下滑动。有了这一点，法向分量和横向分量的完全分离将是可能的。这种脱钩将为测量开辟一条道路，否则是不可能的，导致目前无法进入的开创性研究。例如，修正的Young方程显示了单位长度的线能量k与液滴半径之间的线性比例关系。因此，为了保持k与直线长度无关，接触角应该随液滴大小而变化很大。正如许多研究人员所表明的那样，从实验上看，这种情况不会发生，接触角随液滴大小的变化几乎可以忽略不计。该仪器将解决理论和实验之间长期存在的差异(仅举一个例子)。在许多领域中，表面液滴接触角是最常见的表面表征方法之一。液滴作为表征工具的广泛使用在一定程度上是由于其相对简单，然而，与对这一现象的物理理解相关的许多谜题，以及对液滴用作表征工具的系统的限制。我们将在拉马尔大学建造的仪器将解决这些问题。它将通过允许任何液滴达到其最大和最小接触角来解决目前的限制，最大和最小接触角对应于滑动液滴通过表面所需的力。因此，它将允许对用旧技术无法表征的系统进行适当的液滴表征。它还将通过允许改变滑动液滴所需的力而不同时改变液滴在表面上的压力(这是目前在不改变正常压力的情况下改变滑动力的唯一方法)来解决物理上的理解(除了可用系统的增加所产生的)。这种独立操纵平行于表面的力的特征将使表面科学发生革命性的变化，因为它可以解决该领域长期存在的难题。例如，一个长期存在的问题：为什么接触角没有像理论上预期的那样随着液滴的大小而变化。

Technical AbstractA first instrument of its kind to measure lateral adhesion forces between drops and surfaces will be build in Lamar University. The instrument will use centrifugal forces to drive drops past contacting surfaces. The centrifugal arm could tilt so that it would be either horizontal or perpendicular with respect to gravity. The horizontal alignment will allow measurements of drop-surface lateral adhesions of any practical force as opposed to the very weak adhesive force limitation of the current tilt stage method. In the vertical alignment, however, the centrifuge will modify the normal force until the drop will slide down due to gravity. With this, a complete decoupling of the normal and lateral components will be possible. Such decoupling will open a way for measurements that are otherwise impossible, leading to breaking ground research that is currently inaccessible. For example, the modified Young equation shows linear proportionality between the line energy per unit length, k, and the radius of the drop. Therefore to keep k independent of line length, the contact angle should change considerably with drop size. As shown by many investigators, experimentally this does not happen, the contact angle changes negligibly, if at all, with drop size. The proposed instrument will address this long standing discrepancy between theory and experiment (just to name one example).Lay AbstractDrops contact angle on surfaces serve as one of the most common ways for surface characterization in a wide variety of fields. The vast use of drops as characterization tools is in part due to its relative simplicity, yet, there are many puzzles associated with the physical understanding of this phenomenon, as well as limitations on the systems with which drop can be used as a characterization tool. The instrument that we will build at Lamar University will address these issues. It will address the current limitations by allowing any drop to reach its maximal and minimal contact angles, which correspond to the force required to slide the drop past the surface. Thus it will allow proper drop characterization for systems that could not have been characterized with older techniques. It will also address the physical understanding (in addition to what will emanate from the increase in available systems) by allowing to vary the force required to slide the drop without varying at the same time the force by which the drop presses on the surface (this is the only way currently to vary the sliding force without varying the normal pressing force). This feature of independent manipulation of the force parallel to the surface will revolutionize surface science as it allows addressing long standing puzzles in the field. For example the long standing question: why the contact angle does not change with drop size as expected theoretically.