MRI: Developing Instrumentation for Measuring Lateral Drop Adhesion

第一台测量液滴与表面间横向粘附力的仪器将在拉马尔大学建成。仪器将使用离心力驱动液滴通过接触表面。离心臂可以倾斜，使得其相对于重力水平或垂直。水平对齐将允许测量任何实际力的液滴表面横向粘附，而不是当前倾斜台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，直到液滴由于重力而向下滑动。这样，法向分量和侧向分量的完全解耦将是可能的。这种脱钩将为其他方法无法实现的测量开辟一条道路，导致目前无法实现的突破性研究。例如，修正的杨氏方程显示了每单位长度的线能量k与液滴半径之间的线性比例。因此，为了保持k与线长度无关，接触角应随液滴尺寸显著变化。正如许多研究人员所示，在实验上这不会发生，接触角的变化可以忽略不计，如果有的话，与液滴大小。所提出的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）。Lay AbstractDrops表面接触角作为表面表征的最常见方法之一，广泛应用于各种领域。液滴作为表征工具的广泛使用部分是由于其相对简单，然而，存在与这种现象的物理理解相关的许多难题，以及液滴可用作表征工具的系统的限制。我们将在拉马尔大学建立的工具将解决这些问题。它将通过允许任何液滴达到其最大和最小接触角来解决当前的限制，这对应于使液滴滑过表面所需的力。因此，它将允许对不能用旧技术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压在表面上的力（这是目前改变滑动力而不改变法向压力的唯一方式）来解决物理理解（除了将从可用系统的增加中产生的内容之外）。这种独立操纵平行于表面的力的特征将彻底改变表面科学，因为它允许解决该领域长期存在的难题。例如，长期存在的问题：为什么接触角不像理论上预期的那样随着液滴尺寸而变化。

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.