The Czech Academy of Sciences , Institute of Scientific Instruments , Královopolská 147 , 61264 Brno , Czech Republic.
Center for Nonlinear Dynamics and Department of Physics , University of Texas at Austin , Austin , Texas 78712 , United States.
Langmuir. 2019 Apr 30;35(17):5809-5820. doi: 10.1021/acs.langmuir.8b04074. Epub 2019 Apr 19.
The adhesion of micro- and nanoparticles to solid substrates immersed in liquids is a problem of great scientific and technological importance. However, the quantitative characterization of such nanoscale adhesive contacts without rupturing them still presents a major experimental challenge. In this article, we introduce mechanical contact spectroscopy (MCS), an experimental technique for the nondestructive probing of particle adhesion in liquid environments. With MCS, the strength of adhesive contacts is inferred from residual position fluctuations of adherent particles excited by thermal forces. In particular, the strength of adhesion is correlated with the standard deviation of the particle lateral position x, with smaller position standard deviations [Formula: see text] indicating higher adhesive strength. For a given combination of particles, substrate, and immersion medium, the adhesion is characterized by the mechanical contact spectrum, which is a histogram of ξ values obtained from tracking an ensemble of adherent particles. Because the energy of thermal excitation at room temperature is very small in comparison to the typical total energy of adhesive contacts, the studied contacts remain in equilibrium during the measurement. Using MCS, we study the adhesion of micrometer-sized particles to planar solid substrates under a wide range of environmental conditions, including liquid immersion media of varying ionic strength and adhesion substrates with different chemical functionality of their surfaces. These experiments provide evidence that MCS is capable of reproducibly detecting minute changes in the particle-substrate work of adhesion while at the same time covering the range of adhesive contact strength relevant in the context of surface chemistry, biology, and microfabrication.
浸入液体中的微纳米颗粒与固体基底的附着是一个具有重要科学和技术意义的问题。然而，在不破坏它们的情况下，对这种纳米级粘附接触进行定量描述仍然是一个主要的实验挑战。在本文中，我们介绍了机械接触光谱学（MCS），这是一种用于在液体环境中无损探测颗粒附着的实验技术。利用 MCS，通过热作用力激发的附着颗粒的残余位置波动，可以推断出粘附接触的强度。具体来说，粘附强度与附着颗粒横向位置 x 的标准偏差[Formula: see text]相关联，较小的位置标准偏差[Formula: see text]表示较高的粘附强度。对于给定的颗粒、基底和浸液组合，粘附强度由机械接触谱来表征，这是通过跟踪一组附着颗粒获得的 ξ 值的直方图。由于室温下热激励的能量与典型的粘附接触总能量相比非常小，因此在测量过程中研究的接触处于平衡状态。我们利用 MCS 研究了在广泛的环境条件下，包括具有不同离子强度的浸液介质和具有不同表面化学功能的粘附基底，微米级颗粒与平面固体基底之间的粘附。这些实验证明，MCS 能够在同时覆盖与表面化学、生物学和微制造相关的粘附接触强度范围的情况下，重复检测到颗粒-基底粘附功的微小变化。
