Investigating the Ubiquitous Presence of Nanometric Water Films on Surfaces

Abstract

When we speak of nanometric water films on surfaces we are speaking about a truly ubiquitous phenomenon in nature. All surfaces exposed to ambient conditions are covered by a thin film of water that affects or mediates surface chemistry, general physical-chemical processes on surfaces, and even solid–solid interactions. We have investigated this phenomenon for over a decade by exploiting dynamic atomic force microscopy and have (1) described how these layers affect apparent height measurements, (2) analyzed the excitation of subharmonics, (3) investigated its effects on surface functionality over time (“aging”), (4) monitored and quantified the time-dependent wettability of several relevant surfaces such as highly oriented pyrolytic graphite and monolayer systems, and (5) developed high-resolution and highly stable modes of imaging. Here, we discuss these findings to elucidate the present and future of the field. We further provide a brief but general discussion of solvation and hydration layers in vacuum, liquid, and air that center around current controversies and discuss open possibilities in the field.

A New Approach to Characterizing the Partitioning of Volatile Organic Compounds to Cotton Fabric

“…At this value, water molecules in the fabric are likely strongly sorbed to hydrophilic surface groups to form the first water layer, while other molecules are weakly bound to these hydrophilic groups as outer water layers. , We note that it is unlikely that a uniform film of water exists on the surface. Rather, it is generally understood that water sorbs to solids in the form of clusters of multilayer “islands”. , …”

Nanoscopic Study of Water Uptake on Glass Surfaces with Organic Thin Films and Particles from Exposure to Indoor Cooking Activities: Comparison to Model Systems

“…We note that even though AFM imaging is operated in tapping mode, when working at high RH levels, water multilayers are expected to form on hydrophilic surfaces such as glass. 70,71 There are tip−sample interactions throughout the imaging process that perturb water layers or lead to the formation of capillary bridges between the tip and surface. 72 These effects are more difficult to account for considering the differences in hydrophilicity between the glass surface and organic films and particles.…”

Hydration Dynamics and the Future of Small-Amplitude AFM Imaging in Air

“…Previous reconstruction experiments, as a function of surface aging, show that variations in the tip–surface force can be dramatic, even for a given tip and sample as the surfaces age in air ( Figure 1 ). The phenomenon that we term “aging” in this work relates to the changes that occur on a surface upon exposure to the air environment [ 35 ], including the effects that varying temperature and relative humidity (RH) might have on it over time [ 16 ]. The processes and phenomena can be molecularly identified with airborne molecules, such as hydrocarbons or water molecules [ 37 , 38 ], adhering to surfaces over time.…”

“…Molecules might permanently or semi-permanently adhere [ 39 ] and there may or may not be order and structure in such nanometric films, depending on the surface’s atomic structure and composition [ 16 ]—even when the surface is immersed in water [ 12 ]. Over the past decade, our group has been mostly interested in the role of water adsorption and the resulting adsorption kinetics and corresponding variations on nanoscale forces [ 27 , 34 , 35 , 40 ]. Nanoscale forces can be investigated by means of force–distance profiles, force of adhesion maps, or other methods [ 33 ].…”

“…Previously, we have discussed the different regimes that are available when imaging in air with small amplitudes [ 32 , 33 ] in two imaging extremes, i.e., fresh and ambient-aged samples in air environments. We have also discussed the variations of force measurements as a function of time [ 27 , 34 ] and the effects on AFM measurements due to the presence of water films on surfaces [ 35 ]. The latter line of research provides information about the evolution of force profiles, but the connection between such evolution and the emergence of force regimes is stated mostly, or only, with respect to extreme conditions, i.e., fresh samples and aged samples.…”