We report the temporal evolution of the wettability of highly ordered pyrolytic graphite (HOPG) exposed to environmental conditions. Macroscopic wettability is investigated by static and dynamic contact angles (SCA and DCA) obtaining values comparable to the ones presented in the literature. SCA increases from ∼68° to ∼90° during the first hour of exposure after cleaving, whereas DCA is characterized by longer-scale (24 h) time evolution. We interpret these results in light of Fourier transform infrared spectroscopy, which indicates that the evolution of the HOPG wettability is due to adsorption of molecules from the surrounding atmosphere. This hypothesis is further confirmed by nanoscopic observations obtained by atomic force microscope (AFM)-based force spectroscopy, which monitor the evolution of surface properties with a spatial resolution superior to macroscopic experiments. Moreover, we observe that the results of macro- and nanoscale measurements evolve in similar fashion with time and we propose a quantitative correlation between SCA and AFM measurements. Our results suggest that the cause of the transition in the wettability of HOPG is due to the adsorption of hydrocarbon contaminations and water molecules from the environment. This is corroborated by annealing the HOPG is vacuum conditions at 150°, allowing the desorption of molecules on the surface, and thus re-establishing the initial macro and nano surface properties. Our findings can be used in the interpretation of the wettability of more complicated systems derived from HOPG (i.e., graphene).

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The irreversible loss of energy that occurs when a nanoscale tip vibrates over a surface can be monitored and quantified in amplitude modulation atomic force microscopy (AM AFM). Furthermore, two distinct dissipative processes can be identified and related to viscous and hysteretic forces respectively. Here, experimental evidence of a transition from viscous to hysteretic prevalent dissipation during mechanical contact is provided as the size of the tip increases from a few nm to 10 nm or more. Long range dissipation, defined as distances for which mechanical contact does not occur, is also investigated and related to capillary interactions. Experiments conducted on freshly cleaved mica samples show that energy dissipation increases with tip size and relative humidity in the long-range before mechanical contact occurs. Longand short-range interactions are discussed in terms of observables both experimentally and by numerically integrating the equation of motion.

Wetting at the nanoscale is investigated and discussed in relation to samples presenting amphiphilic domains and by employing dynamic atomic force microscopy (AFM) operating in the amplitude modulation (AM) mode. First, the capability of monitoring the growth and subsequent reduction of nanoscale water films on flat and homogeneous surfaces, i.e., graphite surfaces, with an AFM is demonstrated. The AM AFM data provide spectroscopy-like footprints of the presence and amount of water on the surface in terms of variations in nanoscale force profiles, i.e., conservative and dissipative interactions. These results are corroborated by means of attenuated total reflectance infrared spectroscopy. An important strength of the AFM technique presented here is that it allows controllably reducing invasiveness. This is particularly important in studies concerning soft matter systems. These capabilities are demonstrated on stearic acid monolayer films, soft nanoscale films that present low affinity to water, on a mica surface. The characteristic conservative and dissipative footprints of water are found on the hydrophilic mica surface only. When probing the stearic acid films, peak repulsive forces are controllably reduced until the stearic acid samples show no significant wear or damage (∼10 pN).

Active research in nanotechnology contemplates the use of nanomaterials for environmental engineering applications. However, a primary challenge is understanding the effects of nanomaterial properties on industrial device performance and translating unique nanoscale properties to the macroscale. One emerging example consists of graphene oxide (GO) membranes for separation processes. Thus, here we investigate how individual GO properties can impact GO membrane characteristics and water permeability. GO chemistry and morphology were controlled with easy-to-implement photoreduction and sonication techniques and were quantitatively correlated, offering a valuable tool for accelerating characterization. Chemical GO modification allows for fine control of GO oxidation state, allowing control of GO architectural laminate (GOAL) spacing and permeability. Water permeability was measured for eight GOALs characterized by different GOAL chemistry and morphology and indicates that GOAL nanochannel height dictates water transport. The experimental outputs were corroborated with mesoscale water transport simulations of relatively large domains (thousands of square nanometers) and indicate a no-slip Darcy-like behavior inside the GOAL nanochannels. The experimental and simulation evidence presented in this study helps create a clearer picture of water transport in GOAL and can be used to rationally design more effective and efficient GO membranes.