Effect of Airborne Hydrocarbons on the Wettability of Phase Change Nanoparticle Decorated Surfaces

Abstract

We present here a detailed study of the wettability of surfaces nanostructured with amorphous and crystalline nanoparticles (NPs) derived from the phase-change material Ge2Sb2Te5 (GST). Particular attention was devoted to the effect of airborne surface hydrocarbons on surface wetting. Our analysis illustrates that a reversible hydrophilic–hydrophobic wettability switch is revealed by combined ultraviolet-ozone (UV-O3) treatments and exposure to hydrocarbon atmospheres. Indeed, the as-prepared surfaces exhibited a hydrophilic state after thermal annealing or UV-O3 treatment which can partially remove hydrocarbon contaminants, while a hydrophobic state was realized after exposure to hydrocarbon atmosphere. Using high-angle annular dark-field scanning transmission electron microscopy for the specially designed GST NP decorated graphene substrates, a network of hydrocarbon connecting GST NPs was observed. Our findings indicate that airborne hydrocarbons can significantly enhance the hydrophobicity of nanostructured surfaces. Finally, the experiments reveal that previously defined hydrophilic materials can be used for the design of hydrophobic surfaces even if the meniscus is highly adhered to a solid surface, which is in agreement with our qualitative model involving the contribution of the nanomeniscus formed between the substrate and a decorating NP.

Tunable wettability of polymer films by partial engulfment of nanoparticles

“…In our previous study [20], a hypothesis has been formulated that the increase of the SCA of a surface could be generated by the nanomeniscus, whose existence has been proved by experiments [32][33][34] and theoretical analysis [35][36][37], formed between the substrate and the decorating NPs. Subsequently, it is reasonable to assume that the effect would become weaker when the NPs are partially submerged into the substrate, and the untreated samples have to demonstrate the highest SCA.…”

“…Therefore, the first step to check the hypothesis is to allow the Cu NPs to induce a difference in the wettability of the PMMA and then measure the variation of the wettability after high-pressure CO 2 treatments. Knowing that the surfaces with higher NP coverage C N (the ratio of the area covered with NPs with respect to the overall area as determined by the TEM images, which is the same definition used in our previous works [20,24]) tend to show large SCA [24], we started from the preparation of high-C N Cu NPs/PMMA samples. The morphology as well as the SCA of the Cu NPs decorated PMMA samples are shown in Figs.…”

“…Neither of the two widely-used Wenzel [9] and Cassie-Baxter [10] models is suitable for analyzing the wettability of the Cu NP decorated PMMA surfaces. On the one hand, the materials used in this work are relatively hydrophilic with similar contact angles (81.5 ± 0.5°for PMMA as the substrate material and 79°for Cu [20] as the NP material), which makes impossible to generate hydrophobicity within the Wenzel model. On the other hand, the Cu NPs decorated PMMA surfaces were not in the Cassie-Baxter state, because the measured large contact angle hysteresis [see Figs.…”

“…Using microsized square pillars with various sizes and concentrations, Forsberg et al [18] revealed the microscopic details of the contact line pinning behavior, and bridged the relationship between the wettability and the varied microsized decorations. Furthermore, the contact line pinning behavior could be analyzed to a nanometer scale, [16,19] where the mechanism of pinning at a nanometric scale might be attributed to the nanomeniscus formed between the substrate and the nanoscale decoration [20]. Also, simulations of the contact line pinning effect on nanoscale textured surfaces [21] and the pinning effect of a single nanoparticle [22] were conducted to give a deep understanding of the relationship between wettability and nanostructure.…”

Wettability of Nanoparticle Decorated Surfaces

“…Although micro/nanoscale surface roughness can lead even to superhydrophobicity, the control of wettability via control of the nanostructure of surfaces is far from trivial. Although the two well-known models have enabled the explanation of the wettability of surfaces with various types of morphology, several other studies 7,46,8,25,47 have demonstrated complex cases of surface wettability, where both the Wenzel and the Cassie-Baxter models could not explain the experimental data. Therefore, more efforts were devoted to understanding of the relationship between wettability and surface morphology.…”