Size effects on water adsorbed on hydrophobic probes at the nanometric scale

Calero, Carles; Gordillo, M. C.; Martı́, Jordi

doi:10.1063/1.4807092

Cited by 10 publications

(13 citation statements)

References 59 publications

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“…Since previously reported MD simulations have shown that water molecules form a layer-like structure when interacting with the surface of a CNT, [20][21][22][23][24] the physisorbed water molecules are modeled as a layer which adheres to the previously reported density profile (see Figure 1b). [21] As illustrated by Figure 1d, the wall defects of the CNTs allow for unrestricted adsorption of Kr molecules, but since water molecules require large openings ( 0.6 nm due to an equilibrium water-CNT wall separation of ∼ 0.3 nm [21]) to access the internal region of the CNT, the adsorption of the water molecules is taken as only exohedral in nature (see Figure 2b for an illustration of the model geometry).…”

Section: Theoretical Frameworkmentioning

confidence: 99%

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Exohedral Physisorption of Ambient Moisture Scales Non-monotonically with Fiber Proximity in Aligned Carbon Nanotube Arrays

et al. 2014

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Here we present a study on the presence of physisorbed water on the surface of aligned carbon nanotubes (CNTs) in ambient conditions, where the wet CNT array mass can be more than 200% larger than that of dry CNTs, and modeling indicates that a water layer > 5 nm thick can be present on the outer CNT surface. The experimentally observed non-linear and non-monotonic dependence of the mass of adsorbed water on the CNT packing (volume fraction) originates from two competing modes. Physisorbed water cannot be neglected in the design and fabrication of materials and devices using nanowires/nanofibers, especially CNTs, and further experimental and ab initio studies on the influence of defects on the surface energies of CNTs, and nanowires/nanofibers in general, are necessary to understand the underlying physics and chemistry that govern this system.One dimensional nanoscale systems, such as nanowires, nanofibers, and nanotubes, are well known for their phenomenal electrical, [1][2][3][4] thermal, [5][6][7][8] and mechanical properties, [9][10][11] which could enable the design and manufacture of next-generation materials with unprecedented properties. [12][13][14][15][16][17][18] However, while many studies have previously explored the synthesis of new architectures and devices using one dimensional nanomaterials, specifically carbon nanotubes (CNTs), the properties they reported were far lower than the properties of predicted using current theory.[12] Some of the main reasons why existing models cannot accurately predict the behavior of CNTs in scalable architectures, such as aligned CNT arrays, are the various CNT morphology and proximity effects, [13][14][15]19] which can strongly impact properties, but are not well understood and cannot be properly integrated into theoretical frameworks. Here we report the presence of a commonly neglected morphological effect, an unexpectedly large (compared to the CNT mass) amount of moisture located on the surface of CNTs in aligned CNT (A-CNT) arrays at ambient conditions; show the non-linear and non-monotonic dependence of this effect on array porosity, which suggests two competing mechanisms; and discuss the strong impact such an effect can have on the structure and properties of nanocomposite architectures composed of A-CNTs.Previous studies on how water interacts with the outer surface of a CNT illustrated that the water molecules form a layer-like shell surrounding the CNTs, [20][21][22][23] and that the water layer density varies greatly and non- * wardle@mit.edu.monotonically with its thickness. [21,22] A recent study on the physisorption of water onto the external surface of a suspended ∼ 1.1 − 1.2 nm diameter single walled CNT showed that more than one layer of water is present on the CNT surface in water vapor, and that water molecules more easily adsorb onto larger diameter CNTs.[24] However, this study was limited to isolated and defect-free CNTs, [24,25] meaning that the interaction of moisture present in ambient air with multiwalled CNTs, which normally have nativ...

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Section: Theoretical Frameworkmentioning

confidence: 99%

“…Previous studies on how water interacts with the outer surface of a CNT illustrated that the water molecules form a layer-like shell surrounding the CNTs, [20][21][22][23] and that the water layer density varies greatly and non- * wardle@mit.edu.…”

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confidence: 99%

Exohedral Physisorption of Ambient Moisture Scales Non-monotonically with Fiber Proximity in Aligned Carbon Nanotube Arrays

et al. 2014

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“…Once the b ij coefficients are known, Calero et al [52] compute F(ρ, T) in Equation (1), as reported in Figure 2 for T = 298 K. Curves for T = 310 and 323 K (not shown) are similar to those for 298 K, but displaced to lower values of F. From the the minima and the shape of F as function of ρ and T one can evaluate the stability of the adsorbed water layer.…”

Section: Thermodynamic Stabilitymentioning

confidence: 99%

“…Calero et al [52] calculate the radial oxygen density profiles of water and the corresponding hydrogen-bond (HB) distributions. They adopt a geometrical definition of the HB in which two water molecules are H-bonded when their oxygen-oxygen distance is d OO < 3.37 Å and the OOH angle is < 30 • [54].…”

Section: Structure and Hydrogen Bondingmentioning

confidence: 99%

“…In order to perform a meaningful study of the adsorption of water on CNTs and graphene, Calero et al [52] determine the limiting densities for the thermodynamic stability of a coat of water on those substrates. For a given phase, a thermodynamically stable layer of water uniformly covers the substrate without denser or sparser regions.…”

Section: Thermodynamic Stabilitymentioning

confidence: 99%

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Structure and Dynamics of Water at Carbon-Based Interfaces

Martı́

Calero

Franzese

2017

Entropy

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Water structure and dynamics are affected by the presence of a nearby interface. Here, first we review recent results by molecular dynamics simulations about the effect of different carbon-based materials, including armchair carbon nanotubes and a variety of graphene sheets-flat and with corrugation-on water structure and dynamics. We discuss the calculations of binding energies, hydrogen bond distributions, water's diffusion coefficients and their relation with surface's geometries at different thermodynamical conditions. Next, we present new results of the crystallization and dynamics of water in a rigid graphene sieve. In particular, we show that the diffusion of water confined between parallel walls depends on the plate distance in a non-monotonic way and is related to the water structuring, crystallization, re-melting and evaporation for decreasing inter-plate distance. Our results could be relevant in those applications where water is in contact with nanostructured carbon materials at ambient or cryogenic temperatures, as in man-made superhydrophobic materials or filtration membranes, or in techniques that take advantage of hydrated graphene interfaces, as in aqueous electron cryomicroscopy for the analysis of proteins adsorbed on graphene.

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