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Water Transport through Nanotubes with Varying Interaction Strength between Tube Wall and Water.

ABSTRACT: We present the results from extensive molecular dynamics simulations to study the effect of varying interaction strength, ?NT-OW, between the nanotube atoms and water's oxygen atom. We find the existence of a narrow transition region (?NT-OW ? 0.05 - 0.075 kcal/mol) in which water occupancy within a nanotube and flux through it increases dramatically with increasing ?NT-OW, with the exact location defined by nanotube diameter and length. This transition region narrows with increasing nanotube diameter to nearly a step-change in water transport from no flow to high water flux between ?NT-OW= 0.05 kcal/mol to 0.055 kcal/mol for tube diameter 1.6 nm. Interestingly, this transition region (?NT-OW= 0.05 - 0.075 kcal/mol) also coincides with water contact angles close to 90° on an unrolled nanotube surface hinting at a fundamental link between nanotube wetting characteristics and water transport through it. Finally, we find that the observed water flux is proportional to the average water occupancy divided by the average residence time within the nanotube, with a proportionality constant found to be 0.36, independent of the nanotube diameter and length.

SUBMITTER: Melillo M

PROVIDER: S-EPMC4297660 | biostudies-other | 2011 Oct

REPOSITORIES: biostudies-other

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Water Transport through Nanotubes with Varying Interaction Strength between Tube Wall and Water.

Melillo Matthew M Zhu Fangqiang F Snyder Mark A MA Mittal Jeetain J

The journal of physical chemistry letters 20111001 23

We present the results from extensive molecular dynamics simulations to study the effect of varying interaction strength, εNT-OW, between the nanotube atoms and water's oxygen atom. We find the existence of a narrow transition region (εNT-OW ≈ 0.05 - 0.075 kcal/mol) in which water occupancy within a nanotube and flux through it increases dramatically with increasing εNT-OW, with the exact location defined by nanotube diameter and length. This transition region na ...[more]

PMID: 25606067

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Project description:A series of one-dimensional column experiments was conducted to examine the effects of tube length on the transport and deposition of 4-ethoxybenzoic acid functionalized multi-wall carbon nanotubes (MWCNTs) in water-saturated porous media. Aqueous MWCNTs suspensions were prepared to yield three distributions of tube lengths; 0.02-1.3 ?m (short), 0.2-7.5 ?m (medium), and 0.2-21.4 ?m (long). Results of the column studies showed that MWCNT retention increased with increasing tube length. Nevertheless, more than 76% of the MWCNT mass delivered to the columns was detected in effluent samples under all experimental conditions, indicating that the functionalized MWCNTs were readily transported through 40-50 mesh Ottawa sand. Examination of MWCNT length distributions in the effluent samples revealed that nanotubes with lengths greater than 8 ?m were preferentially deposited. In addition, measured retention profiles exhibited the greatest MWCNT deposition near the column inlet, which was most pronounced for the long MWCNTs, and decreased sharply with travel distance. Scanning electron microscope (SEM) images showed that MWCNTs were deposited on sand surfaces over the entire column length, while larger MWCNT bundles were retained at grain intersections and near the column inlet. A mathematical model based on clean bed filtration theory (CBFT) was unable to accurately simulate the measured retention profile data, even after varying the weighting function and incorporating a nonuniform attachment rate coefficient expression. Modification of the mathematical model to account for physical straining greatly improved predictions of MWCNT retention, yielding straining rate coefficients that were four orders-of-magnitude greater than corresponding attachment rate coefficients. Taken in concert, these experimental and modeling results demonstrate the potential importance of, and need to consider, particle straining and tube length distribution when describing MWCNT transport in water-saturated porous media.

Dataset Information

Water Transport through Nanotubes with Varying Interaction Strength between Tube Wall and Water.

Publications

Water Transport through Nanotubes with Varying Interaction Strength between Tube Wall and Water.

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