Nanoimmiscibility: Selective Absorption of Liquid Methanol–Water Mixtures in Carbon Nanotubes

Abstract

Despite the continuing research interests in CNT-liquid systems, the microscopic structure and transport behavior of liquid mixtures in carbon nanotubes (CNTs) remain poorly understood. Methanol and water liquids are completely miscible across the entire range of concentration; however, recent research reveals that they are immiscible at a molecular level. In this work, we carried out classical molecular dynamics to study the molecular distribution, structure ordering, clustering and transport behavior of liquid methanol-water mixtures within CNT confinement. We found that CNTs preferentially absorbed methanol over water molecule even though the latter has a smaller molecular size, indicating that chemical effect such as molecular hydrophilicity plays a crucial role in the molecular absorption of CNTs. Due to the selective absorption of CNTs, methanol aqueous solution changes from microscopically immiscible to macroscopically immiscible at nanoscale. This nanoscale immiscibility may be utilized in various applications of CNTs including direct methanol fuel cells, nanosensors, molecular sieves, nanofluidic chips, and capsules for drug delivery.

Alcohol-induced drying of carbon nanotubes and its implications for alcohol/water separation: A molecular dynamics study

“…Inspired by these findings, in this paper, we investigate whether SWNTs can be used to separate alcohols, which are also hydrophilic, from their aqueous solutions. We note here that, the selective adsorptions of methanol 28,29 and ethanol 30, 31 over water onto SWNTs' inner surfaces had been recently observed by some researchers through computer simulations. However, a systematic investigation of adsorption of alcohols inside SWNTs is still lacking, and the physical mechanism underlying the aforementioned selective adsorption of alcohols inside nanotubes is still not very clear.…”

Small Molecules and Peptides Inside Carbon Nanotubes: Impact of Nanoscale Confinement

“…These results also have implications on understanding the urea-induced denaturation of proteins by providing further evidence of the potential existence of a "dry globule"-like transient state [65] during early stage of protein unfolding and the "direct interaction mechanism" whereby urea attacks protein directly via favorable dispersion interaction, rather than disrupts water structure as a "water breaker". In addition, this study points out the crucial role of dispersion interaction in the selective absorption of molecules inside hydrophobic nanopores [54][55][56], which might be important for nanoscience and nanotechnology.…”

“…Molecules confined inside nanoscale space such as narrow nanotubes or membrane proteins can form one-dimensional (1D) molecular wires, which have attracted intense interest recently because of their scientific importance and potential applications in nanotechnology [1,21,[40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56]. Among them, it is of particular interest in determining the structure and dynami-cal behavior of water wires [1,21,[40][41][42][43][44][45][46][47][48][49] which have been found to exist in narrow nanotubes [1,21,[40][41][42][46][47][48] and biological channels [43][44][45].…”

“…Water wires have many interesting properties, such as wavelike density distributions [1,46], rapid and concerted motions [1,40,43], orientation-ordered structures and collective flips [1,21,41,48], and excellent on-off gating behaviors [46,47]. In addition, it has been observed that the methane [56], methanol [54], and gas molecules (O 2 , H 2 , and CO 2 ) [55] preferentially bind to the interiors of narrow SWNT over water and form 1D molecular wires. Despite the above progress, the properties of molecular wires have not been fully understood, particularly for the molecular wires formed by larger polar organic molecules.…”

Collective Effect of Fluid's Coriolis Force and Nanoscale's Parameter on Instability Pattern and Vibration Characteristic of Fluid-Conveying Carbon Nanotubes

“…Fluid-conveying CNTs have broad application in nanofluidicdevice, biomedical, and nanomedicine procedures [1][2][3]. Experimental background indicates that fluid can flow inside the CNTs in both form of aligned bundle embedded in a membrane [4], or an individual CNT without having surrounding medium [5,6].…”