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8 Fast Transport of Liquids and Gases Through Carbon Nanotubes

8 Fast Transport of Liquids and Gases Through Carbon Nanotubes

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7 Nanomechanics – Nanophotonics – Nanofluidics

Fig. 7.37 (a) Structure of the hydrogen-bonded water chain inside a carbon nanotube (CNT)

[7.136]. (b) High-resolution transmission electron micrograph (HRTEM) of the cross-section of

a double-walled carbon nanotube (DWNT) in a Si3 Nx membrane [7.137]. (Reprinted with permission from [7.136] (a) and [7.137] (b). © 2001 Nature Publishing Group (a) and © 2006 AAAS (b))

configuration (Fig. 7.37a) that is unseen in bulk water. Such 1D hydrogen-bonded

structures are highly reminiscent of the water wires observed in the biological

aquaporin water-transporting channels (see Sect. 11.5) with also a hydrophobic

lining inside (see [7.135]). In CNTs, the friction at the channel walls is so low

that the water transport is no longer governed by Hagen–Poiseuille flow, but

nanotube entrance and exit. The calculated water transport rates approach 5.8

water molecules per nanosecond per nanotube, similar to the transport rates in

aquaporins (see [7.135]), yet – due to the different dimensions of the two systems – one cannot imply that the same mechanism is responsible for CNTs

and aquaporins.

The experimentally determined water transport rates in sub-2 nm double wall

carbon nanotube (DWNT, Fig. 7.37b) membranes reveal a flow enhancement that

is at least 2–3 orders of magnitude faster than no-slip, hydrodynamic flow calculated using the Hagen–Poiseuille equation whereas the calculated slip length for

sub-2 nm CNTs is as large as hundreds of nanometers, which is almost three orders

of magnitude larger than the pore size [7.135]. The measured water flux compares

well with that predicted by MD simulations (see [7.135]).

MD simulations further show that water infiltration into and defiltration out of

CNTs is influenced by gas molecules [7.138].




7.8.3 Gas Transport in CNTs

MD simulations (see [7.135]) show that gas flux in CNTs reaches a value almost

three orders of magnitude higher than in zeolites with equivalently sized pores.

Transport of hydrogen in CNTs is calculated to be as fast as 10 cm2 /s due to the

predominantly specular nature of the molecule-wall collisions inside the CNTs.

The measured gas flows are up to 100 times higher than the predictions of the

conventional Knudsen model for gas transport (see [7.135]).

7.9 Nanodroplets

Nanodroplets are of interest in a variety of fields. As discussed in the following, the behavior of water in nanoconfinement can be studied in water nanopools

enclosed in reverse micelles [7.139]. Nanoscale emulsions are extensively used by

the foods, cosmetic, and coating industries, where double emulsions provide the

ability to carry both polar and non-polar cargos [7.140]. By employing zeptoliter

(10−21 l) alloy droplets, the crystallization mechanisms of nanometer-sized fluid

drops can be investigated [7.141] and in suprafluid He nanodroplets, spectroscopy

and low-temperature chemical reactions of molecules can be performed [7.142] (see


7.9.1 Dynamics of Nanoscopic Water in Micelles

A wide variety of biological processes occurs in very crowded aqueous surroundings with the solvating water often playing an important role. Thus it has been shown

that the dynamics of water in the first hydration layer of a protein are slowed down

relative to bulk water. Fluctuations in this hydration shell may dictate internal protein motions [7.143]. The dynamics of water in the nanopores of Nafion fuel-cell

membranes differ substantially from those of bulk water and vary with the hydration level (pore size) of the membrane (see [7.139]). This makes the understanding

of the properties of water in confined environments and near interfaces desirable.

The dynamics of water confined in two different types of reverse micelles (see

Fig. 7.38) in dependence of the diameter of the water pool can be studied by

spectroscopy of the OD stretch of HOD in H2 O [7.139]. Reverse micelles of the

surfactant AOT (ionic head group) in isooctane and of the surfactant Igepal CO520

(non-ionic head group) in cyclohexane/hexane are prepared with the same diameter

of 4 nm of the water nanopools. The infrared absorption spectra of the hydroxyl

stretch are in both micelles blue shifted relative to bulk water. The orientational

dynamics of the water molecules are found to be very similar for the confined water

in the two types of reverse micelles and slowed down compared to bulk water. The

results demonstrate that confinement by an interface to form a nanoscopic water

pool is the primary factor governing the dynamics of nanoscopic water rather than

the presence of the charged groups at the interface.


7 Nanomechanics – Nanophotonics – Nanofluidics

Fig. 7.38 A protonated

non-ionic aqueous inverse

micelle with the neutral

surfactant diethylene glycol

monodecyl ether

[CH3 (CH2 )11 (OC2 H4 )2 OH]

(C12 E2 ). Oxygens (red),

hydrogens (white), surfactants

(cyan), and hydronium (blue,

larger size). (Reprinted with

permission from [7.144].

© 2009 Royal Society of


7.9.2 Nanoscale Double Emulsions

Water-in-oil-in-water (WOW) double emulsions can be prepared by using block

copolypeptide surfactants with the structure poly(L-lysine · HBr)x -b-poly(racemicleucine)y , Kx (rac-L)y (Fig. 7.39a). For the preparation of a nanoscale double emulsion, ultrasonic homogenization is used to generate a K40 (rac-L)20 emulsion with

subsequent passages through a microfluidic homogenizer and ultra-centrifugation,

yielding droplets ranging from 10 to 100 nm in diameter (Fig. 7.39b). The compartmentalization of hydrophilic quantum dots (red) into the inner aqueous phase,

hydrophobic pyrene (blue) into the oil phase and the labeled polypeptide (green)

stabilizing the outer interface is shown in Fig. 7.39c.

7.9.3 Zeptoliter Liquid Alloy Droplets and Surface-Induced


The controlled delivery of fluids is a key process in many areas of science and

technology. The volume of a droplet from an inkjet printer is about 2 picoliters

(2 × 10−12 l) [7.145]. Recently a pipette has been developed [7.141], which,

observed by electron microscopy, delivers a Au72 Ge28 alloy melt with zeptoliter

(10−21 l = 1 zl) resolution. The liquid–solid transition provides evidence for a crystallization pathway of nanosized fluid drops that avoids nucleation in the interior, but

instead proceeds via liquid-state surface faceting as a precursor to surface-induced





Fig. 7.39 (a) Structure of the Kx (rac-L)Y block copolypeptide surfactant. (b) Cryogenic transmission electron micrograph of size-fractionated double emulsion droplets isolated from a

K40 (rac-L)20 -stabilized double emulsion by centrifugation and ultra-centrifugation. Scale bar,

200 nm. (c) Fluorescence micrographs of double emulsions containing polar and non-polar cargos.

Double emulsion stabilized by FITC-labeled K40 (rac-L)10 , loaded with both pyrene and quantum

dots. The oil phase fluoresces blue because of the entrapped pyrene and the internal aqueous phase

fluoresces red because of encapsulation of InGaP quantum dots. The polypeptides are labeled with

fluorescein isothiocyanate (FITC) and therefore fluoresce green; scale bar, 5 μm. (Reprinted with

permission from [7.140]. © 2008 Nature Publishing Group)

The zeptoliter pipette with the Au–Ge alloy (Fig. 7.40a) encapsulated in a multilayer shell of crystalline carbon (Fig. 7.40b) is heated in a transmission electron

microscope above the eutectic temperature TE = 361◦ C. The expulsion of alloy melt

(Fig. 7.40d) with an initial volume of 3 zl is triggered by opening a pipette “nozzle” in the C-shell by briefly focusing a tight (∼ 1 nm) electron beam onto the shell

(Fig. 7.40c). The high pressure (>1 GPa) generated by the C-shell [7.146] plays the

key role of driving the fluid flow and expulsion.

The “pendant droplet” geometry (Fig. 7.40d) permits the observation that

a few centigrades above the crystallization point, the droplets develop surface

facets (Fig. 7.40e, f) which continuously form and decay without showing distinct reflections characteristic for crystalline order. From this it is concluded

[7.141] that the nanoscale liquid Au72 Ge28 droplets close to crystallization

develop some degree of ordering, at least locally, in the areas showing transient



7 Nanomechanics – Nanophotonics – Nanofluidics

Fig. 7.40 Dispensing and surface-induced crystallization of zeptoliter liquid Au72 Ge28 droplets.

(a) Fluid Au–Ge melt reservoir encapsulated into a multilayer carbon shell (b). (c) Opening of the

carbon coating by a nanometer electron beam and expulsion of a Au–Ge melt droplet (d) during

operation of the zeptoliter pipette at 425◦ C. (e–f) Transient faceting of a 30 nm Au72 Ge28 liquid

droplet near the liquid–solid phase transition. The same droplet is imaged at various times. The

arrows mark extended planar surface facets. (g) Frozen in crystalline shape of a “free” Au72 Ge28

cluster. Transmission electron micrograph (TEM) of a crystalline cluster that underwent extensive

transient surface faceting in the liquid state. (h) Projections of the icosahedral motif bounded by

(111) facets, oriented to match the facets in the upper left section of the cluster shown in (g).

(Reprinted with permission from [7.141]. © 2007 Nature Publishing Group)

Lowering of the temperature induces freezing of the pendant droplets with transient surface faceting into a cluster shape containing faceted segments that match the

projection of an icosahedral cluster (Fig. 7.40g, h). Given the preference of larger

Au nanoclusters for the stable fcc structure and truncated octahedron morphology,

the formation of facets with icosahedral symmetry suggests (see [7.141]) crystallization originating at close-packed (111)-like surface planes, that is, a surface-induced

crystallization templated by the transient surface facets of “free” liquid droplets.

7.9.4 Superfluid Helium Nanodroplets

Helium nanodroplets (Fig. 7.41a) with typical diameters of 4.4 nm containing about

103 4 He atoms are used as containers for spectroscopy with little broadening due




Fig. 7.41 (a) Computer simulation showing an OSC molecule inside a 4 He droplet made up

of 500 atoms; 4 He blue, O red, S yellow, C black. (b–c) Results of density-functional calculations of the dependence of particle density (PD) on droplet radius (RD ) of a pure 4 He droplet of

N = 1000 atoms (b) [7.142] and a 4 He droplet of N = 1000 atoms doped with a single SF6 molecule

(c) [7.147]. (Reprinted with permission from [7.142] (a) (b) and [7.147] (c). © 2004 Wiley-VCH

(a) (b) and © 1998 American Institute of Physics (c))

to the superfluid characteristics and for the synthesis of new molecular complexes

[7.142]. By doping, e.g., with an SF6 molecule, a strong restructuring of the He

droplet density appears (Fig. 7.41c) compared to the homogeneous density of a pure

4 He droplet (Fig. 7.41b). The temperature of 4 He droplets from free jet gas expansion is about 0.4 K whereas the temperature of 3 He droplets is ≈ 0.15 K. For SF6

in 4 He droplets sharp rotational lines of the vibrational transition can be observed

where, however, the moments of inertia are about three times higher than in the gas

phase which is attributed to a stronger coupling of the molecular rotation to the 4 He

bath [7.142].

Nanodroplets of ultracold helium can serve as nanoscopic cryoreactors for

probing reactions of, e.g., alkali–metal clusters with water clusters [7.148].

For para-H2 (pH2 ) it was predicted [7.149] that, since at low temperatures paraH2 molecules are spinless bosons, these molecules might undergo a transition to a

superfluid state, which may be located between 2 and 3 K (see [7.142]. It was additionally predicted [7.150] that small pH2 clusters with less than 18 molecules should

remain fluid at T = 0 and exhibit superfluidity below about 2 K. From rotational

spectroscopy of pH2 clusters with n = 14–17 molecules in helium droplets a large

decrease in the moment of inertia was observed, much below the expected classical


7 Nanomechanics – Nanophotonics – Nanofluidics

value. This is considered to be a manifestation of superfluidity of pH2 clusters (see

[7.142]) which is also studied theoretically [7.151].

7.10 Nanobubbles

Gas–liquid two-phase system with bubbles down to sub-micrometer scales play a

role as contrast agents for ultrasound imaging, aerated food and personal care products, and foamed construction materials (see [7.152]). In addition, highly stable

nanobubbles are present, e.g., on hydrophobized surfaces submerged in water (see

[7.153]). Furthermore, as finally discussed her, a single electron immersed into liquid helium forms a nanobubble which can be employed for tracking the motion of

the electron [7.154].

7.10.1 Stable Surface Nanobubbles

Surface nanobubbles (diameter ∼ 100 nm) on hydrophobic surfaces submerged in

water (see Fig. 7.42) appear to be much more stable than anticipated taking into

account the high Laplace pressure inside the bubbles causing a fast diffusive outflux of gas. This stability has been modeled by a dynamic equilibrium mechanism

[7.155]. It is, moreover, demonstrated [7.153] that these nanobubbles do not act as

nucleation sites for shock wave-induced cavitation on surfaces.

Fig. 7.42 Atomic force

micrograph (AFM) of

nanobubbles on a Si (100)

wafer hydrophobized by a

layer of 1H, 1H, 2H, 2H-perfluorodecyldimethylchlorosilane

(PFDCS) and immersed in

water. (Reprinted with

permission from [7.153].

© 2007 American Physical


7.10.2 Polygonal Nanopatterning of Stable Microbubbles

A nanometer-scale hexagonal patterning of microbubbles (Fig. 7.43) can arrest the

shrinkage of bubbles and identify a route to fabricate highly stable dispersions of

microbubbles [7.152].




Fig. 7.43 Nanotextured surfaces of microbubbles. (a) Transmission electron micrograph (TEM)

of a micrometer-sized bubble covered with hexagons ∼ 50–100 nm in diameter. The platinum

shadowing of the surface replica reveals that the domains are buckled outward. (b) Schematic of

the air–liquid interfacial structure. The domains are modeled with spherical caps whose geometry (a, Rc ) results from the packing of sucrose mono- and distearate (red and blue), respectively.

(Reprinted with permission from [7.152]. © 2008 AAAS)

A very stable gas dispersion can be obtained by trapping air into sucrose

stearate surfactant shells within a viscous glucose syrup bulk phase with gas cells

ranging from hundreds of nanometers to tens of micrometers [7.152]. Hexagonal

nanometer-scale domains that buckle outward from the bubble fully cover the air–

liquid interface (Fig. 7.43a). This structuring originates from the self-assembly of

the sucrose stearate surfactant molecules with the hydrophilic head groups (in the

aqueous phase) occupying substantially more surface area than the microbubbles

(Fig. 7.43b). According to thermodynamic modeling [7.152], the bending elasticity of the nanoscale domains resists the compression of the interface and, thereby,

stops or substantially reduces bubble shrinkage. This gives rise to the observed

longevity of the dispersion.

7.10.3 Bubbles for Tracking the Trajectory of an Individual

Electron Immersed in Liquid Helium

An electron injected into liquid helium forms a tiny bubble (diameter ∼ 4 nm)

around itself (see [7.154]) due to the repulsive interaction between the electron and

the electrons of the helium atoms, which arises from the Pauli exclusion principle. A


7 Nanomechanics – Nanophotonics – Nanofluidics

Fig. 7.44 Image of a bubble with an electron moving under the combined influence of an upward

convective flow of liquid He at 2.4 K and an electric field of –150 V applied to the electrode

shown as a bright spot at the top of the window. (b) Image of an electron bubble following a

snake-like track which may relate to the electron being trapped on and sliding along a vortex line

in superfluidic He at 1.5 K. (Reprinted with permission from [7.154]. © 2009 American Physical


negative pressure in an acoustic pulse causes the electron bubble to expand to about

10 μm making it visible due to strong light scattering.

Figure 7.44a shows an electron bubble moving upward in liquid He at 2.4 K

following the convective fluid flow until it is deflected to the left by a repelling –

150 V voltage applied to an electrode. In Fig. 7.44b an electron bubble is shown

moving in superfluid liquid He at 1.5 K. The zigzag motion evident in this picture

can be attributed to the trapping of the electron on the core of a quantized vortex line

yielding a constraint to follow the meandering of the vortex core across the cell. The

electron bubble can be trapped on the vortex because of the Bernoulli force exerted

on the bubble that arises from the increasing velocity of the superfluid flow near the

vortex core.

7.11 Summary

Mechanical, optical, and fluid properties of nanostructures are of growing interest.

Nanoelectromechanical systems (NEMSs) are used for sub-single charge electrometry, single-electron spin paramagnetic resonance, zeptogram mass sensing,

zeptonewton sensing and they can also provide a way to observe the imprint of

quantum phenomena directly. The transition from mechanics to quantum mechanics

is going to be studied by means of high-frequency laser-cooled NEMS structures. Nanomaterials mimicking gecko toes are developed for bioinspired adhesion.

Single-photon and entangled-photon sources and photon detectors based on quantum dots may be most useful for quantum communication and computation.

Plasmon excitation on metallic nanostructure is of interest for sensors, medical therapy, and potential invisibility cloaks. Nanophotonics can be unified with



nanomechanics and nanofluidics. Fluid properties may be significantly altered on

the nanoscale by surface interactions. The boundary conditions for a fluid on a wall

depend on the wetting properties – no-slip for a wetting situation and slip lengths

of some tens of nanometers in a non-wetting situation or on superhydrophobic surfaces. The hydrophobic walls in carbon nanotubes give rise to transport of water

and gas by orders of magnitudes faster than in other pores of the same size, similar to the transport mechanism in biological membrane ion channels. Nanodroplets

in emulsions are used extensively by the foods, cosmetics, and coating industries

and double emulsions provide the ability to carry both polar and non-polar cargos.

In 4 nm water nanodroplets, the dynamics of water molecules are slowed down

compared to bulk water. Nanobubbles in gas–liquid systems play a role as contrast

agents for ultrasound imaging, aerated food, and personal care products.
































M. Li et al., Nature 456, 480 (2008)

D. Psaltis et al., Nature 442, 381 (2006)

C. Monat et al., Nat. Photon. 1, 106 (2007)

A.H.J. Yang et al., Nature 457, 71 (2009)

H.G. Craighead, Science 290, 1532 (2000)

S.C. Masmanides et al., Science 317, 780 (2007)

A.N. Cleland, M.L. Roukes, Nature 392, 160 (1998)

D. Rugar et al., Nature 430, 329 (2004)

C.L. Degen et al., Phys. Rev. Lett. 100, 137601 (2008); C.L. Degen et al., Proc. Natl.

Acad. Sci. 106, 1313 (2009)

Y.T. Yang et al., Nano Lett. 6, 583 (2006)

T.P. Burg et al., Nature 446, 1066 (2007)

H.J. Mamin, D. Rugar, Appl. Phys. Lett. 79, 3358 (2001)

A. Naik et al., Nature 443, 193 (2006)

W.C. Fon et al., Nano Lett. 5, 1968 (2005)

K.C. Schwab, M.L. Roukes, Phys. Today. 58 (7), 36 (2005)

P. Curie, J. Curie, Bull. Soc. Minéral. Fr. 3, 90 (1880)

M. Li et al., Nat. Nanotechnol. 2, 114 (2007)

X.L. Feng et al., Nat. Nanotechnol. 3, 342 (2008)

H.B. Peng et al., Phys. Rev. Lett. 97, 087203 (2006)

B. Witkamp et al., Nano Lett. 6, 2904 (2006)

A.M. Fennimore et al., Nature 424, 408 (2003)

W.W. Jang et al., Appl. Phys. Lett. 92, 103110 (2008)

J. Eisert, Phys. J. 6 (3), 22 (2007)

A. Schliesser et al., Nat. Phys. 4, 415 (2008)

W. Marshall et al., Phys. Rev. Lett. 91, 130401 (2003)

P. Ball, Nature 453, 22 (2008)

M. Schlosshauer, Decoherence and the Quantum-to-Classical Transition (Springer,

Heidelberg, 2007)

F. Károlyházy, Nuovo Ciment. 52, 390 (1966)

R. Penrose in Mathematical Physics 2000, eds. by A. Fokas et al. (Imperial College,

London, 2000), p. 226

V.B. Braginsky, F. Ya. Khalili, Quantum Measurements (Cambridge University Press,

New York, 1992)


7 Nanomechanics – Nanophotonics – Nanofluidics






























M.D. LaHaye et al., Science 304, 74 (2004)

D. Vitali et al., Phys. Rev. Let. 98, 030405 (2007)

I. Wilson-Rae et al., Phys. Rev. Lett. 92, 075507 (2004)

S. Mancini et al., Phys. Rev. Lett. 88, 120401 (2002)

M. Pinard et al., Europhys. Lett. 72, 747 (2005)

S. Gigan et al., Nature 444, 67 (2006)

D. Kleckner, D. Bouwmeester, Nature 444, 75 (2006)

A. Schliesser et al., Phys. Rev. Lett. 97, 243905 (2006)

A.N. Cleland, Nat. Physics 5, 458 (2009)

S. Etaki et al., Nat. Phys. 4, 785 (2008)

M.P. Blencowe, Nat. Phys. 4, 753 (2008)

E.P. Chan et al., MRS Bull. 32, June 2007, p. 496

K. Hammerer et al., Phys. Rev. Lett. 102, 020501 (2009)

A. Jagota et al., MRS Bull. 32, June 2007, p. 492

B.N. J. Person, MRS Bull. 32, June 2007, p. 486

C. Creton, S. Grob, MRS Bull. 32, June 2007, p. 466

K. Autumn, Am. Sci. March-April 2006, p. 124

Y. Tian et al., Proc. Natl. Acad. Sci. USA 103, 19320 (2006)

L.H. Ge et al., Proc. Natl. Acad. Sci. USA 104, 10792 (2007)

H.S. Lee et al., Nature 448, 338 (2007)

A. Mahdavi et al., Proc. Natl. Acad. Sci. USA 105, 2307 (2008)

S. Reddy et al., Adv. Mater. 19, 3833 (2007)

K.A. Daltorio et al., MRS Bull. 32, June 2007, p. 504

N.M. Pugno, J. Phys.: Condens. Matter 19, 395001 (2007)

B. Yurdumakan et al., Chem. Commun. 30, 3799 (2005)

L.T. Qu et al., Science 322, 238 (2008)

P. Michler et al., Science 290, 2282 (2000)

P. Michler, C. Becher, Physikal. Blätter 57 (9), 55 (2001)

D. Bouwmeester, A. Ekert, A. Zeilinger, The Physics of Quantum Information (Springer,

Berlin 2000)

B. Lounis, M. Orrit, Rep. Prog. Phys. 68, 1129 (2005)

Z.L. Yuan et al., Science 295, 102 (2002)

S. Kako et al., Nat. Mater. 5, 887 (2006)

S. Strauf et al., Nat. Photo. 1, 704 (2007)

A. Högele et al., Phys. Rev. Lett. 100, 217401 (2008)

A. Einstein et al., Phys. Rev. 47, 777 (1935)

J.S. Bell, Rev. Mod. Phys. 40, 229 (1968)

N. Akopian et al., Phys. Rev. Lett. 96, 130501 (2006)

R.M. Stevenson et al., Nature 439, 179 (2006)

O. Benson, Phys. J. 5, Nr. 4, 22 (2006)

J.C. Blakesley et al., Phys. Rev. Lett. 94, 067401 (2005)

E.J. Gansen et al., Nat. Photon. 1, 585 (2007)

D. Bimberg et al., MRS Bull. July 2002, p. 531

R. Dingle, C.H. Henry, U.S. Patent No. 3, 982, 207 (1976)

H. Saito et al., Appl. Phys. Lett. 69, 3140 (1996)

R. Schur et al., Jpn. J. Appl. Phys., Part 2: Lett. 35, L357 (1997)

J.A. Lott et al., Electron. Lett. 33, 1150 (1997)

N.N. Ledentsov et al., Memories of the Institute of Scientific and Industrial Research,

vol. 57 (March 2001), special issue “Advanced Nanoelectronics: Devices, Materials and

Computing”, 3rd Sanken International Symposium (ISIR, Osaka, 2000), p. 80

V.I. Klimov, M.G. Bawendi, MRS Bull. Dec. 998 (2001)

Y.T. Chan et al., Appl. Phys. Lett. 86, 073102 (2005)

Nat. Nanotechnol. 3, 5 (2008)






















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