A High-Flux, Flexible Membrane with Parylene-encapsulated Carbon Nanotubes Page: 3 of 6
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A High-Flux, Flexible Membrane with Parylene-encapsulated Carbon Nanotubes
H. G. Park*, J. In**, S. Kim***, F. Fornasiero*, J. K. Holt*,
C. P. Grigoropoulos**, A. Noy* and O. Bakajin*,***
*Lawrence Livermore National Laboratory, LLNS LLC, Livermore, CA, USA, bakajin1 @llnl.gov
**Mechanical Engineering, University of California, Berkeley, CA, USA, cgrigoro @me.berkeley.edu
***NSF Center for Biophotonics Science & Technology, Univ. of California Davis, Sacramento, CA, USA
We present fabrication and characterization of a
membrane based on carbon nanotubes (CNTs) and
parylene. Carbon nanotubes have shown orders of
magnitude enhancement in gas and water permeability
compared to estimates generated by conventional theories
[1, 2]. Large area membranes that exhibit flux enhancement
characteristics of carbon nanotubes may provide an
economical solution to a variety of technologies including
water desalination  and gas sequestration . We report
a novel method of making carbon nanotube-based, robust
membranes with large areas. A vertically aligned dense
carbon nanotube array is infiltrated with parylene. Parylene
polymer creates a pinhole free transparent film by
exhibiting high surface conformity and excellent crevice
penetration. Using this moisture-, chemical- and solvent-
resistant polymer creates carbon nanotube membranes that
promise to exhibit high stability and biocompatibility. CNT
membranes are formed by releasing a free-standing film
that consists of parylene-infiltrated CNTs, followed by
CNT uncapping on both sides of the composite material.
Thus fabricated membranes show flexibility and ductility
due to the parylene matrix material, as well as high
permeability attributed to embedded carbon nanotubes.
These membranes have a potential for applications that may
require high flux, flexibility and durability.
Keywords: membrane, carbon nanotube, parylene, high-flux
Carbon nanotubes provide unique structures in studying
nanoscale mass transport and flow phenomena that can be
employed in a variety of important applications. Having
nanometer-scale diameters of innermost walls whose
graphitic surface is atomically smooth, they give rise to
newly discovered phenomena of ultra-efficient transport of
water through these ultra-narrow molecular pipes .
According to the experiment, water and gas flows through
carbon nanotubes are enhanced by 3-5 and 1-2 orders of
magnitudes, respectively, compared to conventional
theories [1, 2]. One can employ these unique nanoscale
phenomena in energy efficient filtration such as water
desalination  and gas sequestration .
For the use of the CNT-based membranes in those
applications, required are scaling up the membrane area and
keeping flexibility and durability of those large-area
membranes. To achieve this goal, choice of materials
considering chemical/biological/mechanical compatibility
with CNTs, ease of fabrication, flexibility and durability is
As a course of effort toward scaling up the size of the
carbon nanotube-based membrane, we explore a parylene-
CNT composite in terms of fabrication and mass transport
characterization. In section 2, briefly addressed are
currently available CNT-based membrane techniques and
so far revealed flow behaviors in CNTs. Properties of
parylene and its composite with CNTs will follow in
section 3. Then, we present a preliminary result of gas and
water flows through a membrane of a parylene-CNT
2 FLOW THROUGH CNTS
2.1 Water Transport - Simulation
The task of observing and understanding fluid and gas
flows in CNT pores raises a set of unique fundamental
questions . First, it is surprising that hydrophilic liquids,
especially water, enter and fill very narrow and
hydrophobic CNTs. If water does enter CNTs, what
influence does extreme confinement have on the water
structure and properties? It is important to evaluate how
these changes in structure influence the rates, efficiency,
and selectivity of the transport of liquids and gases through
CNTs. As is often the case, MD (molecular dynamics)
simulations have provided some of the first answers to
these questions. Hummer et al.  have used MD
simulations to observe the filling of a (6,6) CNT (0.81 nm
in diameter and 1.34 nm in length) with water molecules.
Surprisingly, they find that water fills the empty cavity of a
CNT within a few tens of picoseconds and the filled state
continues over the entire simulation time (66 ns). More
importantly, the water molecules confined in such a small
space form a single-file configuration that is unseen in the
bulk water. Several experimental studies also provide some
evidence of water filling of CNTs [8,9]. Further analysis of
the simulation results of Hummer et al. shows that water
molecules inside and outside a nanotube are in
thermodynamic equilibrium. This observation illustrates
one of the more important and counterintuitive phenomena
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Park, H G; In, J; Kim, S; Fornasiero, F; Holt, J K; Grigoropoulos, C P et al. A High-Flux, Flexible Membrane with Parylene-encapsulated Carbon Nanotubes, article, March 14, 2008; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc900584/m1/3/: accessed July 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.