Meso-and nanotubes

Details Meso-and nanotubes Meso-and nanotubes

2002-01-29

2003-12-23

Edwards, N. (Department: 1774)

Stock material or miscellaneous articles

Coated or structually defined flake, particle, cell, strand,...

Rod, strand, filament or fiber

C428S364000, C428S397000, C428S376000, C264S029100

Reexamination Certificate

active

06667099

ABSTRACT:

The invention relates to meso- and nanotubes, i.e. tubes or hollow fibers having an internal diameter in the nanometer to micron region, to a process for their production, and to the use of these tubes or hollow fibers.
The term hollow fibers, mesotubes or nanotubes is taken to mean tubes having an internal diameter of less than 0.1 mm.
Tubes or hollow fibers having small internal diameters are known and are employed, in particular, for separation purposes, for example in medical dialysis, for gas separation or osmosis of aqueous systems, for example for water treatment (see Kirk-Othmer, Encyclopedia of Chemical Technology, 4
th
Ed., Vol. 13, pp. 312-313). The fiber material usually consists of polymers, which may in addition have pores, i.e. properties of semi-permeable membranes. The hollow fibers used for separation purposes usually have a surface area of 100 cm
2
per cm
3
of volume with an internal diameter of from 75 &mgr;m to 1 mm.
A further application of hollow fibers is in microelectronics. Here, supraconducting fibers about 60 &mgr;m in diameter are produced from supraconducting material by filling hollow fibers made from polymers with a material which, after thermal degradation of the polymer, has supraconducting properties (J. C. W. Cien, H. Rinsdorf et al., Adv. Mater., 2 (1990) p. 305).
Tubes of small internal diameter are generally produced by extrusion spinning processes; a number of extrusion spinning processes are described in Kirk-Othmer, Encyclopedia of Chemical Technology, 4
th
Ed., Vol. 13, pp. 317-322.
With the aid of extrusion spinning processes, hollow fibers having an internal diameter of up to 2 &mgr;m can be produced. The production of hollow fibers having smaller internal diameters is not possible by this process. Very thin fibers without a cavity can be produced using the electrostatic spinning method. Here, polymer melts or polymer solutions are extruded through cannulas under a low pressure in an electric field. The principles of this method are given, for example, in EP 0 005 035, EP 0 095 940, U.S. Pat. No. 5,024,789 or WO 91/01695. With the aid of the electrostatic spinning method, solid fibers having a diameter of 10-3000 nm can be produced; however, the production of hollow fibers is not possible by this method either.
Hollow fibers having a very small internal diameter have hitherto only been accessible by electrochemical synthesis, as described in L. A. Chemozantonskii, Chem. Phys. Lett. 297, 257, (1998), by the methods of supramolecular chemistry (S. Demoustier-Champagne et al., Europ. Polym. J. 34, 1767, (1998), or using self-organizing membranes as templates (E. Evans et al., Science, Vol. 273, 1996, pp. 933-995). Hollow carbon fibers based on fullerene chemistry (carbon nanotubes having single- or multi-wall structures made from a single rolled-up graphite layer (layer of six-membered carbon rings fused to one another on all sides) or concentrically arranged graphite cylinders are described, for example, in “Fullerenes and related structures”, Ed. A. Hirsch, Springer Verlag 1999, pp. 189-234, or N. Grobert, Nachr. Chem. Tech. Lab., 47 (1999), 768-776.
Hollow fibers of ceramic materials are described in WO 97/26225, EP 0 195 353 and U.S. Pat. No. 5,094,906, hollow fibers of metals having an internal diameter of from 1 to 1000 &mgr;m are described in FR 1 511 581 and DE28 23 521.
However, these methods can only be applied to specific materials and cannot be employed for the production of industrially useful, i.e. mechanically and chemically stable, hollow fibers.
It would be desired for many applications, for example in the separation of gases, to employ hollow fibers having small external and/or internal diameters made from various materials matched to the respective area of application. In particular, the materials should be capable of withstanding thermal, mechanical and chemical loads, if desired have a porous structure, should be either electrical conductors or insulators and should consist of polymers, inorganic materials or metals.
The object of the present invention was therefore to provide hollow fibers of industrially usable materials having an internal diameter in the nm to &mgr;m range.
Surprisingly, it has been found that hollow fibers having an internal diameter in the desired dimensions can be produced precisely and from an extremely wide variety of materials, such as polymers, inorganic materials or even metals.
The present invention relates to hollow fibers having an internal diameter of from 10 nm to 1 &mgr;m and an outer wall built up from metals and/or polymers.
The hollow fibers according to the invention preferably have internal diameters of from 100 nm to 1 &mgr;m, from 500 nm to 1 &mgr;m, from 10 nm to 1 &mgr;m or from 100 nm to 500 nm.
The length of the hollow fibers is determined by the application and is generally from 50 &mgr;m to several mm or cm.
The wall thickness, i.e. the thickness of the outer walls of the hollow fibers, is variable and is generally from 10 to 5000 nm, preferably from 10 to 1000 nm, particularly preferably from 10 to 250 nm.
Besides the very small internal diameters, hollow fibers in accordance with the present invention have a number of properties which make them suitable for use in the areas of medicine, electronics, catalysis, chemical analysis, gas separation, osmosis or optics.
Thus, the outer walls of the hollow fibers according to the invention can be built up from an extremely wide variety of materials, such as, for example, from polymers, metals or inorganic metal-containing compounds. The outer walls can have one layer of these materials, i.e. can consist entirely thereof, or have a plurality of layers made from identical or different materials. The very small internal diameter ensures a very high ratio between surface area and volume of the hollow fibers; this can be between 500 and 2,000,000 cm
2
/cm
3
, preferably from 5000 to 1,000,000 cm
2
/cm
3
, particularly preferably from 5000 to 500,000 cm
2
/cm
3
.
For the purposes of the present invention, polymers are polycondensates, polyaddition compounds or products of chain growth polymerization reactions, but not graphite-like compounds of pure or doped carbon.
The present invention furthermore relates to a process for the production of the hollow fibers.
The process for the production of the hollow fibers according to the invention can be carried out by coating, at least once, a fiber of a first, degradable material with polymers and/or metals and subsequently degrading the first material, with the proviso that the hollow fiber obtained in this way has an internal diameter of from 10 nm to 1 &mgr;m.
The hollow fibers according to the invention can also contain a core, for example as shown in
FIG. 1
d
. In another embodiment of the present invention, a first, non-degradable material is coated successively with a second, degradable material and at least one further material, and the second, degradable material is degraded, with the proviso that, based on the at least one further material, a hollow fiber having an internal diameter of from 10 nm to 1 &mgr;m, an outer wall of polymers and/or metals and a core of the first material is obtained.
In the case of hollow fibers according to the invention having a core, the latter preferably has a mean distance from the outer wall of from 10 to 300 nm and can be built up from carbon fibers, ceramic fibers, polymers and/or metals. Preferred materials are presented below.
FIGS. 1
b
),
c
) and
d
) show possible embodiments of the hollow fibers and of the process for their production.
In one variant, a fiber (
FIG. 1
b
, I) of a first, degradable material is firstly coated (
FIG. 1
b
, II). This fiber can consist of a thermally, chemically, radiochemically, physically, biologically, plasma-, ultrasound- or solvent extraction-degradable material. These fibers can be produced using the electrostatic spinning method.
Details on the electrostatic spinning method are given, for example, in D. H. Reneker, I. Chun, Nanotechn. 7, 216 (1996). The principle of the construction of an electros

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