U.S. patent application number 10/193918 was filed with the patent office on 2003-02-06 for tubes having internal diameters in the nanometer range.
This patent application is currently assigned to CREAVIS GESELLSCHAFT F. TECHN. U. INNOVATION MBH. Invention is credited to Averdung, Johannes, Greiner, Andreas, Hou, Haoqing, Landwehr, Dierk, Wendorff, Joachim H., Zeng, Jun.
Application Number | 20030026985 10/193918 |
Document ID | / |
Family ID | 7691219 |
Filed Date | 2003-02-06 |
United States Patent
Application |
20030026985 |
Kind Code |
A1 |
Greiner, Andreas ; et
al. |
February 6, 2003 |
Tubes having internal diameters in the nanometer range
Abstract
Hollow fibers having an internal diameter from 1 nm to 100 nm
can be produced by coating degradable materials with nondegradable
materials and then degrading the degradable materials. The hollow
fibers are useful in separation technology, catalysis,
microelectronics, medical technology, materials technology or the
clothing industry.
Inventors: |
Greiner, Andreas;
(Amoeneburg, DE) ; Wendorff, Joachim H.; (Marburg,
DE) ; Hou, Haoqing; (Marburg, DE) ; Zeng,
Jun; (Marburg, DE) ; Landwehr, Dierk;
(Duelmen, DE) ; Averdung, Johannes;
(Gelsenkirchen, DE) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
CREAVIS GESELLSCHAFT F. TECHN. U.
INNOVATION MBH
Paul-Baumann Strasse 1
Marl
DE
D-45764
|
Family ID: |
7691219 |
Appl. No.: |
10/193918 |
Filed: |
July 15, 2002 |
Current U.S.
Class: |
428/373 ;
264/129; 264/209.1; 264/211.16; 264/442; 264/483 |
Current CPC
Class: |
B01J 20/28023 20130101;
D01D 5/0007 20130101; D01D 5/24 20130101; B82Y 30/00 20130101; Y10T
428/2929 20150115 |
Class at
Publication: |
428/373 ;
264/129; 264/442; 264/483; 264/209.1; 264/211.16 |
International
Class: |
D01D 005/24 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2001 |
DE |
101 33 393.5 |
Claims
1. A hollow fiber having an internal diameter from 1 nm to 100 nm
and an outer wall comprising a metal-containing inorganic compound,
a polymer, a metal or a combination thereof.
2. The hollow fiber according to claim 1, wherein said internal
diameter is from 1 nm to 10 nm.
3. The hollow fiber according to claim 1, wherein said outer wall
comprises a homopolymer, a copolymer or a blend of compounds
selected from the group consisting of poly(p-xylylene),
polyacrylamide, polyimides, polyesters, polyolefins,
polycarbonates, polyamides, polyethers, polyphenylene, polysilanes,
polysiloxanes, polybenzimidazoles, polybenzothiazoles,
polyoxazoles, polysulfides, polyester, amides,
polyarylenevinylenes, polylactides, polyether ketones,
polyurethanes, polysulfones, ormocers, polyacrylates, silicones,
aromatic copolyesters, poly-N-vinylpyrrolidone, polyhydroxyethyl
methacrylate, polymethyl methacrylate, polyethylene terephthalate,
polybutylene terephthalate, polymethacrylonitrile,
polyacrylonitrile, polyvinyl acetate, neoprene, Buna N,
polybutadiene, polytetrafluoroethene, modified cellulose,
unmodified cellulose, alginates, and collagen.
4. The hollow fiber according to claim 1, wherein said outer wall
comprises a metal or an alloy of metals selected from the group
consisting of metals of groups Ia, Ib, Ia, IIb, IIIa, IIIb, IVa,
IVb, Vb, VIb, VIb, VIIb of the periodic table, and mixtures
thereof.
5. The hollow fiber according to claim 1, wherein said outer wall
comprises glass, glass ceramics, SIO.sub.x, perovskite, ceramics,
aluminas or zirconias.
6. The hollow fiber according to claim 1, wherein said outer wall
comprises a plurality of layers.
7. The hollow fiber according to claim 1, having a dielectric
constant of less than 4.
8. A process for preparing a hollow fiber, comprising: coating a
fiber of a first, degradable material with at least one coating of
at least one second material; and degrading the first, degradable
material to obtain the hollow fiber; wherein said hollow fiber has
an internal diameter from 1 nm to 100 nm.
9. The process according to claim 8, wherein the first, degradable
material comprises 10-60% by weight of a noble metal salt.
10. The process according to claim 8, wherein the first, degradable
material further comprises a basic compound.
11. The process according to claim 8, wherein the second material
comprises an inorganic compound, a polymer, a metal or a mixture
thereof.
12. The process according to claim 8, wherein the second material
comprises homopolymers, copolymer or blends of compounds selected
from the group consisting of poly(p-xylylene), polyacrylamide,
polyimides, polyesters, polyolefins, polycarbonates, polyamides,
polyethers, polyphenylene, polysilanes, polysiloxanes,
polybenzimidazoles, polybenzothazoles, polyoxazoles, polysulfides,
polyester amides, polyarylenevinylenes, polylactides, polyether
ketones, polyurethanes, polysulfones, ormocers, polyacrylates,
silicones, aromatic copolyesters, poly-N-vinylpyrrolidone,
polyhydroxyethyl methacrylate, polymethyl methacrylate,
polyethylene terephthalate, polybutylene terephthalate,
polymethacrylonitrile, polyacrylonitrile, polyvinyl acetate,
neoprene, Buna N, polybutadiene, polytetrafluoroethene, modified
cellulose, unmodified cellulose, alginates, and collagen.
13. The process according to claim 8, wherein the second material
comprises a metal or an alloy of metals selected from the group
consisting of metals of groups Ia, Ib, Ia, IIb, IIa, IIIb, IVa,
IVb, Vb, VIb, VIb, VIIb of the periodic table, and mixtures
thereof.
14. The process according to claim 8, wherein the second material
comprises metal oxides, glass, glass ceramics SiO.sub.x,
perovskite, ceramics, aluminas, silicon carbide, boron nitride,
carbon or zirconias.
15. The process according to claim 8, wherein the second material
is obtained by polymerization of one or more monomers.
16. The process according to claim 15, wherein the second material
is obtained by homopolymerization or copolymerization of a compound
selected from the group consisting of methacrylate, styrene,
styrene sulfonate, 1,6-hexamethylene diusocyanate,
4,4'-methylenebiscyclohexyl dilsocyanate,
4,4'-methylenebis(benzyl-diisocyanate), 1,4butanediol,
ethylenediamine, ethylene, styrene, butadiene, 1-butene, 2-butene,
vinyl alcohol, acrylonitrile, methyl methacrylate, vinyl chloride,
fluorinated ethylenes, terephthalate or mixtures thereof.
17. The process according to claim 8, wherein the degrading of the
first, degradable material is effected thermally, chemically,
biologically, radiation-induced, photochemically, by plasma, by
ultrasound or by extraction with a solvent.
18. A separation medium or storage medium for gases, liquids or
particle suspensions, comprising: the hollow fiber according to
claim 1.
19. A method for removal of a metabolite or an enzyme from
cytoplasm, comprising: contacting said cytoplasm with the hollow
fiber according to claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to nanotubes, i.e., tubes or hollow
fibers having an internal diameter in the nanometer range, to a
process for their production and to the use of these tubes or
hollow fibers.
[0003] 2. Discussion of the Background
[0004] Hollow fibers, mesotubes and nanotubes are generally tubes
having an internal diameter of less than 0.1 mm.
[0005] Tubes or hollow fibers having a small internal diameter are
known and are employed in particular for separation duties, 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.sup.th Ed., Vol. 13, pp.
312-313). The fiber material usually comprises polymers, which may
in addition have pores, i.e. properties of semipermeable membranes.
The hollow fibers used for separation duties usually have a surface
area of 100 cm.sup.2/cm.sup.3 of volume coupled with an internal
diameter of from 75 .mu.m to 1 mm.
[0006] A further application of hollow fibers is in micro
electronics. Here, superconducting fibers about 60 .mu.m in
diameter are produced using superconducting material by filling
hollow polymeric fibers with a material which, after
thermodegradation of the polymer, possesses superconducting
properties (J. C. W. Cien, H. Ringsdorf et al., Adv. Mater., 2
(1990) p. 305).
[0007] Tubes having a 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.sup.th Ed., Vol 13, pp. 317-322.
[0008] Extrusion spinning processes provide hollow fibers having an
internal diameter of down to 2 .mu.m. However, the production of
hollow fibers having smaller internal diameters is not possible by
these processes.
[0009] Very thin fibers without internal cavity can be produced by
electrostatic spinning, or electrospinning. In electrospinning,
polymer melts or polymer solutions are extruded through cannulas
under a low pressure in an electric field. The principles of this
technique are described, for example, in EP 0 005 035, EP 0 095
940, U.S. Pat. No. 5,024,789 or WO 91/01695. Electrospinning
provides solid fibers which are 10-3000 nm in diameter; but not
hollow fibers.
[0010] Hollow fibers having a very small internal diameter have
hitherto only been obtainable by electrochemical synthesis, as
described in L. A. Chernozantonskii, Chem. Phys. Lett. 297, 257,
(1998), by methods of supra molecular chemistry (S.
Demoustier-Champagne et al., Europ. Polym. a. 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-walled structures made of 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).
[0011] However, these methods can only be applied to specific
materials and cannot be employed to produce industrially useful,
i.e. mechanically and chemically stable, hollow fibers.
[0012] Hollow fibers having internal diameters in the .mu.m range
are known. For instance, WO 97/26225, EP 0 195 353 and U.S.
5,099,906 disclose hollow fibers which are composed of ceramic
materials and have an internal diameter of at least 1 .mu.m. Hollow
fibers which are composed of metals and have an internal diameter
of 1-1 000 .mu.m are described in FR 12 11 581 and DE 28 23
521.
[0013] WO 01/09414 discloses meso- and nanotubes having internal
diameters in the range from 10 nm to 50 pm that are preferably
produced by electrospinning. However, the electrospinning process
disclosed therein does not allow the production of smaller fibers,
since a fiber produced when the material to be spun is thinned out
to any degree is irregular and has thick portions.
[0014] There are many applications, for example the separation of
gases, in which it is desirable to employ hollow fibers having very
small external and/or internal diameters that are composed of
various materials optimized to the particular area of application.
More particularly, the materials should be capable of withstanding
thermal, mechanical and chemical stresses, if desired have a porous
structure, selectively be electrical conductors or insulators and
be composed of polymers, inorganics or metals.
SUMMARY OF THE INVENTION
[0015] It is therefore an object of the present invention to
provide hollow fibers of industrially usable materials that have an
internal diameter in the nm range.
[0016] This and other objects have been achieved by the present
invention the first embodiment which includes a hollow fiber having
an internal diameter from 1 nm to 100 nm and an outer wall
comprising a metal-containing inorganic compound, a polymer, a
metal or a combination thereof.
[0017] In another embodiment the present invention provides a
process for preparing a hollow fiber, comprising:
[0018] coating a fiber of a first, degradable material with at
least one coating of at least one second material; and
[0019] degrading the first, degradable material to obtain the
hollow fiber;
[0020] wherein said hollow fiber has an internal diameter from 1 nm
to 100 nm.
[0021] In yet another embodiment the present invention relates to a
method for removal of a metabolite or an enzyme from cytoplasm,
comprising:
[0022] contacting said cytoplasm with the hollow fiber.
BRIEF DESCRIPTION OF DRAWINGS
[0023] FIG. 1 shows an electrospinning apparatus, embodiments of
hollow fiber, and a process for production of the hollow fiber.
[0024] FIG. 2 shows a scanning electron photomicrograph of
polylactide template fibers.
[0025] FIG. 3 shows a tunneling electron micrograph of polylactide
template fibers.
[0026] FIG. 4 shows a tunneling electron photomicrograph of
polyamide template fibers.
[0027] FIG. 5 shows a scanning electron micrograph of
poly(p-xylene) fibers.
[0028] FIG. 6 shows a scanning electron micrograph of
poly(p-xylene) fibers.
[0029] FIG. 7 shows a tunneling electron photomicrograph of
poly(p-xylene) fibers.
[0030] FIG. 8 shows a tunneling electron micrograph of
poly(p-xylene) fibers.
[0031] FIG. 9 shows a wide angle X-ray graph.
DETAILED DESCRIPTION OF THE INVENTION
[0032] It has been surprisingly found that hollow fibers having an
internal diameter in the desired run range are producible in a
precise manner from a wide variety of materials such as polymers,
inorganics or even metals.
[0033] The present invention accordingly provides a hollow fiber
having an internal diameter from 1 nm to 100 nm and an outer wall
constructed of metal-containing inorganic compounds, metals and/or
polymers or combinations thereof.
[0034] The internal diameter of the hollow fibers according to the
invention is preferably in the range from 1 nm to 5 nm, more
preferably in the range from 1 nm to 9 nm and most preferably in
the range from 1 nm to 5 nm. The internal diameter includes all
values and subvalues therebetween, especially including 1.5, 2.5,
3, 3.5, 4 and 4.5 nm.
[0035] The hollow fiber length is determined by the intended use
and is generally in the range of from 50 .mu.m up to several mm or
cm. The hollow fiber length includes all values and subvalues
therebetween, especially including 100, 200, 300, 400, 500, 600,
700, 800, 900 .mu.m; 1, 2, 3, 4, 5, 6, 7, 8, 9 mm; 1, 2, 3, 4, 5,
6, 7, 8 and 9 cm.
[0036] The wall thickness, i.e., the thickness of the outer wall of
the hollow fiber, is variable and is generally in the range from 1
to 500 nm, preferably in the range of from 1 to 100 nm and more
preferably in the range from 10 to 25 nm. The thickness of the
outer wall includes all values and subvalues therebetween,
especially including 10, 50, 100, 150, 200, 250, 300, 350, 400 and
450 nm.
[0037] Hollow fibers according to the present invention as well as
the very small internal diameters, have a number of properties
which make them suitable for use in the fields of medicine,
electronics, catalysis, chemical analysis, gas separation, osmosis
or optics.
[0038] Thus, the outer wall of the hollow fiber according to the
present invention can be constructed from the most diverse
materials, for example from polymers, metals or metal containing
inorganic compounds. The outer wall can have one layer of these
materials, i.e., consist entirely thereof or have a plurality of
layers composed of the same or different materials. The very small
internal diameter ensures a very high ratio of hollow fiber surface
area to volume which can be between 500 and 2 000 000
cm.sup.2/cm.sup.3, preferably in the range from 5 000 to 1 000 000
cm.sup.2/cm.sup.3 and more preferably in the range from 5 000 to
500 000 cm.sup.2/cm.sup.3. The ratio of hollow fiber surface area
to volume includes all values and subvalues therebetween,
especially including 1,000; 10,000, 50,000, 100,000, 200,000,
300,000, 400,000, 500,000, 600,000, 700,000, 800,000, 900,000,
1,000,000, 1,200,000, 1,400,000, 1,600,000 and 1,800,000
cm.sup.2/cm.sup.3.
[0039] The metal-containing inorganic compounds of the hollow fiber
according to the invention are for example metal oxides, metal
mixed oxides, spinel, metal nitrides, metal sulfides, metal
carbides, metal aluminates or metal titanates. Boron compounds or
metal-doped carbon nanotubes having single- and 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 not metal-containing
compounds for the purposes of the present invention. Materials
similar to carbon nanotubes having concentrically arranged
polyhedral or cylindrical layer structures such as for example
WS.sub.2, MoS.sub.2 and VS.sub.2 are likewise not metal-containing
compounds for the purposes of the present invention.
[0040] For the purposes of the present invention, the polymers are
polycondensates, polyaddition compounds or products of chain growth
polymerization reactions, but not graphite-like compounds composed
of pure or doped carbon.
[0041] The present invention further provides a process for
producing the hollow fiber.
[0042] The process for producing the hollow fiber according to the
present invention comprises coating a fiber of a first, degradable
material with at least one further material. Subsequently, the
first material is degraded in such a way that the hollow fiber thus
obtained has an internal diameter from 1 nm to 100 nm.
[0043] In a preferred embodiment of the process, the first,
degradable material may be admixed with 0.1-10% by weight of a
basic compound, such as pyridine which is preferable when
polyamides are used and can be used for example as a solvent
additive in electrospinning. The amount of basic compound includes
all values and subvalues therebetween, especially including 0.5, 1,
1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9 and
9.5% by weight.
[0044] In another preferred embodiment of the process, the
degradable material is admixed with 10-60% by weight and preferably
25-50% by weight of a noble metal salt. The amount of noble metal
includes all values and subvalues therebetween, especially
including 20, 30, 40 and 50% by weight. Preference is given to
platinum, nickel, cobalt, rhodium and palladium salts of organic
acids, such as acetate or formate. It is also possible to add the
hereinbelow specified metals of groups I to XIII, a and b of the
periodic table. This embodiment of the process makes is possible to
produce nanotubes having small noble metal crystals on the inner
surface. These nanotubes are especially useful as catalysts. It is
also possible to apply the above two embodiments of the process at
the same time.
[0045] Preferred embodiments of the hollow fiber and of the process
for production thereof are illustrated in FIG. 1 (b and c).
[0046] In another embodiment preferred of the process, the initial
step comprises subjecting a fiber (FIG. 1, b, I) composed of a
first, degradable material to a coating operation (FIG. 1, b, II).
This fiber may be composed of a material which is degradable
thermally, chemically, radiochemically, physically, biologically or
by means of plasma, ultra-sound or extraction with a solvent. These
fibers may be produced by electrospinning.
[0047] Details concerning electrospinning technology are described,
for example in D. H. Reneker, I. Chun., Nanotechn. 7, 216 (1996).
The basic construction of an electrospinning apparatus is shown in
FIG. 1 (a).
[0048] The diameter of the degradable fibers should be in the same
order of magnitude as the later desired internal diameter of the
hollow fibers. In general, the later cavity in the hollow fibers is
of approximately the same size as the diameter of the degradable
fibers or coatings. The precise dimensions depend on the materials
used and their changes during the degradation operation and can be
determined without difficulty by preliminary experiments. Useful
degradable fiber materials include organic or inorganic materials,
especially polymers such as polyesters, polyethers, polyolefins,
polycarbonates, polyitrethanes, natural polymers, polylactides,
polyglycosides, poly-a-methylstyrene and/or polyacrylonitriles. The
electrospinning process also makes it possible to produce
multicomponent fibers, i.e., fibers having different materials in
different layers or fibers having a certain surface topography,
i.e., having smooth or porous surfaces.
[0049] The surface finish of the fiber or layer of degradable
materials also determines the surface topography of the subsequent
coatings. If, for example, a rough or micro structured inner
surface is desired for the hollow fibers, this can be achieved by
means of a correspondingly rough fiber of a degradable material.
Rough or microstructured fibers can be obtained by electrospinning
a polymer solution containing a volatile solvent. Furthermore,
additives such as salts, for example sodium sulfate, metallic
nanopowders, conductive polymers such as polypyrroles or graphite
can distinctly enhance the conductivity of the spun material.
[0050] The coating with the at least one further nondegradable
material can be effected by gas phase deposition, plasma
polymerization or application of the material in a melt or in
solution. The coating can be effected in various layers and using
various materials and forms the outer wall of the hollow fiber.
[0051] This coating, i.e. the construction of the outer walls can
be effected for example by gas phase deposition, knife coating,
spin coating, dip coating, spraying or plasma deposition of
polymers such as poly(p-xylylene), polyacrylamide, polyimides,
polyesters, polyolefins, polycarbonates, polyamides, polyethers,
polyphenylene, polysilanes, polysiloxanes, polybenzimidazoles,
polybenzothiazoles, polyoxazoles, polysulfides, polyester amides,
polyarylenevinylenes, polylactides, polyether ketones,
polyurethanes, polysulfones, ormocers, polyacrylates, silicones,
aromatic copolyesters, poly-N-vinylpyrrolidone, polyhydroxyethyl
methacrylate, polymethyl methacrylate, polyethylene terephthalate,
polybutylene terephthalate, polymethacrylonitrile,
polyacrylonitrile, polyvinyl acetate, neoprene, Buna N,
polybutadiene, polytetrafluoroethene, cellulose (modified or
unmodified), alginates or collagen, homopolymers or copolymers
and/or blends thereof.
[0052] Furthermore, the degradable layers or fibers may be coated
with a further material obtained by polymerization of one or more
monomers. Preferred monomers for the homo- or copolymerization
include, for example, methacrylate, styrene, styrenesulfonate,
1,6-hexamethylene diisocyanate (HDI),
4,4'-methylenebiscyclo-hexyl-diisocyanate (HMDI),
4,4'methylenebis-(benzyl-diisocyanate) (MDI), 1,4-butanediol,
ethylenediamine, ethylene, styrene, butadiene, 1-butene, 2-butene,
vinyl alcohol acrylonitrile, methyl methacrylate, vinyl chloride,
fluorinated ethylenes and/or terephthalates.
[0053] The coating, i.e., the construction of the outer wall of the
hollow fibers, can be composed of metals of the groups la, Ib, Ia,
IIb, IIa, IIIb, IVa, IVb, Vb, VIb, VIIb and/or VIIIb of the
periodic table, each as a pure metal or as an alloy. Preferred
metals include for example gold, palladium, aluminum, platinum,
silver, titanium, cobalt, ruthenium, rhodium, sodium, potassium,
calcium, lithium, vanadium, nickel, tungsten, chromium, manganese
and/or silicon. The coating can be effected by vapor deposition of
the metals or by decomposition of suitable organometal-containing
compounds using chemical vapor deposition (CVD) methods.
[0054] Polymeric coating materials may further bear functional
groups such as esters, amides, amines, silyl groups, siloxane
groups, thiols, hydroxyl groups, urethane groups, carbamate groups,
nitrite groups, C.dbd.C groups, C.dbd.C groups, carboxylic acid
halide groups, sulfoxide groups, sulfone groups, pyridyl groups,
arylphosphine groups or else ionic groups such as carboxylic acids,
sulfonic acids or quaternary amines. The functional groups can be
attached to the inner and/or outer surface of the hollow fibers to
improve the surface properties of the hollow fibers in separation
or osmosis processes. The functional groups can also be chemically
modified subsequently by polymer-analogous reactions, for example
by hydrolysis of esters.
[0055] Appropriate functionalization, furthermore, can be used to
have active ingredients such as antibiotics, anesthetics, proteins
such as insulin, antifouling agents and agrochemicals such as
herbicides or fungicides reversibly fixed in the hollow fibers
and/or gradually released again in specific concentrations at a
controlled rate.
[0056] The outer wall of the hollow fibers, i.e., the nondegradable
further material, can also be constructed of glass, glass ceramics,
SiO.sub.x, perovskite, ceramics, aluminas or zirconias, optionally
of silicon carbide, boron nitride, carbon and metal oxides. Useful
methods here likewise include gas phase deposition processes (CVD
or physical vapor deposition (PVD)) or else hydrothermal
processes.
[0057] Preferred perovskites have the general formula
LaXYMgO
[0058] wherein X=Ca, Sr or Ba; and Y=Ga or Al; (without
stoichiometry) which have oxygen ion conductance properties.
[0059] The degradation of the degradable material can be effected
thermally, chemically, radiation-induced, biologically,
photochemically or by means of plasma, ultrasound or extraction
with a solvent. Thermal degradation is particularly preferred in
practice. The decomposition conditions vary with the material
ranging from 100 to 500.degree. C. and from 0.001 mbar to 1 bar,
particularly preferably from 0.001 to 0.1 mbar. The decomposition
temperature includes all values and subvalues therebetween,
especially including 150, 200, 250, 300, 350, 400 and 450.degree.
C. The decomposition pressure includes all values and subvalues
therebetween, especially including 0, 005, 0.01, and 0.05 mbar.
Degradation of the material provides a hollow fiber whose wall
material is composed of the coating materials.
[0060] As shown in FIG. 1 (b and c), it is also possible for a
plurality of layers of different materials to be applied to the
fiber. This provides hollow fibers having different inner and outer
surfaces or hollow fibers where the outer walls can be constructed
of a plurality of layers. The different layers can perform
different functions in that, for example, the inner layer can have
particular separation properties for chromatographic purposes, for
example, and the outer layer can have high mechanical
stability.
[0061] The following layer sequences for the hollow fibers
according to the invention may be mentioned by way of example:
[0062] glass/metal
[0063] metal/glass
[0064] glass/polymer
[0065] polymer/glass
[0066] polymer/polymer
[0067] metal/metal
[0068] metal-containing inorganic compound/metal-containing
inorganic compound
[0069] ceramic/ceramic
[0070] polymer/metal
[0071] metal/polymer
[0072] ceramic/polymer
[0073] polymer/ceramic
[0074] metal/ceramic
[0075] ceramic/metal
[0076] polymer/metal/polymer
[0077] metal/polymer/metal
[0078] metal/ceramic/metal
[0079] polymer/ceramic/polymer
[0080] ceramic/polymer/ceramic
[0081] polymer/glass/polymer
[0082] glass/polymer/glass.
[0083] Hollow fibers according to the present invention are useful
in particular as a separation or storage medium for gases, liquids
or particle suspensions and for filtering or purifying compositions
of matter. Preferred applications here are as a membrane for gases,
especially H.sub.2 or liquids, for particle filtration, in
chromatography, for oil/water separation, as an ion exchanger in
dialysis, for size separation of cells, bacteria or viruses, as a
constituent of an artificial lung, for desalination, for drainage
or irrigation or as a filter for dewatering power fuels.
[0084] Hollow fibers according to the invention may further be used
in sensor technology for solvent, gas, moisture or biosensors, in
capillary electrophoresis, in catalytic systems, in scanning probe
microscopy or as materials of construction in superlightweight
building construction, as a mechanical reinforcement similar to
glass fibers, as a noise or vibration abate, as a composite
material or filler, as a controlled release or drug delivery
system, in medical separation technologies, in dialysis, as an
artificial lung, as a protein store or in tissue engineering.
[0085] The hollow fibers according to the invention may be used in
the clothing/textile industry as a thennal insulator in clothing or
sleeping bags, in photo- or thermochromic clothing through
embedding of dyes in the tube interior or as an authenticator
through markers in the tubes interior.
[0086] Hollow fibers according to the invention also find use in
electronics, optics or energy production the hollow fibers can be
used to produce wires, cables or capacitors, micromachines (for
example for piezoelectric, shaping, nanoperistaltic pumps or for
shaping photoadrressable polymers) or interlayer dielectrics.
Further uses for hollow fibers according to the invention are
microreactors, for example for catalytic reactions, template
reactions and bioreactions, heat generation through conversion of
sunlight (solar a systems) or in chip technology as flexible
devices or microscopy as a sensor constituent (for example; as tips
or probes for scanning probe microscopes br SNOM instruments).
[0087] The hollow fibers according to the present invention have a
very low dielectric constant and therefore can also be used as a
dielectric, in particular as an interlayer dielectric in electronic
components. For example, in chip manufacture, interlayer
dielectrics having a low dielectric constant are important in the
production of new chip generations having even smaller dimensions
or higher storage densities due to the high proportion of included
air per unit volume. The hollow fibers according to the invention
have a dielectric constant of less than 4, preferably less than 3,
most preferably less then 2, ideally less than 1.5.
[0088] The hollow fibers are preferably used as a web or mat for
dielectric applications due to the large surface area of the hollow
fibers according to the invention, these can also be used in fuel
cells, batteries or electrochemical reactions. For such uses, the
outer wall of the hollow fibers is advantageously composed of
oxygen ion conductors, for example perovskites. In oxidation
reactions, the hollow fibers may be surrounded by the reactant, an
olefin for example, while oxygen is passed through the cavities of
the fibers. The oxidation product is formed on the outside of the
hollow fibers and transported away.
[0089] The hollow fibers according to the present invention can be
used as a catalytic system. It is thus possible, for example, to
use hollow fibers composed of noble metals such as platinum or
palladium as denoxing catalysts in motor vehicles.
[0090] Hollow fibers according to the invention which are composed
of cell-compatible materials or have appropriately modified
surfaces can be incorporated introduced into cell membranes and
used for the separation and also recovery or removal of
metabolites, enzymes and other components of the cytoplasm within
cells or cytoplasmic components and hence for the recovery of
biopharmaceuticals.
[0091] Having generally described this invention, a further
understanding can be obtained by reference to certain specific
examples which are provided herein for purposes of illustration
only, and are not intended to be limiting unless otherwise
specified.
EXAMPLES
Example 1
Production of Polylactide Template Fibers by Electrospinning
[0092] A 5% solution of poly-L-lactide in dichloromethane
(conductivity <10.sup.-7 .mu.s/cm) containing 50% by weight of
Pd(OAc).sub.2, based on the polylactide, was electrospun at a
voltage of 48 kV in the apparatus of FIG. 1 (a). The separation of
the cannula tip (diameter 0.3 mm) from the substrate plate (glass)
was 10 cm. The fibers were further used without further treatment.
A scanning electron photomicrograph of the fibers is shown in FIG.
2. FIG. 3 shows a tunneling electron micrograph of the material
thus obtained.
Example 2
Production of Polyamide Template Fibers by Electrospinning
[0093] An 8% solution of nylon 46 containing 2% by weight of
pyridine, based on N46, in formic acid was electrospun at a voltage
of 55 kV in the apparatus shown in FIG. 1(a). The separation of the
cannula tip (diameter 0.3 mm) from the substrate plate (glass) was
15 cm. The fibers were further used without further treatment. A
tunneling electron photomicrograph of the fibers is shown in FIG.
4.
Example 3
Production of poly(p-xylylene) Hollow Fibers by Coating from the
Gas Phase
[0094] Polyamide template fibers produced by electrospinning as per
Example 1 were placed in a gas phase deposition apparatus.
Subsequently 37 mg of analytically pure [2.2] paracyclophane were
evaporated at 220.degree. C./0.1 mbar and pyrolyzed at 800.degree.
C., causing the formation of 25 poly(p-xylene) (PPX) in the sample
space at about 20.degree. C.
[0095] The poly(p-xylylene) polylactide composite fabric was
extracted with chloroform for 24 hours. The formation of
poly(p-xylylene) hollow fibers having an internal diameter from
about 6 to 20 nm was confinmed by scanning electron microscopy
(FIGS. 5, 6).
Example 4
Production of poly(p-xylylene) Hollow Fibers by Coating from the
Gas Phase
[0096] Polyamide template fibers produced by electros: pinning as
per Example 2 were placed in a gas phase deposition apparatus.
Subsequently 37 mg of analytically pure [2.2]paracyclophane were
evaporated at 220.degree. C./0.1 mbar and pyrolyzed at 800.degree.
C., causing the formation of poly(p-xylylene) (PPX) in the sample
space art about 20.degree. C.
[0097] The poly(p-xylylene) polyamide composite was extracted with
fonmic acid for 24 hours. The formation of the hollow fibers having
an internal diameter of 45 nm is discernible from the tunneling
electron photomicrograph in FIG. 7.
Example 5
Production of poly (p-xylylene)/Hollow Fibers by Coating from the
Gas Phase
[0098] Polylactide template fibers produced by electrospinning as
per Example 1 were placed in a gas phase deposition apparatus.
Subsequently 40 mg of analytically pure [2.2]paracyclophane were
evaporated at 220.degree. C./10.1 mbar and pyrolyzed at 700.degree.
C., causing the formation of poly(p-xylylene) in the sample space
at about 20.degree. C. The poly(p-xylylene) polylactide composite
fabric was thenmally treated in a vacuum oven at 285.degree.
C./0.01 mbar for 8 hours. The fonmation of poly(p-xylylene)/hollow
fibers laving an average internal diameter of about 17 nm was
confirmed by scanning electron microscopy (FIG. 8).
[0099] Thermal degradation gives palladium crystallites 4-10 nm in
size on the inner surface of the tube is shown in FIG. 8. FTIR
spectroscopy confirms the degradation of the polylactide. The
conversion of palladium acetate to metal-containing palladium is
confirmed by wide angle X-ray spectroscopy (FIG. 9).
[0100] German patent application 10133393.5, filed Jul. 13, 2001,
is incorporated herein by reference.
[0101] Numerous modifications and variations on the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *