U.S. patent application number 11/342725 was filed with the patent office on 2007-02-01 for assembly of free-standing films using a layer-by-layer process.
Invention is credited to Nicholas A. Kotov, Arif A. Mamedov.
Application Number | 20070023957 11/342725 |
Document ID | / |
Family ID | 22710903 |
Filed Date | 2007-02-01 |
United States Patent
Application |
20070023957 |
Kind Code |
A1 |
Kotov; Nicholas A. ; et
al. |
February 1, 2007 |
Assembly of free-standing films using a layer-by-layer process
Abstract
A method for the layer-by-layer assembly of a free standing thin
film includes the steps of preparing a support with a suitable
substrate; forming a thin film having a plurality of layers onto
the substrate utilizing a layer-by-layer assembly process; removing
the substrate and thin film from the support; and separating the
substrate from the thin film. Various compounds improving the
strength, flexibility, tension and other mechanical properties may
be included in the assembly to improve the structural quality of
the film. Similar effect may also be achieved by cross-linking the
applied layers.
Inventors: |
Kotov; Nicholas A.;
(Superior, MI) ; Mamedov; Arif A.; (Stillwater,
OK) |
Correspondence
Address: |
FELLERS SNIDER BLANKENSHIP;BAILEY & TIPPENS
THE KENNEDY BUILDING
321 SOUTH BOSTON SUITE 800
TULSA
OK
74103-3318
US
|
Family ID: |
22710903 |
Appl. No.: |
11/342725 |
Filed: |
January 30, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09818001 |
Mar 27, 2001 |
7045087 |
|
|
11342725 |
Jan 30, 2006 |
|
|
|
60192750 |
Mar 28, 2000 |
|
|
|
Current U.S.
Class: |
264/255 |
Current CPC
Class: |
B01D 2325/14 20130101;
B82Y 30/00 20130101; B01D 69/12 20130101; B01D 2325/04 20130101;
B29D 7/01 20130101; C08J 5/18 20130101; B01D 69/141 20130101; B29C
41/14 20130101; B29C 41/22 20130101; B82Y 40/00 20130101; B01D
69/122 20130101; B05D 1/185 20130101; B01D 2325/16 20130101; B01D
67/0069 20130101; B01D 71/02 20130101; B05D 7/56 20130101 |
Class at
Publication: |
264/255 |
International
Class: |
B28B 7/22 20060101
B28B007/22 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] The development of the subject matter of this application
was partially supported by a grant from the National Science
Foundation (NSF-CAREER, 1-5-53689). Accordingly, the U.S.
government may have rights in this invention.
Claims
1-8. (canceled)
9. A free-standing stratified composite polymeric membrane
comprising: a first layer having a first high molecular weight
material; a second layer adjacent to said first layer, said second
layer having a second high molecular weight material; wherein each
of said layers have a thickness less than 100 nm; and wherein said
high molecular weight materials have an affinity for each
other.
10. The membrane of claim 9 further comprising additional layers
wherein said additional layers alternately comprise said first high
molecular weight material and said second high molecular weight
material.
11. The membrane of claim 9 wherein said high molecular weight
materials are chosen from the group consisting of polyelectrolytes,
proteins, nanoparticles, nanowires, nanotubes, exfoliated clays,
dyes, vesicles, viruses, DNAs, RNAs, oligonucleotides, organic and
inorganic colloids.
12. The membrane of claim 9 wherein said affinity between said
first high molecular weight material and said second high molecular
weight material is electrostatic attraction.
13. The membrane of claim 9 wherein said affinity between said
first high molecular weight material and said second high molecular
weight material is van der Waals forces, hydrogen forces, or
electron exchange.
14. The membrane of claim 9 wherein said first high molecular
weight material and said second high molecular weight material are
chemically cross-linked.
15. The membrane of claim 9 wherein at least one of said first high
molecular weight material and said second high molecular weight
material is a biological compound that retains its biological
activity.
16. The membrane of claim 9 further comprising a third layer having
a third high molecular weight material.
17. The membrane of claim 10 further comprising additional layers
having additional high molecular weight materials.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of prior filed copending
U.S. provisional application Ser. No. 60/192,750 filed Mar. 28,
2000.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] This invention relates generally to a method for the
assembly of free-standing films using a layer-by-layer process.
More particularly, but not by way of limitation, the present
invention. relates to a method for producing ultra-thin membranes
wherein the membrane is first assembled on a soluble or otherwise
removable substrate. Upon completion of the membrane assembly, the
substrate is dissolved in a suitable solvent or removed by other
means leaving behind the free-standing membrane.
[0005] 2. Background
[0006] Thin film technology, wherein inorganic particles with sizes
on the order of 1-100 nm are arranged in layers to form a film, is
being used presently for an increasingly large number of different
technological applications, including, among other things,
information storage systems, chemical and biological sensors,
fiber-optical systems, magneto-optical and optical devices,
pervaporation membranes, protective coatings and light emitting
diodes. Current techniques for preparing such films include
chemical vapor deposition (in which no discrete inorganic particles
are involved), sol-gel technology (producing porous materials that
can be sintered to get uniform films), or deposition from colloidal
dispersions (spin-coating, dip-coating, Langmuir-Blodgett
deposition, etc.).
[0007] Layer-by-layer assembly (LBL) is a method of thin film
deposition which is often used for oppositely charged polymers or
polymers otherwise having affinity and has recently been applied to
the preparation of thin films of nanoparticles. Its simplicity and
universality, complemented by the high quality films produced
thereby, make the layer-by-layer process an attractive alternative
to other thin film deposition techniques. LBL can be applied to a
large variety of water-soluble compounds and is especially suitable
for the production of stratified thin films in which layers of
nanometer thickness are organized in a specific predetermined
order. Such a process is described in U.S. patent applications Ser.
Nos. 60/151,511 and 09/492,951, which disclosures are incorporated
herein by reference.
[0008] Typically, layer-by-layer films are assembled on a solid
substrate material such as a glass slide or silicon wafer.
Deposition of the film material onto the substrate is performed in
a cyclic manner, made possible by the overcompensation of surface
charge which often takes place when polyelectrolytes and other high
molecular weight species are adsorbed on a solid-liquid interface.
As used herein, a "high molecular weight" material refers to
polymers, including proteins, nanoparticles, exfoliated clays and
other organic and inorganic species, having a molecular weight
greater than about 1000 atomic units. In one example of a
layer-by-layer assembly process, after preparation of the
substrate, a film is deposited on the substrate by repeating the
process of: 1) immersion of the substrate in an aqueous solution of
polyelectrolyte; 2) washing with neat solvent; 3) immersion in an
aqueous dispersion of nanoparticles; and 4) final washing with neat
solvent. This process is repeated as many times as necessary,
depending on the number of layers required in order to obtain the
specific properties of the desired material.
[0009] In the prior art, this process has been limited to
applications wherein the substrate and the assembled film remain
intact as a unitary structure. This limits the minimum thickness of
a film and limits the application of films produced through this
process to those tolerant of the substrate material. The present
invention, however, provides a process wherein the assembled thin
film may be separated from the substrate to form a free-standing
thin film material overcoming these and other limitations.
[0010] Membranes are typically prepared by casting a solution of a
polymer on a solid substrate. In this technique, the structure of
the membrane is determined by the chemical structure of the casting
material. Extensions of this generic method, including casting on
an immiscible solvent or post factum surface grafting, can also
yield asymmetrical membranes with chemically modified membrane
surfaces.
[0011] It is thus an object of the present invention to provide a
method for the assembly of free-standing thin film materials using
a layer-by-layer process.
[0012] It is a further object of the present invention to provide a
method for the assembly of free-standing thin film materials using
a layer by layer process wherein the assembled thin film material
exhibits structural properties which allow for manipulation of the
assembled material.
[0013] It is another object of the present invention to provide a
method for the assembly of free-standing thin film material which
permits improved control over a membrane structure allowing for the
production of stratified multifunction membranes.
[0014] It is yet another object of the present invention to provide
a method for the assembly of free-standing thin film material which
permits the incorporation of biological compounds into the membrane
structure while retaining the biological activity of the
compounds.
[0015] It is still another object of the present invention to
provide a free standing thin film material wherein at least one
layer of the material includes an inert structural stabilizing
element, such as exfoliated montmorillonite clay platelets, or
wherein cross-linking of layer by layer films is achieved, to
improve the structural properties of the thin film material.
SUMMARY OF THE INVENTION
[0016] These and other objects and advantages are achieved in a
method for the assembly of free standing thin film material using a
layer-by-layer process. First, a desirable sequence of layers is
assembled on a substrate utilizing the LBL technique. At this step,
the structure and functionality of the thin film or membrane is
defined. Second, the substrate is separated from the assembled
layers, leaving behind a free-standing thin film or membrane. In
this form or after minor modification, the thin film or membrane
can be used in designated applications.
[0017] In the present inventive method, the layer-by-layer
deposition process is initially carried out on a solid substrate.
When a degree of structural sophistication and/or a desirable
thickness is achieved, the assembled thin film material is
separated from the substrate. Soluble substrates may be dissolved
with suitable organic solvents, or the substrate may be removed by
other means, such as decomposition or restructuring of the layer
connecting the membrane and the substrate. In some instances, the
prepared film can be mechanically removed from the substrate.
[0018] In one embodiment, a soluble substrate is supported by a
glass slide to facilitate lift-off of the completed assembly and
for realization of the dipping cycle. The layer-by layer assembly
is carried out in a conventional manner by: 1) dipping the
supported substrate in a first aqueous solution of a water-soluble
first substance, the first substance possessing an affinity for the
substrate; 2) rinsing in neat solvent, such as deionized water,
methanol or other suitable compositions free of the substances
being applied; 3) dipping in a second aqueous solution of a
water-soluble second substance, the second substance having an
affinity for the first substance; and 4) rinsing in neat solvent.
These steps are repeated in a cyclic fashion until the desired
number of layers have been deposited. As used herein, one substance
can be said to have an affinity for another substance via either an
electrostatic attraction or by virtue of van der Waals' forces,
hydrogen forces or electron exchange.
[0019] The sequence of the layers, i.e., the membrane structure, is
determined by the order of dipping. The substances that are
adsorbed at various layers may be easily varied such that layers of
different materials can be combined depending on the required
functionality or combination of functions required. Thus,
sequential adsorption of monolayers of polyelectrolytes, dyes,
nanoparticles (metal, semiconducting, magnetic, etc.), polymers,
proteins, vesicles, viruses, DNAs, RNAs, oligonucleotides, organic
and inorganic colloids and other substances on layers of, for
example, a polyelectrolyte having an affinity therefor allows for
the unprecedented control over membrane structure, production of
multifunctional membranes, incorporation of biological compounds
into the membrane structure while retaining their biological
activity, and improvement of the performance of membranes in most
applications.
[0020] After depositing the appropriate number of layers, the
substrate is removed by dissolution in an appropriate solvent, or,
alternatively, the substrate may be removed through other chemical
treatment, heat treatment, pH-change, ionic strength change, or
other means suitable to achieve the appropriate separation. In one
case, a film may be assembled on a metallic gallium substrate,
which is melted away. After the substrate has been removed, a
free-standing thin film is left.
[0021] Films produced by this process may be extremely thin, on the
order of a few hundred nanometers. It has been found that by
including steps wherein layers of exfolliated montmorillonite clay
platelets are deposited into the film, the mechanical strength of
the film may be radically improved. Alternatively, one can also use
chemical, radiative, photo or other means to achieve cross-linking
amongst the layers to improve the mechanical properties of the
films.
[0022] The free-standing LBL films produced in accordance with the
present invention allow for the exploitation of these assemblies as
ultrathin membranes with a variety of possible applications, which,
by way of example and not limitation, include: gas separation;
desalination; decontamination; ion-separation; sensing devices;
optical devices; micromechanical devices and protective devices, as
well as in the creation of biological devices such as skin
prosthetics, biocompatible implants, cell membranes, artificial
organs, and artificial blood vessels and cornea. Preparation of
such films from inorganic colloids affords a rich palette of
mechanical, chemical, optical, electrical and magnetic properties.
These properties are complemented by the mechanical durability of
the polymers and biological activity of proteins, DNAs, RNAs, etc.
that can also be incorporated into the LBL film. The LBL mode of
their preparation makes possible the degree of structural
organization of such membranes, which is hardly attainable by
traditional methods of their production.
[0023] A better understanding of the present invention, its several
aspects, and its objects and advantages will become apparent to
those skilled in the art from the following detailed description,
taken in conjunction with the attached drawings, wherein there is
shown and described the preferred embodiment of the invention,
simply by way of illustration of the best mode contemplated for
carrying out the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a cross-sectional representation of a film
prepared by the inventive process prior to removal from the support
and substrate media.
[0025] FIG. 2 is a cross-sectional representation of a
free-standing film prepared by the inventive process.
[0026] FIG. 3 is a cross-sectional representation of a free
standing film prepared by the inventive process which includes
alumosilicate layers therein.
[0027] FIG. 4 provides XPS spectra of the solution side of a
free-standing film created as in Example 2.
[0028] FIG. 5 provides XPS spectra of the cellulose acetate side of
a free standing film created as in Example 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] Before explaining the present invention in detail, it is
important to understand that the invention is not limited in its
application to the details of the construction illustrated and the
steps described herein. The invention is capable of other
embodiments and of being practiced or carried out in a variety of
ways. It is to be understood that the phraseology and terminology
employed herein is for the purpose of description and not of
limitation.
[0030] The preferred embodiment of the present inventive method
encompasses the assembly of a free-standing, ultra-thin membrane of
mono- or multilayers, by means of a layer-by-layer ("LBL")
self-assembly technique. In the inventive method, the thin film
material is first assembled on a substrate. After the desired
number of layers have been applied, the substrate is removed,
leaving the free standing thin film.
[0031] More particularly, the process for the assembly of
free-standing thin films, utilizing in this case a soluble
substrate, includes the steps of: [0032] on a suitable support
having been cleaned to remove surface contaminants, casting a
solution of a substrate material dissolved in a suitable solvent
onto a surface of the support; [0033] evaporating the solvent to
leave a film of substrate on the surface of the support; [0034]
forming at least one layer of thin film material by the substeps
of: [0035] a.) immersion of the substrate in a first aqueous
solution or dispersion of a first substance, the first substance
having an affinity for the substrate, so as to apply one layer of
said first substance to the substrate; [0036] b.) rinsing the
substrate with neat solvent; [0037] c.) immersion of the substrate
in a second solution or dispersion of a second substance, the
second substance having an affinity for the first substance, so as
to apply one layer of said second substance upon said first
substance; and [0038] d.) final washing with neat solvent; [0039]
repeating the previous substeps to accumulate the desired number of
layers of said first and second substances (or layers of differing
substances of appropriate affinity) to achieve the required
thickness or obtain the desired properties; [0040] peeling the
substrate and film from the support as a unit; and [0041] immersion
of the substrate and film in a suitable solvent which will dissolve
the substrate material without harming the thin film.
[0042] The support may comprise glass, quartz, plastics or other
suitable inert materials as are known in the art.
[0043] When a soluble substrate is used, the substrate material is
limited only by the conditions that it 1) is soluble in an organic
solvent which will not harm the thin film material; and 2) has an
affinity with the first applied substance forming the first film
layer, serving as a foundation for the film. These requirements are
satisfied, for example, for cellulose acetate, a preferred
substrate, which is insoluble in water, but dissolves readily in
acetone at room temperature. Concomitantly, the surface of
cellulose acetate is fairly hydrophilic displaying contact angles
of 50-55 degrees. It also carries some negative charge from partial
hydrolysis of surface ester groups.
[0044] In the preferred embodiment, the first aqueous solution or
dispersion of an oppositely electrostatically charged first
substance comprises a positively charged polyelectrolyte. The
electrostatic attraction between the polyelectrolyte and the
substrate results in the adsorption of a layer of polyelectrolyte
to the substrate. It should be understood, however, that the first
substance may be one of a variety of materials, as aforedescribed,
having a positive electrostatic charge and contained in a solution
or dispersion or otherwise having an affinity for the
substrate.
[0045] The second solution or dispersion of an electrostatically
charged second substance comprises, in the preferred embodiment, a
negatively charged material such as, by way of example and not
limitation, polyelectrolyte, polymers, proteins, dyes, metal and
semiconductor nanoparticles, magnetic nanoparticles, vesicles,
viruses, DNA, RNA and the like.
[0046] Substitutions of substances with a like charge or affinity
may be made for said first and second substances to achieve the
sequential adsorption of layers of a plurality of substances
resulting in desired membrane properties.
[0047] The process as described above allows for the accumulation
of a variety of different materials adsorbed into a film at desired
levels. In one embodiment of the inventive process inert structural
stabilizing elements, such as exfoliated montmorillonite clay
platelets, carbon nanotubes, carbon fibers or similar materials,
are deposited into the film to improve the mechanical properties of
the resulting film.
[0048] Referring now to the drawings, wherein like reference
numerals designate identical or corresponding parts throughout the
several views, and, more specifically, to FIG. 1, there is
illustrated a thin film 10 constructed in accordance with the
preferred embodiment of the present invention. The film 10 is
formed on a substrate 12 which, in the examples, is soluble in an
organic solvent. The substrate 12 is preferably deposited onto a
support 14 to aid in the dipping process, Individual layers of one
substance 16 are arranged by virtue of the LBL assembly process in
layers separated by layers of another substance having affinity
thereto 18.
[0049] Typically, substrate 12 is first applied to support 14.
Support 14 is preferably a glass slide, silicon wafer, or other
suitable rigid structure. Preferably, substrate 12 is cast onto a
cleaned surface of support 14. Next, the film 10 is assembled onto
the substrate 12 in a layer-by-layer technique as outlined above by
alternating layers of a first substance 18, e.g. of a positive
charge, and layers of a second substance, e.g. of a negative
charge, having an affinity to the first substance 16.
[0050] After completion of the LBL assembly as detailed above, the
film 10 and substrate 12 are peeled as a unit from the support 14.
The film 10 and substrate 12 are then separated. If by dissolution,
the film 10 and substrate 12 are placed in a suitable solvent which
dissolves the substrate 12 while leaving the film 10 unharmed.
Referring to FIG. 2, upon complete removal of the substrate 12, a
free-standing film 10 of the desired structure is left.
[0051] In one embodiment of the inventive method as shown in FIG.
3, exfolliated montmorillonite clay platelets 22 are deposited into
the film 20 in every-other dipping of negative material to improve
the structural properties of the resulting film. As can be seen,
this process results in alternating layers of clay 22 and one or
more additional layers of negatively charged material 16 separated
by layers of positively charged material 18.
[0052] The present invention will be further understood with
reference to the following non-limiting experimental examples.
EXAMPLE 1
[0053] A glass slide was selected as the support material for the
substrate. The glass surface was throughly cleaned in hot
H.sub.2O.sub.2/H.sub.2SO.sub.4 (1:3) mixture for 5 minutes.
Subsequent to drying, a few drops of 15% solution of cellulose
acetate in acetone were cast on the slide and allowed to spread
forming a uniform coating. The slide was immediately placed in a
desiccator and the solvent was allowed to slowly evaporate. When
the film solidified, traces of acetone were completely removed in a
vacuum.
[0054] The LBL assembly was performed by a cyclic repetition of the
following operations: 1) dipping of the cellulose acetate coated
slide in 1% aqueous solution of poly(dimethyldiallylammonium
bromide) 400-500 kDa, P, for one minute; 2) rinsing in deionized
water for 1 minute; 3) dipping in a solution of negatively charged
colloid for 1 minute; and 4) rinsing in deionized water.
[0055] The films were made using colloidal solution of negatively
charged magnetite nanoparticles which were 8 to 10 nanometers in
diameter. Aqueous dispersions of magnetite nanoparticles were
prepared according to the procedure published by Correa-Duarte, M.
A.; Giersig, M.; Kotov, N. A.; Liz-Marzan, L. M. in Langmuir, 1998,
14, 6430-6435, said publication being incorporated herein by
reference. Briefly, 20 mL of FeCl.sub.3 (1M) and 5 mL of FeSO.sub.4
(2M) in 2M HCl were added to 250 mL of NH.sub.40H (0.7 M) under
rapid mechanical stirring, which was allowed to continue for 30
minutes. The black solid product was decanted with the help of a
magnet. The sediment was then redispersed in 50 mL of distilled
water, and subsequently three aliquots of 10 mL tetramethylammonium
hydroxide solution (1M) were added, again with rapid stirring.
Finally, water was added to the dispersion up to a total volume of
250 mL. In this way a stable dispersion of crystalline,
approximately spherical magnetite nanoparticles are obtained with
an average diameter of 12 nm.
[0056] The stability of the colloid originated primarily from the
strong electrostatic repulsion of the particles, and, to a lesser
degree, from the physisorption of bulky tetraalkylammonium cations
preventing their physical contact. Electrostatic and van-der-Waals
interaction with the positive monolayer caused destabilization of
the colloid, which made absorption virtually irreversible. At the
same time, the negative charge acquired by the film surface limited
absorption to essentially a monolayer of nanoparticles. Due to the
cyclic nature of the deposition process, the film produced in n
deposition cycles is hereinafter referred to as (M).sub.n. One
dipping sequence, (M).sub.1, resulted in the addition of a
polyelectrolyte-magnetite layer combination with an average
thickness of 8.+-.0.5 nanometers. This increment remained virtually
constant for at least 50 deposition cycles as observed from the
linearity of the integrated optical density as the assembly
progressed. Atomic force microscopy images of (M).sub.1 revealed
that the film was made of densely packed nanoparticles.
[0057] After depositing an appropriate number of layers and
thorough drying, the thin cellulose acetate substrate, along with
the LBL film, was peeled off the glass support and immersed in
acetone for 24 hours. The substrate dissolved leaving a dark
colored film freely suspended in the solution. The film was
transferred into a fresh acetone bath to completely wash away
remaining cellulose acetate molecules. As expected, the thin film
obtained through this process retained the magnetic properties of
the nanoparticles: the film moved in a wave-like manner through the
solution toward a permanent magnet placed near the side of the
beaker.
[0058] From the suspended state, the films could be transferred
onto any solid or porous substrate. In light of the fact that the
thickness of the prepared films, i.e. (M).sub.15 and (M).sub.30,
was in the range of a few hundred nanometers, they may be
considered to be quite fragile.
EXAMPLE 2
[0059] Layer-by-layer assembly affords manipulation of the order of
deposited layers. To strengthen the film, every-other layer of
magnetite may be replaced with a layer of exfoliated
montmorillonite clay platelets, the assembly of n layers of which
is hereinafter referred to as (C/M).sub.n. Clay platelets have a
thickness of 1.0 nanometer, while extending 150-300 nanometers in
the other dimensions. On polyelectrolytes, they formed a layer of
overlapping alumosilicate sheets with an average thickness of
3.8.+-.0.3 nanometers. Being adsorbed virtually parallel to the
surface of the substrate, their large size allowed them to cover
approximately 400 nanoparticles at once, thereby cementing the
assembly. (C/M).sub.30 free-standing film prepared following the
procedure outlined above could be easily picked up with tweezers,
transferred, cut, moved around a solid surface, and handled in any
other way. Taking advantage of this architecture, free standing
films with as few as 5 repeating C/M units were assembled. Without
the alumosilicate framework, this was impossible.
[0060] The (C/M).sub.30 assembly was imbedded in epoxy resin and
cross-sectioned to investigate by optical microscopy and
transmission electron microscopy (TEM). The optical microscopy
image demonstrated that the film was continuous and flexible. The
thickness of the film, as determined by TEM, was 350 nanometers,
virtually identical to the estimate predicted by adding the
cumulative M and C layers. For (C/M).sub.30 film: (3.8
(nm/alumosilicate layer)+8.0 (nm/magnetite layer))*30 layers=354 nm
Well within the tolerances measured previously in the foregoing
example.
[0061] In this example, it was important to establish the identity
of both surfaces of the assembled film to ensure completeness of
the cellulose acetate removal, which might have contributed to the
strength of the film. Scanning electron microscopy and XPS data
taken on the side facing the solution (FIG. 4) and the cellulose
acetate side (FIG. 5) during the deposition revealed complete
identity of each surface in respect to both composition and relief.
In particular, the observation of the Fe 2p1 100 and Fe 3p3 102
peaks (1121 eV and 1198 eV, respectively) would not have been
possible on the cellulose acetate side of the film if any cellulose
acetate, even a film of a few nanometers, remained. This clearly
indicates the self-supporting nature of the film subsequent to
lift-off from the substrate. The identical intensity of the iron
peaks referenced to the intensity of the carbon is peak 104 for
both surfaces of a film, clearly indicates completeness of the
cellulose acetate removal.
[0062] It will be apparent to those skilled in the art that this
technique can be extended to a variety of other compounds utilized
in LBL research, i.e. polymers, proteins, dyes, metal and
semiconductor nanoparticles, vesicles, viruses, DNA, and the like.
The functional properties of a given film may be adjusted by
varying the layer sequence.
[0063] It will also be apparent to those skilled in the art that
the process herein described for improving the physical properties
of a film could be applied to a large variety of thin film
assemblies.
[0064] While the invention has been described with a certain degree
of particularity, it is manifest that many changes may be made in
the details of the process of assembly without departing from the
spirit and scope of this disclosure. It is understood that the
invention is not limited to the experimental methods set forth
herein for purposes of exemplification.
* * * * *