U.S. patent application number 16/759684 was filed with the patent office on 2020-12-31 for two-dimensional sheet stabilized emulsion based inks.
This patent application is currently assigned to University of Connecticut. The applicant listed for this patent is University of Connecticut. Invention is credited to Douglas H. Adamson, Elizabeth Brown, Feiyang Chen.
Application Number | 20200407571 16/759684 |
Document ID | / |
Family ID | 1000005150921 |
Filed Date | 2020-12-31 |
United States Patent
Application |
20200407571 |
Kind Code |
A1 |
Adamson; Douglas H. ; et
al. |
December 31, 2020 |
Two-Dimensional Sheet Stabilized Emulsion Based Inks
Abstract
The present disclosure provides advantageous sheet stabilized
emulsion based inks, and improved methods for fabricating and using
such inks. More particularly, the present disclosure provides
improved methods for fabricating conductive inks derived from
water-in-oil emulsions stabilized by sheets exfoliated from layered
materials (e.g., substantially pristine and non-oxidized graphite
or hexagonal boron nitride), and related methods of use. A layered
material (e.g., substantially pristine and non-oxidized graphite or
hexagonal boron nitride) can be exfoliated into individual sheets,
and these sheets can be utilized to stabilize water-in-oil
emulsions. In certain embodiments, by utilizing long chain alkanes
(e.g., hexadecane), one can advantageously fabricate emulsions with
high viscosity and stability. In this form, the emulsions can be
used as inks, thereby advantageously providing an inexpensive route
to printing electrically conducting and/or insulating lines and
shapes.
Inventors: |
Adamson; Douglas H.;
(Mansfield Center, CT) ; Chen; Feiyang; (Vernon,
CT) ; Brown; Elizabeth; (Mansfield Center,
CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Connecticut |
Farmington |
CT |
US |
|
|
Assignee: |
University of Connecticut
Farmington
CT
|
Family ID: |
1000005150921 |
Appl. No.: |
16/759684 |
Filed: |
October 31, 2018 |
PCT Filed: |
October 31, 2018 |
PCT NO: |
PCT/US18/58532 |
371 Date: |
April 27, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62580214 |
Nov 1, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08K 2003/385 20130101;
C08K 3/042 20170501; C09D 11/023 20130101; C09D 11/52 20130101;
C08K 3/38 20130101; C09D 11/38 20130101 |
International
Class: |
C09D 11/023 20060101
C09D011/023; C09D 11/52 20060101 C09D011/52; C09D 11/38 20060101
C09D011/38; C08K 3/04 20060101 C08K003/04; C08K 3/38 20060101
C08K003/38 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] This invention was made with government support under Grant
#DMR1535412 awarded by the National Science Foundation. The
government has certain rights in the invention.
Claims
1. A method for fabricating an ink comprising: a) providing a phase
separated system of two non-mixing solvents, the phase separated
system including: (i) a first solvent and a second solvent, and
(ii) an interface between the first and second solvents; b)
introducing a layered material to the interface of the phase
separated system; c) forming an emulsion of the first and second
solvents, at least a portion of the layered material stabilizing
the emulsion; and d) applying the emulsion to a substrate to form
an electrically conductive pattern on the substrate.
2. The method of claim 1, wherein the first solvent is a long chain
alkane and the second solvent is water.
3. The method of claim 1, wherein the first solvent includes at
least one alkane and the second solvent is water.
4. The method of claim 1, wherein the layered material is
substantially pristine graphite or hexagonal boron nitride; and
wherein after step c) the emulsion is stabilized by layers or
sheets of the substantially pristine graphite or hexagonal boron
nitride.
5. The method of claim 1, wherein the emulsion is formed via a
formation step selected from the group consisting of hand mixing,
hand shaking, mechanical mixing, mechanical shaking, and
combinations thereof.
6. The method of claim 1, wherein the emulsion is a water-in-oil
emulsion.
7. The method of claim 1, wherein the emulsion is applied to the
substrate via brushing or screen printing.
8. The method of claim 1, wherein the substrate is flexible.
9. The method of claim 1, wherein the first solvent is hexadecane
and the second solvent is water.
10. The method of claim 1, wherein the first solvent includes
heptane and hexadecane, and the second solvent is water.
11. The method of claim 1, wherein the emulsion has a steady state
viscosity of about 4,000,000 cP shear thinning to about 15,000
cP.
12. The method of claim 1, wherein the layered material introduced
includes flakes, the flakes having a flake size of about 1
.mu.m.
13. The method of claim 1, wherein the layered material introduced
includes graphite flakes, the graphite flakes having a flake size
of about 1 .mu.m.
14. The method of claim 1, wherein the first solvent includes
alkanes larger than octadecane.
15. The method of claim 1, wherein the layered material is
substantially pristine and non-oxidized graphite or hexagonal boron
nitride; and wherein after step c) the emulsion is stabilized by
layers or sheets of the substantially pristine and non-oxidized
graphite or hexagonal boron nitride.
16. The method of claim 1, wherein the emulsion is applied to the
substrate via spraying or ink-jetting.
17. A method for fabricating an ink comprising: a) providing a
phase separated system of two non-mixing solvents, the phase
separated system including: (i) a first solvent and a second
solvent, and (ii) an interface between the first and second
solvents; b) introducing a layered material to the interface of the
phase separated system; c) forming an emulsion of the first and
second solvents, at least a portion of the layered material
stabilizing the emulsion; and d) applying the emulsion to a
substrate to form an electrically conductive pattern on the
substrate; wherein the first solvent is a long chain alkane and the
second solvent is water; wherein the layered material is
substantially pristine and non-oxidized graphite or hexagonal boron
nitride; wherein after step c) the emulsion is stabilized by layers
or sheets of the substantially pristine and non-oxidized graphite
or hexagonal boron nitride; wherein the emulsion is formed via hand
mixing; wherein the emulsion is a water-in-oil emulsion; wherein
the emulsion is applied to the substrate via brushing or screen
printing; wherein the substrate is flexible; wherein the emulsion
has a steady state viscosity of about 4,000,000 cP shear thinning
to about 15,000 cP; and wherein the layered material introduced
includes flakes, the flakes having a flake size of about 1 .mu.m.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application entitled "Two-Dimensional Sheet Stabilized Emulsion
Based Inks," which was filed on Nov. 1, 2017, and assigned Ser. No.
62/580,214, the contents of which are herein incorporated by
reference in their entirety.
FIELD OF THE DISCLOSURE
[0003] The present disclosure relates to sheet stabilized emulsion
based inks and related methods of use and fabrication and, more
particularly, to conductive inks derived from water-in-oil
emulsions stabilized by sheets exfoliated from layered materials
(e.g., substantially pristine and non-oxidized graphite or
hexagonal boron nitride), and related methods of fabrication.
BACKGROUND OF THE DISCLOSURE
[0004] In general, flexible displays and wearable sensors can
require conductive materials that are able to bend and deform
without cracking or breaking. Some potential and current
applications include, for example, electronic and wearable
textiles, 3D antennas and conformal printing, electromagnetic
interference (EMI) shielding, 3D printed electronics, indium tin
oxide (ITO) replacements, printed piezoresistives, bio sensors,
printed memory, organic light-emitting diode (OLED) and large area
LED lighting, and large area heaters.
[0005] Commercial conductive inks can contain metals (e.g., silver)
suspended in a solution. These inks are expensive, can fail after
repeated bending, can require high temperature annealing, and have
been known to lead to irritation when placed next to the skin.
Newly introduced graphitic based inks are derived from oxidized
graphite, and are thus expensive, lack long-term stability, can
require damaging post-application treatment, and do not have the
high conductivity of pristine graphene.
[0006] Flexible patterns are often produced with inks loaded with
high concentration of metals such as, for example, gold or silver.
Conductive cloth can be produced by electroplating with metals such
as, for example, silver or nickel. The use of metals can be costly
as well as lead to skin irritation in some cases.
[0007] Thus, an interest exists for improved conductive inks, and
related methods of use and fabrication. These and other
inefficiencies and opportunities for improvement are addressed
and/or overcome by the systems, assemblies and methods of the
present disclosure.
SUMMARY OF THE DISCLOSURE
[0008] The present disclosure provides advantageous sheet
stabilized emulsion based inks, and improved methods for
fabricating and using such inks. More particularly, the present
disclosure provides improved methods for fabricating conductive
inks derived from water-in-oil emulsions stabilized by sheets
exfoliated from layered materials (e.g., substantially pristine and
non-oxidized graphite or hexagonal boron nitride), and related
methods of use.
[0009] Research has shown that the insolubility of pristine
graphene/graphite can be utilized as a means to fabricate water/oil
emulsions, with graphene/graphite stabilizing the spheres formed,
and with the emulsions utilized as the frameworks to make
composites (e.g., foam composites). See, e.g., U.S. Pat. No.
9,646,735, the entire contents of which being hereby incorporated
by reference in its entirety.
[0010] As described and disclosed in U.S. Pat. No. 9,646,735, by
using an interface trapping method, the lack of solubility of
pristine graphene/graphite can be utilized to both exfoliate and
trap graphene/graphite, as well as form stable emulsions used as
the framework for polymer/graphene/graphite composites (e.g.,
hollow polymer/graphene/graphite composites).
[0011] Other research has shown film climbing using an interface
trapping method in a heptane and water mixture. See, e.g., U.S.
Pat. No. 9,685,261, and Woltornist, S. J., Oyer, A. J., Carrillo,
J.-M. Y., Dobrynin, A. V & Adamson, D. H., Conductive Thin
Films Of Pristine Graphene By Solvent Interface Trapping, ACS Nano
7, 7062-6 (2013), the entire contents of each being hereby
incorporated by reference in their entireties.
[0012] In exemplary embodiments of the present disclosure, a
layered material (e.g., substantially pristine and non-oxidized
graphite or substantially pristine and non-oxidized hexagonal boron
nitride) is exfoliated into individual sheets (e.g., individual
graphene sheets), and these sheets are utilized to stabilize
water-in-oil emulsions.
[0013] In certain embodiments, by utilizing long chain alkanes
(e.g., hexadecane, which is a chain of 16 carbon atoms), one can
advantageously fabricate emulsions with high viscosity and
stability. The viscosity can be similar to emulsions such as
mayonnaise, and can also be similar to the viscosity found in inks
used for screen-printing. In this form, the emulsions can be used
as inks, thereby advantageously providing an inexpensive route to
printing electrically conducting and/or insulating lines and
shapes.
[0014] The present disclosure provides for a method for fabricating
an ink including a) providing a phase separated system of two
non-mixing solvents, the phase separated system including: (i) a
first solvent and a second solvent, and (ii) an interface between
the first and second solvents; b) introducing a layered material to
the interface of the phase separated system; c) forming an emulsion
of the first and second solvents, at least a portion of the layered
material stabilizing the emulsion; and d) applying the emulsion to
a substrate to form an electrically conductive pattern on the
substrate.
[0015] The present disclosure also provides for a method for
fabricating an ink wherein the first solvent is a long chain alkane
and the second solvent is water. The present disclosure also
provides for a method for fabricating an ink wherein the first
solvent includes at least one alkane and the second solvent is
water.
[0016] The present disclosure also provides for a method for
fabricating an ink wherein the layered material is substantially
pristine graphite or hexagonal boron nitride; and wherein after
step c) the emulsion is stabilized by layers or sheets of the
substantially pristine graphite or hexagonal boron nitride.
[0017] The present disclosure also provides for a method for
fabricating an ink wherein the emulsion is formed via a formation
step selected from the group consisting of hand mixing, hand
shaking, mechanical mixing, mechanical shaking, and combinations
thereof. The present disclosure also provides for a method for
fabricating an ink wherein the emulsion is a water-in-oil
emulsion.
[0018] The present disclosure also provides for a method for
fabricating an ink wherein the emulsion is applied to the substrate
via brushing or screen printing. The present disclosure also
provides for a method for fabricating an ink wherein the substrate
is flexible.
[0019] The present disclosure also provides for a method for
fabricating an ink wherein the first solvent is hexadecane and the
second solvent is water. The present disclosure also provides for a
method for fabricating an ink wherein the first solvent includes
heptane and hexadecane, and the second solvent is water.
[0020] The present disclosure also provides for a method for
fabricating an ink wherein the emulsion has a steady state
viscosity of about 4,000,000 cP shear thinning to around 15,000 cP.
The present disclosure also provides for a method for fabricating
an ink wherein the layered material introduced includes flakes, the
flakes having a flake size of about 1 .mu.m. The present disclosure
also provides for a method for fabricating an ink wherein the
layered material introduced includes graphite flakes, the graphite
flakes having a flake size of about 1 .mu.m.
[0021] The present disclosure also provides for a method for
fabricating an ink wherein the first solvent includes alkanes
larger than octadecane.
[0022] The present disclosure also provides for a method for
fabricating an ink including a) providing a phase separated system
of two non-mixing solvents, the phase separated system including:
(i) a first solvent and a second solvent, and (ii) an interface
between the first and second solvents; b) introducing a layered
material to the interface of the phase separated system; c) forming
an emulsion of the first and second solvents, at least a portion of
the layered material stabilizing the emulsion; and d) applying the
emulsion to a substrate to form an electrically conductive pattern
on the substrate; wherein the first solvent is a long chain alkane
and the second solvent is water; wherein the layered material is
substantially pristine graphite or hexagonal boron nitride; wherein
after step c) the emulsion is stabilized by layers or sheets of the
substantially pristine graphite or hexagonal boron nitride; wherein
the emulsion is formed via hand mixing; wherein the emulsion is a
water-in-oil emulsion; wherein the emulsion is applied to the
substrate via brushing or screen printing; wherein the substrate is
flexible; wherein the emulsion has a steady state viscosity of
about 4,000,000 cP shear thinning to about 15,000 cP; and wherein
the layered material introduced includes flakes, the flakes having
a flake size of about 1 .mu.m.
[0023] Any combination or permutation of embodiments is envisioned.
Additional advantageous features, functions and applications of the
disclosed systems, assemblies and methods of the present disclosure
will be apparent from the description which follows, particularly
when read in conjunction with the appended figures. All references
listed in this disclosure are hereby incorporated by reference in
their entireties.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Features and aspects of embodiments are described below with
reference to the accompanying drawings, in which elements are not
necessarily depicted to scale.
[0025] Exemplary embodiments of the present disclosure are further
described with reference to the appended figures. It is to be noted
that the various steps, features and combinations of steps/features
described below and illustrated in the figures can be arranged and
organized differently to result in embodiments which are still
within the scope of the present disclosure. To assist those of
ordinary skill in the art in making and using the disclosed
systems, assemblies and methods, reference is made to the appended
figures, wherein:
[0026] FIG. 1 shows exemplary lines of ink printed on a
substrate;
[0027] FIG. 2A depicts graphite trapped at the oil and water
interface; FIG. 2B is an illustration of graphite trapped in the
oil and water interface; FIG. 2C is an illustration of graphite
that exfoliates into graphene at the oil and water interface;
[0028] FIG. 3A shows a graphene emulsion ink poured onto paper;
FIG. 3B is an optical image of the graphene emulsion ink (ink was
diluted using oil phase to separate the spheres);
[0029] FIG. 3C is an illustration of a water-in-oil emulsion with
graphene stabilizing the interface;
[0030] FIG. 4A displays a UCONN logo printed on paper using a
graphene emulsion ink;
[0031] FIG. 4B shows a plot of resistance of a printed ink line vs.
the number of cycles the ink line is rolled into a 7.62 cm diameter
tube;
[0032] FIG. 5 shows different exfoliation stages of graphene ink
prepared using increasing graphite loading from vial 1 to vial 8;
all eight vials had 3 ml of C16 (hexadecane), 7 ml of DI H.sub.2O,
and the graphite loading of each vial was as follows: vial 1: 0.01
g, vial 2: 0.02 g, vial 3: 0.03 g, vial 4: 0.04 g, vial 5: 0.05 g,
vial 6: 0.1 g, vial 7: 0.2 g, vial 8: 0.3 g; this image shows after
day one, after each vial was shaken for 40 s;
[0033] FIG. 6 shows different exfoliation stages of graphene ink
prepared using increasing graphite loading from vial 1 to vial 8;
all eight vials had 3 ml of C16 (hexadecane), 7 ml of DI H.sub.2O,
and the graphite loading of each vial was as follows: vial 1: 0.01
g, vial 2: 0.02 g, vial 3: 0.03 g, vial 4: 0.04 g, vial 5: 0.05 g,
vial 6: 0.1 g, vial 7: 0.2 g, vial 8: 0.3 g; this image shows after
day two, after each vial was shaken again for 40 s;
[0034] FIG. 7 shows different exfoliation stages of graphene ink
prepared using increasing graphite loading from vial 1 to vial 8;
all eight vials had 3 ml of C16 (hexadecane), 7 ml of DI H.sub.2O,
and the graphite loading of each vial was as follows: vial 1: 0.01
g, vial 2: 0.02 g, vial 3: 0.03 g, vial 4: 0.04 g, vial 5: 0.05 g,
vial 6: 0.1 g, vial 7: 0.2 g, vial 8: 0.3 g; this image shows after
day twelve, after each vial was shaken again at day five and day
twelve for 40 s;
[0035] FIG. 8 shows stress vs. shear rate at 25.degree. C. of inks
prepared by using a different alkane as the oil phase (C7: heptane,
C10: octane, C12: dodecane; C14: tetradecane; C16: hexadecane);
[0036] FIG. 9 shows an emulsion size distribution of different inks
(C7: heptane, C10: octane, C12: dodecane; C14: tetradecane; C16:
hexadecane);
[0037] FIG. 10 shows the percent bleeding of lines printed using
different inks on paper vs. the number of prints each line was
(repeatedly) printed; (C7: heptane, C10: octane, C12: dodecane;
C14: tetradecane; C16: hexadecane);
[0038] FIG. 11 shows the resistance of a 4 pt width, 5 cm length
C16 ink line versus the number of prints; and
[0039] FIGS. 12A-12E show the resistance vs. 1/(XN) of different
inks; FIG. 12A is C7 ink; FIG. 12B is C10 ink; FIG. 12C is C12 ink;
FIG. 12D is C14 ink; FIG. 12E is C16 ink.
DETAILED DESCRIPTION OF DISCLOSURE
[0040] The exemplary embodiments disclosed herein are illustrative
of advantageous sheet stabilized emulsion based inks, and systems
of the present disclosure and methods/techniques thereof. It should
be understood, however, that the disclosed embodiments are merely
exemplary of the present disclosure, which may be embodied in
various forms. Therefore, details disclosed herein with reference
to exemplary inks/fabrication methods and associated
processes/techniques of assembly and use are not to be interpreted
as limiting, but merely as the basis for teaching one skilled in
the art how to make and use the advantageous inks/systems and/or
alternative inks/systems of the present disclosure.
[0041] The present disclosure provides improved sheet stabilized
emulsion based inks, and improved methods for fabricating and using
such inks. More particularly, the present disclosure provides
advantageous methods for fabricating conductive inks derived from
water-in-oil emulsions stabilized by sheets exfoliated from layered
materials (e.g., substantially pristine and non-oxidized graphite
or hexagonal boron nitride), and related methods of use.
[0042] Exfoliated sheets such as, for example, graphene or
hexagonal boron nitride can be utilized to stabilize water-in-oil
emulsions. Using certain oil phases, these emulsions can be very
stable, lasting for months and displaying viscosities similar to
mayonnaise. In certain embodiments, by utilizing long chain alkanes
(e.g., hexadecane, which is a chain of 16 carbon atoms), one can
advantageously fabricate emulsions with high viscosity and
stability. In this form, the emulsions can be used as inks, thereby
advantageously providing an inexpensive route to printing
electrically conducting and/or insulating lines and shapes.
[0043] The inks can be applied with a brush, by screen printing, or
other techniques (e.g., sprayed; ink-jetted; etc.) to produce
conductive patterns on flexible surfaces such as, for example,
cloth or plastic. Applications of such inks can include, without
limitation, wearable electronics, flexible displays, bendable
energy storage devices, and roll to roll produced solar cells.
[0044] In certain embodiments, the conductive ink is fabricated by
exfoliating a layered material (e.g., substantially pristine and
non-oxidized graphite) into individual sheets (e.g., individual
graphene sheets), and using these sheets to stabilize water-in-oil
emulsions. This stabilization is a result of kinetic trapping of
graphene sheets or several layers of graphene flakes at a
solvent/solvent interface. In exemplary embodiments, the
systems/methods of the present disclosure advantageously produce
emulsions of graphene/graphite with liquids (e.g., two non-mixing
solvents, such as oil and water) on both the inside and the outside
of the graphene/graphite.
[0045] In general, fabrication of the sheet stabilized emulsion
based inks begins with a layered material (e.g., substantially
pristine and non-oxidized graphite, such as graphene sheets or
layers of graphite) being placed at the interface of a phase
separated system (e.g., at an interface of two non-mixing solvents,
such as a alkane/water system). In the interface trapping method,
exfoliated sheets are instantly adsorbed to the high-energy
liquid-liquid interface, where they are trapped because of the
lowering of the interfacial energy of the system that the sheet
provides. As more sheets are exfoliated, they climb up the
interface to continue to minimize the interfacial energy as much as
possible.
[0046] In order to continue the interfacial energy minimization,
spheres are formed, thereby creating more surface area for the
sheets (e.g., graphene/graphite sheets) to adsorb on to. The
resulting emulsion can be utilized as a conductive ink (e.g.,
applied to a substrate to form an electrically conductive pattern
on the substrate).
[0047] In one specific oil/water system, the emulsion consists of
spheres of water, coated with graphene, and surrounded by at least
one alkane (e.g., a long chain alkane; a high molecular weight (MW)
alkane).
[0048] FIG. 1 shows exemplary lines 12 of ink printed on a
substrate 10 (e.g., artificial leather; paper, etc.). As such, FIG.
1 illustrates some printed lines 12 of ink onto artificial leather
10. These lines 12 are electrically conductive, even when the
substrate 10 is bent or twisted.
[0049] Printable inks can allow for the development of flexible
electronics on various substrates 10 (e.g., paper or plastic). This
in turn can enable applications such as, for example, wearable
medical sensors, antennas, and even batteries and displays. The
applicability of the advantageous inks of the present disclosure to
screen-printing is important, as this can be the approach of choice
for commercial printing (as opposed to the ink jet printing
approach).
[0050] In exemplary embodiments, layered materials (e.g., graphite
or hexagonal boron nitride) are exfoliated without the need for
expensive or damaging approaches. By using long chain alkanes for
the oil phase to stabilize the emulsions against coalescence, the
advantageous emulsions can be fabricated. Using these emulsions,
one can utilize them with standard screen printing to
create/fabricate electrically conductive lines on substrates (e.g.,
paper, fabric, etc.).
[0051] It is noted that other approaches to using graphene in inks
rely on either expensive and damaging oxidation or mechanical
exfoliation. Oxidation creates defect sites on the graphene sheets
that lowers the conductivity and leads to chemically unstable
materials, while mechanical methods break the sheets into small
fragments and degraded properties. In exemplary embodiments, the
exfoliation systems and methods of the present disclosure
advantageously produce large graphene sheets (e.g., about 1 .mu.m
sheets) in substantially pristine or pristine condition with
negligible cost.
[0052] As described in U.S. Patent Pub. No. 2015/0307730 (the '730
publication), this publication attempts to provide a graphene ink
from un-oxidized graphene. In an attempt to work, the formulation
includes a hydrophobic solvent and a stabilizer, with ethyl
cellulose being the stabilizer. The hydrocarbon described includes
hexane, heptane, octane. The '730 publication reports attempting to
exfoliate the graphite with sonication and the preponderance of
very small (tens of nanometers) graphene flakes. By comparison,
exemplary systems/methods of the present disclosure utilize water
and a high MW alkane, do not require sonication, and
contain/provide larger (e.g., about 1 .mu.m sheets), and thus more
conductive, graphene. In addition, the exemplary methods of the
present disclosure do not require a dispersing agent as does the
'730 publication.
[0053] It is noted that FIG. 2A of the present disclosure depicts
graphite trapped at the oil and water interface. FIG. 2B is an
illustration of graphite trapped in the oil and water interface.
FIG. 2C is an illustration of graphite that exfoliates into
graphene at the oil and water interface.
[0054] FIG. 3A shows a graphene emulsion ink poured onto paper.
FIG. 3B is an optical image of the graphene emulsion ink (ink was
diluted using oil phase to separate the spheres). FIG. 3C is an
illustration of a water-in-oil emulsion with graphene stabilizing
the interface.
[0055] FIG. 4A displays a UCONN logo printed on paper using a
graphene emulsion ink. FIG. 4B shows a plot of resistance of a
printed ink line versus the number of cycles the ink line is rolled
into a 7.62 cm diameter tube.
[0056] FIG. 5 shows different exfoliation stages of graphene ink
prepared using increasing graphite loading from vial 1 to vial 8.
All eight vials had 3 ml of C16 (hexadecane), 7 ml of DI H.sub.2O,
and the graphite loading of each vial was as follows: vial 1: 0.01
g, vial 2: 0.02 g, vial 3: 0.03 g, vial 4: 0.04 g, vial 5: 0.05 g,
vial 6: 0.1 g, vial 7: 0.2 g, vial 8: 0.3 g; this image shows after
day one, after each vial was shaken for 40 seconds.
[0057] FIG. 6 shows different exfoliation stages of graphene ink
prepared using increasing graphite loading from vial 1 to vial 8.
All eight vials had 3 ml of C16 (hexadecane), 7 ml of DI H.sub.2O,
and the graphite loading of each vial was as follows: vial 1: 0.01
g, vial 2: 0.02 g, vial 3: 0.03 g, vial 4: 0.04 g, vial 5: 0.05 g,
vial 6: 0.1 g, vial 7: 0.2 g, vial 8: 0.3 g; this image shows after
day two, after each vial was shaken again for 40 seconds.
[0058] FIG. 7 shows different exfoliation stages of graphene ink
prepared using increasing graphite loading from vial 1 to vial 8.
All eight vials had 3 ml of C16 (hexadecane), 7 ml of DI H.sub.2O,
and the graphite loading of each vial was as follows: vial 1: 0.01
g, vial 2: 0.02 g, vial 3: 0.03 g, vial 4: 0.04 g, vial 5: 0.05 g,
vial 6: 0.1 g, vial 7: 0.2 g, vial 8: 0.3 g; this image shows after
day twelve, after each vial was shaken again at day five and day
twelve for 40 seconds.
[0059] FIG. 8 shows stress versus shear rate at 25.degree. C. of
inks prepared by using a different alkane as the oil phase (C7:
heptane, C10: octane, C12: dodecane; C14: tetradecane; C16:
hexadecane).
[0060] FIG. 9 shows an emulsion size distribution of different inks
(C7: heptane, C10: octane, C12: dodecane; C14: tetradecane; C16:
hexadecane).
[0061] FIG. 10 shows the percent bleeding of lines printed using
different inks on paper versus the number of prints each line was
(repeatedly) printed (C7: heptane, C10: octane, C12: dodecane; C14:
tetradecane; C16: hexadecane).
[0062] FIG. 11 shows the resistance of a 4 pt width, 5 cm length
C16 ink line versus the number of prints.
[0063] FIGS. 12A-12E show the resistance versus 1/(XN) of different
inks. FIG. 12A is C7 ink. FIG. 12B is C10 ink. FIG. 12C is C12 ink.
FIG. 12D is C14 ink. FIG. 12E is C16 ink.
[0064] Table 1 below shows the hysteresis of different alkanes with
graphene.
TABLE-US-00001 TABLE 1 average average advancing weight receding
weight solvent gain (mg) retained (mg) hysteresis C7 32.6 37.7
0.157 C10 39.5 44.8 0.133 C12 41.3 43.9 0.064 C14 45.7 45.8 0.001
C16 40.2 45.1 0.120
With Equation 1:
[0065] R = 1 X .times. N R 0 ##EQU00001##
And where: [0066] R: resistance of the printed line (Me) [0067] X:
Width of the line (pt) [0068] N: Number of prints on the same line
[0069] R.sub.0: resistance per print per points of the line
(M.OMEGA.print.sup.-1pt.sup.-1)
[0070] Table 2 below shows the Resistance per print per points
(R.sub.0) of different inks and the coefficient of determination
(R.sup.2) of different inks.
TABLE-US-00002 TABLE 2 Ink R.sub.0 (M.OMEGA. print.sup.-1
pt.sup.-1) R.sup.2 C7 ink 19.57 0.35 C10 ink 28.91 0.84 C12 ink
64.97 0.72 C14 ink 44.17 0.58 C16 ink 124.18 0.95
[0071] The present disclosure will be further described with
respect to the following examples; however, the scope of the
disclosure is not limited thereby. The following examples
illustrate the advantageous systems/methods of the present
disclosure of fabricating improved conductive inks derived from
water-in-oil emulsions stabilized by sheets exfoliated from layered
materials.
Example 1
[0072] An exemplary sample of ink can be produced/fabricated by
adding graphite flakes to water and hexadecane (e.g., three to one
ratio of water to hexadecane in some embodiments; nearly equal
volumes of water and hexadecane in other embodiments). This mixture
is then mixed or shaken (e.g., via hand mixing, hand shaking,
mechanical mixing, mechanical shaking, and combinations thereof)
for an amount of time (e.g., for less than ten seconds) to produce
the emulsion/ink. That is it.
[0073] The ink is stable to coalescence relative to the length of
time investigating it (e.g., substantially no coalescence observed
for more than three months). The mayonnaise-like consistency (e.g.,
about 15,000 cP, but can be varied; in some embodiments the
emulsion has a steady state viscosity of about 4,000,000 cP shear
thinning to about 15,000 cP) of the ink is perfect for screen
printing, and numerous printed designs have been fabricated.
[0074] Current research is concerned with exploring the use of
different alkanes and ratios of alkanes, as well as different
graphite flake sizes.
[0075] An initial alkane utilized in the fabrication method was C16
(hexadecane). Current tests include inks made with various ratios
of C16 and C7 (heptane) during the fabrication method.
[0076] Some findings thus far are that the C16 can be cut with C7
to a significant extent without losing the high viscosity of the
resultant ink/emulsion.
[0077] With just only C7, however, the emulsion flows freely. In
addition, one can test graphene with larger flake sizes.
[0078] Some embodiments utilize around 1 .mu.m flakes (1 .mu.m
equals 1,000 nanometers). This is due the fast exfoliation of this
size flake. Larger flakes, however, are expected to be more
conductive, and one can utilize mixing techniques and/or microwaves
in efforts to make inks with larger flakes in a reasonable amount
of time.
[0079] Another direction one can take is to utilize longer alkanes
(e.g., larger than C18, octadecane) with higher melting
temperatures. These are typically called waxes, and should be able
to form emulsions either at elevated temperatures or when cut with
C7. If one is able to use waxes with high melting temperatures in
the emulsification process, then remove the water and C7, one may
be able to make very low density conductive pastes. These
approaches can lead to the control of viscosity and rheological
properties of the ink, and provide a pathway for meeting a range of
industrial needs.
[0080] In printing applications, it has been noted that the
conductivity of the lines 12 increases with multiple prints. This
is important for understanding the mechanism, but also for allowing
for changing conductivity on the same surface/substrate. This is an
aspect that more expensive silver based inks lack, and is useful
for various applications where the material interacts with
electromagnetic waves.
[0081] Some future objectives of the present disclosure are to more
fully understand the source of emulsion stability in these
exemplary inks, to develop additional formulations and approaches
to manufacture such inks, and to provide additional examples and
test samples for use/testing.
[0082] Whereas the disclosure has been described principally in
connection with graphite and/or graphene, such description has been
utilized for purposes of disclosure and is not intended as limiting
the disclosure. To the contrary, it is recognized that the
disclosed systems, methods, techniques and assemblies are capable
of use with other materials having a layered structure or the like,
such as, for example, boron nitride (e.g., hexagonal or graphitic
boron nitride) or graphene oxide or the like.
[0083] Although the systems and methods of the present disclosure
have been described with reference to exemplary embodiments
thereof, the present disclosure is not limited to such exemplary
embodiments and/or implementations. Rather, the systems and methods
of the present disclosure are susceptible to many implementations
and applications, as will be readily apparent to persons skilled in
the art from the disclosure hereof. The present disclosure
expressly encompasses such modifications, enhancements and/or
variations of the disclosed embodiments. Since many changes could
be made in the above construction and many widely different
embodiments of this disclosure could be made without departing from
the scope thereof, it is intended that all matter contained in the
drawings and specification shall be interpreted as illustrative and
not in a limiting sense. Additional modifications, changes, and
substitutions are intended in the foregoing disclosure.
Accordingly, it is appropriate that the appended claims be
construed broadly and in a manner consistent with the scope of the
disclosure.
* * * * *