U.S. patent application number 15/229583 was filed with the patent office on 2016-11-24 for metal nanoparticle-sulfonated polyester composites and green methods of making the same.
This patent application is currently assigned to XEROX CORPORATION. The applicant listed for this patent is XEROX CORPORATION. Invention is credited to Alana Desouza, Valerie M. Farrugia, Sandra J. Gardner.
Application Number | 20160340490 15/229583 |
Document ID | / |
Family ID | 55851932 |
Filed Date | 2016-11-24 |
United States Patent
Application |
20160340490 |
Kind Code |
A1 |
Farrugia; Valerie M. ; et
al. |
November 24, 2016 |
METAL NANOPARTICLE-SULFONATED POLYESTER COMPOSITES AND GREEN
METHODS OF MAKING THE SAME
Abstract
A method includes heating a sulfonated polyester resin in an
organic-free solvent adding an aqueous solution of silver (I) ion
to the heated resin to form a mixture and heating the mixture to
effect the reduction of silver (I) ion to silver (0) in the absence
of an external reducing agent. A composite includes a sulfonated
polyester matrix and a plurality of silver nanoparticles dispersed
within the matrix; the composite lacks trace residual byproducts
from external reducing agents.
Inventors: |
Farrugia; Valerie M.;
(Oakville, CA) ; Desouza; Alana; (London, CA)
; Gardner; Sandra J.; (Oakville, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
XEROX CORPORATION |
NORWALK |
CT |
US |
|
|
Assignee: |
XEROX CORPORATION
|
Family ID: |
55851932 |
Appl. No.: |
15/229583 |
Filed: |
August 5, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14531862 |
Nov 3, 2014 |
9458305 |
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15229583 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08K 2003/0806 20130101;
C08K 3/08 20130101; C08L 67/02 20130101; C08K 2201/011 20130101;
C08K 3/08 20130101; C08K 2201/019 20130101 |
International
Class: |
C08K 3/08 20060101
C08K003/08 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. A composite comprising: a sulfonated polyester matrix; and a
plurality of silver nanoparticles dispersed within the matrix,
wherein the composite lacks trace residual byproducts from external
reducing agents due to the formation of the plurality of silver
nanoparticles in situ by reduction of silver ion mediated by the
sulfonated polyester matrix itself.
16. The composite of claim 15, wherein the sulfonated polyester
matrix is a branched polymer.
17. The composite of claim 15, wherein the sulfonated polyester
matrix is a sodium, lithium, or potassium salt of a polymer
selected from the group consisting of
poly(1,2-propylene-5-sulfoisophthalate),
poly(neopentylene-5-sulfoisophthalate),
poly(diethylene-5-sulfoisophthalate),
copoly-(1,2-propylene-5-sulfoisophthalate)-copoly-(1,2-propylene-terphtha-
late),
copoly-(1,2-propylenediethylenesodio-5-sulfoisophthalate)-copoly-(1-
,2-propylene-diethylene-terephthalatephthalate),
copoly(ethylene-neopentylene-5-sulfoisophthalate)-copoly-(ethylene-neopen-
tylene-terephthalatephthalate), and copoly(propoxylated bisphenol
A)-copoly-(propoxylated bisphenol A-sodio 5-sulfoisophthalate).
18. The composite of claim 15, wherein the sulfonated polyester
matrix comprises a polyol monomer unit selected from the group
consisting of trimethylolpropane, 1,2-propanediol, diethylene
glycol, and combinations thereof.
19. The composite of claim 15, wherein the sulfonated polyester
matrix comprises a diacid monomer unit selected from the group
consisting of terephthalic acid, sulfonated isophthalic acid, and
combinations thereof.
20. The composite of claim 15, wherein a loading of silver is
present in the composite is in a range from about 100 ppm to about
10,000 ppm.
Description
BACKGROUND
[0001] The present disclosure relates to composites. In particular,
the present disclosure relates to composites comprising metal
nanoparticles dispersed throughout the composite matrix.
[0002] There is an increasing interest in mixed inorganic/organic
composite systems due to the property benefits each of the
individual constituents confers on the composite material. One
particular area of interest is silver nanoparticle (AgNP)-laden
polymer composites. Such composites may be useful in antimicrobial
and antibacterial applications, biosensor materials, composite
fibers, cryogenic superconducting materials, cosmetic products, and
electronic components. The unique properties of AgNPs, including
size and shape-dependent optical, electrical, and magnetic
properties, as well as antimicrobial and antibacterial properties,
has resulted in increasing usage in consumer and medical
products.
[0003] Many methods for the manufacture of metal/polymer
nanostructured materials require pre-fabrication of metal
nanoparticles by reduction of a metal salt precursor prior to
incorporation into polymer matrices. For example, conventional
methods for making silver/polymer nanostructured materials, in
particular, generally require melt mixing or extrusion of silver
nanoparticles (AgNPs) in polymer matrices. Unfortunately, these
methods often suffer from silver nanoparticle aggregation.
SUMMARY
[0004] In some aspects, embodiments herein relate to methods
comprising heating a sulfonated polyester resin in an organic-free
solvent adding an aqueous solution of silver (I) ion to the heated
resin to form a mixture and heating the mixture to effect the
reduction of silver (I) ion to silver (0) in the absence of an
external reducing agent.
[0005] In some aspects, embodiments herein relate to composites
comprising a sulfonated polyester matrix and a plurality of silver
nanoparticles dispersed within the matrix, wherein the composite
lacks trace residual byproducts from external reducing agents.
BRIEF DESCRIPTION OF DRAWINGS
[0006] Various embodiments of the present disclosure will be
described herein below with reference to the figures wherein:
[0007] FIG. 1 shows a postulated mechanism of sulfonated polyester
self-assembly in the presence of silver ion without use of an
external reducing agent;
[0008] FIG. 2 shows overlaid ultraviolet-visible (UV-Vis)
absorption spectra of Samples 1-6 with varying concentration of a
branched sulfonated polyester (BSPE) and a constant loading of
silver nitrate (AgNO.sub.3) after 3 hours of heating;
[0009] FIG. 3 shows overlaid UV-Vis absorption spectra of Samples
1-6 of FIG. 2 after 5 hours of heating;
[0010] FIG. 4 shows overlaid UV-Vis absorption spectra of Samples
1-6 of FIG. 2 after 22 hours of heating;
[0011] FIG. 5 shows overlaid UV-Vis absorption spectra the
reduction of silver (I) ion over time in a vial containing the most
BSPE (Sample 5);
[0012] FIG. 6A shows a plot of UV-Vis absorption as a function of
concentration of BSPE and absorbance of BSPE-Ag nanocomposites at
440 nm for each time interval;
[0013] FIG. 6B shows a plot of UV-Vis absorption as a function of
time at various concentrations of BSPE at 440 nm;
[0014] FIG. 7 shows a scanning electron microscope (SEM) image of
reduced silver present in the exemplary BSPE matrix prepared in
accordance with embodiments herein;
[0015] FIG. 8 shows the Energy Dispersive X-ray Spectroscopy (EDS)
spectrum which displays the elemental distribution in a sample
surface at a depth of about 1 to about 2 microns; the aluminum peak
is from the background film that the sample was plated on; the
platinum peak is from the coating of the sample during SEM
analysis;
[0016] FIG. 9A shows Samples 1-5 of increasing BSPE concentration
from left to right and constant loading AgNO.sub.3 concentration of
0.32% (w/w) after 22 hours;
[0017] FIG. 9B shows a control Sample with no BSPE and constant
loading AgNO.sub.3 concentration of 0.32% (w/w) after 22 hours;
[0018] FIG. 10A shows a black precipitate observed when taking
UV-Vis measurement of Sample 6 at 5 hours; Sample 6 contains BSPE
at a concentration of about 0.024 g/mL and 1% Trisodium citrate
dihydrate as an external reducing agent;
[0019] FIG. 10B shows Sample 5 after 14 days; it contains only BSPE
at a concentration of 0.032 g/mL and no external reducing agent;
and
[0020] FIG. 11 shows Samples 5 (left) and 6 (right) after 14 days;
Sample 5 is still stable (no precipitate) while Sample 6 (with
external reducing agent) has a significant amount of black
precipitate.
DETAILED DESCRIPTION
[0021] Embodiments here provide methods to reduce silver ion during
the self-assembly of sulfonated polyesters (SPEs) in water without
the need for an external reducing agent. The methods facilitate the
formation of silver nanoparticle-laden composite structures with
sulfonated polyester matrices. Methods herein are environmentally
friendly because (1) they are conducted in organic-free solvents,
i.e. water and (2) they eliminate the need for external reducing
agents, such as sodium borohydride, sodium thiosulfate and other
conventional reducing agents that require proper waste disposal.
The sulfonated polyester requires minimal time to self-assemble in
water in the presence of silver (I) ion and does not require
solvents beyond hot water.
[0022] Methods disclosed herein exhibit an ability to control the
rate of silver (I) reduction and improve emulsion stability when
higher amounts of silver are needed in a polymer matrix. As
disclosed herein, the rate of silver (I) reduction can be
controlled by polymer loading and/or changing the
heating/temperature profile of the reaction. Methods herein are
also useful in cases where a specific amount of silver (I)
reduction is desired because of the "tunable" reduction conditions
where the reduction reaction can be quenched by cooling to room
temperature to impede further reduction.
[0023] Methods disclosed herein eliminate the presence of extra
ions, such as citrate ion, as byproducts associated with the use of
an external reducing agent. These byproduct ions that can adsorb to
the Ag-polymer composites and interfere with the attachment of
specific ligands needed to detect/chelate an analyte of interest
when the composite is used in sensing applications and/or other
applications. Thus, the composites disclosed herein benefit from
the absence of trace byproducts of external reducing agents that
would typically be employed to reduce silver (I) to silver (0).
[0024] The sulfonated polyester resins disclosed herein possess a
hydrophobic backbone and hydrophilic sulfonate groups attached to
the chain. Without being bound by theory, it is postulated that
when placed in water and heated, the hydrophobic portions interact
with each other to form a hydrophobic core and the hydrophilic
moieties (sulfonate groups) face the surrounding water as indicated
in FIG. 1. Therefore, the sulfonated polyester self-assembles into
a higher order, spherical nanoparticle without additional reagents,
thus effecting self-assembly in water.
[0025] Embodiments provide methods of synthesizing AgNPs
simultaneously during the self-assembly process without the use of
a reducing agent. Silver ions are trapped within the polymer matrix
during the self-assembly of the sulfonated polyesters while
simultaneously being reduced to AgNPs. As disclosed herein, when
more sulfonated polyester (SPE) was added to emulsion (i.e., higher
solids content), the reduction of silver occurred faster. When
higher loadings of silver nitrate are needed for reduction, the SPE
provided excellent stability compared to AgNP/SPE nanocomposites
synthesized with an external conventional reducing agent. Overall
the amount of SPE:silver nitrate ratio can be tuned to control
reduction time, reduction amount and overall stability of the
Ag-polymer emulsion.
[0026] In embodiments, the reduction can be monitored over time by
UV-VIS absorption spectroscopy because nanosized silver particles
have a plasmon absorption peak around 400 nm. The broader the peak,
the smaller the nanoparticles. The higher the .lamda.max, the
greater the amount of AgNPs reduced within the polymer matrix.
[0027] Without being bound by theory it has been postulated that
the sulfonated polyester resin has numerous functions in the
synthesis of the composites disclosed herein including: (1)
potentially acting as in reducing capacity, as evidenced by
increased reduction at higher polymer concentrations; (2)
stabilizing the silver nanoparticles within the polymer matrix
(capping agent), and (3) utilizing its own sulfonate groups as
"self-stabilizers" in an aqueous medium.
[0028] At high solids content, such as about more than about 40%
weight percent of the sulfonated polyester (SPE) solution, the
solution becomes thick and may impair the ability of silver ions to
associate with the polymer due to mobility interference with the
polymer chains. However, this may be remedied by longer mixing
times prior to heating to allow for more uniform dispersion of
silver ion. However, the rate of reduction is not expected to be
delayed by the presence of large amounts of the SPE matrix in
solution. Regardless of the concentration, the matrix may play an
important role in uniformly dispersing the silver nanoparticles in
water. By contrast, composites made by mechanical mixing of
pre-fabricated silver nanoparticles (AgNPs) with molten polymers
usually lead to inhomogeneous particle dispersions. The AgNPs have
high surface reactivity and are inclined to aggregate with each
other into larger domains or clusters instead of dispersing within
the polymer matrix.
[0029] In embodiments, there are provided methods comprising
heating a sulfonated polyester resin in an organic-free solvent,
adding a solution of silver (I) ion to the heated resin in water to
form a mixture, and heating the mixture to effect the reduction of
silver (I) ion to silver (0) in the absence of an external reducing
agent. In embodiments, the organic-free solvent is water.
[0030] As used herein, the term "external reducing agent" refers to
conventional reducing agents that might be added to a mixture of
polymer and silver salt to effect an in situ reduction. Examples of
external reducing agents include, without limitation, citrate
salts, thiosulfate, hydride-based reagents such as sodium
borohydride, free-reducing sugars, ascorbic acid, and the like. As
disclosed herein, there is a correlation between concentration of
sulfonated polyester (SPE) resin and effective reducing capacity at
elevated temperatures in aqueous silver (I)/SPE systems suggesting
that the sulfonated polyester matrix may serve a role as a reducing
agent.
[0031] In embodiments, methods further comprise monitoring the
reduction of silver (I) ion to silver (0). Monitoring may be
accomplished by any detection means. As shown in the Examples
below, an easy detection method may include UV-Vis absorption
monitoring based on the plasmon absorption peak around 400 nm.
Other methods that may be used to monitor the progress of reduction
include, scanning electron microscopy (SEM), transmission electron
microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS or
EDX).
[0032] In embodiments, methods further comprise cooling the mixture
when a target silver (0) concentration is obtained. In embodiments,
cooling from ambient temperature to below about 65.degree. C. can
sufficiently slow or stop reduction. In embodiments, cooling is
effected by simply removing the heating source. As indicated in the
Examples below, reduction can be carried out at elevated
temperatures and the progress monitored. In embodiments, the
reduction is carried out initially at an elevated temperature of
from about 65.degree. C. to about 95.degree. C., with a
particularly good target temperature of about 90.degree. C. In
embodiments, the temperature is from about 80.degree. C. to
90.degree. C. In a particular embodiment, the initial elevated
temperature is from about 88.degree. C. to about 92.degree. C. The
reduction can be quenched by reducing the temperature of the
mixture, thus allowing targeting of the silver (0) concentration.
In embodiments, the quenching is performed by reducing the
temperature from about 95.degree. C. to about 30.degree. C., or
from about 90.degree. C. to about 21.degree. C. In a particular
embodiment, the temperature is reduced ambient temperature. In
embodiments, the target silver (0) concentration is in a range from
about 100 to about 10,000 ppm. Concentrations of silver (0) in the
range of about 5 ppm-1,000 ppm are suitable for antimicrobial and
catalysis applications. Antimicrobial concentrations may range from
about 5 ppm to about 1,000 ppm or from about 20 ppm to about 500
ppm, or from about 30 ppm to about 100 ppm. Concentrations of 100
ppm-100,000 ppm are suitable for enhancing the thermal properties
of a material, such as thermal conductivity. Thermal enhancement
and other physical properties (tensile strength) may be realized
from about 100 ppm to about 100,000 ppm, or from about 500 ppm to
about 50,000 ppm, or from about 1,000 ppm to about 10,000 ppm.
Concentrations of 10,000 ppm have been reported to improve the
mechanical properties of polymer-silver composites, such as
elongation at break, maximum tensile strength and Young
modulus.
[0033] In embodiments, methods further comprise adding a second
portion of sulfonated polyester resin while heating the mixture. In
such embodiments, an initial incubation with SPE and silver (I) ion
may serve to establish an equilibrium association between silver
(I) ion and the SPE polymer matrix. The second portion of
sulfonated polyester resin may be added before, during, or after
heating. The second portion may be provided as a non-external
reducing agent source.
[0034] In embodiments, an amount of the sulfonated polyester resin
to silver (I) ion may be in a range from about 1:100 to about 1:1,
or from about 1:25 to about 1:3. In embodiments, the ratio is a
function of the extent of reduction which can be tuned via
reduction time at the elevated temperature. Thus, a standard plot
of absorbance as a function of time for a given concentration of
polymer matrix at fixed temperature will allow a determination of
the time needed for a given absorbance. Silver absorbance at 440 nm
serves as a measure of the extent of reduction. FIG. 6B provides an
example of such a plot. Complete reduction may be measured by
surface-enhanced Raman spectroscopy (SERS).
[0035] The stability of the resultant composites can be evaluated
via measurement of the zeta potential. As a point of reference, an
exemplary stock solution with 25.5% polymer solids from Example 1
below has a high stability of about -60 mV, as indicated in the
table below. Sample 5 in the Examples below was stable after 14
days of aging at ambient temperature (sample shown in FIG.
10B).
[0036] In embodiments, heating is conducted at a temperature from
about 65.degree. C. to about 90.degree. C. The exact temperature
selected may be a function of how fast the desired reduction is to
be effected. It may be desirable to run reduction at lower
temperatures where small loadings of nanoparticles are desirable.
It was observed experimentally that reduction commences measurably
at about 60.degree. C.; higher temperatures will generally be
beneficial for timely reduction.
[0037] In embodiments, a source of silver (I) ion is selected from
the group consisting of silver nitrate, silver sulfonate, silver
fluoride, silver perchlorate, silver lactate, silver
tetrafluoroborate, silver oxide, and silver acetate.
[0038] In embodiments, the silver nanoparticles may comprise solely
elemental silver or may be a silver composite, including composites
with other metals. Such metal-silver composite may include either
or both of (i) one or more other metals and (ii) one or more
non-metals. Suitable other metals include for example Al, Au, Pt,
Pd, Cu, Co, Cr, In, and Ni, particularly the transition metals for
example Au, Pt, Pd, Cu, Cr, Ni, and mixtures thereof. Exemplary
metal composites are Au--Ag, Ag--Cu, Au--Ag--Cu, and Au--Ag--Pd.
Suitable non-metals in the metal composite include for example Si,
C, and Ge. The various components of the silver composite may be
present in an amount ranging for example from about 0.01% to about
99.9% by weight, particularly from about 10% to about 90% by
weight. In embodiments, the silver composite is a metal alloy
composed of silver and one, two or more other metals, with silver
comprising for example at least about 20% of the nanoparticles by
weight, particularly greater than about 50% of the nanoparticles by
weight. Unless otherwise noted, the weight percentages recited
herein for the components of the silver-containing nanoparticles do
not include the stabilizer.
[0039] Silver nanoparticles composed of a silver composite can be
made for example by using a mixture of (i) a silver compound (or
compounds, especially silver (I) ion-containing compounds) and (ii)
another metal salt (or salts) or another non-metal (or non-metals)
during the reduction step.
[0040] Those skilled in the art will appreciate that metals other
than silver may be useful and can be prepared in accordance with
the methods disclosed herein. Thus, for example, composites may be
prepared with nanoparticles of copper, gold, palladium, or
composites of such exemplary metals.
[0041] In embodiments, the sulfonated polyester resin is a branched
polymer. In embodiments, the sulfonated polyester resin is a linear
polymer. In embodiments, the sulfonated polyester resin is a
sodium, lithium, or potassium salt of a polymer selected from the
group consisting of poly(1,2-propylene-5-sulfoisophthalate),
poly(neopentylene-5-sulfoisophthalate),
poly(diethylene-5-sulfoisophthalate),
copoly-(1,2-propylene-5-sulfoisophthalate)-copoly-(1,2-propylene-terphtha-
late),
copoly-(1,2-propylenediethylene-5-sulfoisophthalate)-copoly-(1,2-pr-
opylene-diethylene-terephthalatephthalate),
copoly(ethylene-neopentylene-5-sulfoisophthalate)-copoly-(ethylene-neopen-
tylene-terephthalatephthalate), and copoly(propoxylated bisphenol
A)-copoly-(propoxylated bisphenol A-5-sulfoisophthalate). In
embodiments, the counteraction to the sulfonate group can be any
non-participatory cation, as known to those skilled in the art, and
may include without limitation, sodium, potassium, lithium, and the
like.
[0042] In embodiments, wherein the sulfonated polyester resin
comprises a polyol monomer unit selected from the group consisting
of trimethylolpropane, 1,2-propanediol, diethylene glycol, and
combinations thereof. In embodiments, wherein the sulfonated
polyester resin comprises a diacid monomer unit selected from the
group consisting of terephthalic acid, sulfonated isophthalic acid,
and combinations thereof.
[0043] In embodiments, there are provided composites comprising a
sulfonated polyester matrix and a plurality of silver nanoparticles
dispersed within the matrix, wherein the composite lacks trace
residual byproducts from external reducing agents.
[0044] Significant differences in stability via zeta potential
measurements can be observed when reduction is performed with or
without a reducing agent. These differences in zeta potential are
independent of thermal (T.sub.g) or molecular weight properties.
Comparing two dispersions of equal solids and Ag content, the
dispersion with no reducing agent is substantially more stable and
this is believed to be due to the reducing agent causing some
charge differential and slight aggregation. As an example, a sample
lacking a reducing agent had a zeta potential of -80.7 mV versus a
sample prepared with trisodium citrate which had a zeta potential
of -56.0 mV.
[0045] The following Examples are being submitted to illustrate
embodiments of the present disclosure. These Examples are intended
to be illustrative only and are not intended to limit the scope of
the present disclosure. Also, parts and percentages are by weight
unless otherwise indicated. As used herein, "room temperature"
refers to a temperature of from about 20.degree. C. to about
25.degree. C.
EXAMPLES
[0046] General Process: A method for preparing emulsion
compositions containing silver nanoparticles silver (I) salts,
reducing agents and sulfonated polyester resins where an emulsion
latex comprised of sulfonated polyester resin particles are
produced comprises (i) heating resin in water at a temperature from
about 65.degree. C. to 90.degree. C. and (ii) adding an aqueous
solution of silver nitrate drop-wise to emulsion. This will result
in AgNP-BSPE composite particles that can range anywhere from about
5 to about 500 nanometers in diameter depending on process
conditions such as sulfonated polyester solids loadings, amount of
silver, rpm, temperature, etc.
[0047] In particular embodiments, a composite preparation may be
prepared by dispersing a branched sulfonated polyester (BSPE) in
water at about 90.degree. C., followed by addition of a silver
nitrate solution and lastly heating to effect the reduction of
Ag(I) to Ag(0).
Example 1
[0048] This example describes the preparation of a branched sodio
sulfonated amorphous polyesters (BSPE-1).
[0049] A branched amorphous sulfonated polyester resin comprised of
0.425 mole equivalent of terephthalate, 0.080 mole equivalent of
sodium 5-sulfoisophthalic acid, 0.4501 mole equivalent of
1,2-propanediol, and 0.050 mole equivalent of diethylene glycol,
was prepared as follows. In a one-liter Parr reactor equipped with
a heated bottom drain valve, high viscosity double turbine
agitator, and distillation receiver with a cold water condenser was
charged 388 grams of dimethylterephthalate, 104.6 grams of sodium
5-sulfoisophthalic acid, 322.6 grams of 1,2-propanediol (1 mole
excess of glycols), 48.98 grams of diethylene glycol, (1 mole
excess of glycols), trimethylolpropane (5 grams) and 0.8 grams of
butyltin hydroxide oxide as the catalyst. The reactor was heated to
165.degree. C. with stirring for 3 hours and then again heated to
190.degree. C. over a one hour period, after which the pressure was
slowly reduced from atmospheric pressure to about 260 Torr over a
one hour period, and then reduced to 5 Torr over a two hour period.
The pressure was then further reduced to about 1 Torr over a 30
minute period and the polymer was discharged through the bottom
drain onto a container cooled with dry ice to yield 460 grams of
sulfonated-polyester resin. The branched sulfonated-polyester resin
had a glass transition temperature measured to be 54.5.degree. C.
(onset) and a softening point of 154.degree. C.
Example 2
BSPE-1 Stock Solution for Dilution
[0050] A stock solution of BSPE-1 in water was made by adding 0.5 g
BSPE-1 to 125 mL distilled water. The stock solution had a
[BSPE-1]=0.004 g/mL. Six 10 mL glass vials were rinsed three times
with distilled water, three times with acetone and allowed to air
dry. Various volumes of water and stock BSPE solutions were added
to the vials as outlined in Table 1 below. The vials were equipped
with a magnetic stir bar and capped with aluminum foil. The vials
were heated to 90.degree. C. and stirred at 950 rpm. After 1 hour,
1.884 mL of 0.1M AgNO.sub.3 solution was added to each vial with a
micropipette. To vial 6, 2.116 mL of 1% trisodium citrate dihydrate
reducing agent was added with a micropipette. The solutions were
mixed for 22 hours at 90.degree. C. at 950 rpm. UV-Vis measurements
were done 3 hours after the addition of AgNO.sub.3, 5 hours and 22
hours. The reduction of silver was apparent by the colour change to
yellow/brown.
TABLE-US-00001 Vol. total Vol. of Stock [BSPE] in vial AgNO3 in
Vol. 0.1M Vol. DIW Vol. Red agent Sample (mL) 0.004 g/mL BSPE (mL)
(g/mL) vial (g) AgNO3 (mL) (mL) (mL) 1 10 0 0 0.032 1.884 8.116 0 2
10 2 0.008 0.032 1.884 6.116 0 3 10 4 0.016 0.032 1.884 4.116 0 4
10 6 0.024 0.032 1.884 2.116 0 5 10 8 0.032 0.032 1.884 0.116 0 6
10 6 0.024 0.032 1.884 0.000 2.116
[0051] AgNPs display surface plasmon resonance (SPR) upon
irradiation with light resulting in SPR peaks in the UV-VIS
wavelength range. The SPR phenomenon is a result of the
interactions between the incident light and the free electrons in
the conduction band of the AgNPs. Luoma, S. N. 2008. Project on
Emerging Nanotechnologies, The Pew Charitable Trusts; Tolaymat, T.,
et al. Sci. Tot. Environ., (408)5:999-1006 (2010). FIGS. 2-4 show
the UV-Vis absorption spectra of the six AgNP-BSPE dispersions
prepared as given in Table 1 shown above. Significant increases in
.lamda.max are seen when the amount of BSPE is increased relative
to Ag.sup.+. As the heating time progressed, the .lamda.max peak
for each sample increased dramatically as indicated in FIG. 4.
Although some evaporation was observed after 22 hours, the overall
trend of increased silver reduction is clear. In FIG. 4, it can be
seen that after 22 hours, the control sample with no BSPE (Sample
1) showed a slightly yellow colour and peak at 440 nm. This can be
explained by the thermal decomposition of aqueous AgNO.sub.3, given
by the following equation: 2AgNO.sub.3.fwdarw.2Ag(s)+2NO.sub.2
(g)+O.sub.2 (g) .DELTA.H.degree.298.15=314.97 kJ. The equilibrium
constant (K.sub.c) for this reaction is 2.13.times.10-30 and
1.98.times.10-6 at 295.15K and 400K, respectively. Stern, K. H.
1972. High temperature properties and decomposition of inorganic
salts. Part 3 Nitrates and Nitrites. J. Phys. Chem. Ref. Data, (1)
3:767 At the temperature used in this experiment (363 K), the
equilibrium constant should lie between these values. This
relatively low magnitude of the equilibrium constant indicates that
this is a minor interference thereby contributing an insignificant
amount of discolouration to Vial 1.
[0052] FIGS. 2-4 show UV-Vis absorption spectra of samples with
varying concentration of BSPE and a constant loading of AgNO.sub.3.
FIG. 2 shows spectra after 3 hours of heating, FIG. 3 shows spectra
after 5 hours of heating and FIG. 4 shows spectra after 22 hours of
heating. FIG. 5 shows the reduction of Ag.sup.+ over time in the
vial containing the most BSPE (vial 5) as the reducing agent. FIG.
6 shows the relationship between concentration of BSPE and
absorbance of BSPE-Ag nanocomposites at 440 nm for each time
interval. It is evident that as BSPE concentration increases so
does the amount of reduced silver measured at 440 nm. The
relationship of absorbance and BSPE concentration at each time
measurement is highly correlated as seen by the r-squared for each
trend line.
[0053] FIG. 7 shows SEM of reduced Ag in BSPE matrix and FIG. 8
shows the Energy Dispersive X-ray Spectroscopy or EDS which
displays the elemental distribution in a sample surface at a depth
of 1-2 microns. The aluminum peak is from the background film that
the sample was plated on; the platinum peak is from the coating of
the sample during SEM analysis.
[0054] The reduction of Ag.sup.+ using BSPE can be controlled by
temperature changes. The reduction of Ag.sup.+ occurs readily at
90.degree. C., however does not occur at room temperature
(22.degree. C.). This is shown in FIGS. 9A/B.
[0055] FIG. 9A Samples of increasing [BSPE] from left to right and
constant loading [AgNO.sub.3] of 0.32% (w/w) after 22 hours. FIG.
9B Sample with no BSPE and constant loading [AgNO.sub.3] of 0.32%
(w/w) after 22 hours.
[0056] If the addition of a strong reducing agent (in this Example
trisodium citrate dihydrate) is rapid in the presence of silver,
the silver can reduce quickly, agglomerate and become destabilized.
This can be seen by the brown/black precipitate observed when
taking the UV-Vis measurement of Sample 6 after 5 hours (FIG. 10A).
FIG. 10A Black precipitate observed when taking UV-Vis measurement
of vial 6 at 5 hours. Vial 6 contains BSPE at a concentration of
0.024 g/mL and 1% trisodium citrate dihydrate (reducing agent).
FIG. 10B Sample 5 after 14 days, contains only BSPE at a
concentration of 0.032 g/mL.
[0057] FIG. 11 shows 14 days after the completion of the
experiment, vial 5 is still stable (no precipitate) however vial 6
has a significant amount of black precipitate.
* * * * *