U.S. patent application number 14/074578 was filed with the patent office on 2015-05-07 for thermally switchable composition.
This patent application is currently assigned to XEROX CORPORATION. The applicant listed for this patent is XEROX CORPORATION. Invention is credited to Brynn DOOLEY, Matthew HEUFT, Gabriel IFTIME, Carolyn MOORLAG, Gordon SISLER, Gail SONG.
Application Number | 20150126661 14/074578 |
Document ID | / |
Family ID | 52829945 |
Filed Date | 2015-05-07 |
United States Patent
Application |
20150126661 |
Kind Code |
A1 |
IFTIME; Gabriel ; et
al. |
May 7, 2015 |
THERMALLY SWITCHABLE COMPOSITION
Abstract
A composition including a stimulus-responsive polymer, a base
polymer and a catalyst, wherein the surface free energy of the
stimulus-responsive polymer is reversibly adjustable from a first
surface free energy state to a second surface free energy state
when heated to an activation temperature, and wherein the base
polymer does not include a platinum catalyst is described. A method
of preparing the composition and a method of adjusting a surface
free energy of the composition is also described.
Inventors: |
IFTIME; Gabriel;
(Mississauga, CA) ; SISLER; Gordon; (Stoney Creek,
CA) ; MOORLAG; Carolyn; (Mississauga, CA) ;
HEUFT; Matthew; (Oakville, CA) ; SONG; Gail;
(Milton, CA) ; DOOLEY; Brynn; (Toronto,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
XEROX CORPORATION |
Norwalk |
CT |
US |
|
|
Assignee: |
XEROX CORPORATION
Norwalk
CT
|
Family ID: |
52829945 |
Appl. No.: |
14/074578 |
Filed: |
November 7, 2013 |
Current U.S.
Class: |
524/365 |
Current CPC
Class: |
C08F 8/00 20130101; C09D
133/26 20130101; C09D 183/04 20130101; C08L 83/00 20130101; C09D
133/26 20130101; C08L 83/04 20130101 |
Class at
Publication: |
524/365 |
International
Class: |
C09D 183/04 20060101
C09D183/04; C09D 133/26 20060101 C09D133/26 |
Claims
1. A composition comprising a stimulus-responsive polymer, a base
polymer and a catalyst, wherein the surface free energy of the
stimulus-responsive polymer is reversibly adjustable from a first
surface free energy state to a second surface free energy state
when heated to an activation temperature, and wherein the base
composition does not include a platinum catalyst.
2. The polymer composition according to claim 1, wherein the
surface free energy of the first surface free energy state is from
about 25 to about 65 dynes/cm, and the surface free energy of the
second surface free energy state is from about 8 to about 30
dynes/cm.
3. The polymer composition according to claim 1, wherein the
catalyst is an organometallic catalyst comprising tin or
titanium
4. The polymer composition according to claim 1, wherein the
stimulus-responsive polymer comprises a monomer unit selected from
the group consisting of N-isopropylacrylamide, N-ethylacrylamide,
N-n-propylacrylamide, N-ethyl,N-methylacrylamide,
N,N-diethylacrylamide, N-isopropyl,N-methylacrylamide,
N-cyclopropylacrylamide, N-acryloylpyrrolidine,
N-acryloylpiperidine, N-vinyl-caprolactam, 2-alkyl-2-oxazoline, an
alkyl-substituted cellulose, and mixtures thereof.
5. The polymer composition according to claim 1, wherein the
stimulus-responsive polymer is selected from the group consisting
of poly-(N-isopropylacrylamide), poly-(N-ethylacrylamide),
poly-(N-n-propylacrylamide), poly(N-ethyl,N-methylacrylamide),
poly(N,N-diethylacrylamide), poly(N-isopropyl,N-methylacrylamide),
poly(N-cyclopropylacrylamide), poly(N-acryloylpyrrolidine),
poly(N-acryloylpiperidine), poly(N-vinyl-caprolactam,
poly(2-alkyl-2-oxazoline), alkyl-substituted celluloses, and
mixtures thereof.
6. The polymer composition according to claim 1, wherein the
activation temperature is from about 10.degree. C. to about
120.degree. C.
7. The polymer composition according to claim 1, wherein the base
polymer comprises a silicone polymer.
8. The polymer composition according to claim 1, wherein the
stimulus-responsive polymer is selected from the group consisting
of a polymer of Formula I: ##STR00011## wherein, R.sub.1 and
R.sub.2 are independently a hydrogen or alkyl having from 1 to
about 10 carbon atoms, cycloalkyl with a number of carbons from
about 3 to about 10, or a heterocycle incorporating the nitrogen
atom in Formula I that is capable of forming hydrogen bonds, the
heterocycle having with a number of carbons from 3 to 5, and n is a
number from 1 to 1000; a polymer of Formula II: ##STR00012##
wherein n is as defined above; a polymer of Formula III:
##STR00013## wherein R is an alkyl group selected from the group
consisting of propyl, isopropyl, and ethyl, and n is as defined
above; a polymer of Formula IV: ##STR00014## wherein n is as
defined above; and mixtures thereof.
9. The polymer composition according to claim 1, wherein the
stimulus-responsive polymer is present in an amount of from about
5% to about 80% compared to the base polymer.
10. The polymer composition according to claim 1, wherein the
polymer composition comprises poly-(N-isopropylacrylamide) as the
stimulus-responsive polymer, the base polymer is formed from a room
temperature vulcanizing silicone polymer, and the catalyst is a tin
catalyst.
11. A device comprising the polymer composition according to claim
1.
12. A method of preparing a polymer composition, the method
comprising: mixing a stimulus-responsive polymer, a base polymer,
and a catalyst to create a mixture; wherein the surface free energy
of the stimulus-responsive polymer is reversibly adjustable from a
first surface free energy state to a second free energy state when
heated to or above an activation temperature, and wherein the
catalyst is not a platinum catalyst.
13. The method according to claim 12, wherein the method further
comprises curing the mixture.
14. The method according to claim 12, wherein the
stimulus-responsive polymer is present in an amount of from about
5% to about 80% compared to the base polymer.
15. The method according to claim 12, wherein before the mixing,
the base polymer contains the catalyst, and the base polymer
containing the catalyst, and the stimulus-responsive polymer, are
each separately dispersed in a solvent.
16. The method according to claim 15, wherein the solvent used to
separately disperse the base polymer containing the catalyst and
the stimulus-responsive polymer is the same solvent.
17. The method according to claim 12, wherein the
stimulus-responsive polymer is selected from the group consisting
of poly-(N-isopropylacrylamide), poly-(N-ethylacrylamide),
poly-(N-n-propylacrylamide), poly(N-ethyl,N-methylacrylamide),
poly(N,N-diethylacrylamide), poly(N-isopropyl,N-methylacrylamide),
poly(N-cyclopropylacrylamide), poly(N-acryloylpyrrolidine),
poly(N-acryloylpiperidine), poly(N-vinyl-caprolactam,
poly(2-alkyl-2-oxazoline), alkyl-substituted celluloses, and
mixtures thereof.
18. The method according to claim 12, wherein the base polymer is
formed from a room temperature vulcanizing silicone polymer.
19. The method according to claim 12, wherein the catalyst is a tin
catalyst.
20. A method of adjusting a surface free energy of a composition
comprising a silicone polymer, a catalyst, and a
stimulus-responsive polymer, the method comprising: heating the
composition to an activation temperature, wherein the catalyst is
not a platinum catalyst, and the adjustment of the surface free
energy of the composition is reversible by cooling the composition.
Description
TECHNICAL FIELD
[0001] The present disclosure is related to thermally switchable
compositions and methods of making the thermally switchable
compositions.
RELATED APPLICATIONS
[0002] U.S. patent application Ser. No. 13/746,910, filed on Jan.
22, 2013, in the name of Carolyn Moorlag et. al, entitled
"Thermally Switchable Transfix Blanket Made with Grafted Switchable
Polymer for Aqueous Inkjet Printing," describes a polymer
composition comprising a stimulus-responsive polymer dispersed in a
base polymer matrix, wherein the surface free energy of the
stimulus-responsive polymer is reversibly adjustable from a first
surface free energy state to a second surface free energy state
when heated to a predetermined critical activation temperature.
[0003] U.S. patent application Ser. No. 13/746,920, filed on Jan.
22, 2013, in the name of Carolyn Moorlag et. al, entitled
"Thermally Switchable Transfix Blanket Made with Grafted Switchable
Polymer for Indirect Printing," describes a polymer composition
comprising a first polymer layer comprising a base polymer, and a
second polymer layer grafted onto the first polymer layer, wherein
the second polymer layer comprises a stimulus-responsive polymer,
and the surface free energy of the stimulus-responsive polymer is
reversibly adjustable from a first surface free energy state to a
second surface free energy state when heated to a predetermined
critical activation temperature.
[0004] U.S. Patent Application Publication No. 2010/0251914 to Zhou
et al. describes an imaging member comprising a substrate and a
surface layer comprising a heat sensitive material permitting
reversible switching between compatible and non-compatible states
within one second.
[0005] The entire disclosures of the above-mentioned applications
are fully incorporated herein by reference.
BACKGROUND
[0006] The traditional approach to materials development has been
to design materials with enhanced performance. Advanced materials
are generally designed to perform one function. One problem is that
maximizing one property, for example, adhesion of a substance to a
surface, affects other properties, for example, the release of the
substance from the surface. Solutions to these problems have
generally been focused on adding more components with the
expectation of independently controlling each property. However,
often times, the additional component then interacts with other
materials in the composition, thus adversely affecting different
properties.
[0007] Additionally, the addition of many different specialized
components explains why many of today's products and parts are made
of very complex materials sets. However, high complexity products
are prone to malfunction, high cost, and significant waste
generation.
[0008] A switchable surface has the unique property of changing
between two states that have different physical properties when
activated by a stimulus, for example, heat. The switch is
controllable and reversible. The switching between different states
is associated with changes in the physical properties of the
composition. For example, the ability to switch the surface free
energy of a composition is associated with control of properties
such as adhesion and release of a substance from the surface of a
different composition.
[0009] The ability of switching is enabled by incorporation of a
switchable material which is ultimately responsible for the
switching. Products made with switchable materials require fewer
components, and are thus more reliable, have lower cost, and reduce
waste.
[0010] In view of the above, there is a need for developing
improved compositions that incorporate switchable materials. The
focus of the present disclosure is on surfaces which can change
their wettability (in other words their surface free energy) when
activated by heat.
SUMMARY
[0011] The present disclosure describes a composition comprising a
stimulus-responsive polymer, a base polymer, and a catalyst,
wherein the surface free energy of the stimulus-responsive polymer
is reversibly adjustable from a first surface free energy state to
a second surface free energy state when heated to an activation
temperature, and wherein the base polymer does not include a
platinum catalyst.
[0012] The present disclosure also describes a method of preparing
a polymer composition, the method comprising mixing a
stimulus-responsive polymer, a base polymer, and a catalyst to
create a mixture, wherein the surface free energy of the
stimulus-responsive polymer is reversibly adjustable from a first
surface free energy state to a second free energy state when heated
to an activation temperature, and wherein the catalyst is not a
platinum catalyst.
[0013] The present disclosure further describes a method of
adjusting a surface free energy of a composition comprising a
silicone polymer, a catalyst, and a stimulus-responsive polymer,
the method comprising heating the composition to an activation
temperature, wherein the catalyst is not a platinum catalyst, and
the adjustment of the surface free energy of the composition is
reversible.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic representation of a two-step printing
process.
[0015] FIG. 2 is a diagram illustrating the difference in hydrogen
bonding of a poly(n-isopropylacrylamide) polymer above and below a
lower critical solution temperature (LCST).
[0016] FIG. 3 is a graph showing the contact angle of a droplet of
water on that can be consistently switched successively between a
higher and a lower contact angle value.
EMBODIMENTS
[0017] As used herein, the modifier "about" used in connection with
a quantity is inclusive of the stated value and has the meaning
dictated by the context (for example, it includes at least the
degree of error associated with the measurement of the particular
quantity). When used in the context of a range, the modifier
"about" should also be considered as disclosing the range defined
by the absolute values of the two endpoints. For example, the range
"from about 2 to about 4" also discloses the range "from 2 to
4."
[0018] The terms "hydrocarbon" and "alkane" refer, for example, to
branched and unbranched molecules having the general formula
C.sub.nH.sub.2n+2, in which n is a number of 1 or more, such as
from about 1 to about 60. Exemplary alkanes include methane,
ethane, n-propane, isopropane, n-butane, isobutene, tort-butane,
octane, decane, tetradecane, hexadecane, eicosane, tetracosane, and
the like. Alkanes may be substituted by replacing hydrogen atoms
with one or more functional groups to form alkane derivative
compounds.
[0019] The term "functional group" refers, for example, to a group
of atoms arranged in a way that determines the chemical properties
of the group and the molecule to which it is attached. Examples of
functional groups include halogen atoms, hydroxyl groups,
carboxylic acid groups, and the like.
[0020] The term "alkyl group" refers, for example, to hydrocarbon
groups that are linear or branched, saturated or unsaturated, and
cyclic or acyclic, and with from about 1 to about 50 carbon atoms,
such as from about 5 to about 35 carbon atoms, or from about 6 to
about 28 carbon atoms.
[0021] The term "oleophobic" refers, for example, to a physical
property of a molecule relating to having a lack of a strong
affinity for oils. Water and fluorocarbons can be examples of
oleophobic compounds. The term "oleophilic" refers, for example, to
a physical property of a molecule relating to having an affinity
for oils.
[0022] The present disclosure describes a composition comprising a
stimulus-responsive polymer, a base polymer, and a catalyst,
wherein the surface free energy of the stimulus-responsive polymer
is reversibly adjustable from a first surface free energy state to
a second surface free energy state when heated to an activation
temperature, and wherein the base polymer does not include a
platinum catalyst.
[0023] The stimulus-responsive polymer may be any polymer the
changes its conformation in response to a stimulus, for example,
heat. The stimulus-responsive polymer may comprise, for example, a
unit of Formula (I):
##STR00001##
wherein, "R.sub.1" and "R.sub.2" are independently hydrogen or
alkyl having from 1 to about 10 carbon atoms, such as from about 1
to about 6 carbon atoms, or cycloalkyl with a number of carbons
from about 3 to about 10, or may be a heterocycle incorporating the
nitrogen atom that is capable of forming hydrogen bonds with a
number of carbons from 3 to 5, and "n" is a number from 1 to
1000.
[0024] However, not all combinations of R groups may provide a
thermally switchable polymer. One of ordinary skill is able to
determine which combination of R groups is able to provide a
thermally switchable polymer. For example, some combinations with
very small alkyl groups are fully soluble in water, such as
polymers where the NR.sub.1R.sub.2 group is NH.sub.2, NHCH.sub.3,
and N(CH.sub.3).sub.2. Others are totally insoluble in water
because the R groups render them too non-polar and do not allow the
chain reconfiguration for thermal switching. Such examples include
those where the NR.sub.1R.sub.2 group is
NH(CH.sub.2CH.sub.2CH.sub.2CH.sub.3), NHC(CH.sub.3).sub.3,
N(CH.sub.2CH.sub.3)(CH.sub.2CH.sub.2CH.sub.3), and
N(CH.sub.2CH.sub.2CH.sub.3).sub.2.
[0025] Specific examples of suitable R groups are shown in the
Table 1, from Galaev, I. Y. and B. Mattiasson, 15(5) Enzyme and
Microbial Technology 354 (1993), the disclosure of which is
incorporated by reference herein in its entirety.
TABLE-US-00001 TABLE 1 Chemical structures, names, and switching
temperatures of suitable thermally responsive poly(N-substituted
acrylamides) Activation temperature --NR.sub.1R.sub.2 [LCST]
(.degree. C.) NH--CH.sub.2--CH.sub.3 82
NH--CH.sub.2--CH.sub.2--CH.sub.3 22 NH--CH--(CH.sub.3).sub.2 32-34
N(CH.sub.3)(CH.sub.2--CH.sub.3) 56 N (CH.sub.2--CH.sub.3).sub.2
32-42 N(CH.sub.2--(CH.sub.3).sub.2)(CH.sub.3) 25 ##STR00002## 47
##STR00003## 55 ##STR00004## 4
[0026] All other combinations of hydrogen and/or alkyl groups with
up to about 6 carbon atoms may not be thermally responsive
[0027] The stimulus-responsive polymer that may comprise a unit of
Formula I may be, for example, a homopolymer or a copolymer. In a
homopolymer, the monomeric units of the homopolymer are
substantially the same. In a copolymer, the monomeric units of the
copolymer may be different. For example, the stimulus-responsive
polymer may be a poly-(N-alkylacrylamide) polymer, such as, for
example, poly-(N-isopropylacrylamide), poly-(N-ethylacrylamide),
poly-(N-n-propylacrylamide), poly(N-ethyl,N-methylacrylamide),
poly(N,N-diethylacrylamide), poly(N-isopropyl,N-methylacrylamide),
poly(N-cyclopropylacrylamide), poly(N-acryloylpyrrolidine), and
poly(N-acryloylpiperidine) and mixtures thereof.
[0028] In one example, R.sub.1 may be isopropyl and R.sub.2 may be
H, so that the stimulus-responsive polymer is
poly(N-isopropylacrylamide) (PNIPA) (for example, a homopolymer) or
an N-isopropylacrylamide copolymer (NIPAM). PNIPA, has the
following formula:
##STR00005##
wherein n may be an integer of from about 3 to about 1000, such as
from about 5 to about 500, or from about 10 to about 300. PNIPA is
a heat sensitive material that exhibits a large change in surface
energy in response to a small change in temperature. See, for
example, N. Mori et al., Temperature Induced Changes in the Surface
Wettability of SBR+PNIPA Films, 292, Macromol. Mater. Eng. 917,
917-22 (2007), the entire disclosure of which is incorporated
herein in its entirety. PNIPA has a hydrophobic isopropyl group on
a side chain. It is soluble in water below 32.degree. C. and
becomes insoluble when heated above this critical temperature. This
switching temperature (32.degree. C.) between hydrophilic and
hydrophobic states is called the lowest critical solution
temperature (LCST). The contact angle of a water drop placed onto a
PNIPA polymer film may change dramatically above and below the
LCST. For example, the contact angle of a water drop placed onto
the PNIPA film changed from about 60.degree. (hydrophilic) below
32.degree. C. to over about 93.degree. (hydrophobic) when heated
above 32.degree. C.
[0029] When the polymer is an N-isopropylacrylamide (NIPAM)
copolymer, the acrylamide monomer may comprise from about 30 to
about 100% of the repeating units of the copolymer, or from about
30% to about 100 mole % of the copolymer. The other comonomer of
the copolymer may be, for example, styrene, bisphenol-A, acrylic
acid, 4-vinylphenylboronic acid (VPBA), ethylmethacrylate;
methylmethacrylate (MMA), butylmethacrylate (BMA),
N,N-diethylaminoethyl methacrylate (DEAEMA), or methacrylic acid
(MAA). The other comonomer could also be a fluorinated alkyl
acrylate or fluorinated alkyl methacrylate, such as
hexafluoroisopropylmethacrylate (HFIPMA) or
2,2,3,3,4,4-hexafluorobutylmethacrylate (HFBMA). The other
comonomer could also be another acrylamide monomer, such as
N-ethylacrylamide (NEAM), N-methylacrylamide (NMAM),
N-n-propylacrylamide (NNPAM), N-t-butylacrylamide (NtBA), or
N,N-dimethylacrylamide (DMAM).
[0030] The stimulus-responsive polymer may comprise, for example,
poly(N-vinyl-caprolactam), represented by a unit of Formula II,
which switches at a temperature of about 31.degree. C.:
##STR00006##
[0031] The stimulus-responsive polymer may comprise, for example a
poly(2-alkyl-2-oxazoline), represented by the Formula III:
##STR00007##
wherein R is an alkyl group selected from propyl, isopropyl or
ethyl, and n is as defined above.
[0032] The switching temperatures are about 62.degree. C. for when
R is ethyl, about 36.degree. C. for when R is isopropyl, and about
25.degree. C. for when R is n-propyl.
[0033] The stimulus-responsive polymer may comprise
alkyl-substituted celluloses, for example, methylcellulose, with a
switching temperature of about 50.degree. C., as represented by
Formula IV, wherein n is as defined above.
##STR00008##
[0034] The stimulus-responsive polymer is mixed with a base
polymer. A base polymer may be any polymer that does not completely
prevent the stimulus-responsive polymer from changing its
conformation in response to a stimulus. As a general guiding rule,
the miscibility between the stimulus responsive polymer and the
base polymer is limited. Limited miscibility refers, for example,
to a dry film made of a coating composition that will form separate
domains of thermally switchable polymer dispersed into base polymer
material.
[0035] The base polymer may be, for example, silicone materials,
such as fluorosilicones, and silicone rubbers, such as room
temperature vulcanization (RTV) silicone rubbers, high temperature
vulcanization (HTV) silicone rubbers, and low temperature
vulcanization (LTV) silicone rubbers. These rubbers are known and
readily available commercially, such as SILASTIC.TM. 735 black RTV
and SILASTIC.TM. 732 RTV, both from Dow Corning; 106 RTV Silicone
Rubber and 90 RTV Silicone Rubber, both from General Electric; and
JCR6115CLEAR HTV and SE4705U HTV silicone rubbers from Dow Corning
Toray Silicones. Other suitable silicone materials include the
siloxanes (such as polydimethylsiloxanes); fluorosilicones
(including partially fluorinated fluorosilicones and fully
fluorinated fluorosilicones) such as Silicone Rubber 552, available
from Sampson Coatings, Richmond, Va.; liquid silicone rubbers such
as vinyl crosslinked heat curable rubbers or silanol room
temperature crosslinked materials; and the like. Another specific
example is Dow Corning Sylgard 182. Commercially available LSR
rubbers include Dow Corning Q3-6395, Q3-6396, SILASTIC.TM. 590 LSR,
SILASTIC.TM. 591 LSR, SILASTIC.TM. 595 LSR, SILASTIC.TM. 596 LSR,
and SILASTIC.TM. 598 LSR from Dow Corning.
[0036] A precursor to form the base material may be, for example, a
silanol terminated polymer with weight average molecular weights
ranging from 1,000 to 150,000. Before mixing with the
stimulus-responsive polymer, the base material may be partially
cross-linked, and then mixed with the stimulus-responsive polymer
before the base material is fully cured. The base polymer may be
stored in the partially cross-linked form until needed for mixing
with the stimulus-responsive polymer. For example, in a silanol
terminated polymer, the polymer may be reacted with an excess of
moisture-sensitive multi-functional silanes that contain, for
example, acetoxy compounds, as shown below.
##STR00009##
[0037] As shown above, the silicone has two acetoxy groups at each
end. This allows for cross-linking of the polymer by hydrolysis,
for example, by exposing the partially cross-linked polymer to
moisture. When exposed to moisture, a second stage reaction occurs
at the end acetoxy groups, thus forming the cured base polymer. In
the example, above, the cured base polymer would have the formula
shown below.
##STR00010##
[0038] In order to speed the cross-linking discussed above, a
catalyst may be added to the polymer. In other words, before mixing
the base polymer with the stimulus-response polymer, a catalyst may
be mixed with the base polymer, such that the base polymer contains
the catalyst when mixed with the stimulus-response polymer.
Alternatively, the base polymer, stimulus-response polymer, and the
catalyst may be mixed together as individual components. A catalyst
refers, for example to, a substance that increases the rate of a
chemical reaction. The catalyst can be a transition metal
organometallic compound or a base. An organometallic compound
refers, for example to, a metal atom bonded to an organic group or
groups.
[0039] The organometallic catalyst may be, for example, a tin (Sn)
compound, for example, stannous octoate, dibutyl tin dilaurate,
dioctyl tin dilaurate, dibutyl tin mercaptide, dioctyltin
carboxylate, tetrabutyl tin stannoxane, dibutyltin ketonate,
dioctyltin carboxylate, dimethyltin carboxylate, dibutyl tin
diricinoleate, Ca(OCH(CH.sub.3).sub.2).sub.2, NaOCH.sub.3,
NaOC.sub.2H.sub.5, and the like, and mixtures thereof. The
organometallic catalyst may be a titanium (Ti) alkoxylate compound.
For example the catalyst may be titanium (IV)
di-alkoxy-di-acetylacetonate of a general structure
Ti(OR).sub.2(acetylacetonate).sub.2, where R is an alkyl group, for
example, methyl, ethyl propyl, isopropyl, and butyl.
[0040] It has been found that acid compounds are not suitable for
catalyzing the cross-linking of the base materials when PNIPA
polymer is present. It is believed that the acid catalyst is
deactivated by forming hydrogen bonds with the nitrogen atoms for
the PNIPA polymer.
[0041] However, the catalyst may not include a platinum catalyst.
It has been found that, when stimulus-responsive polymer is mixed
with a base polymer and a catalyst, if a platinum catalyst is
included in the mixture, the platinum catalyst interferes with the
mixture's ability to cure. Without being bound by this theory, it
is theorized that a platinum catalyst is deactivated due to
chemical co-ordination of the by nitrogen atoms present in, for
example, the PNIPA polymer.
[0042] Before mixing the stimulus-responsive polymer, the base
polymer, and the catalyst together, the stimulus-responsive polymer
and the base polymer may each be separately dispersed in a solvent.
The solvent may be the same solvent, or a different solvent.
However, the solvent used to disperse the stimulus-responsive
polymer should be compatible with the base polymer, and the solvent
used to disperse the base polymer. Similarly, the solvent used to
disperse the base polymer should be compatible with the
stimulus-responsive polymer, and the solvent used to disperse the
stimulus-responsive polymer. Compatible refers, for example, to a
solvent that is miscible with another solvent, and does not cause a
substantial amount of the stimulus-responsive polymer or the base
polymer to precipitate out of the mixture. "Substantial amount"
refers, for example, to an amount greater than about 50% of the
stimulus-responsive polymer or the base polymer precipitating out
of the solution.
[0043] Suitable solvents include, for example, water and/or organic
solvents including, tetrahydrofuran (THF), acetone, acetonitrile,
carbon tetrachloride, chlorobenzene, diethyl ether, dimethyl ether,
dimethyl formamide, dimethyl sulfoxide, methylene chloride,
pentane, methyl ethyl ketone, cyclohexanone combinations thereof,
and the like.
[0044] The stimulus-responsive polymer may be mixed with the base
polymer and the catalyst to form the polymer composition in an
effective amount to impart to the polymer composition the desired
property and degree of surface free energy adjustment. For example,
the stimulus-responsive polymer is mixed with the base polymer in
proportions of from about 5 to about 80% compared to the base
polymer, such as from about 10% to about 70%, or from about 15% to
about 50%. In addition, the catalyst may be included in the mixture
in an amount that increases the rate of cross-linking of the base
polymer. For example, the catalyst may be added in an amount
ranging from 0.1 mol % to about 20.0 mol %, from about 0.2 mol % to
about 15.0 mol %, or from about 1.0 mol % to about 5.0 mol %.
[0045] Other optional components may be included in the mixture as
desired to impart other desirable properties to the composition.
For example, a binder material may be added to improve adhesion of
the mixture to a particular surface, a filler material may be added
to increase the viscosity or thickness of the composition, and/or
colorant may be added to impart a particular color to the mixture.
However, the other optional component(s) should not prevent the
mixture from substantially curing, or prevent the stimulus
responsive polymer from responding to a particular stimulus.
"Substantially curing" refers, for example, to at least 80% of the
mixture curing.
[0046] After mixing the stimulus-responsive polymer, the base
polymer, the catalyst, and other optional component(s), the mixture
may be deposited onto a suitable substrate or cast into any desired
shape.
[0047] The substrate may include, for example, metals, rubbers, and
fabrics. Metals include, for example, steel, aluminum, nickel,
their alloys, and like metals and the alloys of the like metals.
Examples of suitable rubbers include, for example, ethylene
propylene dienes, fluoroelastomers, n-butyl rubbers, silicone
rubbers and other elastomers and the like. A "fabric material"
refers, for example, to a textile structure comprised of
mechanically interlocked fibers or filaments, which may be woven or
nonwoven. Fabrics are materials made from fibers or threads and
woven, knitted, or pressed into a cloth or felt type structures.
"Woven" refers, for example, to fabrics closely oriented by warp
and filler strands at right angles to each other. "Nonwoven"
refers, for example, to randomly integrated fibers or filaments.
Examples of fabrics include woven or nonwoven cotton fabric,
graphite fabric, fiberglass, woven or nonwoven polyimide, woven or
nonwoven polyamide (for example, KEVLAR.TM., available from DuPont
or nylon) or polyphenylene isophthalamide (for example, NOMEX.TM.,
of E. I. DuPont of Wilmington, Del.), polyester, aramids,
polycarbonate, polyacryl, polystyrene, polyethylene, polypropylene,
cellulose, polysufone, polyxylene, polyacetal, and the like, and
mixtures thereof. The substrate may have any desired thickness.
[0048] The polymer composition may be deposited on the substrate by
any suitable process. Methods for depositing the mixture on the
substrate include draw-down coating, spray coating, spin coating,
flow coating, dipping, spraying such as by multiple spray
applications of very fine thin films, casting, web-coating,
roll-coating, extrusion molding, laminating, or the like. The
thickness of the surface coating may be any of any suitable
thickness that allows for the mixture to cure. For example, the
thickness of the surface coating may range from about 1 micron to
about 3 cm, from about 5 microns to about 1 cm, or from about 10
microns to about 0.5 cm. For example, the thickness of the surface
coating may be from about 5 to about 500 microns thick, such as
from about 10 to about 400 microns, or from about 20 to about 300
microns. After coating the mixture onto a substrate, the mixture
may be cured.
[0049] Casting involves pouring the mixture into a mold, and then
curing. The mold may be of any desired shape or size. After the
mold has been filled with the desired amount of the mixture, the
mixture may be cured. The polymer mixture may be coated or poured
into a mold for casting at any appropriate temperature. For
example, the polymer mixture may be coated or poured into a mold
for casting at a temperature of from about 35.degree. C. to about
55.degree. C., or from about 40.degree. C. to about 50.degree. C.,
such as about 40.degree. C., in order to maintain compatibility in
the hydrophobic state.
[0050] The mixture may be cured over a time period at any desired
temperature that is below the melting point of the cured mixture.
The time period needed to cure depends on many factors, for
example, the thickness of the coating or mold, the relative
humidity in the air, and the temperature at which the mixture is
cured, and one of ordinary skill understands how to determine the
time needed to cure the mixture based on these factors.
[0051] For example, the mixture may be cured for about 0.5 hours to
about 48 hours, such as from about 1 hour to about 36 hours, or
from about 2 hours to about 24 hours. The polymer mixture may be
cured at an appropriate temperature that is below the melting point
of the cured mixture, such as from about 10.degree. C. to about
200.degree. C., or from about 20.degree. C. to about 150.degree.
C., or from about 30.degree. C. to about 130.degree. C. For
example, the mixture may be cured at room temperature. "Room
temperature" refers, for example, to a temperature of about
20.degree. C. to about 25.degree. C.
[0052] After the composition has substantially cured, the surface
free energy of the composition may be switched in response to a
stimulus, such as being heated to an activation temperature. Thus,
the surface free energy of the composition may be adjusted. For
example, the adjustment of the surface free energy may enable both
wetting of a surface of the composition, or a transfer of a
substance on the surface of the composition to a different
surface.
[0053] More particularly, it is believed that the
stimulus-responsive polymer itself exhibits the property that
reversibly adjusts from a first surface free energy state to a
second surface free energy state when exposed to an activation
temperature. In turn, because the stimulus-responsive polymer is
mixed with the base polymer to form the polymer composition, the
stimulus-responsive polymer, when incorporated into the polymer
composition in an effective amount, imparts to the polymer
composition as a whole the property of reversibly adjusting from a
first surface free energy state to a second surface free energy
state when exposed to an activation temperature.
[0054] In addition, as a general matter, the wettability or spread
of a liquid on a surface is governed by the forces of interaction
between the liquid, the surface, and the surrounding air, and in
particular the surface free energy, as relating to the surface
chemistry and surface topology. Surface tension is a parameter that
can be described as the interaction between the forces of cohesion
and the forces of adhesion, which determines whether or not
wetting, or the spreading of liquid across a surface, occurs.
[0055] Young's Equation, which defines the balance of forces caused
by a wet drop on a dry surface, stipulates that:
.gamma..sub.SL+.gamma..sub.LV cos .theta.=.gamma..sub.SV
wherein .gamma..sub.SL=forces of interaction between a solid and
liquid; .gamma..sub.LV=forces of interaction between a liquid and
surrounding air; .gamma..sub.SV=forces of interaction between a
solid and surrounding air; and .theta.=contact angle of the drop of
liquid in relation to the surface. Young's Equation also shows
that, if the surface tension of the liquid is lower than the
surface energy, the contact angle is zero and the liquid wets the
surface. The surface energy depends on several factors, such as the
chemical composition and crystallographic structure of the solid,
and in particular of its surface, the geometric characteristics of
the surface and its roughness, and the presence of molecules
physically adsorbed or chemically bonded to the solid surface.
[0056] As discussed above, the surface free energy of the cured
composition may be switched from a first surface free energy state
to a second surface free energy state in response to a change in
temperature. For example, the surface free energy of the cured
composition may be reversibly switched from a relatively higher
surface free energy state to a relatively lower surface free energy
state when heated to an activation temperature. However, the
direction in which the stimulus-responsive polymer switches when
heat is applied may vary. For example, the surface free energy of
cured composition may increase when the cured composition is heated
above the activation temperature. Alternatively, the surface free
energy of the stimulus-responsive polymer may decrease when the
cured composition is heated above the activation temperature.
Accordingly, for example, the cured composition described above may
be hydrophilic at temperatures below the activation temperature,
and hydrophobic at elevated temperatures. Alternatively, for
example, the cured composition may be oleophilic at temperatures
below the activation temperature and oleophobic at elevated
temperatures.
[0057] In addition, for example, the cured polymer composition may
reversibly switch from a relatively higher first surface free
energy state to a relatively lower second surface free energy state
when heated to a temperature at or greater than an activation
temperature. A higher surface free energy state may result in
smaller contact angles, for example, with a droplet of water, and
indicates that the surface is more hydrophilic. A lower surface
free energy state may result in higher contact angles, for example,
with a droplet of water, and indicates that the surface is more
hydrophobic. When the temperature of the cured polymer composition
is less than the activation temperature, the polymer composition
may switch to the relatively higher surface free energy state.
Thus, for example, the surface free energy of the polymer
composition may be switched reversibly and controllably when heated
between two states: a higher surface free energy state and a lower
surface free energy state. The lower surface free energy state may,
for example, enable transfer of a substance on a surface of the
cured composition, while the higher surface free energy state may
enable spreading (wetting). A surface free energy state that
enables the spreading (wetting) step may have a surface free energy
that is greater than the surface tension of the liquid ink, while a
surface free energy state that enables transfer may have a surface
free energy that is lower than the surface free energy of the dry
(resin) ink.
[0058] The surface free energy of the stimulus-responsive polymer
in the first surface free energy state may be from about 25 to
about 65 dynes/cm, such as from about 30 to about 60 dynes/cm, or
from about 30 to about 55 dynes/cm. The second surface free energy
state may be, for example, from about 8 to about 30 dynes/cm, such
as from about 10 to about 25 dynes/cm, or from about 15 to about 25
dynes/cm. Surface free energy is calculated by measuring three
liquids' contact angle. The three liquids are water, formamide, and
diiodomethane. The surface free energy, acid and base components of
the polar surface energy, as well as the dispersive component were
calculated using Lewis acid-base method. Lewis acid-base theory is
given by the following equation for the solid-liquid interfacial
energy:
.gamma. j ( 1 + cos .theta. j ) = 2 ( .gamma. s LW .gamma. j LW ) 1
2 + 2 ( .gamma. s - .gamma. j + ) 1 2 + 2 ( .gamma. s + .gamma. j -
) 1 2 ##EQU00001##
where (LW), (+), (-) are the dispersive, acid and base components
of the SFE index, j refers to liquids 1, 2, 3, .theta..sub.j is the
contact angle of the jth liquid on the substrate, .gamma..sub.j is
the surface tension of liquid j, and subscript s refers to the
solid.
[0059] Additionally, characterization of the wetting properties of
the cured polymer composition may be carried out by measuring the
water droplet contact angle at a given temperature. The water
contact angle may be measured, for example, by a Fibro DAT1100
instrument manufactured by System AB, a FTA1000 instrument
manufactured by First Ten Angstroms, or a Dataphysics DCAT 21
dynamic contact angle measuring instrument. The contact angle
represents an average of the wetting performance of the base
materials and the stimulus-responsive polymer. For example, below
the activation temperature, the cured polymer composition may have
a water contact angle of from about 80.degree. to about
150.degree., such as from about 90.degree. to about 140.degree., or
from about 100.degree. to about 130.degree.. In embodiments, at or
above the activation temperature, cured polymer composition may
have a water contact angle of from about 10.degree. to about
70.degree., such as from about 15.degree. to about 50.degree., or
from about 20.degree. to about 45.degree..
[0060] The degree of wettability change (that is, the difference in
wettability between the polymer composition in the first surface
free energy state and the second surface free energy state) may be
adjusted through selection and concentration of the components of
the mixture. For example, the blended polymer may include from
about 50% to about 95% of a polymer base material having a
relatively low surface free energy (that is, in embodiments, having
a fixed surface free energy of from about 10 to about 25 dynes/cm,
such as from about 10 to about 23 dynes/cm, or from about 15 to
about 20 dynes/cm), and, thus, the wetting of the surface may be
switched between a less hydrophobic and a more hydrophobic state.
The degree of wettability change may also be controlled by
selection of a particular base polymer (for example, a base polymer
having a desired surface free energy), as well as by adjustment of
the concentration of the stimulus-responsive polymer in the blend.
The difference between the contact angle in the first surface free
energy state and the contact angle of the polymer composition in
the second surface free energy state may be from about 5.degree. to
about 140.degree., such as from about 10.degree. to about
100.degree., or from about 10.degree. to about 60.degree.. For
example, the cured composition may change water contact angles of
the liquid on the surface of the cured composition from about
95.degree. to about 118.degree. when heated from room temperature
to about 70.degree. C.
[0061] Any suitable temperature source may be used to cause the
temperature change in the cured composition to be at least the
activation temperature. The heat sources include, for example, a
heat lamp, an optical heating device, for example, a laser or an
LED bar, including IR light LED bar, a thermal print head,
resistive heating fingers, or a microheater array. A resistive
heating finger is an array of finger-like micro-electrodes that
result in resistive heating when the fingers are in contact with
the surface that is to be heated. The cured composition may cool on
its own from contact with a colder substrate and after the removal
of heat. Optionally, an air jet could be used to accelerate
cooling.
[0062] The stimulus-responsive polymer may be considered as
activate (for example, switch between a relatively higher surface
free energy and a relatively lower surface free energy) when heated
to an activation temperature of from about 10.degree. C. to about
120.degree. C., from about 15.degree. C. to about 100.degree. C.,
or from about 20.degree. C. to about 80.degree. C. In other words,
the stimulus-responsive polymer may switch states when heated to a
temperature greater than about 10.degree. C. and less than about
120.degree. C., such as from about 25.degree. C. to about
90.degree. C., or from about 30.degree. C. to about 70.degree.
C.
[0063] In addition, the switch between, for example, a relatively
higher surface free energy and a relatively lower surface free
energy may be reversible, for example, by cooling the composition
to any temperature below the activation temperature.
[0064] However, it is also understood that the activation
temperature of the stimulus-responsive polymer may be generally
affected by the solvent, optional component(s) (such as a binder),
or polymer matrix in general. The values reported in Table 1 above
are for solutions in water. However, it is known that the presence
of organic binder increases the activation temperature for a given
thermally switchable material. For example,
poly-(N-isopropylacrylamide) changes its surface free energy, for
example, switches its surface free energy from a first higher state
to a second lower surface free energy state, at 32.degree. C. in
water, but at 41.degree. C. in mixture with an organic polymer such
as SBR rubber. When dissolved in an organic solvent such as THF,
the activation temperature shifted to 60.degree. C. See N. Mori et
al., Temperature Induced Changes in the Surface Wettability of
SBR+PNIPA Films, 292 Macromol. Mater. Eng. 917, 917-22 (2007).
[0065] Without being bound by any particular theory, it is believed
that the thermally switchable property of the stimulus-responsive
polymer is due to the intermolecular hydrogen bonding interactions
of the stimulus-responsive polymer. For example, at a temperature
below LCST, the PNIPA chains form expanded structures caused by
intermolecular hydrogen bonding occurring predominantly between the
PNIPA chains and the water molecules present in the applied
solution. This intermolecular bonding contributes to the
hydrophilicity of the PNIPA-modified surface. However, at
temperatures above the LCST, hydrogen bonding occurs predominantly
between the PNIPA chains themselves, with the carbonyl oxygen atom
of one PNIPA chain bonding to the hydrogen atom on the nitrogen
atom of the adjacent PNIPA chain. This intermolecular hydrogen
bonding between the C.dbd.O and N--H groups of adjacent PNIPA
chains results in a compact conformation wherein the C.dbd.O and
N--H groups are not available to interact with water molecules,
which results in hydrophobicity at temperatures above the LCST.
These two states (for example, when the temperature is less than
the LCST and when the temperature is greater than the LCST) are
illustrated in FIG. 2. This interaction is not dependent on the
isopropyl chain, and thus should apply to other polymers as
well.
[0066] The polymer composition may be used in any suitable
apparatus where the ability to switch the surface free energy of a
composition is desired. For example, polymer composition may be
used as an intermediate transfer member that is suitable for use in
indirect printing.
Examples
Coating Materials Composition
[0067] A stock solution of a one part RTV silicone precursor was
prepared by dispersing 2 grams (g) of a commercially available
clear silicone containing a premixed tin catalyst in 5 g of methyl
ethyl ketone (MEK) as a solvent. The solution was shaken with high
speed shaker for 10-15 minutes. The stock solution was used in the
next 30 minutes to prevent uncontrollable curing. Separately a
stock solution of 20% PNIPA (weight average molecular weight
(M.sub.W)=40,000 from Polysciences, Inc.) in MEK solvent was
prepared.
[0068] 3 g of the stock silicone solution in MEK and 1.05 g of the
PNIPA solution in MEK were mixed for 5 minutes with a high speed
shaker (2500 rpm) followed by additional shaking at a lower speed
(700 rpm) for 10 minutes.
[0069] Coating and Curing
[0070] A plastic polyethylene terephthalate (PET) substrate
(Mylar.RTM.) was cleaned with tetrahydrofuran (THF) and dried. Then
the PNIPA/silicone solution was coated with a blade having a gap of
10 mils, at low speed. The coating was allowed to cure at room
temperature for 24 hours prior to testing (Example 1).
[0071] A coating of the silicone stock solution was also coated and
cured as described above for comparison (Comparative Example
1).
[0072] For Comparative Example 2, stock solutions of a two part
silicone precursor system (Silgard 184) which incorporates a
platinum catalyst and PINIPA were prepared in methyl ethyl ketone
(MEK) a solvent, coated. The films did not cure even when heated at
temperatures up to 155.degree. C. for several hours. Comparative
samples which did not contain PNIPA cured under the same curing
conditions.
[0073] Testing of the Cured Coating
[0074] A droplet of water was placed onto each cured film. The
contact angle of the water was measured by using an FTA200 Contact
Angle Instrument.
[0075] A FTA200 is a flexible video system for measuring contact
angle, surface and interfacial tensions, wettability, and
absorption. The contact angle of the water droplet was measured on
substrate at different temperatures by mounting a heating mantle
under the substrate while keeping the liquid at constant elevated
temperature, or at room temperature. Measurements were performed at
room temperature (23.degree. C.) and at 70.degree. C. Samples were
allowed to equilibrate to the selected temperature for 5 minutes
prior to each measurement. For each sample and temperature, two
measurements were taken and the average value is reported in Table
2.
TABLE-US-00002 TABLE 2 Contact Angle at Temperature @ 23.degree. C.
@ 70.degree. C. Average Average % PNIPA Contact Standard Contact
Standard Sample (dry film) Angle Dev. Angle Dev. Comparative 0.00%
106.11 2.64 104.13 0.82 Example 1 Example 1 19.60% 95.62 0.25
118.15 1.82
[0076] As shown in Table 2, in Example 1, a significant change of
the contact angle at room temperature occurred when compared with
the value measured for the heated sample. At room temperature, the
contact angle (CA) was about 95.degree., meaning that the sample
has a more hydrophilic character. At 70.degree. C. the CA was about
118.degree., meaning that the sample has a high hydrophobic
character.
[0077] For comparison, Comparative Example 1, which contains only
the cured silicone and no switchable material (PNIPA), had a CA of
about 106.degree. at room temperature, and showed no significant
change in the CA when heated to 70.degree. C., (a CA of about
104.degree.).
[0078] Reversibility Testing
[0079] Next, the reversibility of the switchable material was
tested.
[0080] Multiple switching was tested by measuring the contact angle
of a sample for multiple heat/cool cycles. The contact angle was
measured at each temperature (23.degree. C. and 70.degree. C.)
after allowing the sample to equilibrate for 5 minutes at the
selected temperature, as described above. The cycling results are
shown in FIG. 3.
[0081] As can be seen in FIG. 3, while there is some variation in
the CA at each temperature. However, the sample could be
consistently switched successively between a higher and a lower
contact angle value.
[0082] It will be appreciated that various of the above-disclosed
and other features and functions, or alternatives thereof, may be
desirably combined into many other different systems or
applications. Also, various presently unforeseen or unanticipated
alternatives, modifications, variations or improvements therein may
be subsequently made by those skilled in the art, and are also
intended to be encompassed by the following claims.
* * * * *