Stock material or miscellaneous articles – Surface property or characteristic of web – sheet or block
Reexamination Certificate
2001-10-16
2004-10-05
Jackson, Monique R. (Department: 1773)
Stock material or miscellaneous articles
Surface property or characteristic of web, sheet or block
C428S420000, C428S426000, C428S446000, C428S457000, C204S157150
Reexamination Certificate
active
06800370
ABSTRACT:
The present invention relates to surfaces which can alter their wetting properties when subjected to an external stimulus. More particularly, the present invention relates to photoresponsive surfaces, and methods for altering their wettability, articles comprising such surfaces and methods for preparing said surfaces.
Wetting plays a decisive role in the success or failure of many industrial and natural Photographic film production, pigment dispersion, mineral flotation, the movement of water in soils, printing, optical filters and aspects of gene therapy are all controlled in large measure by wetting and dewetting processes. The liquid phase involved is most commonly, but not exclusively, water.
The wetting of a surface is characterized by the Young equation
&ggr;
SV
=&ggr;
SL
+&ggr;
LV
cos &thgr; (I)
which describes the balance between the interfacial tensions (&ggr;) which exist at the three-phase line of contact between solid (S), liquid (L) and vapour (V). A change in the wetting of a surface by a liquid is reflected by the contact angle (&thgr;) which is measured through the denser phase as the angle that the tangent to the liquid-vapour interface makes with the solid surface at the contact line.
The change in wettability and in the contact angle is predicted by
cos
θ
(
p
H
)
=
cos
θ
(
p
H
pzc
)
-
Δ
F
dl
(
p
H
)
γ
Iv
1
where &thgr; is the contact angle at the solid-liquid-vapour interface.
&ggr;
Iv
is the liquid-vapour surface tension, pH
pzc
is the pH where the surface bears zero charge and &Dgr;F
dl
is the free energy of double layer formation. Correspondingly, the free energy of formation of a single double layer is given by
Δ
F
dl
=
-
∫
0
ψ
0
σ
0
ⅆ
ψ
2
where &PSgr;
0
is the electrical potential of the solid-liquid interface and &sgr; is the surface charge. This equation is valid for Nernstian surfaces i.e. for those for which &PSgr;
0
(pX) (where X is the potential determining ion) obeys the Nernst equation. For non-Nerstian surfaces, configurational contributions can be included in equation 2. The &Dgr;F
dl
contribution in Equation 2 can be readily calculated from electrical double layer theory. For Nernstian surfaces this is achieved by calculating &thgr;
0
(&PSgr;
0
) from the Polsson-Boltzmann equation and performing the integration in Equation 2, In this case, for a flat diffuse double layer,
Δ
F
dl
=
-
8
n
0
kT
κ
{
cos
h
zeψ
0
2
kT
}
3
where n
0
is the concentration of the symmetric z:z electrolyte, k is the Boltzmann constant, &kgr; the reciprocal double layer thickness and e the elementary charge. The relationship between surface charge, pH and the influence of ionic strength is thus complete. By way of illustration only, when a molecular surface ionizes as the pH increases above its pKa, say, by one pH unit, where H
+
sq
is the potential determining ion, the increased surface charge causes the contact angle to decrease and the surface becomes more wettable with respect to the wetting phase. Thus, by changing the surface charge or pKa of a surface, its wetting properties can conceivably be altered.
It has now been found that certain molecules attached as a thin layer or film to the surface of a substrate, impart a photoresponsitivity to the substrate surface such that the wettability of the surface changes when it is irradiated with light of an appropriate wavelength.
Accordingly, in a first aspect, the present invention provides an article having a photoresponsive surface, said article comprising a substrate having photoionisable moieties capable of undergoing dimerization attached to at least a portion of a surface thereof, the proximity of said moieties to one another being such that irradiation with light of an appropriate wavelength results in dimerization of at least a portion of said moieties thereby altering the wettability of the surface.
In another aspect, the present invention also provides a method for preparing a substrate having a photoresponsive surface which method comprises attaching to at least a portion of the substrate surface, photoionisable moieties capable of undergoing dimerization wherein the proximity of said moieties to one another on the substrate surface is such that irradiation of said moieties with light of an appropriate wavelength results in dimerization of at least a portion of said moieties, thereby altering the wettability of the surface.
In yet a further aspect, the invention provides a method for altering the wettability of a surface of a substrate, said substrate having attached to at least a portion of said surface photoionisable moieties capable of undergoing dimerization, wherein the proximity of said moieties to one another on said surface is such that dimerization can occur, said method comprising irradiating said surface with light at an appropriate wavelength sufficient to dimerize at least a portion of the photoionisable moieties.
The present invention is based on the finding that certain molecules, when irradiated by light of an appropriate wavelength, can covalently couple to give a dimeric form which has a different pKa value to that of the individual molecule. When such molecules (i.e. the monomer) are attached to a substrate surface, in a way that they can dimerize, this can provide a photoresponsive surface whose wettability may be altered by irradiation at the appropriate wavelength.
The ionisable moiety may be any moiety which is ionisable upon irradiation with light of a suitable wavelength and which is capable of undergoing dimerization upon ionisation. In a preferred form, the ionisable moieties contemplated by the present invention are nitrogenous heterocyclic moieties, eg. a 5-7-membered ring having 1 or 2 nitrogen atoms and preferably at least one double bond available for dimerization.
Of the nitrogenous heterocyclic moieties, a particularly preferred class of photoionisable moieties are pyrimidine-related and incorporate the substructure (I):
wherein
is an optional double bond and, where valency dictates, the trivalency of the nitrogen atom is completed by H, methyl, ethyl or propyl. In a preferred form, there is at least one double bond, more preferably a, is a double bond. In a particularly preferred form a is a double bond and b and c are single bonds.
Optionally, one or more carbon atoms may be further substituted by a substituent selected from methyl, ethyl, propyl (n- or iso-), oxo, halo (fluoro, chloro, bromo, iodo), halomethyl, hydroxy, methoxy, ethoxy, propoxy, C
1-3
acyloxy; amino, carboxy, carboxyethyl and carboxymethyl.
Another class of nitrogenous heterocyclic moieties contemplated are the spiropyrans, for example spiroindoline.
With respect to the pyrimidine-related moieties, the “dimerization” will generally be a [2+2] cyclisation to form a cyclobutane ring. Thus, the position of the substituents and double bonds within (I) must be such that ionisation and subsequent dimerization of at least a portion of the moieties can occur upon irradiation of light with an appropriate wavelength. The placement of the substituents on (I) will affect the steric bulk of the moiety, thereby influencing the final proximity of these moieties to one another on attachment to the substrate surface and, therefore, the efficiency of the dimerization.
The person skilled in the art will also recognise that judicious selection of the substituents of (I) will influence the hydrophobicity/hydrophilicity of the photoresponsive surface.
Examples of suitably substituted pyrimidine-related moieties include thymine, uracil, cytosine, orotic acid and barbituric acid. Another class of moieties which contain the substructure (I) are the purine bases such as adenine and guanine.
The skilled person will recognise that dimerization may occur between two identical moieties or two diff
Abbott Scott J.
Hayes Robert A.
Ralston John
Reynolds Geoffrey D.
Jackson Monique R.
Seed IP Law Group PLLC
University of South Australia
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