Patent Grant
8574713
The present invention relates to fibers exhibiting a water contact angle of above 150° and water contact angle hysteresis of below 15°, methods of producing the same, and applications thereof. The present invention further relates to superhydrophobic fiber mats, methods of producing the same, and applications thereof.
Electrospinning is a versatile method to produce polymer fibers with diameters in the micron, sub-micron and nano (<100 nm) range. Numerous polymeric materials have been electrospun into continuous, uniform fibers, and various applications of the fibers have been widely recognized. The method employs electrostatic forces to stretch a polymer jet and make superfine fibers. Electrohydrodynamic instabilities that occur in electrospinning, charge density of the electrified jet (and indirectly, solution conductivity), surface tension, and viscoelasticity of the solution have been shown to play important roles both in making the production of fibers possible and in controlling the size and uniformity of the fibers. The development of internal structure in such fibers has generally been limited to crystallization of homopolymer or macrophase separation of a polymer blend during the drying and solidification of the fiber, inclusion of immiscible additives such as clays, nanotubes and metallic or oxide particles. Surface structures attributed to “breath figures” have also been shown.
Block copolymers offer an alternative method by which internal structure can be induced in electrospun fibers via microphase separation. In bulk, block copolymers are known to form microphase separated structures such as spheres, cylinders, gyroids and lamellae, depending on molecular weight, volume fractions of components and the degree of immiscibility of the different polymer blocks. In thin films, it has been shown that surface forces and confinement effects are strong enough to alter the phase separation behavior. However, no such information is currently available on microphase separation in a confined cylindrical, sub-micrometer sized and fiber-like geometry. Electrospinning of block copolymers is therefore not only promising for applications involving surface chemistry, drug delivery and multi-functional textiles, but is also of intrinsic scientific interest.
The wetting behavior of a solid surface is important for various commercial applications and depends strongly on both the surface energy or chemistry and the surface roughness. Currently, surfaces with a water contact angle above 150° are considered to be “superhydrophobic” and are the subject of great interest for their water proof and self-cleaning usages. There is a need to develope fiber-forming processes and products that would demonstrate the desired surface characteristics, such as superhydrophobicity, as well as other properties, such as mechanical strength and integrity.
In one embodiment, this invention provides a fiber comprising a copolymer wherein said fiber exhibits a water contact angle of above 150° and water contact angle hysteresis of below 15°.
In one embodiment, this invention provides a superhydrophobic fiber mat, wherein said mat comprises fibers comprising a copolymer and wherein said mat exhibits a water contact angle of above 150° and water contact angle hysteresis of below 15°.
In one embodiment, this invention provides a method for preparing a superhydrophobic fiber or fibers, the method comprising the step of electrospinning a solution comprising a copolymer, wherein said copolymer comprises a component, comprising a silicon structure and having a surface energy of less than 1 mJ/m2, said solution exhibits conductivity, surface tension and viscoelasticity fluidic properties, and whereby said electrospinning produces a superhydrophobic fiber or fibers exhibiting a water contact angle of above 150° and water contact angle hysteresis of below 15°.
In one embodiment, the method further comprises the step of producing a superhydrophobic mat comprising said fibers.
In one embodiment, this invention provides a composition comprising a fiber of this invention.
In one embodiment, the invention provides an article of manufacture comprising a fiber or mat of this invention.
In one embodiment, this invention provides a fiber comprising a copolymer wherein said fiber exhibits a water contact angle of above 150° and water contact angle hysteresis of below 15°.
In one embodiment, this invention provides a superhydrophobic fiber mat, wherein said fiber comprises a copolymer and wherein said mat exhibits a water contact angle of above 150° and water contact angle hysteresis of below 15°.
In one embodiment of this invention, the water contact angle may be above 160°. In another embodiment, the water contact angle may be about 163°. In another embodiment, the water contact angle may be between 160°-165°. In another embodiment, the water contact angle may be between 150°-160°. In another embodiment, the water contact angle may be between 160°-165°. In another embodiment, the water contact angle may be between 160°-170°. In another embodiment, the water contact angle may be between 160°-175°.
In one embodiment of this invention, the water contact angle hysteresis may be between 10°-15°. In another embodiment, the water contact angle hysteresis may be between 10°-14°. In another embodiment, the water contact angle hysteresis may be between 8°-13°. In another embodiment, the water contact angle hysteresis may be between 6°-12°. In another embodiment, the water contact angle hysteresis may be between 5°-10°. In another embodiment, the water contact angle hysteresis may be between 0°-5°.
In one embodiment of this invention, the fiber may exhibit surface roughness properties.
In one embodiment of this invention, the mat may be electrospun. In another embodiment, the mat may exhibit wettability properties. In another embodiment, the mat may be composed solely of fibers. In another embodiment, the fibers within the mat are uniform. In another embodiment, the mat may be composed solely of fibers randomly oriented within a plane. In one embodiment of this invention, the mat may exhibit a water contact angle of above 160°. In another embodiment, the mat may exhibit a water contact angle of about 163°. In another embodiment, the mat may exhibit a water contact angle of between 160°-165°. In another embodiment, the mat may exhibit a water contact angle of between 150°-160°. In another embodiment, the mat may exhibit a water contact angle of between 160°-165°. In another embodiment, the mat may exhibit a water contact angle of between 160°-170°. In another embodiment, the mat may exhibit a water contact angle of between 160°-175°.
In one embodiment of this invention, the mat may exhibit a water contact angle hysteresis of between 10°-15°. In another embodiment the mat may exhibit a water contact angle hysteresis of between 10°-14°. In another embodiment, the mat may exhibit a water contact angle hysteresis of between 8°-13°. In another embodiment, the mat may exhibit a water contact angle hysteresis of between 6°-12°. In another embodiment, the mat may exhibit a water contact angle hysteresis of between 5°-10°. In another embodiment, the mat may exhibit a water contact angle hysteresis of between 0°-5°.
In one embodiment of this invention, the mat may exhibit an isotropic nature of the contact angle, contact angle hysteresis or a combination thereof.
In one embodiment of this invention, the mat may exhibit a non-isotropic nature of the contact angle, contact angle hysteresis or a combination thereof.
In one embodiment of this invention, the mat may include:
In one embodiment of this invention, the mat may exhibit surface roughness properties.
In one embodiment of this invention, the mat may exhibit pore sizes of between 0.01-100 micron. In another embodiment, the mat may exhibit pore sizes of between 0.1-100 micron. In another embodiment, the mat may exhibit pore sizes of between 0.1-50 micron. In another embodiment, the mat may exhibit pore sizes of between 0.1-10 micron. In another embodiment, the mat may exhibit pore sizes of between 0.1-5 micron. In another embodiment, the mat may exhibit pore sizes of between 0.1-2 micron. In another embodiment, the mat may exhibit pore sizes of between 0.2-1.5 micron. In another embodiment, the pore size may be non-uniform. In another embodiment, the pore size may be uniform.
In one embodiment of this invention, the diameter of the fiber, or, in another embodiment, fibers in the mat, which in some comprise only some fibers, or in other embodiments comprises fibers mostly having a diameter of between 1 nm-5 micron, or in another embodiment, the diameter is between 1 nm-500 nm, or in another embodiment, the diameter is between 1 nm-100 nm, or in another embodiment, the diameter is between 100 nm-300 nm, or in another embodiment, the diameter is between 100 nm-500 nm, or in another embodiment, the diameter is between 50 nm-400 nm, or in another embodiment, the diameter is between 200 nm-500 nm, or in another embodiment, the diameter is between 300 nm-600 nm, or in another embodiment, the diameter is between 400 nm-700 nm, or in another embodiment, the diameter is between 500 nm-800 nm, or in another embodiment, the diameter is between 500 nm-1000 nm, or in another embodiment, the diameter is between 1000 nm-1500 nm, or in another embodiment, the diameter is between 1500 nm-3000 nm, or in another embodiment, the diameter is between 2000 nm-5000 nm, or in another embodiment, the diameter is between 3000 nm-4000 nm.
In one embodiment of this invention, the fiber may be an electrospun fiber.
In one embodiment of this invention, the fiber may exhibit a microphase-separation.
In one embodiment of this invention, the fiber may include, inter alia, a component, wherein the surface energy of the component is below 5 mJ/m2. In one embodiment of this invention, the fiber may include, inter alia, a component, wherein the surface energy of the component is below 1 mJ/m2. In another embodiment, the surface energy of the component is between 0.1-1 mJ/m2. In another embodiment, the surface energy of the component is between 0.1-0.5 mJ/m2. In another embodiment, the surface energy of the component is between 0.5-0.9 mJ/m2.
In one embodiment of this invention, the component may segregate to the surface of the fiber. In another embodiment, the component may be a part of the copolymer. In another embodiment, the component may include, inter alia, a silicon structure. In another embodiment, the silicon structure may be, inter alia, a resin, linear, branched, cross-linked, cross-linkable silicone structure or any combination thereof. In another embodiment, the silicon structure may include, inter alia, poly-dimethylsiloxane (PDMS). In another embodiment, the silicon structure may include, inter alia, fluorine.
In one embodiment of this invention, the copolymer may include, inter alia, polyisobutylene, polyolefin, polystyrene, polyacrylate, polyurethane, polyester, polyamide, polyetherimide, any derivative thereof or any combination thereof. In another embodiment, the copolymers according to the invention may be substituted or unsubstituted. In another embodiment, the copolymers according to the invention may be saturated or unsaturated. In another embodiment, the copolymers according to the invention may be linear or branched. In another embodiment, the copolymers according to the invention may be alkylated. In another embodiment, alkylated may be methylated. In another embodiment, the copolymers according to the invention may be halogenated. In another embodiment, the copolymers according to the invention may be chlorinated. In another embodiment, the polyolefin may include, inter alia, polyisobutylene, polyethylene, polypropylene or any combination thereof. In another embodiment, the copolymers according to the invention may be fluorinated. In another embodiment, the copolymer may include, inter alia, poly(alphamethyl)styrene.
In another embodiment, the copolymer may include, inter alia, a block, graft, star or random copolymer. In another embodiment, the block copolymer may include, inter alia, poly(styrene-co-dimethylsiloxane) (PS-PDMS), or in another embodiment, poly(dimethylsiloxane-co-etherimide).
In one embodiment of this invention, the molecular weight of the PS-PDMS may be higher than about 100K. In another embodiment, the molecular weight of the PS-PDMS may range between about 100K-5000K. In another embodiment, the molecular weight of the PS-PDMS may range between about 100K-1000K. In another embodiment, the molecular weight of the PS-PDMS may range between about 100K-500K. In another embodiment, the molecular weight of the PS-PDMS may range between about 200K-300K. In another embodiment, the molecular weight of the PS-PDMS may be higher than about 250K. In another embodiment the molecular weight of the PS-PDMS may be 150K, or about 150K. In one embodiment, the term “about” refers to a deviance from the stated value or range of values by +/−1%, or in another embodiment, by +/−2%, or in another embodiment, by +/−5%, or in another embodiment, by +/−7%, or in another embodiment, by +/−10%, or in another embodiment, by +/−13%, or in another embodiment, by +/−15%, or in another embodiment, by +/−18%, or in another embodiment, by +/−20%.
In one embodiment of this invention, the fiber may include, inter alia, poly-dimethylsiloxane (PDMS) blocks non-uniformly dispersed within a polystyrene (PS) matrix. In one embodiment of this invention, the fiber may include, inter alia, polystyrene-polydimethylsiloxane copolymer blocks non-uniformly dispersed within a siloxane matrix.
In one embodiment of this invention, the copolymer may include, inter alia, polystyrene (PS). In another embodiment, the volume fraction of PS in the copolymer may be between 0.05-0.9. In another embodiment, the volume fraction of PS in the copolymer may be between 0.1-0.6. In another embodiment, the volume fraction of PS in the copolymer may be between 0.3-0.5. In another embodiment, the volume fraction of PS in the copolymer may be between 0.4-0.9. In another embodiment, the volume fraction of PS in the copolymer may be 0.45. In another embodiment, the volume fraction of PS in the mixture may be between 0.1-0.9. In another embodiment, the volume fraction of PS in the mixture may be between 0.3-0.6. In another embodiment, the volume fraction of PS in the mixture may be 0.57. In another embodiment, the volume fraction of PS in the mixture may be 0.813. In another embodiment, the volume fraction of PS in the mixture may be 0.05-0.9, and exhibit may exhibit a cylindrical morphology upon microphase separation in the bulk.
In one embodiment of this invention, the poly-dimethylsiloxane (PDMS) blocks may segregate to the surface of the fiber.
In one embodiment of this invention, the poly-dimethylsiloxane (PDMS) blocks may be aligned along the fibers axis.
In one embodiment, this invention provides a superhydrophobic nonwoven mat including submicron diameter fibers of poly(styrene-co-dimethylsiloxane) (PS-PDMS) block copolymers blended with homopolymer polystyrene (PS). In one embodiment, the PS/PDMS system of this invention, has a larger Flory interaction parameter compared to the conventional styrene-diene block copolymers. In one embodiment, the PS/PDMS system of this invention, exhibits a pronounced surface activity of the PDMS block. In one embodiment of this invention, the Flory interaction of the PS/PDMS system and the pronounced surface activity of the PDMS block facilitate the microphase separation in the electrospun fibers even without any post treatment. In one embodiment, the superhydrophobicity of the electrospun mats according to the invention may be determined by static and dynamic contact angle attributed to both the surface roughness and surface excess of the PDMS blocks. In one embodiment, the superhydrophobicity of the electrospun mats according to the invention may be obtained without the presence of microspheres within the mat. In one embodiment, the superhydrophobicity of the electrospun mats according to the invention may exhibit an isotropic nature of the contact angle hysteresis. In another embodiment, the isotropic nature of the contact angle hysteresis may be attributed to the random in-plane arrangement of fibers, which may mitigate pinning effects on the liquid drop. In one embodiment, the high surface tension at the air/polymer interface and/or the confinement of the microphase separated structures to the fiber geometry and/or the aligning effect of the elongational flow according to the invention may have some effects on the morphologies of the block copolymers.
In one embodiment, this invention provides a method for preparing a fiber, wherein the fiber includes a copolymer and wherein the fiber exhibits a water contact angle of above 150° and water contact angle hysteresis of below 15°, the method may include, inter alia, the step of electrospinning a solution including, inter alia, the copolymer.
In one embodiment, this invention provides a method for preparing a superhydrophobic fiber mat, wherein the fiber includes a copolymer and wherein the mat exhibits a water contact angle of above 150° and water contact angle hysteresis of below 15°, the method may include, inter alia, the step of electrospinning a solution including, inter alia, the copolymer.
In one embodiment of this invention, the concentration of the poly(styrene-co-dimethylsiloxane) (PS-PDMS) in the solution is 21%. In another embodiment, the concentration of the poly(styrene-co-dimethylsiloxane) (PS-PDMS) in the solution is about 21%. In another embodiment, the concentration of the poly(styrene-co-dimethylsiloxane) (PS-PDMS) in the solution is between 5-10%. In another embodiment, the concentration of the poly(styrene-co-dimethylsiloxane) (PS-PDMS) in the solution is between 10-20%. In another embodiment, the concentration of the poly(styrene-co-dimethylsiloxane) (PS-PDMS) in the solution is between 20-25%. In another embodiment, the concentration of the poly(styrene-co-dimethylsiloxane) (PS-PDMS) in the solution is between 15-25%. In another embodiment, the concentration of the poly(styrene-co-dimethylsiloxane) (PS-PDMS) in the solution is between 20-30%. In another embodiment, the concentration of the poly(styrene-co-dimethylsiloxane) (PS-PDMS) in the solution is between 20-40%.
In some embodiments, the polystyrene-polydimethylsiloxane copolymer is mixed with a siloxane resin such as MQ siloxane resin (Dow Corning 407), at various ratios, for example, 18:5, 15:10, 12:12 copolymer to resin, or in another embodiment, about 10-25:5-15 copolymer to resin ratio. In some embodiments, the total solids level is 25%, or in another embodiment, 23%, or in another embodiment, 24%, or in another embodiment, about 18%-30%. In one embodiment, the mixture is dissolved in 3:1 THF-DMF solvent.
In one embodiment of this invention, the solution includes a solvent. In another embodiment, the solvent is an organic solvent. In another embodiment, the solvent may include, inter alia, tetrahydrofuran, diethylformamide or a combination thereof. In another embodiment, the solvent may include, inter alia, tetrahydrofuran and diethylformamide in a ratio of 3:1. In another embodiment, the solvent may include, inter alia, chloroform, toluene or a combination thereof. In one embodiment, the solvent comprises chloroform:diethylformamide in a ratio of 4:1.
In one embodiment of this invention, the solution may include additives. In another embodiment, the additives may include, inter alia, inorganic salts, organic salts, surfactants or any combination thereof. In another embodiment, the additives may include, inter alia, any material that increases the conductivity of the solution. In another embodiment, the additives may include, inter alia, any material that decreases the surface tension of the solution. In another embodiment, the additives may include, inter alia, a dye. In another embodiment, the additives may include, inter alia, a colorant. In another embodiment, the additives may include, inter alia, a labeling agent.
In one embodiment of this invention, the solution exhibits conductivity, surface tension and viscoelasticity fluidic properties. In one embodiment of this invention, the zero shear rate viscosity of the solution may be between 0.1-10 PaS. In another embodiment, the zero shear rate viscosity of the solution may be between 0.5-10 PaS. In another embodiment, the zero shear rate viscosity of the solution may be between 1-10 PaS. In another embodiment, the zero shear rate viscosity of the solution may be between 5-8 PaS. In another embodiment, the zero shear rate viscosity of the solution may be about 6 PaS.
In one embodiment of this invention, the extensional viscosity of the solution may be between 0.1-100,000 PaS. In another embodiment, the extensional viscosity of the solution may be between 100-1000 PaS. In another embodiment, the extensional viscosity of the solution may be between 1-100 PaS. In another embodiment, the extensional viscosity of the solution may be between 5-50 PaS. In another embodiment, the extensional viscosity of the solution may be about 10 PaS.
In one embodiment of this invention, the solution conductivity may be between 0.01-25 mS/m. In another embodiment, the solution conductivity may be between 0.1-10 mS/m. In another embodiment, the solution conductivity may be between 0.1-5 mS/m. In another embodiment, the solution conductivity may be between 0.1-1 mS/m. In another embodiment, the solution conductivity may be between 0.1-0.5 mS/m. In another embodiment, the solution conductivity may be about 0.3 mS/m.
In one embodiment of this invention, the surface tension of the solution may be between 10-100 mN/m. In another embodiment, the surface tension of the solution may be between 20-80 mN/m. surface tension of the solution may be between 20-50 mN/m. In another embodiment, the surface tension of the solution may be about 30 mN/m.
In one embodiment of this invention, the dielectric constant of the solution may be between 1-100. In another embodiment, the dielectric constant of the solution may be between 5-50. In another embodiment, the dielectric constant of the solution may be between 10-70. In another embodiment, the dielectric constant of the solution may be between 1-20. In another embodiment, the dielectric constant of the solution may be about 10.
In one embodiment of this invention, the zero shear rate viscosity of the solution may be 6 Pa S, the extensional viscosity of the solution may be 10 Pa S, the solution conductivity may be 0.3 mS/m and the surface tension of the solution may be 30 mN/m.
In one embodiment of this invention, the molecular weight of the PS-PDMS may be about 240K, the concentration of the PS-PDMS in the solution may be about 21%, and the solution includes THF and DMF in a ratio of 3:1.
In one embodiment of this invention, the term “percent” or “%” may refer to weight percent.
In one embodiment of this invention, the voltage applied in the electrospinning may range between 5-50 KV. In another embodiment, the voltage applied in the electrospinning may range between 10-40 KV. In another embodiment, the voltage applied in the electrospinning may range between 15-35 KV. In another embodiment, the voltage applied in the electrospinning may range between 20-30 KV. In another embodiment, the voltage applied in the electrospinning may be about 30 KV.
In one embodiment of this invention, the distance between electrodes in the electrospinning may range between 10-100 cm. In another embodiment, the distance between electrodes in the electrospinning may range between 20-75 cm. In another embodiment, the distance between electrodes in the electrospinning may range between 30-60 cm. In another embodiment, the distance between electrodes in the electrospinning may range between 40-50 cm. In another embodiment, the distance between electrodes in the electrospinning may be about 50 cm.
In one embodiment of this invention, the flow rate in the electrospinning may range between 0.005-0.5 ml/min. In another embodiment, the flow rate in the electrospinning may range between 0.005-0.1 ml/min. the flow rate in the electrospinning may range between 0.01-0.1 ml/min. the flow rate in the electrospinning may range between 0.02-0.1 ml/min. the flow rate in the electrospinning may be about 0.05 ml/min.
In one embodiment of this invention, the electric current in the electrospinning may range between 10-10,000 nA. In another embodiment, the electric current in the electrospinning may range between 10-1000 nA. In another embodiment, the electric current in the electrospinning may range between 50-500 nA. In another embodiment, the electric current in the electrospinning may range between 75-100 nA. In another embodiment, the electric current in the electrospinning may be around 85 nA.
In one embodiment of this invention, the voltage applied in the electrospinning may be about 30 KV, the flow rate may be the electrospinning is about 0.05 mL/min and the electric current in the electrospinning may be about 85 nA.
In one embodiment of this invention, a parallel plate setup may be used in the electrospinning.
In one embodiment, electrospinning may be conducted with the aid of any suitable apparatus as will be known to one skilled in the art.
In one embodiment, the methods of this invention, may further include post treatment of the fibers. In one embodiment, the methods of this invention may further include annealing of the fibers. In another embodiment, the annealing of the fibers may enhance the hydrophobicity for these fibers. In another embodiment, the annealing of the fibers may enhance the regularity of the microphases for these fibers.
In one embodiment, this invention provides a composition including any fiber according to the invention.
In one embodiment, this invention provides an article of manufacture including any fiber according to this invention. In another embodiment, this invention provides an article of manufacture including any mat according to this invention. In another embodiment, the article of manufacture may be, inter alia, a waterproof substance. In another embodiment, the article of manufacture may be, inter alia, a water resistant substance. In another embodiment, the article of manufacture may be, inter alia, a self-cleaning substance. In another embodiment, the article of manufacture may be, inter alia, a water draining substance. In another embodiment, the article of manufacture may be, inter alia, a coating substance. In another embodiment, the coating substance reduces drag. In another embodiment, the coating substance reduces drag in a gas, in a liquid or in both. In another embodiment, the gas may be air. In another embodiment, the liquid may be water.
In another embodiment of this invention, the article of manufacture may be a membrane.
In another embodiment of this invention, the article of manufacture may be, inter alia, manufacture is a fabric. In another embodiment, the fabric may be, inter alia, a breathable fabric. In another embodiment, the fabric may have, inter alia, a filtration functionality. In another embodiment, the fabric may have, inter alia, an absorptive functionality. In another embodiment, the fabric may be, inter alia, a non-woven fabric. In another embodiment, the fabric may be, inter alia, a waterproof fabric. In another embodiment, the fabric may be, inter alia, a water resistant fabric.
In one embodiment of this invention, the fabric may be a superhydrophobic fabric. In another embodiment, the fabric may be an electrospun fibrous fabric. In one embodiment of this invention, the fabric may exhibit a water contact angle of above 160°. In another embodiment, the fabric may exhibit a water contact angle of about 163°. In another embodiment, the fabric may exhibit a water contact angle of between 160°-165°. In another embodiment, the fabric may exhibit a water contact angle of between 150°-160°. In another embodiment, the fabric may exhibit a water contact angle of between 160°-165°. In another embodiment, the fabric may exhibit a water contact angle of between 160°-170°. In another embodiment, the fabric may exhibit a water contact angle of between 160°-175°.
In one embodiment of this invention, the fabric may exhibit a water contact angle hysteresis of between 10°-15°. In another embodiment the fabric may exhibit a water contact angle hysteresis of between 10°-14°. In another embodiment, the fabric may exhibit a water contact angle hysteresis of between 8°-13°. In another embodiment, the fabric may exhibit a water contact angle hysteresis of between 6°-12°. In another embodiment, the fabric may exhibit a water contact angle hysteresis of between 5°-10°. In another embodiment, the fabric may exhibit a water contact angle hysteresis of between 0°-5°.
In another embodiment of this invention, the article of manufacture may be, inter alia, a drug delivery system. In another embodiment, the article of manufacture may be, inter alia, a bandage or patch. In another embodiment, the bandage or patch may include, inter alia, a drug.
In one embodiment of the invention, the term “contact angle” may refer to the angle on the liquid side tangential line draw through the three phase boundary where a liquid, gas and solid intersect.
In one embodiment of the invention, the term “static contact angle” may refer to the contact angle measured of a Sessile drop on a solid substance when the three phase line is not moving.
In one embodiment of the invention, the term “dynamic contact angle” may be divided into “advancing contact angle” and “receding contact angle” which may refer to, according to embodiments of the invention, to the contact angles measured when the three phase line is in controlled movement by wetting the solid by a liquid or by withdrawing the liquid over a pre-wetted solid, respectively. In another embodiment, the liquid is water.
In one embodiment of the invention, the term “contact angle hysteresis” may refer to the difference between the measured advancing and receding contact angles.
In one embodiment of the invention, the term “wettability” may refer to the process when a liquid spreads on (wets) a solid substrate. In another embodiment wettability may be estimated by determining the contact angle.
In one embodiment of the invention, the term “surface tension” may refer to the measurement of the cohesive (excess) energy present at a gas/liquid interface.
In one embodiment of the invention, the term “viscoelasticity” may refer to a combination of viscous and elastic properties in a material with the relative contribution of each being dependent on time, temperature, stress and strain rate.
In one embodiment of the invention, the terms “viscosity” or “viscous” may refer to the resistance of a material to flow under stress.
The following examples are presented in order to more fully illustrate some embodiments of the invention. They should, in no way be construed, however, as limiting the scope of the invention.
A Poly(styrene-co-dimethylsiloxane) diblock copolymer was synthesized at Dow Corning Corp. laboratories by sequential controlled anionic polymerization of styrene and then hexamethylcyclotrisiloxane (D3) as shown in
The size exclusion chromatography (SEC) chromatogram of PS-PDMS is shown in
Electrospinning:
A 21 wt % solution of the above material was prepared by dissolution in a 3:1 mixture by weight of tetrahydrofuran (THF): dimethylformamide (DMF) (Aldrich). It formed a milky gel-like solution that was stable (no further solidification or precipitation takes place during storage) at room temperature. This solution was electrospun using a parallel plate setup as described previously [Shin, Y. M.; Hohman, M. M.; Brenner, M. P.; Rutledge, G. C. Polymer 2001, 42, 9955].
The electrical potential, solution flow rate, the protrusion of the spinnerette from the upper plate and the distance between the capillary tip and the collector were adjusted so that spinning was stable and dry nanofibers were obtained (Table 1).
Scanning Electron Microscope (SEM)
A JEOL-6060SEM (JEOL Ltd, Japan) scanning electron microscope (SEM) was used to observe the general features of the fibers. The fibers were sputter-coated with a 2-3 nm layer of gold for imaging using a Desk II cold sputter/etch unit (Denton Vacuum LLC, NJ). The fiber diameters were determined using AnalySIS image processing software (Soft Imaging System Corp., Lakewood, USA).
Transmission Electron Microscope (TEM):
A JEOL JEM200 CX (JEOL Ltd, Japan) transmission electron microscope (TEM) was used to observe internal features of the fibers. For lateral viewing the fibers were deposited directly onto a copper TEM grid. For axial viewing, the fibers were fixed in a glycol methacrylate based embedding system. (JB-4 Plus Embedding Kit, TED PELLA. INC.), and then sectioned into 100 nm slices using an ultramicrotome (RMC Scientific Corp. Tucson, Ariz.) with a diamond knife. No staining was necessary, as the intrinsic difference in electron density of PS block and PDMS block provided adequate contrast.
Differential Scanning Calorimeter (DSC):
The thermal transitions in the as-electrospun fibers of the block copolymer were characterized using a Q1000 modulated differential scanning calorimeter (DSC) (TA Instrument Inc., DE). The measurements were carried out under a nitrogen atmosphere and the sample was scanned for two cycles from −100 to 200° C. with a rate of 10° C. per minute.
X-Ray Photoelectron Spectrometer (XPS):
Surface chemistry of the fibers was characterized using a Kratos Axis Ultra X-ray photoelectron spectrometer (XPS) (Kratos Analytical, Manchester) with a monochromatized A1 Kα X-ray source. The XPS signals from the silicon and oxygen of the PDMS block were used to distinguish the two polymer blocks and to obtain the composition of the fiber surface.
Contact Angle and Contact Angle Hysteresis Measurements:
The contact angle of water on the electrospun mat was measured using a Contact Angle Meter G10 (Kruss, Germany). The final result was obtained by averaging at least 4 separate runs. Contact angle hysteresis was obtained by the sessile drop method [Lau, K. K. S.; Bico, J.; Teo, K. B. K.; Chhowalla, M.; Amaratunga, G. A. J.; Milne, W. I.; McKinley, G. H.; Gleason, K. K. Nano Lett., 2003, 3, 1701]. To study the sliding behavior, water droplets were dripped on a fiber mat tilted at 17° and the motion of the droplets was observed using a video recorder.
The PS/PDMS diblocks are expected to be very strongly segregated due to the non-polar nature of the PDMS block. A rough estimate for the Flory interaction parameter χ is obtained by group contribution methods, χ=(100 cm3/mol)/RT)(δPS−δPDMS)2, [Bristow, G. M.; Watson, W. F. Trans. Faraday Soc., 1958, 54, 1731] where δPS=18.6 (J/cm3)1/2 and δPDMS=15.4 (J/cm3)1/2 are the Hildebrandt solubility parameters for PS and PDMS, respectively [‘Polymer Handbook’ (Eds J. Brandrup and E. H. Immergut). 3rd Edn, Wiley, New York, 1989, P. VII/557]. For a degree of polymerization N=2771, χN=1130, well in excess of χN=10.5 required for microphase separation in a symmetric diblock copolymer according to mean field theory [Leibler, L. Macromolecules, 1980, 13, 1602].
Strong segregation of the PS and PDMS blocks is further evidenced by the glass transition temperature Tg of 105° C. exhibited in the DSC curve of
From the material composition, the average atomic ratio of carbon to silicon is about 8.8. According to the XPS data shown in
The contact angle measurement and the sliding behavior of the water on the PS-PDMS electrospun mat are shown
The advancing and receding contact angles measured by the sessile drop method were 164° and 149°, respectively, giving a hysteresis of 15°. The wetting behavior of the PS-PDMS fiber mat were compared with that of a pure PS fiber mat with comparable fiber sizes (average diameter=300 nm) and pore size distribution (pore sizes ranging from 0.200 to 1.5 mm, as determined by Hg porosimetry, Quantachrome Instruments Poremaster 33). It was found that the PS fiber mat not only had a smaller contact angle (138°) but also showed a sliding behavior characterized by a much bigger contact area between the mat and the droplet than in the case of PS-PDMS block copolymer fiber, as shown on
Table 2 presents the composition and conditions for the preparation of additional electrospun superhydrophobic fibers. A number of additional fibers and mats comprising the same were produced using various copolymers, which yielded a water contact angle of above 150°.
Some embodiments of mats were prepared, as described hereinabove, via electrospinning of a polystyrene-polydimethylsiloxane copolymer solution at a concentration of 12.95% in Chloroform, yielding a fibrous mat with a contact angle of 170.5 degrees.
Some embodiments of mats of this invention were prepared via electrospinning of the polystyrene-polydimethylsiloxane copolymer described herein, mixed in various ratios of copolymer to MQ siloxane resin (Dow Corning 407), dissolved in 3:1 THF-DMF solvent, electrospun to form a fibrous mat
Some embodiments of mats of this invention were prepared via electrospinning of a polystyrene-polydimethylsiloxane copolymer having a total molecular weight of 153000 and a volume ratio of polystyrene=0.813, dissolved in a 4:1 chloroform-DMF solvent mixture. Fibrous mat with a water contact angle of 168° were obtained. Based on this example, copolymers with a volume percent of as little as 19 of silicone produce superhydrophobic fibrous mats.
Some embodiments of mats of this invention were prepared via electrospinning of a poly(dimethylsiloxane)etherimide copolymer with 35-40% polydimethylsiloxane electrospun from a 15 weight percent solution in chloroform to form a fibrous mat, which had a water contact angle of 157.8°.
These results indicate that a number of superhydrophobic fibers and mats can be prepared according to the methods of this invention.
This Application claims the benefit of U.S. Provisional Application Ser. No. 60/659,907, filed Mar. 10, 2005, which is hereby incorporated by reference in its entirety.
This invention was made with government support awarded by the Army Research Office under ARO Grant No. DAAD19-02-D-0002. The government has certain rights in this invention.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3354022 | Johnson, Jr. et al. | Nov 1967 | A |
| 3686355 | Gaines et al. | Aug 1972 | A |
| 4861830 | Ward, Jr. | Aug 1989 | A |
| 4920168 | Nohr et al. | Apr 1990 | A |
| 5589563 | Ward et al. | Dec 1996 | A |
| 5641835 | Smith et al. | Jun 1997 | A |
| 5733657 | Macheras et al. | Mar 1998 | A |
| 5856245 | Caldwell et al. | Jan 1999 | A |
| 5856416 | Bachmann et al. | Jan 1999 | A |
| 5954966 | Matsuura et al. | Sep 1999 | A |
| 6127507 | Santerre et al. | Oct 2000 | A |
| 6664306 | Gaddam et al. | Dec 2003 | B2 |
| 20020151634 | Rohrbaugh et al. | Oct 2002 | A1 |
| 20020170690 | Buchsel et al. | Nov 2002 | A1 |
| 20030080049 | Lee et al. | May 2003 | A1 |
| 20040052957 | Cramer et al. | Mar 2004 | A1 |
| 20040138083 | Kimbrell et al. | Jul 2004 | A1 |
| 20040176556 | Bowers et al. | Sep 2004 | A1 |
| 20040266302 | DiSalvo et al. | Dec 2004 | A1 |
| 20050008876 | Teranishi et al. | Jan 2005 | A1 |
| 20050053782 | Sen et al. | Mar 2005 | A1 |
| 20050148264 | Varona et al. | Jul 2005 | A1 |
| Number | Date | Country |
|---|---|---|
| 1397668 | Feb 2003 | CN |
| 1449642 | Aug 2004 | EP |
| WO 2005021843 | Mar 2005 | WO |
| Entry |
|---|
| Frenot et al. Polymer nanofibers assembled by electrospinning. Current Opinion in Colloid and Interface Science, 8, (2003), pp. 64-75. |
| Gibson, P., H. Schreuder-Gibson, and D. Rivin, Transport properties o.fporous membranes based on electrospun nanojibers. Colloids and Surfaces A, 2001. 187: p. 469-481. |
| Schreuder-Gibson, H, P. Gibson, K. Senecl, M, Sennett, J. Walker, W. Yeomana, O, Ziegler, and F, P. Tsai, Protective textile materials based on electrospun nanofibers. Journal of Advanced Materials, 2002. 34(3): p. 44-55. |
| Schreuder-Gibson, Hi.. Q. Truong, J.E. Walker, J,R, Owens, J.D, Wander, and W.E, Jones. Chemical and biological protection and detection in fabrics for protective clothing. MRS Bulletin, 2003 2R(8): p. 574-578. |
| Li. D. and Y,N, Xia. Electrospinning of nanofibers: Reinventing the wheel? Advanced Materials, 2004. 16(1): p. 1151-1170. |
| Frenot, A. and I.S, Chronakis, Polymer nanefibers assembled by electrospzfl fling. Current Opinion in Colloid & Interface Science, 2003. 8(1): p. 64-75. |
| Deitzel, J.M., 'jAY, Kosik, Se, McKnight, N,C,B. Tan, J,M. DeSimone, and S. Crette, Eiectrospinnin.g ofpolymer nanofibers with specific surface chemistry. Polymer, 2002. 43(3): p. 1025-1029. |
| Gibson, P. and H. Schreuder-Gibson, Patterned electrosprav fiber structures. International Nonwovens Technical Conference, Sep. 15-18, 2003: p. 1. |
| Miwa. M.. A. Nakajirna. A. Fujishima, K. Hashimoto. and T. Watanabe, Effects of the Surface Roughness on Sliding Angles of Water Droplets on Superhydrophobie Surfaces. Lannuir, 2000. 16: p. 5754-5760. |
| Slang, L., V. Zflao, and J, Thai, A lotus-leaf like superhydrophobic surface: A porous inicrosphere/nanofiber composite fl/rn prepared by elecirohydrodynamics, Aflgewandto Chenhie—Intensational Edition. 2004.43(33): p. 4338-4=41. |
| Feng, U, S.H. Li, H.J. Li, J. Zhai. V,L, Song, L. Jiang, and D,B. Zhu, Super-hydrophobic surface ofal&gnedpolyaciy/onitrile nanofibers. Angewandte Chemie-International Edition. 2002, 41(7): p. 1221-. |
| Supplementary European Search Report for EP 06737690, Aug. 5, 2009. |
| Number | Date | Country | |
|---|---|---|---|
| 20060292369 A1 | Dec 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60659907 | Mar 2005 | US |
