Patent ID: 12221363

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following disclosure is presented to provide an illustration of the general principles of the present invention and is not meant to limit, in any way, the inventive concepts and embodiments contained herein. All terms defined herein should be afforded their broadest possible interpretation, including any implied meanings as dictated by a reading of the specification as well as any words that a person having skill in the art and/or a dictionary, treatise, or similar authority would assign thereto.

Further, it should be noted that, as recited herein, the singular forms “a”, “an”, and “the” include the plural referents unless otherwise stated. Additionally, the terms “comprises”, “comprising”, “includes”, “including”, “has” and the like, when used herein specify that certain features are present in that embodiment; however, such terms should not be interpreted to preclude the presence or addition of additional steps, operations, features, components, and/or groups thereof.

With specific reference now to the accompanying drawings,FIGS.1-4represent schematic illustrations of a method involving the trap-and-release of oils and the regeneration of smart membrane surfaces in accordance with one embodiment of the present invention. InFIG.1, a body of water (e.g., seawater)10is contaminated with oil12, which is shown schematically in the form of bubbles or droplets.FIG.2shows the oil12trapped within oxidized mesh membranes14.FIG.2Ashows an oil droplet12adhered to the oxidized polymer surface of one of the mesh membranes14illustrated inFIG.2, wherein a DBS group16of the polymer has its hydrophobic tail exposed. As shown inFIG.3, reduced polymer surfaces of the membranes14cause collected oil droplets12to be released from the membranes14(through sliding or permeating).FIG.3Ashows an oil droplet12being released from (e.g., by sliding or permeating) the reduced polymer surface of one of the mesh membranes14illustrated inFIG.3, wherein the DBS group16of the polymer has its hydrophilic head exposed.FIG.4shows the membranes14after they have been oxidized to thereby regenerate their membrane surfaces in preparation for reuse of the membranes14as oil collection agents.

In an embodiment, a substrate cooperates with a conjugated polymer to form a composite mesh structure. The result is a smart membrane that includes: (1) conjugated polymer; (2) CNTs; and (3) SS mesh. On the SS mesh, CNTs17a(seeFIG.2B) are directly grown using chemical vapor deposition to form the substrate for the conjugated polymer. Finally, the surfactant-doped conjugated polymer film is coated atop the CNTs17ausing electropolymerization to complete the composite mesh structure.

In an embodiment, multiwalled carbon nanotubes (CNTs)17acan be directly grown from 304 stainless steel (SS) meshes (Size 200×200, McMaster-Carr, Robbinsville, NJ) using atmospheric pressure chemical vapor deposition (APCVD). SS meshes were cut, rinsed, dried and then placed in the center of a 200 quartz tube in a horizontal three zone chemical vapor deposition (CVD) furnace and heated to 750° C. under the flow of 60 sccm hydrogen (H2, Praxair, Newark, NJ) and 500 sccm Argon (Ar, Praxair, Newark, NJ). Then, additional ethylene (C2H4, Praxair, Newark, NJ) was fed through the system at flow rates of 100 sccm for 7 mins for CNTs growth. Subsequently, the samples were rapidly cooled to room temperature by blowing air into the furnace.

After CNT growth, PPy(DBS) film was electropolymerized atop the CNT-covered SS mesh surface. First, 1 mL pyrrole monomer (reagent grade, 98%, Sigma-Aldrich, St. Louis, MO) was thoroughly mixed with 150 mL 0.1 mol/L sodium dodecylbenzenesulfonate (NaDBS, technical grade, Sigma-Aldrich, St. Louis, MO) solution. Then, a CNT-covered SS mesh, a saturated calomel electrode (SCE, Fisher Scientific Inc., Pittsburgh, PA), and another SS mesh (5 cm×5 cm) were submerged in the solution as the working, reference, and counter electrode, respectively. The coating of PPy(DBS) surfaces was carried out using a potentiostat (263A, Princeton Applied Research, Oak Ridge, TN) by applying 0.7 V to the working electrode (vs. SCE) and stopped once surface charge density reached 1 C/cm2. Instead of CNTs, SS meshes were deposited with 10 nm chromium (Cr) and 30 nm gold (Au) films using an e-beam evaporator (Explorer 14, Denton Vacuum, Moorestown, NJ), and then also coated with PPy(DBS) surfaces. After fabrication, the PPy(DBS) mesh surfaces were rinsed and dried in air overnight before any further characterizations.

It should be noted that CNTs are optional in the foregoing embodiment. However, the CNTs are preferred, as the in situ switch time decreases because the CNTs allow for a higher surface area, which increases the amount of DBS molecules desorbed from PPy(DBS) surfaces under reduction, thereby facilitating more rapid decrease of oil/water interfacial tension and retention force.

In another embodiment, a conductive carbon foam17bcan be used directly for PPy(DBS) electropolymerization after necessary cutting and dicing (seeFIG.2B). The pristine carbon foam17bis extremely porous and has a 3D microstructure. It is also lightweight. The 2.5×0.5×0.2 cm carbon foam weighs only 0.025 g, compared to a 2×3 cm PPy(DBS) mesh, which weighs 0.2 g. After PPy(DBS) electropolymerization, the whole surface of carbon foam17bcan be evenly and uniformly covered with PPy(DBS) surfaces. Results show that the PPy(DBS) surface inherits the 3D porous structure of the carbon foam17bwithout blocking the pores. In testing conductive carbon foam as a substrate for PPy(DBS) electropolymerization, results further show that the resulting PPy(DBS) foam exhibits much higher absorbing capacity compared with the PPy(DBS) mesh. To summarize, the PPy(DBS) foam had 3 times more absorption capacity with only 1/10 of the weight, versus the PPy(DBS) mesh. Such higher absorption capacity is attributed to the abundant surface area in the 3D porous structure of the foam17b. By fabricating PPy(DBS) surfaces on conductive carbon foam, the absorption capacity of absorbent made of PPy(DBS) material significantly increases.

The PPy(DBS) foam's longevity was tested, and it still absorbed and released DCM oil after 100 redox cycles. Additionally, the foam proved in tests its ability to absorb and release hexane and diesel. Such 3D printed PPy(DBS) has the potential for further improving the absorbing capacity and tailoring absorbent structure for different oil cleanup scenarios, as well as the development of other applications using PPy(DBS) surfaces and its wettability characteristic that can be varied in response to changing parameters (i.e., tunable wettability).

In another embodiment, 3D printing is used to directly print PPy(DBS) materials with a 3D porous structure to form PPy(DBS) absorbents. In this way, the structure and physical/mechanical properties of PPy(DBS) absorbents can be tailored and the mass production of PPy(DBS) absorbents will be possible. In order to test the feasibility of 3D printing of PPy(DBS), the PPy(DBS) solution was prepared and later cast on flat substrates (i.e., glass slides, Au-coated Si) to form freestanding PPy(DBS) films. Then, the resulting freestanding PPy(DBS) films were tested for their tunable wettability and switchable adhesion toward oils.

To prepare the PPy(DBS) solution, PPy(DBS) surfaces must be dissolved in organic solvents. However, it is suggested that electropolymerized PPy(DBS) is insoluble in either organic or inorganic solvents due to its high degree of cross-linking. Thus, electrochemical oxidization is used instead to prepare PPy(DBS) material, in which the polymerization is started by adding oxidants (e.g., iron(III) chloride, FeCl3) into the solution with pyrrole monomer and NaDBS.

With careful controlling of the molecular ratio/concentration of pyrrole/NaDBS/FeCl3and the polymerization duration, PPy(DBS) particles were synthesized and precipitated, which were then filtered out and thoroughly rinsed and dried. For example, 0.5 mL (0.0075 mL) of pyrrole monomer was mixed with 75 mL of 0.1 mol/L NaDBS solution for one hour. Then, 5 mL of 0.25 mol/L FeCl3solution was added dropwise to start the polymerization process. After 10 minutes, the precipitates were filtered out using centrifugation, washed extensively with water three times, and dried in air at 60° C. for 72 hours. Subsequently, the PPy(DBS) particles were dissolved in dimethylformamide (DMF) to form a stable suspension. To test the tunable wettability of PPy(DBS) made from electrochemical oxidization, one drop of such suspension was applied on a glass slide and dried overnight to form a freestanding film. The resulting PPy(DBS) freestanding film was then tested for tunable wettability.

This initial result suggests that the PPy(DBS) films made by a casting PPy(DBS) particle solution also exhibit tunable wettability, demonstrating the feasibility of making an oil absorbent via the 3D printing of PPy(DBS). Thus, with a careful design of the structure based on the oil cleanup requirement, the PPy(DBS) oil absorbent can be fabricated using 3D printing. Such oil absorbent can have both high absorbing capacity, as well as in situ surface regeneration ability, making it suitable for highly efficient next generation oil cleanup technology.

By way of example, DCM droplets on freestanding PPy(DBS) surfaces are characterized by a spherical shape and contact angle of ˜60° when no voltage was applied to the surface. However, when −0.9V was applied, the DCM droplet exhibited flattening behavior, similar to the shape change observed in those droplets on the reduced electropolymerized PPy(DBS) surface. A DCM droplet once adhered to the oxidized PPy(DBS) surface rolled away after 60 seconds of reduction, demonstrating tunable adhesion.

Any of the smart membranes described hereinabove can be incorporated into an unmanned, robotic surface vessel adapted for oil cleaning and recovery from a body of oil-contaminated water. For purposes of discussion only, the membranes14will be described in connection with one practical, potentially commercial embodiment of such a vessel20, which is shown schematically inFIGS.5and6.

With particular reference now toFIGS.5and6, the vessel20includes a reduction chamber22with a reservoir24of electrolyte and a plurality of electrodes26in the form of passive rollers having a negative electric voltage. The vessel20also includes an oxidation chamber28with a reservoir30of electrolyte and a plurality of electrodes32in the form of passive rollers having a positive electric voltage.

A conveyor belt34includes a plurality of the smart membranes14, which are spaced apart and electrically insulated from one another along the entire length of the conveyor belt34. Active (i.e., driven) rollers36function as motive means for assisting in the performance of a method which includes the following steps: (i) passing the oxidized membranes14through the body of oil-contaminated water10, where the lowest submerged portion of the membranes' surface (stable in the oxidized state) collects oil droplets12from the body of water10; (ii) passing the membranes14through the reservoir24of electrolyte in the reduction chamber22, where the membranes14are electrochemically reduced to thereby release collected oil droplets12with an assist from the simultaneous application of a dynamic pressure; and (iii) passing the membranes14through the reservoir30of electrolyte in the oxidation chamber28, where the membranes14are oxidized to thereby regenerate them for reuse as oil-collection agents when they are subsequently passed back into the body of oil-contaminated water10.

In connection with the performance of the aforementioned method, the membranes14can be reduced in the reduction chamber22by applying a negative voltage (e.g., −0.9 volts) to the rollers/electrodes26versus a 13 mm×35 mm platinum (Pt) mesh (i.e., counter-electrode). The subsequent oxidation of the membranes14can be achieved by applying a positive voltage (e.g., 0.1 volt) to the rollers/electrodes32versus a 13 mm×35 mm platinum (Pt) mesh (i.e., counter-electrode).

A partition38between the reduction chamber22and the oxidation chamber28electrically insulates the two chambers from each other so that the requisite and appropriate negative and positive voltages may be applied to the membranes14as they pass between the reduction chamber22and the oxidation chamber28, respectively. The partition38also creates a physical barrier that inhibits collected oil40in the reduction chamber22from migrating to the oxidation chamber28. The collected oil40may be cleaned in the reduction chamber22to thereby avoid re-contaminating the body of water10outside the vessel20.

The rollers/electrodes26,32are arranged inside the reduction and oxidation chambers,22,28respectively, so as to maximize the amount of collected oil40housed within the vessel20. The rollers/electrodes26,32also serve to support the conveyor belt34as it passes through the reduction and oxidation chambers22,28, respectively.

In addition to the active rollers36, which function as motive means (i.e., a drive system) for the conveyor belt34, the vessel20includes a simple electric propulsion system (not shown), an onboard microcontroller (not shown) supporting remote control of the drive and propulsion systems, and a lithium polymer battery (not shown). The vessel20is designed to be sufficiently positively buoyant to take on additional weight during the performance of an oil-collection operation.

FIGS.7and8relate to an alternate implementation or embodiment of the present invention. In one aspect, an embodiment of the present invention is directed to a moveable belt adapted for use as an oil collection apparatus, and in a further aspect, the invention is directed to an apparatus including a moveable belt where an oxidation state of at least a portion of the belt can be controlled to enable collection and release of oil from a body of water. Configurations and procedures for voltage biasing for adherence and/or release of oil to the belt are explained hereinbelow. In an embodiment, at least a portion of the belt can possess a tunable wettability characteristic based on an oxidation or reduction state of at least a portion of the belt that can be varied in response to an applied voltage. For example, when electrochemically oxidized, (e.g., by applying a positive voltage), at least a portion of the belt's surface can include a strong adhesion to oil, thereby allowing the belt to collect oil as it is exposed to a body of water including oil. In some further embodiments, when at least a portion of the belt is reduced (e.g., by applying a negative voltage), that portion of the belt can release the trapped oil into, for example, an interior reservoir of a surface vessel. In some embodiments, like those discussed above, the belt may be combined with a conveyor belt in a small-scale, oil-cleaning surface robot adapted to access oil spills in confined areas, such as under piers and in the small spaces between vessels and piers.

Referring toFIG.7, showing a side cross-sectional view of a mobile system110for collection of spilled oil128from a body of water126, andFIG.8, showing a perspective cross-sectional view of the mobile system110ofFIG.1according to one embodiment of the invention, the system110comprises a segmented belt120that can be positioned to pass through the oil contaminated water126, and then into a collection container122. In some embodiments, the segmented belt120is an elastic segmented belt capable of providing an elastic mechanical response as a function of tension or compression of the segmented belt120. In some embodiments of the invention, at least a portion of the segmented belt120can be coated with the polymer15which can be pre-oxidized in preparation for uptake of oil from a body of water. In this state, the segmented belt120can be prepared for uptake of the oil128onto the surface of the polymer115as the segmented belt120passes through any oil suspended in or on the water126, causing it to attach to the segmented belt120. Some embodiments of the invention include the following capabilities: 1) to be used for both light and heavy oils (i.e., oils that are lighter and heavier than water); 2) to provide scalability for addressing large areas covered by oil and collection of large oil volumes; and 3) to control electrical isolation to ensure the proper electrochemical state of the polymer15immobilized on the segmented belt20to allow absorption (by the polymer15in its oxidized state) and release (by polymer15in its reduced state) of oils.

During operation of the embodiment shown inFIGS.7and8, the segmented belt120passes from the collection container122according to the direction denoted by the arrows adjacent to the belt (see arrows shown in Figure. 7). Initially, the segmented belt120is clean of oil and is pre-oxidized by application of a negative bias (e.g., using approximately −0.9 V) followed by a positive bias (e.g., using approximately +0.6 V) to oxidize at least the surface of the segmented belt120, thereby making it attractive to oil. In some embodiments, movement of the segmented belt120through the body of water126can be facilitated by a series of rollers140. The non-limiting embodiment ofFIGS.7and8shows a series of rollers140, some of which are submerged in the water126(e.g., rollers143), and others of which are positioned above the surface of the water126(e.g., rollers141). Further, in some embodiments, the use of an alternating arrangement of submerged rollers143and non-submerged rollers141can enable the system110to increase the exposure of the segmented belt120to the surface oil128because the segmented belt120can pass through an increased area of surface oil128, and thus can spend more time exposed to the surface oil128.

The non-limiting embodiment illustrated inFIG.7shows a break-line representing the length of the segmented belt120and the number of rollers140,141,143, it being understood that such number can be greater than that shown. Further, the submerged rollers140,143are shown that can assist in conveying the segmented belt120, which is now an oil-carrying belt, on a return path towards the collection vessel148. In some embodiments, the segmented belt120can consist of a plurality of individual conductive segments positioned on an elastic backing that can be stretched to electrically separate one or more portions of the segmented belt120from each other. Using this arrangement, when a section of the segmented belt120is un-stretched, the individual segments in the section are electrically contiguous and conductive as a whole. However, under tension, the segments separate from one another and become electrically isolated. In some embodiments, this behavior allows the segmented belt120in the oil release area of the collection chamber122to be electrically isolated from the segmented belt120outside of the collection chamber122, and biased negatively for oil release, which occurs in the collection chamber122. In other embodiments, the segmented belt120segments can be separated by conventional mechanical linkages enabling one or more segments to be mechanically separated from one another. In some embodiments, this enables one or more segments or portions of the segmented belt120to be electrically isolated from one or more other segments or portions of the segmented belt120. In one embodiment, as the oil-carrying segmented belt120passes into the collection vessel148, one or more tension rollers138can cause one or more sections or segments of the segmented belt120inside the collection vessel148to be stretched, and to become electrically disconnected or isolated from the other sections or segments of the segmented belt120(i.e., those segmented belt120sections not within the collection vessel148). The stretched portion of the segmented belt120is represented inFIG.7as a region117of the belt with a reduced diameter of the segmented belt120.

In some embodiments, the polymer115applied to at least some portions of the segmented belt120can comprise at least one conjugated polymer. Thus, in some embodiments, an exposed surface or layer of the segmented belt120can include a conjugated polymer that can function to promote the collection of oil on the exposed surface of the segmented belt120when the conjugated polymer is oxidized. In some embodiments, when the conjugated polymer is reduced, it can function to release oil from the exposed surface of the segmented belt120. In some embodiments, the aforementioned oxidation and reduction of the conjugated polymer can be performed electrochemically. In some embodiments, electrochemical oxidation can be performed by applying a positive voltage to the conjugated polymer, while electrochemical reduction can be performed by applying a negative voltage to the conjugated polymer. In some embodiments, the positive electric voltage can lie in a range of from greater than 0 to about 1.5 volts, while the negative electric voltage can lie in a range of from about −0.6 to about −1.5 volts. For example, in some embodiments, the oil-coated belt section in the collection chamber122can be negatively biased via spring-loaded electrical contacts, releasing the oil from the belt and into the collection chamber122, wherein it is collected as “collected oil” (seeFIG.7).

Any of the rollers shown (for example, the tension rollers138shown inFIG.7) can be constructed such that the outer circumference of the roller is comprised of a conductive metallic material, or alternatively an insulating polymeric material. In embodiments where the tension rollers138include a conductive metallic material, the conductive surface may be used to establish electrical connection with the segmented belt120with which they make continuous contact. In embodiments where the rollers include an insulating surface, the insulating surface makes no electrical connection to the segmented belt120, and thus does not change the potential of the segmented belt120at the point of contact.

Note that the representative rollers138,140,141,143shown inFIGS.1and2do not encompass the entirety of rollers that would be built into the system to accommodate system design constraints such as overall system dimensions. Numerous rollers could be built into the system expressly for making redundant electrical contact; here, the rollers shown for regulating belt tension or for setting the belt path can also serve as electrical connections to the segmented belt120. Furthermore, rollers with the characteristics described can be arbitrarily placed in any number of locations within the specific areas in which oil collection or oil release are accomplished for the purpose of setting the electrical potential in the respective location.

In some embodiments, the captured and released oil can flow to a resting position in the collection chamber122based on its density relative to that of the water present. For example, in one non-limiting embodiment, after passing into the collection chamber122, at least a portion of the polymer115on the segmented belt120can be subjected to an applied negative voltage bias. For example, in some embodiments, the applied voltage bias can be approximately −0.9 V, resulting in a reduction of at least a portion of the polymer115on the segmented belt120, and the consequent “oil release” as shown inFIGS.1and2.

In some embodiments, as the segmented belt120continues out of the collection chamber122, and through a partition124, a positive electric voltage can be applied to oxidize the polymer115of the segmented belt120to provide a strong adhesion toward oils as it proceeds out of the collection vessel148and passes into a body of water through the surface oil128as shown inFIGS.1and2. In some embodiments, the positive electric voltage can be applied directly to the polymer115through an underlying electrode coated on the surface of the segmented belt120, and the water126can be grounded.

In an embodiment, the conjugated polymer can be dodecylbenzenesulfonate-doped polypyrrole (“PPy(DBS)”). In some embodiments, the conjugated polymer can comprise an electrically conductive dodecylbenzenesulfonate-doped polypyrrole foam, abbreviated as “PPy(DBS) foam” having a porous 3D structure. In one embodiment, the conjugated polymer is a surfactant-doped conjugated polymer film. In an embodiment, the segmented belt120can comprise carbon nanotubes and/or a stainless-steel mesh. For example, in some embodiments, the segmented belt120can also include a substrate cooperating with and/or at least partially coupled to the conjugated polymer to form a composite structure (e.g., such as a continuous conveyor belt with an applied layer of conjugated polymer).

In some embodiments, the underwater wettability of the conjugated polymer (e.g., PPy(DBS)) can be switched in-situ upon application of voltages as low as ±1 V. For example, in some embodiments, when a positive electric voltage (e.g., 0.1 V) is applied, the PPy(DBS) surface is oxidized with a strong adhesion toward oils. As a result, the segmented belt120can adsorb oils by adhering the oils on their PPy(DBS) surface. In further embodiments, when a negative electric voltage (e.g., −0.9 V) is applied, the PPy(DBS) surface is reduced, whereby previously attached oil droplets can roll off the segmented belt120or permeate through the belt's mesh.

In some embodiments, the process described above can be actuated using very low voltages (e.g., such as voltages less than 1 V), and can be repeatable for many (e.g., hundreds) of cycles, thereby resulting in high efficiency and long durability. Furthermore, as the segmented belt120of the present invention can be incorporated into a conveyor belt, track, rope, or chain that runs along the exterior hull of a small unmanned surface vessel (such as previously discussed unmanned surface vessel20), the present invention is also directed to a method which allows the aforementioned oil collection process to be automated. Altogether, the various aspects and embodiments of the present invention enable a versatile, highly efficient, fully-automatic oil cleanup and recovery technology that can be provided as a boom150extended from a vessel (e.g., such as a boat, ship, or submersible), or alternatively from an on-shore structure such as a pier, dock, or other structure situated adjacent a body of water. Further, the boom150and/or any related assembly including the segmented belt120described herein can be incorporated into an unmanned, robotic surface vessel adapted for oil cleaning and recovery from a body of oil-contaminated water.

As discussed earlier, in some embodiments, voltages can be applied directly to the polymer through an underlying electrode coated on the surface of the conveyer belt, and the water is grounded. In some embodiments, the segmented belt120can include PPy(DBS)-polymer-coated conductive segments on an insulating elastic support belt. In some embodiments, at rest, i.e., without intentionally stretching the belt, these segments can come together, forming an electrically contiguous belt. However, under sufficient tension, the segments can be drawn apart, becoming electrically isolated from one another and allowing different sections of the belt to be maintained at disparate electrical potentials.

InFIG.1, the tension rollers138on the left and right sides of the chamber122(only the left ones are labeled as138), can allow a portion of the belt inside the chamber122to be electrically isolated from the section of the segmented belt120outside the chamber122. The electrical isolation occurs in the belt section just between pairs of rollers. Thus, the portion of the segmented belt120inside the chamber122is biased for oil release, while the portion of the segmented belt120outside is biased for collection. In some embodiments, the segmented belt120can have an appearance similar to that of the track of a tracked military vehicle (such as a tank), or alternatively an escalator in a department store, i.e., segmented sections that move together with the proximity of segments to one another controlled by a system of tensioning rollers. The segments can be intentionally separated to produce a selective electrical isolation at that point. The purpose of the tension rollers138is to provide the means for electrical isolation of the belt into distinct sections, functioning separately for oil collection and oil recovery.

Some embodiments include a suction tube134extending from a pump132to the collection chamber122. In some embodiments, the suction tube134can be adjusted in height to allow it to access the oil in the collection chamber122, and to then remove it by pumping through an outlet pipe133(shown as oil recovery130). Some further embodiments include a vent-or-pressure line136that is used to allow the system pressure in the collection chamber122to equilibrate with the ambient pressure. Alternatively, the pressure can be raised in the collection chamber122by the introduction of compressed air, nitrogen or other inert gas to provide more favorable conditions for oil removal by pumping via the pump132.

In an embodiment, the substrate of the segmented belt120can be a stainless-steel mesh that can further include carbon nanotubes. In some embodiments, the carbon nanotubes can be grown thereon via chemical vapor deposition. In embodiments in which carbon nanotubes are used, the conjugated polymer may be coated on the carbon nanotubes via electro-polymerization. In another embodiment, the substrate of the segmented belt120can include an electrically conductive carbon foam having a porous 3D structure. In such an embodiment, the conjugated polymer can be applied to the substrate so that the conjugated polymer inherits the porosity of the conductive carbon foam. In such embodiments, the CNTs and carbon foam can be applied and used in a similar matter as described hereinabove with carbon nanotubes17aand carbon foam17b.

It will be understood that the embodiments described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as defined in the appended claims.