Patent Application
20140360689
1. Field of the Invention
The present invention relates to paper and, more specifically, to a superamphiphobic paper.
2. Description of the Related Art
Common cellulosic paper is made from wood fibers that have been dried from a suspension in water and then pressed into a flat sheet. Typical paper (e.g., newsprint, writing paper and the like) is both hydrophilic (readily absorbs water) and oleophilic (readily absorbs oils).
In certain applications it is desirable to make paper either hydrophobic (not absorbing water), oleophobic (not absorbing oil), or both. Typically, paper is coated with layers of waxes or polymers to make it have these properties. However, such coatings can degrade over time when in contact with certain substances. Also, such coatings can introduce certain undesirable properties to the papers.
In diagnostic applications, such as biochemical assay applications, a superamphiphobic sheet (in which a drop of liquid has an apparent contact angle of greater than 150° on the sheet) can be useful. For example, a superamphiphobic sheet with a region of functionalized molecules printed thereon could be used to detect the presence of certain antibodies in blood samples or components in other bodily fluid samples to indicate the presence of a disease. The functionalized molecules would attach to the antibodies as the blood sample rolled off of the paper and a resulting change in appearance would indicate the presence of the target antibody.
In certain special applications, super-hydrophobic surfaces and super-oleophobic surfaces can be made by adding an array of nail head-shaped nanostructures onto a substrate through complex lithographic processes. However, such structures require special materials and making such structures can be cost prohibitive. Such sheets and structures are also quite rigid and fragile.
Paper, on the other hand, is made from inexpensive wood pulp. Therefore, many papers can be made quite inexpensively. Paper is also quite flexible and strong.
Therefore, there is a need for a superamphiphobic paper and a method of making superamphiphobic paper.
The disadvantages of the prior art are overcome by the present invention which, in one aspect, is a method of making a paper that is phobic at least to a first liquid, in which a fibrous pulp is refined in water to generate fibrils of an average diameter. The water is drained from the fibrils through a mesh. A less polar than water liquid is added to the fibrils, thereby suspending the fibrils therein so as to inhibit agglomeration between the fibrils. The less polar than water liquid and any remaining water are drained from the fibrils. The fibrils are pressed and dried so as to form the paper in which the fibrils have an average spacing. Amorphous phase cellulose is removed from the paper. A predetermined compound is deposited onto a selected surface of the paper. The average diameter and average spacing are chosen so that the paper is phobic to the first liquid.
In another aspect, the invention is a superamphiphobic paper that includes a plurality of fibrils and a surface treatment. The plurality of fibrils has an average diameter and an average spacing selected so as to make the paper phobic to a low surface tension liquid. The surface treatment is applied to the paper and is configured to cause the paper to be phobic to the low surface tension liquid and phobic to a high surface tension liquid that is different from the low surface tension liquid.
These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure.
BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS
A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. Unless otherwise specifically indicated in the disclosure that follows, the drawings are not necessarily drawn to scale. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of “a,” “an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.”
As shown in
The paper can be made phobic, and even superphobic, to different liquids by selecting the average diameter of the fibrils, the average distance between fibrils, the surface coating compound and the time spent etching.
As shown in
Attainment of superoleophobicity relies heavily on distinct roughness geometries of the paper. Specifically, the contact angles of low surface tension fluids are enhanced by surface structures with reentrant angles. The bottom half of a cylindrical fiber offers reentrant angles or overhang constructs that are similar to lithographically created structures. The critical physical parameters of superoleophobic substrates are the dimensions and spacing of the structures.
As shown in
where the apparent contact angle (θ*) is a function of the center-to-center distance between two fibers (L), the fiber diameter (D=2R), and equilibrium contact angle (θe). The size and spacing of surface structures can easily be varied when produced lithographically, whereas for fiber-based mesh screens and woven fabrics, L and D are established by the manufacturing process, fiber size, and weave.
In one experimental embodiment, a superamphiphobic paper was made using southern hardwood Kraft fibers (from Alabama River Pulp Co.). The fibers were refined according to the TAPPI standardized method T 248 sp-08 whereby dry fiber sheets were soaked in deionized water overnight and then loaded in a PFI (Pulp and Fiber Research Institute) refiner (from Test Machines Inc.) and exposed to different levels of refining as defined by the number of revolutions.
Handsheets (small test sheets of paper) were formed made using sec-butanol (from Alfa Aesar, anhydrous, 99%), the refined pulp was first drained through a 75 μm pore mesh screen. The water filtrate was discarded and sec-butanol (100 mL) is added to the drained pulp. The pulp was then remixed for 2 minutes and again drained through a 75 μm screen. After the sec-butanol/water mixture has drained from the pulp, the sheet was pressed and then dried overnight on a stainless steel plate.
The paper samples were etched and subsequently exposed to fluorocarbon film deposition in a parallel plate (13.56 MHz) vacuum plasma reactor. Both steps were conducted at 110° C. using a power of 120 W. To etch the paper, oxygen was introduced to the reactor at 75 standard cubic centimeters per minute (SCCM), and allowed to reach an equilibrium pressure of 5.0×10−1 Torr. The fluoropolymer coating was deposited using a plasma composed of 40 SCCM Ar and 20 SCCM pentafluoroethane (Praxair) at an operating pressure of 1.0 Torr. While etch times were varied, the deposition step was constant at 2 minutes, yielding a coating thickness of about 400 nm.
A micrograph of unrefined wood fibers is shown in
The above described embodiments, while including the preferred embodiment and the best mode of the invention known to the inventor at the time of filing, are given as illustrative examples only. It will be readily appreciated that many deviations may be made from the specific embodiments disclosed in this specification without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is to be determined by the claims below rather than being limited to the specifically described embodiments above.
This application claims the benefit of US Provisional Patent Application Ser. No. 61/832,304, filed Jun. 7, 2013, the entirety of which is hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61832304 | Jun 2013 | US |
