Polymer surface with t-shaped microstructure and fabrication method therefor and applications thereof

Abstract

The present invention discloses polymer surfaces with T-shaped microstructure and their fabrication method and applications. The polymer surfaces with the T-shaped microstructure are characterized in that T-shaped microposts arrange orderly on them, and nanobulges arrange orderly on the top surfaces of the micronails of the T-shaped microposts. A flexible insert is designed and manufactured according to the geometry of the T-shaped microposts, and nanogrooves are manufactured on the cavity surface of an injection mold according to the geometry of the nanobulges on the top surfaces of the micronails. The flexible insert is mounted on the injection mold cavity. An injection molding machine is used to inject the molten polymer into the injection mold cavity. Then the polymer surfaces with the T-shaped microposts, on the top surfaces of the micronails of which the nanobulges arrange orderly, are molded. The polymer surfaces with the T-shaped microstructure exhibit robust Cassie-Baxter state and moderate surface adhesion to water droplets, and can be used for quantitative collection, lossless transportation or micromixing of microdroplets.

Claims

1. A polymer surface comprising a T-shaped microstructure, wherein the T-shaped microstructure comprises T-shaped microposts arranged on the polymer surface an upper portion of the T-shaped microposts comprises micronails and nanobulges arranged on top surfaces of micronails of the T-shaped microposts; wherein the micronails have cross-sectional dimensions of 20-80 μm and heights of 20-80 μm, and the nanobulges have cross-sectional dimensions of 10-900 nm.

2. The polymer surface according to claim 1, wherein the cross-sectional shape of the T-shaped microposts is round, ellipse, polygon, arch, or multi-arc; and the multi-arc is obtained by connecting multi-segment arcs.

3. The polymer surface according to claim 1, wherein the microposts have cross-sectional dimensions of 5-35 μm and heights of 20-80 μm, and the central distances between two adjacent microposts are 50-100 μm.

4. The polymer surface according to claim 1, wherein the nanobulges are on the polymer surface below the T-shaped microstructure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1a is an SEM micrograph of the polymer surface with the T-shaped microstructure according to embodiment 1 of the present invention.

(2) FIG. 1b is a schematic view of various embodiments of the T-shaped micropost arrays according to the present invention.

(3) FIG. 2 is a sectional view of various embodiments of the injection mold with the flexible insert mounted on its cavity surface according to the present invention.

(4) FIGS. 3a and 3b are images of a 4-μL, water droplet on the polymer surface with the T-shaped microstructure when placed horizontally and vertically, respectively, according to embodiment 1 of the present invention.

(5) FIG. 4 is a relationship between the critical roll-off angle and accumulated droplet volume for the droplets on the polymer surface with the T-shaped microstructure according to embodiment 1 of the present invention.

(6) FIG. 5 is typical images of a 4-μL, water droplet (a) before, (b) during, and (c, d) after squeezing it using two polymer surfaces with the T-shaped microstructure according to embodiment 1 of the present invention. Arrows represent moving direction.

(7) FIG. 6 is typical images of the squeezed and recovered 4-μL, water droplet (displayed in FIG. 5) during transferring according to embodiment 1 of the present invention.

(8) FIGS. 7a and 7b are schematic views of the microfluidic device with the T-shaped microposts arranged on the surface of its micro channels according to embodiment 1 of the present invention, in which FIG. 7a is front view and FIG. 7b is side view.

(9) FIG. 8 is a schematic view of the wetting state of a 4-μL water droplet on the polymer surface with the T-shaped microstructure when placed horizontally according to embodiment 2 of the present invention.

(10) FIG. 9 is a schematic view of rolling-off of a water droplet on the polymer surface with the T-shaped microstructure when placed at 60° titled angle according to embodiment 2 of the present invention.

(11) FIG. 10 is a sectional view of the T-shaped micropost arrays according to embodiment 4 of the present invention.

(12) FIG. 11 is a sectional view of the injection mold with the flexible insert mounted on its cavity surface according to embodiment 4 of the present invention.

(13) FIG. 12 is a schematic view of the wetting state of a water droplet on the polymer surface with the T-shaped microstructure when the droplet is under external pressure according to embodiment 4 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(14) The invention will be described in more detail with the aid of the embodiments and the accompanying drawings, but the mode for carrying out the invention is not limited to what described as follows.

Embodiment 1

(15) The present embodiment discloses a polymer surface 1 with T-shaped microstructure. With reference to FIG. 1, T-shaped microposts 2 arrange orderly on the polymer surface 1 with the T-shaped microstructure. Nanobulges 4 arrange orderly on the top surfaces of the micronails 3-1 of the T-shaped microposts 2.

(16) The cross-sectional shape of the T-shaped microposts 2 is rectangle.

(17) As for the T-shaped microposts 2, the micronails 3-1 have a cross-sectional width of 45 μm and height of 12 μm, the microposts 3-2 have a cross-sectional width of 30 μm and height of 70 μm, the central distance between two adjacent T-shaped microposts 2 is 55 μm.

(18) The cross-section of the nanobulges 4 on the top surfaces of the micronails 3-1 is arched and has a dimension of 900 nm.

(19) The fabrication method for the aforesaid polymer surface 1 with the T-shaped microstructure comprises the following steps.

(20) (1) Referring to FIG. 2, a flexible insert 5 is designed and manufactured according to the geometry of the T-shaped microposts 2 on the polymer surface. Micropores, which are used to form the T-shaped microposts 2 on the polymer surface, arrange orderly in the flexible insert 5. Nanogrooves are manufactured on the cavity surface of an injection mold 6 according to the geometry of the nanobulges 4 on the top surfaces of the micronails 3-1 of the T-shaped microposts on the polymer surface.

(21) (2) The flexible insert 5 is mounted on the cavity surface of the injection mold 6. The injection mold 6 is heated to a temperature of 120° C. An injection molding machine is employed to plasticize and melt the polymer, and then inject the molten polymer into the cavity of the injection mold 6. The polymer melt fills the cavity of the injection mold 6 as well as the micropores in the flexible insert 5 and the nanogrooves on the cavity surface of the injection mold 6.

(22) (3) The polymer melt within the cavity of the injection mold 6 is packed and cooled. Then the molded part is taken out of the mold 6. The microposts can be detached from the insert 5 with slight deformation and without residue during demolding due to its flexibility. Finally, the polymer surface 1 with the T-shaped microposts 2, on the top surfaces of the micronails 3-1 of which the nanobulges 4 arrange orderly, is molded.

(23) As for the micropores in the flexible insert 5 in said step (1), the portion for forming the micronails 3-1 of the T-shaped microposts 2 has a cross-sectional width of 45 μm, and the portion for forming the microposts 3-2 has a cross-sectional width of 30 μm. The nanogrooves on the cavity surface of the injection mold 6 have a cross-sectional dimension of 900 nm.

(24) In said step (2), the polymer is polypropylene.

(25) Referring to FIGS. 3a and 3b showing the images of a 4-μL, water droplet on the polypropylene surface 1 with the T-shaped microstructure when placed horizontally and vertically, respectively, the droplet exhibits a contact angle of 151° and a roll-off angle of larger than 90°.

(26) Micro-droplets are continuously added onto the polypropylene surface 1 with the T-shaped microstructure tilted at six different angles (80°, 70°, 60°, 50°, 40°, and 30°). The pinned droplets grow in size until they overcome the surface adhesion and roll off the surface under the gravitation effect. FIG. 4 illustrates the accumulated droplet volumes for rolling off at the six angles. Through fitting the obtained data with a polynomial, the following equation is established for the relationship between the critical roll-off angle (y; degree) and accumulated droplet volume (x; μL): y=0.17x.sup.2−7.8x+120.9. The polypropylene surface 1 with the T-shaped microstructure provides a moderate water adhesion, and so can be used for quantitative collection of microdroplets. With reference to FIGS. 5a, 5b, 5c, and 5d, a 4-μL, droplet can still recover its spherical shape after squeezing it using two polypropylene surfaces 1 with the T-shaped microstructure, implying that the polypropylene surface 1 with the T-shaped microstructure can stabilize the Cassie-Baxter state. Further, the aforesaid squeezed and recovered 4-μL droplet is contacted by a filter paper downward. Referring to FIGS. 6a and 6b, the droplet adheres to the filter paper completely and then spreads out instantaneously once they touch each other, indicating that lossless droplet transportation can be achieved on the polypropylene surface 1 with the T-shaped microstructure.

(27) Microfluidic device with the aforesaid T-shaped microposts arranged on the surface of its micro channels can be used for the micromixing of droplets due to the moderate water adhesion. Reference is now made to FIG. 7, in a microfluidic device 8, the micro channel 9 is arranged at 60° titled angle, the micro channel 10 is arranged at 45° titled angle, and the micro channel 11 is arranged at 30° titled angle. The aforesaid T-shaped microposts are arranged on the surfaces of the micro channels 9, 10, and 11. Using micropumps, three microdroplets with the same volume are jetted into the three micro channels, respectively, at the same rate. According to the aforesaid established quantitative relationship between the critical roll-off angle and accumulated droplet volume, the droplets in the three micro channels roll down to the end of the channels when they are accumulated into larger droplets with different volumes. Thus, micromixing of the three droplets is completed with different ratios.

Embodiment 2

(28) The present embodiment discloses a polymer surface 1 with the T-shaped microstructure. Compared with embodiment 1, there are the following differences for embodiment 2.

(29) The cross-sectional shape of the T-shaped microposts 2 is round.

(30) As for the T-shaped microposts 2, the micronails 3-1 have a cross-sectional diameter of 60 μm and height of 30 μm, the microposts 3-2 have a cross-sectional diameter of 15 μm and height of 40 μm, the central distance between two adjacent T-shaped microposts 2 is 90 μm.

(31) The cross-section of the nanobulges 4 on the top surfaces of the micronails 3-1 is trapezoid and has a dimension of 500 nm.

(32) As for the micropores in the flexible insert 5 in said step (1), the portion for forming the micronails 3-1 of the T-shaped microposts 2 has a cross-sectional diameter of 60 μm, and the portion for forming the microposts 3-2 has a cross-sectional diameter of 15 μm. The nanogrooves on the cavity surface of the injection mold 6 have a cross-sectional dimension of 500 nm.

(33) In said step (2), the polymer is polyethylene.

(34) Referring to FIG. 8 showing a schematic view of the wetting state of a 4-μL, water droplet 7 on the polyethylene surface 1 with the T-shaped microstructure when placed horizontally, the droplet 7 exhibits a contact angle of 155° and a roll-off angle of larger than 90°.

(35) Referring to FIG. 9 showing a schematic view of rolling-off of a water droplet 7 on the polyethylene surface 1 with the T-shaped microstructure when placed at 60° titled angle, the polyethylene surface 1 with the T-shaped microstructure exhibits a moderate water adhesion and so can be used for quantitative collection of microdroplets.

Embodiment 3

(36) The present embodiment discloses a polymer surface 1 with the T-shaped microstructure. Compared with embodiment 1, there are the following differences for embodiment 3.

(37) The cross-sectional shape of the T-shaped microposts 2 is regular hexagon.

(38) As for the T-shaped microposts 2, the micronails 3-1 have a cross-sectional width of 30 μm and height of 10 μm, the microposts 3-2 have a cross-sectional width of 10 μm and height of 30 μm, the central distance between two adjacent T-shaped microposts 2 is 45 μm.

(39) The cross-section of the nanobulges 4 on the top surfaces of the micronails 3-1 is regular triangle in shape and has a width of 300 nm.

(40) As for the micropores in the flexible insert 5 in said step (1), the portion for forming the micronails 3-1 of the T-shaped microposts 2 has a cross-sectional width of 30 μm, and the portion for forming the microposts 3-2 has a cross-sectional width of 10 μm. The nanogrooves on the cavity surface of the injection mold 6 have a cross-sectional width of 300 nm.

(41) In said step (2), the polymer is polycarbonate.

(42) A 4-μL water droplet on the polycarbonate surface 1 with the T-shaped microstructure exhibits a contact angle of 153° and a roll-off angle of larger than 90°.

Embodiment 4

(43) The present embodiment discloses a polymer surface 1 with the T-shaped microstructure. Compared with embodiment 1, there are the following differences for embodiment 4.

(44) As for the T-shaped microposts 2, the micronails 3-1 have a cross-sectional width of 60 μm and height of 30 μm, the microposts 3-2 have a cross-sectional width of 12 μm and height of 40 μm, the central distance between two adjacent T-shaped microposts 2 is 90 μm.

(45) With reference to FIG. 10, nanobulges 12 arrange orderly on the bottom surface of the T-shaped microstructure.

(46) The cross-section of the nanobulges 12 is regular triangle in shape and has a width of 100 nm and depth of 200 nm.

(47) Reference is now made to FIG. 11, nanogrooves are manufactured on the surface of the flexible insert 5 according to the geometry of the nanobulges 12 on the bottom surface of the T-shaped microstructure.

(48) As for the micropores in the flexible insert 5 in said step (1), the portion for forming the micronails 3-1 of the T-shaped microposts 2 have a cross-sectional width of 60 μm, and the portion for forming the microposts 3-2 has a cross-sectional width of 12 μm.

(49) FIG. 12 shows a schematic view of the wetting state of a water droplet 7 on the polypropylene surface 1 with the T-shaped microstructure when the droplet 7 is under external pressure. As can be seen, when the droplet 7 is squeezed by a slab 13, it may penetrate into the gaps between the T-shaped microposts, but can be kept from impregnating the bottom surface of the T-shaped microstructure thank to the nanobulges 12.

(50) The foregoing description and the drawings are illustrative of the present invention and are not to be taken as limiting, other embodiments are also allowed. Still other variants and rearrangements of parts within the spirit and scope of the present invention are possible and will be readily apparent to those skilled in the art.