Ultrahigh sensitive pressure-sensing film based on spiky hollow carbon spheres and the fabrication method thereof

Abstract

The present invention relates to an ultrahigh sensitive pressure-sensing film based on spiky hollow carbon spheres and the fabrication method thereof. The fabricated spiky hollow carbon spheres composed polydimethylsiloxane sensing film whose spheres were well dispersed in the matrix. The spiky structure is useful for the spheres to trigger Fowler-Nordheim (F-N) tunneling effect and thus enhancing the sensitivity of the material. The carbon material fabricated by the precursor transformation method contains a proper Nitrogen doping, which has efficiently increased the carrier migration ability. The hollow structure can both regulate the density of fillers and help to improve its temperature independence. Calcine the spheres under an inert atmosphere to transform the spiky hollow organic spheres into a carbon one, in this process the Nitrogen fraction and graphitization can be adjusted. The above carbon spheres then can be assembled with polydimethylsiloxane to achieve the composite film. The material of the present invention exhibits ultrahigh sensitivity, high sensing density, transparent, low hysteresis, temperature noninterference, and its processing method is simple, maturity and environment friendly.

Claims

1. An ultrahigh sensitive pressure-sensing film based on a spiky hollow carbon sphere, comprising conductive spiky hollow carbon spheres and siloxane materials with dielectric properties, wherein the mass percentage of the conductive spiky hollow carbon spheres relative to the siloxane materials ranges between 0.5%-20%.

2. The pressure-sensing film according to claim 1, having a fabricating thickness of 0.1 μm to 200 μm.

3. The pressure-sensing film according to claim 1, wherein the mass percentage of nitrogen relative to carbon in said spiky hollow carbon spheres ranges between 0.2%-15%; the mass percentage of oxygen relative to carbon in said spiky hollow carbon spheres ranges between 2%-35%.

4. A fabrication method of the ultrahigh sensitive pressure-sensing film based on spiky hollow carbon sphere according to claim 1, comprising the following steps: (1) At 10-30° C., adding 0.1-1 g of a microsphere template and 0.1-0.5 g of a precursor into 10 ml deionized water, dispersing by ultrasonication for 8-18 minutes to obtain a first solution, sealing the first solution and stirring for 1-8 hours, then adding to the first solution a polymerization initiator corresponding to the precursor and stirring for 18-28 hours, and by centrifugation and freeze-drying, a kind of organic spiky hollow spheres is obtained from the first solution; (2) Said spheres obtained from step (1) are then heated to 330-360° C. under an N.sub.2 atmosphere for 50-70 minutes and further heated to 600-950° C. for 1-2 hours to obtain conductive spiky hollow carbon spheres; (3) Coating a sacrifice layer onto a substrate for later use; (4) Mixing said spiky hollow carbon spheres obtained from step (2) and siloxane materials with dielectric properties in an ice bath for 4.5-5.5 hours with high speed to obtain a slurry for fabricating the pressure-sensing film, wherein the mass percentage of said conductive spiky hollow carbon spheres relative to said siloxane materials ranges between 0.5%-20%; (5) Coating said slurry from step (4) onto said substrate from step (3), then curing it in a 60-120° C. oven for 15-180 minutes, and then immersing said substrate into a second solution for dissolving the sacrifice layer for 2 hours to obtain said ultrahigh sensitive pressure-sensing film.

5. The fabrication method of the ultrahigh sensitive pressure-sensing film according to claim 4, wherein said precursor in step (1) comprises one or more of aniline, pyrrole, dopamine, melamine, and amino-acid.

6. The fabrication method of the ultrahigh sensitive pressure-sensing film according to claim 4, wherein said microspheres template in step (1) comprises one or more of nano polystyrene spheres, nano silicon dioxide spheres and nano polymethyl methacrylate spheres.

7. The fabrication method of the ultrahigh sensitive pressure-sensing film according to claim 4, wherein the diameter of said spiky hollow carbon spheres in step (2) ranges between 100-1000 nm.

8. The fabrication method of the ultrahigh sensitive pressure-sensing film according to claim 4, wherein said coating in step (5) comprises one or more of spin coating, tape casting, spray coating, draw-off method, drip method, and molding.

9. The fabrication method of the ultrahigh sensitive pressure-sensing film according to claim 4, wherein the material of said sacrifice layer in step (3) comprises one or more of polyvinyl alcohol, polymethyl methacrylate, and dextran.

10. The fabrication method of the ultrahigh sensitive pressure-sensing film according to claim 4, wherein said siloxane material in step (4) is polydimethylsiloxane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the SEM and TEM images of the spiky conductive spheres with a diameter of 600 nm.

(2) FIG. 2 is a photo of the peeled off thin film in a petri dish. Scale bar: 15 mm.

(3) FIG. 3 shows the light transmittance spectrum.

(4) FIG. 4 shows the resistance response and pressure sensitivity of the pressure sensor.

(5) FIG. 5 shows the instant response of the pressure sensor.

(6) FIG. 6 shows the resistance of the sensor in the fatigue test.

(7) FIG. 7 shows the response of the sensor to different applied pressures from 25° C. to 160° C.

(8) FIG. 8 shows the device for testing the resistance response in PBS solution, scale bar: 10 mm.

(9) FIG. 9 shows the resistance response and pressure sensitivity of the pressure sensor in the PBS solution.

(10) FIG. 10 shows detection by a 64×64 pixel pressure sensor, wherein (a) is the testing photo, (b) is the real-time result graph.

(11) FIG. 11 shows the XPS survey spectrum of the samples in embodiment 1.

(12) FIG. 12 shows the resistance response and pressure sensitivity of the sensor in embodiment 2.

(13) FIG. 13 shows the XPS survey spectrum of the samples in embodiment 2.

DETAILED DESCRIPTION

(14) The present invention is further described in the following embodiments, and not only limited to these embodiments. Meanwhile, all the procedures are normal methods and all raw materials are from commercial access unless otherwise specified.

Embodiment 1

(15) A total of 0.5 g polystyrene spheres with a diameter of 600 nm was dispersed into 10 ml deionized water. After ultrasonic treatment for 10 min under room temperature, 0.5 g aniline was added and stirred at 100 rpm for 3 hours. Then the above solution was added with 100 ml 0.5 M Fe(NO3)3 aqueous solution and accelerated the stir to 300 rpm for 24 h. The obtained spheres were washed with deionized water three times by centrifugal treatment with a speed of 5000 rpm and dried in a freeze dryer for 48 h.

(16) The powder obtained by drying process was then heated with 350° C. under an N2 atmosphere for 1 h and further heated to 900° C. for 1 h to obtain spiky hollow carbon spheres. FIG. 1 shows the SEM and TEM images of the spiky conductive spheres.

(17) 0.4 g of the obtained spiky hollow carbon spheres were dispersed in 10 ml PDMS (A:B=10:1, Sylgard™ 184, Dow-Corning) and stirred with 500 rpm in an ice bath for 5 h. The mixture was spin-coated onto a petri dish with a sacrifice layer of PVA. The spin coating program is 600 rpm for 9 s and then 5000 rpm for 35 s. After 3 h curing time under 80° C., 30 ml of deionized water was poured into the petri dish. Then after holding for 12 h at room temperature, the transparent ultrahigh sensitive sensing film was obtained, as shown in FIG. 2.

(18) FIG. 3 shows the ability of light transmittance from various wavelength, its transparency is close to a coverslip.

(19) FIG. 4 shows the resistance response and pressure sensitivity of the pressure sensor.

(20) FIG. 5 shows the instant response of the pressure sensor, which exhibits a response time of 60 ms for loading and 30 ms for unloading.

(21) FIG. 6 shows the resistance of the sensor at a pressure loading and unloading process in 5,000 cycles fatigue test.

(22) FIG. 7 shows the response of the sensor to different applied pressures from 25° C. to 160° C.

(23) FIG. 8 shows the device for testing the resistance response in a 20 cm depth of PBS solution (which is used for simulating the human body fluid environment).

(24) FIG. 9 shows the resistance response and pressure sensitivity of the pressure sensor in the PBS solution.

(25) FIG. 10 shows the discriminate ability by detecting two very slight objects with a 64×64 pixel on 3.2 cm×3.2 cm pressure sensor array.

(26) FIG. 11 shows the XPS survey spectrum of the samples in embodiment 1.

Embodiment 2

(27) A total of 0.8 g polystyrene spheres with a diameter of 800 nm was dispersed into a 10 ml Trish buffer solution which PH is 8.5. After ultrasonic treatment for 10 min under room temperature. 0.3 g dopamine and 0.1 g ammonium persulfate were added in order and stirred at 200 rpm. After 12 hours, the obtained spheres were washed with deionized water and ethanol three times by centrifugal treatment with speed of 5000 rpm, respectively. Then dried in a freeze dryer for 48 h.

(28) The spheres were then heated with 350° C. under an N2 atmosphere for 1 h and further heated to 800° C. for 1 h to obtain spiky hollow carbon spheres.

(29) Then, 0.35 g of the obtained spiky hollow carbon spheres were dispersed in 10 ml PDMS (A:B=10:1, Sylgard™ 184, Dow-Corning) and stirred with 500 rpm in an ice bath for 5 h. The mixture was spin-coated onto a petri dish, which was coated with a sacrifice layer of PVA. The spin coating program is 600 rpm for 9 s and then 5000 rpm for 35 s. After 3 h curing time under 80° C., 30 ml of deionized water was poured into the petri dish. Then after holding for 12 h at room temperature, the transparent ultrahigh sensitive sensing film was obtained.

(30) FIG. 12 shows the resistance response and pressure sensitivity of the sensor in embodiment 2.

(31) FIG. 13 shows the XPS survey spectrum of the samples in embodiment 2.