Capacitive flexible pressure sensor and preparation method and application thereof
Technical Field
The invention belongs to the technical field of flexible pressure sensors, and particularly relates to a capacitive flexible pressure sensor and a preparation method and application thereof.
Background
In recent years, wearable electronic products are widely used in the biomedical field, including wearable bracelets, smart watches, smart glasses, and the like. However, the rigid outer shell of these products has prevented their wider application, and therefore, the field of flexible electronics is aimed at designing and researching highly flexible sensing devices for detecting physiological signals of human body.
Among many physiological signals of the human body, pulse is one of the most important physiological signals. Ancient Chinese medicine can diagnose various diseases of human body through pulse, and the accuracy rate is very high. In western medicine, pulse signals are also important indicators of the health of the heart and vascular system. Therefore, the method has important significance for pulse detection and real-time monitoring.
Pulse signals are essentially pressure signals, so that many people propose to use flexible pressure sensors to realize real-time pulse monitoring. However, the weak pulse makes it difficult for the flexible pressure sensor to accurately detect the pulse signal. Even if the individual sensor can detect the frequency of the pulse, the accurate waveform of the pulse cannot be identified, and important physiological information is missed.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a preparation method of a capacitive flexible pressure sensor, which is based on a polycarbonate template method, a high-sensitivity flexible pressure sensor dielectric layer is prepared, a lodging polydimethylsiloxane micro-column array is arranged on the surface of the dielectric layer, and the capacitive flexible pressure sensor is formed by assembling the dielectric layer with an upper electrode and a lower electrode.
It is another object of the present invention to provide a capacitive type flexible pressure sensor capable of monitoring a pulse signal.
The purpose of the invention is realized by the following technical scheme.
A capacitive-type flexible pressure sensor comprising: the solid polydimethylsiloxane structure comprises a solid polydimethylsiloxane layer, an upper electrode layer and a lower electrode layer, wherein the upper electrode layer is positioned on the top surface of the solid polydimethylsiloxane layer, the lower electrode layer is positioned on the bottom surface of the solid polydimethylsiloxane layer, the solid polydimethylsiloxane layer is made of polydimethylsiloxane, the solid polydimethylsiloxane layer is composed of a flat structure and a polydimethylsiloxane micro-column array connected to the top end of the flat structure, and the upper electrode layer comprises: a first polyimide film and silver nanowires randomly adhered to an upper surface of the first polyimide film, the lower electrode layer comprising: a second polyimide film and silver nanowires randomly adhered to a lower surface of the second polyimide film.
In the technical scheme, the height of the polydimethylsiloxane micro-column array is 7-20 microns.
In the above technical solution, the density of the polydimethylsiloxane micro-pillars in the polydimethylsiloxane micro-pillar array on the flat plate-shaped structure is 1 × 106~6×106Per cm2。
In the technical scheme, the diameter of the polydimethylsiloxane microcolumn is 5-10 microns.
In the technical scheme, the thickness of the flat-plate-shaped structure is 130-170 mu m.
In the technical scheme, the polydimethylsiloxane micro-column is in a lodging shape.
In the technical scheme, the silver nanowires are 20-50 microns long and 25-35 nm in diameter.
The preparation method of the capacitive flexible pressure sensor comprises the following steps:
1) preparation of polydimethylsiloxane films:
uniformly mixing a polydimethylsiloxane main agent and a curing agent to obtain a mixture A, spreading the mixture A on a substrate to form a film, curing the film at 75-80 ℃ for 3.5-4 hours, immersing the substrate into a dichloromethane aqueous solution for at least 6 hours, and separating the substrate to obtain the polydimethylsiloxane film, wherein the ratio of the polydimethylsiloxane main agent to the curing agent is (8-10): 1;
in the step 1), the mixture A is uniformly spread to form the film.
In the step 1), the thickness of the polydimethylsiloxane film is 100-120 μm.
In the step 1), the method for spreading the mixture A to form a film comprises the following steps: and placing the mixture A on a substrate, and rotating at the rotating speed of 500-550rpm by using a spin coater to obtain the thin film on the substrate.
In the step 1), the polydimethylsiloxane main agent and the curing agent are mixed and stirred for 3-5 minutes to realize uniform mixing.
In the step 1), the substrate is immersed in a dichloromethane aqueous solution for 5-10 hours.
In the step 1), the concentration of dichloromethane in the dichloromethane aqueous solution is 98-99 wt%.
2) Spreading liquid polydimethylsiloxane on the surface of the polydimethylsiloxane film to obtain a polydimethylsiloxane film liquid layer on the polydimethylsiloxane film;
in the step 2), the method for spreading the liquid polydimethylsiloxane on the surface of the polydimethylsiloxane film comprises the following steps: and (3) placing liquid polydimethylsiloxane on the surface of the polydimethylsiloxane film, and rotating at the rotating speed of 2200rpm by using a spin coater at 2000-plus, so as to obtain a polydimethylsiloxane film liquid layer with the thickness of 30-50 mu m on the polydimethylsiloxane film.
In said step 2), every 1cm2The above-mentionedThe mass of the liquid polydimethylsiloxane spread by the polydimethylsiloxane film is 0.3-0.5 g.
3) Preparing a template, wherein a plurality of through holes with the aperture of 5-10 mu m are formed in the template, placing the template on the surface of the polydimethylsiloxane thin film liquid layer so as to enable polydimethylsiloxane in the polydimethylsiloxane thin film liquid layer to be filled into the through holes under the action of capillary force, forming polydimethylsiloxane micro-columns in the through holes after curing, taking down the template, and forming a polydimethylsiloxane micro-column array by all the polydimethylsiloxane micro-columns to obtain a solid polydimethylsiloxane layer;
in the step 3), the curing time is 3-4 hours.
In the step 3), the method for removing the template comprises the following steps: washed with aqueous dichloromethane.
In the step 3), the porosity of the through holes on the template is 4-20%.
In the step 3), the thickness of the template is 7-20 μm.
4) Placing an upper electrode on the top surface of the solid polydimethylsiloxane layer, and placing a lower electrode on the bottom surface of the solid polydimethylsiloxane layer, wherein the preparation method of the upper electrode comprises the following steps: coating a silver nanowire ethanol solution on the upper surface of the first polyimide film, wherein the preparation method of the lower electrode comprises the following steps: and coating the lower surface of the second polyimide film with a silver nanowire ethanol solution.
In the step 4), the thickness of each of the first polyimide film and the second polyimide film is 20 to 25 μm.
In the step 4), in the upper electrode and lower electrode preparation method, the number of times of coating the silver nanowire ethanol solution is 2-3, and the coating is performed for the next time after drying for 10-15 minutes after each coating.
In the step 4), the concentration of the silver nanowires in the silver nanowire ethanol solution is 19.5-20.5 mg/mL.
The preparation method is applied to improving the sensitivity of the pressure sensor.
Compared with the prior art, the capacitive flexible pressure sensor and the preparation method thereof have the following beneficial effects:
the invention firstly provides a method for preparing the capacitive flexible pressure sensor by utilizing a polycarbonate template. The sensitivity of the manufactured capacitive flexible pressure sensor reaches 5.8kPa-1On the premise of weak pulse, the capacitive flexible pressure sensor can still accurately detect pulse signals and can identify the waveform of the pulse.
Drawings
FIG. 1 is a pulse waveform measured by a capacitive type flexible pressure sensor prepared in example 1 of the present invention;
FIG. 2 is an enlarged view of FIG. 1;
FIG. 3 is a graph showing the sensitivity comparison between the capacitive type flexible pressure sensor obtained in example 1 and the sensors in comparative examples 1 to 5.
Detailed Description
The technical scheme of the invention is further explained by combining specific examples.
In the following examples, the reagents involved and the sources of purchase characterizing the test devices are as follows:
(1) dow Corning SYLGARD 184 polydimethylsiloxane as a base and curing agent, available from Korea of Japan, Inc.
(2) An aqueous dichloromethane solution having a dichloromethane concentration of 98 wt%, manufactured by Tianjin Yueli chemical Co., Ltd.
(3) Whatman polycarbonate template, shanghai radication biotechnology limited.
(4) Silver nanowire ethanol solution, Nanjing Xiancheng Nano Co.
(5) Polyimide clear film, Baohe county, Beijing Electrical materials works.
In the following examples, the types of instruments involved are as follows:
(1) KW-4A spin coater, Beijing Saidekais electronic responsibility Co., Ltd.
(2) AIGU-ZP-200 manometer, ETOOL GmbH
(3) LCR digital bridge
Examples 1 to 3
A capacitive-type flexible pressure sensor comprising: the solid polydimethylsiloxane layer is made of polydimethylsiloxane, and consists of a flat structure and a polydimethylsiloxane micro-column array connected (integrally formed) at the top end of the flat structure, wherein the polydimethylsiloxane micro-column array comprises: the thickness of a flat structure of a plurality of polydimethylsiloxane micro-columns which are randomly arranged is 139 mu m, and the height of a polydimethylsiloxane micro-column array is 11 mu m. The density of the polydimethylsiloxane micro-column in the polydimethylsiloxane micro-column array on the flat structure is 3 multiplied by 106Per cm2The polydimethylsiloxane micro-column is in a lodging shape. The upper electrode layer includes: a first polyimide film and silver nanowires randomly adhered to an upper surface of the first polyimide film, the lower electrode layer including: a second polyimide film and silver nanowires randomly adhered to a lower surface of the second polyimide film. The silver nanowires have a length of 20-50 μm and a diameter of 25-35 nm. The diameter of the polydimethylsiloxane microcolumn is X μm.
The preparation method of the capacitive flexible pressure sensor comprises the following steps:
1) preparation of polydimethylsiloxane films:
mixing polydimethylsiloxane main agent and curing agent, stirring for 5 min to realize uniform mixing to obtain mixture A, placing 1.5g of mixture A on a glass slide, and rotating at 520rpm for 1min by using a spin coater to obtain a film (the area of the film is 7.5 cm)2). Then placing the glass slide into an oven to be cured for 4 hours at the temperature of 80 ℃, soaking the glass slide into a dichloromethane water solution for 6 hours to separate the glass slide from substances on the glass slide, and obtaining a polydimethylsiloxane film with the thickness of 110 mu m, wherein the polydimethylsiloxane film is counted by mass partsThe ratio of the main siloxane agent to the curing agent is 10: 1;
2) placing 1.5g of liquid polydimethylsiloxane on the surface of the polydimethylsiloxane film, and rotating the polydimethylsiloxane film for 1min at 2000rpm by using a spin coater to obtain a polydimethylsiloxane film liquid layer with the thickness of 40 mu m on the polydimethylsiloxane film. Wherein each 1cm2The mass of the polydimethylsiloxane film spread out the liquid polydimethylsiloxane was 0.4 g.
3) A template having a thickness of 11 μm was prepared, on which a plurality of through holes having an aperture of X μm were formed, the through holes were arranged in a random pattern, and the porosity of the through holes on the template was 12%. Placing the template on the surface of a polydimethylsiloxane thin film liquid layer for 3min to enable polydimethylsiloxane in the polydimethylsiloxane thin film liquid layer to be filled into the through hole under the action of capillary force, forming polydimethylsiloxane micro-columns in the through hole after curing for 4 hours, cleaning the template for 10min by using a dichloromethane aqueous solution to take down the template, and forming a polydimethylsiloxane micro-column array by using all the polydimethylsiloxane micro-columns to obtain a solid polydimethylsiloxane layer;
4) placing an upper electrode on the top surface of the solid polydimethylsiloxane layer, and placing a lower electrode on the bottom surface of the solid polydimethylsiloxane layer, wherein the preparation method of the upper electrode comprises the following steps: and coating the silver nanowire ethanol solution on the upper surface of the first polyimide film for 3 times, and coating the silver nanowire ethanol solution for the next time after drying for 15 minutes after each coating. The preparation method of the lower electrode comprises the following steps: and coating the lower surface of the second polyimide film with the silver nanowire ethanol solution for 3 times, and coating the lower surface of the second polyimide film again after drying for 15 minutes after each coating. The first polyimide film and the second polyimide film each had a thickness of 22 μm. The concentration of the silver nanowires in the silver nanowire ethanol solution is 20 mg/mL.
Examples
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X (Unit: mum)
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Example 1
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5
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Example 2
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8
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Example 3
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10 |
The sensitivity of the capacitive type flexible pressure sensor obtained in examples 1 to 3 was measured, and the sensitivity of the capacitive type flexible pressure sensor obtained in example 1 was 5.8kPa-1The sensitivity of the capacitive type flexible pressure sensor obtained in example 2 was 4.5kPa-1The sensitivity of the capacitive type flexible pressure sensor obtained in example 3 was 3.6kPa-1。
The sensitivity test method comprises the following steps:
the capacitive flexible pressure sensor is placed on a flat desktop, and a pressure gauge probe is utilized to apply pressure with a specific numerical value to the upper surface of the capacitive flexible pressure sensor. And leading out wires from the upper electrode and the lower electrode of the capacitive flexible pressure sensor respectively, connecting the wires with the LCR digital bridge, and measuring the capacitance value of the capacitive flexible pressure sensor.
Sensitivity S ═ Δ C/(C × P), where Δ C is the amount of change in capacitance value, i.e., Δ C ═ C-C0,C0And C is the capacitance value after the pressure gauge probe applies pressure to the upper surface of the capacitance type flexible pressure sensor. P is the value of the pressure applied by the manometer probe. The capacitance is given in pF and the pressure is given in kPa. In general, sensitivity is related to the cylinder diameter. The polydimethylsiloxane layer microcolumn of example 1 is easily deformed under pressure, and thus has high sensitivity.
The capacitive flexible pressure sensor prepared in example 1 was placed at the wrist pulse position, fixed with medical tape, and the upper and lower electrodes of the capacitive flexible pressure sensor were connected to the LCR digital bridge, respectively, and capacitance values were continuously collected. And finally, drawing the acquired capacitance value into a curve by using Excel software to obtain the pulse waveform, as shown in figure 1. Fig. 2 is an enlarged view of the 6 th to 7 th waveforms of fig. 1.
To more clearly illustrate the sensitivity of the capacitive flexible pressure sensor obtained in accordance with the present invention, a capacitive flexible pressure sensor obtained in accordance with example 1 of the present invention is now compared with a comparative example, which is as follows:
comparative example 1
Y.Joo,J.Byun,N.Seong,J.Ha,H.Kim,S.Kim,T.Kim,H.Im,D.Kim,Y.Hong,Nanoscale 2015,7,6208.
Comparative example 2
S.Kang,J.Lee,S.Lee,S.Kim,J.-K.Kim,H.Algadi,S.Al-Sayari,D.-E.Kim,D.Kim,T.Lee,Adv.Electron.Mater.2016,2,1600356.
Comparative example 3
S.C.B.Mannsfeld,B.C.-K.Tee,R.M.Stoltenberg,C.V.H.-H.Chen,S.Barman,B.V.O.Muir,A.N.Sokolov,C.Reese,Z.Bao,Nat.Mater.2010,9,859.
Comparative example 4
Y.Wan,Z.Qiu,Y.Hong,Y.Wang,J.Zhang,Q.Liu,Z.Wu,C.F.Guo,Adv.Electron.Mater.2018,4,1700586.
Comparative example 5
Z.He,W.Chen,B.Liang,C.Liu,L.Yang,D.Lu,Z.Mo,H.Zhu,Z.Tang,X.Gui,ACSAppl.Mater.Inter.2018,10,12816.
As shown in fig. 3, it can be seen that the capacitive flexible pressure sensor of the present invention has high sensitivity in a small pressure range (<1.75kPa), and this feature makes the capacitive flexible pressure sensor of the present invention have a good advantage in the field of weak signal detection including pulse signals.
The invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.