阅读说明：本技术 柔性电致变色纸单侧电极及其制备方法 (Flexible electrochromic paper single-side electrode and preparation method thereof ) 是由 范苏娜 黄翔宇 张耀鹏 邵惠丽 胡学超 于 2019-08-22 设计创作，主要内容包括：本发明涉及一种柔性电致变色纸的单侧薄膜电极及其制备方法,先在柔性基底层表面制成透明导电层,再在透明导电层表面采用电化学聚合法沉积电致变色层,制得柔性电致变色纸的单侧薄膜电极；制得的单侧薄膜电极具有复合层结构,柔性基底层为丝素蛋白纳米纤维薄膜,透明导电层为分散有丝素蛋白纳米纤维的聚苯胺纤维薄膜,电致变色层为具有纳米片状结构的聚苯胺薄膜；具有纳米片状结构的聚苯胺薄膜主要由聚苯胺纤维膜以及呈分散状分布在聚苯胺纤维膜表面的纳米片状聚苯胺组成,电致变色层中的聚苯胺纤维膜与纳米片状聚苯胺以及透明导电层中的聚苯胺纤维薄膜通过氢键及静电相互作用结合。本发明的制备方法简单,制得的单侧薄膜电极的电致变色性能优异。(The invention relates to a single-side film electrode of flexible electrochromic paper and a preparation method thereof, wherein a transparent conducting layer is firstly prepared on the surface of a flexible substrate layer, and then an electrochromic layer is deposited on the surface of the transparent conducting layer by adopting an electrochemical polymerization method to prepare the single-side film electrode of the flexible electrochromic paper; the prepared single-side film electrode has a composite layer structure, the flexible substrate layer is a silk fibroin nanofiber film, the transparent conductive layer is a polyaniline fiber film dispersed with silk fibroin nanofibers, and the electrochromic layer is a polyaniline film with a nano flaky structure; the polyaniline film with the nano-sheet structure mainly comprises a polyaniline fiber film and nano-sheet polyaniline which is distributed on the surface of the polyaniline fiber film in a dispersed manner, and the polyaniline fiber film in the electrochromic layer is combined with the nano-sheet polyaniline and the polyaniline fiber film in the transparent conductive layer through hydrogen bonds and electrostatic interaction. The preparation method is simple, and the prepared single-side film electrode has excellent electrochromic performance.)

1. The single-side film electrode of the flexible electrochromic paper has a composite layer structure, and comprises an adjacent flexible substrate layer, a transparent conductive layer and an electrochromic layer, and is characterized in that: the flexible substrate layer is a silk fibroin nanofiber film, the transparent conductive layer is a polyaniline fiber film dispersed with silk fibroin nanofibers, and the electrochromic layer is a polyaniline film with a nano-sheet structure;

the polyaniline film with the nano-sheet structure mainly comprises a polyaniline fiber film and nano-sheet polyaniline which is distributed on the surface of the polyaniline fiber film in a dispersion shape, wherein the nano-sheet polyaniline is not connected with each other and has a certain gap;

polyaniline fibers in the polyaniline fiber membrane are formed by arranging stretched polyaniline molecular chains, and the repeating unit of polyaniline is in a 1, 4-disubstituted configuration; the nano flaky polyaniline is formed by stacking polyaniline molecular chains with a cross-linked structure, and the repeating unit of the polyaniline is in a 1,2, 4-trisubstituted configuration;

the nitrogen atoms connected with the quinone ring in the extended polyaniline molecular chain and the polyaniline molecular chain with a cross-linked structure are combined with the cation of protonic acid to form-NH⁺The anion of the protic acid is attached to-NH in the form of an ionic bond⁺The polymer is suspended on a stretched polyaniline molecular chain, and the protonic acid is camphorsulfonic acid;

the polyaniline fiber film in the electrochromic layer is respectively combined with the nano-flaky polyaniline and the polyaniline fiber film in the transparent conductive layer through hydrogen bonds and electrostatic interaction.

2. The single-sided film electrode of flexible electrochromic paper as claimed in claim 1, wherein the electrochromic contrast of the electrochromic layer of the single-sided film electrode of flexible electrochromic paper is 60 to 73%, the coloring time is 1.5 to 3.0s, and the fading time is 3.0 to 6.0 s.

3. The single-sided film electrode of flexible electrochromic paper according to claim 1, wherein the flexible base layer, the transparent conductive layer and the electrochromic layer have thicknesses of 30 to 40 μm, 10 to 20 μm and 5 to 10 μm, respectively.

4. The single-sided thin film electrode of flexible electrochromic paper according to claim 1, wherein the nano-flaky polyaniline is distributed on the surface of the polyaniline fiber film on the single side away from the transparent conductive layer, the coverage rate of the nano-flaky polyaniline on the surface of the polyaniline fiber film on the single side is 70-90%, the length of the nano-flaky polyaniline is 2-10 μm, the width of the nano-flaky polyaniline is 0.5-2 μm, the thickness of the nano-flaky polyaniline is 0.5-1 μm, and the width of the gap is 50-100 nm.

5. The single-sided thin film electrode of flexible electrochromic paper as claimed in claim 1, wherein the content of the silk fibroin nanofibers in the transparent conductive layer is 5-10 wt%.

6. A method for preparing a single-sided thin film electrode of flexible electrochromic paper as claimed in any of claims 1 to 5, characterized in that: firstly, preparing a transparent conductive layer on the surface of a flexible substrate layer to obtain a transparent conductive layer/flexible substrate layer, and then depositing an electrochromic layer on the surface of the transparent conductive layer by adopting an electrochemical polymerization method to prepare a single-side film electrode of flexible electrochromic paper;

when an electrochromism layer is deposited by adopting an electrochemical polymerization method, the adopted electrolyte comprises aniline and protonic acid with the molar ratio of 1: 10-1: 30, and the protonic acid is camphorsulfonic acid;

when the electrochemical polymerization method is adopted for deposition, a constant potential mode or a constant current mode is adopted, and the voltage or current application time is 300-600 s.

7. The method according to claim 6, wherein the electrolyte comprises aniline, protonic acid and water, and the concentration of aniline is 0.05-0.5 mol/L.

8. The method of claim 6, wherein the deposition by electrochemical polymerization is carried out at a temperature of 20 to 30 ℃; when a constant potential mode is adopted, the voltage is 0.7-0.85V; when a constant current mode is adopted, the current is 3-10 mA; when the electrochemical polymerization method is adopted for deposition, a three-electrode system is adopted, and three electrodes are a working electrode, a counter electrode and a reference electrode; the working electrode is a transparent conductive layer/flexible substrate layer; the counter electrode is a platinum electrode; the reference electrode is a saturated calomel electrode.

9. The method of claim 6, wherein the flexible substrate layer is made by vacuum suction filtering a solution of silk fibroin nanofibers on a Polycarbonate (PC) membrane.

10. The method as claimed in claim 6, wherein the transparent conductive layer is prepared by adding an oxidant aqueous solution into the composite solution, reacting at 0-5 ℃ for 12-24 h to obtain a polyaniline/silk fibroin nanofiber composite suspension, and then spin-coating the supernatant of the polyaniline/silk fibroin nanofiber composite suspension on the flexible substrate layer;

the composite solution comprises aniline, silk fibroin nano-fibers, hydrochloric acid and water, wherein the concentrations of the aniline, the silk fibroin nano-fibers and the hydrochloric acid are respectively 1-3 mmol/L, 0.1-0.5 wt% and 0.5-1.5 mol/L;

the oxidant is ammonium persulfate, ferric chloride or potassium permanganate, and the concentration of the oxidant aqueous solution is 0.5-1.5 mmol/L;

the volume ratio of the composite solution to the oxidant aqueous solution is 4: 1-1: 4.

Technical Field

The invention belongs to the technical field of functional polymer materials, and relates to a flexible electrochromic paper single-side electrode and a preparation method thereof.

Background

The electrochromic material generates an oxidation-reduction reaction under an external electric field to generate reversible color change, and is widely applied to the fields of intelligent windows, anti-glare rearview mirrors for vehicles, electronic display screens and the like which do not need quick color change. The organic polymer electrochromic material overcomes the defects of long discoloration response time, high oxidation potential, poor cycle stability, low brittleness, toughness and the like of common inorganic electrochromic materials such as tungsten trioxide and the like in the aspects of color types, contrast, response speed and the like, is more suitable for flexible devices, and can be accurately printed, stamped, sprayed and spin-coated into expected device patterns. Among them, polyaniline has the advantages of simple preparation, stable chemical properties, unique doping mechanism, reversible electrochemical properties and the like, and is one of the most promising conductive polymer electrochromic materials for practical application.

Unlike conventional electronic devices, flexible electrochromic devices (ECDs) require good performance when bent, folded and stretched, and even good biocompatibility, in order to be integrated into wearable or implantable devices. This requires the development of suitable flexible substrate materials. The existing flexible ECD usually uses poly (terephthalic acid) (PET), Polyimide (PI), or Polycarbonate (PC) as a substrate, and although it has a certain flexibility, it still cannot resist bending at a large angle, and lacks biocompatibility. The selection of the bio-based material from natural renewable resources as the flexible substrate to construct sustainable electronic devices is an important research direction for future development. Researchers (Foldable electrochromic Enable by NanopaperTransfer method, advanced Functional Materials 2015.25(27):4203-4210.) constructed a flexible electrochromic paper that withstands forward and reverse 180 DEG turnover and resists to tungsten trioxide at 633nm by transferring the silver nanowires (AgNW) to the surface using the adhesiveness of the surface of the cellulose nanocellulose filmThe contrast reached a maximum (41%), and the tinting and fading times were 11.8s and 20.1s, respectively. Also, researchers (freestyling electrochromism paper. journal of Materials Chemistry C,2016.4(41):9680-₂Mixing with CNF to obtain self-supporting flexible electrochromic paper, TiO dispersed in bulk phase₂The particles act as a light reflecting layer, and the ECD constructed by using the particles as a substrate still maintains good electrochromic performance after 100 cycles. Silk Fibroin (SF) is a natural biological polymer, has good mechanical strength and flexibility, can be peeled to a Nano scale and processed into a film, can obtain a transparent flexible SF film (Single Molecular Layer of Silk Nanobion as positional basic building Block of Silk materials. ACS Nano,2018.12:11860-11870), and is an ideal sensor substrate/packaging material. However, no report of the use of SF films for flexible electrochromic papers has been found yet.

ECDs generally have a multi-layered structure including a transparent conductive layer, an electrochromic layer, an electrolyte layer, and an ion storage layer, wherein the transparent conductive layer plays an important role as a power supply unit of the device. Indium Tin Oxide (ITO) conductive glass is used as a transparent conductive layer of many electronic or optoelectronic devices including ECD, but its high manufacturing cost and hard and fragile physical characteristics are contrary to the development of green and low-consumption flexible devices. Researchers have constructed a transparent conductive layer using various materials instead of ITO, including Carbon Nanotubes (CNTs), graphene, metal nanowires, metal grids, organic conductive polymers, and composites of the above materials. Researchers (A high lyble flexible electrode for organic electronic devices, 2019.66:86-93.) utilized the excellent conductivity and flexibility of CNT to grow PANI (PANI-CNT) in situ on the CNT, and the PANI/PANI-CNT/PET flexible device is used as a transparent conductive layer to construct a PANI/PANI-CNT/PET flexible device, which can still maintain the electrochemical performance after 100 bending tests, but has low electrochromic contrast (about 34%), and large coloring and fading time (20-40 s).

The conduction of electrons in the organic polymer color changing layer has great influence on the optical contrast, response speed and stability of the device; meanwhile, the speed of transmission of ions in the electrolyte layer and the color changing layer determines the response speed of the whole ECD, and the depth of entry of ions in the color changing layer is related to the optical contrast and the coloring efficiency of the device. Researchers (Free-Standing Single-Molecule polymers. Nano Letters,2017.17(3): 1655) -1659; high-ordered lamellar amorphous films via electrochemical polymerization and post-growth reactions, RSC Advances,2017.7(7): 3819-3822) improved conventional electrochemical polymerization methods, prepared Highly ordered layered amorphous and crystalline PANI without template, whose internal molecular chains are arranged in a vertically offset arrangement with benzene rings, and whose inter-molecular chains have a large number of "groove" structures that increase the internal space of the system, facilitating the transport of ions or protons, but may hinder the entry of electrolytes into the system, thereby reducing the contrast ratio and response speed, etc.

Therefore, the research on the flexible electrochromic paper single-side electrode with excellent electrochromic performance and the preparation method thereof have very important significance.

Disclosure of Invention

The invention aims to solve the problem that the electrochromic performance of a flexible electrochromic paper single-side electrode in the prior art is to be further improved, and provides a flexible electrochromic paper single-side electrode and a preparation method thereof. The silk fibroin nanofiber membrane is used as a flexible substrate layer, a transparent conducting layer is manufactured on the surface of the flexible substrate layer, aniline and protonic acid are prepared into electrolyte according to a certain proportion, an electrochromism layer is deposited on the surface of the transparent conducting layer by adopting an electrochemical polymerization method, and the single-side membrane electrode of the flexible electrochromism paper is obtained; the prepared polyaniline film has excellent electrochromic performance (namely, relatively high electrochromic contrast and relatively high response speed).

In order to achieve the purpose, the invention adopts the following scheme:

the single-side film electrode of the flexible electrochromic paper has a composite layer structure and comprises an adjacent flexible substrate layer, a transparent conducting layer and an electrochromic layer, wherein the flexible substrate layer is a silk fibroin nanofiber film (composed of silk fibroin nanofibers and having excellent optical performance, and the transmittance of the silk fibroin nanofiber film in a visible light range of 400-800 nm is as high as 95%), the transparent conducting layer is a polyaniline fiber film dispersed with the silk fibroin nanofibers, and the electrochromic layer is a polyaniline film with a nano-sheet structure;

the polyaniline film with the nano-sheet structure mainly comprises a polyaniline fiber film and nano-sheet polyaniline which is distributed on the surface of the polyaniline fiber film in a dispersion shape, wherein the nano-sheet polyaniline is not connected with each other and has a certain gap;

polyaniline fibers in the polyaniline fiber membrane are formed by arranging stretched polyaniline molecular chains, and the repeating unit of polyaniline is in a 1, 4-disubstituted configuration; the nano flaky polyaniline is formed by stacking polyaniline molecular chains with a cross-linked structure, and the repeating unit of the polyaniline is in a 1,2, 4-trisubstituted configuration;

1, 4-disubstituted configuration

1,2, 4-trisubstituted configuration

The nitrogen atoms connected with the quinone ring in the extended polyaniline molecular chain and the polyaniline molecular chain with a cross-linked structure are combined with the cation of protonic acid to form-NH⁺The anion of the protic acid is attached to-NH in the form of an ionic bond⁺The polymer is suspended on a stretched polyaniline molecular chain, and the protonic acid is camphorsulfonic acid;

the polyaniline fiber film in the electrochromic layer is respectively combined with the nano-flaky polyaniline and the polyaniline fiber film in the transparent conductive layer through hydrogen bonds and electrostatic interaction.

The single-side film electrode of the electrochromic paper has excellent electrochromic performance, and the main reasons are as follows:

(1) the nano-sheet polyaniline is contained, the interface of the film, which is contacted with the electrolyte, is composed of a plurality of nano-sheets, the specific surface area is increased due to the dispersed two-dimensional sheet structure, the utilization rate of electrolyte ions is higher, and when an electrochromic test is carried out, the larger electrochromic contrast can be realized with less charge consumption, and the coloring efficiency is high;

(2) the cross-linking configuration of the nano-sheet polyaniline, namely, a single polyaniline sheet is formed by cross-linking polyaniline molecular chains with 1,2, 4-trisubstituted repeating units, electrons and current carriers can be conducted in the whole surface along the molecular chains, and when an electrochromic test is carried out, a larger film area can be successfully discolored with less charge consumption, so that the coloring efficiency is high; from the view point of the whole film, although the sheet-shaped polyaniline covers a large area, the sheets are not connected with each other, and a plurality of gaps exist, so that the ion in and out of the electrolyte is less obstructed, a shorter ion path is provided, and the short ion path greatly shortens the film coloring and fading time during the electrochromic test, namely, the quick response is realized;

(3) the polyaniline-containing fiber membrane has the advantages that in the electrochromic test process, when ions are embedded in/removed from the nano flaky polyaniline, a small amount of ions are embedded in the fiber membrane and stored in gaps among fibers, and the stored ions can accelerate coloring and fading;

(4) the polyaniline molecular chain constituting the nano-sheet polyaniline is suspended with anions (X) of protonic acid^-) The protonic acid is camphorsulfonic acid and has sulfonic acid group (-SO)₃H) And a steric group with a C ═ O chemical bond, as shown below:

X^-to-SO on₃H is hung on a molecular chain in an ionic bond mode, and meanwhile C ═ O and-NH-on an adjacent molecular chain generate hydrogen bond action, so that the adjacent molecular chain is fixed, a nano flaky structure stably exists, the nano flaky structure is not easy to crack and decompose in an electrochromic test process, the nano flaky structure is used as a functional layer of flexible electrochromic paper, and the performance of the flexible electrochromic paper is free from being bent for 100-200 timesThe reduction is obvious;

(5) the nano-sheet polyaniline and the polyaniline fiber membrane as well as the polyaniline fiber membrane and the polyaniline fiber membrane in the transparent conductive layer are combined through hydrogen bonds among polyaniline molecular chains and electrostatic interaction, the whole structure has stability, the membrane can still keep better electrochromic performance after 500-1000 cycles, compared with the initial state, the contrast after the cycle is only reduced by 5-12%, and the coloring time and the fading time are not obviously changed;

(6) in addition, silk fibroin molecules in the nano fibers have two conformations of β folding (crystalline region) and random curling (amorphous region), so that the nano fibers have higher mechanical strength and toughness and are introduced into the flexible substrate layer and the transparent conductive layer, the mechanical property of the film electrode is favorably improved, and the film electrode can be used in the states of bending, folding, stretching and the like.

As a preferable scheme:

according to the single-side film electrode of the flexible electrochromic paper, the electrochromic contrast of the electrochromic layer of the single-side film electrode of the flexible electrochromic paper is 60-73%, the coloring time is 1.5-3.0 s, and the fading time is 3.0-6.0 s. The prior art polyaniline electrochromic data are shown in the following table, and the data source is J.Mater.chem.C,2018,6, 5707-5715.

The thickness of the flexible substrate layer, the thickness of the transparent conductive layer and the thickness of the electrochromic layer of the single-side film electrode of the flexible electrochromic paper are respectively 30-40 mu m, 10-20 mu m and 5-10 mu m, and each layer should have a proper thickness. If the thickness is too large, the transmittance of the whole electrode is low, the color change effect is not obvious, and the contrast is low; if the thickness is too low, the supporting function is reduced, and the bending and folding in the using process cannot be borne.

According to the single-side thin film electrode of the flexible electrochromic paper, the nano-flaky polyaniline is distributed on the surface of the polyaniline fiber film, which is far away from the transparent conductive layer, the coverage rate of the nano-flaky polyaniline on the surface of the polyaniline fiber film is 70-90%, the length of the nano-flaky polyaniline is 2-10 micrometers, the width of the nano-flaky polyaniline is 0.5-2 micrometers, the thickness of the nano-flaky polyaniline is 0.5-1 micrometer, and the width of a gap is 50-100 nm.

According to the single-side thin film electrode of the flexible electrochromic paper, the content of the silk fibroin nanofibers in the transparent conductive layer is 5-10 wt%; the content of the silk fibroin nanofibers in the transparent conductive layer can be properly adjusted, but the adjustment range is not too large. If the content is too low, the layer is almost all polyaniline, and cannot play a role in combining fibroin in the layer with fibroin at the bottom layer, so that the interlayer adhesion is poor; if the content is too high, the transmittance of the film may decrease.

The invention also provides a method for preparing the single-side film electrode of the flexible electrochromic paper, which comprises the steps of firstly preparing a transparent conducting layer on the surface of a flexible substrate layer to obtain a transparent conducting layer/flexible substrate layer, and then depositing an electrochromic layer on the surface of the transparent conducting layer by adopting an electrochemical polymerization method to prepare the single-side film electrode of the flexible electrochromic paper;

when an electrochromism layer is deposited by adopting an electrochemical polymerization method, the adopted electrolyte comprises aniline and protonic acid with the molar ratio of 1: 10-1: 30, and the protonic acid is camphorsulfonic acid;

when the electrochemical polymerization method is adopted for deposition, a constant potential mode or a constant current mode is adopted, the voltage or current application time is 300-600 s, and the voltage or current application time is not suitable to be too long or too short. If the application time is too short, the quantity of the nano flaky polyaniline is less; if the application time is too long, the film thickness becomes large, which adversely affects the contrast.

Drawings

FIG. 1 is a time-current graph of the electrochemical polymerization deposition of polyaniline;

FIG. 2 is a scanning electron micrograph of nanoplatelets polyaniline;

Detailed Description

The invention will be further illustrated with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.