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Flexible and Reusable Non-woven Fabric Photodetector Based on Polypyrrole/Crystal Violate Lactone for NIR Light Detection and Writing

  • Shuangping Yang
  • Daniel K. Macharia
  • Sharjeel Ahmed
  • Bo Zhu
  • Qiuping Zhong
  • Haifeng Wang
  • Zhigang ChenEmail author
Research Article
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Abstract

Rapid NIR light detection and/or writing has drawn much attention, but their practical applications have been limited by obtaining such NIR photodetectors. To address this problem, we have developed a simple and versatile strategy to prepare a non-woven fabric photodetector. The blue non-woven fabric photodetector has been prepared by coating photo-thermochromic ink (including crystal violet lactone (CVL) as the thermo-sensitive dye, polypyrrole (PPy) nanospheres as the photothermal component and hydroxyethyl cellulose (HEC) as the polymer matrix) on white non-woven fabric. When the blue fabric photodetector is irradiated by NIR (808-nm as model, 0.75 W cm−2) laser, the discoloration occurs in 35 s, and higher laser intensity confers more rapid discoloration. This discoloration results from the photothermal effect of PPy which confers the elevation of temperature (> 50 °C) and then converts CVL to its leuco form (colorless). When the laser is turned off, the temperature drops to below the transition temperature (< 43 °C), and then CVL reverts to its initial blue color. Moreover, different figures and images can be easily printed on the fabric photodetector by 808 nm laser, and then they can be erased automatically under ambient conditions, with excellent cycling stability. Therefore, this fabric photodetector may act as a new platform for rapid NIR light detection and writing.

Keywords

Non-woven fabric Photodetector Photothermal effects NIR light detection 

Introduction

Photodetectors are the devices that convert the optical signals into electrical signals or pixels, and they have been widely used in various applications such as optical communication, biomedical science, target acquisition and night vision [1, 2, 3, 4]. Currently, different photodetectors have been developed, and they respond to different light including ultraviolet (UV), visible (Vis) and near-infrared (NIR). Among them, NIR photodetectors have attracted increasing interests, since NIR light is abundant in the solar spectrum and importantly it is not easy to be perceived by the human eye. Conventional NIR photodetectors can be categorized into bulk semiconductors (such as CuSbS2 [5], InAsSb [6], and GaSb [7]) and nanomaterial detectors (such as 0D quantum dots [8], 1D nanowires [9], and 2D sheets [10]). These NIR photodetectors exhibit high responsivity, speed, efficiency, and broad detection wavelength. However, they suffer from some limitations, such as excessive costs, complex preparation processes and complicated equipment that lead to high energy consumption [11]. Therefore, it is still necessary to develop new NIR photodetectors that are low-cost and are easy to be directly observed by eyes.

Smart fabrics with rewritable features are an emerging field, and they have drawn significant interests owing to their potential benefits such as resource sustainability and mainly performing additional functions that conventional fabrics cannot. Several smart fabrics with color response have been prepared, including SiO2-naphthopyran fabrics [12], epoxy-modified thermochromic fabric [13] and reversible thermochromic fibers [14]. Nevertheless, they suffer from some drawbacks, including photoinstability, the need for direct heating, and lack of printing/erasing features. To solve these problems, photoreversible color switching systems (PCSS) have been proposed, and they are generally composed of metal oxides as photocatalytic agents, redox dyes as reversible color indicators, and polymers as the matrix. When the PCSS are irradiated by UV/visible light, metal oxide nanomaterials in the PCSS produce photogenerated holes which are captured by the sacrificial electron donors (SEDs), whereas the remaining electrons rapidly reduce the dyes to their leuco form. The recoloration process is predominantly triggered by O2 in the presence of heat or visible/NIR light in some cases. Several color switching media have been reported such as TiO2-based [15, 16], SnO2–x-based [17], Au-based [18] and WO3-based [19, 20]. However, the successful application of PCSS has been mostly in rewritable papers and smart inks. In addition, most of these systems rely on ultraviolet or visible light for writing and direct heating for erasing which is detrimental to the polymer substrate [15]. To improve the performance, our group has prepared the smart fabric by coating TiO2–x/Dye/HEC (smart ink) on cotton fabric, which can remotely and rapidly respond to 365 nm for writing and 808-nm for erasing [21]. However, this system still requires a light source for recoloration. In some cases, there is a need to come up with new systems that can re-color automatically without the need for a light source. If such systems are conveyed on a non-woven fabric to prepare a photodetector, they can be applied in many fields, such as visual sensors, wearable displays and secure communication.

It is well known that thermo-sensitive dyes can change color through several mechanisms including reversible interconversion of isomers, molecular rearrangement, molecular orientations and changes in the crystal packing [22, 23]. Usually, the color of thermo-sensitive dyes can disappear when heated above the transition temperature, and re-appear when the temperature is below the transition temperature. For example, crystal violet lactone (CVL) is a typical three-component thermochromic dye, including color former, color developer and solvent [22]. The color transition temperature of CVL can be adjusted in the range of 30–70 °C by the solvent used and/or molar ratios of components [24, 25, 26]. In addition, our group has demonstrated that some NIR photothermal nanomaterials (such as CuS [27, 28], W18O49 [29] and Polypyrrole (PPy) [30]) can efficiently convert NIR laser into heat for many applications (such as the phototherapy of tumors, NIR-shielding film). Among them, PPy is very attractive due to their advantages including broad NIR photoabsorption range, high stability and photothermal effect [31, 32]. Inspired by thermo-sensitive dyes and NIR photothermal effects of PPy nanomaterials, herein we have proposed a prototype of flexible and reusable non-woven fabric photodetector. With CVL as a model of dye, PPy nanomaterials as photothermal agent and hydroxyethyl cellulose (HEC) as the polymer matrix, we have developed a photo-thermochromic ink which is used to coat on non-woven fabric. The blue PPy/CVL/HEC-coated non-woven fabric photodetector exhibits excellent and rapid NIR (808-nm as model) light detection abilities. Upon irradiation of 808-nm laser (0.75 W cm−2), it changes color from blue to colorless in 35 s. When 808-nm laser is turned off, it reverts to the original color under ambient conditions in 60 s. Especially, figures/images can be remotely printed on the surface of the fabric by 808-nm laser and then erased automatically under ambient conditions.

Experimental Section

Materials

Iron chloride hexahydrate (FeCl3·6H2O, 99%), pyrrole monomer (98%), cetyl alcohol, bisphenol A and sodium dodecyl sulfate (SDS) were received from Sino pharm Chemical Regent Co., Ltd (China). Polyvinyl alcohol (PVA) and hydroxyethyl cellulose (HEC) was purchased from Aladdin (Shanghai) Co., Ltd. Crystal violet lactone (CVL) was purchased from Anhui Kuer Biological Engineering Co., Ltd (China). The non-woven fabrics were purchased from Nantong Jikang Non-woven fabric Co., Ltd (China). Other chemicals are commercially available and were used without further purification.

Synthesis of PPy Nanospheres and CVL

PPy nanospheres were prepared by a modified one-step method [33]. In a typical process, FeCl3 (2.3 mmol, 0.622 g) and PVA (0.8 g) were added into 30 mL deionized water, and the solution was stirred for 1 h in an ice bath (~ 5 °C). Then, pyrrole monomer (1 mmol, 70 μL) was added into the above solution to react for 4 h. Then, PPy sample was centrifuged and washed for three times with distilled water.

Crystal violet lactone (CVL) was synthesized by a typical method [22]. Briefly, cetyl alcohol (20 g) was heated at 50 °C to melting state, and then leuco crystal violet lactone (colorless, 0.2 g) and bisphenol A (3 g) were added into the above solution. The resulting CVL solution was continuously stirred at 90 °C for 1 h. After cooling down to room temperature, CVL powder was obtained, and it exhibited an intense blue color.

Preparation of PPy/CVL/H2O ink

To investigate the photodetection properties in liquid form, PPy/CVL/H2O ink was prepared in a two step method. The first step was to prepare the CVL solution by adding blue CVL powder (0.5 g) and SDS (0.01 g) into distilled water (20 mL), and then the solution was heated to 55 °C for 1 h under magnetic stirring at 2000 rpm. In the second step, an aqueous solution (1 mL) of PPy dispersion (60 µg mL−1) was then added into the above CVL solution (5 mL). Then, the resulting solution was stirred for 20 min, and 3 mL solution was transferred into a glass cuvette for subsequent tests. To discolor, the PPy/CVL/H2O ink was irradiated by a NIR light (808-nm as the model, 0.75 W cm−2) for 0–12 s. To recolor, the glass cuvette was allowed to cool in ambient conditions. The absorption spectra of solution were recorded during the discoloration and recoloration process by UV–vis-NIR spectrophotometer (Shimadzu UV-2550).

Construction and Color Switching of Non-woven Fabric Photodetector

Non-woven fabrics were tailored to have the sizes of 6 × 6 cm2. To prepare the viscous ink, as-prepared PPy/CVL/H2O ink (6 mL) was mixed homogeneously with HEC solution (4 mL, 33.33 mg mL−1) under magnetic stirring for 15 min. Then the PPy/CVL/HEC ink was coated on the surface of the non-woven fabrics by doctor’s blade method. The resultant fabric was dried at room temperature for 12 h, forming a smooth, flexible and dark blue colored fabric.

To investigate the photodetection properties, the non-woven fabric was irradiated with 808-nm laser (0.75 W cm−2), and its photoabsorption spectra were recorded. To monitor the reverse color transition, the fabric was allowed to recolor under ambient conditions. To investigate the photothermal effects, the non-woven fabric photodetector was irradiated with 808-nm laser with various intensities (0.25, 0.50, 0.75 and 1.00 W cm−2), and their corresponding temperatures were real-time recorded by using a thermographic camera (FLIR-A300, FLIR Systems Inc.). To study the rewritable features of the non-woven fabric, figures were printed by irradiating the fabric with 808-nm laser through photomasks with various designs.

Characterization and Measurement

The sizes and morphologies were examined by scanning electron microscope (SEM, Hitachi S-4800) and/or transmission electron microscopy (TEM, FEI Talos F200S). Fourier transform infrared (FT-IR) spectrum was performed by IRPrestige-21 spectrometer (Shimadzu). The hydrodynamic diameter of PPy nanospheres was measured by a Zetasizer Nano ZS (Malvern). The thermal analysis of CVL was measured by differential scanning calorimeter (DSC) (Mettler-Toledo, Switzerland). Photoabsorption spectra of PPy suspension and PPy/CVL/H2O ink were recorded on a UV–vis-NIR spectrophotometer (Shimadzu UV-2550). The diffuse spectra of the non-woven fabric were measured by a UV–vis-NIR spectrophotometer (Shimadzu UV-3600) and a white standard of BaSO4 was used as a reference.

Results and Discussion

PPy nanospheres were prepared by a modified one-step method [33]. The size and morphology of PPy samples were investigated by SEM (Fig. 1a). PPy sample is composed of spherical berry-like shapes with uniform diameter of ~ 50 nm and smooth surfaces, resulting from the synergic effects of FeCl3 initiator and PVA ligands [34]. Besides, TEM image (Fig. 1b) further confirms the formation of PPy nanospheres with an average diameter of ~ 50 nm. Subsequently, the chemical composition of PPy nanospheres was investigated by FTIR spectroscopy (Fig. 1c). The peak centered at 1567 cm−1 can be assigned to the stretching vibration of C = C bond of the pyrrole ring [35]. The peak at 1327 cm−1 is due to the stretching vibration of C–N adsorption [36]. The band at 3288 and 1423 cm−1 are attributed to the = C–N in plane deformation vibrations [37]. All the above are characteristic peaks of the pyrrole ring and suggest the successful synthesis of PPy [38]. To investigate the hydrodynamic size distribution, PPy nanospheres were studied by the laser particle size analyzer (Malvern). The hydrodynamic diameter of PPy nanospheres is ~ 60 nm with a narrow diameter distribution (Fig. 1d), which is slightly higher by 10 nm compared to the diameter displayed in TEM image. These findings indicate that successful preparation of evenly sized PPy nanospheres.
Fig. 1

SEM (a) and TEM (b) images, FTIR spectrum (c) and DLS size distributions (d) of PPy nanospheres

The aqueous dispersions containing PPy nanospheres exhibit an intense black color especially at higher concentrations (the inset of Fig. 2a). They show high stability when stored at room temperature for several weeks. Furthermore, the optical property was studied by UV–vis-NIR spectroscopy (Fig. 2a). PPy nanospheres exhibit short-wavelength absorption with an edge at 570 nm. Importantly, the aqueous dispersions of PPy nanospheres display an increase in photoabsorption from 570 to 980 nm which agrees well with previous reports [31, 39]. Besides, with the increase of PPy concentration from 10 to 60 µg mL−1, the absorption intensity goes up as well, suggesting a concentration-dependent photoabsorption. In fact, the enhanced absorption band from the visible region to NIR region is the characteristics of the bipolaronic metallic state of doped pyrrole [31]. As a result of their distinct photoabsorption, PPy nanospheres can absorb visible light partly and NIR light strongly. To further investigate NIR photothermal performance, the temperature elevation of PPy aqueous dispersions were determined during the exposure to NIR laser with 808-nm as the model. Under the irradiation of 808-nm laser (0.75 Wcm−2), the temperatures of PPy dispersions (10–60 µg mL−1) go up rapidly from room temperature (19.2 °C) to 45.6, 55.3, 76.4 and 98.2 °C in ~ 90 s, respectively, and then exhibits slow heating rate from 90 to 360 s. The temperature change shows a concentration-dependent pattern similar to the photoabsorption. In contrast, pure water shows no significant temperature elevation (4.7 °C) under similar conditions (Fig. 2b). According to the measurement method developed by Roper et al. [40], the photothermal conversion efficiency of PPy nanospheres was determined to be 38.2% under 808-nm laser irradiation (Figure S1), which is close to blue Te nanoneedles (43.9%) [41] and higher than Au nanorods (21%) [41]. These results imply that PPy possesses broad NIR absorption and high photothermal effects.
Fig. 2

a UV–vis-NIR absorption spectra of aqueous dispersions containing PPy nanospheres (10–60 µg mL−1); Inset: Photo of the aqueous dispersions. b Temperature changes of aqueous PPy dispersions (0–60 µg mL−1) versus the irradiation time with 808-nm laser (0.75 W cm−2)

It is well known that CVL is a type of thermochromic dye that is composed of a color former, a color developer, and a solvent. In this work, crystal violet lactone (CVL) was selected as a model thermo-sensitive dye. Typically, the thermochromic mechanism is similar to other studies reported in the literature [23, 42, 43, 44, 45]. Briefly, room temperature is below the transition temperature of CVL, causing the lactone ring of CVL to open, and CVL exhibits an intense blue color. When heated to the melting point (above the transition temperature), the lactone ring closes and CVL becomes colorless. Therefore, the thermochromic effect is based on a temperature-driven phase change mechanism, accompanied by a molecular structural change of CVL (Fig. 3a). To determine the thermal property of CVL, the CVL powder was heated from 20 to 70 °C in the air at a heating rate of 3 °C min−1, and the heating response was investigated by DSC (Fig. 3b). CVL’s endotherm starts at 43.4 °C and ends at 49.7 °C. This indicates that the phase transition of CVL occurs from the solid to liquid phase and is much closer to the melting point of cetyl alcohol (~ 50 °C).
Fig. 3

The color change and thermochromic scheme (a) and DSC curve (b) of crystal violet lactone (CVL)

Since PPy exhibits strong NIR photothermal effect and CVL has reversible thermal-induced color switching feature, herein we prepared a photo-thermochromic PPy/CVL/H2O ink. The reversible color response of PPy/CVL/H2O ink was evaluated by the irradiation of 808-nm laser or under ambient conditions (laser off, 25 °C). Before the irradiation, the ink has an intense blue color (Fig. 4a) and displays a peak at 603 nm which is consistent with the absorption peak of CVL [46, 47]. When 808-nm laser is used to irradiate the ink, the blue color rapidly fades and becomes colorless in 12 s. To further investigate the color evolution, the absorption spectra were also recorded by UV–vis-NIR spectroscopy. With the increase of the irradiation time from 0 to 12 s, the peak at 603 nm decreases and vanishes, indicating the efficient discoloration process by 808-nm laser. In contrast, when the ink is left under ambient conditions (laser off, 25 °C), the colorless ink rapidly changes to its initial blue color in 10 s (Fig. 4b). Subsequently, the peak at 603 nm appears and completely recovers in 10 s. Therefore, blue PPy/CVL/H2O ink becomes colorless under 808-nm laser irradiation, while the color can revert rapidly under ambient conditions after the laser is turned off.
Fig. 4

UV − Vis–NIR spectra of PPy/CVL/H2O ink during the discoloration process under 808-nm laser irradiation (0.75 W cm−2) for different time (a) or during the recoloration process in ambient conditions for different time (b)

The color-switching features of CVL have been widely used in many applications such as printed textiles [48, 49], safety and quality control and temperature monitoring [50]. However, there are no reports on its application as an NIR photodetector. To design such NIR photodetector, PPy/CVL/HEC ink was used to coat a non-woven fabric substrate due to its cheap cost and recyclability. Herein, PPy/CVL/HEC ink with a suitable viscosity was prepared by homogeneously mixing the PPy/CVL/H2O and hydroxyethyl cellulose (HEC), where HEC acts as the polymer matrix that assists in the formation of a coating layer on the pre-coated fabric (Fig. 5a). Before the coating, the non-woven fabric is white (Fig. 5b). SEM image (Fig. 5c) shows that the pristine non-woven fabric is composed of an entangled fibrous structure containing fiber filaments with smooth surfaces of ∼ 20 μm in diameter. The cross-sectional SEM image shows that the fabric also consists of random bundles of fiber ends in the woven structure (Fig. 5d). When the ink is coated on the fabric, the surface becomes blue at room temperature (Fig. 5e). Surface SEM image (Fig. 5f) suggests that the fabric maintains the entangled fibrous structure but the filament fibers have rough surfaces due to the coating layer. The cross-sectional SEM image (Fig. 5g) indicates that there is a distinct layer of PPy/CVL/HEC coating with a thickness of ∼ 20 μm. These findings suggest the successful coating of PPy/CVL/HEC layer on the non-woven fabric.
Fig. 5

a Schematic illustration for coating PPy/CVL/HEC ink on the non-woven fabric. Photo b and surface/cross-sectional SEM images (c, d) of non-woven fabric before the coating. Photo e and surface/cross-sectional SEM images (f, g) of non-woven fabric after the coating

To realize the color-switching, the non-woven fabric was discolored by 808-nm (0.75 W cm−2) laser and then recolored under ambient conditions (laser off, 25 °C). During laser irradiation, the blue color of the non-woven fabric rapidly disappears with the increase of the irradiation time from 0 to 35 s (Fig. 6a). Simultaneously, the photoabsorption peak of CVL at 603 nm gradually goes down as irradiation time increases, until it almost flattens in 35 s (Fig. 6b). On the contrary, when 808-nm laser is turned off, the colorless non-woven fabric gradually displays a blue color under ambient conditions, and it finally exhibits the initial blue color in 60 s (Fig. 6c). At the same time, the absorption spectra of the non-woven fabric rise rapidly with the increased time, and it completely reverts to the original absorption point in 60 s (Fig. 6d). The present discoloration and recoloration time (35 s and 60 s) are very short, which exhibits excellent 808-nm response as well as fast ambient recoloration of the non-woven fabric.
Fig. 6

Photos a and UV–vis-NIR spectra (b) during the discoloration process of PPy/CVL/HEC-coated non-woven fabric under 808-nm laser irradiation (0.75 W cm−2). Photos c and UV–vis-NIR spectra (d) during the recoloration process under ambient conditions (laser off, 25 °C)

To investigate the discoloration reason and effects of laser intensity, two non-woven fabrics with PPy/CVL/HEC or CVL/HEC (without PPy) coating were obtained, and then, respectively irradiated by 808-nm laser at various intensities (0, 0.25, 0.5, 0.75 and 1.0 W cm−2) for 90 s. During the irradiation, the photo and thermographic images were captured after 30 s. Before the irradiation, the CVL/HEC-coated non-woven fabric exhibits a blue color at room temperature (Fig. 7a). After the irradiation, the CVL/HEC-coated fabric shows no apparent change in color with the increase in laser intensity from 0.25 to 1.0 W cm−2 (Fig. 7a). Similarly, there is no obvious decrease in the photoabsorption spectra during irradiation at different intensities (Fig. 7b). Correspondingly, the thermographic images display no obvious temperature elevation when different intensities are used (Fig. 7a). The temperature change curves are consistent with the photos, photoabsorption spectra and thermal images, suggesting that there is no significant increase in temperature after 808-nm irradiation at different intensities. In fact, the temperature increases only from 27.1 °C (room temperature) to 27.8, 29.3, 31.1, and 32.5 °C after irradiation at 0.25, 0.5, 0.75 and 1.0 W cm−2 (Fig. 7c). This fact indicates that the fabric with CVL/HEC coating cannot efficiently absorb laser light, resulting in unobvious elevation of temperature and thus no discoloration effect. On the contrary, when PPy nanospheres are present, PPy/CVL/HEC-coated non-woven fabric has obvious color change with the increase in laser intensity. Compared to the control group (0 W cm−2), the fabric irradiated by 0.25 W cm−2 laser shows no apparent change in color; but from 0.5 to 1.0 W cm−2, the change is more vivid (Fig. 7d). Similarly, the photoabsorption spectra show a decreasing trend as the laser intensity increases. For example, the absorption at 603 nm decreases from 1.24 to 1.09, 0.91, 0.69 and 0.57 when the laser intensity increases from 0 to 0.25, 0.5, 0.75 and 1.0 W cm−2 (Fig. 7e). Likewise, the thermographic images show an increase in the heat produced as the laser intensity increases (Fig. 7d). These results are corroborated by the temperature change curves, which indicate that the temperature increases from 27.1 to 39.1, 53.2, 59.5 and 67.8 °C for the laser intensity ranging from 0.25 to 1.0 W cm−2 (Fig. 7e). Obviously, when laser intensity exceeds 0.5 W cm−2, the temperatures (53.2, 59.5 and 67.8 °C) of PPy/CVL/HEC-coated fabric are higher than the transition temperature (~ 49.7 °C) of CVL, conferring the efficient discoloration. It should be noted that NIR laser with low intensity (such as 808 nm, < 0.5 W cm−2) is safe for human skin exposure [27], while NIR laser with high intensity (> 0.5 W cm−2) is harmful but invisible. Thus, in most cases, high intensity NIR laser needs to be detected visually. In the present work, PPy/CVL/HEC non-woven fabric has the laser intensity-dependent discoloration ability, and can be used as a visual sensor to detect 808-nm laser.
Fig. 7

Photos and IR thermographic images (a), UV–vis-NIR diffuse spectra (b) and temperature changes (c) of CVL-HEC-coated non-woven fabric (without PPy) under 808-nm laser irradiation with different laser intensities (0–1.0 W cm−2). Photos and IR thermographic images (d), UV–vis-NIR diffuse spectra (e) and temperature changes (f) of PPy/CVL/HEC-coated non-woven fabric under 808-nm laser irradiation with different laser intensities (0–1.0 W cm−2)

For the practical application of such non-woven fabric, one requirement is the good reversibility and stability. To evaluate the cycle stability, PPy/CVL/HEC-coated non-woven fabric was illuminated by 808-nm laser (laser on: 35 s, laser off: 60 s) repeatedly. The photoabsorption intensity at 603 nm were real-time recorded at each 808-nm irradiation and ambient recoloration process (Fig. 8). During the 25 cycles, there is no obvious change in the absorption minima/maxima. After these cycles, the non-woven fabric photodetector does not show any appearance of creases or browning. These facts confirm that PPy/CVL/HEC-coated non-woven fabric has good reversibility and stability.
Fig. 8

The cycle tests for absorption intensity at 603 nm of PPy/CVL/HEC-coated non-woven fabric with or without 808-nm laser irradiation (0.75 W cm−2)

Considering the excellent 808-nm detection and color switching performance of the non-woven fabric, a model fabric was prepared to test its potential applications as rewritable smart device. A piece of non-woven fabric (25 mm × 25 mm) was prepared by coating the PPy/CVL/HEC ink on the surface of the fabric. Under the irradiation of 808-nm laser (with photomasks), the different images can be written on the fabric remotely (Fig. 9a). For example, the shape of a star, a rabbit, a butterfly or a plane (Fig. 9b–d) can be printed on the fabric. The color of the irradiated regions turns grey, whereas the un-irradiated regions maintain the original blue color of PPy/CVL/HEC ink. When the laser is turned off, all figures can be erased automatically after 60 s under ambient conditions, with excellent cycling and stability. These results suggest that the non-woven fabric can not only be used to detect 808-nm laser, but also be used as the smart fabric with photo-writing and automatic erasure functions for visual sensors, information displays and secure communication.
Fig. 9

a Schematic illustration of the writing and erasing process on the non-woven fabric. bg Photos of different figures before and after 808-nm irradiation (0.75 W cm−2) using different photomasks

Conclusions

Blue non-woven fabric photodetector has been prepared by coating PPy/CVL/HEC ink on white non-woven fabric. Under the irradiation of 808-nm laser (0.75 W cm−2), the blue PPy/CVL/HEC-coated non-woven fabric rapidly changes to a greyish color in 35 s due to the photothermal effect of PPy. This effect confers the rapid elevation of temperature (> 50 °C) and then converts CVL to its leuco form (colorless). When the laser is turned off, the temperature drops to below the transition temperature (< 43 °C), and then CVL reverts to its initial blue color. Moreover, various figures and images can be easily printed on the fabric photodetector by 808-nm laser, and then erased automatically under ambient conditions, with excellent cycling stability. Therefore, the present non-woven fabric with rewritable features has great potential to be applied in areas such as anti-counterfeit technology, visual sensors and secure communications.

Notes

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (51773036 and 51972056), Shanghai Shuguang Program (18SG29), Natural Science Foundation of Shanghai (18ZR1401700), Innovation Program of Shanghai Municipal Education Commission (2017-01-07-00-03-E00055), the Fundamental Research Funds for the Central Universities, and DHU Distinguished Young Professor Program.

Supplementary material

42765_2019_22_MOESM1_ESM.docx (186 kb)
Supplementary material 1 (DOCX 186 kb)

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Copyright information

© Donghua University, Shanghai, China 2020

Authors and Affiliations

  1. 1.State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and EngineeringDonghua UniversityShanghaiChina

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