Chen Su, Nanjing University of Technology "ACS Appl.Mater. Interfaces": Based on microfluid spinning technology in-situ construction of ordered fluorescent fibers in white LED and wearable devices application research progress.
Nanofibers or fiber microreactors have received widespread attention in recent years because of their important applications in tissue engineering, sensors and wearable devices. It is very difficult to produce highly ordered fibers on the nanometer or micrometer size. In recent years, many efforts have been made to prepare highly ordered, flexible and light-weight fluorescent fiber films. The most reported methods in this area mainly focus on electrospinning, melt spinning, centrifugal spinning, and wet spinning. Among these technologies, electrospinning is the most common method for manufacturing fibers with various polymers, such as polymethylmethacrylate (PMMA), poly(L-lactic acid) PLLA, polyvinyl alcohol (PVA) and poly Styrene (PS).
However, electrospinning requires special equipment, a high-voltage power supply, is sensitive to changes in solution conductivity, requires a conductive target, and it is difficult to prepare orderly fluorescent fibers. Although some emerging methods (continuous stretch spinning, spray coating and inkjet printing technology) have recently emerged to prepare ordered microfiber arrays, these devices are expensive and time-consuming.
Figure 1. Preparation of fluorescent fiber membrane and its application in coding, WLED and wearable bracelets. (A) Schematic diagram of the preparation of fluorescent fiber membrane and its application in wearable bracelets. (B) Schematic diagram of CdSe QD/PVP fiber prepared by in-situ reaction under the node of Y-type microfluidic chip. (C) Schematic diagram of ordered fluorescent codes (red, green and blue).
Professor Chen Su’s research group from the School of Chemical Engineering, Nanjing University of Technology reported a very simple method for the preparation of highly ordered and in-situ ultra-long (1413 m) CdSe quantum dot fluorescent fibers-Microfluid Spinning Technology (MST) ( Figure 1). MST has attracted much attention because of its ideal preparation and orderly fluorescent fiber platform, continuous operation, high efficiency, flexibility and environmental protection. In this work, they demonstrated a method of combining MST with different chips to prepare ordered fibers with diameters ranging from 0.8 μm to 20 μm.
First, they successfully constructed a white fluorescent film for the preparation of wearable devices using fluorescent quantum dots (QDs) through three-phase microfluidics technology. The fluorescent fiber membrane prepared by this method has excellent optical properties and transparency (~84%), as well as good flexibility and mechanical properties (mechanical stretching ~190%).
Figure 2. In situ preparation of CdSe QDs fiber membranes by MST. (A) Schematic diagram of in-situ synthesis of CdSe QD by Y-type microfluidic chip. (B) Green, (c) Yellow, (d) Red. Fluorescence microscope image of a single layer of CdSe/PVP fluorescent fiber. (E) PL emission spectra of green, yellow and red CdSe/PVP fluorescent fibers. (Λ= 542 nm, 571 nm and 638 nm). (F) HRTEM image of CdSe/PVPQDs fiber. (G) EDS spectrum of CdSe/PVP fiber powder. (H) Fluorescence lifetime of green, yellow and red CdSe/PVP fluorescent fibers. (I) Sample image of fluorescent fiber array, (j) green, (k) yellow, (L) fluorescence microscopic image of red CdSe/PVP fluorescent fiber array.
Then, they also developed a microfiber reactor platform for green synthesis of QDs with the help of MST. When the two ions (Cd2 + and Se2-) meet at the junction of the Y-type microchip, the CdSe QDs/PVP hybrid fluorescent microfiber will be generated immediately. The proposed method not only breaks through the limitation of in-situ reaction, but is also fast (within 30 minutes) at a mild reaction temperature (110°C) (lower than the traditional method of preparing CdSe quantum dots (about 230°C)) And large-scale (6 cm×6 cm) synthesis of CdSe QDs fiber membrane provides a green way.
Then, the produced CdSe quantum dot optical fibers are ground into phosphors to prepare white light emitting diodes (WLEDs). (Figure 2) WLED display color rendering index is 72 and color gamut coordinates (0.3251, 0.2667). Finally, they also developed a controllable microfluidic guidance method for the easy construction of a series of fluorescent codes. This method is simple, low-cost and efficient. Compared with the latest methods (digital adjustment method, cut-off lithography), it contains a variety of encoded information (Figure 3).
It is worth mentioning that these fluorescent fiber films may have potential application value in optical devices, especially in anti-counterfeiting and fluorescent coding. The research work was published on ACS Appl. Mater. Interfaces 2018, 10, 30785-30793. The first author of the paper is Cui Tingting, a doctoral student in the School of Chemical Engineering, Nanjing University of Technology, and the corresponding author is Professor Chen Su, the School of Chemical Engineering, Nanjing University of Technology.
Figure 3. Fluorescence characteristics and optical applications of fluorescent fiber membranes. (A) Sample image of CdSeQDs/PVP fluorescent fiber film. (B) Digital photo of CdSe/PVP powder under ultraviolet light. (C) EL spectrum of WLED based on CdSe/PVP powder operating at 350mA, illustration: photo of WLED under daylight. (D) WLED emission spectrum on CIE1931 chromaticity diagram. (E) Photograph of WLED in the dark. (F) Sample image of WLED wearable bracelet.
These work were supported by the National Natural Science Foundation of China (21474052 and21736006), the National Key Research and Development Program (2016YFB0401700), and the State Key Laboratory of Materials and Chemical Engineering Fund (ZK201704 and ZK201716).
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