Smart Sunglasses and Goggles Based on thieno[3,4-b][1,4]dioxepine] (PProDOT-Me2), to fabricate and characterize the lens of prototype smart sunglasses. The PProDOT- Electrochromic Polymers Me2 EC film exhibits high transmittance contrast ratio (Δ%T) between blue color and transparent state, low operation potentials, high Chao Ma, Minoru Taya and Chunye Xu* conductivity and high thermal stability6. The lens of smart sunglasses and goggles are multilayer Center of Intelligent Materials and Systems, University of Washington, structured ECD, as schemed in Figure 1. The electrochromic working Box 352600, Seattle, WA 98115 layer, PProDOT-Me2 film, is deposited on Indium Tin oxide (ITO) coated glass. The counter layer of the device is vanadium oxide (V2O5) *Corresponding author: [email protected] film, also deposited on ITO glass. The V2O5 film serves as an ion storage layer and works with the PProDOT-Me2 film as a pair. When ABSTRACT the EC film is reduced with an applied potential and changes color to - Today, people concern more and more about the sun’s harmful blue, the V2O5 film will absorb ClO4 simultaneously. When the EC film effects on the eyes and safety issues. Sunglasses and goggles can is oxidized with an opposite potential and changes to transparent state, + meet this need to protect the eyes from sun light damages and the V2O5 film will absorb Li . During switching, the V2O5 film maintains influences. This paper discusses the design, process and performance a light green color. There is also a transparent polymer gel electrolyte, - + of prototype smart sunglasses and goggles based on cathodic which is a good conductor for small ions such as ClO4 and Li and a electrochromic (EC) polymers, which show several merits compared to insulator for electrons, sandwiched between the working and counter traditional sunglasses materials as well as other smart window layers. It is an ion transport layer and ions move quickly inside during materials. It is a multilayer design of device. The conjugated polymer, switching. A transparent anti ultra-violet (UV) layer is added to protect poly [3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine] the eyes from harmful UV rays. This layer also prevents organic (PProDOT-Me2), is utilized as the electrochromic working layer. The materials breaking down in the radiation of UV rays. counter layer of the device is vanadium oxide (V2O5) film, which serves During deposition, the electric potential drop caused by the as an ion storage layer. There is also a polymer gel electrolyte as the surface resistance of ITO glass will make the EC film ununiform. In this ionic transport layer, sandwiched between the working and counter paper, we adopted low sheet resistance ITO glass and copper tape layers. The characters of prototype device are reported, including electrode, on the extended parts of ITO glass, to overcome this issue. transmittance (%T), driving power, response time, open circuit memory and lifetime.
INTRODUCTION After the first sunglasses invented by Sam Foster in the 1920’s, they were used almost for every purpose but not only as a fashion item. Today people have known more and more about the sun’s harmful effects on the eyes, such as cataracts, macular degeneration, and photokeratitis. Therefore, the primary function of sunglasses and goggles has been providing a protection to the eyes from sun light damages and influences1-3. The traditional sunglasses materials 4 include plastic (polycarbonate and CR-39 resins) and crown glass , (a) which are transparent or tinted. Sunglasses and goggles of this design have only one fixed color state and the transparency is uncontrollable. We know that during outdoor activities such as motorcycling and skiing, sunlight conditions can vary considerably, and the varying light conditions could be a problem to users with traditional sunglasses and goggles. Smart window materials are characterized by their ability to adjust the light transmission upon application of an electric potential, and can be utilized to solve this problem. Current active materials used in smart window devices mainly include suspended particles, liquid crystals and (b) electrochromics5. Suspended particle devices (SPD) and liquid crystal devices (LCD) are capable of switching quickly and perform high Figure 1. Schematic representation of the ECD construction (a), and transmission range, but their drawbacks are also obvious. High voltage the design of lens of smart sunglasses (b) is needed for both of SPD and LCD to operate. The high production cost, complex manufacturing, lack of memory function, and limited EXPERIMENTAL color availability restrict them from being used in developing smart The EC material, PProDOT-Me2 monomer was synthesized in our 7, 8 sunglasses and goggles. lab via an improved route reported in the literature . Electrochromic materials can change their color when a potential All materials were purchased from Aldrich, except Tetra-n-butyl is applied due to electrochemical oxidation and reduction. Current ammonium perchlorate (TBAP, electrochemical grade) and Lithium available technologies employ inorganic electrochromic materials, such perchlorate (99% anhydrous, packed under argon), which were as WO3. However, this transition metal oxide electrochromics show a purchased from Alfa Aesar. Because the EC film is sensitive to slow response time (tens of seconds) and high processing cost. moisture and air, which affect the performance of devices, all the Compared with these smart window materials, electrochromic materials were dried before use and stored in glove box filled with polymers (EC) have the most promising future in developing smart argon. sunglasses and goggles. Electrochromic polymers based devices The gel electrolyte was based on poly(methylmethacrylate) (ECD) have shown several merits: they require power only during (PMMA) and lithium perchlorate (LiClO4) and plasticized by propylene switching; the operation voltage and energy consumption are low; carbonate (PC) and ethylene carbonate (EC) to from a highly quick response time; open circuit memory function; great repeatability; transparent and conductive gel. rich color availability; and ease in fabrication large scale and flexible The EC film was deposited from 0.01M monomer in a 0.1M devices. LiClO4/Acetonitrile (ACN) solution. Electrochemical deposition of the Our laboratory has developed kinds of new electrochromic film was carried out by using an electrochemical analyzer (CHI 605A, polymer materials with blue, red or green color. In this paper, we CH Instruments), utilizing the chronoamperometry method. A three utilized a cathodic EC polymer material, [3,3-dimethyl-3,4-dihydro-2H- electrode cell with Ag wire as a reference, ITO glass (Thin Film Device)
as a working electrode and a Pt plate as a counter electrode was used for electro-polymerizing the polymer film 0 V 50 a Vanadium pentoxide (V2O5) film was deposited on ITO glass by 0.2 V the chronoamperometry method in V O ·nH O sol-gel solution. The 0.3 V 2 5 2 0.4 V gels of V2O5 ·nH2O were synthesized using a method reported in 40 0.5 V previous literature9. 0.6 V 0.7 V Both of the EC film and V2O5 film need to be placed into a 0.1M 30 0.8 V LiClO /PC electrolyte solution after polymerization. The films were 0.9 V
4 electrochemically conditioned by the chronocoulometry method in 1.0 V 20 1.1 V order to change the inorganic ions in the films and have them be 1.2 V 10 familiar with a LiClO4/PC environment . Transmittance(%T) 1.3 V 1.4 V An EC film coated ITO glass surface was entirely covered with a 10 uniform and thin layer of gel electrolyte. A V2O5 film coated ITO glass was then placed on top and clamped together. A UV curing epoxy 0 (OG112-4, EPOXY TECHNOLOY) was used as a hermetic barrier to 400 500 600 700 800 seal the device. The assembly process was also done in a glove box Wavelength(nm) filled with argon.
CHARACTERIZATION AND DISCUSSION 50 After assembly, we characterized optical performance b (transmittance) of the lens of smart sunglasses, on a spectrophotometer (V-570, JASCO). Figure 2 gives the photo spectrum 40 curves of the lens from 380nm to 800nm wavelengths. 1.2V DC was applied with positive and negative direction to achieve colored and 30 transparent state. At 580nm wavelength, the transmittance (%T) of the
lens is 45% on transparent state, and 5% on colored state. 20
Transparent Transmittance(%T) 50 Colored 10
40 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Voltage(V)
30 Figure 3. a. Photo spectrum curves of lens between 380nm and
%T 800nm with potential from 0.2~1.4V; b. Transmittance at 580nm with 20 potential from 0.2~1.4V.
10
0 300 400 500 600 700 800 Wavelength(nm)
Figure 2. Photo spectrum curves of lens between 380nm and 800nm in the transparent and colored state
The spectrum date shows that the lens of smart sunglasses exhibits an ability to change its optical performance, transparent or colored, as a function of the applied potential. Meanwhile, the transmittance of light on colored state can be adjusted by applying different potentials. The photo spectrum curves of different applied potential are shown in Figure 3. Before each applied voltage, a 1.2V Figure 4. Response time for lens of smart sunglasses, with ±1.2V DC DC potential was applied to the lens, in order to make it transparent, potential and then an opposite 0.2~1.4V DC was applied for 1s to color the lens. As we can see, the transmittance of light keeps decreasing while we Not only is the driving power of the lens low, but the amount of raise the applied voltage, but the change became smaller gradually. electric charge needed to switch the optical state is also small. Namely, After 1.2V DC, the spectrum curves almost overlay with each other. the energy consumption during switching is low. We measured the During outdoor activities, sunglasses and goggles require fast electric charge consumption. When switching lens to fully colored state, response to adapt to various environments. Therefore, the color it is less than 0.02C. The lens of smart sunglasses based on EC changing response time of the lens was characterized, and is polymer films can be powered by commercialized cell batteries, whose performed in Figure 4. With ±1.2V DC potential, the lens can be turned standard electric capacity is around 100C. This is also demonstrated in to fully colored state in 1s and to fully transparent state in 2s. This Figure 5: our EC films based lenses were powered by a single cell response time is much shorter than that of the inorganic electrochromic battery with 1.55V DC potential (Energizer EPX 76), and reached their materials, and is quite enough for hiking, skiing or motorcycling. fully colored and transparent state. The charge time of this demonstration is 2s.
5. Xu C.; Liu L.; Legenski S. E.; Ning D.; Taya M. J. Mater. Res., 2004, 19(7), 2072. 6. Schwendeman I.; Hickman R.; Sönmez G.; Schottland P.; Zong K.; Welsh D. M.; Reynolds J. R.; Chem. Mater. 2002, 14, 3118. 7. Xu C.; Tamagawa H.; Uchida M.; Taya M.; Proceeding of SPIE. 2002, 4695, 442,. 8. Welsh D. M.; Kumar A.; Meijer E. W.; Reynolds J. R.; Advanced Materials, 1999, 11(16), 1379. 9 Kaneko C.; Xu C.; Liu L.; Dai N.; Taya M. Proc. of SPIE. 2005, 5759, 518. 10 Ning D.; Xu C.; Liu L.; Kaneko C.; Taya M. Proc. of SPIE. 2005, 5759, 260.
Figure 5. Lenses of smart sunglasses switch optical state, powered by a cell battery
PProDOT-Me2 films based EC devices have long lifetime and open circuit memory function, as it is reported by Ning et al.10. After over 100,000 cycles of switching between the fully colored and fully transparent state, the EC device showed only 6% change in the transmittance. The device was also kept in a colored or transparent state without electric charge for 30 days. The transmittance at 580nm changed less than 6% on the fully colored state and maintained almost no change on the fully transparent state.
CONCLUSIONS Lenses of smart sunglasses and goggles, with a multilayer structure design, was fabricated and characterized. A cathodic EC polymer film (PProDOT-Me2) and V2O5 film were deposited on ITO glasses as two electrodes. There is also a transparent gel electrolyte sandwiched between the two electrodes. This EC film based device exhibited adjustable transmittance of light (5%~45%), fast response time (1~2s), low driving power (1.2-1.5V DC) and energy consumption. These characters proved that EC polymer based lenses could be widely used in the development of smart sunglasses and goggles.
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