Yujie Ding

Conductivity Trends of PEDOT-PSS Impregnated Fabric and the Effect of Conductivity on Electrochromic Textile

A stretchable e-textile was fabricated by simply soaking Spandex fabric in a conductive polymer aqueous dispersion, PEDOT-PSS. The resulting conductive fabric had an average conductivity of 0.1 S/cm. Subjecting the fabric to more than one soaking step increased the conductivity of the fabric up to ca. 2.0 S/cm resulting in a 33% faster switching speed. This simple methodology is not limited to Spandex (50% nylon/50% polyurethane). Several other fabric compositions were investigated for their conductivity via this process, including 100% cotton, 60% cotton/40% polyester, 95% cotton/5% Lycra, 60%polyester/40% rayon, 100% polyester, and 80% nylon/20% Spandex, listed in order of decreasing hydrophilicity. Those fabrics with higher water uptake resulted in higher conductivities upon soaking in PEDOT-PSS. Electrochromic polymers coated on the fabric could be switched between their different colored states, even upon stretching of the Spandex. SEM revealed that the electrochromic polymer coated on the substrate separated under stretching, uncovering the color of the base conducting fabric. It was found that the PEDOT-PSS was not a film on the Spandex but rather homogenously dispersed nanoparticles within the fabric matrix forming a percolated network.

Preparation of conjugated polymers inside assembled solid-state devices.

Herein we describe a method for the preparation of solid-state devices without the need for solution-based conversion or deposition steps. Precursor polymers are converted to their conjugated, electrochromic counterpart inside assembled solidstate devices; we refer to this process as in situ conversion. There are three main advantages to this method. First, we have shown that the previously required clean and defect-free substrates are not necessary for in situ conversion. Therefore, neither a rigorous cleaning step nor pristine processing environments are needed for device assembly. This is particularly advantageous for large-area applications where the probability of defects increases with the size of the substrate and thus windows or other such devices would benefit greatly from this method. Second, we have eliminated the solution step in the device preparation process. This step could be either electrodeposition or electrochemical conversion of a precursor system in an electrolyte bath. In situ conversion eliminates the need for this costly and wasteful step by preparing the conjugated material inside a solid-state device. Thus, there is no need for the disposal of toxic organic solvents and salt systems. Finally, devices prepared by in situ conversion retain the entirety of the precursor material used. No leeching of monomer or oligomer into the discarded electrolyte occurs because the process is contained within a sealed solid-state device. In situ conversion would be useful in the preparation of a myriad of devices which utilize conjugated polymers in conjunction with redox processes, such as capacitors, sensors, drug delivery applications, thin film transistors, and electrochromics, among others. Figure 1 shows images and chemical structures for an assembled, in situ solid-state device at each stage of this method. The precursor polymer approach to conjugated polymers is attractive in its own right. Precursor polymers are soluble materials which can be converted to conjugated polymers after deposition on a substrate. Herein, we utilize copolymers of aromatic and silane units. Oxidative conditions cause cleavage of the Si–C bonds and subsequent coupling of the aromatics to form the conjugated electrochromic. This approach allows for the incorporation of a variety of electroactive monomers in different ratios into the final conjugated backbone, something not always feasible by electrodeposition. Many different approaches to addressing solubility have been explored, typically relying on alkylor alkoxy-substitution. These approaches could be limited in terms of industrial processing due the rigidity of the polymeric backbone, which results in high glass transition temperatures (Tg) despite their solubilizing units. We have made use of precursor polymer systems, whereby a copolymer with an alkyl-substituted silane or siloxane is used. Alternatively, a pendant chromophore on a solubilizing norbornene backbone has been employed. The precursor materials exhibit Tgs ranging from 9 8C to 80 8C. Precursor polymers may be processed by any traditional solution-based method, including ink jet printing, electrostatic spinning, spin coating, spray coating, dip-coating, doctor blading, etc., in addition to non-solution-based methods, such as melt-processing. Previous work has shown the ability to photopattern these precursors, as well. The creation of nanofiber mats of electrochromic materials results in unique morphologies which are controllable and reproducible, something impossible to mimic with electrodeposition. This adds yet another facet to the versatility of in situ conversion. Electrochemical polymerization requires clean and defect-free conductive substrates in order to achieve uniform films due to the nucleation and growth mechanism of deposition. Devices built without clean ITO (using intentionally unclean substrates) were found to undergo in situ conversion without visible defects in the final device, making this method attractive for large-scale processing. In the past, this oxidative conversion has been carried out in a quasi-reusable electrolyte bath resulting in desilylation and coupling of the aromatic units to form the p-conjugated electrochromic material. Afterwards, they were assembled into a device and characterized. We were able to achieve the conversion from a precursor polymer to its conjugated counterpart inside an assembled device, effectively removing the need for any solution steps. This method utilizes an assembled electrochromic sandwich device, which is a two-electrode cell, to achieve the same electrochemistry as a three-electrode cell in solution. The in situ method is not limited only to this device architecture, however. The precursor polymer used for this study is poly(bis[3,4-ethylenedioxythiophene]thiophene-dioctylsilane) (PBEDOT-T-Si[Octyl]2), Tg1⁄4 40 8C, and is a light-yellow colored material when cast as a film. The converted product is a conjugated, electrochromic polymer which switches from a red state when neutral to a blue state when oxidized. The conversion process from a yellow to a blue/red is irreversible. Any such precursor that formed a uniform film upon processing has yielded similar film quality when converted in

A simple, low waste and versatile procedure to make polymer electrochromic devices

Herein we present a simple and elegant method for the creation of solid-state conjugated polymer devices. Their electrochromic properties were fully explored in this study, but one could envision the extension of this method to displays, solar cells, OLEDs, transistors, or many other applications. We prepared conductive polymer composites or blends within a polymer electrolyte using electrochemical polymerization of these monomers inside an assembled solid-state device. This method will work for any monomer that can be dissolved in the gel electrolyte. This technique offers simplicity in device construction, is easily adapted to patterned systems and comprises a low-waste assembly process. Our novel approach of assembling polymer electrochromic devices avoids the tedious cleaning process of the substrates, produces almost no waste, and by inkjetting insulating materials to mask the substrates, letters and high-resolution images could be achieved inside the converted polymer devices. Electrochromic devices utilizing PEDOT assembled by our method showed compatible switching speed and durability with a slightly higher contrast ratio.

Solid‐State High‐Throughput Screening for Color Tuning of Electrochromic Polymers

Diffusion of two monomers and their oxidative copolymerization inside a solid-state gel electrolyte is utilized as a method to match the monomer feed ratio to a color resulting from a conjugated copolymer having a single absorption in the visible region. Here, a combination of two monomers is used to generate a solid-state electrochromic device of any color, except black and green, in the colored state with all other colors going to transmissive sky blue in the bleached state.