Diffuse color patterning using blended electrochromic polymers for proof‐of‐concept adaptive camouflage plaques

A study using three different pairs of electrochromic polymers (ECPs) synthesized onto plaques by means of a modified vapor phase polymerization (VPP) technique is presented. Restriction of the respective polymerization times, allowed both faster and slower polymerizing monomers to be controlled, and produced blended plaques with visually diffuse interfaces. The ECPs within the blended plaques retain their individual electrochromic behavior and when encapsulated into an electrochromic device, show outstanding optical switching performance with little degradation evident over 10,000 cycles, coupled with a switching time of the order of 1 second. Blends also allow multiple diffuse color changes within an electrochromic device, due to the difference in oxidation potentials of the individual ECPs, making them candidates for adaptive camouflage use. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42158.     

Faradaic charge corrected colouration efficiency measurements for electrochromic devices

We report a new technique for measuring colouration efficiency (CE) for electrochromic polymers and devices. Faradaic charge associated with redox activity leading to chromic change was extracted from the total charge flow during a device switch. Typically, Faradaic charge is extracted from the total charge by first measuring a blank device (i.e. no polymer deposited). This is used as the baseline and subtracted from subsequent measurements with the polymer deposited into the device. The method is open to inaccuracies if the surface area before and after polymer deposition is different or if the inherent capacitance of the device is altered by the addition of the polymer(s). The new technique does not suffer from this drawback as it dispenses with the need to measure blank devices. To investigate the utility of this method a poly(3,4-ethylenedioxthiophene) (PEDOT) and polyaniline (PANI) electrochromic cell was tested. CE measurements at an optical density change of 95% (λ = 555 nm) were recorded for the following three conditions: uncorrected, CE_UC = 388 cm²/C; background corrected, CE_BC = 391 cm²/C and; Faradaic corrected, CE_FC = 2173 cm²/C. The result highlights the fact that the CE value of chromic polymers or devices may be higher than what is currently being reported.     

WETTABILITY AND SURFACE ENERGETICS OF ROUGH FLUOROPOLYMER SURFACES

Hydrophobic solid surfaces with controlled roughness were prepared by coating glass slides with an amorphous fluoropolymer (Teflon® AF1600, DuPont) containing varying amounts of silica spheres (diameter 48 μm). Quasi-static advancing, θ_A, and receding, θ_R, contact angles were measured with the Wilhelmy technique. The contact angle hysteresis was significant but could be eliminated by subjecting the system to acoustic vibrations. Surface roughness affects all contact angles, but only the vibrated ones, θ_V, agree with the Wenzel equation. The contact angle obtained by averaging the cosines of θ_A and θ_R is a good approximation for θ_V, provided that roughness is not too large or the angles too small. Zisman's approach was employed to obtain the critical surface tension of wetting (CST) of the solid surfaces. The CST increases with roughness in accordance with Wenzel equation. Advancing, receding, and vibrated angles yield different results. The θ_A is known to be characteristic of the main hydrophobic component (the fluoropolymer). The θ_V is a better representation of the average wettability of the surface (including the presence of defects).     

Development of a Liquid Rocket Ground Demonstrator Through Thermal Analyses

Abstract

CIRA, the Italian Aerospace Research Center, manages the HYPROB (HYdrocarbon PROpulsion test Bench) Program, supported by the Italian Ministry of University and Research, with the aim of improving the national capabilities to develop rocket engines for future applications. A system line, named HYPROB-BREAD, focusing on liquid oxygen/liquid Methane (LOX/LCH₄) technology and relative breadboards, is included. A step-by-step approach has been adopted to validate critical design aspects by simplified technological breadboards. The reliable operation of an engine is ensured by thermally efficient cooling jackets, which require the in-depth comprehension of the coolant behavior. For this purpose, a specific breadboard has been designed and tested. Another important issue is the evaluation of the thermal loads, transferred by the combustion hot gases to the thrust chamber walls. In this view, a Subscale Calorimetric Breadboard has been designed; 13 disks surround the chamber: they are fed up by water and provide the cooling and the measurement of the exchanged thermal power. The final article is a 3-ton-class LOX/LCH₄ regenerative demonstrator, whose coolant is liquid methane, flowing in a cooling system, made by several axial channels. This paper aims at describing the thermal investigations, conducted in the design and the verification phase for the aforementioned breadboards and demonstrator cooling jacket.     

Gel electrolytes with ionic liquid plasticiser for electrochromic devices

The comparative performance of conducting polymer electrochromic devices (ECDs) utilising gel polymer electrolytes (GPEs) plasticised with ethylene carbonate/propylene carbonate or (N-butyl-3-methylpyridinium trifluoromethanesulphonylimide (P₁₄TFSI) has been made. Lithium perchlorate and lithium trifluoromethanesulphonylimide salts were used in the GPEs to provide enhanced ionic conductivity and inhibit phase separation of the polyethyleneoxide (PEO) and plasticiser. ECDs were assembled from cathodically colouring, polyethylenedioxythiophene (PEDOT), and anodically colouring, polypyrrole (PPy), conducting polymer electrochromes deposited by vapour deposition. The photopic contrast switching over the visible light spectrum, switching speeds and device stability of the ECDs were obtained. These studies demonstrate that the ionic liquid (IL) plasticised GPEs are a suitable replacement for pure IL based devices and volatile organic solvent plasticisers based upon ethylene carbonate/propylene carbonate mixtures.     

In-situ QCM-D analysis reveals four distinct stages during vapour phase polymerisation of PEDOT thin films

Gaining a deeper understanding of the growth of poly(3,4-ethylenedioxythiophene) (PEDOT) films by vapour phase polymerisation (VPP) is essential for the rational design and optimization of such films. The VPP process was used to synthesise films of PEDOT on oxidant-coated substrates. Atomic force microscopy images showed that the morphology of the films changed considerably with time. Utilising a quartz crystal microbalance with dissipation measurement (QCM-D), we found that the kinetics of polymerisation and the viscoelastic properties of the films varied. The data reveal four distinct stages in film growth. Each stage produces a layer having different conductivity values, from a low of 276 S cm⁻¹ to a high of 1196 S cm⁻¹. Conductivity and electrochromic optical contrast, Δ%Tx, can thus be maximized by appropriate termination of the polymerisation reaction. Factors determining the polymerisation rate and changes in conductivity and optical performance are discussed.     

Vacuum vapour phase polymerised poly(3,4-ethyelendioxythiophene) thin films for use in large-scale electrochromic devices

Large-scale electrochromic devices were manufactured using vacuum vapour phase polymerised (VPP) poly(3,4-ethylenedioxythiophene) (PEDOT). Homogeneous 3,4-ethylenedioxythiophene (EDOT) and water vapour distribution within the large 115 L VPP chamber is paramount for the reproducible synthesis of high conductivity PEDOT thin films. Obtaining these conditions, however, was not trivial. The issue was resolved by synthesising PEDOT under vacuum, however, this altered the dynamics of the polymerisation process. As a result, surfactant addition, monomer and water vapour distribution, monomer and chamber temperature, and polymerisation times were all systematically investigated. Controlling these parameters has resulted in PEDOT with conductivity exceeding 1100 S · cm⁻¹, with a best of 1485 S · cm⁻¹, and electrochromic devices with an optical switch of Δ%Tx ≥ 50%. The resulting high conductivity and optical range are due to long undisrupted PEDOT polymer chains coupled with low levels of oligomers within the matrix.     

WETTABILITY AND SURFACE ENERGETICS OF ROUGH FLUOROPOLYMER SURFACES

Hydrophobic solid surfaces with controlled roughness were prepared by coating glass slides with an amorphous fluoropolymer (Teflon® AF1600, DuPont) containing varying amounts of silica spheres (diameter 48?μm). Quasi-static advancing, θ_A, and receding, θ_R, contact angles were measured with the Wilhelmy technique. The contact angle hysteresis was significant but could be eliminated by subjecting the system to acoustic vibrations. Surface roughness affects all contact angles, but only the vibrated ones, θ_V, agree with the Wenzel equation. The contact angle obtained by averaging the cosines of θ_A and θ_R is a good approximation for θ_V, provided that roughness is not too large or the angles too small. Zisman's approach was employed to obtain the critical surface tension of wetting (CST) of the solid surfaces. The CST increases with roughness in accordance with Wenzel equation. Advancing, receding, and vibrated angles yield different results. The θ_A is known to be characteristic of the main hydrophobic component (the fluoropolymer). The θ_V is a better representation of the average wettability of the surface (including the presence of defects).     

Vacuum vapour phase polymerization of high conductivity PEDOT: Role of PEG-PPG-PEG,the origin of water,and choice of oxidant

Vacuum vapour phase polymerization (VVPP) is a facile means of producing flexible PEDOT thin films having conductivities in excess of 1500 S cm^?1. The process is understood to utilize water as the effective proton scavenger during synthesis. The originating source of water, under vacuum condition however, was unknown. The location of the water within the oxidant solution was examined, with individual components desiccated and thermo-gravametric analysis (TGA) performed to ascertain the root source. The co-polymer PEG-PPG-PEG provides some water, while the majority originates from coordinated water associated with the iron tosylate oxidant, and from free water residing within the solvent carrier. Importantly, with the incorporation of the co-polymer water remains locked within the oxidant layer under vacuum and this allows the VVPP reaction to proceed without the need for an external water supply. Furthermore PEG-PPG-PEG serves the multi-functional role of inhibiting crystal formation within the oxidant layer, and reducing the effective reactivity of the oxidant. Finally, an examination of literature suggests that the choice of oxidant may depend on the type of VPP process used.     

High conductivity PEDOT resulting from glycol/oxidant complex and glycol/polymer intercalation during vacuum vapour phase polymerisation

Vacuum vapour phase polymerisation (V-VPP) was used to synthesis high conductivity poly(3,4-ethylenedioxythiophene) (PEDOT) on glycol/oxidant coated substrates. Thermo gravimetric analysis (TGA) indicated that up to 15 wt.-% glycol was able to complex with the Fe(Tos)₃ oxidant solution and that this loading produced PEDOT with the highest conductivity, namely 1487 S cm⁻¹. Further addition beyond 15 wt.-% resulted in an unbounded excess of glycol which appeared to inhibit the polymerisation process, resulting in reduced doping levels and conductivity. XPS data showed that glycol was incorporated within the PEDOT matrix after polymer synthesis, and that this may contribute to the high conductivity achieved using the V-VPP technique. XPS data also confirmed that the highest conductivity coincided with the highest recorded doping level, d = 28.4%.