Electrochromics for smart windows: Oxide-based thin films and devices

Hydrochromic materials have been actively investigated in the context of humidity sensing and measuring water contents in organic solvents. Here we report a sensor system that undergoes a brilliant blue-to-red colour transition as well as 'Turn-On' fluorescence upon exposure to water. Introduction of a hygroscopic element into a supramolecularly assembled polydiacetylene results in a hydrochromic conjugated polymer that is rapidly responsive (<20 μs), spin-coatable and inkjet-compatible. Importantly, the hydrochromic sensor is found to be suitable for mapping human sweat pores. The exceedingly small quantities (sub-nanolitre) of water secreted from sweat pores are sufficient to promote an instantaneous colorimetric transition of the polymer. As a result, the sensor can be used to construct a precise map of active sweat pores on fingertips. The sensor technology, developed in this study, has the potential of serving as new method for fingerprint analysis and for the clinical diagnosis of malfunctioning sweat pores.

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Hydrochromic conjugated polymers for human sweat pore mapping

Imaging Latent Fingerprints by Electrochemiluminescence

Hierarchical structure Ti-doped WO3 thin films are prepared by a template-free hydrothermal method. The influence of Ti doping on the electrochromic properties of WO3 thin films is investigated in the visible-infrared region. Ti doping can lead to significant surface morphology change and lower the crystallization, which plays an important role in the electrochromic properties of WO3 films. The large transmittance modulation (49.1% at 750 nm, 64.6% at 2000 nm and 59.3% at 10 μm), fast switching speed (1.7 s and 1.6 s) and high coloration efficiency (68 cm2 C−1 at 750 nm) are achieved for the low Ti-doped WO3 film. The enhancement in the electrochromic performance of the low Ti-doped WO3 films is attributed to their low crystallization, a star-like structure which has low charge transfer and ion diffusion resistance, leading to superior electrical conductivity and reaction kinetics.

Hierarchical structure Ti-doped WO3 film with improved electrochromism in visible-infrared region

Synthesis and electrochemical sensing application of poly(3,4-ethylenedioxythiophene)-based materials: A review.

Spatially selective electrodeposition of poly-3,4-ethylenedioxythiophene (PEDOT) thin films on metallic surfaces is shown to be an effective means of visualizing latent fingerprints. The technique exploits the fingerprint deposit as an insulating mask, such that electrochemical processes (here, polymer deposition) may only take place on deposit-free areas of the surface between the ridges of the fingerprint deposit; the end result is a negative image of the fingermark. Use of a surfactant (sodium dodecylsulphate, SDS) to solubilise the EDOT monomer allows the use of an aqueous electrolyte. Electrochemical (coulometric) data provide a total assay of deposited material, yielding spatially averaged film thicknesses, which are commensurate with substantive filling of the trenches between fingerprint deposit ridges, but not overfilling to the extent that the ridge detail is covered. This is confirmed by optical microscopy and AFM images, which show continuous polymer deposition within the trenches and good definition at the ridge edges. Stainless steel substrates treated in this manner and transferred to background electrolyte (aqueous sulphuric acid) showed enhanced fingerprints when the contrast between the polymer background and fingerprint deposit was optimised using the electrochromic properties of the PEDOT films. The facility of the method to reveal fingerprints of various ages and subjected to plausible environmental histories was demonstrated. Comparison of this enhancement methodology with commonly used fingerprint enhancement methods (dusting with powder, application of wet powder suspensions and cyanoacrylate fuming) showed promising performance in selected scenarios of practical interest.

/pdf/electrochromic-enhancement-of-latent-fingerprints-by-poly-3-1yppiakipo.pdf

Electrochromic enhancement of latent fingerprints by poly(3,4-ethylenedioxythiophene)

To address the challenge of capturing latent fingerprint evidence from metal surfaces, a new method of latent fingerprint enhancement based on electrochromic polymer films has recently been developed. Here, we present a study comparing the development and visualization of nonvisible fingerprints on stainless steel substrates using this electrochromic enhancement approach with three classical methods (dusting, wet powder, and cyanoacrylate fuming). Two variants of the electrochromic enhancement method were utilized with polyaniline and poly(3,4-ethylenedioxythiophene) as the electrochromic materials. Fingerprint samples were taken from different donors (varying in age and gender) and were exposed to different environments for systematically varied periods of time (up to 28 days). The environments represent plausible evidential scenarios: left under ambient conditions, washed with aqueous soap solution, washed with acetone, submerged in water, and maintained at elevated temperature. The electrochromic enhancement procedure frequently outperformed the traditional methods, particularly for samples exposed to more challenging histories.

Rachel M. Brown

Papers

Electrochromic enhancement of latent fingerprints by poly(3,4-ethylenedioxythiophene)

Comparative Study of Electrochromic Enhancement of Latent Fingerprints with Existing Development Techniques