71 research outputs found
Label-free vapor selectivity by polymer-inorganic composite photonic crystals sensors
The lack of sensors for continuous and extensive detection of vapor pollutants is a concern for health and safety. Colorimetric sensors, such as polymer distributed Bragg reflectors, could achieve this task thanks to their low cost and easy signal transduction, but are affected by low vapor permeability and lack of selectivity without chemical labels. We demonstrate label-free selective sensing of organic volatile compounds by all-polymer Bragg reflectors relying on a high free volume hybrid inorganic-polymer nanocomposite to achieve vapor permeability, and on different intercalation kinetic of organic analytes to achieve selectivity
Thin Polymer Films: Simple Optical Determination of Molecular Diffusion Coefficients
The possibility to assess diffusion coefficients of small molecules in packaging polymer films directly on the shelf, or even along the fabrication line, without the use laboratory equipment commonly employed for gravimetric methods would represent a paradigm changer in the evaluation of barrier properties and byproduct formation in goods packaging and device encapsulation. In this work, we demonstrate a simple, effective and versatile method for the determination of the molecular diffusion coefficients that exploits simple UV-Vis spectroscopy and is suitable for any polymer film. This simple method also allows the direct identification of the intercalating molecule without the need for chemical targeting or of complex laboratory equipment. For this purpose, we report on the assessment of diffusion coefficients of both polar and non-polar molecules including water, ammonia, methanol, ethanol, toluene, and even hexafluorobenzene into polyvinyl chloride wrap commercialized for food packagin
Planar microcavities: Materials and processing for light control
Microcavities are a class of optical structures providing a versatile approach to engineering light matter interactions. In light of recent developments in materials processing technologies, in particular for organic and hybrid ones, and of the need for high efficiency optical systems, there has been extensive innovation and improvement in their design and realization leading to a multitude of structures and materials. Among these, closed multi-material microcavities or microresonators based on the effect of dielectric contrast have been attractive for their low losses, applicability in a wide spectral range, and customizability. High-dielectric contrast microcavities based on distributed Bragg reflectors have been adapted early on for their highly controlled fabrication and strong light confinement and proved to be essential in current technologies including lasers and light emitting diodes. In this review, we map their evolution from planar one-dimensional inorganic structures to more sophisticated designs incorporating various categories of organic and hybrid materials. Additionally, we provide an overview of state-of-the-art developments and limitations of this class of structures
Solution Processed Polymer-ABX4 Perovskite-Like Microcavities
Thanks to solution processability and broad emission in the visible spectral range, 2D hybrid perovskite-like materials are interesting for the realization of large area and flexible lighting devices. However, the deposition of these materials requires broad-spectrum solvents that can easily dissolve most of the commercial polymers and make perovskites incompatible with flexible photonics. Here, we demonstrated the integration of broadband-emitting (EDBE)PbCl4 (where EDBE = 2,2-(ethylenedioxy)bis(ethylammonium)) thin films with a solution-processed polymer planar microcavities, employing a sacrificial polymer multilayer. This approach allowed for spectral and angular redistribution of the perovskite-like material, photoluminescence, that can pave the way to all-solution-processed and flexible lightning devices that do not require complex and costly fabrication techniques
2,5-Diisopropenylthiophene by Suzuki\u2013Miyaura cross-coupling reaction and its exploitation in inverse vulcanization: a case study
A novel thiophene derivative, namely 2,5-diisopropenylthiophene (DIT) was synthetized by Suzuki\u2013Miyaura
cross-coupling reaction (SMCCR). The influence of reaction parameters, such as temperature, solvent,
stoichiometry of reagents, role of the base and reaction medium were thoroughly discussed in view of
yield optimization and environmental impact minimization. Basic design of experiment (DoE) and
multiple linear regression (MLR) modeling methods were used to interpret the obtained results. DIT was
then employed as a comonomer in the copolymerization with waste elemental sulfur through a green
process, inverse vulcanization (IV), to obtain sulfur-rich polymers named inverse vulcanized polymers
(IVPs) possessing high refractive index (n z 1.8). The DIT comonomer was purposely designed to (i) favor
the IV process owing to the high reactivity of the isopropenyl functionalities and (ii) enhance the
refractive index of the ensuing IVPs owing to the presence of the sulfur atom itself and to the high
electronic polarizability of the p-conjugated thiophene ring. A series of random sulfur-rdiisopropenylthiophene (S-r-DIT) copolymers with sulfur content from 50 up to 90 wt% were
synthesized by varying the S/DIT feed ratio. Spectroscopic, thermal and optical characterizations of the
new IVPs were carried out to assess their main chemical\u2013physical feature
Directional Fluorescence Spectral Narrowing in All-Polymer Microcavities Doped with CdSe/CdS Dot-in-Rod Nanocrystals
We report on the fluorescence properties of high optical quality all-polymer planar microcavities embedding core 12shell dot-in-rod CdSe/CdS nanocrystals. Properly tuned microcavities allow a 10-fold sharpening of the nanocrystals fluorescence spectrum, resulting in a reduction of the bandwidth from 24 to 2.4 nm, which corresponds to a quality factor larger than 250. A 5-fold peak photoluminescence intensity enhancement is measured, while the overall number of emitted photons is reduced. Time-resolved photoluminescence and quantum yield for microcavities and suitable references show the presence of two decays related to differences in nanocrystal size distribution. The slower decay rate, which becomes faster when the nanocrystals are embedded into the microcavity, is assigned to longer nanorods with emission spectrally overlapped to the cavity mode. Conversely, the short-living component, which is assigned to an impurity of shorter nanorods, remains unaffected by the microcavity
On the development of electrochemical sensors coated with polycaprolactone
The main aim of this study was to test the biopolymer polycaprolactone (PCL) as an electrode modifier for the electrochemical detection of dopamine (DA). PCL was chosen following a search for polymers with the appropriate geometry and functional groups for dopamine detection. The chemical structure and the average molecular weight of the synthesized PCL were determined by 1H-NMR, while DSC measurements showed a decrease in the crystallinity of a star-shaped polymer compared to a linear polymer. Atomic force microscopy and wettability tests performed on PCL-coated ITO electrodes demonstrated the influence of polymer architecture and functional groups on hydrophilicity and film morphology. Electrochemical studies revealed that electrodes coated with star polymers ending with carboxyl groups show good activity and selectivity, thus demonstrating the effectiveness and applicability of the developed sensors for the electrochemical detection of DA
Colorimetric Detection of Perfluorinated Compounds by All-Polymer Photonic Transducers
We report on the highly sensitive optical and
colorimetric detection of perfluorinated compounds in the
vapor phase achieved by all-polymer dielectric mirrors. High
optical quality and uniformly distributed Bragg reflectors were
fabricated by alternating thin films of poly(N-vinylcarbazole)
and Hyflon AD polymers as high and low refractive index
medium, respectively. A new processing procedure has been
developed to compatibilize the deposition of poly(N-vinylcarbazole)
with the highly solvophobic Hyflon AD polymer
layers to achieve mutual processability between the two
polymers and fabricate the devices. As a proof of principle,
sensing measurements were performed using the Galden
HT55 polymer as a prototype of the perfluorinated
compound. The Bragg stacks show a strong chromatic response upon exposure to this compound, clearly detectable as both
spectral and intensity variations. Conversely, Bragg mirrors fabricated without fluorinated polymers do not show any detectable
response, demonstrating that the Hyflon AD polymer acts as the active and selective medium for sensing perfluorinated species.
These results demonstrate that organic dielectric mirrors containing perfluorinated polymers can represent an innovative
colorimetric monitoring system for fluorinated compounds, suitable to improve both environmental safety and quality of life
All-Polymer Photonic Microcavities Doped with Perylene Bisimide J-Aggregates
Thanks to exciting chemical and optical features, perylene bisimide (PBI) J-aggregates
are ideal candidates to be employed for high-performance plastic photonic devices.
However, they generally tend to form - stacked H-aggregates that are unsuitable for
implementation in polymer resonant cavities. In this work, we demonstrate the efficient
compatibilization of a tailored perylene bisimide forming robust J-aggregated
supramolecular polymers into amorphous polypropylene. The new nanocomposite was
then implemented into an all-polymer planar microcavity which provides strong and
directional spectral redistribution of the J-aggregate photoluminescence, owing to a
strong modification of the photonic states. A systematic analysis of the photoemitting
processes, including photoluminescence decay and quantum yields, shows that the
optical confinement in the polymeric microcavity does not introduce any additional nonradiative
de-excitation pathways to those already found in the J-aggregate
nanocomposite film and pave the way to PBI-based high-performance plastic photonic
devices
All-Polymer Microcavities for the Fluorescence Radiative Rate 2 Modification of a Diketopyrrolopyrrole Derivative
Controlling the radiative rate of emitters with 6 macromolecular photonic structures promises flexible devices with 7 enhanced performances that are easy to scale up. For instance, radiative rate enhancement empowers low-threshold lasers, while rate suppression affects recombination in photovoltaic and photochemical processes. However, claims of the Purcell effect with polymer structures are controversial, as the low dielectric contrast typical of suitable polymers is commonly not enough to provide the necessary confinement. Here we show all-polymer planar microcavities with photonic band gaps tuned to the photoluminescence of a diketopyrrolopyrrole derivative, which allows a change in the fluorescence lifetime. Radiative and nonradiative rates were disentangled systematically by measuring the external quantum efficiencies and comparing the planar microcavities with a series of references designed to exclude any extrinsic effects. For the first time, this analysis shows unambiguously the dye radiative emission rate variations obtained with macromolecular dielectric mirrors. When different0 waveguides, chemical environments, and effective refractive index effects in the structure were accounted for, the change in the radiative lifetime was assigned to the Purcell effect. This was possible through the exploitation of photonic structures made of polyvinylcarbazole as a high-index material and the perfluorinated Aquivion as a low-index one, which produced the largest dielectric contrast ever obtained in planar polymer cavities. This characteristic induces the high confinement of the radiation electric field within the cavity layer, causing a record intensity enhancement and the steering the radiative rate. Current limits and requirements to achieve the full control of radiative rates with polymer planar microcavities are also addressed
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