Quantum efficiencies remain a critical issue for general applications of semiconducting polymers in optoelectronics and others. In this work, we demonstrate that nearly 100% quantum efficiencies ...(η’s) in thin solid films can be reached when the polymer molecules are mechanically stretched into molecular confinement. We selected three conjugated polymers of varied backbone stiffness and interchain coupling, prepared in both diluted and pristine states. All of the polymers when highly diluted (c = 0.1 wt %) exhibited massive η increases after stretching to very large strains (∼300–500%) via micronecking, with the rigid polyfluorene (PFO) and semirigid MEH-PPV both manifesting η ≈ 90%, while the most flexible yet regioregular polythiophene (P3HT-rr) exhibited a 10-fold increase to ∼21%. In the pristine state, molecular aggregation and interchain coupling curtail development of the molecular confinement, but the large-strain deformation still enhances η’s significantly, to ∼90% (PFO) and ∼55% (MEH-PPV) despite no increases for the crystalline P3HT-rr. Moreover, upon substitution by a bulkier side-group to reduce interchain coupling, the pristine films of polythiophene (P3EHT) exhibited a ∼3-fold increase of η after the stretching. The nearly 100% of η’s in fully stretched molecules indicates that the in situ self-trapping occurring via sub-picosecond backbone interactions can be mostly responsible for energy dissipations and quite suppressible by segmental stress control. The mechanical confinement effects also indicate the fundamental role of molecular mechanics during stabilization and migration of photoexcited charges.
An efficient scheme for the synthesis of 1,1-cyclopentylenylbisphenol (bisphenol CP) has been developed starting from dicyclopentadiene, a C5 byproduct from the petroleum cracking process. The ...synthetic steps leading to bisphenol CP consist of mostly isomerization and addition reactions, which are higher in their atom-economy efficiencies than those based upon condensation reactions. In addition, alkoxylation by cyclic carbonates converted bisphenol CP into ethoxylated and propoxylated ether diols. The transformation of hydroxyl functional groups from bisphenols to alkoxylated alcohols increased the reactivity of their hydroxyl groups toward isocyanates, as evidenced by achieving >3 times higher molecular weights of the segmented polyurethanes (PUs) in GPC analysis using alkoxylated diols as chain extenders instead of bisphenols. In addition, the incorporation of five-membered cardo-type groups onto the PU side chains through alkoxyl diols of bisphenol CP also significantly enhances the phase mixing of the resulting hard and soft segments, leading to a series of robust PUs.
In this study, we developed a novel in situ hydrothermal method to fabricate self-assembled P3HT/TiO2 hybrid nanowires, wherein a facile one-step synthetic strategy was utilized to co-organize P3HT ...molecules and titanium precursors into highly elongated hybrid nanowires, followed by a hydrothermal process in an autoclave to in situ transform the titanium precursors into crystalline TiO2 nanoparticles on the P3HT nanofibrils. P3HT nanofibrils were utilized as a structure-directing motif to achieve a favorable dispersion of electron acceptor (A) TiO2 nanocrystals of 10-15 nm in diameter embossed along the nanofibrils, as well as an efficient electron donor (D) for the nanohybrid. In particular, the crystallization temperature of anatase-phase TiO2 nanoparticles with high crystallinity obtained via the hydrothermal method was significantly reduced to 130 degree C in an elevated pressure of similar to 7 bars as compared to the conventional calcination temperature of 450 degree C at ambient pressure for TiO2 nanocrystal synthesis, therefore, allowing the synergistic one-step fabrication of both highly crystalline TiO2 nanoparticles embossed on highly crystalline long-range ordered P3HT nanofibrils. As a consequence of the structural development, this P3HT/TiO2 embossed nanohybrid could afford significant improvements in its D/A interfacial contact area for effective charge separation without the need for capping ligands typically used in ex situ D/A blend systems, as well as an efficient pathway for charge transport, leading to enhanced optoelectronic properties and device performance. The highest conversion efficiency of 0.14% was presented by the P3HT/TiO2 embossed hybrid device, which was a remarkable improvement as compared to only 0.03% from an ex situ P3HT/TiO2 hybrid device. This novel in situ approach shows a feasible way to fabricate organic/inorganic nanohybrid materials of conjugated copolymers with different inorganic nanoparticles for the applications of future optoelectronic devices.
Zeolitic imidazolate framework-L (ZIF-L) is an emerging ZIF material possessing a unique two-dimensional layered crystal structure and a leaf-like crystal morphology. This paper reports a novel ...approach towards the incorporation of single-walled aluminosilicate nanotubes (AlSiNTs) into the interlayer of ZIF-L for the synthesis of AlSiNT@ZIF-L nanocomposites. The interlayer in ZIF-L is formed by hydrogen bonding between adjacent imidazoles. The resulting nanocomposites were subjected to a number of solid-state characterization techniques (SEM, TEM, powder XRD, EDS, TGA, nitrogen physisorption, and FT-IR) to elucidate the conformation of their microstructure. It was found that the AlSiNT@ZIF-L composite possesses an average crystal size considerably smaller than that of pure ZIF-L (1.1 μm for AlSiNT@ZIF-L and 7.8 μm for pure ZIF-L). Interestingly, ZIF-L and AlSiNTs are both microporous; however, the mesoporosity was achieved through the incorporation of AlSiNTs into ZIF-L crystals. A control experiment related to the synthesis of AlSiNT@ZIF-8 composites was performed to gain insight into the assembly pathway towards the formation of AlSiNT@ZIF-L crystals. Failure in the formation of AlSiNT@ZIF-8 supports the supposition that the assembly pathway involves the incorporation of AlSiNTs into the interlayer of ZIF-L, thereby facilitating the nucleation of ZIF-L crystals.
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•Highly porous hydrogels based on mixtures of PEG and poloxamer can be fabricated via solvent-induced phase separation.•The porosity from 20% to 75% and open/closed pore structure can ...be fine-tuned by varying composition and solvent type.•The subcutaneous implantation results suggest good cytocompatibility of the material implant.•Highly biocompatible and superporous hydrogel scaffolds show potential to be used as corneal periphery in the future.
Biocompatible and highly porous network hydrogel scaffolds were fabricated for the development of artificial cornea (AC) periphery/skirt that could be used to enhance the long-term retention of the implants. In this study, a series of hydrogel scaffolds for this application was fabricated from the photo-polymerization of a mixture of poly(ethylene glycol) (PEG)- and poloxamer (P407)-based macromer solutions in dichloromethane in which solvent-induced phase separation (SIPS) arose to form scaffolds with macroporous structure and high water content. The overall porosity ranging from 20% to 75% and open/closed pore structure of the hydrogel scaffolds could be finely tuned by varying the ratio of P407/PEG in the macromer solution and solvent type. The total porosity and open-cell structure of the macropores in the synthesized hydrogel scaffolds affected the swelling behavior, dynamic properties such as the storage moduli of the hydrogels as well as their degradation rates. Based on the subcutaneous implantation in rats, superporous hydrogel scaffolds induced the formation of thinner fibrous capsules around the implants and showed less inflammatory reaction, suggesting that the hydrogel scaffolds made from SIPS exhibited good cytocompatibility. The combined results of swelling ratio, porosity, physical strength and subcutaneous implant tests indicated that the superporous hydrogels with porosity >50% showed potentials to be used for cornea periphery application.
Solution processing of π-conjugated polymers constitutes a major low-cost manufacturing method for the fabrication of many new organic optoelectronic devices. The solution self-assembly kinetics of ...π-conjugated rod-coil block copolymers of symmetric poly(3-hexyl thiophene)-b-poly(2-vinyl pyridine) (P3HT-P2VP) during drying and the phase transformations of the subsequently dried samples were studied by using a combination of TEM, SAXS, WAXS and DSC measurements. During solution drying in chlorobenzene, a good solvent for the copolymer, P3HT-P2VP first formed nanoseed aggregates followed by the directional growth of nanofibrils driven by the formation of prevailing form II P3HT crystals within its nanofibril core confined by the surrounding domain of P2VP blocks. This result was in sharp contrast when a similar molecular weight P3HT homopolymer was solution self-assembled in chlorobenzene, nearly free from confinement, in which case the resulting nanofibrils consisted of a mixture of majority form I and form II crystals. Solvent-cast films of P3HT-P2VP nanofibrils with form II crystals were heat-/cold-treated and showed solid-state phase transformations from form II crystals to form I crystals, both within nanofibrils with annealing, indicating the metastability of the form II crystals with temperature. A disordered state followed with increasing temperatures which, when cooled, induced the formation of a thermodynamically stable lamellar phase with only form I P3HT crystals. Correspondingly, the study provides new strategies for controlling polymorphs and nanostructures of π-conjugated block copolymers for future applications using solution processing and subsequent heat treatment.
The radiation hardening of various UV curable resins provides a simple but powerful method to fabricate thin films or membranes with desirable physical and chemical properties. In this study, we ...proposed to use this method to fabricate a novel proton exchange membrane (PEM) for direct methanol fuel cells (DMFC) with good mechanical, transport and stability properties. The PEM was prepared by crosslinking a mixture of a photoinitiator, a bifunctional aliphatic urethane acrylate resin (UAR), a trifunctional triallyl isocyanate (TAIC) crosslinker and tertrabutylammonium styrenesulfonate (SSTBA) to form a uniform network structure for proton transport. Key PEM parameters such as ion exchange capacity (IEC), water uptake, proton conductivity, and methanol permeability were controlled by adjusting the chemical composition of the membranes. The IEC value of the membrane was found to be an important parameter in affecting water uptake, conductivity as well as the permeability of the resulting membrane. Plots of the water uptake, conductivity, and methanol permeability vs. IEC of the membranes show a distinct change in the slope of their curves at roughly the same IEC value which suggests a transition of structural changes in the network. It is demonstrated that below the critical IEC value, the membrane exhibits a closed structure where hydrophilic segments form isolated domains while above the critical IEC value, it shows an open structure where hydrophilic segments are interconnected and form channels in the membrane. The transition from a closed to an open proton conduction network was verified by the measurement of the activation energy of membrane conductivity. The activation energy in the closed structure regime was found to be around 16.5
kJ
mol
−1 which is higher than that of the open structure region of 9.6
kJ
mol
−1. The membranes also display an excellent oxidative stability, which suggests a good lifetime usage of the membranes. The proton conductivities and the methanol permeabilities of all membranes are in the range of 10
−4 to 10
−2
S
cm
−1 and 10
−8 to 10
−7
cm
2
s
−1, respectively, depending on their crosslinking density. The membranes show great selectivity compared with those of Nafion
®. The possibility of using this PEM for DMFC devices is suggested.
ICTACS 2006 Ho, Bao T; Dong, Thuy T. B; Duong, Due A ...
2007., 2006-12-29
eBook
This volume brings together many contributions from leading research scientists, engineers and practitioners in computer science. Selected by program committee members, the topics describe innovative ...research and new technologies in the following areas of interest: image processing, computer vision and pattern recognition; computational linguistics and natural language processing; artificial intelligence, machine learning and algorithms; software engineering; computer networks and security; and bioinformatics.
Current intraocular pressure (IOP) measurement using air puff could be erroneous without applying proper corrections. Although noncontact tonometry is not considered to be accurate, it is still ...popularly used by eye clinics. It is thus necessary to extract the correct information from their results. This study proposes a practical approach to correctly measure IOP in vivo. By embedding a new model-based correction to the Corvis® ST, we can extract the corneal Young’s modulus from the patient data. This Young’s modulus can be used to correct the IOP readings. The tests were applied to 536 right eyes of 536 healthy subjects (228 male and 308 female) between March of 2012 and April of 2016. The tests were applied to patients at the Department of Ophthalmology, National Taiwan University Hospital and the Hung-Chuo Eye Clinics. The statistical analysis showed that the value for the Young’s modulus was independent of all the other parameters collected from the Corvis ST, including the corneal thickness and the intraocular pressure. Therefore, it is important to independently measure the Young’s modulus instead of depending on the correlation with the other parameters. This study adds the methodology of measuring corneal stiffness in vivo for ophthalmologists’ reference in diagnosis.
An ordered nanostructure can be created from the hybrid materials of self-assembly poly(3-hexyl thiophene-b-2-vinyl pyridine) and nicotinic acid-modified titanium dioxide nanoparticles ...(P3HT-b-P2VP/TiO2). TEM and XRD analyses reveal that the TiO2 nanoparticles (NPs) are preferentially confined in the P2VP domain of P3HT-b-P2VP whereas TiO2 NPs interact with either pure P3HT or a blend of P3HT and P2VP to produce microsized phase segregation. The morphologies of lamellar and cylindrical structures are disturbed when the loading of TiO2 NPs is 40 wt % or higher. Cylindrical P3HT-b-P2VP/TiO2 exhibits a small blue shift in absorption and photoluminescence spectra with increasing TiO2 loading as compared to P3HT/TiO2. The NPs cause a slightly misaligned P3HT domain in the copolymer. Furthermore, the PL quenching of P3HT-b-P2VP/TiO2 becomes very large as a result of efficient charge separation in the ordered nanodomain at 16 nm. Solar cells fabricated from self-assembly P3HT-b-P2VP/TiO2 hybrid materials exhibit a >30 fold improvement in power conversion efficiency as compared to the corresponding 0.3P3HT-0.7P2VP/TiO2 polymer blend hybrid. This study paves the way for the further development of high-efficiency polymer−inorganic nanoparticle hybrid solar cells using a self-assembled block copolymer.
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