Property Performance Relationships Research Articles

Bipolar Host Materials: A Chemical Approach for Highly Efficient Electrophosphorescent Devices

The future of organic light-emitting devices (OLEDs) is drifting from electrofluorescence toward electrophosphorescence due to the feasibility of realizing 100% internal quantum efficiency. There is limited availability of transition metals (TMs) such as Ir, Os, and Pt, which are used for color-tunable phosphorescent emitters, and the use of the host-guest strategy is necessary for suppressing the detrimental triplet-triplet annihilation inherently imparted by the TM-centered emitters. The inevitable demands of organic host materials provide organic chemists with tremendous opportunities to contribute their expertise to this technology. With suitable molecular design and judicious selection of chemical structures featured with different electronic nature, the incorporation of hole-transporting (HT) and electron-transporting (ET) moieties combines the advantages of both functional units into bipolar host materials, which perform balanced injection/transportation/recombination of charge carriers and consequentially lead the OLEDs to have higher performances and low roll-off efficiencies. This review highlights recently developed bipolar host materials with the focus on molecular design strategies and the structure-property-performance relationships of various classes of bipolar host materials, which are classified into several categories according to the structural features of their constituents (HT/ET blocks and spacers).

Crystal chemistry and properties of mixed ionic-electronic conductors

Oxides exhibiting mixed oxide-ion and electronic conducting (MIEC) properties have been attracting great interest in recent years due to their technological applications in solid-state electrochemical devices such as solid oxide fuel cells (SOFC), oxygen separation membranes, and electrochemical sensors. This article provides an overview of the composition-structure–property-performance relationships of several mixed conducting oxides: disordered ABO3 perovskite oxides, A-site ordered layered LnBaCo2O5+δ (Ln = lanthanide) perovskite oxides, Ruddlesden-Popper series of perovskite-based (La,Sr)n+1MnO3n+1 (n = 1–3 and M = Fe, Co, and Ni) intergrowth oxides, and hexagonal RBa(Co1-yMy)4O7 (R = rare earth or alkaline earth and M = Zn) oxides. Based on the available data, the role of chemical composition, crystal chemistry, and chemical bonding on the electrical and ionic transport, thermal, and electrochemical properties is discussed.

Poly[octanediol‐co‐(citric acid)‐co‐(sebacic acid)] elastomers: novel bio‐elastomers for tissue engineering

AbstractThis review focuses on a new class of elastomers, namely poly[octanediol‐co‐(citric acid)‐co‐(sebacic acid)] (p(OCS)), synthesised from 1,8‐octanediol, citric acid and sebacic acid in a catalyst‐free polyesterification reaction. The review begins with a detailed description of the synthesis, characterisation and structure–property–performance relationship of some reported elastomers suitable for tissue engineering. The control of the physicochemical properties of the new p(OCS) by simple variation of initial monomer concentrations in polyesterification forms the pivotal part of the synthesis. As tissue engineering requires complex designs, thin films and porous three‐dimensional structures of p(OCS) were fabricated to demonstrate their ease of processing. The fundamental material properties of p(OCS) are discussed for p(OCS) pre‐polymers and final polymers. The elastomers exhibit versatility in mechanical properties, hydration and hydrolytic degradation, as determined by their chemical structure. Surface analysis of spin‐coated p(OCS) suggests that the surface morphology, chemistry and concentration of the surface functional groups can be controlled simply by varying the initial citric acid/sebacic acid concentration in polyesterification. These tunable molecular architectures and material properties are crucial in biological interactions. Thein vitrobiocompatibility testing of p(OCS) with MG63 osteoblast‐like cells suggests that p(OCS) is an excellent candidate for potential elastic biomaterials for tissue engineering applications without the need for any post‐synthesis modification. Copyright © 2011 Society of Chemical Industry

Preparation and property–performance relationships in samarium-doped ceria nanopowders for solid oxide fuel cell electrolytes

In a systematic study, Samarium doped ceria (SDC) nanopowders, SmxCe1−xO2−x/2 (x=0.1, 0.2 or 0.3), were prepared by a low temperature citrate complexation route. The synthesis and crystallisation of the SDC powders were followed by thermochemical techniques (TGA/DTA), X-ray diffraction, elemental analysis, specific surface area determination (BET) and electron microscopy (SEM and TEM). Mean crystallite sizes were found to be around 10nm for all compositions calcined at 500°C. Dense electrolyte bodies were prepared at 1300°C, 1400°C and 1450°C using two sintering times, 4h or 6h. Densities of 91–97% of theoretical were obtained, with a marked improvement in density on going from 1300°C to higher sintering temperatures. Grain size analysis was conducted using SEM. Grain size distributions were related to %Sm and sintering conditions. Impedance spectroscopy was used to determine the total, bulk and grain boundary conductivities, the related activation energies and enthalpies of defect association and ion migration. Sintering at 1400°C/6h or 1450°C/4h gave superior grain structure and conductivity, with oversintering occurring after more severe treatments. At 600°C the highest total ionic conductivity was 1.81×10−2Scm−1 for Sm0.2Ce0.8O1.9. The relationships between chemical composition, sintering parameters, grain structure and electrochemical performance are discussed.

Design of a Semisolid Vaginal Microbicide Gel by Relating Composition to Properties and Performance

Develop a preclinical in vitro algorithm enabling de novo design of semisolid vaginal drug delivery gels, by using biomechanical modeling of gel spreading in the vaginal canal and empirically relating gel composition to mechanical properties and predicted performance. Gel performance was defined through a multivariate objective function constructed from gels' mechanical properties and selected performance criteria for gel spreading within the vaginal canal. Mixture design of experiment was used to establish a semi-empirical relationship linking composition-property and property-performance relationships for gels with varying concentrations of hydroxyethylcellulose and Carbopol 974P. This permits definition of a local optimum for gel composition and volume of administration, within a defined gel composition space. Rheological behavior and, consequently, the value of the objective function varied broadly with composition. The algorithm indicated a 3.0 wt% HEC gel as the near optimal composition for a 3.5 mL applied volume for gels designed to spread throughout the vagina. The algorithm introduced herein is a novel tool that facilitates an understanding of the composition-property-performance relationship for vaginal semisolid drug delivery gels. This approach has promise as a scientific methodology for evaluation and optimization of vaginal gels prior to in vivo investigations.

Residual strain and hardness as predictors of the fatigue ranking of steel welds

This work has investigated the potential of information contained in the microhardness and residual transverse strain profiles just below the weld toe and at mid-depth in the plate, to predict the fatigue performance ranking for a series of 12 MIG welds made in RQT701 steel under different conditions. The experimental matrix included two plate thicknesses, two heat inputs and three types of filler metal. Results have demonstrated that there is significant potential to predict the fatigue performance of welds using parameters that characterise the residual strain/stress and hardness/mechanical property profiles across the weld zone. This type of information would allow a more analytical interpretation to be developed of process–property–performance relationships than has been possible in the past and would assist in process optimisation for service performance under dynamic loading.

Process–property–performance relationships for titanium dioxide coatings engineered from nanostructured and conventional powders

Nanostructured (Nano), fused and crushed (F&C) and plasma-fused (PF) titania (TiO 2) powder particles were thermally sprayed via flame spray (FS), air plasma spray (APS) and high velocity oxy-fuel (HVOF) on low carbon steel substrates. Flame spray processing, although widely employed industrially, generally has received very limited attention in academic papers. However, the results of this research have demonstrated that a FS Nano titania coating was the best performing among all coatings tested, exhibiting no measurable signs of mass/volume loss after dry-sliding wear testing (ball-on-disk) and the highest deposition efficiency (DE) level. This is regarded as an important result, considering the fact that among these three processing techniques FS is the least expensive, the most portable and exhibits the lowest energy consumption levels. In addition, scanning electron microscopy (SEM) analysis demonstrated that the sliding wear scars of the FS and HVOF-sprayed Nano coatings were smooth, without significant irreversible deformation or formation of ridges. These characteristics are not typical of ceramic materials. It is hypothesized that this plastic-like behaviour and resilience exhibited by FS and HVOF-sprayed Nano coatings explain their improved performance under dry-sliding wear.

Engineering nanostructured thermal spray coatings: process–property–performance relationships of ceramic based materials

Nanostructured powders were deposited using thermal spraying to produce coatings having internal features of nanosized dimensions. Several ceramic based materials were studied, including WC–12 wt-%Co, TiO2, hydroxyapatite, Al2O3–13 wt-%TiO2 and yttria stabilised zirconia. The effect of the thermal spray conditions on the microstructure, phase composition, properties and performance was investigated. Key nanostructural features of the coatings were identified and their potential benefit in contributing to enhanced behaviour explored. Issues relating to design strategies and process control for engineering these types of coatings with performance characteristics tailored for targeted applications are discussed.

Investigation of processing parameters for pulsed closed-field unbalanced magnetron co-sputtered TiC–C thin films

Titanium carbide is a well-established wear resistant coating due to its excellent tribological properties including high hardness and elastic modulus, good wear resistance, low coefficient of friction against steel, and high temperature stability. Recent advances in sputtering technology have resulted in improvements in the properties and performance of wear resistant coatings. Closed-field unbalanced magnetron sputtering and pulsed magnetron sputtering have greatly improved the structure and properties of titanium carbide films by increasing ion bombardment at the substrate. The goal of this research was to investigate how processing ties into the structure–property–performance relationship for these types of films. An electrostatic quadrupole plasma analyzer was used to measure the energy of ions at the substrate position. Energy ranges from 0.5 to 280 eV were observed under different pulsing conditions. Excessively high ion energy during deposition was found to erode the tribological performance of films.

Formulation of Drugs in Block Copolymer Micelles: Drug Loading and Release

Block copolymer micelles have become accepted as a viable strategy for drug formulation and delivery. Block copolymer micelles may serve as solubilizers and/or true drug carriers depending on their drug retention properties in vivo. Indeed the formulation of hydrophobic drugs in these micelle systems has been shown to provide up to a 30,000 fold increase in the water solubility of some compounds. In addition, the administration of drugs in copolymer micelles has been shown to reduce their toxicity and improve their therapeutic efficacy. The present review is focused on the drug loading and release properties of block copolymer micelles. Specifically, the properties of the drug, properties of the micelle core and the presence of interactions between the drug and the core-forming block are discussed in terms of their influence on the drug loading and release properties of the micelles. The various methods employed to prepare drug-loaded micelles are reviewed and the in vitro release assays used to predict the in vivo release characteristics of the formulations are discussed. The balance between drug loading and micelle stability is highlighted as a critical factor in the optimization of micelle-based formulations. The in vivo performance of micelles as delivery systems is evaluated by comparing the pharmacokinetics of free drug and drug administered in micelle-based formulations. Overall, the composition-property and property-performance relationships outlined in this review may aid in guiding the rational design of block copolymer micelles for drug delivery. In addition, suggestions for future research in this area are provided as a means to assist in furthering block copolymer micelles as one of the leading advanced drug delivery technologies for the systemic administration of drugs.

Structure–property–performance relationships of sulfonated poly(arylene ether sulfone)s as a polymer electrolyte for fuel cell applications

This article focuses on structure–property–performance relationships of directly copolymerized sulfonated polysulfone polymer electrolyte membranes. The chemical structure of the bisphenol-based disulfonated polysulfones was systematically alternated by introducing fluorine moieties or other polar functional groups such as benzonitrile or phenyl phosphine oxide in the copolymer backbone. Ac impedance measurements of the polymer electrolyte membranes indicated that fluorine incorporation increased proton conductivity, while polar functional group incorporation decreased conductivity. Likewise, other properties such as water uptake and ion exchange capacity are impacted by the incorporation of fluorine moiety or polar groups. These properties are critically tied with H 2/air and direct methanol fuel cell performance. We have rationalized fuel cell performance of these selected copolymers in light of structure–property relationships, which gives useful insight for the development and application of next generation polymer electrolytes.

Effects of mechanical and chemical properties on transport in fluoropolymers. II. Permeation

This is the second part of a study of chemical structure-physical property-performance relationships among several fluoropolymers and liquid penetrants, focusing on their permeation behavior. That behavior was consistent with the chemical and physical characteristics of the polymers, in that it depended on thermodynamic properties of the various penetrants (e.g., molecular volume, solubility parameters, and polarity). Relatively inert PFA showed effects only of molecular size. Similarly inert, but structurally modified ETFE showed nearly random dependence on all the properties. In contrast, ECTFE exhibited dipole-dipole bonds and PVDF embodied H-bonds; and both types of bonding affected permeability systematically. For example, ECTFE was most susceptible to polar compounds (dichloromethane and chlorobenzene), and PVDF was most susceptible to H-bonded liquids (phenol and methyl ethyl ketone). The permeation behaviors of several combinations showed unusual dependence on time, thickness, and other factors such as temperature, processing conditions, chemical structure, and swelling due to relaxation. The Cattaneo-Maxwell model was used to fit transient permeation-rate data of relatively well-behaved ETFE. In contrast, a new kinetic model was devised to interpret more complex transient permeation behavior, particularly the observed acceleration in ECTFE. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 477–492, 1997

Effects of mechanical and chemical properties on transport in fluoropolymers. I. Transient sorption

This is the first part of a study of chemical structure-physical property-performance relationships among several fluoropolymers and liquid penetrants, focusing on their diffusivities and solubilities. Transient sorption experiments conducted with perfluoroalkoxy, fluorinated ethylene propylene, and ethylene tetrafluoroethylene exhibited Fickian diffusion. The first two exhibited concentration-independent diffusivity, while the last displayed concentration-dependent diffusivity. Conversely, polyvinylidene fluoride (PVDF) and ethylene chlorotrifluoroethylene (ECTFE) exhibited non-Fickian behavior, including acceleration as saturation approached. Suspected causes for the unusual sorption behavior were structural characteristics due to processing (e.g., skin or orientation with respect to processing direction), intrinsic chemical structure, and morphological deformation induced by swelling. Stress-strain tests indicated that mechanical properties depend similarly on the presence of penetrants to transport properties. Weak swelling agents exhibited Fickian transport and a negligible change of mechanical properties. In contrast, strong swelling agents induced non-Fickian diffusion and caused significant changes of mechanical properties. A new kinetic model fit the transient sorption results, particularly the observed acceleration in PVDF and ECTFE. The model accounts for structural changes due to swelling and relaxation resulting from free-volume creation, which is assumed to be proportional to the amount of liquid sorbed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 455–476, 1997