3D Printing All‐Aromatic Polyimides using Mask‐Projection Stereolithography: Processing the Nonprocessable

High‐performance, all‐aromatic, insoluble, engineering thermoplastic polyimides, such as pyromellitic dianhydride and 4,4′‐oxydianiline (PMDA–ODA) (Kapton), exhibit exceptional thermal stability (up to ≈600 °C) and mechanical properties (Young's modulus exceeding 2 GPa). However, their thermal resistance, which is a consequence of the all‐aromatic molecular structure, prohibits processing using conventional techniques. Previous reports describe an energy‐intensive sintering technique as an alternative technique for processing polyimides with limited resolution and part fidelity. This study demonstrates the unprecedented 3D printing of PMDA–ODA using mask‐projection stereolithography, and the preparation of high‐resolution 3D structures without sacrificing bulk material properties. Synthesis of a soluble precursor polymer containing photo‐crosslinkable acrylate groups enables light‐induced, chemical crosslinking for spatial control in the gel state. Postprinting thermal treatment transforms the crosslinked precursor polymer to PMDA–ODA. The dimensional shrinkage is isotropic, and postprocessing preserves geometric integrity. Furthermore, large‐area mask‐projection scanning stereolithography demonstrates the scalability of 3D structures. These unique high‐performance 3D structures offer potential in fields ranging from water filtration and gas separation to automotive and aerospace technologies.     

In situ nanomechanical behaviour of coexisting insulating and metallic domains in VO<Subscript>2</Subscript> microbeams

Measuring the electrical and mechanical responses of coexisting phases at nanoscale provides a platform to engineer micro-/nanoscale pattern of metallic and insulating domains with control over properties to make novel devices. Here, we employ several in situ characterization techniques, namely Raman, optical imaging and electrical measurements, to identify the phase coexistence of metallic and insulating domains. Further, we performed site-specific in situ nanoindentation to address the spatial variation in nanomechanical properties in vanadium dioxide (VO₂) single-crystal microbeams in proximity to metal–insulator transition temperature. We also investigated load or contact depth dependence on elastic modulus at various temperatures to avoid the interference of indentation size effect on nanomechanical properties across the phase transition. The obtained results confirm the abrupt increase in elastic modulus (~17 GPa) and nanohardness (1 GPa) across the transition from monoclinic (insulator) to rutile (metal) phase.     

Thermodynamic properties of the system toluene — 1, 1, 1-trichloroethane

Data on molar excess enthalpy on mixing at 298.15 K and 308.15 K, vapor-liquid equilibrium, latent heats of vaporization at 91.444 kPa and vapor pressures for the system toluene – 1, 1, 1-trichloroethane are presented. A simple adiabatic calorimeter designed for molar excess enthalpy measurements is described, tested and used.     

On a generalized Watson's Relation for latent heat of vaporisation

The 0.38 latent heat law due to Watson is examined and it is found that the exponent (0.38) in Watson's relation is characteristic of the substance. A method of evaluating the exponent is outlined.     

Knowledge-based system for the computer aided design of ingot casting processes

The complexity of the design in thermal manufacturing processes stems from the need to simulate complicated heat transfer, fluid flow and phase change phenomena and couple the results with the design rules and knowledge available of these processes to obtain satisfactory designs. In this regard, the ability of expert systems to use heuristic reasoning has proved to be a powerful tool in the computer-aided-design of thermal manufacturing systems.In this paper, the salient features of a knowledge-based system developed for the design of the ingot casting process has been outlined. A Prolog-based decision-making front-end is interfaced with a Fortran-based computational engine for rapid design. The results from the heat transfer analysis, obtained from the computational module, are coupled to the evaluation module, which checks for satisfaction of the design critera and violation of the design constraints. The decision-making module uses a set of design rules to manipulate the variables until the design specifications are satisfied. Modularity and flexibility are maintained using an object-oriented format. Several interesting design acceleration features like design inheritance from simpler models and design extraction from previous designs are illustrated. The main features of this knowledge-based tool and the savings in time resulting from using these special features are discussed in detail.