The working curve informs resin properties and print parameters for stereolithography, digital light processing, and other photopolymer additive manufacturing (PAM) technologies. First demonstrated ...in 1992, the working curve measurement of cure depth vs radiant exposure of light is now a foundational measurement in the field of PAM. Despite its widespread use in industry and academia, there is no formal method or procedure for performing the working curve measurement, raising questions about the utility of reported working curve parameters. Here, an interlaboratory study (ILS) is described in which 24 individual laboratories performed a working curve measurement on an aliquot from a single batch of PAM resin. The ILS reveals that there is enormous scatter in the working curve data and the key fit parameters derived from it. The measured depth of light penetration Dp varied by as much as 7x between participants, while the critical radiant exposure for gelation Ec varied by as much as 70x. This significant scatter is attributed to a lack of common procedure, variation in light engines, epistemic uncertainties from the Jacobs equation, and the use of measurement tools with insufficient precision. The ILS findings highlight an urgent need for procedural standardization and better hardware characterization in this rapidly growing field.
•The working curve is a fundamental measurement to characterize vat photopolymerization resins.•Despite 30 years of history, there is no documentary standard method for measuring a working curve.•An interlaboratory study distributed identical resin aliquots to 24 participants.•The reported fit parameters to vary by as much as 70x from one lab to another.•A documentary standard is required for working curves to have translational value in academic or industrial environments.
Photopolymerizable materials are the focus of extensive research across a variety of fields ranging from additive manufacturing to regenerative medicine. However, poorly understood material ...mechanical and rheological properties during polymerization at the relevant exposure powers and single‐voxel length‐scales limit advancements in part performance and throughput. Here, a novel atomic force microscopy (AFM) technique, sample‐coupled‐resonance photorheology (SCRPR), to locally characterize the mechano‐rheological properties of photopolymerized materials on the relevant reaction kinetic timescales, is demonstrated. By coupling an AFM tip to a photopolymer and exposing the coupled region to a laser, two fundamental photopolymerization phenomena: (1) timescales of photopolymerization at high laser power and (2) reciprocity between photodose and material properties are studied. The ability to capture rapid kinetic changes occurring during polymerization with SCRPR is demonstrated. It is found that reciprocity is only valid for a finite range of exposure powers in the verification material and polymerization is highly localized in a low‐diffusion system. After polymerization, in situ imaging of a single polymerized voxel is performed using material‐appropriate topographic and nanomechanical modalities of the AFM while still in the as‐printed environment.
Sample‐coupled‐resonance photorheology detects the fast, local photopolymerization of a microscale voxel by analyzing the resonant properties of a coupled atomic force microscope cantilever. The method achieves millisecond scale temporal resolution and sub‐micrometer scale spatial resolution, enabling characterization of spatial variations in cure and testing of light‐dosage reciprocity.
Interrupted tensile tests were performed on an AISI 4130 pressure vessel steel and investigated by neutron diffraction and scanning microscopy techniques. Analysis of the neutron diffraction patterns ...reveal a partitioning of ferrite and martensite phases resulting from deformation. A modified Williamson-Hall approach was used to model the broadening of Bragg peaks associated with the two phases as a function of applied strain, revealing an order of magnitude increase in their dislocation densities when the material was strained beyond the ultimate tensile strength (UTS). Lattice strains measured in the ferrite phase were consistently larger than those measured in the martensite phase for all the applied strain levels investigated. Moreover, a strain-induced phase transformation from a predominately martensitic steel to a ferritic steel was observed, with the average martensite phase fraction of an as-received specimen going from 78% to 22% when pulled to failure. Electron Backscatter Diffraction (EBSD) and Scanning Kelvin Probe Force Microscopy (SKPFM) were used to characterize the microstructure and phase fractions of ferrite and martensite associated with the various strain levels. These results agree well with those obtained from neutron diffraction and demonstrate the utility of SKPFM to distinguish between metallic phases with similar crystal structures that may be difficult to detect using conventional methods such as EBSD.
Morphological changes resulting from the oxidation of zero valent iron (ZVI) nanoparticles were measured as an assessment of their mechanical robustness in mixed matrix membranes for water treatment ...applications. Upon oxidation from metallic iron to iron oxide hydroxide, FeO(OH), particles underwent a significant transformation in size and morphology from 100 nm diameter spherical particles to plate-like crystalline particles with a hydrodynamic diameter greater than 450 nm. Atomic force microscopy (AFM) was used to mechanically degrade the FeO(OH) crystallites during repeated imaging. To determine whether similar degradation would occur during water filtration in a mixed matrix membrane, force under standard membrane operating conditions was calculated. Such force calculations were used to compare the shear forces exerted during water flux in a mixed matrix membrane to the normal forces imparted by AFM. Analysis suggested that the oxidized ZVI nanoparticles will experience a 10
−19
N maximum shear force in pore channels, much lower than the imaging forces in AFM, suggesting the mechanical stability of the particles during water remediation. Additional quartz crystal microbalance experiments were performed to confirm the mechanical stability of the oxidized iron nanoparticles in the flow environments of ultrafiltration. Taken together, the results of this study demonstrate that the mechanical properties of the nanoparticle composite membranes are such that minimal mechanical degradation of the nanoparticles will occur during water filtration.
AFM measurements show mechanical decay of ZVI nanoparticles, but the force is much higher than that found in membranes.
The mechanocatalytic formation of carbonaceous films at the interface between sliding metallic contacts is simultaneously advantageous for reducing friction and adhesion in several tribological ...applications and detrimental for electrical contacts as they can induce device failure by increasing the contact resistance. Yet, remarkably little is still known about the chemistry, structural and mechanical properties, and tunability of these interfacial layers. In this study, we performed contact pressure-dependent tribological experiments in dry nitrogen containing trace organics on four, nanocrystalline Pt–Au alloys (Au from 0 at.% to 10 at.%) – a promising class of alloys for ultralow wear and electrical contact applications. The ex-situ, multi-technique characterization results did not only provide insights into the chemical nature and mechanical behavior of the mechanocatalytic, carbon-rich films formed on Pt–Au surfaces, but also revealed the interplay between catalytic and mechanochemical tribofilm formation controlled by the composition-dependent electronic structure of the Pt–Au substrate and the applied contact pressure. The results of this work provide guidelines for tailoring nanocrystalline alloys to control their mechanocatalytic activity on the basis of variations of the alloy mechanical properties and element's electronic structure with the alloy stoichiometry.
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Reliable bonding of high-performance membranes onto polymeric supporting structures is critical for capitalizing their potentials within practical filtration applications. The successful bonding ...typically requires infiltration of the membrane pores by a thermoplastic polymer, driven by capillary pressure and/or external pressure. In this work, we systematically examine the capillary infiltration of a polypropylene (PP) within polyethersulfone (PES) membranes with a highly asymmetric pore structure, a nominal pore size of 20 nm, and varying degrees of hydrophilicity. Most significantly, the infiltration kinetics was strongly influenced by the asymmetric pore structure in two aspects: (1) the time to achieve full infiltration from the large-pore side was approximately 4 times shorter than that from the tight-pore side; (2) When bonding from the tight-pore side, the infiltration depth, L(t) showed L (t) ∼ t1.6, instead of characteristic L (t) ∼ t0.5. The accelerated infiltration rate over time was successfully modelled with the Cai model using depth-dependent pore size that captures the asymmetric pore structure. Furthermore, chemical modification reduced initial infiltration rate only, which is attributed to the reduction in surface porosity. No significant difference in infiltration kinetics at the later stage was observed. Mechanical integrity tests of the bonded samples display complex debonding behaviors including complete peeling, incomplete peeling, and complete membrane failure. The peel force corresponding to membrane failure appeared larger than the other two debonding modes, all of which showed insignificant dependence on the membrane chemistry or infiltration depth. Post-mortem analysis of the completely peeled sample showed PP nanofibers were pulled out of the PES membranes during debonding, emphasizing relatively weak mechanical interlocking due to the low surface porosity.
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•Capillary infiltration kinetics of PP within highly asymmetric PES membranes were determined.•The infiltration kinetics shows strong dependency on the asymmetric pore structure.•The infiltration kinetics is modelled by the Cai model with pore-size gradient.•The bonded PP/PES membrane display complete peeling, incomplete peeling and membrane fracture behaviors.
Capillary infiltration of porous medium impacts applications across oil recovery, soil science, and hydrology. The infiltration kinetics is typically captured by a range of models that differ in the ...approximation of pore structures, fluid properties, and filling ratio. Capillary bonding of a porous membrane by a polymer melt is important for membrane device manufacturing. However, both the capillary infiltration kinetics and the resulting bonding strength or mechanical integrity have not been reported. In this work, we measure the kinetics of capillary infiltration of a viscous polypropylene (PP) in polyethersulfone (PES) membranes with a normal pore size of 200 nm and varying degrees of hydrophilicity. The time-dependent infiltration depth was quantified ex situ by imaging the cross-sections of the bonded PP film/PES membranes. The microscopic details of the bonded interface were characterized by high-resolution nanomechanical imaging, while the contact angles of PP on the PES surfaces were measured by the sessile droplet method. The results show that the infiltration kinetics at 180 °C is better described by the Cai model that incorporates membrane pore structures (porosity, tortuosity, pore size), compared with the basic Lucas Washburn model intended for isolated cylindrical pores. The infiltration kinetics at 200 °C appears significantly slower than the predictions of both models, which is hypothesized to be a result of pore deformation/collapse due to the capillary pressure when the PES approaches the rubbery state. Regardless of bonding temperature, the resulting mechanical integrity of the bonded PP film/PES membrane, as quantified by a modified T-peel test, is dictated by the fracture strength of the membranes and weakly decreases with the increase of infiltration depth.
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•Capillary infiltration kinetics of PP within PES membranes were determined•The relevant thermodynamic and thermo-mechanical properties of the PP and PES membranes were determined•The infiltration kinetics data is better described by Cai model than Lucas Washburn model•Membrane failure is the dominant failure mode for the bonded PP/PES membrane•The peak load of the bonded PP/PES appear to decrease with increase of infiltration depth
Polyelectrolyte complexes (PECs), assemblies of oppositely charged polymers with powerful properties and wide‐ranging applications, are currently not melt‐processable via any conventional means and ...have been limited commercially to applications only as coatings. Herein, a unique strategy of pairing a polycation with an oppositely charged photopolymerizable monomer is employed. Vat photopolymerization of this mixture yields 3D spatial control over PECs for the first time. The properties of these 3D‐printed PECs are evaluated and are found to be similar to conventionally studied PEC materials. The water sensitivity of the PEC parts is adjustable through the incorporation of a small amount of a hydrophilic covalent crosslinker, highlighting potential future applications of these materials in 4D printing. Finally, the upcyclability of the additively manufactured PECs is demonstrated through the dissolution of a printed part and its incorporation into virgin resin to yield a part composed of partially recycled material. This chemistry has the potential to dramatically expand the application space of PEC materials and is a step towards a more circular economy for the field of additive manufacturing.
A polyelectrolyte complex is additively manufactured for the first time through vat photopolymerization. The mechanical properties of parts can be tuned through thermal treatment and by altering the resin chemistry. The ionic bonds that form these parts can be reversed through exposure to base and the part can be reprinted, showing promise for a circular 3D printing economy.
Using simple and inexpensive processing methodologies afforded by two‐stage reactive polymer networks (TSRPs) tunable mechanical anisotropy is displayed, defect‐independent guiding of cohesive ...fracture paths through soft material is demonstrated for the first time, and bio‐inspired microstructures are shown to enable performance enhancement beyond what is anticipated by the rule‐of‐mixtures in composites. The ability to pattern rubbery (stage I) and glassy (stage II) domains within a TSRP using photomasks and UV light is investigated through atomic force microscope (AFM) nanomechanical mapping techniques. AFM modulus mapping shows that the resulting stiffness anisotropy between stage I and stage II regions is length scale dependent. A gradient interface in elastic modulus between stage I and stage II materials is observed and, when patterned with an angled stage I pathway, the gradient interface exhibits remarkable resilience during failure, repeatedly deflecting cracks away from stage II regions, even while turning cracks at angles up to 135° When stage I and stage II domains are patterned in a nacre‐inspired microstructure, toughening beyond rule‐of‐mixtures’ prediction is observed.
Simple and inexpensive processing methodologies provide spatial control over mechanical heterogeneities in two‐stage reactive polymer networks. Photopatterning of heterogeneities enables programming of mechanical anisotropy, guiding of cohesive crack paths along high turn angles, and performance enhancement beyond what is anticipated by the rule‐of‐mixtures in composites through implementation of a nacre‐inspired microstructure.
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