Polyether ether ketone (PEEK) is introduced as a material for the additive manufacturing process ... more Polyether ether ketone (PEEK) is introduced as a material for the additive manufacturing process called fused filament fabrication (FFF), as opposed to selective laser sintering (SLS) manufacturing. FFF manufacturing has several advantages over SLS manufacturing, including lower initial machine purchases costs, ease of use (spool of filament material vs powder material), reduced risk of material contamination and/or degradation, and safety for the users of the equipment. PEEK is an excellent candidate for FFF due to its low moisture absorption as opposed to other common FFF materials, such as Acrylonitrile Butadiene Styrene (ABS). PEEK has been processed into a filament and samples have been manufactured using several build orientations and extrusion paths. The samples were used to conduct tensile, compression, flexural, and impact testing to determine mechanical strength characteristics such as yield strength, modulus of elasticity, ultimate tensile strength and maximum elongation,...
The current time-resolved SANS study captures different stages of self-assembly process commencin... more The current time-resolved SANS study captures different stages of self-assembly process commencing from nucleation as a function of sonication.
Strategies enabling solution processing of covalent organic framework (COF) thin films will becom... more Strategies enabling solution processing of covalent organic framework (COF) thin films will become increasingly important as these versatile materials are integrated into a wide range of electronic and optical devices. This work highlights an approach to yield thin film synthesis of TAPA‐PDA (TAPA: tris(4‐aminophenyl)amine, PDA: terephthalaldehyde) and TAPB‐PDA (TAPB: 1,3,5‐tris(4‐aminophenyl)benzene) imine COFs using azomethine compounds which can be drop cast onto a variety of substrates. High crystalline COF films are shown to form on various electronically‐relevant substrates. Grazing incidence wide angle X‐ray scattering characterization reveals COF films with a preferred horizontal orientation in the case of TAPA‐PDA COF and a more mixed/vertical orientation in the TAPB‐PDA COF film regardless of the substrate. As this exciting class of crystalline organic materials becomes more relevant for various device applications, solution processing techniques will be vital to take advantage of the properties of thin film COFs.
Conference proceedings of the Society for Experimental Mechanics, Nov 5, 2016
In Fused Deposition Modeling (FDM), filaments of heated thermoplastic are extruded from a tip tha... more In Fused Deposition Modeling (FDM), filaments of heated thermoplastic are extruded from a tip that moves in a raster-like motion. Depending on filament material properties and the processing parameters, the extruded beads and the fusion-bond between them could result in anisotropic properties (particularly with regard to strength). In this work, the focus is on characterizing the interlaminar fracture toughness of coupons produced by FDM with varying road-to-road offsets producing positive, zero and negative air gaps between neighboring roads resulting in coupons of varying density (void content). The resulting bond line formation is assessed through measuring and analyzing changes in the mesostructure and the contact attained at the interfaces between the adjoining roads. The bond quality is assessed by evaluating plane-strain fracture toughness using compact tension specimens. Results demonstrate an approximate five-fold increase in fracture toughness with varying air gaps.
Controlled synthesis of single crystal gold nanorods (Au NRs) with desired dimensions, narrow pol... more Controlled synthesis of single crystal gold nanorods (Au NRs) with desired dimensions, narrow polydispersity, and minimal byproducts depends critically on the state of the seed solution. Herein, we clarify the growth of cetyltrimethylammonium bromide stabilized Au seeds and their impact on conventional seed-mediated growth of Au NRs. UV–vis spectroscopy, TEM microscopy, and small-angle X-ray scattering reveal that during aging of the seed solution, constituents evolve from solubilized Au-salt precursors (Au[III]) to Au nanoclusters (Aun) to multitwinned Au nanocrystals. The most consistent single crystal Au NR growth, with minimal byproducts, occurs when the seed solution contains the maximum concentration of small (<1 nm) nanoclusters (n < 55, 1 min < tage < 10 min at T = 25 °C). This point can be identified spectroscopically between 300 and 480 nm. Additionally, the optimal clusters coincide approximately with a relative shift in structural equilibrium of closed-shell Au nanoclusters from predominately ...
Polyether ether ketone (PEEK) is introduced as a material for the additive manufacturing process ... more Polyether ether ketone (PEEK) is introduced as a material for the additive manufacturing process called fused filament fabrication (FFF), as opposed to selective laser sintering (SLS) manufacturing. FFF manufacturing has several advantages over SLS manufacturing, including lower initial machine purchases costs, ease of use (spool of filament material vs powder material), reduced risk of material contamination and/or degradation, and safety for the users of the equipment. PEEK is an excellent candidate for FFF due to its low moisture absorption as opposed to other common FFF materials, such as Acrylonitrile Butadiene Styrene (ABS). PEEK has been processed into a filament and samples have been manufactured using several build orientations and extrusion paths. The samples were used to conduct tensile, compression, flexural, and impact testing to determine mechanical strength characteristics such as yield strength, modulus of elasticity, ultimate tensile strength and maximum elongation,...
The current time-resolved SANS study captures different stages of self-assembly process commencin... more The current time-resolved SANS study captures different stages of self-assembly process commencing from nucleation as a function of sonication.
Strategies enabling solution processing of covalent organic framework (COF) thin films will becom... more Strategies enabling solution processing of covalent organic framework (COF) thin films will become increasingly important as these versatile materials are integrated into a wide range of electronic and optical devices. This work highlights an approach to yield thin film synthesis of TAPA‐PDA (TAPA: tris(4‐aminophenyl)amine, PDA: terephthalaldehyde) and TAPB‐PDA (TAPB: 1,3,5‐tris(4‐aminophenyl)benzene) imine COFs using azomethine compounds which can be drop cast onto a variety of substrates. High crystalline COF films are shown to form on various electronically‐relevant substrates. Grazing incidence wide angle X‐ray scattering characterization reveals COF films with a preferred horizontal orientation in the case of TAPA‐PDA COF and a more mixed/vertical orientation in the TAPB‐PDA COF film regardless of the substrate. As this exciting class of crystalline organic materials becomes more relevant for various device applications, solution processing techniques will be vital to take advantage of the properties of thin film COFs.
Conference proceedings of the Society for Experimental Mechanics, Nov 5, 2016
In Fused Deposition Modeling (FDM), filaments of heated thermoplastic are extruded from a tip tha... more In Fused Deposition Modeling (FDM), filaments of heated thermoplastic are extruded from a tip that moves in a raster-like motion. Depending on filament material properties and the processing parameters, the extruded beads and the fusion-bond between them could result in anisotropic properties (particularly with regard to strength). In this work, the focus is on characterizing the interlaminar fracture toughness of coupons produced by FDM with varying road-to-road offsets producing positive, zero and negative air gaps between neighboring roads resulting in coupons of varying density (void content). The resulting bond line formation is assessed through measuring and analyzing changes in the mesostructure and the contact attained at the interfaces between the adjoining roads. The bond quality is assessed by evaluating plane-strain fracture toughness using compact tension specimens. Results demonstrate an approximate five-fold increase in fracture toughness with varying air gaps.
Controlled synthesis of single crystal gold nanorods (Au NRs) with desired dimensions, narrow pol... more Controlled synthesis of single crystal gold nanorods (Au NRs) with desired dimensions, narrow polydispersity, and minimal byproducts depends critically on the state of the seed solution. Herein, we clarify the growth of cetyltrimethylammonium bromide stabilized Au seeds and their impact on conventional seed-mediated growth of Au NRs. UV–vis spectroscopy, TEM microscopy, and small-angle X-ray scattering reveal that during aging of the seed solution, constituents evolve from solubilized Au-salt precursors (Au[III]) to Au nanoclusters (Aun) to multitwinned Au nanocrystals. The most consistent single crystal Au NR growth, with minimal byproducts, occurs when the seed solution contains the maximum concentration of small (<1 nm) nanoclusters (n < 55, 1 min < tage < 10 min at T = 25 °C). This point can be identified spectroscopically between 300 and 480 nm. Additionally, the optimal clusters coincide approximately with a relative shift in structural equilibrium of closed-shell Au nanoclusters from predominately ...
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Papers by Hilmar Koerner