1043wileyonlinelibrary.com and autonomous materials. [22][23][24] Porous materials not only mediate transport of fl uids in fi ltration, [ 25 ] but also regulate ion exchange in battery electrodes [ 26 ] and separator fi lms, [ 27 ] facilitate new tissue growth in bioscaffolds, [28][29][30][31] and increase strength-to-weight ratio in structural solids. [ 32 ] No fabrication technique has emerged with the fl exibility to control size and dimensionality across all of these applications.Esser-Kahn et al. [ 23 ] recently introduced the vaporization of sacrifi cial components (VaSC) technique. In their work, 1D poly(lactic acid) (PLA) fi bers are treated with tin(II) oxalate (SnOx) catalyst to undergo thermal depolymerization and vaporization at ≈200 °C. After embedding "sacrifi cial" PLA in a thermoset composite and subsequent thermal treatment, the fi bers vaporized, forming vasculature that is their inverse replica. By introducing various functional fl uids into the microvasculature, desirable properties were imparted on the composite, such as thermal regulation, magnetic or electrical modulation, and in situ reaction of chemical species. [ 23 ] In this work, we extend the application of VaSC by introducing sacrifi cial templates across all levels of spatial dimensionality and spanning several orders of magnitude in size, enabling a wide range of vascular and porous architectures.Complex multidimensional vascular polymers are created, enabled by sacrificial template materials of 0D to 3D. Sacrifi cial material consisting of the commodity biopolymer poly(lactic acid) is treated with a tin catalyst to accelerate thermal depolymerization, and formed into sacrifi cial templates across multiple dimensions and spanning several orders of magnitude in scale: spheres (0D), fi bers (1D), sheets (2D), and 3D printed. Templates are embedded in a thermosetting polymer and removed using a thermal treatment process, vaporization of sacrifi cial components (VaSC), leaving behind an inverse replica. The effectiveness of VaSC is verifi ed both ex situ and in situ, and the resulting structures are validated via fl ow rate testing. The VaSC platform is expanded to create vascular and porous architectures across a wide range of size and geometry, allowing engineering applications to take advantage of vascular designs optimized by biology.
Electrospun fibers are a promising method for encapsulation of reactive agents in selfhealing coatings. Healing is initiated by mechanical damage to the coating causing the fibers to rupture and release their core materials into the damage region. Prior work has demonstrated autonomous healing in coatings containing electrospun fibers, but full characterization of the electrospun fiber microstructure and healing performance of the coating is lacking. In this study, we utilize electrospun fibers containing liquid healing agents to achieve a crosslinking reaction of poly(dimethylsiloxane) (PDMS) to a crosslinking agent poly(diethoxysiloxane) (PDES), initiated by the catalyst dibutyltindilaurate (DBTL), to fill a damaged region and reseal the metal substrate. Fiber morphology is characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and confocal fluorescence microscopy (CFM). Successful delivery of healing agents to the damage region and subsequent crosslinking reaction is observed using SEM and chemically using infrared spectroscopy. The performance of the healed coating is evaluated electrochemically using linear polarization, where the coatings were subjected to a corrosive environment. The self-healing electrospun coating exhibits lower corrosion current than in control cases, resulting in an 88% corrosion inhibition efficiency.
A series of tin(II) amide alkoxides ([(OR)Sn(NMe(2))](n)) and tin(II) alkoxides ([Sn(OR)(2)](n)) were investigated as precursors for the production of tin oxide (SnO(x)) nanowires. The precursors were synthesized from the metathesis of tin dimethylamide ([Sn(NMe(2))(2)](2)) and a series of aryl alcohols {H-OAr = H-OC(6)H(4)(R)-2: R = CH(3) (H-oMP), CH(CH(3))(2) (H-oPP), C(CH(3))(3) (H-oBP)] or [H-OC(6)H(3)(R)(2)-2,6: R = CH(3) (H-DMP), CH(CH(3))(2) (H-DIP), C(CH(3))(3) (H-DBP)]}. The 1:1 products were all identified as the dinuclear species [(OAr)Sn(μ-NMe(2))](2) where OAr = oMP (1), oPP (2), oBP (3), DMP (4), DIP (5), DBP (6). The 1:2 products were identified as either a polymer ([Sn(μ-OAr)(2)](∞) (where OAr = oMP (7), oPP (8)), dinuclear [(OAr)Sn(μ-OAr)](2) (where OAr = oBP (9), DMP (10) or DIP/HNMe(2) (11)), or mononuclear [Sn(DBP)(2)] (12) complexes. These novel families of compounds (heteroleptic 1-6, and homoleptic 7-12) were evaluated for the production of SnO(x) nanowires using solution precipitation (SPPT; oleylamine/octadecene solvent system) or electrospinning (ES; THF solvent) processing conditions. The SPPT route that employed the heteroleptic precursors yielded mixed phases of Sn(o):romarchite [1 (100:0); 2 (80:20); 3 (68:32); 4 (86:14); 5 (66:35); 6 (88:12)], with a variety of spherical sized particles [1 (350-900 nm); 2 (150-1200 nm); 3 (250-950 nm); 4 (20-180 nm); 5 (80-400 nm); 6 (40-200 nm)]. For the homoleptic precursors, similar phased [7 (80:20); 8 (23:77); 9 (15:85); 10 (34:66); 11 (77:23); 12 (77:23)] spherical nanodots were isolated [7 (50-300 nm); 8: (irregular); 10 (200-800 nm); 11 (50-150 nm); 12 (50-450 nm)], except for 9 which formed polycrystalline rods [Sn(o):romarchite (15:85)] with aspect ratios >100. From ES routes, the heteroleptic species were found to form 'tadpole-shaped' materials whereas the homoleptic species formed electrosprayed nanodots. The one exception noted was for 7, where, without use of a polymer matrix, nanowires of Sn(o), decorated with micron sized 'balls' were observed. Due to the small amount of material generated, PXRD patterns were inconclusive to the identity of the generated material; however, cyclic voltammetry on select samples was used to tentatively identify the final Sn(o) (from 7) with the other sample identified as SnO(x) (from 1).
The synthesis and characterization of a series of group 4 carboxylate derivatives ([M(ORc)4] where M = Ti, Zr, Hf) was undertaken for potential utility as precursors to ceramic nanowires. The attempted syntheses of the [M(ORc)4] precursors were undertaken from the reaction of [M(OBu(t))4] with a select set of carboxylic acids (H-ORc where ORc = OPc (O2CCH(CH3)2), OBc (O2CC(CH3)3), ONc (O2CCH2C(CH3)3)). The products were identified by single-crystal X-ray diffraction studies as [Ti(η(2)-OBc)3(OBu(t))] (1), [Zr2(μ3-O)(μ-OPc)4(μ,η(2)-OPc)(η(2)-OPc)]2 (2), [H]2[Zr(η(2)-OBc)2(OBc)2(OBc)2] (3), [Zr(μ-ONc)2(η(2)-ONc)2]2 (4), or [Hf(μ-ORc)2(η(2)-ORc)2]2 [ORc = OPc (5), OBc (6, shown), ONc (7)]. The majority of compounds (4-7) were isolated as dinuclear species with a dodecahedral-like (CN-8) bonding mode around the metals due to chelation and bridging of the ORc ligand. The two monomers (1 and 3) were found to adopt a capped trigonal prismatic and CN-8 geometry, respectively, due to chelating ORc and terminal ORc or OBu(t) ligands. The metals of the oxo-species 2 were isolated in octahedral and CN-8 arrangements. These compounds were then processed by electrospinning methods (applied voltage 10 kV, flow rate 30-60 μL/min, electric field 0.5 kV/cm), and wire-like morphologies were isolated using compounds 4, 6 (shown), and 7.
BIOPOLYMERSS. R. White and co-workers develop sacrificial templates of 0D to 3D used to create vascular and porous architectures in polymers on page 1043. Embedded sacrificial templates are removed using a thermal treatment process, VaSC, leaving behind an inverse replica. This reconstruction of microCT imaging shows 3D channel architecture created using a 3D printed sacrificial template and the pressure distribution of fluid flow.
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