Ultra-low-density digitally architected carbon with a strutted tube-in-tube structure

Porous materials with engineered stretching-dominated lattice designs, which offer attractive mechanical properties with ultra-light weight and large surface area for wide-ranging applications, have recently achieved near-ideal linear scaling between stiffness and density. Here, rather than optimizing the microlattice topology, we explore a different approach to strengthen low-density structural materials by designing tube-in-tube beam structures. We develop a process to transform fully dense, three-dimensional printed polymeric beams into graphitic carbon hollow tube-in-tube sandwich morphologies, where, similar to grass stems, the inner and outer tubes are connected through a network of struts. Compression tests and computational modelling show that this change in beam morphology dramatically slows down the decrease in stiffness with decreasing density. In situ pillar compression experiments further demonstrate large deformation recovery after 30-50% compression and high specific damping merit index. Our strutted tube-in-tube design opens up the space and realizes highly desirable high modulus-low density and high modulus-high damping material structures

Ruthenium(II)-Catalyzed Intermolecular Cyclo(co)trimerization of 3-Halopropiolamides with Internal Alkynes

A highly chemo- and regioselective cyclo(co)trimerization between 3-halopropiolamides and symmetrical internal alkynes is reported. The reaction is catalyzed by Ru(II)-complexes and proceeds at ambient temperature in ethanol to deliver fully substituted dihalogenated isophthalamides. 1,4-Butynediol was found to undergo spontaneous lactonization with halopropiolamides after trimerization to provide 5,7-dihalo-phthalide products.</div

Ruthenium(II)-Catalyzed Intermolecular Cyclo(co)trimerization of 3-Halopropiolamides with Internal Alkynes

<div>A highly chemo- and regioselective cyclo(co)trimerization between 3-halopropiolamides and symmetrical internal alkynes is reported. The reaction is catalyzed by Ru(II)-complexes and proceeds at ambient temperature in ethanol to deliver fully substituted dihalogenated isophthalamides. 1,4-Butynediol was found to undergo spontaneous lactonization with halopropiolamides after trimerization to provide 5,7-dihalo-phthalide products.</div

Post-Hydration Crosslinking of Ion Exchange Membranes to Control Water Content

Crosslinking is a common approach toward mitigating excess water uptake by ion exchange membranes. Most crosslinking reactions are performed when the ionomer is in anhydrous form, before the membrane self-segregates into hydrophilic and hydrophobic domains upon exposure to water. Here we use numerical and molecular simulations to investigate the prospect of crosslinking the polymer after casting and partial hydration of the membrane at subsaturated conditions. Such a process would allow the membranes to develop their nanosegregated morphology and establish well-connected but narrow water channels, while limiting further sorption of water. We find that post-hydration crosslinking of membranes has the ability to dramatically reduce membrane swelling. These results show that crosslinking after membrane casting and hydration may be a viable option for controlling water uptake. Further, we suggest chemical crosslinking strategies that may yield sufficiently high membrane gel fractions based on our analyses

Selective and Orthogonal Post-Polymerization Modification using Sulfur(VI) Fluoride Exchange (SuFEx) and Copper-Catalyzed Azide–Alkyne Cycloaddition (CuAAC) Reactions

Functional polystyrenes and polyacrylamides, containing combinations of fluorosulfate, aromatic silyl ether, and azide side chains, were used as scaffolds to demonstrate the postpolymerization modification capabilities of sulfur­(VI) fluoride exchange (SuFEx) and CuAAC chemistries. Fluorescent dyes bearing appropriate functional groups were sequentially attached to the backbone of the copolymers, quantitatively and selectively addressing their reactive partners. This combined SuFEx and CuAAC approach proved to be robust and versatile, allowing for a rare accomplishment: triple orthogonal functionalization of a copolymer under essentially ambient conditions without protecting groups

Exponential Water Uptake in Ionomer Membranes Results from Polymer Plasticization

Water content is the most influential factor in the performance of ion exchange membranes (IEM), controlling their mechanical rigidity, ionic conductivity, and degradation rates. Membranes absorb water exponentially at high water activity (aw), making that region of the sorption isotherm the most influential on membrane properties. Plasticization of the polymer by water has been proposed to cause this exponential uptake at high aw. However, an integrated microscopic picture of the structure, thermodynamic, and mechanical properties of IEM as a function of aw has remained elusive. Here we use large-scale molecular simulations validated with experimental measurements to compute the sorption isotherms, Young’s modulus, polymer dynamics and structure of IEM. The simulations unveil that the exponential increase in water uptake coincides in all cases with the glass to rubber transition of the membrane, as measured through its Young’s modulus and segmental polymer dynamics. Functionalization of the polymer with alkyl groups further contributes to the plasticization of the polymer, increasing the water uptake at a given ion exchange capacity (IEC) and aw. We conclude that the alkyl chains act synergistically with water to plasti-cize the polymer matrix and allow water penetration in the membrane. The simulations reveal that the width of the water chan-nels depends on the ratio λ of water to ions in the membrane but is independent of its IEC. We conclude that differences in the polymer matrix –not the water channels- are responsible for the distinct uptake response of ion exchange membranes to the thermodynamic driving force of water activity

3D Printing of High Viscosity Reinforced Silicone Elastomers

Recent advances in additive manufacturing, specifically direct ink writing (DIW) and ink-jetting, have enabled the production of elastomeric silicone parts with deterministic control over the structure, shape, and mechanical properties. These new technologies offer rapid prototyping advantages and find applications in various fields, including biomedical devices, prosthetics, metamaterials, and soft robotics. Stereolithography (SLA) is a complementary approach with the ability to print with finer features and potentially higher throughput. However, all high-performance silicone elastomers are composites of polysiloxane networks reinforced with particulate filler, and consequently, silicone resins tend to have high viscosities (gel- or paste-like), which complicates or completely inhibits the layer-by-layer recoating process central to most SLA technologies. Herein, the design and build of a digital light projection SLA printer suitable for handling high-viscosity resins is demonstrated. Further, a series of UV-curable silicone resins with thiol-ene crosslinking and reinforced by a combination of fumed silica and MQ resins are also described. The resulting silicone elastomers are shown to have tunable mechanical properties, with 100–350% elongation and ultimate tensile strength from 1 to 2.5 MPa. Three-dimensional printed features of 0.4 mm were achieved, and complexity is demonstrated by octet-truss lattices that display negative stiffness

Tuning Material Properties of Alkaline Anion Exchange Membranes Through Crosslinking: A Review of Synthetic Strategies and Property Relationships

Alkaline anion exchange membranes (AAEMs) are an enabling component for next generation electrochemical applications, including alkaline fuel cells, alkaline water electrolyzers, CO2 electrochemical reduction, and flow batteries. While commercial systems, notably fuel cells, have traditionally relied on proton-exchange membranes (PEMs), hydroxide-ion conducting AAEMs hold promise as a way to reduce cost-per-device by enabling the use of less expensive non-platinum group electrodes and cheaper cell components. AAEMs have undergone significant material development over the past two decades resulting in substantial improvements in hydroxide conductivity, alkaline stability, and dimensional stability. Despite these advances, challenges still remain in the areas of durability, water management, high temperature performance, and selectivity. In this review we discuss crosslinking as a synthesis tool for tuning various AAEM material properties, such as water uptake, conductivity, alkaline stability, and selectivity, and we describe synthetic strategies for incorporating crosslinks during membrane fabrication

Isolating Chemical Reaction Mechanism as a Variable with Reactive Coarse-Grained Molecular Dynamics: Step-Growth versus Chain-Growth Polymerization

We present a general approach to isolate chemical reaction mechanism as an independently controllable variable across chemically distinct systems. Modern approaches to reduce the computational expense of molecular dynamics simulations often group multiple atoms into a single “coarse-grained” interaction site, which leads to a loss of chemical resolution. In this work we convert this shortcoming into a feature and use identical coarse-grained models to represent molecules that share nonreactive characteristics but react by different mechanisms. As a proof of concept, we use this approach to simulate and investigate distinct, yet similar, trifunctional isocyanurate resin formulations that polymerize by either chain- or step-growth. Because the underlying molecular mechanics of these models are identical, all emergent differences are a function of the reaction mechanism only. We find that the microscopic morphologies resemble related all-atom simulations and that simulated mechanical testing reasonably agrees with experiment