Publications

2021
Fernandes M, Aizenberg J, Weaver J, Bertoldi K. Mechanically robust lattices inspired by deep-sea glass sponges. Nature Materials. 2021;20 (2) :237-241. Publisher's VersionAbstract

The predominantly deep-sea hexactinellid sponges are known for their ability to construct remarkably complex skeletons from amorphous hydrated silica. The skeletal system of one such species of sponge, Euplectella aspergillum, consists of a square-grid-like architecture overlaid with a double set of diagonal bracings, creating a chequerboard-like pattern of open and closed cells. Here, using a combination of finite element simulations and mechanical tests on 3D-printed specimens of different lattice geometries, we show that the sponge’s diagonal reinforcement strategy achieves the highest buckling resistance for a given amount of material. Furthermore, using an evolutionary optimization algorithm, we show that our sponge-inspired lattice geometry approaches the optimum material distribution for the design space considered. Our results demonstrate that lessons learned from the study of sponge skeletal systems can be exploited for the realization of square lattice geometries that are geometrically optimized to avoid global structural buckling, with implications for improved material use in modern infrastructural applications.

Hwang V, Stephenson A, Barkley S, Brandt S, Xiao M, Aizenberg J, Manoharan VN. Designing angle-independent structural colors using Monte Carlo simulations of multiple scattering. Proceedings of the National Academy of Sciences. 2021;118 (4) :e2015551118. Publisher's VersionAbstract

Disordered nanostructures with correlations on the scale of visible wavelengths can show angle-independent structural colors. These materials could replace dyes in some applications because the color is tunable and resists photobleaching. However, designing nanostructures with a prescribed color is difficult, especially when the application—cosmetics or displays, for example—requires specific component materials. A general approach to solving this constrained design problem is modeling and optimization: Using a model that predicts the color of a given system, one optimizes the model parameters under constraints to achieve a target color. For this approach to work, the model must make accurate predictions, which is challenging because disordered nanostructures have multiple scattering. To address this challenge, we develop a Monte Carlo model that simulates multiple scattering of light in disordered arrangements of spherical particles or voids. The model produces quantitative agreement with measurements when we account for roughness on the surface of the film, particle polydispersity, and wavelength-dependent absorption in the components. Unlike discrete numerical simulations, our model is parameterized in terms of experimental variables, simplifying the connection between simulation and fabrication. To demonstrate this approach, we reproduce the color of the male mountain bluebird (Sialia currucoides) in an experimental system, using prescribed components and a microstructure that is easy to fabricate. Finally, we use the model to find the limits of angle-independent structural colors for a given system. These results enable an engineering design approach to structural color for many different applications.

Shirman T, Toops TJ, Shirman E, Shneidman AV, Liu S, Gurkin K, Alvarenga J, Lewandowski M, Aizenberg M, Aizenberg J. Raspberry colloid-templated approach for the synthesis of palladium-based oxidation catalysts with enhanced hydrothermal stability and low-temperature activity. Catalysis Today. 2021;360 :241-251. Publisher's VersionAbstract

It is becoming increasingly urgent to develop and utilize novel, more efficient and stable materials for mobile and stationary emission control applications as the deleterious consequences of anthropogenic air pollution are becoming more evident and pressing. Tightening regulations, particularly related to automotive exhaust treatment, together with continued improvements in engine design, that result in lowering the engine operating temperatures and inadvertently lead to the release of an overwhelming proportion of pollutants during the cold start, present new challenges for materials design, specifically for oxidation catalysts. In particular, improvements in the low-temperature activity while maintaining catalyst stability at high temperatures are required from the next-generation catalyst. Typical catalysts for removal of pollutants from automotive exhaust streams incorporate platinum group metals (PGMs). They tend to be inefficient at low temperatures (below 250 °C), thus accounting for the cold start problem, yet sinter and lose their activity at high temperatures that are frequently encountered during catalyst operation. High PGM loadings are often employed to compensate for catalyst inefficiencies and fast degradation, ultimately resulting in high-cost catalytic converters. We have developed a new approach for the design and formation of catalytic materials that allows for both significantly more efficient PGM incorporation and improved overall catalyst performance at reduced PGM loadings. The method provides control over the composition and geometry of the support through self-assembly of sacrificial composite template — “raspberry” polymeric colloids decorated with catalytic particles — accompanied by infiltration with metal-oxide precursor and subsequent removal of the colloids. This method simultaneously structures the porous network and organizes the catalytic particles within it. Uniquely, the resulting catalytic particles are partially embedded in the support matrix and partially exposed to the pore interior, producing catalytic sites that are both stable and accessible. Herein, the feasibility of this novel and versatile approach for automotive catalytic conversion is demonstrated: the studies include testing alumina-based raspberry-colloid-templated (RCT) catalysts containing Pd nanoparticles (RCT Pd/Al2O3) for oxidation of propane and carbon monoxide under simulated diesel exhaust conditions and hydrothermal aging at 800 °C for 50 h in the simulated stream. The RCT Pd/Al2O3 catalysts exhibit exceptional activity toward CO oxidation, reduced reaction onset temperature, and high stability to elevated temperatures (demonstrated through prolonged exposure to temperatures up to 950 °C) and reactive gas streams, without migration, sintering or loss of the precious metal NPs. Notably, the novel catalyst shows the same or slightly better performance than the commercial catalysts even when the PGM load is reduced by ∼80 % compared to the commercial counterparts. These results provide confidence for the utilization of the RCT approach for the fabrication of robust nanostructured catalysts for next-generation, energy-efficient catalytic converters with improved performance at low and high temperatures and reduced costs. The RCT methodology is, in addition, highly generalizable, and can thus be applied for the design of a wide range of catalytic systems in the automotive sector and beyond.

Chatterjee R, Biswas S, Yashin VV, Aizenberg M, Aizenberg J, Balazs AC. Controllable growth of interpenetrating or random copolymer networks . Soft Matter. 2021;17 (30) :7177-7187. Publisher's VersionAbstract

Interpenetrating and random copolymer networks are vital in a number of industrial applications, including the fabrication of automotive parts, damping materials, and tissue engineering scaffolds. We develop a theoretical model for a process that enables the controlled growth of interpenetrating network (IPNs), or a random copolymer network (RCN) of specified size and mechanical properties. In this process, a primary gel “seed” is immersed into a solution containing the secondary monomer and crosslinkers. After the latter species are absorbed into the primary network, the absorbed monomers are polymerized to form the secondary polymer chains, which then can undergo further crosslinking to form an IPN, or undergo inter-chain exchange with the existing network to form a RCN. The swelling and elastic properties of the IPN and RCN networks can be tailored by modifying the monomer and crosslinker concentrations in the surrounding solution, or by tuning the enthalpic interactions between the primary polymer, secondary monomer and solvent through a proper choice of chemistry. This process can be used repeatedly to fabricate gels with a range of mechanical properties from stiff, rigid materials to soft, flexible networks, allowing the method to meet the materials requirements of a variety of applications.

Filie A, Shirman T, Aizenberg M, Aizenberg J, Friend CM, Madix RJ. The dynamic behavior of dilute metallic alloy Pd x Au 1− x/SiO 2 raspberry colloid templated catalysts under CO oxidation. Catalysis Science & Technology. 2021;(11) :4072-4082. Publisher's VersionAbstract

Dilute palladium-in-gold alloys have potential as efficient oxidation catalysts; controlling the Pd surface distribution is critical. Here, the activity for CO oxidation catalyzed by robust dilute Pd-in-Au nanoparticles supported on raspberry-colloid-templated (RCT) silica depends on the pretreatment and gas environment. The activities of oxygen-pretreated catalysts are different in light-off studies versus after long-term use. Transient increases in activity are also induced by flowing CO/He at 553 K. Altogether, these results indicate changes in Pd distribution at the surface induced by reactive gases and that light-off studies alone are not adequate for evaluation of alloy catalyst performance. Kinetic studies show evidence of both isolated and multiple Pd atoms. A dual-site mechanism is operative over Pd0.02Au0.98 RCT-SiO2, whereas a single-site mechanism governs reaction over Pd0.10Au0.90 RCT-SiO2. The distinct mechanisms suggest that tuning the ratio of isolated to clustered Pd sites is possible, underscoring the importance of characterization under reaction conditions.

Vena A, Kolle S, Stafslien S, Aizenberg J, Kim P. Self‐Stratifying Porous Silicones with Enhanced Liquid Infusion and Protective Skin Layer for Biofouling Prevention. Advanced Materials Interfaces. 2021;8 (22) :2000359. Publisher's VersionAbstract

Liquid-infused silicones are a promising solution for common surface adhesion problems, such as ice accumulation and biofilm formation, yet they generally lack the tunability, mechanical durability and/or longevity essential for industrial applications. Self-stratifying porous silicones (SPS) infused with compatible silicone oil are developed as a passive strategy to address these shortcomings. Through emulsion templating, porosity is formed in the bulk polymer, providing increased free volume for oil infusion, while a non-porous skin layer is formed at the surface. The bulk porosity and pore size distribution of SPS are independently controlled by varying water and surfactant concentration respectively, leading to a higher volume of oil infusion and improved oil retention relative to an unmodified silicone. Despite a higher oil loading and bulk porosity, the skin layer provides liquid-infused SPS with a comparable surface elasticity to liquid-infused silicones. The potential of liquid-infused SPS as a nontoxic fouling release coating for marine applications is demonstrated using laboratory assays against a variety of soft and hard fouling organisms.

2020
Tomholt L, Geletina O, Alvarenga J, Shneidman AV, Weaver JC, Fernandes MC, Mota SA, Bechthold M, Aizenberg J. Tunable infrared transmission for energy-efficient pneumatic building façades. Energy and Buildings. 2020;(226) :110377. Publisher's VersionAbstract

Thermal regulation of buildings in climates with daily and seasonal weather changes can prove challenging and result in high building energy consumption. While adaptable façades with tunable infrared transmitting properties could modulate solar transmittance through the building envelope and, as such, increase energy efficiency, available technologies to meet these needs are often expensive, relatively complicated, and challenging to implement in a lightweight form factor.

Motivated by these limitations, this report presents a novel tunable light-modulating technology for energy-efficient pneumatic façades in the form of polydimethylsiloxane (PDMS) film with a thin gold surface coating. Sequential stretching and relaxing of this film results in strain-induced microscale surface cracks that can significantly modulate both visible and near infrared light transmission, and consequently, the material’s solar heat gain coefficient (SHGC).

The material’s tunability has shown a significant potential to reduce building energy use, as assessed with building simulation software. The technology offers additional advantages for light modulation in pneumatic façades including real-time operation, ease of implementation and control, and predictable performance. Façade design guidelines for the integration of the infrared-regulating film into ethylene tetrafluoroethylene (ETFE) building envelopes and climate suitability are described, and a critical evaluation of material durability, optical clarity, and material costs are provided.

Adera S, Alvarenga J, Shneidman AV, Zhang CT, Davitt A, Aizenberg J. Depletion of Lubricant from Nanostructured Oil-Infused Surfaces by Pendant Condensate Droplets. ACS Nano. 2020;14 (7) :8024–8035. Publisher's VersionAbstract

Due to recent advances in nanofabrication, phase-change condensation heat transfer has seen a renaissance. Compared to conventional heat transfer surfaces, nanostructured surfaces impregnated with chemically matched lubrication films (hereinafter referred to as “nanostructured lubricated surfaces”) have been demonstrated to improve vapor-side phase-change condensation heat transfer by facilitating droplet nucleation, growth, and departure. While the presence of nanoscale roughness improves performance longevity by stabilizing the lubrication film via capillary forces, such enhancement is short-lived due to the eventual loss of lubrication oil by the departing droplets. The objective of this study is to characterize oil depletion caused by pendant droplets during condensation. For our study, we nanostructured, chemically functionalized, and lubricated horizontal copper tubes that are widely used in shell-and-tube heat exchangers in power plants and process industries. Using high-speed fluorescence imaging and thermogravimetric analysis, we show that shedding droplets exert a shear force on the oil in the wetting ridge at the water–oil interface. The viscous shear draws the lubrication film from the nanostructured surface onto the upper portion of the droplet and forms a ring-like oil skirt. Through detailed theoretical analysis, we show that the thickness of this oil skirt scales with the classical Landau–Levich–Derjaguin (LLD) theory for dip-coating. Our results reveal that droplets falling from horizontal tubes break unequally and leave behind small satellite droplets that retain the bulk of the oil in the wetting ridge. This observation is in stark contrast with the earlier description of droplets shedding from tilted flat plates where the entire oil-filled wetting ridge is demonstrated to leave the surface upon droplet departure. By selecting lubrication oils of varying viscosity and spreading coefficient, we provide evidence that the contribution of the wrapping layer to the rate of oil depletion is insignificant. Furthermore, we show that due to the nanoscale features on the tubes, nearly half of the lubrication film remains on the surface after 10 h of continuous steam condensation at ambient pressure, 23 °C, and 60% relative humidity, a 2–3-fold improvement over previous results.The insights gained from this work will provide guidelines for the rational design of long-lasting nanostructured lubricated surfaces for phase-change condensation.

Phillips KR, Zhang CT, Yang T, Kay T, Gao C, Brandt S, Liu L, Yang H, Li Y, Aizenberg J, et al. Fabrication of Photonic Microbricks via Crack Engineering of Colloidal Crystals. Advanced Functional Materials. 2020;(30) :1908242. Publisher's VersionAbstract

Evaporation-induced self-assembly of colloidal particles is one of the most versatile fabrication routes to obtain large-area colloidal crystals; however, the formation of uncontrolled “drying cracks” due to gradual solvent evaporation represents a significant challenge of this process. While several methods are reported to minimize crack formation during evaporation-induced colloidal assembly, here an approach is reported to take advantage of the crack formation as a patterning tool to fabricate microscopic photonic structures with controlled sizes and geometries. This is achieved through a mechanistic understanding of the fracture behavior of three different types of opal structures, namely, direct opals (colloidal crystals with no matrix material), compound opals (colloidal crystals with matrix material), and inverse opals (matrix material templated by a sacrificial colloidal crystal). This work explains why, while direct and inverse opals tend to fracture along the expected {111} planes, the compound opals exhibit a different cracking behavior along the nonclose-packed {110} planes, which is facilitated by the formation of cleavage-like fracture surfaces. The discovered principles are utilized to fabricate photonic microbricks by programming the crack initiation at specific locations and by guiding propagation along predefined orientations during the self-assembly process, resulting in photonic microbricks with controlled sizes and geometries.

Marcella N, Liu Y, Timoshenko J, Guan E, Luneau M, Shirman T, Plonka AM, van der Hoeven JES, Aizenberg J, Friend C, et al. Neural network assisted analysis of bimetallic nanocatalysts using X-ray absorption near edge structure spectroscopy. Physical Chemistry Chemical Physics. 2020;(22) :18902-18910. Publisher's VersionAbstract

X-ray absorption spectroscopy is a common method for probing the local structure of nanocatalysts. One portion of the X-ray absorption spectrum, the X-ray absorption near edge structure (XANES) is a useful alternative to the commonly used extended X-ray absorption fine structure (EXAFS) for probing three-dimensional geometry around each type of atomic species, especially in those cases when the EXAFS data quality is limited by harsh reaction conditions and low metal loading. A methodology for quantitative determination of bimetallic architectures from their XANES spectra is currently lacking. We have developed a method, based on the artificial neural network, trained on ab initio site-specific XANES calculations, that enables accurate and rapid reconstruction of the structural descriptors (partial coordination numbers) from the experimental XANES data. We demonstrate the utility of this method on the example of a series of PdAu bimetallic nanoalloys. By validating the neural network-yielded metal–metal coordination numbers based on the XANES analysis by previous EXAFS characterization, we obtained new results for in situ restructuring of dilute (2.6 at% Pd in Au) PdAu nanoparticles, driven by their gas and temperature treatments.


 
Meeks A, Mac R, Chathanat S, Aizenberg J. Tunable Long-Range Interactions between Self-Trapped Beams driven by the Thermal Response of Photoresponsive Hydrogels. Chemistry of MaterialsChemistry of Materials. 2020. Publisher's Version
Paink GK, Kolle S, Le D, Weaver JC, Alvarenga J, Ahanotu O, Aizenberg J, Kim P. Dynamic Self-Repairing Hybrid Liquid-in-Solid Protective Barrier for Cementitious Materials. ACS Applied Materials & InterfacesACS Applied Materials & Interfaces. 2020;12 (28) :31922 - 31932. Publisher's VersionAbstract
Corrosion and surface fouling of structural materials, such as concrete, are persistent problems accelerating undesirable material degradation for many industries and infrastructures. To counteract these detrimental effects, protective coatings are frequently applied, but these solid-based coatings can degrade or become mechanically damaged over time. Such irreversible and irreparable damage on solid-based protective coatings expose underlying surfaces and bulk materials to adverse environmental stresses leading to subsequent fouling and degradation. We introduce a new concept of a hybrid liquid-in-solid protective barrier (LIB) to overcome the limitations of traditional protective coatings with broad applicability to structural materials. Through optimization of capillary forces and reduction of the interfacial energy between an upper mobile liquid and a lower immobile solid phase, a stable liquid-based protective layer is created. This provides a persistent self-repairing barrier against the infiltration of moisture and salt, in addition to omniphobic surface properties. As a model experimental test bed, we applied this concept to cementitious materials, which are commonly used as binders in concrete, and investigated how the mobile liquid phase embedded within a porous solid support contributes to the material’s barrier protection and antifouling properties. Using industry standard test methods for acid resistance, chloride-ion penetrability, freeze–thaw cyclability, and mechanical durability, we demonstrate that LIBs exhibit significantly reduced water absorption and ion penetrability, improved repellency against various nonaqueous liquids, and resistance to corrosion while maintaining their required mechanical performance as structural materials.Corrosion and surface fouling of structural materials, such as concrete, are persistent problems accelerating undesirable material degradation for many industries and infrastructures. To counteract these detrimental effects, protective coatings are frequently applied, but these solid-based coatings can degrade or become mechanically damaged over time. Such irreversible and irreparable damage on solid-based protective coatings expose underlying surfaces and bulk materials to adverse environmental stresses leading to subsequent fouling and degradation. We introduce a new concept of a hybrid liquid-in-solid protective barrier (LIB) to overcome the limitations of traditional protective coatings with broad applicability to structural materials. Through optimization of capillary forces and reduction of the interfacial energy between an upper mobile liquid and a lower immobile solid phase, a stable liquid-based protective layer is created. This provides a persistent self-repairing barrier against the infiltration of moisture and salt, in addition to omniphobic surface properties. As a model experimental test bed, we applied this concept to cementitious materials, which are commonly used as binders in concrete, and investigated how the mobile liquid phase embedded within a porous solid support contributes to the material’s barrier protection and antifouling properties. Using industry standard test methods for acid resistance, chloride-ion penetrability, freeze–thaw cyclability, and mechanical durability, we demonstrate that LIBs exhibit significantly reduced water absorption and ion penetrability, improved repellency against various nonaqueous liquids, and resistance to corrosion while maintaining their required mechanical performance as structural materials.
acsami.0c06357_final.pdf
Tesler AB, Sheng Z, Lv W, Fan Y, Fricke D, Park K-C, Alvarenga J, Aizenberg J, Hou X. Metallic Liquid Gating Membranes. ACS NanoACS Nano. 2020;14 (2) :2465 - 2474. Publisher's Version
Morim DR, Meeks A, Shastri A, Tran A, Shneidman AV, Yashin VV, Mahmood F, Balazs AC, Aizenberg J, Saravanamuttu K. Opto-chemo-mechanical transduction in photoresponsive gels elicits switchable self-trapped beams with remote interactions. Proceedings of the National Academy of Sciences. 2020;117 (8) :3953. Publisher's VersionAbstract
Self-trapped light beams hold potential for optical interconnects, applications in image transmission, rerouting light, logic gates for computing and, importantly, for the next-generation light-guiding-light signal processing, which envisions a circuitry-free and reconfigurable photonics powered by the dynamic interactions of self-trapped beams. In conventional nonlinear materials, however, self-trapping suffers from either the need for large incident beam powers and loss of beam interactions at large distances, or it is slow and irreversible. We show that rapidly and repeatably switchable self-trapped laser beams with remote communication capabilities can be elicited at exceptionally small intensities in a pliant, processable hydrogel functionalized with a chromophore. The ability to generate self-trapped beams with this unique set of properties offers unprecedented opportunities to develop light-guiding-light technologies.Next-generation photonics envisions circuitry-free, rapidly reconfigurable systems powered by solitonic beams of self-trapped light and their particlelike interactions. Progress, however, has been limited by the need for reversibly responsive materials that host such nonlinear optical waves. We find that repeatedly switchable self-trapped visible laser beams, which exhibit strong pairwise interactions, can be generated in a photoresponsive hydrogel. Through comprehensive experiments and simulations, we show that the unique nonlinear conditions arise when photoisomerization of spiropyran substituents in pH-responsive poly(acrylamide-co-acrylic acid) hydrogel transduces optical energy into mechanical deformation of the 3D cross-linked hydrogel matrix. A Gaussian beam self-traps when localized isomerization-induced contraction of the hydrogel and expulsion of water generates a transient waveguide, which entraps the optical field and suppresses divergence. The waveguide is erased and reformed within seconds when the optical field is sequentially removed and reintroduced, allowing the self-trapped beam to be rapidly and repeatedly switched on and off at remarkably low powers in the milliwatt regime. Furthermore, this opto-chemo-mechanical transduction of energy mediated by the 3D cross-linked hydrogel network facilitates pairwise interactions between self-trapped beams both in the short range where there is significant overlap of their optical fields, and even in the long range––over separation distances of up to 10 times the beam width––where such overlap is negligible.
Zhang CT, Liu Y, Wang X, Wang X, Kolle S, Balazs AC, Aizenberg J. Patterning non-equilibrium morphologies in stimuli-responsive gels through topographical confinement. Soft Matter. 2020;16 (6) :1463 - 1472. Publisher's VersionAbstract
Stimuli-responsive “smart” polymers have generated significant interest for introducing dynamic control into the properties of antifouling coatings, smart membranes, switchable adhesives and cell manipulation substrates. Switchable surface morphologies formed by confining stimuli-responsive gels to topographically structured substrates have shown potential for a variety of interfacial applications. Beyond patterning the equilibrium swelling behavior of gels, subjecting stimuli-responsive gels to topographical confinement could also introduce spatial gradients in the various timescales associated with gel deformation, giving rise to novel non-equilibrium morphologies. Here we show how by curing poly(N-isopropylacrylamide) (pNIPAAm)-based gel under confinement to a rigid, bumpy substrate, we can not only induce the surface curvature to invert with temperature, but also program the transient, non-equilibrium morphologies that emerge during the inversion process through changing the heating path. Finite element simulations show that the emergence of these transient morphologies is correlated with confinement-induced gradients in polymer concentration and position-dependent hydrostatic pressure within the gel. To illustrate the relevance of such morphologies in interfacial applications, we show how they enable us to control the gravity-induced assembly of colloidal particles and microalgae. Finally, we show how more complex arrangements in particle assembly can be created through controlling the thickness of the temperature-responsive gel over the bumps. Patterning stimuli-responsive gels on topographically-structured surfaces not only enables switching between two invertible topographies, but could also create opportunities for stimuli ramp-dependent control over the local curvature of the surface and emergence of unique transient morphologies. Harnessing these features could have potential in the design of multifunctional, actuatable materials for switchable adhesion, antifouling, cell manipulation, and liquid and particle transport surfaces.
Davidson EC, Kotikian A, Li S, Aizenberg J, Lewis JA. 3D Printable and Reconfigurable Liquid Crystal Elastomers with Light-Induced Shape Memory via Dynamic Bond Exchange. Advanced MaterialsAdvanced MaterialsAdv. Mater. 2020;32 (1) :1905682. Publisher's VersionAbstract
Abstract 3D printable and reconfigurable liquid crystal elastomers (LCEs) that reversibly shape-morph when cycled above and below their nematic-to-isotropic transition temperature (TNI) are created, whose actuated shape can be locked-in via high-temperature UV exposure. By synthesizing LCE-based inks with light-triggerable dynamic bonds, printing can be harnessed to locally program their director alignment and UV light can be used to enable controlled network reconfiguration without requiring an imposed mechanical field. Using this integrated approach, 3D LCEs are constructed in both monolithic and heterogenous layouts that exhibit complex shape changes, and whose transformed shapes could be locked-in on demand.
Guan E, Foucher AC, Marcella N, Shirman T, Luneau M, Head AR, Verbart DMA, Aizenberg J, Friend CM, Stacchiola D, et al. New Role of Pd Hydride as a Sensor of Surface Pd Distributions in Pd−Au Catalysts. ChemCatChemChemCatChemChemCatChem. 2020;12 (3) :717 - 721. Publisher's VersionAbstract
Abstract Isolated or contiguous, the surface distributions of Pd atoms in the Pd?Au bimetallic nanoparticle (NP) catalysts often influence activity and selectivity towards specific reactions. In this study, we used a concomitant Pd hydride formation upon H2 exposure as a probe of presence of contiguous Pd regions in bimetallic NPs. For demonstrating this method, we prepared silica supported monometallic Pd and bimetallic Pd?Au NPs with a Pd/Au ratio of 25/75 (Pd25Au75) and used X-ray absorption spectroscopy, scanning transmission electron microscopy and infrared spectroscopy to detect and quantitatively analyze the Pd hydride regions. This work provides a new approach to characterizing intra-particle heterogeneities within the bimetallic NPs at ambient temperature and pressure.
Waters JT, Li S, Yao Y, Lerch MM, Aizenberg M, Aizenberg J, Balazs AC. Twist again: Dynamically and reversibly controllable chirality in liquid crystalline elastomer microposts. Science Advances. 2020;6 (13) :eaay5349. Publisher's VersionAbstract
Photoresponsive liquid crystalline elastomers (LCEs) constitute ideal actuators for soft robots because their light-induced macroscopic shape changes can be harnessed to perform specific articulated motions. Conventional LCEs, however, do not typically exhibit complex modes of bending and twisting necessary to perform sophisticated maneuvers. Here, we model LCE microposts encompassing side-chain mesogens oriented along a magnetically programmed nematic director, and azobenzene cross-linkers, which determine the deformations of illuminated posts. On altering the nematic director orientation from vertical to horizontal, the post’s bending respectively changes from light-seeking to light-avoiding. Moreover, both modeling and subsequent experiments show that with the director tilted at 45°, the initially achiral post reversibly twists into a right- or left-handed chiral structure, controlled by the angle of incident light. We exploit this photoinduced chirality to design “chimera” posts (encompassing two regions with distinct director orientations) that exhibit simultaneous bending and twisting, mimicking motions exhibited by the human musculoskeletal system.
Lerch MM, Grinthal A, Aizenberg J. Viewpoint: Homeostasis as Inspiration—Toward Interactive Materials. Advanced MaterialsAdvanced MaterialsAdv. Mater. 2020;32 (20) :1905554. Publisher's VersionAbstract
Abstract Homeostatic systems combine an ability to maintain integrity over time with an incredible capacity for interactive behavior. Fundamental to such systems are building blocks of ?mini-homeostasis?: feedback loops in which one component responds to a stimulus and another opposes the response, pushing the module to restore its original configuration. Particularly when they cross time and length scales, perturbation of these loops by external changes can generate diverse and complex phenomena. Here, it is proposed that by recognizing and implementing mini-homeostatic modules?often composed of very different physical and chemical processes?into synthetic materials, numerous interactive behaviors can be obtained, opening avenues for designing multifunctional materials. How a variety of controlled, nontrivial material responses can be evoked from even simple versions of such synthetic feedback modules is illustrated. Moreover, random events causing seemingly random responses give insights into how one can further explore, understand and control the full interaction space. Ultimately, material fabrication and exploration of interactivity become inseparable in the rational design of such materials. Homeostasis provides a lens through which one can learn how to combine and perturb coupled processes across time and length scales to conjure up exciting behaviors for new materials that are both robust and interactive.
Yu Y, Brandt S, Nicolas NJ, Aizenberg J. Colorimetric Ethanol Indicator Based on Instantaneous, Localized Wetting of a Photonic Crystal. ACS Applied Materials & InterfacesACS Applied Materials & Interfaces. 2020;12 (1) :1924 - 1929. Publisher's Version

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