Search NASA⌕ Search

SEARCH · Search NASA

Results for “Dendrons”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Impact of peripheral alkyl chain length on mesocrystal assemblies of G2 dendrons

Unique sphere-packing mesophases such as Frank–Kasper (FK) phases have emerged from the viable design of intermolecular interactions in supramolecular assemblies. In this work, a series of C n -G2-CONH 2 dendrons possessing an identical core wedge are investigated to elucidate the impact of peripheral alkyl chain lengths (C n ) on the formation of the close-packed structures. The C 18 and C 14 dendrons, of which the contour lengths of the periphery L p are longer than the wedge length L w , assemble into a uniform sphere-packing phase such as body-centred cubic (BCC), whereas the C 8 dendron with short (L p < L w ) corona environment forms the FK A15 phase. Particularly in the intermediate C 12 and C 10 dendrons (L p ≈ L w ), cooling the samples from an isotropic state leads to cooling-rate-dependent phase behaviours. The C 12 dendron produces two structures of hexagonal columnar and sphere-packing phases (BCC and A15), while the C 10 dendron generates the A15 and σ phases by the fast- and slow-cooling processes, respectively. Our results show the impact of peripheral alkyl chain lengths on the formation of mesocrystal phases, where the energy landscape of the dendrons at L p /L w ≈ 1 must be more complex and delicate than those with either longer or shorter peripheral alkyl chains.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Apex hydrogen bonds in dendron assemblies modulate close-packed mesocrystal structures

The close-packed mesocrystal structures from soft-matter assemblies have recently received attention due to their structural similarity to atomic crystals, displaying various sphere-packing Frank–Kasper (FK) and quasicrystal structures. Herein, diverse mesocrystal structures are explored in second-generation dendrons (G2-X) designed with identical wedges, in which the terminal functionalities X = CONH 2 and CH 2 NH 2 represent two levels of the strong and weak hydrogen-bonding apexes, respectively. The cohesive interactions at the core apex, referred to as the core interactions, are effectively modulated by forming heterogeneous hydrogen bonds between these two functional units. For the dendron assemblies compositionally close to each pure component of G2-CONH 2 and G2-CH 2 NH 2 , their own FK A15 and C14 phases dominate other phases, respectively. We show the existence of the wide-range FK σ including the dodecagonal quasicrystal (DDQC) phases from the dendron mixtures between G2-CONH 2 and G2-CH 2 NH 2 , providing an experimental phase sequence of A15–σ–DDQC–C14 as the core interactions are alleviated. Intriguingly, the temperature dependence of particle sizes shows that the high plateau values of particle sizes are maintained equivalently until each threshold temperature (T th ), followed by a prompt decrease above the T th . A decrease in T th by alleviating the core interactions and its composition dependence suggest that the more size-dispersed particles, the more susceptibility to chain exchange with increasing temperature. Here our results on the formation of supramolecular dendron assemblies provide a guide to understand the core-interaction-dependent mesocrystal structures toward the fundamental principle underlying the temperature dependence of their particle sizes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Mesoscale Frank–Kasper Crystal Structures from Dendron Assembly by Controlling Core Apex Interactions

Single-component polymeric materials open up a great potential for self-assembly into mesoscale complex crystal structures that are known as Frank-Kasper (FK) phases. Predicting the packing structures of the soft-matter spheres, however, remains a challenge even when the molecular design is precisely known. Here, we investigate the role of the molecules' enthalpic interaction in determining the low-symmetry crystal structures. To this end, we synthesize architecturally asymmetric dendrons by varying their apex functionalities and examine the packing structures of the second-generation (G2) dendritic wedges. Our work shows that weakening the hydrogen bonding of the dendron apex makes the particles softer and smaller, and leads to the formation of various FK structures at lower temperatures, including the new observation of a FK C14 phase in the cone-shaped dendron systems. As a consequence of the free energy balance between the particle's interfacial tension and the chain's stretching, various packing structures are mainly tuned by designing the hydrogen bonding interaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Transition Kinetics of Self-Assembled Supramolecular Dodecagonal Quasicrystal and Frank–Kasper σ Phases in AB n Dendron-Like Giant Molecules

A series of noncrystalline AB n dendron-like giant molecules DPOSS–MPOSS n (n = 2–6, DPOSS: hydrophilic polyhedral oligomeric silsesquioxane (POSS) cage; MPOSS: hydrophobic POSS cage) were synthesized. These samples present a thermodynamically stable phase formation sequence from the hexagonal cylinder phase (plane group of P6mm), to the Frank–Kasper (F–K) A15 phase (space group of Pm$\overline{3n}$), and further to the F–K σ phase (space group of P4 2 /mnm), with increasing the number of MPOSS in a single molecule (n, from 2 to 6). Moreover, for DPOSS–MPOSS 5 and DPOSS–MPOSS 6 , an intriguing dodecagonal quasicrystal (DQC) structure has been identified and revealed as a kinetic favorable metastable phase at lower temperatures, while the thermodynamically stable phase is the σ phase. The detailed investigation of the transition kinetics between the DQC and σ phase in these samples makes it possible to identify how the self-assembly directs the phase transition in terms of molecular and supramolecular aspects.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Improved Chemical and Colloidal Stability of Gold Nanoparticles through Dendron Capping

Nanoparticle (NP) stability is imperative for commercialization of nanotechnology. In this study, we compare the stability of Au NPs with surfaces functionalized with oleylamine, dodecanethiol, and two dendritic ligands of different generations. Dendrimer ligands provide a significant increase in the chemical stability of Au NPs when analyzed by cyanide-induced NP decomposition as well as an investigation into their colloidal stability at ambient conditions. These results were supported by absorption measurements, transmission electron microscopy, thermogravimetric analysis, nuclear magnetic resonance, and small-angle transmission X-ray scattering and show that dendrimers play a key role in improving the chemical and colloidal stability of NPs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Nanoparticle Superlattices through Template-Encoded DNA Dendrimers

The chemical interactions that lead to the emergence of hierarchical structures are often highly complex and difficult to program. In this paper, the synthesis of a series of superlattices based upon 30 different structurally reconfigurable DNA dendrimers is reported, each of which presents a well-defined number of single-stranded oligonucleotides (i.e., sticky ends) on its surface. Such building blocks assemble with complementary DNA-functionalized gold nanoparticles (AuNPs) to yield five distinct crystal structures, depending upon choice of dendrimer and defined by phase symmetry. These DNA dendrimers can associate to form micelle-dendrimers, whereby the extent of association can be modulated based upon surfactant concentration and dendrimer length to produce a low-symmetry Ti5Ga4-type phase that has yet to be reported in the field of colloidal crystal engineering. Taken together, colloidal crystals that feature three different types of particle bonding interactions.template-dendron, dendrimer-dendrimer, and DNA-modified AuNP-dendrimer.are reported, illustrating how sequence-defined recognition and dynamic association can be combined to yield complex hierarchical materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Promoting multiexciton interactions in singlet fission and triplet fusion upconversion dendrimers

Abstract Singlet fission and triplet-triplet annihilation upconversion are two multiexciton processes intimately related to the dynamic interaction between one high-lying energy singlet and two low-lying energy triplet excitons. Here, we introduce a series of dendritic macromolecules that serve as platform to study the effect of interchromophore interactions on the dynamics of multiexciton generation and decay as a function of dendrimer generation. The dendrimers (generations 1–4) consist of trimethylolpropane core and 2,2-bis(methylol)propionic acid (bis-MPA) dendrons that provide exponential growth of the branches, leading to a corona decorated with pentacenes for SF or anthracenes for TTA-UC. The findings reveal a trend where a few highly ordered sites emerge as the dendrimer generation grows, dominating the multiexciton dynamics, as deduced from optical spectra, and transient absorption spectroscopy. While the dendritic structures enhance TTA-UC at low annihilator concentrations in the largest dendrimers, the paired chromophore interactions induce a broadened and red-shifted excimer emission. In SF dendrimers of higher generations, the triplet dynamics become increasingly dominated by pairwise sites exhibiting strong coupling (Type II), which can be readily distinguished from sites with weaker coupling (Type I) by their spectral dynamics and decay kinetics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Polymer Coatings on Virus-like Particle Nanoreactors at Low Ionic Strength—Charge Reversal and Substrate Access

Virus-like particles (VLPs) are a class of biomaterials which serve as platforms for achieving the desired functionality through interior and exterior modifications. Through ionic strength-mediated electrostatic interactions, VLPs have been assembled into hierarchically ordered materials. This work builds on predictive models to prepare polymer-coated VLP dusters at very low ionic strength. Zeta potential measurements showed that the clusters carried a strongly positive charge, a complete charge reversal from the VLP building block. SAXS analysis confirmed polymer adsorption onto the VLP exterior. Furthermore, we then studied the activity of an encapsulated enzyme toward small molecular and macromolecular substrates to determine the effect of each component of the hierarchically assembled material. We found that while encapsulation and polymer coating did not have a large effect on access to the enzyme by its native, small molecular substrate, substrate modification with a macromolecule caused the polymer coating and encapsulation to affect the access to the enzyme.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

High-Performance Semiempirical Excited-State Molecular Dynamics Powered by Graphics Processing Units

Here, this Letter introduces excited-state molecular dynamics in PYSEQM, a GPU-accelerated semiempirical quantum chemistry engine implemented in PyTorch. The new module enables Born–Oppenheimer molecular dynamics (BOMD) using configuration-interaction singles and random phase approximation for excited states, allowing long trajectories and large statistical ensembles to be simulated efficiently on a single GPU. We also implement an extended Lagrangian excited-state BOMD (XL-ESMD) scheme that propagates auxiliary electronic variables, enabling relaxed ground and excited-state convergence thresholds without compromising energy conservation. The excited-state BOMD implementation scales smoothly from small chromophores to a nearly 900-atom dendrimer (taking 6.5 s per MD step). PYSEQM also supports batched execution, allowing many geometries or trajectories to be evaluated in a single GPU launch, substantially increasing throughput and making ensemble-based protocols routine. As a demonstration, we compute absorption, emission, and infrared spectra from trajectories propagated on the ground and first excited states. The XL-ESMD scheme yields identical spectra at significantly lower computational cost, establishing the role of extended Lagrangian based dynamics for efficient excited-state BOMD simulations. Beyond raw performance, PYSEQM’s PyTorch foundation provides automatic differentiation for forces, efficient GPU batching, and seamless interfacing with machine learning models. These capabilities position PYSEQM as a practical platform for machine learning-augmented excited-state dynamics and lay the foundation for future data-driven nonadiabatic excited-state dynamics modeling of ultrafast spectroscopic probes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Active Dendrite Suppression by Ferroelectric Membrane Separators in Rechargeable Batteries

Anodic dendrite formation is a critical issue in rechargeable batteries and often leads to poor cycling stability and quick capacity loss. Prevailing strategies for dendrite suppression aim at slowing down the growth rate kinetically but still leaving possibilities for dendrite evolution over time. Herein, we report a complete dendrite elimination strategy using a mesoporous ferroelectric polymer membrane as the battery separator. The dendrite suppression is realized by spontaneously reversing the surface energetics for metal ion reduction at the protrusion front, where a positive piezoelectric polarization is generated and superimposed as the protrusion compresses the separator. This effect is demonstrated first in a Zn electroplating process, and further in Zn–Zn symmetric cells and Zn–NaV 3 O 8 ·1.5H 2 O full cells, where the dendritic Zn anode surfaces are completely turned into featureless flat surfaces. Consequently, a substantially longer charging/discharging cycle is achieved. Furthermore, this study provides a promising pathway toward high-performance dendrite-free rechargeable batteries.

25 ENERGY STORAGE↗
DOE OSTI2020

Electrochemical Healing of Dendrites in Garnet-Based Solid Electrolytes

Garnet oxides are a promising material family for solid-state batteries (SSBs). Dendrite formation in solid electrolytes critically limits the applicability of SSBs because of limiting Coulombic efficiency and power capability. In this study, the authors report operando electrochemical healing of dendrites in a garnet-based solid electrolyte (SE). Dendrites were deliberately formed at high operational current density (2 mA cm –2 ) beyond the critical current density (0.55 mA cm –2 ) of the used garnet SE. Electrochemical impedance spectroscopy and scanning electron microscopy were used to confirm dendrite growth in the SE. Dendrites were subsequently healed electrochemically via plating and stripping at 20 and 1 μA cm –2 current densities. Removal of dendrites was shown by an increase in bulk and interfacial resistance and a progressive increase in polarization during galvanostatic plating and stripping. High local current density at the dendrite tips was identified as the mechanism for preferentially removing dendrites electrochemically. The dendrite detection and healing methods discussed here are crucial for extending the life of SSBs.

25 ENERGY STORAGE↗
DOE OSTI2021

Visualizing Lithium Dendrite Formation within Solid-State Electrolytes

Solid-state electrolyte (SSE) is promising for application in allsolid-state lithium metal batteries because of its reliable safety and longevity. The failure of SSE to suppress dendrite formation of Li metal anodes has been conventionally explained by uneven Li deposition at Li/SSE interfaces and its subsequent dendritic growth. While Li deposition within SSE has been recently proposed as another key cause for SSE failure, little is known regarding the Li growth details inside the SSE itself. In this work, we performed in situ microscopic observation of Li deposition inside the SSE and obtained visualized evidence regarding the dynamic process of Li dendrite formation and growth. Here, Li is seen to directly nucleate and propagate within the SSE, leading to its structural cracking. Such behavior should be caused by the presence of P- and S-based crystalline defects in Li 3 PS 4 SSE, which is consistent with the cryo-transmission electron microscopy observations and theoretical calculations. This observation provides important insights into the growth mechanisms of Li dendrites within a working lithium battery.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Hydride-Based Interlayer for Solid-State Anode-Free Battery

Solid-state batteries (SSBs) are considered a promising approach to realizing an anode-free concept with high energy densities. However, the initial Coulombic efficiency (ICE) has remained insufficient for anode-free batteries using sulfide-based solid electrolytes (SEs). Herein, we incorporated a hydride-based interlayer, 3LiBH 4 -LiI (LBHI), between a typical sulfide SE, Li 6 PS 5 Cl, and the Cu current collector. Further, by investigating the Li plating and stripping behaviors and the (electro)chemical stability between SEs and plated Li, we demonstrated that LBHI can effectively improve interfacial stability, leading to an ICE exceeding 94% in anode-free half cells. This interlayer also improves Coulombic efficiencies and specific capacities in anode-free full cells. Furthermore, the utilization of LBHI enables one to study Li plating behaviors without interference from interfacial (electro)chemical instabilities. The analysis of stack pressure evolution during electrochemical cycling reveals that soft shorting in SSBs arises from both dendrite formation and deformation, offering insights into further optimizing solid-state anode-free batteries.

25 ENERGY STORAGE↗
DOE OSTI2025

Operando Optical Microscopy for Visualization of Dendrite Growth in an Argyrodite LPSCl–Polymer Composite Electrolyte

Herein, we demonstrate the utility of optical microscopy as an accessible technique for the in situ visualization of dendrite growth within polymer–sulfide composite solid-state electrolytes. The composite electrolyte features in situ polymerization and cross-linking of the polymer between ceramic particles, which opens up extensive opportunities for accelerated materials discovery, given the vast array of acrylate/methacrylate monomers available. Specifically, the cross-linked polymer poly(triethylene glycol dimethacrylate) (poly(TEGDMA)) was observed to effectively fill pores and inhibit dendrite growth at the lithium metal interface, attributed to its glassy state at room temperature. This work represents the first application of optical microscopy to illustrate that the incorporation of glassy, undoped polymers such as poly(TEGDMA) can serve as a viable strategy for dendrite suppression in solid-state composite electrolytes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗