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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.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Solution Structure and Scaling Laws of Cylindrical and Tapered Bottlebrush Polymers

Bottlebrush polymers are a unique class of macromolecular architectures with a plethora of potential industrial and pharmaceutical applications that critically depend on the bottlebrush shape and dimensions. Here, a systematic series of 12 cylindrical and 12 cone-shaped (tapered) bottlebrush polymers with poly(tert-butyl acrylate) (PtBA) or polystyrene (PS) side chains were synthesized using the sequential addition of macromonomers ring-opening metathesis polymerization (SAM-ROMP) grafting-through method. Small-angle neutron scattering (SANS) studies on dilute solutions of the two types of bottlebrush polymers provided noninvasive characterization of their structural dimensions and chain conformations. Simulated SANS traces, generated using coarse-grained molecular dynamics simulations, reproduced the distinctive features observed in the experimental SANS signals and provided necessary validation for data modeling. The combined analysis of experimental and simulated SANS signals yielded key structural and conformational parameters, including the bottlebrush radius, length, and Kuhn length as well as the excluded volume parameter and the correlation length of the polymer side chains. Importantly, the obtained structural parameters followed well-defined scaling laws as a function of the backbone and side chain degrees of polymerization, as predicted by mean field theories. In conclusion, these findings provide clear experimental and computational evidence of the interdependence of structural and conformational properties in an important class of polymer architectures.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Dynamics of bottlebrush polymers

Bottlebrushes are an interesting class of polymers which shows intriguing material properties often associated with dynamics. While dynamical phenomena in linear polymers are well understood and existing theories can describe them in a good way, bottlebrush dynamics have only rarely been investigated. Therefore, we performed dielectric spectroscopy and quasi-elastic neutron scattering to study the dynamics of polydimethylsiloxane-based bottlebrush polymers, PDMS-g-PDMS focusing mostly on the segmental dynamics of the side chains. Comparing the relaxation times of the α – relaxation, tracked with dielectric spectroscopy, of bottlebrush polymers with those of their respective linear side chains show a slowing down once the side chains are attached to the backbone. This effect diminishes and finally vanishes with increasing side chain length. The time and length scale, offered by quasi-elastic neutron scattering, fits for the segmental dynamics together with faster processes. The Q -dependence of the segmental relaxation times allows to classify bottlebrush polymers as heterogenous including a non-Gaussian character. For such a dynamical system, the mean square displacement needs to be separated into single processes before an overall mean square displacement can be generated by applying the time temperature superposition principle.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Backbone Dynamics of Bottlebrush Polymers Studied by Neutron Scattering

Bottlebrush polymers have a versatile architecture that is highly customizable due to the combination of a linear backbone and side chains. As a result of the chemical tethering of the side chains, both parts cannot be easily be separated. Huge effort is seen regarding the dynamical behavior of the side chains or the entire bottlebrush polymer, whereas few studies are available considering the backbone. Here, isotopic labeling in combination with quasi-elastic neutron scattering was used to compare the dynamical behavior of the bottlebrush’s backbone with the side chain dynamics. Keeping the side chains deuterated, (h-PNB)- g -(d-PPO), leads to the scattering signal dominated by backbone dynamics, while the fully protonated sample, (h-PNB)- g -(h-PPO), gives side chain dynamics. Both results reveal slower dynamics associated with the backbone with less heterogeneity, as seen for the side chains. Additionally, a plasticizer effect for the backbone dynamics is confirmed by extracting the glass transition temperature and comparing it with pure linear PNB.

neutron scattering↗
DOE OSTI2023

Bottlebrush Polymers at Liquid Interfaces: Assembly Dynamics, Mechanical Properties, and All-Liquid Printed Constructs

Bottlebrush polymer surfactants (BPSs), formed by the interfacial interactions between bottlebrush polymers (BPs) with poly(acrylic acid) side chains dissolved in an aqueous phase and amine-functionalized ligands dissolved in the oil phase, assemble and bind strongly to the fluid-fluid interface. The ratio between N BB (backbone degree of polymerization) and N SC (side chain degree of polymerization) defines the initial assembly kinetics, interface packing efficiency, and stress relaxation. The equilibrium interfacial tension (γ) increases when N BB < N SC , but decreases when N BB $\gg$ N SC , correlating to a pronounced change in the effective shape of the BPs from being spherical to worm-like structures. The apparent surface coverage (ASC), i.e., the interfacial packing efficiency, decreases as N BB increases. The dripping-to-jetting transition of an injected polymer solution, as well as fluorescence recovery after photobleaching experiments, revealed faster initial assembly kinetics for BPs with higher N BB . Furhter, Euler buckling of BPS assemblies with different N BB values was used to characterize the stress relaxation behavior and bending modulus. The stress relaxation behavior was directly related to the ASC, reflecting the strong influence of macromolecular shape on packing efficiency. The bending modulus of BPSs decreases for N BB < N SC , but increased when N BB $\gg$ N SC , showing the effect of molecular architecture and multisite anchoring. All-liquid printed constructs with lower N BB BPs yielded more stable structured liquids, underscoring the importance of macromolecular packing efficiency at fluid interfaces. Overall, this work elucidates fundamental relationships between nanoscopic structures and macroscopic properties associated with various bottlebrush polymer architectures, which translate to the stabilization of all-fluidic printed constructs.

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

Side Chain Dynamics of Poly(norbornene)- g -Poly(propylene oxide) Bottlebrush Polymers

The segmental dynamics of the side chains of poly(norbornene)- g -poly(propylene oxide) (PNB- g -PPO) bottlebrush polymer in comparison to PPO is studied by quasi-elastic neutron scattering. Having experimental time and length scale information simultaneously allows to extract spatial information in addition to relaxation time. Tethering one end of the PPO side chain onto a stiff PNB backbone slows down the segmental relaxation, over the length and time scales investigated. The power law dependence of the relaxation time on the momentum transfer, Q , indicates a more heterogeneous relaxation pattern for the bottlebrush polymer, whereas the linear PPO has less deviations from a homogenous relaxation. Similar conclusions can be drawn from the time dependent mean square displacement, $\langle$ r 2 ( t )$\rangle$, and the non-Gaussian parameter, α 2 ( t ). Herein, the bottlebrush polymer shows a more restricted dynamics, whereas the linear PPO reaches $\langle$ r 2 ( t )$\rangle$∝ t 0.5 at the highest temperature. The deviations from Gaussian behavior are evident at the α 2 ( t ). Both samples show a decaying α 2 ( t ). Finally, the non-Gaussian parameter supports the results from the power law dependence of the relaxation times, with lower α 2 ( t ) values for PPO compared to those for PNB-g-PPO, pointing to less deviations from Gaussian behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Reversed dynamics of bottlebrush polymers with stiff backbone and flexible side chains

The segmental dynamics of bottlebrush polymers with a stiff backbone and flexible side chains has been studied. The segmental relaxation time of side chains attached to a flexible backbone follows the same trend as linear polymers, an increase with the increasing molecular weight, but is slowed down compared to their linear counterparts. Theoretical work predicts a reversal of the molecular weight dependence of the relaxation time for stiff backbones. As a model for a stiff-g-flexible system, bottlebrushes with poly(norbornene) backbone and poly(propylene oxide) side chains, PNB-g-PPO, at a uniform grafting density have been synthesized and characterized with quasi-elastic neutron scattering. Indeed, the anticipated reversed dynamics was found. Increasing the side chain length decreases the segmental relaxation time. This indicates the importance of the characteristics of the grafting site beyond a simplified picture of an attached side chain. The mean square displacement shows a similar trend with longer side chains exhibiting a larger displacement.

Chemistry↗
DOE OSTI2022

Dynamics of Bottlebrush Polymers in Solution by Neutron Spin Echo Spectroscopy

In this work, we present dynamical and morphological studies on poly(dimethylsiloxane) (PDMS)-based bottlebrush polymers in solution. A combination of small-angle neutron scattering (SANS), pulsed field gradient nuclear magnetic resonance (PFG NMR), and neutron spin echo (NSE) spectroscopy was used to identify structural changes inherent in changing the side-chain length while keeping the backbone constant. These morphological changes are mirrored in the diffusion coefficient determined by PFG NMR, resulting in two coefficients for the elongated and one for the more spherical sample. Faster motions are tracked by NSE using the advantage of time- and length-scale resolutions with the diffusion coefficient predetermined by PFG NMR. Hereby, the sample with short side chains relaxes like wormlike micelles considering the longitudinal direction, whereas the dynamics along the radial extension shows a much stronger Q-dependence as known from any theory. The dynamical behavior within the blob region, covered with the more spherical sample, follows the predictions of Zimm as well as of Zilman and Granek (ZG).

36 MATERIALS SCIENCE↗
DOE OSTI2021

Tunable, biodegradable grafting-from glycopolypeptide bottlebrush polymers

The cellular glycocalyx and extracellular matrix are rich in glycoproteins and proteoglycans that play essential physical and biochemical roles in all life. Synthetic mimics of these natural bottlebrush polymers have wide applications in biomedicine, yet preparation has been challenged by their high grafting and glycosylation densities. Using one-pot dual-catalysis polymerization of glycan-bearing α-amino acid N-carboxyanhydrides, we report grafting-from glycopolypeptide brushes. The materials are chemically and conformationally tunable where backbone and sidechain lengths were precisely altered, grafting density modulated up to 100%, and glycan density and identity tuned by monomer feed ratios. The glycobrushes are composed entirely of sugars and amino acids, are non-toxic to cells, and are degradable by natural proteases. Inspired by native lipid-anchored proteoglycans, cholesterol-modified glycobrushes were displayed on the surface of live human cells. Our materials overcome long-standing challenges in glycobrush polymer synthesis and offer new opportunities to examine glycan presentation and multivalency from chemically defined scaffolds.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Understanding interfacial segregation in polymer blend films with random and mixed side chain bottlebrush copolymer additives

Bottlebrush polymers are complex macromolecules with tunable physical properties dependent on the chemistry and architecture of both the side chains and the backbone. Prior work has demonstrated that bottlebrush polymer additives can be used to control the interfacial properties of blends with linear polymers but has not specifically addressed the effects of bottlebrush side chain microstructures. Here, using a combination of experiments and self-consistent field theory (SCFT) simulations, we investigated the effects of side chain microstructures by comparing the segregation of bottlebrush additives having random copolymer side chains with bottlebrush additives having a mixture of two different homopolymer side chain chemistries. Specifically, we synthesized bottlebrush polymers with either poly(styrene-ran-methyl methacrylate) side chains or with a mixture of polystyrene (PS) and poly(methyl methacrylate) (PMMA) side chains. Furthermore, the bottlebrush additives were matched in terms of PS and PMMA compositions, and they were blended with linear PS or PMMA chains that ranged in length from shorter to longer than the bottlebrush side chains. Experiments revealed similar behaviors of the two types of bottlebrushes, with a slight preference for mixed side-chain bottlebrushes at the film surface. SCFT simulations were qualitatively consistent with experimental observations, predicting only slight differences in the segregation of bottlebrush additives driven by side chain microstructures. Specifically, these slight differences were driven by the chemistries of the bottlebrush polymer joints and side chain end-groups, which were entropically repelled and attracted to interfaces, respectively. Using SCFT, we also demonstrated that the interfacial behaviors were dominated by entropic effects with high molecular weight linear polymers, leading to enrichment of bottlebrush near interfaces. Surprisingly, the SCFT simulations showed that the chemistry of the joints connecting the bottlebrush backbones and side chains played a more significant role compared with the side chain end groups in affecting differences in surface excess of bottlebrushes with random and mixed side chains. This work provides new insights into the effects of side chain microstructure on segregation of bottlebrush polymer additives.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Enhanced Interfacial Bonding of Graft Copolymers

To understand how thermoplastic welding strength can be tuned through chemical modifications and macromolecular topology, we combined coarse-grained molecular dynamics (MD) simulations with experimental validation. Our simulations examined the diffusion dynamics of both linear and graft polymers across representative interfaces, revealing that diffusion-controlled interdigitation follows a power law, with the exponent decreasing from 0.34 to 0.11 as grafting density increases from 7.5 to 196% (with side chains grafted to both sides of a monomer unit). The addition of side chains enhances welding efficiency, as dense bottlebrush polymers with high grafting density reach maximum rupture strength faster than linear polymers. However, their saturated rupture strength is lower. This observation is subsequently corroborated by experimental lap-shear tests comparing linear polyethylene with octene grafted polyethylene elastomers. Our MD simulations show that unlike linear polymers, where backbone entanglements dominate, the grafted side chains introduce mechanisms in addition to entanglement dilution. The rapid interdigitation of side chains creates a dense mesh of entropic van der Waals contacts, which can also enhance the film welding. Furthermore, our MD simulations reveal a brittle rupture behavior in linear and comb-like (mildly grafted) polymers, while bottlebrush (densely grafted) polymers display elastomeric behavior with a pronounced stress plateau prior to fracture. Our simulations deconvolute the influence of polymer topology on deformation behavior. The rate of polymer deformation becomes lower than the applied strain rate prior to rupture, and the onset of this deviation is progressively delayed from linear to bottlebrush polymers. This trend highlights the critical role of molecular architecture in governing the mechanical response. In conclusion, these results provide deeper insight into the underlying welding mechanisms of topological polymers and present a potential approach for mitigating the interface anisotropy that is inherent in advanced manufacturing techniques such as fused filament fabrication.

graft copolymers↗
DOE OSTI2023

Highly Conductive Polyoxanorbornene‐Based Polymer Electrolyte for Lithium‐Metal Batteries

Abstract This present study illustrates the synthesis and preparation of polyoxanorbornene‐based bottlebrush polymers with poly(ethylene oxide) (PEO) side chains by ring‐opening metathesis polymerization for solid polymer electrolytes (SPE). In addition to the conductive PEO side chains, the polyoxanorbornene backbones may act as another ion conductor to further promote Li‐ion movement within the SPE matrix. These results suggest that these bottlebrush polymer electrolytes provide impressively high ionic conductivity of 7.12 × 10 −4 S cm −1 at room temperature and excellent electrochemical performance, including high‐rate capabilities and cycling stability when paired with a Li metal anode and a LiFePO 4 cathode. The new design paradigm, which has dual ionic conductive pathways, provides an unexplored avenue for inventing new SPEs and emphasizes the importance of molecular engineering to develop highly stable and conductive polymer electrolytes for lithium‐metal batteries (LMB).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Interfacial Inversion of Stealth Surfactants

Amphiphilic macromolecular surfactants segregate to liquid–liquid interfaces, thereby reducing the interfacial tension and free energy. Here, we investigated “stealth surfactants” in the form of core–shell bottlebrush polymers comprised of pH-responsive diblock copolymer side chains forming a hydrophilic core and a hydrophobic shell, enabling solubility in oil. At liquid–liquid interfaces, these polymers undergo a structural “inversion”, with hydrophilic blocks segregating into the aqueous phase and hydrophobic blocks residing in the oil phase. The reconfiguration kinetics and surfactant properties are influenced by multiple factors, including the molecular weights of the backbone and side chain components, the hydrophilic-to-hydrophobic balance of the side chains, and the pH of the aqueous phase. An observed nonmonotonic dependence of interfacial tension with time is attributed to a progressive structural inversion, where the projected area of the macromolecule onto the interface decreases. To validate this inversion hypothesis, interfacial properties were characterized by sum-frequency generation vibrational spectroscopy, which revealed configurational changes of the core–shell bottlebrush polymers at the fluid interface and revealed a pH-dependent interfacial coverage. Coarse-grained molecular dynamics simulations supported these experimental findings, showing that the pH-responsive core and hydrophobic shell assume a time-averaged configuration with orientations parallel and perpendicular to the plane of the interface, respectively. These findings open routes to design multistimuli-responsive polymeric surfactants and compatibilizers, expanding their potential applications in advanced interfacial systems.

Stealth surfactants↗
DOE OSTI2021

Light-Mediated Synthesis and Reprocessing of Dynamic Bottlebrush Elastomers under Ambient Conditions

We introduce a novel grafting-through polymerization strategy to synthesize dynamic bottlebrush polymers and elastomers in one step using light to construct a disulfide-containing backbone. The key starting material—α-lipoic acid (LA)—is commercially available, inexpensive, and biocompatible. When installed on the chain end(s) of poly(dimethylsiloxane) (PDMS), the cyclic disulfide unit derived from LA polymerizes under ultraviolet (UV) light in ambient conditions. Significantly, no additives such as initiator, solvent, or catalyst are required for efficient gelation. Formulations that include bis-LA-functionalized cross-linker yield bottlebrush elastomers with high gel fractions (83–98%) and tunable, supersoft shear moduli in the ~20–200 kPa range. An added advantage of these materials is the dynamic disulfide bonds along each bottlebrush backbone, which allow for light-mediated self-healing and on-demand chemical degradation. These results highlight the potential of simple and scalable synthetic routes to generate unique bottlebrush polymers and elastomers based on PDMS.

36 MATERIALS SCIENCE↗