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Results for “polymer grafting”

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 OSTI2021

Structure and Dispersion of Free and Grafted Polymer in Nanoparticle Organic Hybrid Materials-Based Solutions by Small-Angle Neutron Scattering

Liquid-like Nanoscale Organic Hybrid Materials or NOHMs consisting of polymer grafted nanoparticles have shown great promise in applications, such as electrochemistry and gas separation, due to their enhanced conductivity, tunability, and negligible vapor pressure. Recently, NOHMs are considered to be used as novel electrolytes in Redox Flow Batteries (RFBs). However, to employ NOHMs in redox flow batteries as electrolytes, it is important to understand the conformation and dispersion of NOHMs in the electrochemical milieu. In this work, we report the use of small-angle neutron scattering to probe the structure and dispersion of Jeffamine M2070 polymer grafted to a SiO 2 nanoparticle in an aqueous solution with and without the presence of a supporting electrolyte. Our results indicate that, in the aqueous environment, there exists a large amount of free polymer in the solution that is not grafted to the functionalized nanoparticles. These protonated free polymers, dispersed in the aqueous solvent, may also strongly interact with the grafted polymer layer and greatly affect the neat structure of NOHMs. Thus, there also exist polymers identified as “interacting” polymers to distinguish them from tethered or truly free polymers in the fluid system. The presence of supporting electrolyte shows a greater effect on the structure of NOHMs-based fluid as it not only alters the structure of the free polymer but also hinders the interaction of the polymer with the functionalized nanoparticles. Moreover, the change in the interaction of the Jeffamine M2070 with the functionalized nanoparticles due to the addition of supporting electrolyte has revealed a drastic change in the viscosities of NOHM solutions. Overall, the dispersion of the free polymer, the interaction of the interacting polymer with grafted polymer, and the change in conformation of free polymer and grafted layers with the addition of supporting electrolyte provide valuable insight into the overall scenario of the electrochemical environment of NOHMs. These results can be applied to fine-tune the structure of liquid-like NOHMs and will aid in a better understanding of their performance as potential electrolytes in RFBs.

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

Deep learning potential of mean force between polymer grafted nanoparticles

Grafting polymer chains on the surfaces of nanoparticles is a well-known route to control their self-assembly and distribution in a polymer matrix. A wide variety of self-assembled structures are achieved by changing the grafting patterns on the surface of an individual nanoparticle. However, an accurate estimation of the effective potential of mean force between a pair of grafted nanoparticles that determines their assembly and distribution in a polymer matrix is an outstanding challenge in nanoscience. We address this problem via deep learning. As a proof of concept, here we report a deep learning framework that learns the interaction between a pair of single-chain grafted spherical nanoparticles from their molecular dynamics trajectory. Subsequently, we carry out the deep learning potential of mean force-based molecular simulation that predicts the self-assembly of a large number of single-chain grafted nanoparticles into various anisotropic superstructures, including percolating networks and bilayers depending on the nanoparticle concentration in three-dimensions. The deep learning potential of mean force-predicted self-assembled superstructures are consistent with the actual superstructures of single-chain polymer grafted spherical nanoparticles. This deep learning framework is very generic and extensible to more complex systems including multiple-chain grafted nanoparticles. Finally, we expect that this deep learning approach will accelerate the characterization and prediction of the self-assembly and phase behaviour of polymer-grafted and unfunctionalized nanoparticles in free space or a polymer matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Many-Body Potential for Simulating Self-Assembly of Polymer-Grafted Nanoparticles in a Polymer Matrix

Many-body interactions between polymer-grafted nanoparticles (NPs) play a key role in promoting their assembly into low-dimensional structures within polymer melts, even when the particles are spherical and isotropically grafted. However, capturing such interactions in simulations of NP assembly is very challenging because explicit modeling of the polymer grafts and melt chains is highly computationally expensive, even using coarse-grained models. Here, we develop a many-body potential for describing the effective interactions between spherical polymer-grafted NPs in a polymer matrix through a machine-learning approach. The approach involves using permutationally invariant polynomials to fit two- and three-body interactions derived from the potential of mean force calculations. The potential developed here reduces the computational cost by several orders of magnitude, thereby, allowing us to explore assembly behavior over large length and time scales. We show that the potential not only reproduces previously known assembled phases such as 1D strings and 2D hexagonal sheets, which generally cannot be achieved using isotropic two-body potentials, but can also help discover interesting phases such as networks, clusters, and gels. We demonstrate how each of these assembly morphologies intrinsically arises from a competition between two- and three-body interactions. Our approach for deriving many-body effective potentials can be readily extended to other colloidal systems, enabling researchers to make accurate predictions of their behavior and dissect the role of individual interaction energy terms of the overall potential in the observed behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Polarized X-ray scattering measures molecular orientation in polymer-grafted nanoparticles

Polymer chains are attached to nanoparticle surfaces for many purposes, including altering solubility, influencing aggregation, dispersion, and even tailoring immune responses in drug delivery. The most unique structural motif of polymer-grafted nanoparticles (PGNs) is the high-density region in the corona where polymer chains are stretched under significant confinement, but orientation of these chains has never been measured because conventional nanoscale-resolved measurements lack sensitivity to polymer orientation in amorphous regions. Here, we directly measure local chain orientation in polystyrene grafted gold nanoparticles using polarized resonant soft X-ray scattering (P-RSoXS). Using a computational scattering pattern simulation approach, we measure the thickness of the anisotropic region of the corona and extent of chain orientation within it. These results demonstrate the power of P-RSoXS to discover and quantify orientational aspects of structure in amorphous soft materials and provide a framework for applying this emerging technique to more complex, chemically heterogeneous systems in the future.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Creating Novel Gas Separation Constructs by Manipulating Free-Volume Distributions in Polymer-Grafted Nanoparticles

Polymer membranes are critical to many sustainability applications that require gas separation primarily based on differences in the sizes of the constituent molecules (“sieving”). The important figures of merit in this context are the rate at which the gas permeates through the membrane (or flux) and the resulting gas purity (as characterized by its selectivity). The overall goal is to maximize both gas permeability and selectivity. Currently, the ability to a priori design polymeric materials (either pure polymers or mixed matrix membranes where polymers are mixed with inorganic nanoparticles) with required permeability and selectivity remains an open challenge.

03 NATURAL GAS↗
DOE OSTI2024

Creating Novel Gas Separation Constructs by Manipulating Free-Volume Distributions in Polymer-Grafted Nanoparticles

Polymer membranes are critical to sustainability applications, and in this work we focused on one key application, the efficient separation of gas mixtures. Despite their widespread use, important challenges remain in the use of polymer membranes in this context – i.e., finding membrane materials with selectively improved transport of the desired mixture component(s) while possessing enhanced strength and improved aging behavior relative to the best current benchmarks. The important separation figures of merit are the gas flux, which is proportional to the permeability, P i = D i × S i (Di is the gas diffusivity and S i its solubility coefficient) and selectivity (i.e., gas purity,α ij = P i /P j ). The goal is to simultaneously maximize P i and α ij . Most research to date has empirically targeted the development of new glassy polymers with improved separation performance. These include thermally rearranged (TR) polymers and polymers of intrinsic microporosity (PIMs).

36 MATERIALS SCIENCE↗
DOE OSTI2020

Ion-Conducting Thermoresponsive Films Based on Polymer-Grafted Cellulose Nanocrystals

Mechanically robust, thermo-responsive, ion-conducting nanocomposite films are prepared from poly(2-phenylethyl methacrylate) grafted cellulose nanocrystals (MxG-CNC-g-PPMA). One-component nanocomposite films of the polymer grafted nanoparticle (PGN) MxG-CNC-g-PPMA are imbibed with 30 wt% imidazolium-based ionic liquid, to produce flexible ion-conducting films. These films with 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (MxG-CNC-g-PPMA/[H]) not only displays remarkable improvements in toughness (>25 times) and tensile strength (>70 times) relative to the corresponding nanocomposites consisting of the ionic liquid imbibed in the two component CNC/PPMA nanocomposite, but also shows higher ionic conductivity than the corresponding neat PPMA with the same wt.% of ionic liquid. Notably, the one-component film containing 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (MxG-CNC-g-PPMA/[E]) exhibits temperature responsive ionic conduction. The ionic conductivity decreases at around 60°C as a consequence of the lower critical solution temperature (LCST) phase transition of the grafted polymer in the ionic liquid, which leads to phase separation. Moreover, holding the MxG-CNC-g-PPMA/[E] film at room temperature for 24 hours returns the film to its original homogenous state. These materials exhibit properties relevant to thermal cutoff safety devices (e.g., thermal fuse) where a reduction in conductivity above a critical temperature is needed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The effect of polymer grafting on the mechanical properties of PEG-grafted cellulose nanocrystals in poly(lactic acid)

Poly(lactic acid) (PLA) is a commercially available bio-based polymer that is a potential alternative to many commodity petrochemical-based polymers. However, PLA's thermomechanical properties limit its use in many applications. Incorporating polymer-grafted cellulose nanocrystals (CNCs) is one potential route to improving these mechanical properties. One key challenge in using these polymer-grafted nanoparticles is to understand which variables associated with polymer grafting are most important for improving composite properties. In this work, poly(ethylene glycol)-grafted CNCs are used to study the effects of polymer grafting density and molecular weight on the properties of PLA composites. All CNC nanofillers are found to reinforce PLA above the glass transition temperature, but non-grafted CNCs and CNCs grafted with short PEG chains (<2 kg mol –1 ) are found to cause significant embrittlement, generally resulting in less than 3% elongation-at-break. By grafting higher molecular weight PEG (10 kg mol –1 ) onto the CNCs at a grafting density where the polymer chains are predicted to be in the semi-dilute polymer brush conformation (~0.1 chains nm –2 ), embrittlement can be avoided.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Polymer grafted aramid nanofiber reinforces immiscible waste polypropylene/poly(ethylene terephthalate)

Polypropylene (PP) and poly(ethylene terephthalate) (PET) are plastics commonly used for packaging because of their excellent barrier and mechanical properties. The properties of these plastics are often diminished after mechanical recycling, inevitably causing down-cycling. Furthermore, this problem is exacerbated when different kinds of polymers mix. Aramid nanofibers have the potential to improve the mechanical properties of polymers due to their excellent mechanical properties but their poor dispersion in polymers is a challenge. Grafting polymers onto nanofibers can help address this challenge. In this work, different loading levels (1%, 2%, and 5%) of polymer grafted aramid nanofibers (ANFs) are blended with waste PP/PET (90/10), simulating a PP waste stream containing traces of PET contaminants. Scanning electronic microscopy, rheology, and differential scanning calorimetry results show the affinity of PP functionalized aramid nanofibers (PP_ANF) towards the PP matrix. At 1 wt% of the nanofiber, the size of the PET droplets in the PP matrix of the PP_ANF blend range from 0.2 to 2.0 μm while that of unmodified ANF and PET_ANF blends are in the range of 0.1–6.2 and 0.5–7.4 μm, respectively. In summary, polymer grafted ANFs have the tendency of improving properties of its like polymers due to similarity in the grafting polymer and the polymer matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Internal Microstructure Dictates Interactions of Polymer-grafted Nanoparticles in Solution

Understanding the effects of polymer brush architecture on particle interactions in solution is requisite to enable the development of functional materials based on self-assembled polymer-grafted nanoparticles (GNPs). Static and dynamic light scattering of polystyrene-grafted silica particle solutions in toluene reveals that the pair interaction potential, inferred from the second virial coefficient, A 2 , is strongly affected by the grafting density, σ, and degree of polymerization, N, of tethered chains. In the limit of intermediate σ (~0.3 to 0.6 nm -2 ) and high N, A 2 is positive and increases with N. This confirms the good solvent conditions and can be qualitatively rationalized on the basis of a pair interaction potential derived for grafted (brush) particles. In contrast, for high σ > 0.6 nm -2 and low N, A 2 displays an unexpected reversal to negative values, thus indicating poor solvent conditions. These findings are rationalized by means of a simple analysis based on a coarse-grained brush potential, which balances the attractive core-core interactions and the excluded volume interactions imparted by the polymer grafts. The results suggest that the steric crowding of polymer ligands in dense GNP systems may fundamentally alter the interactions between brush particles in solution and highlight the crucial role of architecture (internal microstructure) on the behavior of hybrid materials. The effect of grafting density also illustrates the opportunity to tailor the physical properties of hybrid materials by altering geometry (or architecture) rather than a variation of the chemical composition.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Effect of Initiator Density, Catalyst Concentration, and Surface Curvature on the Uniformity of Polymers Grafted from Spherical Nanoparticles

Polymer-grafted nanoparticles (PGNPs) are versatile hybrid materials whose properties critically depend on brush dimensions, uniformity, and grafting density. Herein, we systematically investigated how initiator density, catalyst concentration, and nanoparticle curvature govern the growth of poly(methyl methacrylate) (PMMA) brushes grafted from spherical SiO 2 nanoparticles via surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET ATRP). By tuning the initiator density through a combination of “active” and “dummy” silane initiators anchored on the nanoparticles’ surface and controlling the catalyst concentration, we reveal that increased initiator crowding and smaller surface curvature amplify steric hindrance, leading to decreased initiation efficiency and broader molecular weight distributions. Correlation with the corresponding unattached chains by ARGET ATRP suggests the presence of permanently inaccessible (“buried”) initiation sites, which are a characteristic of surface-grafted systems. At sufficient Cu catalyst concentrations, uniform brush growth is attained across different initiator densities, whereas decreased catalyst concentrations accentuate nonconcurrent initiation and propagation. These findings provide mechanistic insights into the interplay of initiator density, catalyst concentration, and surface curvature, offering design principles for tailoring the PGNP architecture. These results can guide the structural engineering of densely grafted surfaces, including nanoparticles and flat substrates, for applications in nanocomposites, photonics, and functional coatings.

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

Influence of Thermal Treatment on Preceramic Polymer Grafted Nanoparticle Network Formation: Implications for Thermal Protection Systems and Aerospace Propulsion Components

Preceramic polymer grafted nanoparticles (PCP GNPs) offer potential advantages in the production of polymer-derived ceramic composites compared to neat preceramic polymers (PCPs), such as reduced thermal shrinkage and increased char yield. In comparison to traditional composites (particles + free polymer), PCPs avoid issues of compatibility, agglomeration, and phase separation during processing and provide routes to control nanoparticle arrangement. Prior literature has established that the conversion efficiency of PCPs and PCP GNPs to ceramics and ceramic composites is linked to the thermal pretreatment of these precursor polymers (e.g., curing). In this paper, we investigate the material transformations that occur when exposing PCP GNPs to a low-temperature thermal treatment (≤250 °C) prior to pyrolysis. The PCP GNPs explored in this study possessed silica nanoparticle cores but were distinct in their PCP coronas, having poly(1,1-dimethylpropylsilane) (allyl-GNP)- or poly(1,1-dimethylbenzylethylsilane) (styryl-GNP)-grafted polymers. After undergoing low-temperature thermal treatment, these PCP GNPs exhibited increased char yield at 800 °C; however, unlike commercial PCPs (e.g., allylhydridopolycarbosilane (SMP-10)), obvious cross-linkable sites are not present in the PCP corona structure. Differential scanning calorimetry, oscillatory rheology, and X-ray photon correlation spectroscopy were utilized to elucidate the thermally induced material changes in the allyl- and styryl-GNPs. Thermally induced changes to the structure and behavior of the PCP GNPs were determined to be linked to the chemical structure of the grafted polycarbosilane chains. Styryl-GNPs experienced a curing event between 180 and 250 °C, effecting the formation of a network, which contributed to char yield improvement (at 800 °C). The nanoscale dynamics of this material also shows a transition from diffuse behavior to ballistic behavior because of the cross-linking event. Conversely, the allyl-GNPs did not exhibit a curing event under heat treatment but did show an increase in thermally induced physical cross-linking. The allyl-GNP physical network is stronger after the first cycle of thermal treatment, and it is considered that this contributed to the improvement in char yield post thermal treatment. The advancements in the understanding of the cross-linking behavior of these hybrid materials are expected to advance the application of these materials to turbine engine, advanced friction, and heat-shielding components.

36 MATERIALS SCIENCE↗