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1. The superior effect of edge functionalization relative to basal plane functionalization of graphene in enhancing the thermal conductivity of polymer–graphene nanocomposites – a combined molecular dynamics and Green's functions study

   https://doi.org/10.1039/d2cp00146b  

   Muthaiah, Rajmohan ; Tarannum, Fatema ; Danayat, Swapneel ; Annam, Roshan Sameer ; Nayal, Avinash Singh ; Yedukondalu, N. ; Garg, Jivtesh ( June 2022 , Physical Chemistry Chemical Physics)

   To achieve polymer–graphene nanocomposites with high thermal conductivity ( k ), it is critically important to achieve efficient thermal coupling between graphene and the surrounding polymer matrix through effective functionalization schemes. In this work, we demonstrate that edge-functionalization of graphene nanoplatelets (GnPs) can enable a larger enhancement of effective thermal conductivity in polymer–graphene nanocomposites relative to basal plane functionalization. Effective thermal conductivity for the edge case is predicted, through molecular dynamics simulations, to be up to 48% higher relative to basal plane bonding for 35 wt% graphene loading with 10 layer thick nanoplatelets. The beneficial effect of edge bonding is related to the anisotropy of thermal transport in graphene, involving very high in-plane thermal conductivity (∼2000 W m −1 K −1 ) compared to the low out-of-plane thermal conductivity (∼10 W m −1 K −1 ). Likewise, in multilayer graphene nanoplatelets (GnPs), the thermal conductivity across the layers is even lower due to the weak van der Waals bonding between each pair of layers. Edge functionalization couples the polymer chains to the high in-plane thermal conduction pathway of graphene, thus leading to overall high thermal conductivity of the composite. Basal-plane functionalization, however, lowers the thermal resistance between the polymer andmore »the surface graphene sheets of the nanoplatelet only, causing the heat conduction through inner layers to be less efficient, thus resulting in the basal plane scheme to be outperformed by the edge scheme. The present study enables fundamentally novel pathways for achieving high thermal conductivity polymer nanocomposites.« less
2. Release, detection and toxicity of fragments generated during artificial accelerated weathering of CdSe/ZnS and CdSe quantum dot polymer composites

   https://doi.org/10.1039/C8EN00249E  

   Gallagher, Miranda J. ; Buchman, Joseph T. ; Qiu, Tian A. ; Zhi, Bo ; Lyons, Taeyjuana Y. ; Landy, Kaitlin M. ; Rosenzweig, Zeev ; Haynes, Christy L. ; Fairbrother, D. Howard ( January 2018 , Environmental Science: Nano)

   Next generation displays and lighting applications are increasingly using inorganic quantum dots (QDs) embedded in polymer matrices to impart bright and tunable emission properties. The toxicity of some heavy metals present in commercial QDs ( e.g. cadmium) has, however, raised concerns about the potential for QDs embedded in polymer matrices to be released during the manufacture, use, and end-of-life phases of the material. One important potential release scenario that polymer composites can experience in the environment is photochemically induced matrix degradation. This process is not well understood at the molecular level. To study this process, the effect of an artificially accelerated weathering process on QD–polymer nanocomposites has been explored by subjecting CdSe and CdSe/ZnS QDs embedded in poly(methyl methacrylate) (PMMA) to UVC irradiation in aqueous media. Significant matrix degradation of QD–PMMA was observed along with measurable mass loss, yellowing of the nanocomposites, and a loss of QD fluorescence. While ICP-MS identified the release of ions, confocal laser scanning microscopy and dark-field hyperspectral imaging were shown to be effective analytical techniques for revealing that QD-containing polymer fragments were also released into aqueous media due to matrix degradation. Viability experiments, which were conducted with Shewanella oneidensis MR-1, showed a statistically significant decreasemore »in bacterial viability when the bacteria were exposed to highly degraded QD-containing polymer fragments. Results from this study highlight the need to quantify not only the extent of nanoparticle release from a polymer nanocomposite but also to determine the form of the released nanoparticles ( e.g. ions or polymer fragments).« less
3. Hierarchically hydrogen-bonded graphene/polymer interfaces with drastically enhanced interfacial thermal conductance

   https://doi.org/10.1039/C8NR08760A  

   Zhang, Lin ; Liu, Ling ( February 2019 , Nanoscale)

   Interfacial thermal transport is a critical physical process determining the performance of many material systems with small-scale features. Recently, self-assembled monolayers and polymer brushes have been widely used to engineer material interfaces presenting unprecedented properties. Here, we demonstrate that poly(vinyl alcohol) (PVA) monolayers with hierarchically arranged hydrogen bonds drastically enhance interfacial thermal conductance by a factor of 6.22 across the interface between graphene and poly(methyl methacrylate) (PMMA). The enhancement is tunable by varying the number of grafted chains and the density of hydrogen bonds in the unique hierarchical hydrogen bond network. The extraordinary enhancement results from a synergy of hydrogen bonds and other structural and thermal factors including molecular morphology, chain orientation, interfacial vibrational coupling and heat exchange. Two types of hydrogen bonds, i.e. PVA–PMMA hydrogen bonds and PVA–PVA hydrogen bonds, are analyzed and their effects on various structural and thermal properties are systematically investigated. These results are expected to provide new physical insights for interface engineering to achieve tunable thermal management and energy efficiency in a wide variety of systems involving polymers and biomaterials.
4. IN-SITU BENDING PERFORMANCE OF NANOSTRUCTURED CARBON FIBER REINFORCED POLYMER COMPOSITES

   https://doi.org/10.12783/asc37/36507  

   KAYNAN, OZGE ; FALLAHI, HAMED ; JARRAHBASHI, DORRIN ; ASADI, AMIR ( September 2022 , Proceedings Of The American Society for Composites-Thirty-Seventh Technical Conference)

   Depositing carbon nanotubes (CNTs) into carbon fiber reinforced polymer composites (CFRPs) is challenging because of the need for complicated lab-scale processes and toxic chemical dispersants that makes conventional means of processing less compatible with existing industrial procedures for large-scale applications. In this work, a scalable supercritical CO2-assisted atomization technique is used to effectively deposit hybrid CNTs in CFRPs allowing them to boost their functionality and tailor the microstructure. Cellulose nanocrystals (CNCs) are utilized to create hybrid nanostructures with CNTs (CNC bonded CNT) that enables stabilization of CNTs in nontoxic media, i.e., water, and this promotes the scalability of the process. According to Zeta potential values, CNCs successfully stabilize CNTs in water suspension. Scanning electron microscopy (SEM) micrographs show hybrid CNC bonded CNTs are homogeneously dispersed on the carbon fiber surface. According to the in-situ bending test under the optical microscope, crack propagation is hindered by engineered hybrid CNT nanostructures in the modified CFRP whereas neat CFRP exhibits low crack growth resistance due to the uninterrupted crack propagation in the continuous epoxy matrix. Our results imply that this strategy probes the importance of new controlled manufacturing of hybrid nanostructures through evaporation‑induced self‑assembly of nanocolloidal droplets, and allows for tailoring of themore »desired properties of nanostructured composites.

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5. Photosynthesis-assisted remodeling of three-dimensional printed structures

   https://doi.org/10.1073/pnas.2016524118  

   Yu, Kunhao ; Feng, Zhangzhengrong ; Du, Haixu ; Xin, An ; Lee, Kyung Hoon ; Li, Ketian ; Su, Yipin ; Wang, Qiming ; Fang, Nicholas X. ; Daraio, Chiara ( January 2021 , Proceedings of the National Academy of Sciences)

   The mechanical properties of engineering structures continuously weaken during service life because of material fatigue or degradation. By contrast, living organisms are able to strengthen their mechanical properties by regenerating parts of their structures. For example, plants strengthen their cell structures by transforming photosynthesis-produced glucose into stiff polysaccharides. In this work, we realize hybrid materials that use photosynthesis of embedded chloroplasts to remodel their microstructures. These materials can be used to three-dimensionally (3D)-print functional structures, which are endowed with matrix-strengthening and crack healing when exposed to white light. The mechanism relies on a 3D-printable polymer that allows for an additional cross-linking reaction with photosynthesis-produced glucose in the material bulk or on the interface. The remodeling behavior can be suspended by freezing chloroplasts, regulated by mechanical preloads, and reversed by environmental cues. This work opens the door for the design of hybrid synthetic-living materials, for applications such as smart composites, lightweight structures, and soft robotics.