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Seufert L, Elmahmoudy M, Theunis C, Lienemann S, Li Y, Mohammadi M, Boda U, Carnicer-Lombarte A, Kroon R, Persson POÅ, Rahmanudin A, Donahue MJ, Farnebo S, Tybrandt K. Stretchable Tissue-Like Gold Nanowire Composites with Long-Term Stability for Neural Interfaces. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2024:e2402214. [PMID: 38944890 DOI: 10.1002/smll.202402214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2024] [Revised: 06/20/2024] [Indexed: 07/02/2024]
Abstract
Soft and stretchable nanocomposites can match the mechanical properties of neural tissue, thereby minimizing foreign body reactions to provide optimal stimulation and recording specificity. Soft materials for neural interfaces should simultaneously fulfill a wide range of requirements, including low Young's modulus (<<1 MPa), stretchability (≥30%), high conductivity (>> 1000 S cm-1), biocompatibility, and chronic stability (>> 1 year). Current nanocomposites do not fulfill the above requirements, in particular not the combination of softness and high conductivity. Here, this challenge is addressed by developing a scalable and robust synthesis route based on polymeric reducing agents for smooth, high-aspect ratio gold nanowires (AuNWs) of controllable dimensions with excellent biocompatibility. AuNW-silicone composites show outstanding performance with nerve-like softness (250 kPa), high conductivity (16 000 S cm-1), and reversible stretchability. Soft multielectrode cuffs based on the composite achieve selective functional stimulation, recordings of sensory stimuli in rat sciatic nerves, and show an accelerated lifetime stability of >3 years. The scalable synthesis method provides a chemically stable alternative to the widely used AgNWs, thereby enabling new applications within electronics, biomedical devices, and electrochemistry.
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Affiliation(s)
- Laura Seufert
- Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, Norrköping, 602 21, Sweden
| | - Mohammed Elmahmoudy
- Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, Norrköping, 602 21, Sweden
| | - Charlotte Theunis
- Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, Norrköping, 602 21, Sweden
| | - Samuel Lienemann
- Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, Norrköping, 602 21, Sweden
| | - Yuyang Li
- Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, Norrköping, 602 21, Sweden
| | - Mohsen Mohammadi
- Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, Norrköping, 602 21, Sweden
| | - Ulrika Boda
- RISE Research Institutes of Sweden, Digital Systems, Smart Hardware, Printed, Bio- and Organic Electronics, Södra Grytsgatan 4, Norrköping, SE-602 33, Sweden
| | | | - Renee Kroon
- Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, Norrköping, 602 21, Sweden
| | - Per O Å Persson
- Department of Physics, Chemistry and Biology, Linköping University, Linköping, 581 83, Sweden
| | - Aiman Rahmanudin
- Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, Norrköping, 602 21, Sweden
| | - Mary J Donahue
- Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, Norrköping, 602 21, Sweden
| | - Simon Farnebo
- Department of Hand Surgery, Plastic Surgery and Burns, Linköping University Hospital, Linköping, 581 85, Sweden
- Department of Biomedical and Clinical Sciences, Linköping University, Linköping, 581 85, Sweden
| | - Klas Tybrandt
- Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, Norrköping, 602 21, Sweden
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2
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Halford GC, McDarby SP, Hertle S, Kiely AF, Luu JT, Wang CJ, Personick ML. Troubleshooting the influence of trace chemical impurities on nanoparticle growth kinetics via electrochemical measurements. NANOSCALE 2024; 16:11038-11051. [PMID: 38691093 DOI: 10.1039/d4nr00070f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2024]
Abstract
Reproducibility issues resulting from particle growth solutions made with cetyltrimethylammonium bromide (CTAB) surfactant from different lots and product lines in a newly developed synthesis of monometallic palladium (Pd) tetrahexahedra (THH) nanoparticles are investigated via a multi-pronged approach. Time-resolved electrochemical measurements of solution potential, variation of chemical parameters in colloidal synthesis, and correlation to electrodeposition syntheses are used together to uncover the effects of the unknown contaminants on the chemical reducing environment during nanoparticle growth. Iodide-a known impurity in commercial CTAB-is identified as one of the required components for equalizing the reducing environment across multiple CTAB sources. However, an additional component-acetone-is critical to establishing the growth kinetics necessary to enable the reproducible synthesis of THH in each of the CTAB formulations. In one CTAB variety, the powdered surfactant contains too much acetone, and drying of the as-received surfactant and re-addition of solvent is necessary for successful Pd THH synthesis. The relevance of solvent impurities to the reducing environment in aqueous nanoparticle synthesis is confirmed via electrochemical measurement approaches and solvent addition experiments. This work highlights the utility of real-time electrochemical potential measurements as a tool for benchmarking of nanoparticle syntheses and troubleshooting of reproducibility issues. The results additionally emphasize the importance of considering organic solvent impurities in powdered commercial reagents as a possible shape-determining factor during shaped nanomaterials synthesis.
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Affiliation(s)
- Gabriel C Halford
- Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, USA.
- Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459, USA
| | - Sean P McDarby
- Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459, USA
| | - Sebastian Hertle
- Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, USA.
- Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459, USA
| | - Anne F Kiely
- Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459, USA
| | - Jessica T Luu
- Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459, USA
| | - Claire J Wang
- Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459, USA
| | - Michelle L Personick
- Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, USA.
- Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459, USA
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3
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Xin Y, Nagata T, Kato K, Xu Y, Shirai T. Role of polyvinylpyrrolidone in the polyol synthesis of platinum nanoparticles. NANOSCALE ADVANCES 2024; 6:3034-3040. [PMID: 38863791 PMCID: PMC11138182 DOI: 10.1039/d4na00118d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/08/2024] [Accepted: 03/22/2024] [Indexed: 06/13/2024]
Abstract
In this work, platinum (Pt) nanoparticles (NPs) were prepared via the reduction of Pt salts in an ethylene glycol induced polyol process with an altered polyvinylpyrrolidone (PVP)/Pt molar ratio. With the systematic elucidation of the hydrodynamic size in a liquid; the solid-state size and morphology, crystal structure, surface chemical state and thermal decomposition behavior of the synthesized Pt NPs; as well as the reducing dynamic of Pt cations, the role of PVP in the polyol synthesis of Pt NPs is clarified for the first time. It was found that the amount of PVP does not affect the reducing dynamic of Pt cations, but the chemical state of PVP capped on Pt NPs and the resultant particle size significantly depend on the initial PVP/Pt molar ratio in the precursor solution. Dense-packed PVP via the chemisorption of carbonyl oxygen on the surface of Pt NPs occurs in the case of a higher PVP/Pt ratio, suppressing particle growth and resulting in smaller Pt NPs. On the contrary, the chemical structure of PVP is tuned by the cleavage of the N-C bond and results in the chemisorption of the N atom on the surface of Pt NPs, which promotes the production of larger Pt NPs when a lower PVP/Pt ratio is applied.
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Affiliation(s)
- Yunzi Xin
- Advanced Ceramics Research Center, Nagoa Institute of Technolgy Gokiso-cho, Showa-ku Nagoya Aichi 466-8555 Japan
| | - Taku Nagata
- Department of Life Science and Applied Science, Graduate School of Engineering, Nagoya Institute of Technology Gokiso-cho, Showa-ku Nagoy Aichi 466-8555 Japan
| | - Kunihiko Kato
- Advanced Ceramics Research Center, Nagoa Institute of Technolgy Gokiso-cho, Showa-ku Nagoya Aichi 466-8555 Japan
| | - Yuping Xu
- Advanced Ceramics Research Center, Nagoa Institute of Technolgy Gokiso-cho, Showa-ku Nagoya Aichi 466-8555 Japan
| | - Takashi Shirai
- Advanced Ceramics Research Center, Nagoa Institute of Technolgy Gokiso-cho, Showa-ku Nagoya Aichi 466-8555 Japan
- Department of Life Science and Applied Science, Graduate School of Engineering, Nagoya Institute of Technology Gokiso-cho, Showa-ku Nagoy Aichi 466-8555 Japan
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4
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Ying Y, Zheng R, Zheng Y, Wang H, Niu J, Xia H. Synthesis and Reduction Processes of Silver Nanowires in a Silver(I) Sulfamate-Poly (Vinylpyrrolidone) Hydrothermal System. Molecules 2024; 29:1558. [PMID: 38611837 PMCID: PMC11013250 DOI: 10.3390/molecules29071558] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2024] [Revised: 03/25/2024] [Accepted: 03/26/2024] [Indexed: 04/14/2024] Open
Abstract
Silver (Ag) nanowires, as an important one-dimensional (1D) nanomaterial, have garnered wide attention, owing to their applications in electronics, optoelectronics, sensors, and other fields. In this study, an alternative hydrothermal route was developed to synthesize Ag nanowires via modified reduction of Ag+. Silver sulfamate plays an important role in the formation of Ag nanowires via controlled release of free Ag+. Results of controlled experiments and characterizations such as UV-vis spectroscopy, FTIR, XPS, and 1H NMR revealed that sulfamic acid does not function as a reductant, supporting by the generation of free Ag+ instead of Ag nanostructures in hydrothermally treated silver sulfamate solution. The initial reduction of Ag+ was induced by the combination of poly (vinylpyrrolidone) (PVP) end group and degradation products. This phenomenon was supported by abundant free Ag+ in the mixed preheated silver sulfamatic and preheated PVP aqueous solutions, indicating a second and distinct Ag+ autocatalytic reduction. Thus, the roles of different reagents and Ag+ reduction must be studied for nanomaterial syntheses.
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Affiliation(s)
- Yongling Ying
- College of Materials and Chemical Engineering, Southwest Forestry University, Kunming 650224, China;
| | - Rongbo Zheng
- College of Materials and Chemical Engineering, Southwest Forestry University, Kunming 650224, China;
- College of Biological & Chemical Engineering, Zhejiang University of Science and Technology, Hangzhou 310023, China; (J.N.); (H.X.)
| | - Yongjun Zheng
- School of Marine Science and Technology, Shanwei Institute of Technology, Shanwei 516600, China
| | - Hongyan Wang
- Key Laboratory of Bamboo Research of Zhejiang Province, Zhejiang Academy of Forestry, Hangzhou 310023, China;
| | - Junfeng Niu
- College of Biological & Chemical Engineering, Zhejiang University of Science and Technology, Hangzhou 310023, China; (J.N.); (H.X.)
| | - Housheng Xia
- College of Biological & Chemical Engineering, Zhejiang University of Science and Technology, Hangzhou 310023, China; (J.N.); (H.X.)
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Halford GC, Personick ML. Bridging Colloidal and Electrochemical Nanoparticle Growth with In Situ Electrochemical Measurements. Acc Chem Res 2023; 56:1228-1238. [PMID: 37140656 DOI: 10.1021/acs.accounts.3c00112] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
ConspectusProspective applications involving the electrification of industrial chemical processes and electrical energy to chemical fuels interconversion as part of the energy transition to renewable energy sources have led to an increasing need for highly tailored nanostructures immobilized on electrode surfaces. Control of surface facet structure across material compositions is of particular importance for ensuring performance in such applications. Colloidal methods for producing shaped nanoparticles in solution are abundant, particularly for noble metals. However, significant technical challenges remain with respect to rationally designing syntheses for the novel compositions and morphologies required to sustainably enable the above technological advances as well as in developing methods for uniformly and reproducibly dispersing colloidally synthesized nanostructures on electrode surfaces. The direct synthesis of nanoparticles on electrodes using chemical reduction approaches remains challenging, though recent advances have been made for certain materials and structures. Electrochemical nanoparticle synthesis─where an applied current or potential instead of a chemical reducing agent drives the redox chemistry of nanoparticle growth─is poised to play an important role in advancing the fabrication of nanostructured electrodes. Specifically, this Account focuses on the colloidal-inspired design of electrochemical syntheses and the interplay between colloidal and electrochemical approaches in terms of understanding the fundamental chemical reaction mechanisms of nanoparticle growth. An initial discussion of the development of electrochemical particle syntheses that incorporate colloidal synthetic tools highlights the promising emergent capabilities that result from blending these two approaches. Furthermore, it demonstrates how existing colloidal syntheses can be directly translated to electrochemical growth on a conductive surface using real-time electrochemical measurements of the chemistry of the growth solution. Measuring the open circuit potential of a colloidal synthesis over time and then replicating that measured potential during electrochemical deposition leads to the formation of the same nanoparticle shape. These in situ open circuit and chronopotentiometric measurements also give fundamental insight about the changing chemical environment during particle growth. We highlight how these time-resolved electrochemical measurements, as well as correlated spectroelectrochemical monitoring of particle formation kinetics, enable the extraction of information regarding mechanisms of particle formation that is difficult to obtain using other approaches. This information can be translated back into colloidal synthesis design via a directed, intentional approach to synthetic development. We additionally explore the added flexibility of synthetic design for methods involving electrochemically driven reduction as compared to the use of chemical reducing agents. The Account concludes with a brief perspective on potential future directions in both fundamental studies and synthetic development enabled by this emerging integrated electrochemical approach.
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Affiliation(s)
- Gabriel C Halford
- Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459, United States
| | - Michelle L Personick
- Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459, United States
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Morphology normalization of peony flower-like Bi2O2CO3 boosts photocatalytic seawater purification. Colloids Surf A Physicochem Eng Asp 2022. [DOI: 10.1016/j.colsurfa.2022.129915] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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7
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Liu H, Sun Y, Xu H, Qin Y, Huang Q, Chen K, Shu W, Xiao C. Dual-functional design of tubular polyvinyl chloride hybrid nanofiber membranes for the simultaneous oil/water separation and in-situ catalytic degradation. J Memb Sci 2022. [DOI: 10.1016/j.memsci.2022.120955] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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8
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Xiao N, Chen Y, Weng W, Chi X, Chen H, Tang D, Zhong S. Mechanism Understanding for Size Regulation of Silver Nanowires Mediated by Halogen Ions. NANOMATERIALS 2022; 12:nano12152681. [PMID: 35957112 PMCID: PMC9370693 DOI: 10.3390/nano12152681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Revised: 07/29/2022] [Accepted: 08/01/2022] [Indexed: 02/01/2023]
Abstract
The controllable preparation of silver nanowires (AgNWs) with a high aspect ratio is key for enabling their applications on a large scale. Herein, the aspect ratio regulation of AgNWs mediated by halogen ion composition in ethylene glycol system was systematically investigated and the size evolution mechanism is elaborately understood. The co-addition of Br− and Cl− results in AgNWs with the highest aspect ratio of 1031. The surface physicochemical analysis of AgNWs and the density functional theory calculations indicate that the co-addition of Br− and Cl− contributes to the much-enhanced preferential growth of the Ag(111) crystal plane. At the same time, when Cl− and Br− coexist in the solution, the growth of the Ag(100) crystal plane on the AgNWs was restrained compared with that in the single Cl− system. Resultantly, the enhanced growth of Ag(111) and the inhibited growth of Ag(100) contribute to the formation of AgNWs with a higher aspect ratio in the Cl–Br mixed solution. The results can provide new insights for understanding the morphology and size evolution during the AgNWs preparation in ethylene glycol system.
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Affiliation(s)
- Ni Xiao
- School of Materials Science and Engineering, Fuzhou University, Fuzhou 350108, China
| | - Yinan Chen
- Zijin School of Geology and Mining, Fuzhou University, Fuzhou 350108, China
| | - Wei Weng
- Zijin School of Geology and Mining, Fuzhou University, Fuzhou 350108, China
- Fujian Key Laboratory of Green Extraction and High-Value Utilization of Energy Metals, Fuzhou University, Fuzhou 350108, China
| | - Xiaopeng Chi
- Zijin School of Geology and Mining, Fuzhou University, Fuzhou 350108, China
- Fujian Key Laboratory of Green Extraction and High-Value Utilization of Energy Metals, Fuzhou University, Fuzhou 350108, China
| | - Hang Chen
- Zijin Mining Group Co., Ltd., Shanghang 364200, China
- State Key Laboratory of Comprehensive Utilization of Low Grade Refractory Gold Ores, Shanghang 364200, China
| | - Ding Tang
- Zijin Mining Group Co., Ltd., Shanghang 364200, China
- State Key Laboratory of Comprehensive Utilization of Low Grade Refractory Gold Ores, Shanghang 364200, China
| | - Shuiping Zhong
- Zijin School of Geology and Mining, Fuzhou University, Fuzhou 350108, China
- Fujian Key Laboratory of Green Extraction and High-Value Utilization of Energy Metals, Fuzhou University, Fuzhou 350108, China
- Zijin Mining Group Co., Ltd., Shanghang 364200, China
- State Key Laboratory of Comprehensive Utilization of Low Grade Refractory Gold Ores, Shanghang 364200, China
- Correspondence: ; Tel.: +86-152-8038-5768
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9
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Taladriz-Blanco P, Spuch-Calvar M, Del Prado A, Weder C, Rother-Rutishauser B, Petri-Fink A, Rodriguez-Lorenzo L. Impurities in polyvinylpyrrolidone: the key factor in the synthesis of gold nanostars. NANOSCALE ADVANCES 2022; 4:387-392. [PMID: 35178499 PMCID: PMC8765127 DOI: 10.1039/d1na00711d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Accepted: 11/26/2021] [Indexed: 05/11/2023]
Abstract
Control over the synthesis of anisotropic nanoparticles is crucial as slight differences in their size, shape, sharpness, or the number of tips in the case of gold nanostars, has an inordinate influence on their properties and functionality for future applications. Herein, we show that the supplier and purity of polyvinylpyrrolidone (PVP) can significantly alter the synthesis of gold nanostars, demonstrating that impurities, not PVP itself, are the main factor responsible for star-like shape formation. We demonstrate that in the presence of pure PVP and N,N-dimethylformamide, the use of hydrazine leads to the formation of branched nanoparticles. This synthetic approach opens the door to solving issues associated with the use of commercial PVP during the synthesis of gold nanostars.
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Affiliation(s)
- Patricia Taladriz-Blanco
- Adolphe Merkle Institute, University of Fribourg Chemin des Verdiers 4 Fribourg CH-1700 Switzerland
- International Iberian Nanotechnology Laboratory (INL), Water Quality group Av. Mestre José Veiga s/n 4715-330 Braga Portugal
| | - Miguel Spuch-Calvar
- Adolphe Merkle Institute, University of Fribourg Chemin des Verdiers 4 Fribourg CH-1700 Switzerland
| | - Anselmo Del Prado
- Adolphe Merkle Institute, University of Fribourg Chemin des Verdiers 4 Fribourg CH-1700 Switzerland
| | - Christoph Weder
- Adolphe Merkle Institute, University of Fribourg Chemin des Verdiers 4 Fribourg CH-1700 Switzerland
| | | | - Alke Petri-Fink
- Adolphe Merkle Institute, University of Fribourg Chemin des Verdiers 4 Fribourg CH-1700 Switzerland
- Chemistry Department, University of Fribourg Chemin du Musée 9 Fribourg CH-1700 Switzerland
| | - Laura Rodriguez-Lorenzo
- International Iberian Nanotechnology Laboratory (INL), Water Quality group Av. Mestre José Veiga s/n 4715-330 Braga Portugal
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10
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Hakobyan K, Xu J, Müllner M. The challenges of controlling polymer synthesis at the molecular and macromolecular level. Polym Chem 2022. [DOI: 10.1039/d1py01581h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this Perspective, we outline advances and challenges in controlling the structure of polymers at various size regimes in the context of structural features such as molecular weight distribution, end groups, architecture, composition and sequence.
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Affiliation(s)
- Karen Hakobyan
- Key Centre for Polymers and Colloids, School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia
- The University of Sydney Nano Institute (Sydney Nano), Sydney, NSW 2006, Australia
- School of Chemical Engineering, UNSW Sydney, NSW 2052, Australia
| | - Jiangtao Xu
- School of Chemical Engineering, UNSW Sydney, NSW 2052, Australia
| | - Markus Müllner
- Key Centre for Polymers and Colloids, School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia
- The University of Sydney Nano Institute (Sydney Nano), Sydney, NSW 2006, Australia
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11
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Yang TH, Ahn J, Shi S, Qin D. Understanding the Role of Poly(vinylpyrrolidone) in Stabilizing and Capping Colloidal Silver Nanocrystals. ACS NANO 2021; 15:14242-14252. [PMID: 34436857 DOI: 10.1021/acsnano.1c01668] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The ligands anchored to the surface of metal nanocrystals play an important role in controlling their colloidal synthesis for a broad spectrum of applications, but it remains a daunting challenge to investigate the ligand-surface and ligand-solvent interactions at the molecular level. Here, we report the use of surface-enhanced Raman scattering (SERS) to extract structural information about the binding of poly(vinylpyrrolidone) (PVP) to Ag nanocubes as well as its conformational changes in response to solvent quality. When a PVP chain binds to the surface of a Ag nanocube through some of its carbonyl groups, the segments between adjacent binding sites are expelled into the solvent as loops. As a result, the carbonyl peak (νC═O) resolved in the SERS spectrum includes the contributions from those anchored to the surface and those residing on the loops, with their frequencies located at νC═O(Ag) and νC═O(free), respectively. While νC═O(Ag) remains at a fixed frequency due to the coordination between the carbonyl groups with Ag surface, the spectral position of νC═O(free) is dependent on the solvent. As the strength of hydrogen bonding between PVP and solvent increases, the peak position of νC═O(free) shifts toward lower frequencies. When exposed to bad and good solvents in an alternating manner, the PVP loops undergo conformational changes between collapsed and extended states, altering the separation between the free carbonyl groups and the Ag surface and thereby the intensity of the νC═O peak.
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Affiliation(s)
- Tung-Han Yang
- School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
| | - Jaewan Ahn
- School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
| | - Shi Shi
- School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
| | - Dong Qin
- School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
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