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Nanomaterials
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Advances in Stimuli-Responsive Nanomaterials
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Advances in Stimuli-Responsive Nanomaterials

A special issue of Nanomaterials (ISSN 2079-4991). This special issue belongs to the section "Nanofabrication and Nanomanufacturing".

Deadline for manuscript submissions: closed (1 November 2022) | Viewed by 28260

Special Issue Editors

Prof. Dr. Jianguo Guan

E-Mail Website
Guest Editor
State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China
Interests: functional composite materials; metamaterials; micro-/nanorobots; photonic crystals
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Long Ren

E-Mail Website
Guest Editor
State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, China
Interests: stimuli-responsive materials; liquid metal; micro-/nanorobots
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Stimuli-responsive materials, also known as smart materials, are defined as materials that can react or respond to external stimuli, including stress/strain, sound, thermal energy or temperature, electric and/or magnetic fields, light, moisture, pH value, chemicals, and so on. They are regarded as one of most important research frontiers covering from material science to engineering and medicine and have broad applications in electronics, optic devices, electromagnetic devices, energy, information communications, memories, sensors, and actuators.

The research and development of smart stimuli-responsive materials based on nanomaterials has attracted growing interest and attention. Compared with bulk materials, nanomaterials possess unique properties, such as small size effect, surface and boundary effect, and quantum size effect. They may enhance the existing stimuli-responsive properties or generate new responsive capabilities. Hybrid nanomaterials, such as those containing heterojunctions, can further extend the field-responsive capacity to incredible levels, then meeting the requirement of high levels of complexity and efficiency in various functional devices. 

This Special Issue of Nanomaterials on “Advances in Stimuli-Responsive Nanomaterials” will attempt to capture recent advancements in smart nanomaterials. It welcomes both theoretical and experimental approaches, covering aspects from the design and synthesis of novel nanomaterials or nanocomposites with stimuli-responsive properties, characterization, and analysis on the working principle and regulating mechanism of stimuli-responsive activities or performances, and the development of new smart devices based on stimuli-responsive nanomaterials. Both reviews and original research articles are welcome.

Prof. Dr. Jianguo Guan
Prof. Dr. Long Ren
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Nanomaterials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2900 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Stimuli-responsive materials
  • Smart materials and devices
  • Nanomaterials and nanocomposites
  • Electro-/magnetorheological fluid
  • Micro-/nanomotors
  • Metamaterials
  • Field responsive photonic crystals
  • Ferro-/piezoelectric materials
  • Photoelectric and photocatalytic materials
  • Responsive polymers

Published Papers (12 papers)

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Research

Jump to: Review

11 pages, 2084 KiB  
Article
Silver Nanoflakes-Enhanced Anisotropic Hybrid Composites for Integratable Pressure Sensors
by Qingtian Zhang, Guolin Yun, Shida Jin, Zexin Chen, Shi-Yang Tang, Hongda Lu, Haiping Du and Weihua Li
Nanomaterials 2022, 12(22), 4018; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12224018 - 16 Nov 2022
Cited by 1 | Viewed by 1442
Abstract
Flexible pressure sensors based on polymer elastomers filled with conductive fillers show great advantages in their applications in flexible electronic devices. However, integratable high-sensitivity pressure sensors remain understudied. This work improves the conductivity and sensitivity of PDMS-Fe/Ni piezoresistive composites by introducing silver flakes [...] Read more.
Flexible pressure sensors based on polymer elastomers filled with conductive fillers show great advantages in their applications in flexible electronic devices. However, integratable high-sensitivity pressure sensors remain understudied. This work improves the conductivity and sensitivity of PDMS-Fe/Ni piezoresistive composites by introducing silver flakes and magnetic-assisted alignment techniques. As secondary fillers, silver flakes with high aspect ratios enhance the conductive percolation network in composites. Meanwhile, a magnetic field aligns ferromagnetic particles to further improve the conductivity and sensitivity of composites. The resistivity of the composite decreases sharply by 1000 times within a tiny compression strain of 1%, indicating excellent sensing performance. On the basis of this, we demonstrate an integratable miniature pressure sensor with a small size (2 × 2 × 1 mm), high sensitivity (0.966 kPa−1), and wide sensing range (200 kPa). Finally, we develop a flexible E-skin system with 5 × 5 integratable sensor units to detect pressure distribution, which shows rapid real-time response, high resolution, and high sensitivity. Full article
(This article belongs to the Special Issue Advances in Stimuli-Responsive Nanomaterials)
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12 pages, 2509 KiB  
Article
Deformation-Thermal Co-Induced Ferromagnetism of Austenite Nanocrystalline FeCoCr Powders for Strong Microwave Absorption
by Ziwen Fu, Zhihong Chen, Rui Wang, Hanyan Xiao, Jun Wang, Hao Yang, Yueting Shi, Wei Li and Jianguo Guan
Nanomaterials 2022, 12(13), 2263; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12132263 - 30 Jun 2022
Cited by 3 | Viewed by 1387
Abstract
Nanocrystalline soft magnetic alloy powders are promising microwave absorbents since they can work at diverse frequencies and are stable in harsh environments. However, when the alloy powders are in austenite phase, they are out of the screen for microwave absorbents due to their [...] Read more.
Nanocrystalline soft magnetic alloy powders are promising microwave absorbents since they can work at diverse frequencies and are stable in harsh environments. However, when the alloy powders are in austenite phase, they are out of the screen for microwave absorbents due to their paramagnetic nature. In this work, we reported a strategy to enable strong microwave absorption in nanocrystalline austenite FeCoCr powders by deformation-thermal co-induced ferromagnetism via attritor ball milling and subsequent heat treatment. Results showed that significant austenite-to-martensite transformation in the FeCoCr powders was achieved during ball milling, along with the increase in shape anisotropy from spherical to flaky. The saturation magnetization followed parabolic kinetics during ball milling and rose from 1.43 to 109.92 emu/g after milling for 4 h, while it exhibited a rapid increase to 181.58 emu/g after subsequent heat treatment at 500 °C. A considerable increase in complex permeability and hence magnetic loss capability was obtained. With appropriate modulation of complex permittivity, the resultant absorbents showed a reflection loss of below −6 dB over 8~18 GHz at thickness of 1 mm and superior stability at 300 °C. Our strategy can broaden the material selection for microwave absorbents by involving Fe-based austenite alloys and simply recover the ferromagnetism of industrial products made without proper control of the crystalline phase. Full article
(This article belongs to the Special Issue Advances in Stimuli-Responsive Nanomaterials)
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16 pages, 5878 KiB  
Article
Preparation and Characterization of Carvacrol-Loaded Caseinate/Zein-Composite Nanoparticles Using the Anti-Solvent Precipitation Method
by Huaming Zheng, Jiangli Wang, Yiqiang Zhang, Quanwei Xv, Qiaohui Zeng and Jingjing Wang
Nanomaterials 2022, 12(13), 2189; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12132189 - 25 Jun 2022
Cited by 11 | Viewed by 1976
Abstract
Extending shelf life and maintaining the high quality of food are arduous challenges. In this study, the self-assembly properties of zein were used to load carvacrol essential oil, and then sodium caseinate was selected as a stabilizer to fabricate carvacrol-loaded composite nanoparticles. The [...] Read more.
Extending shelf life and maintaining the high quality of food are arduous challenges. In this study, the self-assembly properties of zein were used to load carvacrol essential oil, and then sodium caseinate was selected as a stabilizer to fabricate carvacrol-loaded composite nanoparticles. The results showed that the composite nanoparticles had a high encapsulation efficiency for carvacrol (71.52–80.09%). Scanning electron microscopy (SEM) indicated that the carvacrol-loaded composite nanoparticles were spherical and uniformly distributed, with particle sizes ranging from 80 to 220 nm. First and foremost, the carvacrol-loaded nanoparticles exhibited excellent water-redispersibility, storage-stability, and antioxidant properties, as well as antibacterial properties against Staphylococcus aureus and Escherichia coli. Benefiting from the antimicrobial and antioxidative abilities, the films with carvacrol-loaded composite nanoparticles effectively inhibited food spoilage and prolonged the shelf-life of cherry tomatoes and bananas. Therefore, carvacrol-loaded composite nanoparticles may have potential application prospects in the food industry. Full article
(This article belongs to the Special Issue Advances in Stimuli-Responsive Nanomaterials)
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8 pages, 1965 KiB  
Article
Liquid-Metal-Mediated Electrocatalyst Support Engineering toward Enhanced Water Oxidation Reaction
by Guyue Bo, Peng Li, Yameng Fan, Qiang Zhu, Linlin Xia, Yi Du, Shi Xue Dou and Xun Xu
Nanomaterials 2022, 12(13), 2153; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12132153 - 23 Jun 2022
Cited by 1 | Viewed by 1468
Abstract
Functional and robust catalyst supports are vital in the catalysis field, and the development of universal and efficient catalyst support is essential but challenging. Traditional catalyst fabrication methods include the carbonization of ordered templates and high−temperature dehydration. All these methods involve complicated meso−structural [...] Read more.
Functional and robust catalyst supports are vital in the catalysis field, and the development of universal and efficient catalyst support is essential but challenging. Traditional catalyst fabrication methods include the carbonization of ordered templates and high−temperature dehydration. All these methods involve complicated meso−structural disordering and allow little control over morphology. To this end, a eutectic GaInSn alloy (EGaInSn) was proposed and employed as an intermediate to fabricate low−dimensional ordered catalyst support materials. Owing to the lower Gibbs free energy of Ga2O3 compared to certain types of metals (e.g., Al, Mn, Ce, etc.), we found that a skinny layer of metal oxides could be formed and exfoliated into a two−dimensional nanosheet at the interface of liquid metal (LM) and water. As such, EGaInSn was herein employed as a reaction matrix to synthesize a range of two−dimensional catalyst supports with large specific surface areas and structural stability. As a proof−of-concept, Al2O3 and MnO were fabricated with the assistance of LM and were used as catalyst supports for loading Ru, demonstrating enhanced structural stability and overall electrocatalytic performance in the oxygen evolution reaction. This work opens an avenue for the development of functional support materials mediated by LM, which would play a substantial role in electrocatalytic reactions and beyond. Full article
(This article belongs to the Special Issue Advances in Stimuli-Responsive Nanomaterials)
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14 pages, 5643 KiB  
Article
An Ultrathin Tunable Metamaterial Absorber for Lower Microwave Band Based on Magnetic Nanomaterial
by Jing Ning, Ke Chen, Wenbo Zhao, Junming Zhao, Tian Jiang and Yijun Feng
Nanomaterials 2022, 12(13), 2135; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12132135 - 21 Jun 2022
Cited by 16 | Viewed by 1906
Abstract
At frequencies below 1 GHz, conventional microwave absorbers are limited by their large thickness or narrow absorption bandwidth; therefore, new techniques for efficient absorption for the lower microwave band are highly demanded. Here, we propose and fabricate an ultrathin tunable metamaterial absorber combining [...] Read more.
At frequencies below 1 GHz, conventional microwave absorbers are limited by their large thickness or narrow absorption bandwidth; therefore, new techniques for efficient absorption for the lower microwave band are highly demanded. Here, we propose and fabricate an ultrathin tunable metamaterial absorber combining magnetic nanomaterials and metamaterial resonant structures for use in the lower microwave band (P band). The proposed absorber utilizes electrically controlled varactors to enable frequency tunability and magnetic nanomaterials as dielectric slabs for thickness reduction and bandwidth expansion at low frequencies. By adjusting the bias voltages of varactors, the resonant behavior of the absorbing structure can be dynamically tuned that covers a continuously tunable absorbing band from 0.41 to 1.02 GHz (85.3% in fractional bandwidth) with at least 10 dB reflection reduction. The total thickness of this absorber is 5 mm, which is only about 1/146 the wavelength of the lowest frequency. The agreement between the simulated and measured results validates the proposed design, and the structure has good angular stability that may be used as complex targets for low-RCS applications. Full article
(This article belongs to the Special Issue Advances in Stimuli-Responsive Nanomaterials)
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14 pages, 3070 KiB  
Article
Self-Adaptive Flask-like Nanomotors Based on Fe3O4 Nanoparticles to a Physiological pH
by Tianyu Gao, Jinwei Lin, Leilei Xu and Jianguo Guan
Nanomaterials 2022, 12(12), 2049; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12122049 - 15 Jun 2022
Cited by 7 | Viewed by 1920
Abstract
In living bodies, pH values, which are precisely regulated and closely associated with diseased cells, can act as an efficient biologically intrinsic indicator for future intelligent biomedicine microsystems. In this work, we have developed flask-like carbonaceous nanomotors (FCNMs), via loading Fe3O [...] Read more.
In living bodies, pH values, which are precisely regulated and closely associated with diseased cells, can act as an efficient biologically intrinsic indicator for future intelligent biomedicine microsystems. In this work, we have developed flask-like carbonaceous nanomotors (FCNMs), via loading Fe3O4 nanoparticles (NPs) into a cavity, which exhibit a self-adaptive feature to a specific physiological pH by virtue of the pH-dependent dual enzyme-like activities of Fe3O4 NPs. Specifically, the peroxidase-like activity of Fe3O4 NPs in an acidic pH range, and the catalase-like activity in a near neutral and alkaline pH range, determine the products in the motion system (•OH, ions and O2), whose diffusions from the inner to the outside of the flask result in fluid movement providing the driving force for the movement of the FCNMs. Correspondingly, changes of the product concentrations and species in the physiological pH range (4.4–7.4) result, firstly, in velocity decrease and, then, with increase in pH, increase of the FCNMs occurs. Thanks to the non-linear velocity responsiveness, the FCNMs show intriguing pH taxis towards 6.8 (generally corresponding to the physiological pH in tumor microenvironments), where a maximum velocity appears. Furthermore, the superparamagnetic feature of the Fe3O4 NPs simultaneously endows the FCNMs with the abilities to be magnetic-oriented and easily separated. This work could significantly increase the possibility of nanomotors for targeted therapy of tumors and next-generation biotechnological applications. Full article
(This article belongs to the Special Issue Advances in Stimuli-Responsive Nanomaterials)
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12 pages, 2268 KiB  
Article
Heterogeneous Thermochromic Hydrogel Film Based on Photonic Nanochains
by Hexuan Yan, Luying Si, Gang Li, Lejian Zhao, Wei Luo, Huiru Ma and Jianguo Guan
Nanomaterials 2022, 12(11), 1867; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12111867 - 30 May 2022
Cited by 3 | Viewed by 1876
Abstract
The rapid and robust response to external stimulus with a large volume deformation is of huge importance for the practical application of thermo-responsive photonic crystal film (TRPCF) in actuators, colorimetric sensors, and other color-related fields. Generally, decreasing the size of thermo-responsive photonic crystals [...] Read more.
The rapid and robust response to external stimulus with a large volume deformation is of huge importance for the practical application of thermo-responsive photonic crystal film (TRPCF) in actuators, colorimetric sensors, and other color-related fields. Generally, decreasing the size of thermo-responsive photonic crystals and introducing micropores are considered to be two effective approaches to improve their responsiveness. However, they usually result in a poor mechanical property, which leads to optical instability. To solve these problems, a heterogeneous thermo-responsive photonic crystal film was developed here by integrating a thermosensitive hydrogel matrix poly(N-isopropylacrylamide-co-N-methylolacrylamide) (P(NIPAM-co-NHMA)) with high-modulus, but non-thermosensitive poly(acrylic acid -co-2-hydroxyethyl methacrylate (P(AA-co-HEMA)) hydrogel-based photonic nanochains (PNCs). The as-obtained TRPCF based on PNCs (TRPCF-PNC) well combined the rapid response and improved the mechanical property. Typically, it can complete a response within 12 s from 26 to 44 °C, which was accompanied by a larger deformation of the matrix than that of the PNCs. The unique rapid thermochromic mechanism of the TRPCF-PNC is revealed here. Furthermore, it exhibits a high tensible property along the PNC-orientation direction and excellent optical stability. The response time of the TRPCF-PNC can conveniently modulate by changing the cross-linking degree of the PNCs or the content of the thermosensitive component in the matrix. The heterogeneous TRPCF-PNC is believed to have potential applications in artificial muscle and quick-response actuation devices. Full article
(This article belongs to the Special Issue Advances in Stimuli-Responsive Nanomaterials)
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13 pages, 3827 KiB  
Article
Bifunctional Single-Atom Cobalt Electrocatalysts with Dense Active Sites Prepared via a Silica Xerogel Strategy for Rechargeable Zinc–Air Batteries
by Lijuan Wang, Zixiang Xu, Tingyu Peng, Maosong Liu, Long Zhang and Jianming Zhang
Nanomaterials 2022, 12(3), 381; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12030381 - 24 Jan 2022
Cited by 15 | Viewed by 2789
Abstract
The N-doped cobalt-based (Co) bifunctional single atom catalyst (SAC) has emerged as one of the most promising candidates to substitute noble metal-based catalysts for highly efficient bifunctionality. Herein, a facile silica xerogel strategy is elaborately designed to synthesize uniformly dispersed and dense Co-N [...] Read more.
The N-doped cobalt-based (Co) bifunctional single atom catalyst (SAC) has emerged as one of the most promising candidates to substitute noble metal-based catalysts for highly efficient bifunctionality. Herein, a facile silica xerogel strategy is elaborately designed to synthesize uniformly dispersed and dense Co-Nx active sites on N-doped highly porous carbon networks (Co-N-C SAC) using economic biomass materials. This strategy promotes the generation of massive mesopores and micropores for substantially improving the formation of Co-Nx moieties and unique network architecture. The Co-N-C SAC electrocatalysts exhibit an excellent bifunctional activity with a potential gap (ΔE) of 0.81 V in alkaline medias, outperforming those of the most highly active bifunctional electrocatalysts. On top of that, Co-N-C SAC also possesses outstanding performance in ZABs with superior power density/specific capacity. This proposed synthetic method will provide a new inspiration for fabricating various high-content SACs for varied applications. Full article
(This article belongs to the Special Issue Advances in Stimuli-Responsive Nanomaterials)
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13 pages, 9273 KiB  
Article
Droplet-Based Microfluidic Preparation of Shape-Variable Alginate Hydrogel Magnetic Micromotors
by Cheng Zhang, Yong Wang, Yuduo Chen, Xing Ma and Wenjun Chen
Nanomaterials 2022, 12(1), 115; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12010115 - 30 Dec 2021
Cited by 4 | Viewed by 2264
Abstract
This article introduces a facile droplet-based microfluidic method for the preparation of Fe3O4-incorporated alginate hydrogel magnetic micromotors with variable shapes. By using droplet-based microfluidics and water diffusion, monodisperse (quasi-)spherical microparticles of sodium alginate and Fe3O4 (Na-Alg/Fe [...] Read more.
This article introduces a facile droplet-based microfluidic method for the preparation of Fe3O4-incorporated alginate hydrogel magnetic micromotors with variable shapes. By using droplet-based microfluidics and water diffusion, monodisperse (quasi-)spherical microparticles of sodium alginate and Fe3O4 (Na-Alg/Fe3O4) are obtained. The diameter varies from 31.9 to 102.7 µm with the initial concentration of Na-Alginate in dispersed fluid ranging from 0.09 to 9 mg/mL. Calcium chloride (CaCl2) is used for gelation, immediately transforming Na-Alg/Fe3O4 microparticles into Ca-Alginate hydrogel microparticles incorporating Fe3O4 nanoparticles, i.e., Ca-Alg/Fe3O4 micromotors. Spherical, droplet-like, and worm-like shapes are yielded depending on the concentration of CaCl2, which is explained by crosslinking and anisotropic swelling during the gelation. The locomotion of Ca-Alg/Fe3O4 micromotors is activated by applying external magnetic fields. Under the rotating magnetic field (5 mT, 1–15 Hz), spherical Ca-Alg/Fe3O4 micromotors exhibit an average advancing velocity up to 158.2 ± 8.6 µm/s, whereas worm-like Ca-Alg/Fe3O4 micromotors could be rotated for potential advancing. Under the magnetic field gradient (3 T/m), droplet-like Ca-Alg/Fe3O4 micromotors are pulled forward with the average velocity of 70.7 ± 2.8 µm/s. This article provides an inspiring and timesaving approach for the preparation of shape-variable hydrogel micromotors without using complex patterns or sophisticated facilities, which holds potential for biomedical applications such as targeted drug delivery. Full article
(This article belongs to the Special Issue Advances in Stimuli-Responsive Nanomaterials)
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11 pages, 2799 KiB  
Article
Two-Channel VO2 Memory Meta-Device for Terahertz Waves
by Xueguang Lu, Bowen Dong, Hongfu Zhu, Qiwu Shi, Lu Tang, Yidan Su, Cheng Zhang, Wanxia Huang and Qiang Cheng
Nanomaterials 2021, 11(12), 3409; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11123409 - 16 Dec 2021
Cited by 10 | Viewed by 2522
Abstract
Vanadium oxide (VO2), as one of the classical strongly correlated oxides with a reversible and sharp insulator-metal transition (IMT), enables many applications in dynamic terahertz (THz) wave control. Recently, due to the inherent phase transition hysteresis feature, VO2 has shown [...] Read more.
Vanadium oxide (VO2), as one of the classical strongly correlated oxides with a reversible and sharp insulator-metal transition (IMT), enables many applications in dynamic terahertz (THz) wave control. Recently, due to the inherent phase transition hysteresis feature, VO2 has shown favorable application prospects in memory-related devices once combined with metamaterials or metasurfaces. However, to date, VO2-based memory meta-devices are usually in a single-channel read/write mode, which limits their storage capacity and speed. In this paper, we propose a reconfigurable meta-memory based on VO2, which favors a two-channel read/write mode. Our design consists of a pair of large and small split-ring resonators, and the corresponding VO2 patterns are embedded in the gap locations. By controlling the external power supply, the two operation bands can be controlled independently to achieve at least four amplitude states, including “00”, “01”, “10”, and “11”, which results in a two-channel storage function. In addition, our research may provide prospective applications in fields such as THz switching, photon storage, and THz communication systems in the future. Full article
(This article belongs to the Special Issue Advances in Stimuli-Responsive Nanomaterials)
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Review

Jump to: Research

26 pages, 3433 KiB  
Review
Dynamic and Active THz Graphene Metamaterial Devices
by Lan Wang, Ning An, Xusheng He, Xinfeng Zhang, Ao Zhu, Baicheng Yao and Yaxin Zhang
Nanomaterials 2022, 12(12), 2097; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12122097 - 17 Jun 2022
Cited by 14 | Viewed by 3177
Abstract
In recent years, terahertz waves have attracted significant attention for their promising applications. Due to a broadband optical response, an ultra-fast relaxation time, a high nonlinear coefficient of graphene, and the flexible and controllable physical characteristics of its meta-structure, graphene metamaterial has been [...] Read more.
In recent years, terahertz waves have attracted significant attention for their promising applications. Due to a broadband optical response, an ultra-fast relaxation time, a high nonlinear coefficient of graphene, and the flexible and controllable physical characteristics of its meta-structure, graphene metamaterial has been widely explored in interdisciplinary frontier research, especially in the technologically important terahertz (THz) frequency range. Here, graphene’s linear and nonlinear properties and typical applications of graphene metamaterial are reviewed. Specifically, the discussion focuses on applications in optically and electrically actuated terahertz amplitude, phase, and harmonic generation. The review concludes with a brief examination of potential prospects and trends in graphene metamaterial. Full article
(This article belongs to the Special Issue Advances in Stimuli-Responsive Nanomaterials)
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27 pages, 5561 KiB  
Review
Responsive Liquid Metal Droplets: From Bulk to Nano
by Minghui Duan, Xiyu Zhu, Xiaohui Shan, Hongzhang Wang, Sen Chen and Jing Liu
Nanomaterials 2022, 12(8), 1289; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12081289 - 10 Apr 2022
Cited by 6 | Viewed by 4292
Abstract
Droplets exist widely in nature and play an extremely important role in a broad variety of industrial processes. Typical droplets, including water and oil droplets, have received extensive attention and research, however their single properties still cannot meet diverse needs. Fortunately, liquid metal [...] Read more.
Droplets exist widely in nature and play an extremely important role in a broad variety of industrial processes. Typical droplets, including water and oil droplets, have received extensive attention and research, however their single properties still cannot meet diverse needs. Fortunately, liquid metal droplets emerging in recent years possess outstanding properties, including large surface tension, excellent electrical and thermal conductivity, convenient chemical processing, easy transition between liquid and solid phase state, and large-scale deformability, etc. More interestingly, liquid metal droplets with unique features can respond to external factors, including the electronic field, magnetic field, acoustic field, chemical field, temperature, and light, exhibiting extraordinary intelligent response characteristics. Their development over the past decade has brought substantial breakthroughs and progress. To better promote the advancement of this field, the present article is devoted to systematically summarizing and analyzing the recent fundamental progress of responsive liquid metal droplets, not only involving droplet characteristics and preparation methods, but also focusing on their diverse response behaviors and mechanisms. On this basis, the challenges and prospects related to the following development of liquid metal droplets are also proposed. In the future, responsive liquid metal droplets with a rapid development trend are expected to play a key role in soft robots, biomedicine, smart matter, and a variety of other fields. Full article
(This article belongs to the Special Issue Advances in Stimuli-Responsive Nanomaterials)
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