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Smart and Functional Elastomers, Hydrogels, and Ionogels

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A special issue of Polymers (ISSN 2073-4360).

Deadline for manuscript submissions: closed (31 October 2018) | Viewed by 52997

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Special Issue Editor

Prof. Dr. Hyun-Joong Chung

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Guest Editor

Department of Chemical and Materials Engineering, University of Alberta, 116 Street and 85 Avenue, Edmonton, AB T6G 2V4, Canada
Interests: soft materals; hydrogels; elastomers; bioelectronics; energy storage materials
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue focus on the current state-of-the-art of the fundamentals and applications of elastomers, hydrogels, and ionogels. These polymeric materials, either in dried or in swollen states, exhibit soft and resilient mechanical properties, often with great fracture toughness. Incorporation of functional groups or nanoparticles adds novel functionality or stimuli-responsiveness on top of their their unique mechanical properties, enabling a broad range of potential applications such as flexible or stretchable energy storage, biosensors and biomaterials, soft electronics, and many more.

Papers are sought that discuss the latest research in the area or summarize selected areas of the field. The scope of the Special Issue encompasses the synthesis, characterization, and application of elastomers and gels made of conjugated polymers, organic radical polymers, ion-conducting polymers, metal-containing polymers, or hybrid inorganic/organic motifs.

Of particular interests are on the structure-property relations of these polymeric materials, or on the novel chemistry routes to enable functionalities in these materials, or on their applications on energy and biomedical researches as a stepping stone to an interdisciplinary research.

Prof. Hyun-Joong Chung
Guest Editor

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. Polymers 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 2700 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

Elastomers
Hydrogels
Ionogels
Functional polymer
Smart materials
Electroactive polymer
Electroactive gels
Conjugated polymer
Polyelectrolyte
Metal-containing polymer
Composite
Energy storage
Batteries
Capacitors
Electrochemical transistors
Ion sensing transistors
Sensors

Published Papers (11 papers)

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Research

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18 pages, 3160 KiB

Open AccessArticle

Fabrication of Phosphate-Imprinted PNIPAM/SiO₂ Hybrid Particles and Their Phosphate Binding Property

by Zheng Cao, Yuyuan Chen, Dan Li, Junfeng Cheng and Chunlin Liu

Polymers 2019, 11(2), 253; https://doi.org/10.3390/polym11020253 - 02 Feb 2019

Cited by 9 | Viewed by 3996

Abstract

A SiO₂ microsphere imprinted by phosphate ions was prepared with the use of phosphate ion as the template molecule and tetraethoxysilane as the precursor. Thereafter, the imprinted SiO₂ microspheres were modified with 3-(trimethoxysilyl)propyl methacrylate (TMSPMA@SiO₂), followed by introducing the double bond. In the presence of TMSPMA@SiO₂, using N-isopropylacrylamide as monomer, and potassium persulfate as initiator, polymer/inorganic hybrid particles (PNIPAM/SiO₂) were prepared. Fourier transform infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption-desorption test, and transmission electron microscope were employed for the characterization of molecular imprinted SiO₂ microspheres and PNIPAM/SiO₂ hybrid particles. The effects of phosphate concentration, pH value, and adsorption temperature on the phosphate binding properties of PNIPAM/SiO₂ hybrid particles were studied by UV-vis spectrophotometer. The experimental results shed light on the fact that the PNIPAM structure is beneficial for the improvement of the adsorption ability of phosphate-imprinted SiO₂ microspheres. With the increase in the initial phosphate concentration, the adsorption capacity of hybrid particles to phosphate ions increased to 274 mg/g at pH = 7 and 15 °C. The acid condition and the temperature below the low critical solution temperature (LCST) of PNIPAM are favorable to the adsorption of phosphate ions by PNIPAM/SiO₂ hybrid particles, and the maximum adsorption capacity can reach 287 mg/g (at pH = 5 and 15 °C). The phosphate imprinted polymer/inorganic hybrid material is expected to be put to use in the fields of phosphate ions adsorption, separation, and recovery. Full article

(This article belongs to the Special Issue Smart and Functional Elastomers, Hydrogels, and Ionogels)

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13 pages, 2745 KiB

Open AccessArticle

Self-Healing Cellulose Nanocrystals-Containing Gels via Reshuffling of Thiuram Disulfide Bonds

by Wenyan Li, Shengchang Lu, Mengchan Zhao, Xinxing Lin, Min Zhang, He Xiao, Kai Liu, Liulian Huang, Lihui Chen, Xinhua Ouyang, Yonghao Ni and Hui Wu

Polymers 2018, 10(12), 1392; https://doi.org/10.3390/polym10121392 - 15 Dec 2018

Cited by 41 | Viewed by 5093

Abstract

Self-healing gels based on reshuffling disulfide bonds have attracted great attention due to their ability to restore structure and mechanical properties after damage. In this work, self-healing gels with different cellulose nanocrystals (CNC) contents were prepared by embedding the thiuram disulfide bonds into gels via polyaddition. By the reshuffling of thiuram disulfide bonds, the CNC-containing gels repair the crack and recover mechanical properties rapidly under visible light in air. The thiuram disulfide-functionalized gels with a CNC content of 2.2% are highly stretchable and can be stretched approximately 42.6 times of their original length. Our results provide useful approaches for the preparation of dynamic CNC-containing gels with implications in many related engineering applications. Full article

(This article belongs to the Special Issue Smart and Functional Elastomers, Hydrogels, and Ionogels)

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15 pages, 4988 KiB

Open AccessArticle

Optimizing the Energy Harvesting Cycle of a Dissipative Dielectric Elastomer Generator for Performance Improvement

by Peng Fan and Hualing Chen

Polymers 2018, 10(12), 1341; https://doi.org/10.3390/polym10121341 - 04 Dec 2018

Cited by 9 | Viewed by 2649

Abstract

This paper optimizes the energy harvesting cycle of dissipative dielectric elastomer generators (DEGs) to explore possible approaches for improving the energy harvesting performance. By utilizing the developed theoretical framework, the dissipative performance of the DEG with a constant voltage cycle is analyzed, which shows good agreement with the existing experimental data. On this basis, we design a novel energy harvesting cycle and a corresponding energy harvesting circuit in which a transfer capacitor is utilized to store the charge transferred from the DEG. Then, the energy conversion performance of the DEG with the novel energy harvesting cycle is investigated. The results indicate that both the energy density and conversion efficiency are improved by choosing a high voltage during the discharging process and that as the R-C time constant increases, the enhancement effect of the voltage increases and then approaches to the saturation. In addition, there is an optimal transfer capacitor that can maximize energy density or conversion efficiency, and the optimal transfer capacitor increases with the increase in the R-C time constant. These results and methods are expected to guide the optimal design and assessment of DEGs. Full article

(This article belongs to the Special Issue Smart and Functional Elastomers, Hydrogels, and Ionogels)

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15 pages, 2148 KiB

Open AccessArticle

Smart Shear-Thinning Hydrogels as Injectable Drug Delivery Systems

by Sadaf Samimi Gharaie, Seyed Mohammad Hossein Dabiri and Mohsen Akbari

Polymers 2018, 10(12), 1317; https://doi.org/10.3390/polym10121317 - 28 Nov 2018

Cited by 58 | Viewed by 7806

Abstract

In this study, we fabricated and characterized a smart shear-thinning hydrogel composed of gelatin and laponite for localized drug delivery. We added chitosan (Chi) and poly N-isopropylacrylamide-co-Acrylic acid (PNIPAM) particles to the shear-thinning gel to render it pH-responsive. The effects of total solid weight and the percentage of laponite in a solid mass on the rheological behavior and mechanical properties were investigated to obtain the optimum formulation. The nanocomposite gel and particles were characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), zeta potential, and dynamic light scattering techniques. Finally, release related experiment including degradability, swelling and Rhodamine B (Rd) release at various pH were performed. The results suggest that incorporation of silicate nanoplatelets in the gelatin led to the formation of the tunable porous composite, with a microstructure that was affected by introducing particles. Besides, the optimum formulation possessed shear-thinning properties with modified rheological and mechanical properties which preserved its mechanical properties while incubated in physiological conditions. The release related experiments showed that the shear-thinning materials offer pH-sensitive behavior so that the highest swelling ratio, degradation rate, and Rd release were obtained at pH 9.18. Therefore, this nanocomposite gel can be potentially used to develop pH-sensitive systems. Full article

(This article belongs to the Special Issue Smart and Functional Elastomers, Hydrogels, and Ionogels)

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9 pages, 2347 KiB

Open AccessArticle

Multifunctional Ionogels Incorporated with Lanthanide (Eu³⁺, Tb³⁺) Complexes Covalently Modified Multi-Walled Carbon Nanotubes

by Qiuping Li

Polymers 2018, 10(10), 1099; https://doi.org/10.3390/polym10101099 - 05 Oct 2018

Cited by 7 | Viewed by 3085

Abstract

Ionogels refer to an emerging composite material made from the confinement of ionic liquids within some specific cross-linked network matrices. They have potential applications in areas such as electrochemical and optical-electric materials. Incorporation of lanthanide (Eu³⁺, Tb³⁺) complexes covalently functionalized multi-walled carbon nanotubes (MWCNTs) in ionogels provide new ideas to design and synthesize novel luminescent hybrid materials that have excellent characteristics of luminescence and ionic conductivity. Here, the multifunctional ionogels were synthesized by confining an ionic liquid and the rare earth functionalized MWCNTs in the cross-linked polymethyl methacrylate (PMMA) networks, resulting in a novel optical/electric multifunctional hybrid material. The SEM images and digital photographs suggest that the lanthanide functionalized MWCNTs are evenly dispersed in the hybrid matrices, thus leading to a certain transparency bulky gel. The resulting ionogels exhibit certain viscosity and flexibility, and display an intense red/green emission under UV-light irradiation. The intrinsic conductibility of the embedded ionic liquids and carbon nanotubes in conjunction with the outstanding photoluminescent properties of lanthanide complexes makes the soft hybrid gels a material with great potential and valuable application in the field of optical-electric materials. Full article

(This article belongs to the Special Issue Smart and Functional Elastomers, Hydrogels, and Ionogels)

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12 pages, 4222 KiB

Open AccessArticle

High-Strength Nanocomposite Hydrogels with Swelling-Resistant and Anti-Dehydration Properties

by Bo Xu, Yuwei Liu, Lanlan Wang, Xiaodong Ge, Min Fu, Ping Wang and Qiang Wang

Polymers 2018, 10(9), 1025; https://doi.org/10.3390/polym10091025 - 14 Sep 2018

Cited by 24 | Viewed by 4954

Abstract

Hydrogels with excellent mechanical properties have potential for use in various fields. However, the swelling of hydrogels under water and the dehydration of hydrogels in air severely limits the practical applications of high-strength hydrogels due to the influence of air and water on the mechanical performance of hydrogels. In this study, we report on a kind of tough and strong nanocomposite hydrogels (NC-G gels) with both swelling-resistant and anti-dehydration properties via in situ free radical copolymerization of acrylic acid (AA) and N-vinyl-2-pyrrolidone (VP) in the water-glycerol bi-solvent solutions containing small amounts of alumina nanoparticles (Al₂O₃ NPs) as the inorganic cross-linking agents. The topotactic chelation reactions between Al₂O₃ NPs and polymer matrix are thought to contribute to the cross-linking structure, outstanding mechanical performance, and swelling-resistant property of NC-G gels, whereas the strong hydrogen bonds between water and glycerol endow them with anti-dehydration capacity. As a result, the NC-G gels could maintain mechanical properties comparable to other as-prepared high-strength hydrogels when utilized both under water and in air environments. Thus, this novel type of hydrogel would considerably enlarge the application range of hydrogel materials. Full article

(This article belongs to the Special Issue Smart and Functional Elastomers, Hydrogels, and Ionogels)

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18 pages, 3713 KiB

Open AccessArticle

Rhodamine-Functionalized Mechanochromic and Mechanofluorescent Hydrogels with Enhanced Mechanoresponsive Sensitivity

by Lijun Wang, Wanfu Zhou, Quan Tang, Haiyang Yang, Qiang Zhou and Xingyuan Zhang

Polymers 2018, 10(9), 994; https://doi.org/10.3390/polym10090994 - 06 Sep 2018

Cited by 32 | Viewed by 7617

Abstract

Smart materials responsible to external stimuli such as temperature, pH, solvents, light, redox agents, and mechanical or electric/magnetic field, have drawn considerable attention recently. Herein, we described a novel rhodamine (Rh) mechanophore-based mechanoresponsive micellar hydrogel with excellent mechanochromic and mechanofluorescent properties. We found with astonishment that, due to the favorable activation of rhodamine spirolactam in the presence of water, together with the stress concentration effect, the mechanoresponsive sensitivity of this hydrogel was enhanced significantly. As a result, the stress needed to trigger the mechanochromic property of Rh in the hydrogel was much lower than in its native polymer matrix reported before. The hydrogel based on Rh, therefore, exhibited excellent mechanochromic property even at lower stress. Moreover, due to the reversibility of color on/off, the hydrogel based on Rh could be used as a reusable and erasable material for color printing/writing. Of peculiar importance is that the hydrogel could emit highly bright fluorescence under sufficient stress or strain. This suggested that the stress/strain of hydrogel could be detected quantificationally and effectively by the fluorescence data. We also found that the hydrogel could respond to acid/alkali and exhibited outstanding properties of acidichromism and acidifluorochromism. Up to now, hydrogels with such excellent mechanochromic and mechanofluorescent properties have rarely been reported. Our efforts may be essentially beneficial to the design of the mechanochromic and mechanofluorescent hydrogels with enhanced mechanoresponsive sensitivity, fostering their potential applications in a number of fields such as damage or stress/strain detection. Full article

(This article belongs to the Special Issue Smart and Functional Elastomers, Hydrogels, and Ionogels)

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14 pages, 11721 KiB

Open AccessArticle

Thermosensitive Behavior and Super-Antibacterial Properties of Cotton Fabrics Modified with a Sercin-NIPAAm-AgNPs Interpenetrating Polymer Network Hydrogel

by Yifan Cui, Zijing Xing, Jun Yan, Yanhua Lu, Xiaoqing Xiong and Laijiu Zheng

Polymers 2018, 10(8), 818; https://doi.org/10.3390/polym10080818 - 25 Jul 2018

Cited by 14 | Viewed by 3533

Abstract

Poly(N-isopropylacrylamide) (PNIPAAm), sericin (SS), and silver nitrate were combined to prepare an interpenetrating network (IPN) hydrogel having dual functions of temperature sensitivity and antibacterial properties. The structure and size of AgNPs in such an IPN hydrogel were characterized by the Fourier Transform Infrared spectrum (FT-IR), X-ray powder diffraction (XRD) and Transmission Electron Microscope (TEM), and the thermal properties of the IPN hydrogel were characterized by Differential Scanning Calorimetry (DSC). Based on XRD patterns, Ag⁺ was successfully reduced to Ag⁰ by SS. It was observed by TEM that the particle size of silver particles was lower than 100 nm. The glass transition temperature (T_g) of IPN hydrogel was better than that of the PNIPAAm/AgNPs hydrogels, and lower critical solution temperature (LCST) values of the IPN hydrogel were obtained by DSC i.e. 31 °C. The thermal stability of the IPN hydrogel was successfully determined by the TGA. This IPN hydrogel was then used to modify the cotton fabrics by the “impregnation” method using glutaraldehyde (GA) as the cross-linking agent. The structures and properties of IPN hydrogel modified cotton fabric were characterized by scanning electron microscopy (SEM), FT-IR, and the thermogravimetry analysis (TGA). The results show that NIPAAm was successfully polymerized into PNIPAAm, and that there were neglected new groups in the hydrogel IPN. The IPN hydrogel was then successfully grafted onto cotton fabrics. SEM observations showed that the IPN hydrogel formed a membrane structure between the fibers, and improved the compactness of the fibers. At the temperature close to LCST (≈31 °C), the entire system was easily able to absorb water molecules. However, the hydrophilicity tended to decrease when the temperature was higher or lower than the LCST. The antibacterial rates of the modified cotton fabric against S. aureus and E. coli were as high as 99%. Full article

(This article belongs to the Special Issue Smart and Functional Elastomers, Hydrogels, and Ionogels)

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13 pages, 3678 KiB

Open AccessArticle

High Performance Clean Fracturing Fluid Using a New Tri-Cationic Surfactant

by Jinzhou Zhao, Jinming Fan, Jincheng Mao, Xiaojiang Yang, Heng Zhang and Wenlong Zhang

Polymers 2018, 10(5), 535; https://doi.org/10.3390/polym10050535 - 16 May 2018

Cited by 59 | Viewed by 4629

Abstract

In order to improve the heat resistance of current clean fracturing fluids, a novel cationic surfactant (VES-T), composed of three single-chains and a spacer group, was designed and synthesized as thickener for the fluids. Various performances of such VES-T fluid in the presence of NaSal were evaluated carefully. Study of the rheological properties demonstrated that the fluids with varying concentrations (3–5 wt %) of VES-T have excellent thermal stabilities under ultra-high temperatures ranging from 140 to 180 °C. Until now, this is the highest temperature that the VES fracturing fluid could bear. The VES-T/NaSal fluid exhibited good viscoelasticity and proppant-suspending capability, which was attributed to the three-dimensional network formed by entangled wormlike micelles. Furthermore, the VES fracturing fluids can be completely gel broken by standard brines within 2 h. Thus, the VES-T synthesized in this work has a good prospect for utilization during the development of ultra-high temperature reservoirs. Full article

(This article belongs to the Special Issue Smart and Functional Elastomers, Hydrogels, and Ionogels)

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16 pages, 11297 KiB

Open AccessArticle

Influence of Ethylene Glycol Methacrylate to the Hydration and Transition Behaviors of Thermo-Responsive Interpenetrating Polymeric Network Hydrogels

by Bing Li, Qi Zhong, Dapeng Li, Ke Xu, Lu Zhang and Jiping Wang

Polymers 2018, 10(2), 128; https://doi.org/10.3390/polym10020128 - 29 Jan 2018

Cited by 13 | Viewed by 4835

Abstract

The influence of ethylene glycol methacrylate (EGMA) to the hydration and transition behaviors of thermo-responsive interpenetrating polymeric network (IPN) hydrogels containing sodium alginate, N-isopropylacrylamide (NIPAAm), and EGMA were investigated. The molar ratios of NIPAAm and EGMA were varied from 20:0 to 19.5:0.5 and 18.5:1.5 in the thermo-responsive alginate-Ca²⁺/P(NIPAAm-co-EGMA) IPN hydrogels. Due to the more hydrophilicity and high flexibility of EGMA, the IPN hydrogels exhibited higher lower critical solution temperature (LCST) and lower glass transition temperature (T_g) when the ratio of EGMA increases. The swelling/deswelling kinetics of the IPN hydrogels could be controlled by adjusting the NIPAAm/EGMA molar ratio. A faster water uptake rate and a slower water loss rate could be realized by increase the amount of EGMA in the IPN hydrogel (the shrinking rate constant was decreased from 0.01207 to 0.01195 and 0.01055 with the changing of NIPAAm/EGMA ratio from 20:0, 19.5:0.5 to 18.5:1.5). By using 2-Isopropylthioxanthone (ITX) as a photo initiator, the obtained alginate-Ca²⁺/P(NIPAAm-co-EGMA₃₆₀) IPN hydrogels were successfully immobilized on cotton fabrics. The surface and cross section of the hydrogel were probed by scanning electron microscopy (SEM). They all exhibited a porous structure, and the pore size was increased with the amount of EGMA. Moreover, the LCST values of the fabric-grafted hydrogels were close to those of the pure IPN hydrogels. Their thermal sensitivity remained unchanged. The cotton fabrics grafted with hydrogel turned out to be much softer with the continuous increase of EGMA amount. Therefore, compared with alginate-Ca²⁺/PNIPAAm hydrogel, alginate-Ca²⁺/P(NIPAAm-co-EGMA₃₆₀) hydrogel is a more promising candidate for wound dressing in the field of biomedical textile. Full article

(This article belongs to the Special Issue Smart and Functional Elastomers, Hydrogels, and Ionogels)

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Review

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18 pages, 2564 KiB

Open AccessFeature PaperReview

Internal Status of Visibly Opaque Black Rubbers Investigated by Terahertz Polarization Spectroscopy: Fundamentals and Applications

by Makoto Okano and Shinichi Watanabe

Polymers 2019, 11(1), 9; https://doi.org/10.3390/polym11010009 - 21 Dec 2018

Cited by 11 | Viewed by 3564

Abstract

We discuss the internal status of rubber composites consisting of an insulating rubber matrix and conductive carbon black (CB) fillers (“black rubber”) using polarization-sensitive terahertz time-domain spectroscopy (THz-TDS). The black rubber composites under stretched conditions exhibit a large optical anisotropy or birefringence in the terahertz regime. From systematic studies, it is revealed that the large birefringence of black rubbers is due to the orientation distribution of anisotropically shaped CB aggregates in the rubber matrix and the orientation distribution is strongly linked to the mechanical deformation of the black rubber. A model simulation based on this relation between deformation and reorientation allows conversion of the birefringence (optical) information into strain (mechanical) information. In addition, the spectroscopic information obtained using the THz-TDS technique is useful to evaluate the changes in the internal conductive filler network caused by the mechanical deformation. Our findings demonstrate that the terahertz polarization spectroscopy is a promising nondestructive inspection method for contactless investigation of the internal condition of black rubber composites. Full article

(This article belongs to the Special Issue Smart and Functional Elastomers, Hydrogels, and Ionogels)

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