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Gels
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Colorful Gels
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Colorful Gels

A special issue of Gels (ISSN 2310-2861). This special issue belongs to the section "Gel Chemistry and Physics".

Deadline for manuscript submissions: closed (31 January 2023) | Viewed by 13488

Special Issue Editor

Dr. Hang Zhang

E-Mail Website
Guest Editor
Department of Applied Physics, Aalto University, Espoo, Finland
Interests: hydrogels; self-assembly of nanoparticles; life-inspired soft materials

Special Issue Information

Dear Colleagues,

Color perception is one of the fundamental senses in biological systems. Insects use color to recognize flowers; birds can tell the difference between ripe and unripe fruits by their colors; and squid use skin patterns for camouflage. In artificial systems, color is also one of the most distinguishable properties of a material. For instance, many chemical reactions can be followed by color changes to determine the success of the reaction. In recent years, gels have also become increasingly colorful, both literally and metaphorically,  due to the implementation of novel mechanisms and structural designs to achieve intriguing functionalities. This ranges from structural colors, such as templating with photonic crystals or phase separation-induced broad-band scattering, to luminescent colors based on lanthanide, or dye-based colors using photo-switchable moieties, to name a few. The color can be dynamic, aiming for smart window or sensing applications, or static, to provide for example absorption of light for photothermal effects.

In view of the burgeoning progress on this topic, we call for papers on synthetic or biological gels that show any type of colors, to further contribute to this exciting field. Here color is broadly defined as non-transparent visual appearance. This includes, but is not limited to, the development of fabrication/synthesis approaches of macroscopic or microgels, novel functionalities and applications involving colors, and the study of wet biological tissues with colors. We hope this Special Issue will trigger further interest in colored gel systems and provide inspiration for more complex life-inspired functionalities involving colors.  

Dr. Hang Zhang
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. Gels is an international peer-reviewed open access monthly 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 2100 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

  • color
  • gel
  • structural colors
  • photo-switching
  • scattering
  • luminescence

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Published Papers (5 papers)

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Research

13 pages, 5902 KiB  
Article
Effect of Thermal Treatment on the Structure and Morphology of Vanadium Doped ZnO Nanostructures Obtained by Microwave Assisted Sol–Gel Method
by Cristina Maria Vlăduț, Oana-Cătălina Mocioiu, Silviu Preda, Jeanina Pandele-Cusu, Veronica Bratan, Roxana Trusca and Maria Zaharescu
Gels 2022, 8(12), 811; https://doi.org/10.3390/gels8120811 - 10 Dec 2022
Cited by 5 | Viewed by 1594
Abstract
In this paper, we conducted a fundamental study concerning the effect of thermal treatment on the structure and morphology of 2 mol% vanadium doped ZnO nanopowders obtained by microwave assisted sol–gel method (MW). The samples were analyzed by DTA, FTIR, XRD, SEM, and [...] Read more.
In this paper, we conducted a fundamental study concerning the effect of thermal treatment on the structure and morphology of 2 mol% vanadium doped ZnO nanopowders obtained by microwave assisted sol–gel method (MW). The samples were analyzed by DTA, FTIR, XRD, SEM, and UV–Vis spectroscopy. The DTA results showed that above 500 °C, there was no mass loss in the TG curves, and ZnO crystallization occurred. The XRD patterns of the thermally treated powders at 500 °C and 650 °C showed the crystallization of ZnO (zincite) belonging to the wurtzite-type structure. It was found that in the 650 °C thermally treated powder, aside from ZnO, traces of Zn3(VO4)2 existed. FTIR spectra of the annealed samples confirmed the formation of the ZnO crystalline phase and V–O bands. The micrographs revealed that the temperature influenced the morphology. The increase in the annealing temperature led to the grain growth. The SEM images of the MW powder thermally treated at 650 °C showed two types of grains: hexagonal grains and cylindrical nanorods. UV–Vis spectra showed that the absorption band also increased with the increasing temperature of thermal treatment. The MW sample annealed at 650 °C had the highest absorption in ultraviolet domain. Full article
(This article belongs to the Special Issue Colorful Gels)
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12 pages, 4355 KiB  
Article
The Influence of Gel Preparation and Thermal Treatment on the Optical Properties of SiO2-ZnO Powders Obtained by Sol–Gel Method
by Oana-Cătălina Mocioiu, Cristina Maria Vlăduț, Irina Atkinson, Veronica Brătan and Ana-Maria Mocioiu
Gels 2022, 8(8), 498; https://doi.org/10.3390/gels8080498 - 11 Aug 2022
Cited by 6 | Viewed by 1829
Abstract
The effect of gel preparation and heat treatment on the structural and optical properties of SiO2-ZnO materials prepared by the sol–gel method was investigated. Zinc acetate dehydrate, TEOS (tetraethylortosilicate), ethanol, distillated water and HCl were used as a starting material, solvent [...] Read more.
The effect of gel preparation and heat treatment on the structural and optical properties of SiO2-ZnO materials prepared by the sol–gel method was investigated. Zinc acetate dehydrate, TEOS (tetraethylortosilicate), ethanol, distillated water and HCl were used as a starting material, solvent and catalyst, respectively. Four powders (G1–G4) were prepared in different ways from the starting materials mentioned above. The method of adding Zn precursors during the synthesis differed from one another. For the G1 synthesis, only Zn acetate powder was employed; for the G2 synthesis, Zn acetate was dissolved in distilled water; and for the G3 synthesis, Zn acetate was dissolved in ethanol. When synthesizing G4, TEOS was added last, after Zn acetate had been combined with water and ethanol. The SiO2-ZnO materials were dried at 200 °C and then heat-treated at 700 °C and 900 °C. All samples were investigated by X-ray diffraction and infrared spectroscopy in order to investigate their structure. SEM measurements were performed to investigate the morphology of materials. Optical properties were influenced by gel preparation and heat treatments. A reflectance of over 60% was obtained for G3 and G4 powders, while for G1 and G2, the reflectance was below 30%. In conclusion, synthesis steps and heat treatment can control the structure and properties of the powders. Full article
(This article belongs to the Special Issue Colorful Gels)
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11 pages, 4847 KiB  
Communication
Concentration-Dependent Emission of Annealed Sol-Gel Layers Incorporated with Rhodamine 19 and 6G as the Route to Tunable High-Temperature Luminescent Materials
by Maria Zdończyk, Bartłomiej Potaniec, Marta Fiedot-Toboła, Tomasz Baraniecki and Joanna Cybińska
Gels 2022, 8(7), 408; https://doi.org/10.3390/gels8070408 - 28 Jun 2022
Cited by 1 | Viewed by 2129
Abstract
The sol-gel technology allows for the development of materials for nonlinear optics and photonics through the synthesis of multifunctional ceramic materials. Although the nature of the amorphous matrix allows the material to be doped with a large amount of the active components without [...] Read more.
The sol-gel technology allows for the development of materials for nonlinear optics and photonics through the synthesis of multifunctional ceramic materials. Although the nature of the amorphous matrix allows the material to be doped with a large amount of the active components without quenching, it may affect the spectroscopic characteristics of the dye (e.g., result in a shift of absorption and emission peaks with drying time, presumably with a change of concentration). This study presents the material (SiO2 impregnated with organic dyes—Rhodamine 6G and 19) with tunable emissions obtained by the authors upon annealing at different temperatures within the range of 100–300 °C. Possible observed effects were discussed based on spectroscopic properties and thermal studies of the synthesized material. Concerning annealing at different temperatures, an effect on concentration was observed. At the same time, a longer heating process at 300 °C revealed a protective function of sol-gel-derived silica for the organic dye; the longer heating did not cause any further significant changes in the dye’s emission, which indicates the preservative role of the sol-gel layers. Furthermore, etching tests of thin layers were conducted, resulting in smooth side edges of the waveguide. The tests have shown that it is possible to use dye-doped sol-gel layers as active components in photonics platforms. Full article
(This article belongs to the Special Issue Colorful Gels)
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15 pages, 7099 KiB  
Article
New Insights and Experimental Investigation of High-Temperature Gel Reinforced by Nano-SiO2
by Hongbin Guo, Jijiang Ge, Longjie Li, Guoliang Zhang, Ziwei Li, Wenhui Wang and Mingjia Liu
Gels 2022, 8(6), 362; https://doi.org/10.3390/gels8060362 - 8 Jun 2022
Cited by 5 | Viewed by 2073
Abstract
The properties of a reinforced gel with partially hydrolyzed polyacrylamide (HPAM) as the main agent, water-soluble phenolic resin (WSPR) as the crosslinker, and nano-SiO2 as the stabilizer were evaluated in terms of gelation time, gel strength and thermal stability under the conditions [...] Read more.
The properties of a reinforced gel with partially hydrolyzed polyacrylamide (HPAM) as the main agent, water-soluble phenolic resin (WSPR) as the crosslinker, and nano-SiO2 as the stabilizer were evaluated in terms of gelation time, gel strength and thermal stability under the conditions of 110 °C and 12.124 g/L salinity in water. The results showed that the gelation time of the gel with high strength was adjustable from 3 to 23 h, remaining stable for more than 180 days under stratigraphic conditions, although with a certain degree of early dehydration in the gel. Cryo-scanning electron microscopy (cryo-SEM) and dynamic light scattering (DLS) analysis revealed that nano-SiO2 improves the dispersion of the polymer in water, resulting in a more homogeneous structure of the formed gel and thus improving the strength of the gels. In addition, rheological tests and cryo-SEM showed that the interaction between nano-SiO2 and the polymer could inhibit the degradation of polymer to a certain extent and improve the thermal stability of the gel. However, the oxidative degradation of the gel is still the main cause of early dehydration of water-soluble phenolic resin gel, and the addition of a small amount of hydroquinone to the gelants can significantly improve the antioxidative degradation properties of phenolic resin gel. Full article
(This article belongs to the Special Issue Colorful Gels)
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14 pages, 3619 KiB  
Article
Syneresis Behavior of Polymer Gels Aged in Different Brines from Gelants
by Hongbin Guo, Jijiang Ge, Qianhui Wu, Ziyu He, Wei Wang and Guojuan Cao
Gels 2022, 8(3), 166; https://doi.org/10.3390/gels8030166 - 7 Mar 2022
Cited by 13 | Viewed by 5112
Abstract
Gel syneresis is a common problem in gel treatment for oil recovery applications. In this study, a stable gel was prepared in a soft brine by using a water-soluble phenolic resin as a crosslinker, nanoparticles as a stabilizer, and partially hydrolyzed polyacrylamide (HPAM) [...] Read more.
Gel syneresis is a common problem in gel treatment for oil recovery applications. In this study, a stable gel was prepared in a soft brine by using a water-soluble phenolic resin as a crosslinker, nanoparticles as a stabilizer, and partially hydrolyzed polyacrylamide (HPAM) or copolymers with different contents of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) groups as polymers. The syneresis behavior of the gels formed in a soft brine was evaluated upon aging in hard brines. The results show that when the salinity of the hard brine is lower than 30,000 mg/L, the gel expands, and its strength decreases; when the salinity of the hard brine is higher than 50,000 mg/L, the gel exhibits syneresis, and its strength increases. The effects of various influencing factors on the gel syneresis behavior were also evaluated. It was found that optimizing the polymer structure and adding nanoparticles can effectively overcome gel syneresis and enhance gel stability. Based on the research described in this paper, some proposals for designing salt-resistant polymer gels are presented. Full article
(This article belongs to the Special Issue Colorful Gels)
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