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Gels
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Gel Formation Processes and Materials for Functional Thin Films
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Gel Formation Processes and Materials for Functional Thin Films

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

Deadline for manuscript submissions: 20 May 2026 | Viewed by 3939

Special Issue Editors

Dr. Denitsa K. Elenkova

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Guest Editor
Faculty of Chemistry and Pharmacy, Sofia University, 1164 Sofia, Bulgaria
Interests: rare earth; lanthanoids; MOFs; sensors; luminescence; thin films; sol-gel; coating; gels
Dr. Katerina Lazarova

E-Mail Website
Guest Editor
Institute of Optical Materials and Technologies, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Interests: optical sensors; thin films; nanomaterials
Special Issues, Collections and Topics in MDPI journals
Dr. Joana Zaharieva

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Guest Editor
Faculty of Chemistry and Pharmacy, Sofia University, Sofia, Bulgaria
Interests: coordination chemistry; rare earth complexes; immobilization matrices; photoluminescence
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue on “Gel Formation Processes and Materials for Functional Thin Films” is dedicated to the gels applied for obtaining thin films, which have a variety of applications.

Gels are multi-component soft materials with long mechanical relaxation times that can be deformed with modest stresses. One of the main characteristics of gels is their ability to hold shape. Gelation is the transition of a liquid to a disordered solid via the formation of a network of chemical or physical bonds between the molecules or particles composing the liquid.

Gels are commonly used for a great deal of applications: sustained-release delivery systems, materials responsive to specific molecules (glucose or antigens used as biosensors), diapers, contact lenses, medical electrodes, water–gel explosives, breast implants, paints, coatings, adhesives, recyclable absorbents, bioreactors containing immobilized enzymes, bioassay systems, display devices, actuators, valves, sensors, artificial muscles for robotic devices, chemical memories, optical shutters, molecular separation systems and toys.

Sol–gel processing is a versatile technique that may be employed to create a wide range of materials based on biopolymers, such as glasses, ceramics, and coatings. It is considered an economical and straightforward method. Chemical tailoring of raw materials to produce new functional compositions is more feasible than conventional methods. The sol–gel process entails the chemical transformation of a sol (liquid) into a gel (solid). A polymer solution is formed into a thin film on a substrate using different methods, such dip coating, spin coating, or spray coating. After drying and heating, the coated substrate removes the solvent and promotes crosslinking of the polymer molecules; then, a solid film is formed. By changing the composition of the starting materials and processing conditions, the characteristics of the resulting materials based on polymers can be tailored.

Thin-film coatings have been explored extensively since films are well suited for studying the physical properties of materials and have many scientific, technological, and commercial applications. Among the numerous applications is optical coating, as films are known for their distinctive optical properties that can be applied in electronic devices, data communications, ultra-fast optical data storage, sensor materials, etc. Moreover, films are used as protect coatings with good thermal and electrical properties and high resistance to oxidation. Porous films are used in various fields because of their high surface area. They are used in solar cells and in many surface reactions as catalysis, sensors, and so on.

Since it is impossible to cover all aspects of gel formation processes, we are hoping that this Special Issue will stimulate new research and discoveries in this field.

Dr. Denitsa K. Elenkova
Dr. Katerina Lazarova
Dr. Joana Zaharieva
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. 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

  • sol–gel method
  • gels
  • thin films
  • deep coating
  • spin coating
  • film applications
  • membranes

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Published Papers (6 papers)

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Research

17 pages, 11740 KB  
Article
Structural Characterization of Ordered Mesoporous Silica Prepared by a Sol–Gel Process Using Urea-Based Cationic Gemini Surfactants
by Sarvarjon Kurbonov, Zsolt Czigány, Zoltán Kovács, László Péter, Martin Pisárčik, Miloš Lukáč, Manfred Kriechbaum, Vasyl Ryukhtin, Ana-Maria Lacrămă and László Almásy
Gels 2025, 11(10), 804; https://doi.org/10.3390/gels11100804 - 7 Oct 2025
Viewed by 298
Abstract
Mesoporous silica nanoparticles have been synthesized through sol–gel synthesis in basic conditions. Gemini surfactants having urea in the headgroups were used as pore-forming agents. The effect of the spacer length of the surfactant on the particle morphology was studied on the sub-micrometer and [...] Read more.
Mesoporous silica nanoparticles have been synthesized through sol–gel synthesis in basic conditions. Gemini surfactants having urea in the headgroups were used as pore-forming agents. The effect of the spacer length of the surfactant on the particle morphology was studied on the sub-micrometer and nanometer scales using nitrogen porosimetry, small-angle X-ray scattering (SAXS), ultra-small-angle neutron scattering, and scanning and transmission electron microscopy (SEM, TEM). Depending on the spacer, spherical and/or cylindrical nanoparticles formed in different proportions, as revealed by statistical analysis of SEM micrographs. All prepared materials showed the hexagonal pore structure characteristic of the MCM-41 molecular sieves, with the exception of the sample prepared using the gemini surfactant with the shortest spacer length. The influence of the spacer length on the lattice parameter of the pore network, as well as the average size of the ordered domains, has been assessed by SAXS and TEM. Detailed analysis of the TEM images revealed a spread of the lattice parameter in a range of 10–20%. The broadening of the diffraction peaks was shown to be due to the combination of the effects of the finite domain size and the variance of the lattice parameter across the crystalline domains. The structural differences between the silica gels synthesized with the different surfactants were related to the variation of the micelle morphologies, reported in previous light scattering and small-angle scattering experiments. No connection could be revealed between the micelle shape and size and the pore sizes, showing that surfactants with a broad range of spacer lengths can equally well be used for the preparation of MCM-41 materials. Full article
(This article belongs to the Special Issue Gel Formation Processes and Materials for Functional Thin Films)
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14 pages, 1801 KB  
Article
Constructive Neuroengineering of Axon Polarization Control Using Modifiable Agarose Gel Platforms for Neuronal Circuit Construction
by Soya Hagiwara, Kazuhiro Tsuneishi, Naoya Takada and Kenji Yasuda
Gels 2025, 11(8), 668; https://doi.org/10.3390/gels11080668 - 21 Aug 2025
Viewed by 410
Abstract
Axon polarization is a fundamental process in neuronal development, providing the structural basis for directional signaling in neural circuits. Precise control of axon specification is, thus, essential for the bottom-up construction of neuronal networks with defined architecture and connectivity. Although neurite length and [...] Read more.
Axon polarization is a fundamental process in neuronal development, providing the structural basis for directional signaling in neural circuits. Precise control of axon specification is, thus, essential for the bottom-up construction of neuronal networks with defined architecture and connectivity. Although neurite length and elongation timing have both been implicated as determinants of axonal fate, their relative contributions have remained unresolved due to technical limitations in manipulating these factors independently in conventional culture systems. Here, we developed a constructive neuroengineering platform based on modifiable agarose gel microstructures that enables dynamic, in situ control of neurite outgrowth length and timing during neuronal cultivation. This approach allowed us to directly address whether axon polarization depends primarily on neurite length or the order of neurite extension. Using a single-neurite elongation paradigm, we quantitatively defined two length thresholds for axon specification: a critical length of 43.3 μm, corresponding to a 50% probability of axonal differentiation, and a definitive length of 95.4 μm, beyond which axonal fate was reliably established. In experiments involving simultaneous or sequential elongation of two neurites, we observed that neurite length—not elongation order—consistently predicted axonal identity, even when a second neurite was introduced after the first had already begun to grow. The presence of a competing neurite modestly elevated the effective critical length, suggesting inhibitory interactions that modulate length thresholds. These findings provide the first direct experimental confirmation that neurite length is the primary determinant of axon polarization and demonstrate the utility of constructive microfabrication approaches for dissecting fundamental principles of neuronal polarity. Our platform establishes a powerful experimental foundation for future efforts to achieve complete control over axon and dendrite orientation during the engineered construction of functional neuronal circuits. Full article
(This article belongs to the Special Issue Gel Formation Processes and Materials for Functional Thin Films)
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16 pages, 2603 KB  
Article
Preparation of Uniform-Pore Ceramics from Highly Stable Emulsions via the Sol–Gel Method
by Alena Fedoročková, Dana Ivánová, Gabriel Sučik and Martina Kubovčíková
Gels 2025, 11(8), 638; https://doi.org/10.3390/gels11080638 - 12 Aug 2025
Viewed by 511
Abstract
A facile and cost-effective sol–gel method for the synthesis of uniformly porous alumina (Al2O3) was developed using stable CTAB/hexanol/water microemulsions as soft templates. The phase behavior of the ternary system was investigated to identify compositions that form kinetically stable [...] Read more.
A facile and cost-effective sol–gel method for the synthesis of uniformly porous alumina (Al2O3) was developed using stable CTAB/hexanol/water microemulsions as soft templates. The phase behavior of the ternary system was investigated to identify compositions that form kinetically stable microemulsions, with an optimal ratio of 7.5 wt.% CTAB, 5 wt.% hexanol, and 87.5 wt.% water exhibiting minimal droplet size variation over one week. Gelation was induced by partial neutralization to pH 4.2 with ammonium carbonate, promoting the formation of polynuclear Al species and enabling the uniform entrapment of hexanol droplets. Lyophilization preserved the porous network, and calcination at 500 °C yielded η-Al2O3 with a large specific surface area (~225 m2·g−1) and a narrow mesopore size distribution centered around 100 nm, consistent with the original droplet size. Mercury porosimetry and SEM analyses confirmed a highly porous, low-density material (0.75 g·cm−3) with an interconnected pore morphology. This scalable synthesis method, supported by the high kinetic stability of the microemulsion, provides sufficient processing time and eliminates the need for post-synthesis purification. It shows strong potential for producing advanced alumina materials for use in energy storage, catalysis, and sensor applications. Full article
(This article belongs to the Special Issue Gel Formation Processes and Materials for Functional Thin Films)
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15 pages, 5607 KB  
Article
Constructive Neuroengineering of Crossing Multi-Neurite Wiring Using Modifiable Agarose Gel Platforms
by Soya Hagiwara, Kazuhiro Tsuneishi, Naoya Takada and Kenji Yasuda
Gels 2025, 11(6), 419; https://doi.org/10.3390/gels11060419 - 30 May 2025
Cited by 1 | Viewed by 571
Abstract
Constructing stable and flexible neuronal networks with multi-neurite wiring is essential for the in vitro modeling of brain function, connectivity, and neuroplasticity. However, most existing neuroengineering platforms rely on static microfabrication techniques, which limit the ability to dynamically control circuit architecture during cultivation. [...] Read more.
Constructing stable and flexible neuronal networks with multi-neurite wiring is essential for the in vitro modeling of brain function, connectivity, and neuroplasticity. However, most existing neuroengineering platforms rely on static microfabrication techniques, which limit the ability to dynamically control circuit architecture during cultivation. In this study, we developed a modifiable agarose gel-based platform that enables real-time microstructure fabrication using an infrared (IR) laser system under live-cell conditions. This approach allows for the stepwise construction of directional neurite paths, including sequential microchannel formation, cell chamber fabrication, and controlled neurite–neurite crossings. To support long-term neuronal health and network integrity in agarose microstructures, we incorporated direct glial co-culture into the system. A comparative analysis showed that co-culture significantly enhanced neuronal adhesion, neurite outgrowth, and survival over several weeks. The feeder layer configuration provided localized trophic support while maintaining a clear separation between glial and neuronal populations. Dynamic wiring experiments further confirmed the platform’s precision and compatibility. Neurites extended through newly fabricated channels and crossed pre-existing neurites without morphological damage, even when laser fabrication occurred after initial outgrowth. Time-lapse imaging showed a temporary growth cone stalling at crossing points, followed by successful elongation in all tested samples. Furthermore, the direct laser irradiation of extending neurites during microstructure modification did not visibly impair neurite elongation, suggesting minimal morphological damage under the applied conditions. However, potential effects on molecular signaling and electrophysiological function remain to be evaluated in future studies. Together, these findings establish a powerful, flexible system for constructive neuroengineering. The platform supports long-term culture, real-time modification, and multidirectional wiring, offering new opportunities for studying neural development, synaptic integration, and regeneration in vitro. Full article
(This article belongs to the Special Issue Gel Formation Processes and Materials for Functional Thin Films)
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14 pages, 5969 KB  
Article
Si3N4 Nanoparticle Reinforced Si3N4 Nanofiber Aerogel for Thermal Insulation and Electromagnetic Wave Transmission
by Zongwei Tong, Xiangjie Yan, Yun Liu, Yali Zhao and Kexun Li
Gels 2025, 11(5), 324; https://doi.org/10.3390/gels11050324 - 26 Apr 2025
Cited by 1 | Viewed by 769
Abstract
Traditional nanoparticle aerogels suffer from inherent brittleness and thermal instability at elevated temperatures. In recent years, ceramic nanofiber aerogels, utilizing flexible nanofibers as structural units, have emerged as mechanically resilient alternatives with ultrahigh porosity (>90%). However, their thermal insulation capabilities are compromised by [...] Read more.
Traditional nanoparticle aerogels suffer from inherent brittleness and thermal instability at elevated temperatures. In recent years, ceramic nanofiber aerogels, utilizing flexible nanofibers as structural units, have emerged as mechanically resilient alternatives with ultrahigh porosity (>90%). However, their thermal insulation capabilities are compromised by micron-scale pores (10–100 μm) and overdependence on ultralow density, which exacerbates mechanical fragility. This study pioneers a gas-phase self-assembly strategy to fabricate Si3N4 nanoparticle reinforced Si3N4 nanofiber aerogels (SNP-R-SNFA) with gradient pore architectures. By leveraging methyltrimethoxysilane/vinyltriethoxysilane composite aerogel (MVa) as a reactive template, we achieved spontaneous growth of Si3N4 nanofiber films (SNP-R-SNF) featuring nanoparticle-fiber interpenetration and porosity gradients. The microstructure formation mechanism of SNP-R-SNF was analyzed using field-emission scanning electron microscopy. Layer assembly and hot-pressing composite technology were employed to prepare the SNP-R-SNFA, which showed low density (0.033 g/cm3), exceptional compression resilience, insensitive frequency dependence of dielectric properties (ε′ = 2.31–2.39, tan δ < 0.08 across 8–18 GHz). Infrared imaging displayed backside 893 °C cooler than front, demonstrating superior insulation performance. This study not only provides material solutions for integrated electromagnetic wave-transparent/thermal insulation applications but more importantly establishes an innovative paradigm for enhancing the mechanical robustness of nanofiber-based aerogels. Full article
(This article belongs to the Special Issue Gel Formation Processes and Materials for Functional Thin Films)
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15 pages, 3901 KB  
Article
Distributed Flexible Sensors Based on Supercapacitor Gel Materials
by Chenghong Zhang
Gels 2025, 11(2), 139; https://doi.org/10.3390/gels11020139 - 16 Feb 2025
Viewed by 736
Abstract
Gel material sensors are lightweight, have fast response speeds and low driving voltages, and have recently become a popular research topic worldwide in the bionics field. A sensing unit is formed by pressing two kinds of gel materials together: a positioning layer gel [...] Read more.
Gel material sensors are lightweight, have fast response speeds and low driving voltages, and have recently become a popular research topic worldwide in the bionics field. A sensing unit is formed by pressing two kinds of gel materials together: a positioning layer gel based on acrylamide and lithium chloride and a sensing layer gel based on the ionic liquid BMIMBF4. Based on a stress–strain experiment of the sensing layer gel, a constitutive relationship model of its hyperelastic mechanical properties was established, and the elastic modulus and Poisson’s ratio of the sensing layer material were deduced. The capacitive response of the ion‒gel shunt capacitor to loading was observed to prove its ability to act as a pressure sensor. Although the gel thickness differs, the capacitance and load pressure exhibit a linear relationship. The capacitance was measured via cyclic voltammetry using the equivalent plate capacitor model for the positioning layer gel. The capacitance range of the gel sensor of a certain size was obtained via the cyclic voltammetry integral formula, which provided parameters for circuit design. A plate capacitor model of the sensing layer gel and an open four-impedance branch parallel model of the positioning layer gel were established. Two confirmatory experiments were designed for the models: first, the relationship between the sensing layer force and capacitance was measured, and the function curve relationship was established via a black box model; second, the theoretical and measured points of the positioning layer were compared, and the error was analyzed and corrected. Full article
(This article belongs to the Special Issue Gel Formation Processes and Materials for Functional Thin Films)
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