ArticlePublisher preview available

Fractals, morphogenesis and triply periodic minimal surfaces in sol–gel-derived thin films

Authors:
Olga A. Shilova at Institute of Silicate Chemistry of Russian Academy of Science, Sain-Petersburg, Russia
Olga A. Shilova
  • Institute of Silicate Chemistry of Russian Academy of Science, Sain-Petersburg, Russia
Read publisher preview
Download citation
To read the full-text of this research, you can request a copy directly from the author.

Abstract and Figures

The paper briefly reports on a contemporary view of the fractal structure of tetraethoxysilane (TEOS)- derived sol–gel synthesis products including in the presence of inorganic dopants and organic modifiers (H3PO4, polyionene, i.e., a high molecular weight quaternary ammonium compound, and epoxy resin), relying on the author’s and literature data. Morphological features of thin film surfaces and the effect of additives of inorganic salts and acids (Co(NO3)2, Al(NO3)3, H3BO3, HNO3, and HCl) thereon were analysed. The influence of spin-coating conditions (temperature and relative humidity) was also investigated, as exemplified by borosilicate “spin-on glass” films. The major components of film-forming TEOS-derived sols (TEOS and H3BO3, TEOS and epoxy-resin) were considered as morphogens. Moreover, their contribution to the formation of 2D and 3D stable spatial structures that were close to Turing patterns according to their configuration was assayed. An opportunity of formation of triply periodic minimal surfaces in thin-layer structures in the result of self-organization of viscous epoxy-siloxane sols has been discussed. Self-organization phenomena that are inherent in sol–gel systems based on tetraethoxysilane (TEOS) including those modified with inorganic dopants and organic modifiers are illustrated in TEM-, optical-, and AFM-images of the thin films surface. Two main types of fractal organization (mass and surface fractals) of silicophosphate sols both unmodified and modified with an organic modifier (polyionene) are exemplified in TEM-images. The possibility of the formation of stable spatial structures similar in surface morphology to Turing patterns, including those of the biological objects (animal prints), is illustrated by optical images of the surface morphology of thin epoxy-siloxane films, both unmodified and modified with the additive of detonation nanodiamonds. The possibility of the formation of sol–gel composites close in topology to triply periodic minimal surfaces is illustrated in the AFM-image of an epoxy-siloxane film in comparison with the Spit-P surface model. Self-organization phenomena that are inherent in sol–gel systems based on tetraethoxysilane (TEOS) including those modified with inorganic dopants and organic modifiers are illustrated in TEM-, optical-, and AFM-images of the thin films surface. Two main types of fractal organization (mass and surface fractals) of silicophosphate sols both unmodified and modified with an organic modifier (polyionene) are exemplified in TEM-images. The possibility of the formation of stable spatial structures similar in surface morphology to Turing patterns, including those of the biological objects (animal prints), is illustrated by optical images of the surface morphology of thin epoxy-siloxane films, both unmodified and modified with the additive of detonation nanodiamonds. The possibility of the formation of sol–gel composites close in topology to triply periodic minimal surfaces is illustrated in the AFM-image of an epoxy-siloxane film in comparison with the Spit-P surface model. The TEOS- and dopants-derived sols are usually multilevel fractal objects of mass or surface type.Stable spatial structures of various configurations can form in thin TEOS-derived thin films.Turing patterns can form in thin films obtained by spin-coating from TEOS-derived sols including doped ones.Precursors of sol–gel synthesis (i.e., TEOS–H3BO3, TEOS–epoxy resin) can be considered as morphogens.Viscous epoxy-siloxane sols can form films with a structure close to triply periodic minimal surfaces. The TEOS- and dopants-derived sols are usually multilevel fractal objects of mass or surface type. Stable spatial structures of various configurations can form in thin TEOS-derived thin films. Turing patterns can form in thin films obtained by spin-coating from TEOS-derived sols including doped ones. Precursors of sol–gel synthesis (i.e., TEOS–H3BO3, TEOS–epoxy resin) can be considered as morphogens. Viscous epoxy-siloxane sols can form films with a structure close to triply periodic minimal surfaces.
Self-organization phenomena that are inherent in sol–gel systems based on tetraethoxysilane (TEOS) including those modified with inorganic dopants and organic modifiers are illustrated in TEM-, optical-, and AFM-images of the thin films surface. Two main types of fractal organization (mass and surface fractals) of silicophosphate sols both unmodified and modified with an organic modifier (polyionene) are exemplified in TEM-images. The possibility of the formation of stable spatial structures similar in surface morphology to Turing patterns, including those of the biological objects (animal prints), is illustrated by optical images of the surface morphology of thin epoxy-siloxane films, both unmodified and modified with the additive of detonation nanodiamonds. The possibility of the formation of sol–gel composites close in topology to triply periodic minimal surfaces is illustrated in the AFM-image of an epoxy-siloxane film in comparison with the Spit-P surface model.
Self-organization phenomena that are inherent in sol–gel systems based on tetraethoxysilane (TEOS) including those modified with inorganic dopants and organic modifiers are illustrated in TEM-, optical-, and AFM-images of the thin films surface. Two main types of fractal organization (mass and surface fractals) of silicophosphate sols both unmodified and modified with an organic modifier (polyionene) are exemplified in TEM-images. The possibility of the formation of stable spatial structures similar in surface morphology to Turing patterns, including those of the biological objects (animal prints), is illustrated by optical images of the surface morphology of thin epoxy-siloxane films, both unmodified and modified with the additive of detonation nanodiamonds. The possibility of the formation of sol–gel composites close in topology to triply periodic minimal surfaces is illustrated in the AFM-image of an epoxy-siloxane film in comparison with the Spit-P surface model.
… 
Left: Small-angle X-ray scattering (SAXS) intensity curves in double logarithmic coordinates: (1a) xerogel obtained using Si(OEt)4/H3PO4-based sol at a 1: 5 molar ratio; (2a) xerogel produced using this sol modified with polyionene (PI) additive, i.e., oligomeric quaternary ammonium compound with MM = 4000–7000 (8·10⁻⁴ mol/l of Si(OEt)4. The scattering data (circles) are properly described by the unified Beaucage function. Line segments with numbers above them indicate the slope of curves for each of three modes. Thin and dashed curves indicate contributions of the Guinier scattering at the first, second, or third structural levels. Right: TEM images of the same silicophosphate xerogels (1b and 1c) without PI additive and (2b) – with PI additive. On the insets: schematic images of systems according to the type of the mass fractal (1b), surface fractal (2b) and system with almost smooth surface (1c)
Left: Small-angle X-ray scattering (SAXS) intensity curves in double logarithmic coordinates: (1a) xerogel obtained using Si(OEt)4/H3PO4-based sol at a 1: 5 molar ratio; (2a) xerogel produced using this sol modified with polyionene (PI) additive, i.e., oligomeric quaternary ammonium compound with MM = 4000–7000 (8·10⁻⁴ mol/l of Si(OEt)4. The scattering data (circles) are properly described by the unified Beaucage function. Line segments with numbers above them indicate the slope of curves for each of three modes. Thin and dashed curves indicate contributions of the Guinier scattering at the first, second, or third structural levels. Right: TEM images of the same silicophosphate xerogels (1b and 1c) without PI additive and (2b) – with PI additive. On the insets: schematic images of systems according to the type of the mass fractal (1b), surface fractal (2b) and system with almost smooth surface (1c)
… 
Optical images of the surface of SiO2 thin films spin-coated from TEOS-derived sols in the following molar ratio of components: TEOS:EtOH:H2O:HNO3 = 105:105:1:2.5 (a) and 192:200:17:1 (b) (after: [14])
Optical images of the surface of SiO2 thin films spin-coated from TEOS-derived sols in the following molar ratio of components: TEOS:EtOH:H2O:HNO3 = 105:105:1:2.5 (a) and 192:200:17:1 (b) (after: [14])
… 
Optical images of labyrinth structures in: (a) a “spin-on glass” film composed of 40.4CoO·0.6Al2O3·59SiO2 wt. %; (b) thin-layer films coated with a sol on the based on TEOS and epoxy resin used in the same weight ratio; (c) AFM-images (phase contrast) of the surface of a Pt/Pd-containing “spin-on glass” film of the composition 20PtO2·10PdO·70SiO2 wt.%
Optical images of labyrinth structures in: (a) a “spin-on glass” film composed of 40.4CoO·0.6Al2O3·59SiO2 wt. %; (b) thin-layer films coated with a sol on the based on TEOS and epoxy resin used in the same weight ratio; (c) AFM-images (phase contrast) of the surface of a Pt/Pd-containing “spin-on glass” film of the composition 20PtO2·10PdO·70SiO2 wt.%
… 
Surface morphology of thin films derived from epoxy-siloxane sols: (a) without modifying agent and (b) with 0.2 wt.% of detonation nanodiamond, (c) a “dappled” pattern as resulting from a type a morphogen system
+2
Surface morphology of thin films derived from epoxy-siloxane sols: (a) without modifying agent and (b) with 0.2 wt.% of detonation nanodiamond, (c) a “dappled” pattern as resulting from a type a morphogen system
… 
Figures - available from: Journal of Sol-Gel Science and Technology
This content is subject to copyright. Terms and conditions apply.
A preview of this full-text is provided by Springer Nature.
Learn more
Content available from Journal of Sol-Gel Science and Technology
This content is subject to copyright. Terms and conditions apply.
Journal of Sol-Gel Science and Technology (2020) 95:599–608
https://doi.org/10.1007/s10971-020-05279-y
REVIEW PAPER: SOL-GEL, HYBRIDS AND SOLUTION CHEMISTRIES
Fractals, morphogenesis and triply periodic minimal surfaces
in sol–gel-derived thin films
Olga A. Shilova 1
Received: 30 November 2019 / Accepted: 29 February 2020 / Published online: 25 March 2020
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
The paper briefly reports on a contemporary view of the fractal structure of tetraethoxysilane (TEOS)- derived sol–gel
synthesis products including in the presence of inorganic dopants and organic modifiers (H3PO4, polyionene, i.e., a high
molecular weight quaternary ammonium compound, and epoxy resin), relying on the author’s and literature data.
Morphological features of thin film surfaces and the effect of additives of inorganic salts and acids (Co(NO3)2, Al(NO3)3,
H3BO3,HNO
3, and HCl) thereon were analysed. The influence of spin-coating conditions (temperature and relative
humidity) was also investigated, as exemplified by borosilicate “spin-on glass”films. The major components of film-forming
TEOS-derived sols (TEOS and H3BO3, TEOS and epoxy-resin) were considered as morphogens. Moreover, their
contribution to the formation of 2D and 3D stable spatial structures that were close to Turing patterns according to their
configuration was assayed. An opportunity of formation of triply periodic minimal surfaces in thin-layer structures in the
result of self-organization of viscous epoxy-siloxane sols has been discussed.
Graphical Abstract
Self-organization phenomena that are inherent in sol–gel systems based on tetraethoxysilane (TEOS) including those
modified with inorganic dopants and organic modifiers are illustrated in TEM-, optical-, and AFM-images of the thin films
surface. Two main types of fractal organization (mass and surface fractals) of silicophosphate sols both unmodified and
modified with an organic modifier (polyionene) are exemplified in TEM-images. The possibility of the formation of stable
spatial structures similar in surface morphology to Turing patterns, including those of the biological objects (animal prints),
is illustrated by optical images of the surface morphology of thin epoxy-siloxane films, both unmodified and modified with
the additive of detonation nanodiamonds. The possibility of the formation of sol–gel composites close in topology to triply
periodic minimal surfaces is illustrated in the AFM-image of an epoxy-siloxane film in comparison with the Spit-P
surface model.
*Olga A. Shilova
olgashilova@bk.ru
1Institute of Silicate Chemistry of the Russian Academy of
Sciences, St. Petersburg, Russia
1234567890();,:
1234567890();,:
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Exciting effects are observed in thin spin-on glass films (~100-250 nm) obtained from sols based on hydrolyzed tetraethoxysilane Si(OEt) 4 (TEOS) with a high boric acid content ((30-40)B 2 O 3 ⋅(70-60)SiO 2 wt %, based on dry residue) [6,7]. Patterns formed on the spin-on glass structure of borosilicate films obtained from silica sols with a high H 3 BO 3 concentration vary depending on H 3 BO 3 and TEOS concentrations, as well as on the film deposition conditions (temperature and humidity of the ambient air) and can be identified as Turing patterns [19]. In this respect, precursors of sol-gel synthesis can be considered as morphogens, one of which is a catalyst (H 3 BO 3 ), and another is an inhibitor (Si(OEt) 4 ). ...
... In this respect, precursors of sol-gel synthesis can be considered as morphogens, one of which is a catalyst (H 3 BO 3 ), and another is an inhibitor (Si(OEt) 4 ). Si−O−B bond forming, in this case, is unstable at room temperature and undergoes hydrolysis followed by a recovery [15,19]. The formation of stable Si−O−B covalent bonds commonly takes place during the transformation of organic compounds into inorganic substances at elevated temperatures [6,7]. ...
... Therefore, their structure cannot be characterized by conventional XRD techniques. For their study, small-angle X-ray scattering (SAXS) methods should be used [14,[19][20][21][22] to characterize the hierarchical aggregation structure of sol gelation products and determine the size and the type of fractal or non-fractal organization of the resulting aggregates, as well as estimate their density or surface development features. ...
Sol-Gel Synthesis and Structure of Nanocomposites Based on Tetraethoxysilane and Boron Compounds
Article
Full-text available
  • Dec 2021
  • GLASS PHYS CHEM+
The properties of sol-gel synthesis of borosilicate sols, wet gels and xerogels, as well as thin nano-sized films were studied. Physicochemical processes and phenomena accompanying sol-gel synthesis of borosilicate sols, gels, xerogels, and thin spin-on glass films were analyzed on the basis of reference data and our long-term experience. Particularly, the sol-gel synthesis of borosilicate materials with high boron concentration were described in detail. The morphology, mesostructures and chemical composition of sol-gel derived borosilicate composites with a high boron content (from 30 to 48 wt %, based on B 2 O 3) were studied using a number of complementary research methods (optical, scanning and transmission microscopy, small-angle X-ray scattering, and FTIR spectroscopy). The effect of sol composition (concentrations of Si(OEt) 4 and H 3 BO 3), ofthe addition of polyols (primarily glycerol), of the conditions for synthesis and of aging of target materials on their composition were studied, as well as the morphology and mesostructures of the composites .
View
... At the second stage, the same "flowers" are attached to six sides, and so on. That is, the main property of Nanomaterials 2024, 14, 1813 6 of 9 fractal aggregates is self-similarity [31][32][33]. Figure 5b shows a two-dimensional disordered aggregate, in which the cross morphology is formed from a cruciform structural element. ...
... At the second stage, the same "flowers" are attached to six sides, and so on. That is, the main property of fractal aggregates is self-similarity [31][32][33]. Figure 5b shows a two-dimensional disordered aggregate, in which the cross morphology is formed from a cruciform structural element. The addition of NH4OH significantly affects the structure of the films. ...
The Synthesis of Materials with a Hierarchical Structure Based on Tin Dioxide
Article
Full-text available
  • Nov 2024
This article presents the results of the formation of hierarchical micro–nano structures in nanostructured tin dioxide films obtained from the lyophilic film-forming system SnCl4/EtOH/NH4OH. The classification of the shape and size of the synthesized structures, in relation to the pH of the solution, is presented. Measurements were carried out on an X-ray diffractometer to study the crystal structure of the samples analyzed. It was found that SnO2 and NH4Cl crystallites participate in the formation of the synthesized hierarchical structures. It is shown that the mechanism of the formation of hierarchical structures depends on the amount of ammonium hydroxide added. This makes it possible to control the shape and size of the synthesized structures by changing the ratio of precursors.
View
... The development of dendritic structure is caused by a change in the acidity of film-forming systems due to the introduction of NH4F and NH4OH. Accelerated crystallization occurs from nonequilibrium conditions [46][47][48]. The introduction of NH4OH into the system not only leads to a change in acidity, but also adds functional OHions. ...
... The development of dendritic structure is caused by a change in the acidity of film-forming systems due to the introduction of NH 4 F and NH 4 OH. Accelerated crystallization occurs from nonequilibrium conditions [46][47][48]. The introduction of NH 4 OH into the system not only leads to a change in acidity, but also adds functional OH − ions. ...
The Influence of Lyophobicity and Lyophilicity of Film-Forming Systems on the Properties of Tin Oxide Films
Article
Full-text available
  • Nov 2023
In this work, the effects of lyophobicity and lyophilicity of film-forming systems on the properties of thin nanostructured films was studied. Systematic series of experiments were carried out with lyophilic film-forming systems: SnCl4/EtOH, SnCl4/EtOH/NH4F, SnCl4/EtOH/NH4OH and lyophobic systems: SnO2/EtOH and SnO2/EtOH/NH4F. Film growth mechanisms are determined depending on the type of film-forming system. The surface of the films was studied using a scanning electron microscope and an optical microscope. The spectrophotometric method is used to study the transmission spectra and the extinction coefficient. The surface resistance of the films was determined using the four-probe method. The quality factor and specific conductivity of the films are calculated. It was found that the addition of a fluorinating agent (NH4F) to a film-forming system containing SnO2 in the form of a dispersed phase does not lead to an increase in the specific conductivity of the films. X-ray diffraction analysis proved the incorporation of fluorine ions into the structure of the film obtained from the SnCl4/EtOH/NH4F system by the presence of SnOF2 peaks. In films obtained from SnO2/EtOH/NH4F systems, there are no SnOF2 peaks. In this case, ammonium fluoride crystallizes as a separate phase and decomposes into volatile compounds.
View
... The most common techniques that have been used for the fabrication of TPMS-based lattice structures are multiphoton lithography [14], 3D holographic lithography [15], templates and coating [16], sol-gel [17], and self-assembly [18]. However, the topological design of the minimal surfaces is extremely complex, and it is not easy to maintain accuracy while manufacturing using these methods. ...
... a(x, y, z) e [0, 1] is a monotonous sigmoid weight function. The Sigmoid function is a x, y, z ð Þ ¼ 1 1 þ e ÀkGðx, y, zÞ (17) G(x, y, z) ¼ 0 is the transition boundary which intersects the two TPMS morphologies, k > 0 is used to change the transition gradient; the larger value of k means more abrupt transition between two subsystems. This type of grading is called the hybridization of TPMS-based lattice structures. ...
Additively manufactured mechanical metamaterials based on triply periodic minimal surfaces: Performance, challenges, and application
Article
  • Aug 2021
  • MECH ADV MATER STRUC
Lattice structures with architecture based on triply periodic minimal surfaces (TPMS) have recently attracted much attention due to their mathematically controlled topologies, which give rise to predefined and fascinating mechanical properties. Such materials with topology-dependent properties are generally known as “metamaterials.” The research on the TPMS-based metamaterials was restricted to theoretical knowledge until the recent development of additive manufacturing technology (AM). Herein, the design, properties, challenges, and applications, of TPMS-based mechanical metamaterials are reviewed. This review provides the researcher with a collective resource of numerical and experimental data for the AM of TPMS-based structures.
View
... There is currently a transition taking place in materials science from traditional methods of obtaining layered and film nanostructures [1][2][3][4][5][6][7][8] to active atomic-molecular design and complicated architectonics [9][10][11][12][13], combining designs of several hierarchical [14][15][16][17][18][19][20][21] levels with specific functional properties. ...
... In the last several decades, a research area based on polycrystalline chalcogenides [22][23][24][25][26][27][28][29][30][31][32][33] and their solid solutions for IR photodetectors and emitters [21][22][23][24][25][26] has been successfully developing. The optimization of technological processes is accompanied by the sensitization of materials and the creation of protective oxide shells [28][29][30][31][32] consisting of different chemical compounds, namely PbOх, PbSeO3, bi-and tetra-oxyselenites and oxyselenates (2PbO•PbSeO3, 4PbO•PbSeO3) [29]. ...
The Architectonics Features of Heterostructures for IR Range Detectors Based on Polycrystalline Layers of Lead Chalcogenides
Article
Full-text available
  • Sep 2021
A model is developed for the formation of porous intragranular architectonics of nanostructured polycrystalline layers of lead chalcogenides for photodetectors and IR emitters. The layers are obtained under the conditions of thermal evaporation in a quasi-closed volume by the "hot wall" method followed by sensitizing heat treatment in an iodine-containing atmosphere. Model concepts are developed considering the experimental results of studying the intragranular structure of lead chalcogenides through original combined AFM methods over the cross-section of porous grains (cores) encapsulated by an oxide shell (lateral force microscopy and local tunneling I-V spectroscopy).
View
... One of the most important trends in modern materials science is the transition from traditional methods of obtaining layered and film nanostructures to an active atomicmolecular design combining several hierarchical levels [1][2][3][4]. Such structures, due to synergetic effects and developed interfaces, will have new unique properties. ...
Investigation of Surface Nanoclusters and Paramagnetic Centers of ZnO/Por-Si Structures as the Basis of Sensory Properties
Article
Full-text available
  • Nov 2023
The detection of particles with uncompensated charge and the determination of the features of their interaction during the formation of nanocrystals on substrates with a developed surface are an interesting area of research. The porous surface formed via the electrochemical etching of silicon acquired fractal properties as a result of the deposition of zinc oxide layers. Microscopy methods using different resolutions revealed a hierarchical structure of the surface, where each of the three consecutive levels contains uniformly distributed formations. The deposition of 20 layers of ZnO maximizes the concentration of nanocrystals at the pore boundaries, while the deposition of 25 layers leads to the formation of a continuous layer. The increase in photoluminescence intensity with an increase in the number of deposited layers is due to the saturation of surface nanostructures with electrons through several mechanisms. Electron paramagnetic resonance (EPR) studies have shown that the main mechanism of radiation recombination is the capture of electrons on oxygen vacancies. The different nature of the EPR saturation of the signal of interconnected paramagnetic centers revealed the formation of zinc oxide particles at the boundaries of pores with different sizes. The results of these studies of surface-active structures effectively complement the knowledge about sensory materials.
View
... As the interior structure of aggregates is expected to consist of a complex "fractal-like" micropores, the values of D f (see Table 1) were also extracted by scaling I(q) in the asymptotic regime of Fig. S3, those were 1.78, 2.18, 2.278 and 2.874 for K sol , AK sol , EK gel and EAK gel . We obtained mass fractal with 1 < D f < 3, which has been positively related to the compactness of the scatterer (Shilova, 2020) and thus the free volume in the scatterer can be interpreted, i.e., larger mass fractal indicates smaller volume of the micropore. The closely spaced hydroxyls in the hydrogen-bonded form would endow aggregates substructures with more continuous and better-connected domains. ...
Aggregation of konjac glucomannan by ethanol under low-alkali treatment
Article
Full-text available
  • Aug 2022
Utilizing ethanol in konjac glucomannan (KGM) gelation has important food processing applications. Typically, ethanol positively impacts the formation of low-alkali KGM gels and dramatically changes their physical properties, but the role of ethanol on the aggregation of KGM chains and the resultant gelation is less well understood. This study presents the distinct microstructures of low-alkali KGM gels incorporating ethanol. The fibril diameter and mesh size were determined to be 262.3±22.3 nm and 2.680±0.035 μm in average, contributing to a higher degree of anisotropy of such a gel network. Ethanol favors intermolecular aggregation by increasing the Rg of small-sized aggregates to 2.10 nm. The FTIR and temperature-cycled rheological studies suggest there are hydrophobic interactions stabilizing the gel network with the assistance of hydrogen bonds. The spatial confinement of deacetylated KGM chains as the solvent quality deteriorates by incorporating ethanol may arrange the aggregation and induce the structural reorganization in gel formation.
View
... The coagulation rate and the size of cluster structures depend on the catalyst concentration. The dominant mechanism for the formation of spatial structures is selforganization [25,26]. Along with the self-organization of particles formed in the film-forming system during maturation, the equilibrium in chemical reactions (5) shifts towards the formation of Sn(OH) 4 and NH 4 Cl. ...
The Effect of pH Solution in the Sol–Gel Process on the Structure and Properties of Thin SnO2 Films
Article
Full-text available
  • Jun 2022
The synthesis of surface-active structures is important for creating many applications. The structural formation of SnO2 thin films in the range from 1.4 to 1.53 pH is studied in this work. This process occurs on the surface of the sample in the range of 1.4 to 1.49 and in the volume in the range of 1.51 to 1.53. SnO2 is formed after annealing at 400 ∘C, according to XRD. Doping NH4OH to solution stimulates particle coagulation and gel formation. All of these have an impact on the transparency of samples investigated by spectrophotometric methods. By increasing the pH, the resistance raises at room temperature. The Eg calculation along the fundamental absorption edge shows that it is greater than 3.6 eV’ for SnO2 films. According to the Burstein–Moss effect, a change of the bandgap is related to the increased concentration of the free charge carriers. Elemental analysis has shown that chlorine ions are considered to be additional sources of charge carriers. The value pH = 1.49 is critical since there is a drastic change in the structure of the samples, the decrease in transparency is replaced by its increase, and the energy of activation of impurity levels is changed.
View
A pH‐Sensitive Stretchable Zwitterionic Hydrogel with Bipolar Thermoelectricity
Article
Full-text available
Amid growing interest in using body heat for electricity in wearables, creating stretchable devices poses a major challenge. Herein, a hydrogel composed of two core constituents, namely the negatively‐charged 2‐acrylamido‐2‐methylpropanesulfonic acid and the zwitterionic (ZI) sulfobetaine acrylamide, is engineered into a double‐network hydrogel. This results in a significant enhancement in mechanical properties, with tensile stress and strain of up to 470.3 kPa and 106.6%, respectively. Moreover, the ZI nature of the polymer enables the fabrication of a device with polar thermoelectric properties by modulating the pH. Thus, the ionic Seebeck coefficient (Si) of the ZI hydrogel ranges from −32.6 to 31.7 mV K⁻¹ as the pH is varied from 1 to 14, giving substantial figure of merit (ZTi) values of 3.8 and 3.6, respectively. Moreover, a prototype stretchable ionic thermoelectric supercapacitor incorporating the ZI hydrogel exhibits notable power densities of 1.8 and 0.9 mW m⁻² at pH 1 and 14, respectively. Thus, the present work paves the way for the utilization of pH‐sensitive, stretchable ZI hydrogels for thermoelectric applications, with a specific focus on harvesting low‐grade waste heat within the temperature range of 25–40 °C.
View
View
Bimetallic Pt/Pd nanoparticles in sol–gel-derived silica films and xerogels
Article
Full-text available
  • Nov 2019
  • J SOL-GEL SCI TECHN
This work is devoted to the study of the composition and structure of thin “spin-on glass” films and xerogels prepared from silica sols containing platinum and palladium compounds, both separately and together. The thickness and concentration distribution of Pt/Pd nanoparticles (NPs) in silica films depending on the concentration of precursors of platinum and palladium in silica sols were determined using the method of X-ray reflectometry. The composition and size of Pt/Pd nanoparticles formed in xerogels and thin films were determined in the nanometer and submicron ranges by means of atomic force and transmission electron microscopy of high resolution as well as by means of X-ray diffraction analysis. It was also determined that bimetallic Pt/Pd nanoparticles possess a common crystal lattice forming clusters with the structure of a mixed alloy type.
View
Modeling the process of formation of fractal structures in thin films
Article
Full-text available
  • Dec 2018
This paper presents the results of modeling the features of the formation of fractal structures in thin films of tin dioxide SnO2 obtained by the sol-gel method. The process of hydrolysis of tin tetrachloride SnCl4 leads to the formation of tin acid Sn(OH)4, which has a gel-like structure. Unstable tin acid decomposes to form water and tin dioxide. The formation of cluster structures is considered depending on the "competition" of these two processes. The nonlinear evolution of sol-gel stochastic processes leads to a fractal structure of the film clusters. The peculiarities of the formation of fractal clusters and the morphology of a thin film are estimated depending on the control (technological) parameters.
View
Fractal Features and Structural, Morphological, Optical Characteristics of Sol-Gel Derived Silica Nanoparticled Thin Films
Article
Full-text available
  • Oct 2018
Nanostructured silica films using a simple and effective sol-gel spin coating technique were synthesized and the influence of ammonia/sol ratios on the particle size and thickness of this film was investigated. In addition, fractal dimensions of the prepared films were determined using the scattering response technique. The samples were characterized by atomic force microscopy and UV-vis spectroscopy. Comparing optical method and image analysis of atomic force microscopy micrographs, the fractal dimension of silica nanoparticled thin films was determined. The fractal dimensions of the films verified by atomic force microscopy analysis were found to be around 2.03 which is very close to the values (2.0358, 2.0325, and 2.0335) obtained using optical method. As a result of these findings, precise determination of the nanoparticled silica thin films fractal dimension using both optical and surface analysis methods was realized.
View
Spontaneous formation of spiral-like patterns with distinct periodic physical properties by confined electrodeposition of Co-In disks
Article
Full-text available
  • Jul 2016
Spatio-temporal patterns are ubiquitous in different areas of materials science and biological systems. However, typically the motifs in these types of systems present a random distribution with many possible different structures. Herein, we demonstrate that controlled spatio-temporal patterns, with reproducible spiral-like shapes, can be obtained by electrodeposition of Co-In alloys inside a confined circular geometry (i.e., in disks that are commensurate with the typical size of the spatio-temporal features). These patterns are mainly of compositional nature, i.e., with virtually no topographic features. Interestingly, the local changes in composition lead to a periodic modulation of the physical (electric, magnetic and mechanical) properties. Namely, the Co-rich areas show higher saturation magnetization and electrical conductivity and are mechanically harder than the In-rich ones. Thus, this work reveals that confined electrodeposition of this binary system constitutes an effective procedure to attain template-free magnetic, electric and mechanical surface patterning with specific and reproducible shapes.
View
Processes of film-formation and crystallization in catalytically active ‘spin-on glass’ silica films containing Pt and Pd nanoparticles
Article
  • May 2019
  • J MOL LIQ
This research is devoted to the study of the composition and surface morphology of extremely thin ‘spin-on glass’ films (~20–50 nm) doped with Pt and Pd compounds in concentrations depending on the ratio of precursors in TEOS-derived sols, their aging time and heat treatment temperature. Such methods as spectrophotometry in visible and ultraviolet regions, atomic force and scanning microscopy, X-ray reflectometry, X-ray phase analysis and voltammetry were used to study processes of the formation of sols and films based on them. The authors of this study defined features of sol-gel processes based on acid hydrolysis of TEOS in presence of dopants (Pt and Pd compounds) taken separately and together. It was shown that the combination of two dopants (Pt and Pd compounds) taken in the mole ratio of 1:1 increases catalytic activity of the films towards hydrogen.
View
An Overview of Materials with Triply Periodic Minimal Surfaces and Related Geometry: From Biological Structures to Self-Assembled Systems
Article
Triply periodic minimal surface structures and related geometries are widely identified in many natural systems, such as biological membranes and biophotonic structures in butterfly-wing scales. Inspired by their marvelous and highly symmetrical structures and optimized physical properties, these structures have sparked immense interest for creating novel materials by extracting the design from nature. Significant progress has been made to understand these biological structures and fabricate artificial materials by top-down and bottom-up approaches for numerous applications in chemistry and materials science. Herein, research achievements, including theoretical and experimental discoveries, in both biological systems and the artificial synthesis of materials with triply periodic minimal surface structures and related materials are summarized. Recent developments in self-assembled lyotropic liquid crystal phases, block copolymer systems, and their inorganic replicas are discussed in detail.
View
Structural Features of Silica Coating Obtained from Sol Cooled to the Temperature of Liquid Nitrogen
Article
  • Aug 2017
A new approach to controlling the structure of silica films formed by the sol–gel method is proposed. The models of formation of the silica coatings, obtained from the sol, cooled to the liquid nitrogen temperature, have been developed. It was found that as a result of this process, one can obtain aggregates consisting of spindle-shaped nanoparticles with sizes of the order of tens of nanometers, formed during the preparation of sol. The proposed model predicts aggregate sizes that depend on the synthesis conditions. The results obtained can be useful for the preparation of films with controlled degree of nanocrystallite’s agglomeration.
View
Numerical study of three-dimensional Turing patterns using a meshless method based on moving Kriging element free Galerkin (EFG) approach
Article
  • Jun 2016
  • COMPUT MATH APPL
In this paper a numerical procedure is presented for solving a class of three-dimensional Turing system. First, we discrete the spatial direction using element free Galerkin (EFG) method based on the shape functions of moving Kriging interpolation. Then, to achieve a high-order accuracy, we use the fourth-order exponential time differencing Runge–Kutta (ETDRK4) method. Using this discretization for the temporal dimension, we obtain an explicit scheme and do not need to solve nonlinear system of equations. The EFG method uses a weak form of the considered equation that is similar to the finite element method with the difference that in the EFG method test and trial functions are moving least squares approximation (MLS) shape functions. Since the shape functions of moving least squares (MLS) approximation do not have Kronecker delta property, we cannot implement the essential boundary condition, directly. Also building shape functions of MLS approximation is a time consuming procedure. Because of the mentioned reasons we employ the shape functions of moving Kriging interpolation technique which have the mentioned property and less CPU time is required for building them. For testing this method on three-dimensional PDEs, we select some equations and system of PDEs such as Allen–Cahn, Gray–Scott, Ginzburg–Landau, Brusselator models, predator–prey model with additional food supply to predator. Several test problems are solved and numerical simulations are reported which confirm the efficiency of the proposed scheme.
View
Composition, structure, and morphology of the surface of nanodimensional platinum-containing films obtained from sols
Article
  • Jan 2016
This work is aimed at studying the composition, structure, and morphology of the surface of nanodimensional platinum-containing silica films synthesized according to the sol–gel technology. An analysis of the data of optical and atomic-force microscopy, X-ray reflectometry, and the method of the Rutherford backscattering made it possible to reveal the regularities of the effect of the synthesis conditions such as the concentration of the initial reagents, duration of sol ripening, and temperature of treatment on the structure and composition of the films.
View
The Physics and Chemistry of Sol-Gel Processing
Article
  • Jan 1990
Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing presents the physical and chemical principles of the sol-gel process. The book emphasizes the science behind sol-gel processing with a chapter devoted to applications. The first chapter introduces basic terminology, provides a brief historical sketch, and identifies some excellent texts for background reading. Chapters 2 and 3 discuss the mechanisms of hydrolysis and condensation for nonsilicate and silicate systems. Chapter 4 deals with stabilization and gelation of sols. Chapter 5 reviews theories of gelation and examines the predicted and observed changes in the properties of a sol in the vicinity of the gel point. Chapter 6 describes the changes in structure and properties that occur during aging of a gel in its pore liquor (or some other liquid). The discussion of drying is divided into two parts, with the theory concentrated in Chapter 7 and the phenomenology in Chapter 8. The structure of dried gels is explored in Chapter 9. Chapter 10 shows the possibility of using the gel as a substrate for chemical reactions or of modifying the bulk composition of the resulting ceramic by performing a surface reaction (such as nitridation) on the gel. Chapter 11 reviews the theory and practice of sintering, describing the mechanisms that govern densification of amorphous and crystalline materials, and showing the advantages of avoiding crystallization before sintering is complete. The properties of gel-derived and conventional ceramics are discussed in Chapter 12. The preparation of films is such an important aspect of sol-gel technology that the fundamentals of film formation are treated at length in Chapter 13. Films and other applications are briefly reviewed in Chapter 14. Materials scientists and researchers in the field of sol-gel processing will find the book invaluable.
View