Tetraethoxysilane Content Research Articles

Physicochemical and structural characteristics of hybrid nanocomposites based on branched polyimide with a low content of inorganic component

The series of organic-inorganic hybrid nanocomposites based on branched polyimide matrix and with different amounts of tetraethoxysilane (TEOS) (5, 20, and 50 wt.% of the initial polyamic acid mass) were synthesized and studied using nitroxyl paramagnetic probe, measuring dielectric permittivity, X-ray structural analysis and optical microscopy. It was shown that in some cases the introduction of inorganic component is accompanied by a decrease in the segmental mobility of polyimide matrix as a result of the partial immobilization of organic macrochains during the formation of inorganic microregions. In the presence of inorganic component, a weak dependence of the polymer permeability on the content of the organic component in the system is observed, also the specific density changes little with an increase in TEOS content. Extreme changes in the segmental mobility and dielectric permittivity of the branched matrix formed in the presence of 5 wt% TEOS were found compared to systems of other compositions. This can be caused to a large extent by structural changes in the system. At a low content of TEOS occurs significant «loosening» of organic matrix, a sharp decrease in the dielectric constant and a significant increase in the segmental mobility of the polyimide matrix. Small angle X-ray scattering diffractograms demonstrate drastic changes in polyimide composite heterogeneity in the presence of 5 wt.% TEOS content. According to the optical microscopy data, the introduction of TEOS into polyimide is accompanied by the formation of microaggregates of inorganic nanoparticles in the system, the number and average size of which depend on the SiO2 content and looks most homogeneous at a low TEOS content.

Zwitterion-bearing silica sol for enhancing antifouling performance and mechanical strength of transparent PDMS coatings

The simultaneous improvement of mechanical strength and inhibition of slime attachment for polydimethylsiloxane(PDMS)-based fouling-release coatings remains as a great challenge. In this work, a zwitterionic precursor (N-methoxyacylethyl)-3-aminopropyltriethoxysilane (MAPS) was co-hydrolyzed with tetraethoxysilane (TEOS) to afford zwitterion-bearing silica sols (h-MAPS). The h-MAPS was then simply blended with hydroxyl-terminated PDMS (PDMS-OH, 3060 cSt and 20,000 cSt) to fabricate zwitterion-containing PDMS coatings. The pre-hydrolysis process, including hydrolysis time and TEOS content, is critical to the transparency of the coatings. High optical transparency in the range of 88.1–91.4 % at 550 nm could be reached using appropriate h-MAPS. Both PDMS-OH (3060 cSt)- and PDMS-OH (20,000 cSt)-based coatings presented excellent resistance to slime attachment in real marine environment at relatively high h-MAPS content. An improvement in anti-protein adsorption and anti-bacteria properties was achieved for the coatings based on PDMS-OH (3060 cSt) attributed to the presence of more zwitterions at its surface. Addition of h-MAPS could increase the elastic modulus and tensile strength of PDMS coatings, particularly with high efficiency for the later one. More importantly, although the tensile strength of zwitterion-containing PDMS coatings at high h-MAPS content could be up to 15 MPa, its pseudobarnacle removal strength was lower than 0.4 MPa even after seawater immersion, indicating it retained a good fouling-release performance. As a whole, zwitterion-bearing silica sols can not only provide a new approach for introduction of zwitterions into PDMS coatings, but also efficiently solve the multiple drawbacks of PDMS-based fouling-release coatings, simultaneously.

Improving the Corrosion Performance of Organically Coated Steel Using a Sol-Gel Overcoat.

Organically coated steels are widely used in applications in which they are subjected to the natural environment and therefore require excellent corrosion resistance. Organic clearcoats are typically employed as a barrier that improves the overall corrosion resistance; however, they are typically derived from fossil fuel-based feedstock. A more sustainable alternative could be possible using sol-gel coatings. The application of a simple tetraethoxysilane (TEOS)-based sol-gel was applied to polyurethane-coated steels using a spray coater. The concentration of TEOS was altered to produce coatings containing either 2.5% or 10%. The 10% TEOS resulted in dense, homogeneous coatings that offered a significant improvement in corrosion resistance compared to an uncoated substrate. Whereas the 2.5% TEOS coatings were inhomogeneous and porous, which indicated a limitation of concentration required to produce a uniform coating. The successful demonstration of using a simple TEOS-based coating to improve the corrosion resistance of organically coated steel highlights the potential for further investigation into the use of sol-gels for these applications.

Gold-silica plasmonic nanobones with tunable size and optical bimodality for bioimaging

Silica-coated gold nanotags were developed for multimodal Raman and fluorescent imaging. These nanotags, shaped like bones, offer significant absorption at 700 nm, aligning with the first window of tissue transparency. Gold nanobones were modified with cyanine 5.5 and 7 dyes and a silica shell for stability and biocompatibility via a modified Stober method involving tetraethoxysilane hydrolysis. Folic acid was attached on outer surface of nanotags to serve as a model delivery vector. The nanotags were characterized by dynamic light scattering, transmission electron microscopy, and spectroscopy. These methods showed that a thickness of the silica shell can be precisely controlled via a concentration of tetraethoxysilane. Surface-enhanced Raman scattering and emission spectra were registered and demonstrated the intensity dependent on the distance between the dye and core. Raman mapping of cell samples highlighted the nanotags bioimaging potential and revealed the partial nanotags agglomeration post-cell uptake accompanied by formation of optical hot-spots. Cell viability assays with HeLa and HEP 2 G cell lines suggested the nanotags safety below 0.2 mg/L concentration. These findings highlight the benefits of silica-coated gold nanotags and open the doors in advanced medical imaging.

Sol-Gel-Derived Functional Coatings for Pre-Sowing Seed Treatment

The superatomic structure of film-forming sols obtained by the acid hydrolysis of tetraethoxysilane (TEOS) in an aqueous medium (free of organic solvents) was studied using the SAXS method. The formation of nanoparticles (NPs) was confirmed in alcohol-free silica sols with both a low (1 vol. %) content of TEOS and a high (10 vol. %) content of TEOS, hydrolyzed in an aqueous-alcoholic medium. A trimodal size distribution was revealed for the resulting NPs, with radii ranging from less than 1 nm to ~11 nm. The volume fraction of NPs tends to grow with increases in TEOS concentration, as well as with the introduction of magnetic NPs of iron oxides into silica sols. The synthesized silica sols and suspensions based on silica sols with FexOy NPs were used for the pre-sowing treatment of white and cauliflower cabbage seeds in order to provide a functional coating on their surfaces, thereby improving seed germination, stimulating their growth in the early stages of development, and suppressing the effect of phytopathogens. The effect of the pre-sowing seed treatment in sol-gel compositions on seed germination and the growth characteristics of plant seedlings is analyzed, including the influence of iron-oxide magnetic NPs’ compositions and concentrations in silica sols.

Preparation and properties of silica/hydroxyapatite whiskers porous ceramics scaffold

To investigate the preparation and properties of the novel silica (SiO 2)/hydroxyapatite (HAP) whiskers porous ceramics scaffold. The HAP whiskers were modified by the SiO 2 microspheres using the Stöber method. Three types of SiO 2/HAP whiskers were fabricated under different factors (for the No.1 samples, the content of tetraethoxysilane, stirring time, calcination temperature, and soaking time were 10 mL, 12 hours, 560℃, and 0.5 hours, respectively; and in the No.2 samples, those were 15 mL, 24 hours, 650℃, and 2 hours, respectively; while those in the No.3 samples were 20 mL, 48 hours, 750℃, and 4 hours, respectively). The phase and morphology of the self-made HAP whisker and 3 types of SiO 2/HAP whiskers were detected by the X-ray diffraction analysis and scanning electron microscopy. Taken the self-made HAP whisker and 3 types of SiO 2/HAP whiskers as raw materials, various porous ceramic materials were prepared using the mechanical foaming method combined with extrusion molding method, and the low-temperature heat treatment. The pore structure of porous ceramics was observed by scanning electron microscopy. Its porosity and pore size distribution were measured. And further the axial compressive strength was measured, and the biodegradability was detected by simulated body fluid. Cell counting kit 8 method was used to conduct cytotoxicity experiments on the extract of porous ceramics. The SiO 2 microspheres modified HAP whiskers and its porous ceramic materials were prepared successfully, respectively. In the SiO 2/HAP whiskers, the amorphous SiO 2 microspheres with a diameter of 200 nm, uniform distribution and good adhesion were attached to the surface of the whiskers, and the number of microspheres was controllable. The apparent porosity of the porous ceramic scaffold was about 78%, and its pore structure was composed of neatly arranged longitudinal through-holes and a large number of micro/nano through-holes. Compared with HAP whisker porous ceramic, the axial compressive strength of the SiO 2/HAP whisker porous ceramics could reach 1.0 MPa, which increased the strength by nearly 4 times. Among them, the axial compressive strength of the No.2 SiO 2/HAP whisker porous ceramic was the highest. The SiO 2 microspheres attached to the surface of the whiskers could provide sites for the deposition of apatite. With the content of SiO 2 microspheres increased, the deposition rate of apatite accelerated. The cytotoxicity level of the prepared porous ceramics ranged from 0 to 1, without cytotoxicity. SiO 2/HAP whisker porous ceramics have good biological activity, high porosity, three-dimensional complex pore structure, good axial compressive strength, and no cytotoxicity, which make it a promising scaffold material for bone tissue engineering.

Synthesis of Tetraethoxysilane-Reacted Hydroxyapatite Nanoparticles and Their Stabilization in Phosphate-Buffered Saline.

Hydroxyapatite (HA) particle, which is an inorganic component of biological hard tissues, is being applied as a bioceramic for biotechnology and medicine fields. However, early bone formation is difficult in the implantation of well-known stoichiometric HA into our body. To solve this problem, it is important to control the shapes and chemical compositions of the physicochemical properties of HA to be functionalized as the state similar to the biogenic bone. In this study, the physicochemical properties of the HA particles synthesized in the presence of tetraethoxysilane (TEOS) (SiHA particles) were evaluated and investigated. In particular, the surface layers of the SiHA particles were successfully controlled by adding silicate and carbonate ions in the synthetic, which would be involved in the bone formation process, and their elusive reaction behavior with phosphate-buffered saline (PBS) was also evaluated. The results showed that the ions in the SiHA particles increased with the increase in the added TEOS concentration, and the silica oligomer was also formed on the surfaces. The ions were present not only in the HA structures but also on the surface layers, indicating the formation of the non-apatitic layer containing the hydrated phosphate and calcium ions. The change in state of the particles with the immersion in PBS was evaluated, the carbonate ions eluted from the surface layer into PBS, and the free water component in the hydration layer increased with the immersion time in PBS. Therefore, we successfully synthesized the HA particles containing silicate and carbonate ions, suggesting the important state of the surface layer consisting of the characteristic non-apatitic layers. It was found that the ions in the surface layers can react with PBS and leach out, weakening the interaction of hydrated water molecules on the particle surfaces to increase the free water component in the surface layer.

Polyacrylonitrile Fibers with a Gradient Silica Distribution as Precursors of Carbon-Silicon-Carbide Fibers.

This study presents preparing and characterization of polyacrylonitrile (PAN) fibers containing various content of tetraethoxysilane (TEOS) incorporated via mutual spinning solution or emulsion using wet and mechanotropic spinning methods. It was shown that the presence of TEOS in dopes does not affect their rheological properties. The coagulation kinetics of complex PAN solution was investigated by optical methods on the solution drop. It was shown that during the interdiffusion process phase separation occurs and TEOS droplets form and move in the middle of the dope's drop. Mechanotropic spinning induces the TEOS droplets to move to the fiber periphery. The morphology and structure of the fibers obtained were investigated by scanning and transmission electron microscopy, as well as X-ray diffraction methods. It was shown that during fiber spinning stages the transformation of the TEOS drops into solid silica particles takes place as a result of hydrolytic polycondensation. This process can be characterized as the sol-gel synthesis. The formation of nano-sized (3-30 nm) silica particles proceeds without particles aggregation, but in a mode of the distribution gradient along the fiber cross-section leading to the accumulation of the silica particles either in the fiber center (wet spinning) or in the fiber periphery (mechanotropic spinning). The prepared composite fibers were carbonized and according to XRD analysis of carbon fibers, the clear peaks corresponding to SiC were observed. These findings indicate the useful role of TEOS as a precursor agent for both, silica in PAN fibers and silicon carbide in carbon fibers that has potential applications in some advanced materials with high thermal properties.

Investigation of the tetraethoxysilane‐derived sol–gel process by rheological oscillation test and the effect of different synthetic parameters

AbstractThe tetraethoxysilane (TEOS)‐derived sol–gel process was systematically investigated by the rheological oscillation test and the effect of different synthetic parameters, including TEOS concentration, water content, base catalyst concentration and temperature, on the viscoelastic properties of the formed gel was analyzed. It is found that the rheological oscillation test provides an efficient and accurate way to determine the gelation time in the sol–gel process. The time at which the storage modulus and loss modulus intersect can be regarded as the gelation time in the sol–gel process and it matches well with the time observed with the naked eyes. Furthermore, both the increased TEOS and base catalyst concentration can be beneficial to the improvement of the gel elasticity, which could be related to the increased concentration of silica primary particles and its condensation reaction rate. However, the increased water content and temperature lead to a first increase and then a decrease in the elasticity of the gel. The proper molar ratio of TEOS to water is 0.67:4.01 and the suitable reaction temperature is 318 K in this study.

Evaluation of the Molecular Conformation of Surface Alkyl Chains of Alkylsilane-Derived Hybrid Films Using Sum-Frequency Generation Spectroscopy

Alkylsilane-derived hybrid films exhibiting excellent dynamic dewetting behaviors toward various liquids are promising, since they are smooth, highly transparent, and a low environmental burden. However, the detailed mechanism of their unique dynamic dewetting behaviors and its relation to the surface segregation of alkylsilanes during the film formation have not yet been clearly identified. In this study, we prepared various hybrid films by varying the mixing ratios of tetraethoxysilane (TEOS) and n-dodecyltriethoxysilane (C12TES) and investigated the changes in the s-CH2/s-CH3 peak strength ratios of the resulting hybrid films under dry and wet conditions by sum-frequency generation (SFG) spectroscopy. When the static/dynamic water contact angles significantly changed, it was clearly observed that the s-CH2/s-CH3 ratio of each hybrid film under dry and wet condition also changed markedly. With increasing TEOS concentration, the static contact angles became smaller, while the contact angle hysteresis tended to increase because of the increase in gauche defects at the air interface and hydrogen bonds. This finding suggests that the concentration and conformation of the alkyl chains derived from surface-segregated C12TES molecules play an important role in determining the final dewetting behaviors of the hybrid films to water.

Fabrication of an Organo-Fluoride–Free Hydrophobic Film Using the Sol-Gel Method by Factors Screening and Poly-Acrylic Acid Addition

Improving silica film’s contact angle (CA) using tetraethoxysilane (TEOS) and iso-butyltrimethoxysilane (iso-BTMS) by the sol-gel method without adding organo-fluoride substances is of interest. Five factors, namely type of solvent, molar ratio and amounts of TEOS and iso-BTMS, mixing intensity, sol aging time, and presence and absence of poly-acrylic acid (PAA), were assessed to improve the static water CA of the film and its surface quality. Results revealed that when ethanol was used as the dissolving solvent and after adding initial iso-BTMS and TEOS concentrations of 0.0270 and 0.0194 mol/L (molar ratio = 1.39), respectively, without sonication and adding PAA/TEOS weight ratio of 0.029, then the maximum static CA of the film reached 147°, a nearly super-hydrophobic surface. Under given conditions, long-term film durability was observed, and the added PAA prevented the formation of nonhomogeneous film surfaces caused by the highly clustering aggregation of silanols under high pH conditions.

Designing Waterproof and Breathable Fabric Based on Polyurethane/Silica Dioxide Web Fabricated by Electrospinning

In this research, non-fluorinated polyurethane/silica dioxide (PU/SiO) nanofibrous webs were prepared by electrospinning and hydrothermal treatment. Then the developed webs were laminated onto polyester woven fabrics to examine their practical applications in the textile area. Investigation for surface morphology, pore size, water contact angle (WCA) and hydrostatic pressure was done in detail to examine the waterproofness and breathability of the PU/SiO nanofiber webs and the laminated fabrics. The results showed that when Tetraethoxysilane concentration in electrospun solution was 6 wt%, the fibrous web exhibited the desirable morphology, mechanical properties and hydrophobicity. At this time, SiO2 nanoparticles dispersed uniformly on and in PU nanofibers and fibers had a more uniform diameter. The composite laminated fabrics produced exhibited a value for hydrostatic pressure of 23.5 kPa with water vapor transmission rate (WVTR) of 5.19kg/m2/day.

Co-deposition of silica and proteins at the interface between two immiscible electrolyte solutions

In this work, we have simultaneously examined, electrochemically driven deposition of three proteins (haemoglobin, acid phosphatase, and α-amylase) and silica films at a polarized liquid–liquid interface. The interfacial adsorption of the proteins occurs efficiently within the acidic pH range (pH = 2–4). The interfacial charge transfer reactions recorded in the presence of fully positivity charged macromolecules were followed with cyclic voltammetry on the positive side of the potential window. Faradaic currents attributed to the presence of proteins in the aqueous phase appeared for concentrations equal to ca. 0.1 µM for haemoglobin and acid phosphatase and ca. 1 µM for the α-amylase. Concomitant deposition of silica films was achieved via the addition of tetraethoxysilane molecules to the organic phase (1,2-dichloroethane). The hydrolysis and condensation reactions of tetraethoxysilane were controlled via the interfacial transfer of H+ coinciding with the potential for protein adsorption. The effect of tetraethoxysilane concentration – up to 50% by volume – revealed significant shrinkage of the potential window (the region where capacitive currents are recorded). The optimized platform was then used to prepare silica-proteins co-deposits. These could be easily collected from the interface and further analyzed with infrared spectroscopy and transmission electron microscopy.

In-situ growth of silica nano-protrusions on halloysite nanotubes for interfacial reinforcement in polymer/halloysite scaffolds

The mechanical reinforcing effects of halloysite nanotubes (HNT) on polymer scaffolds were restricted due to poor interfacial adhesion and dispersion. In this study, silica (SiO2) nano-protrusions were in-situ grown on HNT via the hydrolysis of tetraethoxysilane (TEOS) and the polycondensation of its intermediates with the surface O–H groups of HNT. Then, HNT@SiO2 was introduced to poly (L-lactide) (PLLA) scaffolds for better mechanical reinforcing, which were prepared by laser additive manufacturing. The results indicated many irregularly shaped SiO2 nano-protrusions were in-situ grown on HNT with Si-O bonding under a low (L) and medium (M) concentration of TEOS, while there formed many free SiO2 particles under a high (H) concentration. The in-situ grown organosilane-derived SiO2 nano-protrusions effectively strengthened the interaction of HNT@SiO2 with PLLA, contributing to strong interfacial adhesion between HNT@SiO2 and the PLLA matrix as well as good dispersion of HNT@SiO2. As a result, PLLA/HNT@SiO2-L and M scaffolds showed much higher tensile strength and modulus than those of PLLA and PLLA/HNT. Besides, PLLA/HNT@SiO2 scaffolds supported the responses of stem cells, and showed improved apatite-forming ability and hydrophilicity. This study suggested the potential application of HNT@SiO2 in reinforcing polymer-based bone tissue engineering scaffolds.

Characterization of bismuth-silicate soles

The bismuth silicate compound was synthesized by the sol-gel method from bismuth nitrate pentahydrate and tetraethoxysilane, as precursors. The sol-gel method is attractive because the processes for obtaining oxides are developed at room temperature. In addition, it allows precise control over the composition, homogeneity, and deposition of coatings. The impact of bone-related diseases and trauma has increased significantly, in recent decades in developed and developing countries. There are materials such as bioactive glasses, especially silica compounds, which are called to play a very important role in this area, due to properties such as osteoconductivity, osteoproduction, and osteoinduction. For 20 years, the sol-gel method and the supramolecular chemistry of surfactants have been incorporated into the field of bioceramics, which allows the control, on a nanometric scale, of porosity in bioglasses. The sol-gel method has allowed obtaining bioactive materials with high surface area and high porosity. The study consisted of shaping soles by varying the molar concentrations of tetraethoxysilane and assessing the effect on aging, viscosity, determining the presence of specific functional groups and establishing the transformations that take place as a function of temperature. The results allowed characterizing each of the sol for possible application in bioglasses.

Carbon dots-embedded fluorescent silica xerogel

Herein, we describe the dynamics of gel transition of silica sol (tetraethoxysilane (TEOS) in ethanol-H2O to xerogel viaoranogel route. Silica sol made in ethanolic solution turns into an organogel during sol-gel synthesis of TEOS, which eventually makes a phase transition to xerogel following a process of spontaneous dehydration of the gel network at room temperature. It was observed that the gelation time decreased with the increasing concentration of TEOS which was captured from dynamic light scattering profiling of the dynamics, and rheology. In order to tune and improve the functional properties, a nanocomposite xerogel was prepared by incorporating 5 nm size spherical and fluorescent carbon dots (CD) into the gel matrix. Presence of carbon dots significantly reduced both the organo-, and xero-gelation time. Carbon dots were able to impart fluorescence to these gels which may be used for bioimaging and real time tracking of drug delivery route.

The Effect of Tetraethoxysilane on the Phase State, Rheological Properties, and Coagulation Features of Polyacrylonitrile Solutions

The compatibility of tetraethoxysilane (TEOS) with polyacrylonitrile (PAN) solutions in dimethyl sulfoxide, the morphology of the mixed systems, and their rheological behavior have been analyzed. The combination of interferometry, refractometry, and optical microscopy has been employed to study the phase equilibrium realized in mixtures of TEOS with dimethyl sulfoxide and a PAN solution and to plot phase diagrams, which have indicated that TEOS is soluble in the PAN solution up to TEOS concentrations of 10–11%. As the TEOS content is increased within a concentration range of 10–20%, an emulsion with droplet sizes up to 40 µm is formed. At higher TEOS concentrations, the macroscopic separation of the system takes place. It has been shown with the use of rotational rheometry that, in the range of solutions, the presence of TEOS leads to a decrease in their viscosity and elasticity, while the viscosity increases in the range of emulsification. The analysis of the dynamic data has, for the first time, shown the bifurcation of the dependences of the storage modulus on the loss modulus at the point of phase separation. The calculation of the characteristic relaxation time of the ternary system and the dependence of this time on TEOS concentration has indicated a dramatic growth of the relaxation time in the region of emulsification, with this growth being determined by the relaxation properties of interfaces. Considering the obtained systems as a raw material for producing composite fibers, a solution droplet has been used to simulate the effect of TEOS on the kinetics of coagulation of PAN solutions with precipitants having different activities. It has been shown that, depending on TEOS concentration, the precipitation may yield gels with the content of this organosilicon additive either uniformly or nonuniformly distributed over the hypothetic cross section of a fiber.

Ultra-high performance fibre-reinforced cementitious composite with steel microfibres functionalized with silane

This paper explores the effect of fibre functionalization with tetraethoxysilane (TEOS) in the microstructure and mechanical property of ultra-high performance cement composites with steel fibres. Fibres treated with three concentrations of TEOS were evaluated by pullout tests and SEM/EDS analysis. Mixes with treated fibres showed up to 35.6% increase in bond strength and up to 49.5% reduction in the crack opening at the peak pullout load in comparison with reference mixes containing untreated fibres. The Si/Ca ratios in the fibre-matrix transition zone increases with the increment of the concentration of TEOS in the treatment of the fibre. This indicates an increase of C-S-H at the interface that justifies the enhanced mechanical performance.

Synthesis of Monodisperse Silica Nanoparticles via Heterogeneous Tetraethoxysilane Hydrolysis Using L-Arginine as a Catalyst

This paper examines how the hydrodynamic conditions and temperature of the synthesis of silica nanoparticles under heterogeneous tetraethoxysilane (TEOS) hydrolysis conditions with the use of L-arginine as a catalyst influence the particle size and uniformity. It is shown that, up to a TEOS conversion near 0.4, the rate of the chemical reaction is time-independent and corresponds to a zeroth-order chemical reaction with respect to TEOS. Varying the TEOS concentration through dilution with cyclohexane is shown to influence the rate of the chemical reaction.

Fabrication of Hollow Silica Microspheres with Orderly Hemispherical Protrusions and Capability for Heat-Induced Controlled Cracking.

Hollow silica microspheres with orderly protrusions on their outer and inner surfaces were fabricated in three simple steps: (1) suspension polymerization of a polymerizable monomer containing silica nanoparticles to obtain polymeric microspheres with a layered shell of silica particles; (2) sol-gel reaction of tetraethoxysilane (TEOS) on the surface of the microspheres to connect the silica nanoparticles; (3) removal of polymer core by calcination. The shell composed of silica-connected silica nanoparticles remained spherical even after calcination, and the characteristic surface morphology with protrusions were obtained on both inner and outer surfaces. Measurements of the mechanical strength revealed that the compression modulus of the hollow microspheres increased with increasing thickness of the silica layer, which could be controlled by changing the concentration of TEOS in the sol-gel reaction. Rapid heating of the hollow silica microspheres with the thin silica-connected layer led to silica shell cracking, and the cracks were mostly observed in the connecting layer between the silica nanoparticles. The stress was probably concentrated in the connecting layer because of its lower thickness than the nanoparticles. Such characteristic of the hollow microspheres is useful for a capsule with capability for heat-induced controlled cracking caused by internal pressure changes.