Surface Modification Of Silica Particles Research Articles

Surface Modification of Silica Particles with Adhesive Functional Groups or Their Coating with Chitosan to Improve the Retention of Toothpastes in the Mouth.

Silica is widely used in the oral care formulations to act as an abrasive and to give the products its distinct physical properties. In this study, silica particles were synthesized using a co-condensation of tetraethyl orthosilicate with a series of functional silane compounds [(3-mercaptopropyl)trimethoxysilane, (3-glycidyloxypropyl)trimethoxysilane, and (3-acryloxypropyl)trimethoxysilane)]. The surface of the particles based on tetraethyl orthosilicate and (3-glycidyloxypropyl)trimethoxysilane was then further modified with 3-aminophenylboronic acid. Commercial Aerosil R972 Pharma silica particles were also coated with chitosan. Additionally, commercially available (3-maleimido)propyl-functionalized silica particles were used in this study. All these functionalized silica particles were incorporated into toothpaste formulations, and their retentive properties were tested on ex vivo sheep tongue mucosa models using fluorescent microscopy-based flow-through techniques. Those surfaces with chitosan, phenylboronic acid, and acryloyl groups were shown to provide a significant improvement in the retention of the oral care formulations during the retention testing. The retention of toothpastes containing silica functionalized with maleimide and thiol groups was also superior compared to that of unmodified silica particles. This study synthesized and tested a range of silica particles and demonstrated that the functionalized silica incorporated into toothpastes can significantly improve the retention of these formulations on oral mucosal surfaces.

Surface modification of silica powder by mild ball milling

Surface modification of silica particles without a catalyst or solvent was performed using mild ball milling. The effects of the amount of the modifier, hexatrimethoxysilane (HTMS), ball milling time, and the washing process were investigated. HTMS was physically and chemically adsorbed on the silica surface by ball milling; the adsorbed HTMS reacted with the silica particles on the surface during heat treatment. The adsorption amount of HTMS in silica particles increased with the increase in the milling time to 6 h. The modified silica particles were well dispersed in the cyclohexane because the silica was successfully modified by HTMS. In addition, the number of hydroxyl groups on the silica surface affected the adsorption ratio of HTMS; chemical adsorption could be increased using silica with a large number of hydroxyl groups. Therefore, this simple method, by which the amount of chemical adsorption can be easily modulated, is a valuable tool for the homogeneous modification of silica powder.

Effect of Surface Modification of Silica Nanoparticles with Thiol group on the Shear Thickening Behaviors of the Suspensions of Silica Nanoparticles in polyethylene glycol (PEG)

The Fine-tuning of Shear Thickening Fluids (STFs) by surface modification of silica particles has fascinated scientist’s interest worldwide as it results in performance enhancement of STF based on armor systems. In the current study, surface modified Silica nanoparticles (average diameter of 600 nm) possess thiol functional groups which were attained through a reaction with 3-mercaptopropyl-trimethoxysilane in absolute ethanol at 90 °C. Shear thickening fluid of Thiol functionalized Silica nanoparticles were prepared by sonochemical method in polyethylene glycol (PEG-200). The rheological parameters of STFs (modified and unmodified silica Nano particles) were measured using Rheometer MCR 52, Anton Par, Germany. The shear thickening behavior of thiol-based STF shows shear thickening at a higher shear rate compared to only silica-based STF with the decrease in viscosity maximum.

Surface Modification of Silica Particles Taken from Waste Glass by Surfactant Treatment for Light Scattering Application

T his work aims to modify the surface of silicon dioxide particles for high dispersion property in the host matrix. Silicon dioxide powders were obtained from wasted material as broken beaker glass and reduced its particle size by high energy milling process operating at 500 rpm for 30 min. These particles can be proposed as an effective light scatterer and applied in the transparent light planar waveguide for the improvement of light emission performance. However, the main problem of using milled silica powder is the poor dispersion in the polymer matrix. Therefore, the surface modification method is a key role to resolve this obstacle by using polymer surfactant agents as polyvinyl alcohol, polyethylene glycol, and sodium hexametaphosphate. The proper polymer surfactant in the surface modification on silica powders has been revealed. The particle size of each condition was analyzed by a particle analyzer. Modified silica particle size with polymer surfactants trended to decrease lower than 1 μm owing to good dispersion of the particles by polymer chain and interaction between silica and surfactant surface. Chemical functional groups on modified silica powders were investigated by Fourier transform-infrared (FT-IR) spectroscopy. FTIR spectra shown that main chemical components of all samples were composed of silica and borate chemical bonding. Meanwhile, the O-H stretching vibration appeared in the spectra was a key role for particle size and good dispersion of modified surface silica particles in the solution. Moreover, light scattering property and transmission of modified silica with polymer surfactants in dispersion solution were detected by luminance meter and UV-Vis spectrometer to confirm its possibility for application in light scattering material. The best polymer surface for milled silica surface modification in this work was obtained from polyvinyl alcohol, which proved that the adjustment of surface charge and physical properties on the silica surface.

Enhanced mechanical properties of porous silicone composites prepared by silane surface functionalization of hollow silica particles

In this study, mechanical and thermomechanical properties of porous silicone composites with various contents of hollow silica particles, treated by vinyltrimethoxysilane (VTMS) as a silane coupling agent, were investigated using tensile and dynamic mechanical analysis. Series of silicone composites with non-modified hollow silica particles as a reference were also prepared for comparative study. The surface characteristics of VTMS-modified hollow silica particles were analyzed using FT-IR spectroscopy. The vinyl function groups on VTMS-modified hollow silica particles led to a chemical bonding to silicone matrix, resulting in reinforcing the mechanical properties of the silicone composites. Tensile modulus of porous silicone composites without the surface modification of silica particles could be predicted by Einstein and Guth/Gold equations, implying the hydrodynamic reinforcement contribution. On the other hand, considerable improvement in the tensile modulus of silicone composites was achieved by strong interfacial adhesion created by chemical bonding on the surface of VTMS-modified hollow silica particles.

The microscopic mechanism of size effect in silica-particle reinforced silicone rubber composites

Particle reinforced elastomer matrix composites always show a size-dependently mechanical behavior when the particle size shrinks down to micro- or even nano-scale. A systematic investigation on microscopic mechanisms of such a size effect is carried out in this paper based on tensile and tear experiments of silicone rubber elastomer filled with surface modified silica particles, in which the particle size ranges from tens of to several hundreds of nanometers. It is found that, when the particle content is fixed, the ultimate strength, fracture toughness and fracture tensile strain of the composite exhibit monotonic increase with the decrease of particle size. In the composite filled with monodispersed submicro-particles, the improved strength is due to the hindering effect of particles on the crack propagation and the strong interface bonding between particles and matrix, while the improved toughness is mainly resulted from the crack-pinning around particles. In the composite filled with nano-sized particles, both the filler-hindering effect and the strong interface still contribute to the strength of the composite, while not only the crack pinning but also the interface debonding around nanoparticle aggregates will toughen the composite. Furthermore, a hierarchical network structure consisting of differently-sized aggregates and bounded rubbers endows the composite with a better load bearing capacity than the one filled with separately distributed fillers. As a result, the composite filled with small nano-nanoparticles shows remarkably improved mechanical properties in comparison with the composite filled with submicro-particles. The present work should provide insights for optimally designing a flexible composite with both desirable strength and toughness.

Investigating the physical characteristics and cellular interplay on 3D-printed scaffolds depending on the incorporated silica size for hard tissue regeneration

Silica has been widely used in bone tissue regeneration which is known to increase the bone mineral density and reduce bone resorption. In this study, surface modified silica particles with different sizes (100, 500, and 800 nm) were incorporated with polycaprolactone (PCL) to study the influence of silica particle size on physical and biological properties. Controversial results were observed between the physical and biological properties. In terms of physical properties including surface roughness, hydrophilicity, and mechanical strength, the PCL scaffold with 800 nm-sized particles showed significantly enhanced results. However, the scaffold with 100 nm-sized particles significantly upregulated the biological properties such as human mesenchymal stem cell adhesion, proliferation, and differentiation. This was also relevant for the in vivo results. Altogether, the results proved that the silica particle size influence the physical and biological properties of the PCL scaffold.

Genipin crosslinked bioactive collagen/chitosan/hyaluronic acid injectable hydrogels structurally amended via covalent attachment of surface-modified silica particles

Collagen, chitosan and hyaluronic acid based multicomponent injectable and in situ gellating biomimetic hybrid materials for bone tissue engineering applications were prepared in one-step procedure. The bioactive phase in the form of surface-modified silica particles was introduced to the solutions of biopolymers and simultaneously crosslinked with genipin both the biopolymer matrix and dispersed particles at 37 °C. The novel approach presented here involved the use of silica particles which surfaces were priory functionalized with amino groups. That modification makes possible the covalent attachment of silica particles to the polymeric hydrogel network on crosslinking with genipin. That methodology is especially important as it makes possible to obtain the hybrid materials (biopolymer-silica particles) in which the problems related to the potential phase separation of mineral particles, hindering their in vivo application can be eliminated. The hybrids of various compositions were obtained and their physicochemical and biological properties were determined. The in vitro experiments performed under simulated body fluid conditions revealed that the amino-functionalized silica particles covalently attached to the biopolymeric network are still bioactive. Finally, the in vitro cell culture studies shown that the materials developed are biocompatible as they supported MG-63 cells adhesion, proliferation as well as Alkaline phosphatase (ALP) expression.

Preparation and Properties of Cyanate/Epoxy-based Composite with Thermal Conductive Silica Particles

Cyanate/epoxy (CE/EP) was added with surface-modified silica (SiO2) particles to form a composite system. Microstructure of the composites was observed to find the dispersion effect of SiO2 particles in the CE/EP matrix. Thermal conductivity, thermal stability and dielectric properties were also tested to investigate the effects of SiO2 particles. CE/EP-based composite with 50 wt% SiO2 exhibited thermal conductivity of 0.492 W.m−1.K−1, thermal decomposition temperature of 420 °C and dielectric constant of 4.1 at 1 MHz.

From 2D to 3D patches on multifunctional particles: how microcontact printing creates a new dimension of functionality.

A straightforward approach for the precise multifunctional surface modification of particles with three-dimensional patches using microcontact printing is presented. By comparison to previous works it was possible to not only control the diameter, but also to finely tune the thickness of the deposited layer, opening up the way for three-dimensional structures and orthogonal multifunctionality. The use of PEI as polymeric ink, PDMS stamps for microcontact printing on silica particles and the influence of different solvents during particle release on the creation of functional particles with three-dimensional patches are described. Finally, by introducing fluorescent properties by incorporation of quantum dots into patches and by particle self-assembly via avidin-biotin coupling, the versatility of this novel modification method is demonstrated.

Controllable synthesis of anisotropic silica/polymer composite particles via seeded dispersion polymerization

In this work, seeded dispersion polymerization was adopted to prepare anisotropic silica/polymer composite particles with controllable sizes and morphologies using the surface-modified silica particles as the seeds. Through this approach, submicron-sized silica/polymer particles with snowman-like, dumbbell-like, raspberry-like and core-shell structures could be easily fabricated in large scale. Many factors that might affect the morphologies of composite particles including the weight ratio of monomer/silica seeds, the polarity of reaction medium, reaction temperature, reaction time, the amount of crosslinking agent or the polarity of monomers were investigated. The results indicate that the interfacial tension between PS phases and SiO2 particles and the coalescence between growing polymer nodules over silica particles are responsible for the formation of different particle morphologies. It is interesting that snowman-like SiO2/PS particles could be afforded by two different processes: one was normally transformed from raspberry-like particles via the coalescence between growing polymer nodules; the other was formed directly at a high content of monomer. These different morphological particles may have important applications in biological/medical materials, optical materials, sensors, catalyst support, colloidal stabilizer, etc.

A novel shape memory poly(ε-caprolactone) network via UV-triggered thiol-ene reaction

A facile method to prepare shape memory polymers crosslinked by SiO2 is described. A series of biodegradable shape memory networks were obtained through thiol-ene reaction triggered by UV irradiation between surface-thiol-modified SiO2 nanoparticles and end-acrylate poly (e-caprolactone) (PCL). The highly selective thiol-ene reaction ensured a uniform distribution of PCL chains between crosslinkers, contributing well-defined network architecture with enhanced mechanical and shape-memory properties. Thiol-functionalized silica nanoparticle was characterized by using FTIR and XPS analysis, and 1H NMR spectra was used to confirm the successful modification of terminal hydroxyl group of PCL diol. Surface-modified silica particles were found well dispersible in acrylate-capped PCL supported by SEM. Thermal and crystalline behaviors of the obtained polymers were analyzed by DSC and XRD, and DMA measurement proved good mechanical property. The shape memory behavior and tensile strength was somewhat tunable by the length of PCL. Acceptably, sample SiO2-SMP2k presented 99% recovery ratio and 97% shape fixity, and its relatively high tensile strength showed an attractive potential for biomedical application. Finally, a possible molecular mechanism accounting for the shape memory property was illustrated. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 692–701

Flow microreactor synthesis of gold nanoshells and patchy particles

Silica@Au core-shell type composite particles are promising for biomedical applications due to their unique optical and chemical characteristics, although the problem lies in the synthetic processes. They are typically synthesized via batch type reactions including multiple steps, and the complexity in the synthetic process is an obstacle to practical applications. A robust and facile process is thus required. In the present study, we developed a flow synthetic process by applying a microreactor with a high mixing performance to silica@Au nanoshells and patchy particles. Following a concept of selective nucleation and subsequent growth of the gold on the core surface, we mixed a suspension of surface-modified silica particles containing gold ions with a reducing agent solution in the microreactor, and investigated the effects of the core particle size and the type of reducing agents on the composite particle synthesis. Through the investigation, we found that the ratio of the gold ion amount to the surface area of core particles is a key factor for obtaining uniform core-shell particles. In addition, the morphology of gold formed on the core surface was demonstrated to change from spherical nanoparticles to dendritic patches depending on the reducing ability of reducing agents.

Relationship between size and surface modification of silica particles and enhancement and suppression of inflammatory cytokine production by lipopolysaccharide- or peptidoglycan-stimulated RAW264.7 macrophages

Although nanomaterials are used in an increasing number of commodities, the relationships between their immunotoxicity and physicochemical properties such as size or surface characteristics are not fully understood. Here we demonstrated that pretreatment with amorphous silica particles (SPs) of various sizes (diameters of 10–1000 nm), with or without amine surface modification, significantly decreased interleukin 6 production by RAW264.7 macrophages following lipopolysaccharide or peptidoglycan stimulation. Furthermore, nanosized, but not microsized, SPs significantly enhanced tumor necrosis factor-α production in macrophages stimulated with lipopolysaccharide. This altered cytokine response was distinct from the inflammatory responses induced by treatment with the SPs alone. Additionally, the uptake of SPs into macrophages by phagocytosis was found to be crucial for the suppression of macrophage immune response to occur, irrespective of particle size or surface modification. Together, these results suggest that SPs may not only increase susceptibility to microbial infection, but that they may also be potentially effective immunosuppressants.

Surface modification of fumed silica by photo-dimerization reaction of cinnamyl alcohol and cinnamoyl chloride

The surface modification of silica particles by an organic functional group has been intensively studied, and the modified structure can be analyzed by various experiments and simulations. Cinnamyl alcohol and cinnamoyl chloride are well known for their photo-dimerization reactions. By introducing them on the fumed silica surface, it is possible to create a functional silica which can be aggregated by cross-linking under optical irradiation. For surface modification of the fumed silica, an autoclave method was used with the cinnamyl alcohol, while the reflux method was used for the cinnamoyl chloride. Fourier Transform Infrared Spectroscopy (FT-IR), a thermogravimetric analysis (TG) and the Bruneuer–Emmett–Teller (BET) method were used to evaluate the surface structure of the modified silica. In the case of modification with cinnamyl alcohol, the maximum amount of the modifier groups was 1.7-OR/nm2, and the modification degree could be controlled by varying the initial concentration of the modifier in the reaction. On the other hand, the maximum amount of the modifier groups was 0.33-OR/nm2 with cinnamoyl chloride, but it could be increased to 0.69-OR/nm2 when pyridine was used as the catalyst during the modification. The reaction process was evaluated by the MOPAC simulation, and the ultraviolet (UV) absorption based on the structure was calculated by ZINDO. In the photo-irradiation experiment, which used an extra high pressure mercury lamp as a spectral source, it was confirmed that the modifier on the silica surface formed α and β-dimer, the structure of which was decided by the intermolecular distance. In this study, it was confirmed that the cross-linking occurs on interparticle based on the results of the simulation and measurement of the UV absorption. However, a moderate density of the modifier is essential for initiating the interparticle cross-linking.

Effect of surface modification of silica particles on interaction forces and dispersibility in suspension

We evaluated the effect of the molecular structures and amounts of silane-coupling agents – 3-glycidyloxypropyltrimethoxysilane (GPTMS), methacryloxypropyl trimethoxysilane (MPTMS), and vinyltrimethoxysilane (VTMS) – used to generate surface-modified silica on dispersibility according to surface interaction forces. The loading of coupling agents on the silica surface is positively correlated with the amount of coupling agent added. However, if this amount exceeds the single-layer adsorption calculated from the minimum coverage area of the silane-coupling agent, the extent of modification decreases. Additionally, the extent of modification tended to decrease as the coupling reaction temperature increased (40–100°C). Repulsive force was observed for GPTMS-modified silica in water and MPTMS- and VTMS-modified silica in toluene. In contrast, clear repulsion was not observed for GPTMS in toluene and MPTMS- and VTMS-modified silica in water. With GPTMS-modified silica in water and VTMS-modified silica in toluene, the repulsive forces increase with the extent of modification, resulting in good dispersibility. Conversely, for VTMS-modified silica in water and GPTMS-modified silica in toluene, weakly repulsive and attractive forces were observed independent of the extent of modification, and flocculation and sedimentation were noted when the actual dispersibility was examined. These results indicate that the actual dispersibility can be evaluated from the surface interaction forces.

Dental Resin Composites with Enhanced Properties Bycommercial Silica Particles as Fillers

To explore the preparation of novel dental resin composites with enhanced properties, two commercial silica particles with sizes of around 1μm and 40 nm were chosen as inorganic fillers, and firstly surface functionalized by 3-methacryloxypropyltrimethoxysilane (γ-MPS) to incorporate cross-linkable vinyl groups onto the surface of fillers. Then the modified fillers were blended with organic monomers, bisphenolAdiglycidyldimethacrylate (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA), to fabricate the resin compositeswith a three-roll mixer.Resin composites with various weight percentage of fillers and component ratio of microparticle and nanoparticle were prepared. Surface functionalization of silica particles was characterized by fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), and mechanical properties degree of conversion, and depth of cure of the resultant resin composites were investigated byuniversal testing machineand FTIR. The results indicated that surface modification of silica particles was successful and the surface organic contents were 3.29% and 4.34%, respectively. Among the studied resin composites, the resin composite with 75 wt.% silica particles (59 wt.% microparticles and 16 wt.% nanoparticles) presented the highest value of depth of cure (5.52 ± 0.07 mm), and optimum mechanical properties such as flexural strength (149.8 ± 3.3 MPa), flexural modulus (13.8 ± 0.06 GPa), compressive strength (340.6 ± 8.3 MPa) and Vicker’smicrohardness (78.26 ± 2.45 HV). The study of dental resin composites fabricated from commercial silica particles with excellent properties might provide a new sight for realizing the preparation of this kind of dental resin composites in an industrial scale.

Surface modification of silica particles and its effects on cure and mechanical properties of the natural rubber composites

The efficiency of modified silica (SiO2) particles in the reinforcement of natural rubber (NR) vulcanizates was evaluated. The SiO2 particles were synthesized via a sol–gel reaction using tetraethyl orthosilicate as the precursor, and then the formed SiO2 particles were modified with methyl, vinyl or aminopropyl groups using methyltriethoxysilane, vinyltriethoxysilane or aminopropyltrimethoxysilane, respectively. Fourier transform infrared spectroscopy and elemental analysis confirmed the successful modification of the surface of the silica particles. The water contact angle measurement revealed the greater hydrophobicity of the three modified silica preparations compared to the unmodified SiO2. NR vulcanizates filled with modified SiO2 particles were prepared and the mechanical, thermal and dynamic mechanical properties of composites were investigated. The morphology of composite materials was also investigated by scanning electron microscopy. The modified SiO2 particles were well dispersed in the NR matrix leading to the good compatibility between the rubber and filler, and so an improved cure, mechanical, thermal and dynamic mechanical properties of the composite vulcanizate materials.

Surface modification of silica particles with gold nanoparticles as an augmentation of gold nanoparticle mediated laser perforation.

Gold nanoparticle mediated (GNOME) laser transfection/perforation fulfills the demands of a reliable transfection technique. It provides efficient delivery and has a negligible impact on cell viability. Furthermore, it reaches high-throughput applicability. However, currently only large gold particles (> 80 nm) allow successful GNOME laser perforation, probably due to insufficient sedimentation of smaller gold nanoparticles. The objective of this study is to determine whether this aspect can be addressed by a modification of silica particles with gold nanoparticles. Throughout the analysis, we show that after the attachment of gold nanoparticles to silica particles, comparable or better efficiencies to GNOME laser perforation are reached. In combination with 1 µm silica particles, we report laser perforation with gold nanoparticles with sizes down to 4 nm. Therefore, our investigations have great importance for the future research in and the fields of laser transfection combined with plasmonics.

Molecular modeling approach to the prediction of mechanical properties of silica‐reinforced rubbers

ABSTRACTRecently, we have suggested a nanomechanical model for dissipative loss in filled elastomer networks in the context of the Payne effect. The mechanism is based on a total interfiller particle force exhibiting an intermittent loop, due to the combination of short‐range repulsion and dispersion forces with a long‐range elastic attraction. The sum of these forces leads, under external strain, to a spontaneous instability of “bonds” between the aggregates in a filler network and attendant energy dissipation. Here, we use molecular dynamics simulations to obtain chemically realistic forces between surface modified silica particles. The latter are combined with the above model to estimate the loss modulus and the low strain storage modulus in elastomers containing the aforementioned filler‐compatibilizer systems. The model is compared to experimental dynamic moduli of silica filled rubbers. We find good agreement between the model predictions and the experiments as function of the compatibilizer's molecular structure and its bulk concentration. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40806.