Silica Particles Of Different Sizes Research Articles

Identifying the mechanisms behind the stability of silica nano- and micro-particles: Effects of particle size, electrolyte concentration and type of ionic species

Silica nanofluids have emerged as promising agents for various applications, such as water treatment, CO2 absorption, and chemical enhanced oil recovery (CEOR). However, their effectiveness can be hindered when transported through porous media, especially in challenging downhole environments. Aggregation of nanofluid suspensions can damage formation integrity, and brine fluids may unintentionally transport fine micro silica particles, warranting an in-depth examination of micro-particle behavior and stability. This study synthesized silica particles of different sizes (10 nm, 50 nm, 1 μm and 2 μm) and meticulously characterized them using advanced techniques of transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), fourier-transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), thermal gravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) analysis. Subsequently, 560 combinations (in 5 series of 112 experiments) of micro- and nano-fluids in the presence of four different salts (NaCl, CaCl2, MgSO4 and MgCl2) were prepared. The stability and sedimentation of these combinations were investigated based on zeta potential, particle size, pH, electrical conductivity, and UV-spectrophotometry. The results indicated that sodium ions were effective for maintaining suspension stability at lower salt concentrations, while magnesium ions were preferred for higher salinities. Particle size increase led to instability at low salinities but stability at high salinities, where enthalpy dominated over entropy. Derjaguin-Landau-Verwey-Overbeek (DLVO) modeling accurately predicted particle interactions and aggregation tendencies. This investigation enhanced the understanding of the mechanisms governing silica particle stability through diverse analytical methods, addressing their limitations. The analysis of UV data over time revealed insights into sedimentation and aggregation kinetics. In summary, this study comprehensively explored the behavior and stability of silica particles in nano- and micro-fluids, shedding light on their performance in applications ranging from enhanced oil recovery to water treatment.

Sol-gel coatings for solar cover glass: Influence of surface structure on dust accumulation and removal

Soiling of solar cover glass is a major cause for efficiency loss of solar photovoltaic modules. Anti-soiling coatings can be used to reduce the rate of soiling and lower cleaning costs. The efficiency of these coatings has been demonstrated in laboratory and field tests, but the mechanisms and relevant parameters are still not well understood.In this article, we present a study on the influence of surface structure of hydrophilic sol–gel coatings on their anti-soiling performance in terms of both, dust accumulation and subsequent indoor tests for dust removal by wind. The surface structure of the films originates from the addition of colloidal silica particles of different sizes to the sols used for film preparation. In the dust deposition experiments, standardized test dust and dust collected from solar installations were used. Repeated tests were conducted under controlled humidity.In the case of dust deposition, the accumulation of dust particles larger than ∼10 µm is strongly reduced, in relation to bare glass, by the anti-soiling effect of all coatings regardless of their surface structure.For the dust removal via wind, coatings that bear a smoother surface structure are cleaned more easily than coatings with a rougher surface structure.Additionally, larger and rounder dust particles are removed more easily from coatings with a rougher surface structure (structure height over ∼40 nm), while smaller and more irregularly shaped dust particles are removed more easily from coatings with a smoother surface structure.

Experimental Detection of Lubrication Characteristics in a Solid–Liquid Two-Phase Flow Supported Bearing-Rotor System Using Vibration Monitoring Techniques

This work aims to investigate the friction and vibration behaviors of a liquid–solid two-phase flow supported bearing-rotor system for the early monitoring and assessing of oil contamination resulting from externally ingested particles. Based on a Jeffcott rotor test rig, the lubricating oil in journal bearing was mixed with micron-scale silica particles of different sizes and concentrations. The vibration monitoring techniques utilizing eddy current, photoelectric, and piezoelectric sensors were conducted to detect the rotor displacement amplitude and bearing acceleration online. According to the quantitative evaluation, the vibration frequency spectrum, shaft trajectory, and the bearing surface characteristics were analyzed and classified at different conditions of particle parameters. Furthermore, the lubricating mechanism at bearing interface which possesses a strong interactive coupling effect with rotor vibration was deduced and illustrated. The results showed that although the sizes of ingested micron particles were less than the minimum oil-film thickness, they usually exhibited detrimental effects on the flow stability and fluid support. As the particle size or concentration increased, the interaction between particles and bearing surfaces led to the burrs in time-domain waveform, reverse displacements in rotor orbit, higher frequency harmonics in vibration spectrum, and the scratches on the bearing surface. The occurrence of continuous three-body friction could induce misalignment, blockage, oil starvation, and rub-impact fault. Furthermore, the detectability of particle contamination and damage microstructure of bearing surface was described for reference.

Development of ceramic membranes for resource recovery from brine through percrystallization

Availability of efficient methods to fractionate a solution into its solid and liquid components is the key to recycling and reuse of industrial effluents. Percrystallization is a novel membrane process where a thin film of warm permeate present at the membrane surface is evaporated through vacuum to crystalize the soluble compounds. Thus, the process separates a solution into crystalline solute and solvent in a single-step and can partly be operated with sustainable sources of energy such as solar and geothermal heat. Since the process is at early stage of exploration, there is no sufficient knowledge about the suitable membrane features for the percrystallization which hampers its further development and potential progress towards commercialization. This work performs a systematic and groundbreaking investigation to identify and develop suitable membranes for percrystallization applications. The study has been carried out by using silicon carbide (Si-C) and polymeric membranes with different porosities and thicknesses. The effect of pore size and surface hydrophobicity on the process operation was investigated by coating the surface of Si-C membranes with methylated silica particles of different sizes. Inherent hydrophobicity of the polymeric membranes was also modified to test their suitability for the percrystallization applications. All the membranes were tested for separation of NaCl crystals from solution by using different concentrations (3.5, 10 and 17.5 wt%) of NaCl at operating temperatures of 50 °C, 55 °C and 60 °C. It was observed that the membranes with the rate of permeation comparable with the rate of evaporation under the applied vacuum are crucial to operate the process. Thus, only less porous and thick Si-C membranes with liquid entry pressure approaching to 1 bar were suitable for percrystallization. The developed membranes yielded water and NaCl flux in the range of 9.43±2 and 1.2 kg/m2.h, respectively. The process outperformed state-of-the-art membrane processes in terms of productivity and simplicity.

Synthesis and Spatial Order Characterization of Controlled Silica Particle Sizes Organized as Photonic Crystals Arrays.

The natural occurrence of precious opals, consisting of highly organized silica particles, has prompted interest in the synthesis and formation of these structures. Previous research has shown that a highly organized photonic crystal (PhC) array is only possible when it is based on a low polydispersity index (PDI) sample of particles. In this study, a solvent-only variation method is used to synthesize different sizes of silica particles (SiPs) by following the traditional sol-gel Stöber approach. The controlled rate of the addition of the reagents promoted the homogeneity of the nucleation and growth of the spherical silica particles, which in turn yielded a low PDI. The opalescent PhC were obtained via self-assembly of these particles using a solvent evaporation method. Analysis of the spatial statistics, using Voronoi tessellations, pair correlation functions, and bond order analysis showed that the successfully formed arrays showed a high degree of quasi-hexagonal (hexatic) organization, with both global and local order. Highly organized PhC show potential for developing future materials with tunable structural reflective properties, such as solar cells, sensing materials, and coatings, among others.

Dual-Colored Janus Microspheres with Photonic and Plasmonic Faces.

Photonic and plasmonic colors, stemming from nanostructures of dielectric materials and metals, are promising for pigment-free coloration. In particular, nanostructures with structural colors have been employed in stimuli-responsive Janus microparticles to provide active color pixels. Here, the authors report a simple strategy to produce electro-responsive Janus microspheres composed of photonic and plasmonic faces for active color change. The photonic microspheres are first prepared by self-assembly of silica particles in emulsion droplets of photocurable resin. The silica particles form 3D crystalline arrays in the interior and 2D hexagonal arrays on the interface. The emulsion droplets are photocured and the silica particles are selectively removed to make porous photonic microspheres with hexagonal arrays of dimples on the surface. Directional deposition of gold or aluminum on the photonic microsphere develops plasmonic color on the top hemisphere while maintaining photonic color on the bottom hemisphere. Moreover, the metal deposited on one side renders the Janus microspheres electro-responsive. Therefore, the photonic and plasmonic colors are switchable by the orientation control of the Janus microspheres with an external electric field. The photonic and plasmonic colors are independently adjustable by employing two different sizes of silica particles in core-shell emulsion drops.

Elucidating the dominant mechanisms in burn rate increase of thermite nanolaminates incorporating nanoparticle inclusions

It was experimentally found that silica and gold particles can modify the combustion properties of nanothermites but the exact role of the thermal properties of these additives on the propagating combustion front relative to other potential contributions remains unknown. Gold and silica particles of different sizes and volume loadings were added into aluminum/copper oxide thermites. Their effects on the flame front dynamics were investigated experimentally using microscopic dynamic imaging techniques and theoretically via a reaction model coupling mass and heat diffusion processes. A detailed theoretical analysis of the local temperature and thermal gradients at the vicinity of these two additives shows that highly conductive inclusions do not accelerate the combustion front while poor conductive inclusions result in the distortion of the flame front (corrugation), and therefore produce high thermal gradients (up to 1010 K.m−1) at the inclusion/host material interface. This results in an overall slowing down of the combustion front. These theoretical findings contradict the experimental observations in which a net increase of the flame front velocity was found when Au and SiO2 particles are added into the thermite. This leads to the conclusion that the faster burn rate observed experimentally cannot be fully associated with thermal effects only, but rather on chemical (catalytic) and/or mechanical mechanisms: formation of highly-stressed zones around the inclusion promoting the reactant mixing. One additional experiment in which physical SiO2 particles were replaced by voids (filled with Ar during experiment) to cancel the potential mechanical effects while preserving the thermal inhomogeneity in the thermite structure confirms the hypothesis that instead of pure thermal conduction, it is the mechanical mechanisms that dominate the propagation velocity in our specific Al/CuO multilayered films.

An in-situ SAXS approach to probe stratification during drying of inorganic nanoparticle films

Understanding particle motion during drying of colloidal and nanoparticle mixtures can be of great significance to processes such as stratification during film formation. Much of the current research in this field focuses on theory and simulation; however, additional experimental approaches are needed to support these studies. Here, we report a novel way to study film structures by applying an in-situ small angle X-ray scattering (SAXS) approach. We present studies of binary films containing two different sizes of silica particles. Our analysis allows us to probe the difference in particle packing in different layers and at different drying times. Furthermore, we can compare film samples consisting of particles with different initial concentrations and size ratios. Although the sample series presented here is limited, the data demonstrates proof-of-concept of the experimental technique. The method will be beneficial for future studies of structure formation in relatively thick films containing inorganic nanoparticles.

Silica particles incorporated into PLGA-based in situ-forming implants exploit the dual advantage of sustained release and particulate delivery

Poly (lactic-co-glycolic acid) (PLGA) in situ-forming implants are well-established drug delivery systems for controlled drug release over weeks up to months. To prevent initial burst release, which is still a major issue associated with PLGA-based implants, drugs attached to particulate carriers have been encapsulated. Unfortunately, former studies only investigated the resulting release of the soluble drugs and hence missed the potential offered by particulate drug release. In this study, we developed a system capable of releasing functional drug-carrying particles over a prolonged time. First, we evaluated the feasibility of our approach by encapsulating silica particles of different sizes (500 nm and 1 μm) and surface properties (OH or NH2 groups) into in situ-forming PLGA implants. In this way, we achieved sustained release of particles over periods ranging from 30 to 70 days. OH-carrying particles were released much more quickly when compared to NH2-modified particles. We demonstrated that the underlying release mechanisms involve size-dependent diffusion and polymer-particle interactions. Second, particles that carried covalently-attached ovalbumin (OVA) on their surfaces were incorporated into the implant. We demonstrated that OVA was released in association with the particles as functional entities over a period of 30 days. The released particle-drug conjugates maintained their colloidal stability and were efficiently taken up by antigen presenting cells. This system consisting of particles incorporated into PLGA-based in situ-forming implants offers the dual advantage of sustained and particulate release of drugs as a functional unit and has potential for future use in many applications, particularly in single-dose vaccines.

Self-pinning of silica suspension droplets on hydrophobic surfaces

HypothesisSelf-pinning induced by the aggregation of particles at the edge of a pinned drop is a pre-requisite for the coffee ring formation. The edge (three-phase contact line) of a suspension drop on a hydrophobic surface would depin and shrink in the early stage of evaporation process. It is plausible to conjecture that the self-pinning of silica suspension drops depends on the particle size and surface property. ExperimentsTwo substrate materials, the alkylsilane coated surfaces and the polydimethylsiloxane surfaces, and three different sizes of silica particles are used to explore the criterion of self-pinning of silica suspension drops on these hydrophobic surfaces. The evaporation process of droplets is recorded and further analyzed. FindingsThe pinning concentration of silica suspensions of a fixed size linearly depends on the receding contact angle of the surface, irrelevant to the substrate material and initial particle concentration. The pinning concentration decreases along with an increase in particle size. In addition, the pinning concentrations of bi-dispersed silica (e.g. 400 + 1000 nm) suspensions have an excellent agreement with that of larger size (1000 nm) particle system. That implies that the larger particle dominates the system of bi-dispersed silica suspensions to initiate the self-pinning, further verified by SEM images.

Preparation and characterization of polyurethane–silica hybrid films

PurposeThe paper aims to provide a facile approach to the synthesis of polyurethane–silica nanocomposites by introducing self-made aqueous silica sols with different particle sizes into polyurethane materials. This paper investigates the effects of the silica nanoparticles on the polyester polyol, as well as the physical properties and transmittance of the hybrid polyurethane coatings.Design/methodology/approachColloidal silica particles of different sizes were obtained using a sol–gel process and were then embedded into polyester polyol by in-situ polymerization. These polyester polyol–silica resins were synthesized using an azeotrope process, using xylene to remove the water generated in the system and present in the dispersion medium for the colloidal silica. The polyester polyol–silica resins were further cured using isocyanate trimers to form polyurethane–silica hybrid films.FindingsThe paper observed that the viscosity of the polyester polyol–silica nanocomposite resins increased and their appearance changed from transparent to ivory white as the particle size of the added silica was increased. It was found that increasing the hydroxyl content of the silica improved the film transmittance in the visible light region. However, the transmittance decreased sharply once the diameter of the silica particles reached 100 nm.Research limitations/implicationsBecause of the limitation of experimental conditions, some performances have not been tested. Therefore, researchers are encouraged to conduct further tests.Practical implicationsThe paper provides a method of preparing hybrid polyurethane film by using silica; the results indicate that the introduction of nano-silica can improve the wear resistance and glass transition temperature of polyurethane coatings.Originality/valueThe results obtained in this study will be extremely useful to enhance the understanding of organic–inorganic hybrid materials.

Deconstructing the role of shear thickening fluid in enhancing the impact resistance of high-performance fabrics

The role of shear thickening fluid (STF) in enhancing the impact resistance of STF treated fabrics has long been debated. There is a need to clarify whether the dominant mechanism of energy absorption is shear thickening (dilatancy) or friction enhancement. This study establishes that the inherent shear thickening behaviour of STF has a decisive role to play other than just improving the yarn to yarn friction. Kevlar® 363 and Kevlar® 802 F fabrics were treated with STF comprising of 65% (w/w) silica and 35% polyethylene glycol (PEG) 200. Three monodispersed STFs and nine bi-dispersed STFs were prepared from three different particle sizes of silica (100 nm, 300 nm and 500 nm) and their binary mixtures keeping the mass fraction of silica constant (65%). Rheological results showed that STFs prepared form monodispersed silica resulted in higher peak viscosity as well as discontinuous shear thickening. However, bi-dispersed STFs prepared by mixing two different sizes of silica particles, in general, showed lower peak viscosity and continuous shear thickening. In both the fabrics (Kevlar® 363 and Kevlar® 802 F), yarn pull-out force, a measure of yarn to yarn friction, did not show much difference among the fabrics treated with different STFs. However, low velocity impact tests clearly showed enhanced performance in terms of energy absorption and peak force in case of fabrics treated with monodispersed STFs. This correlation between shear thickening and impact resistance conclusively establishes that the former has a dominant role in enhancing the latter of high-performance fabrics.

Influence of Surface Micro-Patterning and Hydrogel Coating on Colloidal Silica Fouling of Polyamide Thin-Film Composite Membranes.

In this work, colloidal fouling by silica particles of different sizes on micro-patterned pristine and poly-(N-isopropylacylamide)-coated polyamide (PA) thin-film composite (TFC) membranes was studied. The competing impacts of surface micro-patterning vs. surface chemical modification on enhancing antifouling propensity in unstirred dead-end filtration conditions were systematically explored. Spatially selective deposition of silica microparticles (500 nm), driven by unequal flow distribution, was observed on micro-patterned membranes such that silica particles accumulated preferentially within the surface pattern’s valleys, while keeping apexes regions not fouled. This interesting phenomenon may explain the substantially enhanced antifouling propensity of micro-patterned PA TFC membranes. A detailed mechanism for spatially selective deposition of silica microparticles is proposed. Furthermore, micro-imprinted surface patterns were revealed to influence deposition behavior/packing of silica nanoparticles (50 nm) resulting in very limited flux decline that was, almost, recovered under influence of triggering stirring stimulus during a continued silica filtration experiment. The current findings provide more insights into the potency of surface micro-patterning consolidated with hydrogel coating toward new fouling-resistant PA TFC membranes.

Structural Coloration with Nonclose-Packed Array of Bidisperse Colloidal Particles.

Colloidal crystals and glasses have their own photonic effects. Colloidal crystals show high reflectivity at narrowband, whereas colloidal glasses show low reflectivity at broadband. To compromise the opposite optical properties, a simple means is suggested to control the colloidal arrangement between crystal and glass by employing two different sizes of silica particles with repulsive interparticle potential. Monodisperse silica particles with repulsive potential spontaneously form crystalline structure at volume fraction far below 0.74. When two different sizes of silica particles coexist, the arrangement of silica particles is significantly influenced by two parameters: size contrast and mixing ratio. When the size contrast is small, a long-range order is partially conserved in the entire mixing ratio, resulting in a pronounced reflectance peak and brilliant structural color. When the size contrast is large, the long-range order is rapidly reduced along with mixing ratio. Nevertheless, a short-range order survives, which causes low reflectivity at a broad wavelength, developing faint structural colors. These findings offer an insight into controlling the colloidal arrangements and provide a simple way to tune the optical property of colloidal arrays for structural coloration.

Ecotoxicity screening of seven different types of commercial silica nanoparticles using cellular and organismic assays: Importance of surface and size

We show that seven different types of commercial, biocide-free, colloidal silica products with mean particle sizes between 17 and 88 nm with 3 different surface chemistries (Na-stabilized, aluminized and silane-modified) are not toxic to the bacterium Pseudomonas putida, and the algae Raphidocelis subcapitata in the concentration range 5–500 mg/L. They are also not acutely toxic to Daphnia magna at concentrations up to 10,000 mg/L. Six silica particles are toxic to the gill cell line RTgill-W1 from Rainbow trout (Oncorhynchus mykiss), showing a clear concentration-response relationship with EC50 values between 13 and 92 mg/L. Toxicity in the fish cells decreases with increasing hydrodynamic size and is dependent on particle surface area. The average EC50 across the tested particles is 2.1 (±0.3) m2/L. Surface modifications clearly impact toxicity, with silane-modified particles showing no cytotoxicity. The reduced number of free silanol groups on the surface of the silane modified particle, in combination with an increased steric hindrance that prevents contact with the cells is a possible mechanism for the observed lack of toxicity. This is also in line with previous studies on silica nanoparticles in human toxicology. Overall, these findings show a generally low ecotoxicity of silica nanoparticles and indicate that silica particles of different sizes but identical surface chemistry could potentially be grouped into an assessment group under regulation such as REACH.

Mechanical and Thermal Properties of Epoxy Composites Containing Amine-Modified Silica Nanoparticles

Epoxy/silica composites were prepared using aminopropyl triethoxysilane (APTES)-modified silica nanoparticles in the sol state. Different sizes of silica particles were synthesized and they were applied into the epoxy/silica composites with different compositions. The mechanical and thermal properties of the composites were investigated and compared with those of pristine epoxy composite. The structure and morphology of the modified silica nanoparticles and epoxy/silica composites were analyzed using field emission scanning electron microscope. The flexural modulus and tensile strength of the epoxy/silica composites were investigated by universal test machine (UTM). Also, glass transition and thermal stability were investigated using thermomechanical analyzer (TMA). Sizes of silica particles in sol state were controlled by using different concentration of the accelerator. The tensile strength of epoxy/silica composites containing 20 wt% of 30 nm silica was found to be 37.98 MPa. In addition, the glass transition temperature (Tg) decreased with increasing silica particle sizes.

Creating innovative composite materials to enhance the kinetics of CO2 capture by hydroquinone clathrates

This study addresses both the preparation of a reactive medium composed of porous particles impregnated with hydroquinone (HQ), an organic compound capable of forming gas clathrates, and an evaluation of the kinetic performance of these composite materials for CO2 capture. Two types of porous silica particles of different sizes and pore diameters were tested. The porous particles were impregnated with HQ by a dry impregnation (DI) method in a fluidized bed, and by a wet impregnation (WI) method. The impregnation effectiveness of the two methods is discussed, and the reactivity of the composite materials formed in terms of CO2 capture and storage capacity is studied experimentally. The experimental results showed that the HQ adheres well on the silica without any chemical modification of the deposit’s structure. We demonstrated that the impregnation technique plays a very important role in the kinetics of CO2 capture. A series of experiments performed using a magnetic suspension balance at 3.0MPa and 323K showed that the silica-based impregnated particles reversibly capture and store CO2, and that the CO2 capture kinetics are significantly enhanced compared to the results obtained with pure powdered HQ. Finally, we demonstrated that CO2 capture is faster with dry-impregnated particles.

Macrophage activation status determines the internalization of mesoporous silica particles of different sizes: Exploring the role of different pattern recognition receptors.

Mesoporous silica-based particles are promising candidates for biomedical applications. Here, we address the importance of macrophage activation status for internalization of AMS6 (approx. 200nm in diameter) versus AMS8 (approx. 2μm) mesoporous silica particles and the role of different phagocytosis receptors for particle uptake. To this end, FITC-conjugated silica particles were used. AMS8 were found to be non-cytotoxic both for M-CSF-stimulated (anti-inflammatory) and GM-CSF-stimulated (pro-inflammatory) macrophages, whereas AMS6 exhibited cytotoxicity towards M-CSF-stimulated, but not GM-CSF-stimulated macrophages; this toxicity was, however, mitigated in the presence of serum. AMS8 triggered the secretion of pro-inflammatory cytokines in M-CSF-activated cells. Class A scavenger receptor (SR-A) expression was noted in both M-CSF and GM-CSF-stimulated macrophages, although the expression was higher in the former case, and gene silencing of SR-A resulted in a decreased uptake of AMS6 in the absence of serum. GM-CSF-stimulated macrophages expressed higher levels of the mannose receptor CD206 compared to M-CSF-stimulated cells, and uptake of AMS6, but not AMS8, was reduced following the downregulation of CD206 in GM-CSF-stimulated cells; particle uptake was also suppressed by mannan, a competitive ligand. These studies demonstrate that macrophage activation status is an important determinant of particle uptake and provide evidence for a role of different macrophage receptors for cell uptake of silica particles.

Organosilane grafted silica: Quantitative correlation of microscopic surface characters and macroscopic surface properties

In polymer composites, organosilanes are often used to modify the surface property of silica nanoparticles and improve the interfacial properties. Surface properties of the modified silica, such as grafting density and consequent surface energy, largely depend on the molecular structure of the silane. Achieving maximum interfacial bonding between the filler and polymer requires precise control of silica surface property. In this work, four silanes with similar molecular structure but different alkyl chain lengths, trimethoxy(propyl)silane, trimethoxy(octyl)silane, hexadecyltrimethoxysilane and trimethoxy(octadecyl)silane, are selected as model agents to study their roles in influencing silica surface property. The grafting density of silane on the silica is well controlled by regulating the reaction conditions. Three main surface characters, silane grafting density, surface energy and surface potential, are measured. More importantly, a linear relationship has been correlated when plotting grafting density vs. surface energy and grafting density vs. surface potential. Utilizing these relationships, a linear model has been developed to predict grafting density and surface energy by simply measuring surface potential. This model has been validated by both commercial silica and synthesized silica particles of different sizes.

Characterization of sapphire chemical mechanical polishing performances using silica with different sizes and their removal mechanisms

Sapphire chemical mechanical polishing (CMP) performances using silica particles with different sizes have been studied. We find that MRR by 10nm silica slurry could appear rather high, approaching to that by 100nm silica slurry. The removal mechanisms of sapphire using different sizes silica have been investigated via X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements. XPS results reveals that the surface polished by 10nm silica could also present aluminum silicate resulting from solid-solid state reaction with silica and sapphire, the same with that by 100nm silica. The effects of silica nanoparticle size on the formation and removal of soft product layer on the atomic step smooth surface are studied through AFM analysis. 10nm silica particles could exhibits the smaller residual product on the surface, and the reaction model of sapphire with silica particles of different sizes is proposed. Meanwhile, 10nm silica particles could realize smoother surface of 0.06nm and straighter atomic step edge.