Monodisperse Colloidal Silica Research Articles

Laser scattering centrifugal liquid sedimentation method for the accurate quantitative analysis of mass-based size distributions of colloidal silica.

This paper proposes a laser scattering centrifugal liquid sedimentation (LS-CLS) method for the accurate quantitative analysis of the mass-based size distributions of colloidal silica. The optics comprised a laser diode light source and multi-pixel photon-counting detector for detecting scattered light intensity. The unique optics can only detect the light scattered by a sample through the interception of irradiated light. The developed centrifugal liquid sedimentation (CLS) method comprised a light-emitting diode and silicon photodiode detector for detecting transmittance light attenuation. The CLS apparatus could not accurately measure quantitative volume- or mass-based size distribution of poly-dispersed suspensions, such as colloidal silica, because the detecting signal includes both transmitted and scattered light. The LS-CLS method exhibited improved quantitative performance. Moreover, the LS-CLS system allowed the injection of samples with concentrations higher than that permitted by other particle size distribution measurement systems with particle size classification units using size-exclusion chromatography or centrifugal field-flow fractionation. The proposed LS-CLS method achieved an accurate quantitative analysis of the mass-based size distribution using both centrifugal classification and laser scattering optics. In particular, the system could measure the mass-based size distribution of approximately 20mgmL-1 poly-dispersed colloidal silica samples, such as in a mixture of the four mono-dispersed colloidal silica, with high resolution and precision, thereby demonstrating high quantitative performance. The measured size distributions were compared with those observed through transmission electron microscopy. The proposed system can be used in practical setups to achieve a reasonable degree of consistency for determining particle size distribution in industrial applications.

Chemical mechanical polishing of silicon wafers using developed uniformly dispersed colloidal silica in slurry

It is a challenge to enhance the material removal rate (MRR) during the chemical mechanical polishing (CMP) of silicon wafers, with increasing the size of a wafer and reducing the feature size of integrated circuit. In this study, potassium ions were employed to improve the MRR of silicon wafers effectively in CMP, which was performed by developed slurry, consisting of monodisperse alkaline colloidal silica, organic/inorganic acids and inorganic salts. Experimental results show that the developed slurry has a good stability and dispersity for colloidal silica. The MRR of silicon wafers in CMP was increased by 53.42 % to 1778.71 Å/min, when the concentration of potassium ions was 125 mmol/L. In addition, the surface roughness Sa was also improved slightly to 0.887 nm. The CMP mechanism was investigated using X-ray photoelectron spectroscopy, friction coefficient meter and electrochemical analysis. It reveals that potassium ions could change the electrical characteristics of the formed soft layer on the silicon wafer surface, dissolving the soft layer and oxidizing the surface of silicon.

Monodisperse colloidal silica with excellent batch-to-batch reproducibility by stoichiometric seeded growth strategy

Monodisperse colloidal silica have been extensively used as models for inter-particle interaction investigation, standards for instrument calibration and polishing agents for global planarization of wafer in integrated circuit manufacturing. Despite marvelous achievements made for colloidal silica synthesis in the past decades, a long-standing challenge for massive production of colloidal silica lies in the batch-to-batch reproducibility. Herein, we present a stoichiometric seeded growth strategy for the massive production of monodisperse colloidal silica, where the silica precursors are designed to exclusively condense on the surface of seed particles with single Q4 Si species, enabling a precise control of resultant colloidal silica size by the feeding precursor/seed ratios, and consequently, achieving excellent batch-to-batch reproducibility. Governed by the stoichiometric correlation, customized size of colloidal silica at high precision (∼1 nm in diameter) can be prepared in large quantity. More importantly, this seeded growth strategy has rather high tolerance on the size distribution of seed particles; monodisperse colloidal silica can be readily obtained from even polydisperse seed particles, significantly lowing the cost of monodisperse particles, therefore, highlighting the feasibility of large-scale application of monodisperse colloidal silica.

Systematic preparation of high‐quality colloidal silica particles by sol–gel synthesis using reagents at low temperature

AbstractWe propose a new approach to obtain monodisperse submicrometer‐sized colloidal silica particles prepared via a modified Stöber synthesis method, leading to high‐quality spherical particles with a narrow size distribution. The novelty of this work consists in setting, previously to the synthesis reaction, the initial temperature of the reagents at low values (6−14°C) in comparison to the constant laboratory room temperature, while fixing other experimental parameters such as humidity and reagent concentrations. A series of samples of monodisperse colloidal silica particles were prepared, with diameters ranging from 600 to 1000 nm and exhibiting quite narrow particle size distributions. According to our results, it was established that the initial temperature of the reagent solutions constitutes a remarkable parameter, affecting the particle size, shape, and monodispersity. This experimental approach even allows the size tunability for the synthesis of large spherical silica particles in a one‐step process. Moreover, in combination with spin‐coating deposition, the proposed technique greatly favors the formation of ordered arrays of monodisperse silica particles over silicon substrates in areas as large as several mm2. This is ideal for thermal insulators, photonic crystals, nanosphere lithography, and other engineering and industrial applications requiring high‐quality extended arrays of monodisperse silica particles.

Monodisperse Clay Microballs for Tuning the Pseudogaps by Adsorption in Amorphous Photonic Structures

AbstractStructural color based on colloidal amorphous arrays has received growing interest in both natural and artificial systems; however few local structures on colloidal particles have been designed to tune the photonic pseudogap. We use an expandable interlayered inorganic nanosheet, a synthetic clay, on monodisperse colloidal silica spheres as constituents in an array. Interlayer expansion of the inorganic nanosheet by a cationic surfactant led to an increase in the size of the colloidal particles, resulting in a spectral redshift of the pseudogap. This phenomenon was related to the change in size of the monodisperse particles, which was induced by changing the defined layered local structure.

Smart Polyacrylate Emulsion Based on a New ABC-Type Triblock Copolymer via RAFT-Mediated Surfactant-Free Miniemulsion Polymerization: Its Multifunctional Properties.

The present investigation deals with the development of an acrylic-based polymeric emulsion that offers multifunctional properties such as superhydrophobic, antimicrobial, anti-icing, and self-cleaning. The said multifunctional waterborne emulsion was prepared via a surfactant-free reversible addition-fragmentation chain transfer (RAFT) polymerization technique. To accomplish this, a new class of ABC-type triblock copolymer (PMTAC-b-PBA-b-PIBA) based on 2-(methacryloyloxy) ethyl ammonium chloride (MTAC), n-butyl acrylate, and isobornyl acrylate (IBA) was synthesized via a polymerization-induced self-assembly technique in a surfactant-free miniemulsion process. The cationic polymer PMTAC was used as a macro-RAFT agent to prepare the rest of the blocks in the presence of nanosize monodisperse colloidal silica particles, leading to a raspberry-like morphology via ionic interaction between anionic silica particles and the cationic block copolymer (BCP). A water contact angle of more than 150° was achieved for the emulsion coating after the fluorosilane treatment which delineates its superhydrophobic nature. The prepared emulsion showed antimicrobial property both in Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The resultant BCP emulsion was coated over different substrates like glass, paper, and cotton, and the coating material showed anti-icing and self-cleaning properties.

Characterization of Colloidal Amorphous Arrays Prepared by Uniaxial Pressure Application.

We prepared a colloidal amorphous array by applying uniaxial pressure to a powder of monodispersed colloidal silica particles. Pellet-shaped samples were obtained that exhibit different structural colors depending on the diameter of the particles. We characterized the optical properties of the arrays by measuring the angle-dependent scattering spectrum wherein several spectral peaks were observed. The peak at the longest wavelength was caused by the short-range order of the particle arrangement. Interestingly, this peak exhibited a smaller shift in wavelength than that observed in similar samples prepared by several different methods. The other spectral peaks were thought to originate from Mie scattering, which produces a color when the diameter of the colloidal particles is appropriately chosen. Our results showed that uniaxial pressure application can be a suitable method to prepare structurally colored pigments with low angle dependence.

Impact of Varying the Concentration of Tetraethyl-OrthoSilicate on the Average Particle Diameter of Monodisperse Colloidal Silica Spheres

In this study, spherical Silica particles with narrow size distribution were prepared by hydrolysis of Tetraethyl OrthoSilicate (TEOS) in Ethanol and the presence of ammonia based on the Stober method. The average particle diameter and monodispersity were controlled by varying the concentration of TEOS. Microscopic analysis showed that a smaller average particle diameter and good degree of monodispersity can be obtained by decreasing the concentration of TEOS.

Self-assembled three-dimensional inverted photonic crystals on a photonic chip

Three dimensional photonic crystals (PhCs) exhibiting a full photonic band gap have high potential in optical signal processing and detector applications. However, the challenges in the integration of the 3D PhCs into photonic circuits have so far hindered their exploitation in real devices. This article demonstrates the fabrication of 3D PhCs exploiting the capillary directed self-assembly (CDSA) of monodisperse colloidal silica spheres, their inversion to silicon shells, and integration with silicon waveguides. The measured transmission characteristics agree with numerical predictions and provide strong indication of a full photonic band gap in the inverted 3D photonic crystals at wavelengths close to 1.55 μm. Silicon inverted photonic crystal self-assembled into a cavity in a waveguide intersection and the corresponding photonic band structure of the crystal, together with the simulated transmission, reflection, and absorption spectra.

Peptides on the Surface: Spin-Label EPR and PELDOR Study of Adsorption of the Antimicrobial Peptides Trichogin GA IV and Ampullosporin A on the Silica Nanoparticles

The properties of antimicrobial peptides adsorbed on inorganic or organic surfaces are of interest for their potential applications in intracellular drug delivery. In this work, continuous-wave (CW) electron paramagnetic resonance (EPR) and pulsed electron-electron double resonance (PELDOR) techniques were applied to study adsorption of the short-sequence trichogin GA IV and the medium-length sequence ampullosporin A antimicrobial peptides on the monodisperse colloidal silica nanospheres of 20 nm diameter. The results obtained by CW EPR support the view that the adsorbed peptides form close-packed clusters. PELDOR data show that both trichogin and ampullosporin adsorbed on the silica surface possess a more disordered conformation as compared to that in solution. For ampullosporin, disordering is much more pronounced than for trichogin. After desorption, the peptides restored their conformations; upon adsorption the peptides in some cases may lose partly their biradical character.

Preparation of Size-Controlled Monodisperse Colloidal Mesoporous Silica Nanoparticles and Fabrication of Colloidal Crystals

Although mesoporous silica particles are useful building blocks for colloidal crystals, mesoporous silica nanoparticles smaller than 100 nm with sufficient monodispersity and colloidal stability to enable thermodynamic assemblies have not been reported. Here, we report that highly monodisperse colloidal mesoporous silica nanoparticles (CMS) can be prepared by combining the preparation of colloidal mesoporous silica nanoparticles with a shortened nucleation time. The nanoparticles exhibited a uniform shape and relatively smooth surface because an undesirable aggregate dispersion process was avoided. In addition, the diameter of the nanoparticles was controlled by seed-growth without spontaneous nucleation, which enabled the investigation of fundamental CMS properties. Using monodisperse CMS, the dependence of the ζ-potential of CMS on the diameter was revealed. Colloidal crystals composed of mesoporous silica nanoparticles were fabricated by drying the colloidal solution. This is the first report regarding the fabrication of colloidal crystals composed of mesoporous silica nanoparticles with a small particle size.

On-Channel Micro-Solid Phase Extraction Bed Based on 1-Dodecanethiol Self-Assembly on Gold-Deposited Colloidal Silica Packing on a Capillary Electrochromatographic Microchip

A fully packed capillary electrochromatographic (CEC) microchip with an on-column micro-solid phase extraction (SPE) bed for the preconcentration and separation of organic analytes was prepared. A linear microchannel with monodisperse colloidal silica packing was formed on a cyclic olefinic copolymer microchip with two reservoirs on both ends. Silver-cemented silica packing frit structure was formed at the entrance of the microchannel by electroless plating treatment as a base layer. A gold coating was formed on it by reducing Au to gold with hydroxylamine. Finally micro-SPE bed was formed by self-assembly adsorption of 1dodecanethiol on it. Micro-SPE beds were about 100-150 m long. Approximately 10 fold sensitivity enhancements for Sulforhodamine B, and Fluorescein in nM concentration levels were possible with 80 s preconcentration. Basic extraction characteristics were studied.

Nanometer‐Scale Precision Tuning of 3D Photonic Crystals Made Possible Using Polyelectrolytes with Controlled Short Chain Length and Narrow Polydispersity

Herein we report the development of an effective method which enables nanometer-scale precision tuning of prefabricated 3D colloidal photonic crystals (PCs). In our approach which involves the layer-by-layer (LbL) electrostatic assembly of polyelectrolytes in the photonic crystals, a key conceptual novelty lies in the development and utilization of polyelectrolytes with controlled short chain lengths and narrow polydispersity as the infi ltrating materials. This allows uniform deposition of the polyelectrolytes in the PCs while circumventing the leading problem in the LbL approach:blockage of the PC interstitial openings by large polyelectrolytes during the early stages of infi ltration. As a result, nanometer-scale precision tuning of photonic stopband of 10 nm or less has been achieved, which few other methods can attain. The method is facile and reproducible, and can be applied to photonic crystal lattices ranging from small to large dimensions. Photonic crystals are an interesting class of photon-control materials characterized by periodic array of dielectric lattices at the scale of light wave lengths. [ 1 ] These materials possess photo nic band gaps or stop bands where light within a range of frequencies is prohibited from propagating along specifi c lattice directions in the structure. As a result, PCs have attracted signifi cant recent attention as powerful tools for the manipulation of photons with potential applications ranging from telecommunications to optical computing. [ 2 ] Three-dimensional photonic crystals can be created by top-down methods such as holographic lithography and direct laser writing or bottom-up methods such as self-assembly of monodisperse colloidal silica or polymer spheres. [ 3 ] In both fabrication methods, the PC structures generated are of a passive nature with fi xed optical properties, and any slight change in the requirement of the photonic band gaps or stop bands, such as in solar cell, light emitting diode or lasing applications, will generally need the fabrication of a new photonic crystal. In comparison, nanometer-scale fi ne tuning of existing photo nic structures through controlled infi ltration represents an attractive and cost-effective alternative. However, since many of these photonic structures possess an interconnected pore network, control at the nanometer regime of the infi ltrated materials is a challenge for designed optical response. [ 4 ] In our efforts to develop post-fabrication strategies to tailor the optical properties of PCs, LbL assembly [ 5 ] of polyelectrolytes (PEs) [ 6 ] in preformed photonic crystal lattices [ 7 ] emerged as a promising approach. Importantly, we found that PEs which possessed controlled short chain lengths and narrow polydispersity were suitable as infi ltrating materials for the fi ne tuning of photonic stop bands. In this Communication, we report the development of the method and the precision tuning of photonic properties on the nanometer scale.

Synthesis and Rapid Characterization of Amine-Functionalized Silica

Amine-functionalized colloidal silica finds use in a variety of applications and fundamental investigations. To explore convenient methods of synthesis and characterization of research-grade materials in relatively large quantities, nearly monodisperse colloidal silica particles were prepared by base-catalyzed hydrolysis of reagent-grade tetraethyl orthosilicate (TEOS) without the traditional time- and energy-consuming distillation step. Radius was varied reliably from 30 to 125 nm by changing the water/TEOS ratio. Asymmetric flow field flow fractionation (AF4) methods with online light scattering detection proved effective in assessing the uniformity of the various preparations. Even highly uniform commercial standards were resolved by AF4. The surface of the colloidal silica was decorated with amino groups using (3-aminopropyl) trimethoxysilane and spacer methyl groups from methyl-trimethoxysilane. The surface density of amino groups was quantified spectrophotometrically after reaction with ninhydrin; the nature of this analysis avoids interference from sample turbidity. As an alternative to the ninhydrin test, an empirical relationship between surface density of amino groups and zeta potential at low pH was found. The size of the colloidal silica was predictably decreased by etching with HF; this method will be effective for some preparations, despite a modest reduction in size uniformity.

Effect of pH on monolayer properties of colloidal silica particles at the air/water interface

Monodisperse colloidal silica particles were prepared by the Stober method and hydrophobized by grafting a silane coupling agent, octadecyltrimethoxysilane. Two different types of silica particles, i.e., hydrophilic and hydrophobic silica particles were spread at the air/water interface to form the Langmuir monolayers. Monolayer properties of those particles were investigated by measuring surface pressure–area (π–A) isotherms at different subphase pH. At pH above the isoelectric point (IEP) of silica, as pH increased the π–A isotherms for the hydrophobic particles slightly shifted to larger surface area whereas those for the hydrophilic particles showed a reverse trend. At pH below the IEP, the π–A isotherms for both types of particles shifted to much larger surface area with different shapes. In order to analyze the π–A isotherm results further, the time dependence of π was examined. When pH is above the IEP, the π for the hydrophilic particles significantly decreased with increasing time and it did more at higher pH. On the other hand, the decrease in π for the hydrophobic particles was insignificant regardless of pH. For both types of silica particles, the decrease in π was minimal at pH below the IEP. These results were discussed in terms of particle desorption into the water subphase and interparticle electrostatic repulsion which is directly influenced by zeta potential.

Synthesis of Monodisperse Silica Nanoparticles Dispersable in Non‐Polar Solvents

AbstractThree synthetic routes to hydrophobic silica nanoparticles are compared in this paper. First, the established synthetic method based on the Stöber process was examined. Monodisperse colloidal silica particles with diameters of 15–25 nm were prepared via the hydrolysis of tetraethyl orthosilicate (TEOS) by aqueous ammonia in ethanol. The surfaces of these particles were rendered hydrophobic with octadecyltrimethoxysilane (ODTMS) after the reaction or, more conveniently, during the growth phase. Secondly, silica particles with diameters of 15–50 nm were prepared using a one‐pot synthesis in which TEOS was hydrolyzed by an amino acid and the resulting particles were coated with ODTMS. Lastly a novel, direct approach to the synthesis of hydrophobic organosilica nanoparticles was developed using ODTMS as the single silica source. Hydrolysis of the ODTMS by aqueous ammonia in ethanol yielded monodisperse colloidal organosilica particles with diameters of 15–30 nm.

Investigation on the controllable growth of monodisperse silica colloid abrasives for the chemical mechanical polishing application

With the rapid development of chemical mechanical polishing technique as well as its increasing application in IC foundry, the abrasives of slurry are required to have different specifications in terms of size and size’s distribution, which play a vital role in the material removal and defect control. In this study, we monitor in detail the growth process of colloidal silica abrasives changing from the tiny nuclei to large nanoparticles by means of the electron microscopy images. Using the procedure we develop, we are capable of producing monodisperse colloidal silica nanoparticles ranging from 60 to 130 nm in diameter, which are mostly often applied as abrasives in chemical mechanical planarization/polishing (CMP) process of integrated circuit (IC) manufacturing. The physicochemical properties of the silica synthesized by our procedure are also characterized by the X-ray diffraction (XRD) patterns and thermal analysis. The polishing test adopting the colloidal silica as abrasives is performed on silicon wafer to evaluate the CMP properties.

High transparent soluble polyimide/silica hybrid optical thin films

Polyimide–silica hybrid thin films (6FDA-6FpDA-4ABA/SiO 2, PS) were prepared from soluble fluorine-containing polyimide and 12 nm monodispersed colloidal silica. The soluble polyimide with carboxylic acid end groups (6FDA–6FpDA–4ABA-COOH) was synthesized from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 4,4′-(hexafluoroisopropylidene) dianiline (6FpDA), and 4-aminobenzoic acid (4ABA). Such end groups could undergo a condensation reaction with colloidal silica to provide organic–inorganic bonding and, thus, prevent macrophase separation. The silica content in the hybrid films was varied from 0 to 50 wt% (PS0-PS50). TGA analysis showed that the hybrid films had high thermal stability and the thermal decomposition temperature ( T d) increased as the silica content increased. The UV-vis spectra indicated the cutoff wavelength of hybrid films was less than 272 nm and could be tunable through the silica content. The n&k analysis illustrated that the refractive index ( n) of the hybrid films was in the range of 1.575–1.479, which could be controlled by the silica content. The extinction coefficients ( k) were almost zero in the 300–900 nm wavelength range, indicating the prepared hybrid films had excellent optical transparency in both the UV and visible regions. TEM images showed that the particle size of silica in the hybrid thin films was similar to the original size of pure silica and could be effectively controlled. The results of SEM and AFM showed that all the prepared hybrid films had a good film formability and planarity. Based on this study, it would be possible to prepare polyimide–silica hybrid thin films using monodispersed colloidal silica instead of preparing silica networks from alkoxysilanes, with no additional coupling agents in the preparation of the hybrids.

Synthesis and Performance of Colloidal Silica Nano-Abrasives with Controllable Size for Chemical Mechanical Planarization

Under the analysis of particle growth mechanism, the monodisperse colloidal silica abrasives for chemical mechanical planarization (CMP) slurry were synthesized by the modified ion-exchanged and hydrothermal step-polymerization process. After the colloidal silica with controllable size was synthesized, its microstructure, stability and CMP performance was characterized and tested by SEM, HRTEM, Zeta potential Analyzer and CMP tester. Results show that the spherical, high stable (Zeta potential: -52.8 mV) colloidal silica with controllable size was achieved. About its CMP performance, the polishing rate for silicon double-side CMP is increased to be 317 nm/min and the polished surface roughness (RMS) was reduced to 0.32 nm.

Modification of Monodisperse Colloidal Silica by Radical Copolymerizatoin of Cationic Surface Active Vinyl Monomers

Adsorption and polymer modification of colloidal silica by radical copolymerization of surface active monomers, i.e., polymerizable surfactant having a vinyl end group, were investigated. Radical copolymerization of amide ammonium monomer and ammonium-type cross-linker (monomer) using a initiator of 2,2′ -azobis(2-amidinopropane) dihydrochloride on colloidal silica successfully led to the formation of monodispersed cross-linked polymer/SiO2 composites, which is stable in organic solvents. Addition of carboxylic acid monomer to the reaction system of two ammonium monomers gave homogeneously polymer-coated silica composites having carboxyl groups. The composites show ξ-potential of –36mV and 0mV in water and ethanol, respectively.