Silica Particles In Aqueous Solutions Research Articles

Studies of the interactions mechanism between DNA and silica surfaces by Isothermal Titration Calorimetry

DNA and RNA (or miRNA) are potential biomarkers that could be applied to the diagnosis and treatment of diseases as liquid biopsy toward precision medicine. However, the quantitative detections of the nucleic acid from the liquid sample will be dependent on a well-defined and qualified nucleic acid extraction as sample preparation for the detections/measurements. For nucleic acid extraction, most of the commercial kits rely on silica adsorption as one of the major steps for purification. Unfortunately, the lack of knowledge of the binding mechanism of using silica as an adsorbent for nucleic acids limits the improvements and applications. This study is aiming to explore the adsorption mechanism by adsorption isotherm measurements and thermodynamics information obtained by isothermal titration calorimetry (ITC). This work demonstrates that the mechanistic aspects underlying the adsorption behaviors of DNA with mesoporous silica particles in aqueous solution. We changed the binding parameters, such as pH values, ionic strength, and types of salt and concentrations. We established the adsorption isotherms and measured the binding enthalpy and entropy by ITC at any given binding condition. The elucidated mechanism could provide a better binding condition design for nucleic acid purification and liquid biopsy applications in detection and data transferability.

Nanostructure of organic-inorganic composite materials based on polymer hydrogels

The initial stage of gelation of organic-inorganic hybrid hydrogels based on poly(N-vinylpyrrolidone) and the products of hydrolytic polycondensation of tetramethoxysilane has been studied by capillary viscometry. The development of strong bonds between polymer molecules and silica particles in aqueous solutions is proved by the electrokinetic sonic amplitude method. The molecular mass of poly(N-vinylpyrrolidone), the concentration of starting components, and their total amount affect the onset time of gelation in poly(N-vinylpyrrolidone)-water-tetramethoxysilane systems. The general scheme of formation of three-dimensional networks in such systems under the conditions of mutual penetration of poly(Nvinylpyrrolidone) coils is suggested. According to this scheme, nanoparticles of the general formula SiOx(OH)y(OR)z linking poly(N-vinylpyrrolidone) macromolecules serve as junctions of the gel network due to the formation of hydrogen bonds between hydrogens of silanol groups of organosilanes and oxygens of carbonyl groups of poly(N-vinylpyrrolidone).

Rheology signature of flocculated silica suspensions

We experimentally study the behavior of suspensions of silica particles in aqueous solution. Despite many studies on these materials, the dependence of the overall rheological properties of the suspension on particle size, solid volume fraction, ionic strength, and strain history remains debated. In this paper, we manage to manufacture materials and develop procedures that allow us (i) to approach this problem in the best possible way and (ii) to check that the results obtained with well controlled systems (monodisperse silica spherical particles) also apply to less controlled suspensions (crushed silica particles). We find that the elastic modulus-particle size and yield stress-particle size relationships follow power laws that disagree with classical models from the literature. We also show that elastic modulus versus yields stress data fall on a single master curve when rescaled by particle size, whatever are solid volume fraction, resting time, and ionic strength. This suggests that the rescaled elastic modulus can play the role of a parameter in a structural kinetics model of the behavior of thixotropic suspensions. Furthermore confocal observations of the system provided evidence that the evolution of the overall properties of the material with resting time cannot be ascribed to changes in the particle network.

Direct force measurements between silica particles in aqueous solutions of ionic liquids containing 1-butyl-3-methylimidazolium (BMIM).

Direct force measurements between silica particles were carried out using the colloidal probe technique, which is based on an atomic force microscope (AFM). The forces were investigated in aqueous solutions of ionic liquids (ILs) containing 1-butyl-3-methylimidazolium (BMIM) cations and chloride, dicyanamide, and thiocyanate as anions up to concentrations of about 1 M. The results were compared with the simple electrolyte KCl. ILs behave similar to the simple electrolyte at low concentrations, as the ILs dissociate fully into ions, and they lead to repulsive double layer forces. At higher concentrations, attractive van der Waals forces set in, but they are enhanced in the presence of ILs by additional attractive force, whose strength depends on the type of IL. This additional attraction probably originates from the interaction of adsorbed IL layers.

One‐Pot Preparation of Conducting Polymer‐Coated Silica Particles: Model Highly Absorbing Aerosols

Near‐monodisperse 0.50 μm and 1.0 μm silica particles are surface‐modified using 3‐(trimethoxysilyl)propyl methacrylate (MPS) and subsequently coated by aqueous deposition of an ultrathin polypyrrole (PPy) overlayer to produce PPy‐coated silica particles. The targeted degree of MPS modification and PPy mass loading are systematically varied to optimize the colloidal stability and PPy coating uniformity. MPS surface modification is characterized by contact angle goniometry and the PPy overlayer uniformity is assessed by scanning electron microscopy. HF etching of the silica cores produces hollow PPy shells, thus confirming the contiguous nature of the PPy overlayer and the core–shell morphology of the original particles. Four‐point probe measurements and XPS studies indicate that the electrical conductivity of pressed pellets of PPy‐coated silica particles increases with PPy surface coverage. Colloidal stabilities of the bare, MPS‐modified, and PPy‐coated silica particles in aqueous solution are assessed using disk centrifuge photosedimentometry. MPS surface modification results in weak flocculation, with subsequent PPy deposition causing further aggregation. In contrast, white light aerosol spectrometry indicates a relatively high degree of dispersion for PPy‐coated silica particles in the gas phase. Such PPy‐coated silica particles are expected to be useful mimics for silica‐rich micrometeorites and may also serve as a model highly absorbing aerosol.

Interactions between large colloids and surfactants

The interfacial adsorption of an anionic SDS and a nonionic surfactant C12E5, above the cmc onto submicron-sized, negatively charged silica particles in aqueous solution has been investigated by using electrokinetics, conductometry and static light scattering. It was found that both surfactants are prone to being adsorbed onto the silica/water interface. Addition of C12E5 to the silica dispersion leads to a decrease in mobility. This reduced surface charge causes a decrease in the stability of the silica particles. Surprisingly, the addition of SDS brings about an increase in the negative electrophoretic mobility of the anionic silica particles, leading to a super-charging effect. Subsequent addition of C12E5 gives rise to even higher negative electrophoretic mobilities. This unexpected hyper-charging effect can only be understood as a cooperative effect based on mixed micelles of C12E5 and non-adsorbed SDS. Not so unexpectedly, the sequence of surfactant addition was found to be decisive, as quite different results are obtained when C12E5 is added before SDS.

Adsorption of Nonionic Surfactant on Silica Nanoparticles: Structure and Resultant Interparticle Interactions

Addition of nonionic surfactant, C(12)E(9), to an aqueous dispersion of charge stabilized silica nanoparticles renders particle aggregation reversible. In contrast, aggregation of the same silica particles in aqueous solutions is irreversible. We use a combination of small-angle X-ray scattering (SAXS) and contrast matching small-angle neutron scattering (SANS) to investigate interparticle interactions and microstructure in dispersions of silica particles in aqueous nonionic surfactant solutions. We show that the silica particles interact through a screened Coulombic interaction in aqueous dispersions; interestingly, this interparticle interaction is hard-sphere-like in surfactant solutions. In surfactant solutions, we show that the final surfactant-particle structure can be modeled as 14 micelles adsorbed (on average) on the surface of each silica particle. This gives rise to the short-range interparticle repulsion that makes particle aggregation reversible, and results in the hard sphere interparticle interaction potential. Finally, we show that adsorption of polyethylene imine on the surface of the silica particles prevents adsorption of surfactant micelles on the particle surface.

Organic-inorganic hybrid hydrogels based on linear poly(N-vinylpyrrolidone) and products of hydrolytic polycondensation of tetramethoxysilane

The initial stage of gelation of organic-inorganic hybrid hydrogels based on poly(N-vinylpyrrolidone) and the products of hydrolytic polycondensation of tetramethoxysilane has been studied by capillary viscometry. The development of strong bonds between polymer molecules and silica particles in aqueous solutions is proved by the electrokinetic sonic amplitude method. The molecular mass of poly(N-vinylpyrrolidone), the concentration of starting components, and their total amount affect the onset time of gelation in poly(N-vinylpyrrolidone)—water—tetramethoxysilane systems. The general scheme of formation of three-dimensional networks in such systems under the conditions of mutual penetration of poly(N-vinylpyrrolidone) coils is suggested. According to this scheme, nanoparticles of the general formula SiOx(OH)y(OR)z linking poly(N-vinylpyrrolidone) macromolecules serve as junctions of the gel network due to the formation of hydrogen bonds between hydrogens of silanol groups of organosilanes and oxygens of carbonyl groups of poly(N-vinylpyrrolidone).

Energy absorption of nanoporous silica particles in aqueous solutions of sodium chloride

An experimental study is carried out on the effect of chemical admixtures, particularly sodium chloride, on the energy absorption behaviour of a hydrophobic nanoporous silica. As the pressure increases, once the capillary effect is overcome, the liquid is forced into the nanopores; and when the pressure is reduced, outflow is difficult, resulting in a pronounced hysteresis. The inflow pressure and the specific absorbed energy are strongly dependent on the sodium chloride concentration, providing a promising way to adjust the system performance.

Preparation of nano‐sized silica/poly(methyl methacrylate) composite latexes by heterocoagulation: comparison of three synthetic routes

AbstractContinuing earlier work, 2,2′‐azobis(isobutyramidine) dihydrochloride (AIBA) was used as a cationic initiator to generate positively charged polymers, and promote interaction of these polymers with the negatively charged surface of colloidal silica particles in aqueous solution. Three different synthetic routes have been investigated. In a first route, emulsion polymerization of MMA, initiated by AIBA, was performed directly in an aqueous suspension of the silica beads using a non‐ionic polyoxyethylenic surfactant (NP30). In a second route, AIBA was first adsorbed on the silica surface, and the free amount of initiator was discarded from the suspension. The silica‐adsorbed AIBA adduct was suspended in water with the help of surfactant, and used to initiate the emulsion polymerization of MMA. In a third route, cationic PMMA particles were synthesized separately and subsequently adsorbed on the silica surface. Whatever the approach used for their elaboration, the colloidal nanocomposites were shown to exhibit a raspberry‐like morphology. Quantitative determination of the amount of surface polymer enabled us to evaluate the efficiency of the heterocoagulation process and establish a comparison among the three synthetic routes. Copyright © 2004 Society of Chemical Industry

Molecular Simulation Study of Polymer Interactions with Silica Particles in Aqueous Solution

This paper describes computational modeling of interactions between components of organic/inorganic polymer hybrid (OIPH) materials, particularly polymer interactions with colloidal silica particles in aqueous solution. Particle surface models have been developed and molecular dynamics simulations applied to a range of systems representing various separations between the particles and different polymer solution concentrations. The equilibrium structures and specific interactions between the polymer, solvent, and silica surfaces with different surface modifications have been examined and molecular mechanisms of interactions involved in the formation of the nanocomposite materials have been suggested. The results presented in this paper complement our previous study of the interactions between precursors used in the synthesis of the OIPHs, thus providing a more complete picture of the atomistic details and mechanisms of interactions between the components of the OIPH materials at various stages of their formation.

Surface forces between sphalerite and silica particles in aqueous solutions

Surface forces between a fractured sphalerite surface and a silica particle in supporting electrolyte solutions were measured using an atomic force microscope. Below pH 8, the long-range surface forces were found to be attractive, decreasing with increasing solution pH. The adhesion force varied from 18 mN/m at pH 4 to 7 mN/m at pH 8. At pH 10, an exponentially decayed repulsive force was measured and no adhesion was observed. The decay length was found to scale with the supporting electrolyte concentration. Although the repulsive force was reduced significantly when up to 0.5 mmol/l calcium ions were added, the surfaces remained non-adhering at contact. In contrast, an attractive force profile was obtained when 0.5 mmol/l cupric ions were added, accompanied by an adhesion force of 16 mN/m. In general, the measured force profile can be accounted for by considering classical van der Waals and electrical double-layer forces for constant surface charge density conditions. The measured force behavior correlates well with the observations in sphalerite-silica heterocoagulation tests.

An Analytic Expression for the Particle Size Dependence of the Surface Acidity of Colloidal Silica

The charge formation on colloidal silica particles in aqueous solutions is described as a dissociation of acid silanol groups. For the relationship between surface charge density and surface potential on spherical particles an approximate solution of the spherical Poisson-Boltzmann equation, given by Ohshima et al., is used. An analytic equation describing the dependence of the apparent acid constant, K app S, on the degree of dissociation of surface silanol groups is derived, as is an analytic expression for calculating surface charge density-pH presentation. Surface charge density measurements on spherical silica particles of different sizes in aqueous 1-1 electrolyte solutions of different ionic strength are carried out using potentiometric titration.

Use of silane monomers for molecular imprinting and enzyme entrapment in polysiloxane-coated porous silica

The use of organic silane monomers in the preparation of substrate-selective polymers by molecular imprinting is described. Silanes are allowed to polymerize on the surface of porous silica particles in aqueous solution. The resulting polysiloxane copolymer becomes covalently anchored to silanol groups of the original silica. such preparations retain the rigidity of the silica matrix and can therefore be used in high-performance liquid chromatography. Polysiloxane copolymers imprinted with the dyes rhodanile blue or safranine O showed preferential binding of the respective compound. The observed recognition is believed to occur because cavities containing specific binding groups for the dyes at defined positions are developed during the polymerization procedure. In this context the synthesis of a new silane, boronatesilane, was carried out. This compound was included in the monomer mixture used for the preparation of a polysiloxane-coated silica showing affinity for the glycoprotein transferrin. Organic silanes were also used for entrapment of enzymes, resulting in block polymers, which after fragmentation yielded relatively high recoveries of enzyme activity. Alternatively, the entrapment/polymerization was allowed to proceed on the surface of porous silica, in analogy with the imprinting procedure, resulting in entrapped enzyme preparations with high mechanical stability.