Investigating the effect of pH on the surface chemistry of an amino silane treated nano silica

Abstract

Purpose -The purpose of this paper is to investigate the effect of different PHS on the surface chemistry of fumed silica treated with aminopropyltrimethoxysilane (APTMS). Design/methodology/approach -The reaction conditions involved variation of pH ranging from acidic to alkaline. Different analytical techniques including FT-IR spectroscopy, thermogravimetric analysis (TGA), CHN and Zeta potential analyses were employed to investigate the surface chemistry of treated particles. In addition, the stability of silanised silica dispersions were studied using turbidimetric and rheometric measurements. Findings -It was revealed that in all conditions silica was more or less chemically grafted by the silane. When the pH of treating bath was adjusted to 1-2 prior and during the reaction, 58 percent grafting was observed, as obtained by CHN and TGA analyses. At very alkaline conditions, however, the grafting content declined to 29 percent. The variations in grafting were dependent on the silane hydrolysis and its further condensation with the silica surface. Zeta potential measurements showed a drastic change from 27.1 mv to þ18.01 mv (at pH 7) for the untreated particle and the one with the highest grafting, respectively. The dispersion stability of differently treated particles varied in solvents with different Hansen solubility parameters (HSP). Moreover, due to the variations of surface chemistry of particles, their rheological behaviours were significantly influenced. Originality/value -The results obtained in this work showed that the surface chemistry of fume silica could be tuned with treating method. The highest content of grafting led to a better dispersion in solvents having greater hydrogen bonding component and to an inferior dispersion in solvents with higher polar component.

The effects of water absorption and surface treatment on mechanical properties of epoxy nanocomposite using response surface methodology

“…The decomposition of aminopropyl groups occurs slowly at 200-400°C, followed by a rapid degradation above 4,008°C. The decomposition of amino silane leads to the formation of ammonia, ethylene, hydrazine and methane which is in good agreement with the literature [19].…”

“…Increasing the affinity of the particle surface to the matrix polymer leads to reduced conglomeration behavior [18]. The surface treatment of the particles with organic molecules enhances compatibility and adhesion between the components [19]. Organosilanes in the treated silica surfaces can form chemical bonds between inorganic and organic composite.…”

“…Thus, an amino silane can act as a bridge between silica and polymer; thereby those interactions will increase. For silica treatment, amino silane is used regularly [19].…”

Effect of reaction conditions on silanisation of sepiolite nanoparticles

“…The rate of sedimentation depends on density and surface chemistry of particles and becomes low if particles have a good interaction with solvent. [38] According to XRD and SEM observation, after the modification of sepiolite, the space between rods of sepiolite has not been wider compared with pristine sepiolite which means that the nanoclay fibrrs do not separate from each other. The grafting of sepiolite, however, changes the surface chemistry of the particles and increases their hydrophobicity.…”

“…The zeta potential is utilised to study the potential of solid at the shear plane to characterise its electrokinetic behaviour, because the surface potential is not directly measurable. [38] Different parameters such as pH of the liquid phase or electrolyte concentration cause changes in electrokinetic results. The results reveal that the pristine sepiolite has an isoelectric point (IEP) at pH 2.7.…”