The role of poly(methacrylic acid) conformation on dispersion behavior of nano TiO2 powder (original) (raw)
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Materials Chemistry and Physics, 2011
We investigate the effects of a foreign substance, silica (SiO 2), on surface chemistry of commercial titania (TiO 2) nanopowder and its chemical interactions with dispersants. The surface of as-received TiO 2 is covered with a 2-3-nm-thick layer of SiO 2 , which gives the nanopowder a low isoelectric point and makes it acidic. Treating the surface with an acidic solution thins the SiO 2 layer to less than 0.5 nm, which allows the TiO 2 nanoparticles to exhibit surface properties similar to uncoated TiO 2 nanoparticles. This variation of surface property of TiO 2 due to acid-treatments results in a great impact on its interactions with dispersants. For as-received TiO 2 nanoparticles, no competitive adsorption is observed between the acidic dispersant, oleic acid (OA), and the alkaline dispersant, oleylamine (OLA). However, for acid-treated TiO 2 nanoparticles, OA competes readily with the adsorption of OLA.
Efficient Dispersants for TiO2 Nanopowder in Organic Suspensions
Journal of the American Ceramic Society, 2015
This article discusses the appropriate dispersant for titania (TiO2) nanopowder in organic‐based suspensions. Four types of oleyl‐based dispersants, namely, oleyl alcohol, oleic acid, oleylamine, and oleyl phosphate, which have the functional groups hydroxyl (–OH), carboxyl (–COOH), amino (–NH2), and phosphorous [–P(=O)(OH)2], respectively, were compared for their ability to disperse TiO2. Experimental results for zeta potential, adsorption, FT‐IR spectroscopy, and rheology, as well as theoretical calculations, indicate that dispersants with –P(=O)(OH)2 and –NH2 were more efficient than those with –COOH or –OH. The primary reason for this difference is related to the different interactions of TiO2 with various dispersants and to different dispersion mechanisms. In addition to the major functional groups, –OH in the chemical structure of dispersants was important, as it might have other effects such as destabilization of the suspensions.
Dyes and pigments, 2006
A series of nano and micron particle size anatase and rutile titanium dioxide (TiO 2) were prepared with various densities of surface treatments in order to examine the influence of the particle size on the photoactivity of the titania particle surface and their degree and nature of interfacial interaction with polymer stabilisers namely, Irganox 1010 (Phenolic type) and Tinuvin 770 (hindered piperidine type). The surface characteristics of the synthesized powders were studied by Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS). The surface area was determined using the Brunauer Emmett Teller (N 2 BET) method, and particle size measurements using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The photochemical activities of the titania particles have been examined by monitoring the oxygen consumption during photo-oxidation of 2-propanol. Surface activity of the titania with stabilisers has also been examined by flow microcalorimetry (FMC) and DRIFTS in order to determine the nature of the interfacial interactions with different polymer stabilisers. Photoactivity assessment verified the higher activity of the nanoparticles. Hydroxyl groups were also found to be accountable for the higher photoactivity of the nanoparticles. The rutile crystal form conferred an inherent photostabilising effect that was further improved by surface coating with alumina. FMC studies revealed that the calcination of nanoanatase increased adsorption activity of hindered phenol and hindered amine probes, with the latter being more strongly adsorbed due to the higher basicity of the amine functionality. DRIFTS indicated adsorption may also occur through the ester functionalities. Calcination of the titania causes a reduction in the surface concentration of TieOH and hence a reduction in the amount of strongly adsorbed water blocking the adsorption sites and possibly bridging the amorphous primary particles on the uncalcined sample. With the calcined samples the adsorption activity was proportional to surface area. The physical and chemical nature of these intermolecular forces are assessed and discussed in relation to the potential effects on polymer stabilisation processes.
Dyes and Pigments, 2006
A series of nano and micron particle size anatase and rutile titanium dioxide (TiO 2 ) were prepared with various densities of surface treatments in order to examine the influence of the particle size on the photoactivity of the titania particle surface and their degree and nature of interfacial interaction with polymer stabilisers namely, Irganox 1010 (Phenolic type) and Tinuvin 770 (hindered piperidine type). The surface characteristics of the synthesized powders were studied by Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS). The surface area was determined using the Brunauer Emmett Teller (N 2 BET) method, and particle size measurements using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The photochemical activities of the titania particles have been examined by monitoring the oxygen consumption during photo-oxidation of 2-propanol. Surface activity of the titania with stabilisers has also been examined by flow microcalorimetry (FMC) and DRIFTS in order to determine the nature of the interfacial interactions with different polymer stabilisers. Photoactivity assessment verified the higher activity of the nanoparticles. Hydroxyl groups were also found to be accountable for the higher photoactivity of the nanoparticles. The rutile crystal form conferred an inherent photostabilising effect that was further improved by surface coating with alumina. FMC studies revealed that the calcination of nanoanatase increased adsorption activity of hindered phenol and hindered amine probes, with the latter being more strongly adsorbed due to the higher basicity of the amine functionality. DRIFTS indicated adsorption may also occur through the ester functionalities. Calcination of the titania causes a reduction in the surface concentration of TieOH and hence a reduction in the amount of strongly adsorbed water blocking the adsorption sites and possibly bridging the amorphous primary particles on the uncalcined sample. With the calcined samples the adsorption activity was proportional to surface area. The physical and chemical nature of these intermolecular forces are assessed and discussed in relation to the potential effects on polymer stabilisation processes.
Polymethacrylic Acid Adsorption and the Aggregation Stability of Titanium Dioxide Suspensions
Adsorption Science & Technology, 1999
The dependence of polymethacrylic acid adsorption on to two rutile samples of titanium dioxide on the adsorbent content in the system and the degree of neutralization of the macromolecules has been studied. A scheme for the adsorption and aggregation processes occurring under the experimental conditions employed has been proposed and a correlation between the extent of polyelectrolyte adsorption and the aggregation stability of the titanium dioxide suspensions established. The extent of adsorption decreased with increasing adsorbent content and this has been explained by the decrease in surface available for macromolecular adsorption. Such decreases can arise from coagulation processes as well as from incomplete redispersion of the titanium dioxide particles. It has been shown that the maximum stability of the titanium dioxide suspensions occurs at polyelectrolyte concentrations well below the concentration necessary for adsorption saturation. As the degree of neutralization of the macromolecules increased the extent of adsorption decreased. the aggregation stability of suspensions in the presence of low molecular weight polymethacrylic acid remaining unchanged while that in the presence of high molecular weight polyacid molecules decreased. The results obtained have been discussed in conjunction with the properties of aqueous solutions of partially neutralized polymethacrylic acid and changes in the conformations of the macromolecules.
Dispersion of alumina-coated TiO 2 particles by adsorption of sodium polyacrylate
Colloids and Surfaces A-physicochemical and Engineering Aspects, 2001
The dispersion of alumina-coated TiO 2 particles by adsorption of the sodium salt of poly(acrylic) acid (PANa) was investigated in regard to the effective charge number of the particles. The effective surface charge number of the particles as well as the electrokinetic mobility only slightly increase with adsorption of PANa. Osmotic stress experiments have shown that PANa (MW 20 000) loses almost all of its effective charge once adsorbed. Moreover, small angle neutron scattering (SANS) experiments on suspensions at various volume fractions have shown that the structural arrangement of the particles is different in presence of adsorbed PANa only at very short distance (high volume fraction). These experimental evidences lead to the conclusion that the decrease of both the apparent viscosity and initial yield stress after adsorption of PANa can mostly be explained by a steric stabilization. The polyelectrolyte on the surface would prevent the weak but still undesirable aggregation of the particles when they collide. : S 0 9 2 7 -7 7 5 7 ( 0 0 ) 0 0 7 0 5 -6
Poly(methacrylic acid) Adsorption and Electrical Surface Properties of Titanium Dioxide Suspensions
Adsorption Science & Technology, 2002
The influence of adsorbed poly(methacrylic acid) (PMAA) of molecular weight 10 × 103 on the aggregation stability of titanium dioxide suspensions and on the zeta potential of the particles has been studied over a wide range of pH (from 2.0 to 12.0). The dependence of the zeta potential of titanium dioxide particles in aqueous suspension on the pH of the system was typical for metal oxides and passed through an isoelectric point at pH0 = 6.2. Adsorption of poly(methacrylic acid) on to titanium dioxide particles had a considerable effect on the dependence of the zeta potential of the particles on the pH of the suspension medium. The change of zeta potential both in the absence and presence of PMAA correlated well with the aggregation stability of the suspensions, which was estimated from the mean radius of the particles. The influence of the adsorbed poly(methacrylic acid) macromolecules on the zeta potential of the particles can be explained according to a scheme which envisages both...
Nanoscale Research Letters, 2011
Characterizing nanoparticle dispersions and understanding the effect of parameters that alter dispersion properties are important for both environmental applications and toxicity investigations. The role of particle surface area, primary particle size, and crystal phase on TiO2 nanoparticle dispersion properties is reported. Hydrodynamic size, zeta potential, and isoelectric point (IEP) of ten laboratory synthesized TiO2 samples, and one commercial Degussa TiO2 sample (P25) dispersed in different solutions were characterized. Solution ionic strength and pH affect titania dispersion properties. The effect of monovalent (NaCl) and divalent (MgCl2) inert electrolytes on dispersion properties was quantified through their contribution to ionic strength. Increasing titania particle surface area resulted in a decrease in solution pH. At fixed pH, increasing the particle surface area enhanced the collision frequency between particles and led to a higher degree of agglomeration. In addition to the synthesis method, TiO2 isoelectric point was found to be dependent on particle size. As anatase TiO2 primary particle size increased from 6 nm to 104 nm, its IEP decreased from 6.0 to 3.8 that also results in changes in dispersion zeta potential and hydrodynamic size. In contrast to particle size, TiO2 nanoparticle IEP was found to be insensitive to particle crystal structure.
Journal of Colloid and Interface Science, 2000
The adsorption of sodium dodecyl sulfate to colloidal titanium dioxide was investigated using the electrophoretic fingerprinting approach. An electrophoretic fingerprint is a contour diagram of the observed electrophoretic mobility as a function of the bulk solution pH and pλ, the log of the bulk solution conductivity. Surfactant adsorption was observed to be strong under acidic conditions, as illustrated in the dramatic changes in the electrophoretic fingerprints. Electrokinetic data were compared with adsorption isotherm data obtained by a depletion method and good qualitative agreement was found. The observed pH changes associated with surfactant adsorption suggested ligand exchange as a possible mechanism of adsorption. Electrophoretic fingerprinting was shown to be a powerful means of examining surfactant adsorption to colloidal particles.