Colloidal Alumina Particles Research Articles

Rheology of 3D printable ceramic suspensions: effects of non-adsorbing polymer on discontinuous shear thickening.

Concentrated suspensions of particles at volume fractions (ϕ) ≥ 0.5 often exhibit complex rheological behavior, transitioning from shear thinning to shear thickening as the shear stress or shear rate is increased. These suspensions can be extruded to form 3D structures, with non-adsorbing polymers often added as rheology modifiers to improve printability. Understanding how non-adsorbing polymers affect the suspension rheology, particularly the onset of shear thickening, is critical to the design of particle inks that will extrude uniformly. In this work, we examine the rheology of concentrated aqueous suspensions of colloidal alumina particles and the effects of adding non-adsorbing polyvinylpyrrolidone (PVP). First, we show that suspensions with ϕalumina = 0.560-0.575 exhibited discontinuous shear thickening (DST), where the viscosity increased by up to two orders of magnitude above an onset stress (τmin). Increasing ϕalumina from 0.550 to 0.575 increased the viscosity and yield stress in the shear thinning regime and decreased τmin. Next, PVP was added at concentrations within the dilute and semi-dilute non-entangled regimes of polymer conformation (ϕPVP = 0.005-0.050) to suspensions with constant ϕalumina = 0.550. DST was observed in all cases and increasing ϕPVP increased the viscosity and yield stress. Interestingly, increasing ϕPVP also increased τmin. We posit that the free PVP chains act as lubricants between alumina particles, increasing the stress needed to induce thickening. Finally, we demonstrate through direct comparisons of suspensions with and without PVP how non-adsorbing polymer addition can extend the extrusion processing window due to the increase in τmin.

Small Molecule Adsorption on Colloidal Alumina and Zirconia Abrasives Used in Chemical-Mechanical Planarization (CMP) Slurries

Small molecule adsorption on CMP slurry abrasive particles has been investigated previously for silica (1) and ceria (2, 3) abrasives using fluorescence correlation spectroscopy (FCS) and attenuated total reflectance – Fourier transform infrared spectroscopy (ATR-FTIR). The need for further characterization of such adsorptive interactions is dictated by the increasing use of abrasive particles in CMP slurries with minimized hydrodynamic diameters (≤ 10 nm) as a means to reduce surface defects created during CMP processes. Incorporation of ever-smaller abrasive particles in CMP slurries will, however, promote the adsorption of chemical additives on a slurry’s abrasive particles due to the increase in the total abrasive particle surface area. In the present study, FCS and ATR-FTIR are employed in the analysis of small molecule adsorption on colloidal alumina and zirconia abrasive particles. This work is motivated by the widespread commercial use of alumina-based slurries in CMP processes for planarization of deposited copper films on dielectric layers and the proposed use (4) of zirconia abrasives in CMP slurries for metal film removal on dielectric metal oxide materials. The reported FCS studies use fluorescent dyes as probes for adsorption sites on alumina and zirconia colloids dispersed in aqueous solution. Described ATR-FTIR analyses summarize the characterization of molecular interactions driving glycine and picolinic acid adsorption on porous thin films of colloidal alumina and zirconia, respectively. The potential for employing these methods in studies modelling the adsorption of CMP slurry additives on a metal film deposited on a silicon wafer surface is also discussed.

Effective infiltration with polyethyleneimine-grafted colloidal alumina particles for silica-based ceramic cores

Effective infiltration with polyethyleneimine-grafted colloidal alumina particles for silica-based ceramic cores

Amino-functionalization of colloidal alumina particles for enhancement of the infiltration behavior in a silica-based ceramic core

The surface characteristics of nano-sized alumina particles were modified to include amine functional groups to enhance the infiltration behavior in a silica-based ceramic core, inhibiting crystallization of the cristobalite phase in order to improve mechanical properties. In this study, polymer-based polyethylenimine (PEI) or silane-based (3-Aminopropyl)triethoxysilane (APTES) were used as precursors in amine group addition. The specimens were characterized by the C-H stretching vibration and N-H bending vibration or the symmetric stretching vibration of siloxane group (Si-O-Si) in the FT-IR spectra, depending on the nature of the molecular structure of the precursor molecule. The dispersion properties were also improved through electrostatic repulsion or steric hindrance. These modifications resulted in a PEI-grafted colloidal alumina particle that induced a more rapid infiltration process with greater efficiency than did the APTES-treated particle. The rapid infiltration of the ceramic core suppressed the formation of the cristobalite phase, improved the flexural strength from 3.2 to 10.2MPa, and reduced the linear shrinkage rate from 1.91–1.05%.

Controlling Mixed-Protein Adsorption Layers on Colloidal Alumina Particles by Tailoring Carboxyl and Hydroxyl Surface Group Densities

We show that different ratios of bovine serum albumin (BSA) and lysozyme (LSZ) can be achieved in a mixed protein adsorption layer by tailoring the amounts of carboxyl (-COOH) and aluminum hydroxyl (AlOH) groups on colloidal alumina particles (d50 ≈ 180 nm). The particles are surface-functionalized with -COOH groups, and the resultant surface chemistry, including the remaining AlOH groups, is characterized and quantified using elemental analysis, ζ potential measurements, acid-base titration, IR spectroscopy, electron microscopy, nitrogen adsorption, and dynamic light scattering. BSA and LSZ are subsequently added to the particle suspensions, and protein adsorption is monitored by in situ ζ potential measurements while being quantified by UV spectroscopy and gel electrophoresis. A comparison of single-component and sequential protein adsorption reveals that BSA and LSZ have specific adsorption sites: BSA adsorbs primarily via AlOH groups, whereas LSZ adsorbs only via -COOH groups (1-2 -COOH groups on the particle surface is enough to bind one LSZ molecule). Tailoring such groups on the particle surface allows control of the composition of a mixed BSA and LSZ adsorption layer. The results provide further insight into how particle surface chemistry affects the composition of protein adsorption layers on colloidal particles and is valuable for the design of such particles for biotechnological and biomedical applications.

Adsorption and Orientation of the Physiological Extracellular Peptide Glutathione Disulfide on Surface Functionalized Colloidal Alumina Particles

Understanding the interrelation between surface chemistry of colloidal particles and surface adsorption of biomolecules is a crucial prerequisite for the design of materials for biotechnological and nanomedical applications. Here, we elucidate how tailoring the surface chemistry of colloidal alumina particles (d50 = 180 nm) with amino (-NH2), carboxylate (-COOH), phosphate (-PO3H2) or sulfonate (-SO3H) groups affects adsorption and orientation of the model peptide glutathione disulfide (GSSG). GSSG adsorbed on native, -NH2-functionalized, and -SO3H-functionalized alumina but not on -COOH- and -PO3H2-functionalized particles. When adsorption occurred, the process was rapid (≤5 min), reversible by application of salts, and followed a Langmuir adsorption isotherm dependent on the particle surface functionalization and ζ potential. The orientation of particle bound GSSG was assessed by the release of glutathione after reducing the GSSG disulfide bond and by ζ potential measurements. GSSG is likely to bind via the carboxylate groups of one of its two glutathionyl (GS) moieties onto native and -NH2-modified alumina, whereas GSSG is suggested to bind to -SO3H-modified alumina via the primary amino groups of both GS moieties. Thus, GSSG adsorption and orientation can be tailored by varying the molecular composition of the particle surface, demonstrating a step toward guiding interactions of biomolecules with colloidal particles.

The role of surface functionalization of colloidal alumina particles on their controlled interactions with viruses

Materials that interact in a controlled manner with viruses attract increasing interest in biotechnology, medicine, and environmental technology. Here, we show that virus–material interactions can be guided by intrinsic material surface chemistries, introduced by tailored surface functionalizations. For this purpose, colloidal alumina particles are surface functionalized with amino, carboxyl, phosphate, chloropropyl, and sulfonate groups in different surface concentrations and characterized in terms of elemental composition, electrokinetic, hydrophobic properties, and morphology. The interaction of the functionalized particles with hepatitis A virus and phages MS2 and PhiX174 is assessed by virus titer reduction after incubation with particles, activity of viruses conjugated to particles, and imaged by electron microscopy. Type and surface density of particle functional groups control the virus titer reduction between 0 and 99.999% (5 log values). For instance, high sulfonate surface concentrations (4.7 groups/nm2) inhibit attractive virus–material interactions and lead to complete virus recovery. Low sulfonate surface concentrations (1.2 groups/nm2), native alumina, and chloropropyl-functionalized particles induce strong virus-particle adsorption. The virus conformation and capsid amino acid composition further influence the virus–material interaction. Fundamental interrelations between material properties, virus properties, and the complex virus–material interaction are discussed and a versatile pool of surface functionalization strategies controlling virus–material interactions is presented.

Controlling protein–particle adsorption by surface tailoring colloidal alumina particles with sulfonate groups

In this study, we demonstrate the control of protein adsorption by tailoring the sulfonate group density on the surface of colloidal alumina particles. The colloidal alumina (d50=179±8nm) is first accurately functionalized with sulfonate groups (SO3H) in densities ranging from 0 to 4.7SO3Hnm−2. The zeta potential, hydrophilic/hydrophobic properties, particle size, morphology, surface area and elemental composition of the functionalized particles are assessed. The adsorption of three model proteins, bovine serum albumin (BSA), lysozyme (LSZ) and trypsin (TRY), is then investigated at pH 6.9±0.3 and an ionic strength of 3mM. Solution depletion and zeta potential experiments show that BSA, LSZ and TRY adsorption is strongly affected by the SO3H surface density rather than by the net zeta potential of the particles. A direct correlation between the SO3H surface density, the intrinsic protein amino acid composition and protein adsorption is observed. Thus a continuous adjustment of the protein adsorption amount can be achieved between almost no coverage and a theoretical monolayer by varying the density of SO3H groups on the particle surface. These findings enable a deeper understanding of protein–particle interactions and, moreover, support the design and engineering of materials for specific biotechnology, environmental technology or nanomedicine applications.

Influence of pressure on filtration of aqueous alumina suspensions

The dispersibility of colloidal alumina particles (median size 310 nm) was related to the surface potential, the solid concentration in a suspension and the pressure applied to the particles. The consolidation behavior of colloidal alumina particles with an isoelectric point pH 8.7 was examined using a developed pressure filtration apparatus at 1–10 MPa of applied pressure. The height of 7 or 20 vol% alumina suspensions at pH 3.0, 7.8 and 9.0 as a function of filtration time was fitted by a filtration model developed for a flocculated suspension rather than a traditional filtration model for a dispersed suspension. An increased pressure, a decrease of particle concentration and a porous microstructure of colloidal cake reduced the consolidation time of alumina suspension. The wet alumina compacts were significantly compressed during filtration but relaxed after the release of the applied pressure. However, the packing density of alumina compact after calcination at 700 °C was almost independent of the filtration pressure and controlled by the structure of network of alumina particles in a solution.

The role of emulsifier in stabilization of emulsions containing colloidal alumina particles

This paper focuses on the study on rheological behaviour of emulsions, stabilized by both differently modified dispersible colloidal Boehmite alumina nanoparticles and a non-ionic emulsifier. Hysteresis loop measurements and dynamic rheological measurements were carried out in linear and non-linear regimes on two different emulsion systems – water-in-oil (W/O) and oil-in-water (O/W) emulsions.Emulsion stabilized by a combination of moderately hydrophobic particles and a non-ionic emulsifier is an O/W emulsion. The addition of emulsifier improved the stability, however, did not show a significant influence on the emulsion flow behaviour. The emulsion, stabilized by both – nanoparticles and emulsifier – showed a complicated behaviour, i.e. sometimes it exhibited thixotropy or antithixotropy and sometimes both of them.Emulsion stabilized by rather hydrophobic particles and a non-polar emulsifier is a W/O emulsion. The emulsion is very homogenous and exhibited very weak thixotropy. Dynamic measurements showed that G’ was almost equal to G” and both parameters were frequency-dependent, indicating a viscous liquid-like system with little network structure if any. With addition of emulsifier, the rather elastic solid-like emulsion structure may be changed into the viscous liquid-like structure.In order to get a better understanding of relationships between rheological behaviour and microstructure, differential scanning calorimetry (DSC) results and optical microscopic images of the emulsions studied were discussed.

Protein adsorption on colloidal alumina particles functionalized with amino, carboxyl, sulfonate and phosphate groups

Colloidal oxide particles in biomedical or biotechnological applications immediately become coated with proteins of the biological medium, a process which is strongly influenced by the surface characteristics of the particles. Fundamental correlations between surface characteristics and the, so far mainly uncontrollable, protein adsorption are still not clear. In this study the surface of colloidal alumina particles (d50=179±8nm) was systematically adjusted with NH2, COOH, SO3H and PO3H2 functional groups to investigate the influence on the adsorption of the three model proteins, bovine serum albumin (BSA), lysozyme (LSZ) and trypsin (TRY). The surface functionalization is characterized and discussed in detail with regard to the morphology, isoelectric point, zeta potential, hydrophilic/hydrophobic properties, functional group density and stability. Protein–particle interaction was then assessed by evaluating the amount of protein adsorbed and the zeta potentials of protein–particle conjugates. Protein adsorption was found to be influenced by the type of functional group as well as the expected electrostatic forces under the given experimental conditions. The level of protein adsorption might, hence, be specifically controlled by the type of surface functionalization. Possible adsorption modes of BSA, LSZ and TRY on the particles are suggested by considering the spatial surface potential distribution of the proteins calculated from the protein database file. The particles presented provide an excellent prerequisite for further investigation of fundamental particle–protein interactions and the design of functionally graded materials for biomedical and biotechnological applications, e.g. as drug carriers or for protein purification.

Naphthalene Sulfonate Functionalized Dendrimers at the Solid−Liquid Interface: Influence of Core Type, Ionic Strength, and Competitive Ionic Adsorbates

The adsorption of naphthalene disulfonic acid surface-functionalized dendrimers (generation 4) on to colloidal alumina particles is reported, considering the role of dendrimer core type (ammonia vs benzylhydrylamine-polylysine) and electrolyte addition on the adsorption affinity and interfacial packing and competitive adsorption. Irrespective of the dendrimer core type, the maximum adsorbed amount increased with increasing ionic strength. The adsorption affinity of a benzylhydrylamine-cored SPL-7013 increased with increasing ionic strength, whereas a decrease was observed for the ammonia-cored SPL-2923. At high ionic strengths (>or=10(-1) M NaCl) dendrimers close pack at the interface as an array of equivalent hard spheres, whereas at lower ionic strengths both dendrimers occupy a lower area than theoretically predicted for either cubic or hexagonal close packing, based on double layer repulsion. The additional attraction between dendrimers is attributed to the intercalation of the neighboring dendrons. Adsorption of SPL-2923 is enhanced by the presence of Ca2+ ions and depressed by the presence of HCO3- and HPO4(2-) ions, whereas SPL-7013 adsorption is only depressed by the presence of HPO4(2-) ions, suggesting a dendrimer-specific competitive adsorption process. This work clearly demonstrates the role of dendrimer architecture on adsorption at an interface, a process of fundamental importance to a wide range of dendrimer applications.

Interactions and dispersion stability of aluminum oxide colloidal particles in electroless nickel solutions in the presence of comb polyelectrolytes

The effect of comb polyelectrolytes on the dispersion stability of colloidal alumina particles in DI water and commercial electroless nickel (EN) solutions was investigated. Adsorption of polyelectrolytes and major EN components onto colloidal alumina was assessed by TGA, chemical analysis, and zeta potential measurements. Zeta potential measurements were made during titrations of comb-polyelectrolyte-stabilized dispersions with EN solutions to full ionic strength for the first time. The compilation of titration curves made with varying amounts of comb polyelectrolytes provides high resolution and novel insight into the particle/surfactant/EN systems. Continuous decrease in particle/EN components surface interactions with the increase in comb polyelectrolyte coverage is observed. Laser diffraction measurements reveal steric stabilization of nano- and submicronmeter alumina dispersions in both DI water and EN solutions with >7 wt% and >2 wt% comb polyelectrolyte, respectively.

Stability of dispersions of colloidal alumina particles in aqueous suspensions

The colloidal stability of suspensions of alumina particles has been investigated by measuring particle size distribution, sedimentation, viscosity, and zeta potential. Alumina particles were found to be optimally dispersed at pH around 3 to 7.8 without dispersant and at pH 8.5 and beyond with dispersant. The above results corroborate zeta potential and viscosity measurement data well. The surface charge of alumina powder changed significantly with anionic polyelectrolyte (ammonium polycarboxylate, APC) and the iep shifted toward more acidic range under different dispersant conditions. It was found that the essential role played by pH and dispersant (APC) on the charge generation and shift in the isoelectric point of alumina manifests two features: (i) the stability decreases on approaching the isoelectric point from either side of pH, and (ii) the maximum instability was found at pH 9.1 for alumina only and at pH 6.8 for alumina/APC, which is close to the isoelectric points for both the system, respectively. Using the model based on the electrical double-layer theory of surfactant adsorption through shift in isoelectric points, the authors could estimate the specific free energy of interaction (7.501 kcal/mol) between particles and dispersant. The interaction energy, zeta potential, sedimentation, and viscosity results, were used to explain the colloidal stability of the suspension.

The flocculation efficiency of polydisperse polymer flocculants

The flocculation performance of three poly(acrylic acid) (PAA) samples ( M w=9×10 4, 2.5×10 5 and 1×10 6 g/mol) has been investigated. Colloidal alumina particles were used as a model system and tests were performed at pH 5. Using a single-component polyacid, it was found that the optimum dosage required to achieve supernatant clarity was similar between the 9×10 4 g/mol PAA (23 ppm) and 2.5×10 5 g/mol PAA (26 ppm), but increased dramatically with the 1×10 6 g/mol PAA (83 ppm). For the two lower molecular weight samples, flocculation occurs through a charge neutralisation mechanism. In contrast, polymer bridging is inferred to be the dominant flocculation mechanism for the high molecular weight sample. The flocculation performance of a polymer mixture, produced by blending the high and low molecular weight polyacids to give an average molecular weight of 2.5×10 5 g/mol, was also studied. Supernatant clarity from this system was found to be comparable to that from the single-component polyacid of the same (average) molecular weight. However, the optimum dosage required for the polymer mixture was about twice as much as that for the single-component reference polymer. The results suggest that for the polymer mixture no synergistic effects occur. Instead, analyses of aggregate sizes indicate an independent behaviour for the two polymers in the blend. We also examined re-suspension (under shear) and re-flocculation of the sediment formed in the initial flocculation experiments. For the three single-polymer systems, rapid re-flocculation after shear was seen for the two lower molecular weight samples suggesting a reversible aggregate breakage. For the high molecular weight sample, re-suspension resulted in the formation of a stable dispersion. This result was attributed to breakage of the high molecular weight polymer sample during re-suspension. In the case of the polymer mixture, rapid re-flocculation was again observed despite the presence of a large amount of the high molecular weight sample. This result may have important practical implications.

Electrical Properties, Rheology and Packing Density of Colloidal Alumina Particles

The mobility of positively and negatively charged alumina particles in concentrated suspensions was analyzed with monitoring the electrical conductivity of the suspensions. The decreased mobility (u) at a lower charge (Q) was due to increased attractive interaction. The increase of volume fraction of moderately charged particles resulted in the decrease of u value because of the increased repulsive interaction with decreased interparticle distance. Too strong repulsive interaction between highly charged particles suppressed the migration of dispersed particles. The mobility of negatively charged particles was lower than that of positively charged particles at a similar Q value because of a stronger effect of chemical bonding between hydrated particle surface. The apparent viscosity of acidic suspensions was lower than that of basic suspensions. This result was also discussed based on three important effects of charge, concentration and nature of hydrated surface of alumina particles. The green densities of alumina compacts consolidated by filtration through gypsum molds were higher for the acidic suspensions than for the basic suspensions.

From Powders to Dispersions in Water: Effect of Adsorbed Molecules on the Redispersion of Alumina Particles

Aqueous dispersions of colloidal alumina particles have been submitted to processes where the dispersion is aggregated, dried, and then redispersed in water. This cycle was performed with alumina particles that had different surface states: bare surfaces with monovalent counterions; surfaces that have been covered with small molecule ligands and have their surface charge reversed. In all cases, redispersion was produced by an increase in the ionic pressure due to the counterions, after immersion of the powder in water at the appropriate pH. In all cases, the pH that produced the appropriate ionic pressure was 5−6 pH units away from the isoelectric point of the surfaces. This was related to the fact that the surfaces were, in all cases, separated by a thin water film, which had a constant thickness (8 Å) set by the strength of binding of water to the alumina surfaces. However, for surfaces that had been covered with high amounts of macromolecular ligands, the minimum separation of surfaces was increased, and redispersion could be obtained at a pH which was closer to the isoelectric point. These phenomena can be accounted for, quantitatively, through a calculation of the balance of surface forces, including van der Waals attractions, hydration forces, and ionic pressures.

Bridging flocculation studied by light scattering and settling

Polymers are used increasingly in solid–liquid separation processes. Bridging flocculation is the most common particle aggregation mechanism in these processes. However, little is known about the structure of the aggregates formed. This paper presents a critical comparison of two of the techniques that can be very useful tools for the characterisation of aggregate structures, i.e. static light scattering and settling. Of particular interest was their applicability for bridging flocculated aggregates. Both techniques were tested on two model systems: salt-induced fast coagulation and polymer-induced bridging flocculation of colloidal alumina particles. For diffusion-limited cluster–cluster aggregation at a high salt concentration, aggregate mass fractal dimensions of 1.75 and 1.65 were obtained from the light scattering and settling experiments, respectively. For bridging flocculation whereby flocs were formed using dual polymers, light scattering and settling gave mass fractal dimensions of 2.12 and 1.85, respectively. It was concluded that each of these techniques has certain advantages and disadvantages, therefore, it is best to view them as complementary. The settling method may be better suited for studying aggregates in bridging flocculation where floc sizes can be quite large which may cause the light scattering technique to become inapplicable.

Addition of alumina to cellulose acetate membranes

Asymmetric ceramic-polymer membranes were prepared by dry and wet phase inversion processes using dispersions containing cellulose acetate, acetone, water and colloidal alumina particles. When the alumina content is low, the microstructure contains macrovoids (pore diameter ∼ 15 μm) below a dense polymer rich skin. The addition of greater amounts of alumina results in a microstructural transition from macrovoids to a uniform small pore network (pore diameter ∼ 2μm). However, the alumina particles have a negligible effect on the porosity of the dense skin that forms at the air/membrane or water immersion bath/ membrane interface. In all membranes, the alumina particles are unagglomerated and uniformly dispersed throughout the cellulose acetate network. Changes in the microstructure are attributed to delayed phase separation of cellulose acetate in the presence of ceramic particles.

Hydrodynamics of a lamella electrosettler

AbstractUsing the principles of conservation of mass and momenturn for each phase, a theory is developed for describing quantitatively the sedimentation of colloidal particles in vessels having electrodes that are inclined to the vertical.As a limiting case, a kinematic settling formula was derived that describes the motion of settling fronts of colloidal alumina particles suspended in tetralin as a function of angle of inclination and strength of applied electric field in terms of electrophoretic mobilities. A hydrodynamic computer model shows the flow patterns and settling behavior of such lamella settlers with and without an applied electric field. The predicted motions of the settling fronts and the thicknesses of the clear boundary layers above the upper wall of the inclined vessels globally agreed with the experimental observations.