Rheological investigation of colloidal systems

Ceramic processing such as cementation and casting are among the most widely used methods for production of commercial products with different size and properties to date. Highly loaded and stable aqueous suspensions whose rheological behavior can be controlled by low content of organic additives are highly desired. To have control over the viscosity and improve fluidity/solid loading of ceramic suspensions, different series of polycarboxylate ether-based copolymers (PCEs) that include acrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, vinylphosphonic acid, and polyethylene glycol-1000 were synthesized. The effect of monomer feed ratio and molecular weight of copolymer on dispersing ability of the copolymers, fluidity of the pastes, and rheological behavior of suspensions were characterized and performance of these copolymers as rheology modifiers was reported. For the first time in literature, dedicated superplasticizers for i) calcium aluminate cement (CAC) and ii) ordinary portland cement-calcined clay-calcium carbonate ternary blends were synthesized such that they caters to the characteristic properties of these systems; i) high rate of surface development and surface charge in CAC and ii) layered structure of calcined clay and high concentration of sulfate ions in ternary blended cement. The effect of PCEs on i) rheological behavior of alumina suspensions and ii) fabrication of highly loaded alumina suspensions and machining of solid cast green bodies were also investigated. While 20 vol. % pure alumina suspensions showed severe particle jamming, 35 vol. % alumina suspensions with more than 1 wt. % copolymers displayed Newtonian behavior. These suspensions found to be suitable for fabrication of solid cast green bodies and provided ability of significant removal of material in machining process

Poly(carboxylate ether)-based superplasticizer achieves workability retention in calcium aluminate cement

Calcium aluminate cement (CAC) suffers from loss of workability in less than an hour (~15 minutes) after first touch of water. Current superplasticizers that are utilized to modify the viscosity of cement admixtures are designed to target ordinary Portland cement (OPC). The high affinity between these superplasticizers and cement particles were found to be detrimental in CAC systems. Utilization of a monomer that, instead, facilitates gradual adsorption of a superplasticizer provides workability retention. For the first time in literature, we report a superplasticizer that caters to the properties of CAC such as high rate of surface development and surface charge. While neat CAC was almost unworkable after 1 hour, with the addition of only 0.4% of the optimized superplasticizer, 90% fluidity retention was achieved

Extensional rheology and stability behavior of alumina suspensions in the presence of AMPS-modified polycarboxylate ether-based copolymers

A series of polycarboxylate ether-based copolymers that include acrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, and polyethylene glycol-1000 was synthesized, and the performance of these copolymers as rheology modifiers in aqueous alumina suspensions was characterized. We discussed the effect of monomer feed ratio and molecular weight on dispersing ability of these copolymers and on extensional behavior of alumina suspensions. Results of zeta potential analysis determined that using the copolymers even at 0.5 wt.% results in all-negative zeta potentials for the entire pH range (2-12). These copolymers immensely affect the extensional rheological behavior of alumina suspensions-while 20 vol.% pure alumina suspension showed severe strain hardening behavior, suspensions with 1 wt.% copolymers and 35 vol.% alumina particles displayed no strain hardening. In this series, the copolymer with lowest molecular weight decreased the extensional viscosity of suspensions at the rupture of thread with three orders of magnitude as well

A PCE-based rheology modifier allows machining of solid cast green bodies of alumina

The performance of a poly(carboxylate ether) (PCE)-based superplasticizer to enable the machining of green bodies that are solid cast from suspensions of alumina was investigated. An alumina loading of 35 vol% in the presence of 1.25 wt% superplasticizer was established to be suitable for lathing and removal of significant amount of material through drilling. A reduction of 77% in the diameter of green bodies that corresponds to a 59% reduction in volume was achieved. The lathed green bodies exhibited smooth terraces without visible cracks. All of the green bodies were sintered without a polymer burnout step

Rheological behavior of poly(acrylonitrile) concentrated solutions: effect of Sb2O3 nanoparticles on shear and extensional flow

This study investigates the effect of antimony trioxide (Sb2O3) nanoparticles on shear and extensional flow properties of concentrated polyacrylonitrile (PAN) solutions. Through shear rheology, a wide variety of rheological observations, such as Payne effect, applicability of Cox-Merz rule, and range of linear viscoelastic behavior (critical strain) were assessed. The presence of Sb2O3 nanoparticles was found to promote the non-linear viscoelasticity of the solutions and give rise to enhanced heterogeneous domains of PAN in the solution. In elongational flow, thinning dynamics of the nanocomposites was tracked to reproduce the dynamics of deformation in the spinline of the dry-jet wet spinning process. Increasing amounts of Sb2O3 nanoparticles in the solution were shown to improve the lifetime of the filament. All solutions were ruptured through elastocapillary behavior, while strengthened strain-hardening behavior was observed after the addition of Sb2O3 nanoparticles to the polymer solution

Shear and extensional rheological characterization of poly(acrylonitrile)/halloysite nanocomposite solutions

The shear and extensional flow properties of polyacrylonitrile (PAN) solution in the presence of halloysite nanotubes (HNTs) were investigated at an industrially relevant concentration of the polymer. In dynamic shear rheology, the elasticity and relaxation time of PAN solutions and the availability of heterogeneous PAN domains were found to increase with HNT content. Extensional flow behavior of PAN solutions were characterized using the capillary breakup extensional rheometry and increasing the amount of HNT content in the solution was found to increase the life-time of the filament and suppress strain hardening at high strains

Single additive enables 3D printing of highly loaded iron oxide suspensions

A single additive, a grafted copolymer, is designed to ensure the stability of suspensions of highly loaded iron oxide nanoparticles (IOPs) and to facilitate three-dimensional (3D) printing of these suspensions in the filament form. This poly (ethylene glycol)-grafted copolymer of N-[3(dimethylamino)propyl]methacrylamide and acrylic acid harnesses both electrostatic and steric repulsion to realize an optimum formulation for 3D printing. When used at 1.15 wt % (by the weight of IOPs), the suspension attains ∼81 wt % solid loading96% of the theoretical limit as calculated by the Krieger−Dougherty equation. Rectangular, thick-walled toroidal, and thin-walled toroidal magnetic cores and a porous lattice structure are fabricated to demonstrate the utilization of this suspension as an ink for 3D printing. The electrical and magnetic properties of the magnetic cores are characterized through impedance spectroscopy (IS) and vibrating sample magnetometry (VSM), respectively. The IS indicates the possibility of utilizing wire-wound 3D printed cores as the inductive coils. The VSM verifies that the magnetic properties of IOPs before and after the ink formulation are kept almost unchanged because of the low dosage of the additive. This particle-targeted approach for the formulation of 3D printing inks allows embodiment of a fully aqueous system with utmost target material content