Time-resolved rheology, small angle X-ray scattering (SAXS), and electron paramagnetic resonance (EPR) techniques were used to study the polymerization of geopolymers. These polymers are inorganically synthesized by alkaline activation an aluminosilicate source (metakaolin) in aqueous solution. The influence alkali activator (Na(+), K(+), Cs(+)) was investigated at room temperature. As observed through variation viscoelastic moduli (G', G"), curing proceeds steps that well pronounced when...

Nitrogen sorption and small- wide-angle X-ray neutron scattering techniques were used to study the porous structure of geopolymers, inorganic polymers synthesized by reaction a strongly alkaline solution an aluminosilicate source (metakaolin). The effects aging use alkali activators (Na + , K ) different sizes investigated at room temperature. influence time on microstructure both geopolymer matrixes was verified in terms pore volume specific surface area. results suggested refinement...

A combination of intrusive and small-angle scattering techniques (USAXS/SAXS SANS) was used to characterize the porous structure metakaolin-based geopolymers. The influence geopolymer paste composition aging time in a 100% relative humidity environment at 293 K were studied. effect alkali activator, water amount silica investigated. results show strong `ink-bottle' effect, indicating two-level pore structure: meso- macroporous network. Both activator have significant impact on porosity...

Significance Quantifying the viscoelastic properties of weak colloidal gels remains challenging due to continuously aging nature these pasty materials. Through time-resolved mechanical and structural spectroscopy application time–connectivity superposition principle we construct moduli over eight decades effective material time. This protocol reveals dual relaxation time spectrum with gel- glass-like characteristics at large small scales, respectively. The structure network critical gel...

Colloidal gels, where nanoscale particles aggregate into an elastic yet fragile network, are at the heart of materials that combine specific optical, electrical and mechanical properties. Tailoring viscoelastic features colloidal gels in real-time thanks to external stimulus currently appears as a major challenge design "smart" soft materials. Here we introduce "rheo-acoustic" class sensitive ultrasonic vibrations. By using combination rheological structural characterization, evidence...

This study focuses on the transition from paste state to solid which occurs during hardening of metakaolin‐based Na‐geopolymers. The occurrence primary interactions and structural properties were investigated using classical oscillatory rheology ( OR ) methods. A time‐frequency‐resolved TF 2R) method was used in order obtain more detailed information about percolation aggregation mechanisms. results obtained show following process: (i) Elastic behavior predominates initially over viscous at...

A combination of original, powerful characterization techniques was used to make a thorough description solid geopolymers and the associated effect varying alkali cation source—NaOH, KOH, or CsOH—and aging for up several years. More specifically, local pore structures were progressively determined from atomic scale nanometers by pair distribution function analysis (PDF), small-angle X-ray scattering (SAXS), longer correlation concerning network, possible diffusion accumulation phenomena...

Recent accelerated simulations of the decondensation silicates by sodium hydroxide open a window on understanding complex mechanisms depolymerization silicate chains. Herein, that involve two water molecules (or OH– groups) are unveiled. The study different solutions, having same chemical composition but in concentration, help one to draw more general conclusions dissociation mechanism solutions. We find is not always assisted single about 20% cases OH–) present near environment. results...

Abstract In the first part of this paper, a new approach to model residence time distribution (RTD) in co‐rotating twin‐screw extruder was proposed. It consists coupling continuum mechanics with chemical engineering one, yielding an RTD curve without any fitting parameter. However, choice ideal reactors that depict behavior each particular profile is not evident. second part, we present experimental study based on two types (Leistritz 30–34 and Clextral BC45), different screw profiles...

Abstract A theoretical model to determine the residence time distribution (RTD) in a co‐rotating twin‐screw extruder is proposed. The method consists of coupling continuum mechanics approach with chemical engineering one and allows us obtain RTD without any adjustable parameter. process parameters are obtained using Ludovic® modeling software, ideal reactors chosen depict screw profile. influence speed, feed rate viscosity on described fictive predictions qualitative agreement literature...

Colloidal gels are out-of-equilibrium soft solids composed of attractive Brownian particles that form a space-spanning network at low volume fractions. The elastic properties these systems result from the microstructure, which is very sensitive to shear history. Here, we take advantage such sensitivity tune viscoelastic colloidal gel made carbon black nanoparticles. Starting fluidized state an applied rate 0, use abrupt flow cessation trigger liquid-to-solid transition. We observe resulting...

Abstract We investigate the shear flow of a sludge mimicking slurries produced by nuclear industry and constituted dispersion non-Brownian particles into an attractive colloidal at total solid volume fraction about 10 %. Combining rheometry ultrasound imaging, we show that, upon decreasing rate, transitions from homogeneous profile in bulk to fully arrested plug-like state with wall slip, through oscillatory regime where strong fluctuations slip velocity propagate along vorticity direction....

Due to rich rheological properties, dispersions of attractive colloidal particles are ubiquitous in industries. Specifically, upon experiencing a sudden reduction shear rate, these may exhibit transient behaviors such as thixotropy-where viscosity increases over time-and anti-thixotropy, characterized by an initial decrease before reaching steady state. While thixotropy has been described competition between structure buildup and disruption, the mechanisms anti-thixotropy remain poorly...