TRANSPORT PROPERTIES OF LIQUID PHASE PERCOLATION CLUSTER IN HIGHLY PERMEABLE GLASSY POLYMERS

Porosity, permeability, and conductivity of PTMSP membranes in ethanol-water mixtures were determined by analyzing the impedance characteristics. The critical volume fraction of porosity at which through conductivity channels are formed was calculated. When the alcohol content in the solution increases, it was 0.29; when it decreases, it was 0.17. The obtained dependencies indicate that the transfer of matter in the membrane occurs the liquid phase elements, forming a percolation cluster as the amount of sorbed liquid increases. The hysteresis effect was observed in the measured values of porosity, permeability, conductivity, and capacity. The porous structure of a dry PTMSP membrane consists of free volume elements that are unconnected to each other. At ⁓30% alcohol concentration, through channels, begin to form, connecting both sides of the membrane. In this case, both permeability and electrical conductivity increase as a power function, in contrast to the porosity that increases linearly. Lichtenecker and Rother’s formula helped to calculate the volume fractions of the conducting and non-conducting phases in the system. The obtained values of the amount of liquid in the membrane at various spatial arrangements of the channels made it possible to establish the structure of the liquid-filled channels. The best agreement with the experimental values was obtained for the chaotic structure. This is consistent with the existing ideas about the structure of the studied membranes and confirms the assumption that the percolation cluster is formed from free volume elements filled with the liquid phase. The observed low values of the zeta potential and, consequently, the low values of the electrostatic component of the wedging pressure indicate that the increase in the size or the number of transport channels is associated with non-electrostatic forces.

Effects of Bentonite Nanoclay and Cetyltrimethyl Ammonium Bromide Modified Bentonite Nanoclay on Phase Inversion of Water-in-Oil Emulsions

The effects of unmodified and modified bentonite nanoclays (with various degrees of surfactant modification) on the catastrophic phase inversion from water-in-oil (W/O) emulsion to oil-in-water (O/W) emulsion were determined experimentally. The bentonite nanoclay (NC-Bt) was suspended in the aqueous phase, and the critical volume fraction of water where phase inversion from W/O to O/W emulsion took place was determined through conductivity measurements. Cetyltrimethyl ammonium bromide (CTAB) was used as a surfactant to modify the nanoclay. The adsorption of CTAB onto nanoclay had a strong influence on the contact angle and the critical volume fraction of water where phase inversion took place. The modification of the nanoclay brought about by the adsorption of CTAB increased the three-phase contact angle (measured through the aqueous phase), thereby making it more hydrophobic, and prolonged the phase inversion point. CTAB alone and CTAB-modified nanoclay delayed the phase inversion process in a similar manner, showing a strong dependence on the CTAB concentration.

DEM-aided method for predicting the hydraulic properties with particle-size distribution of porous media

Purpose The soil water retention curve (SWRC) and unsaturated hydraulic conductivity (UHC) are crucial indices to assess hydraulic properties of porous media that primarily depend on the particle and pore size distributions. This study aims to present a method based on the discrete element model (DEM) and the typical Arya and Paris model (AP model) to numerically predict SWRC and UHC. Design/methodology/approach First, the DEM (PFC3D software) is used to construct the pore and particle size distributions in porous media. The number of particles is calculated according to the AP model, which can be applied to evaluate the relationship between the suction head and the moisture of porous media. Subsequently, combining critical path analysis (CPA) and fractal theory, the air entry value is applied to calculate the critical pore radius (CPR) and the critical volume fraction (CVF) for evaluating the unsaturated hydraulic conductivity. Findings This method is validated against the experimental results of 11 soils from the clay loam to the sand, and then the scaling parameter in the AP model and critical volume fraction value for many types of soils are presented for reference; subsequently, the gradation effect on hydraulic property of soils is analyzed. Furthermore, the calculation for unbound graded aggregate (UGA) material as a special case and a theoretical extension are provided. Originality/value The presented study provides an important insight into the relationship between the heterogeneous particle and hydraulic properties by the DEM and sheds light on the directions for future study of a method to investigate the hydraulic properties of porous media.

Unravelling the effects of size, volume fraction and shape of nanoparticle additives on crystallization of nanocomposite polymers

Adding nanoparticles to polymer depending on the shape may enhance crystallization. However, crystallization retardation may follow due to confinement effects. Equations for critical volume fraction and particle size are derived in confinement limit.

Computational analysis of the intermetallic formation during the dissimilar metal aluminum-to-steel friction stir welding process

The extent of inter-material mixing and the formation of intermetallic compounds play a critical role in the structural integrity and mechanical properties of the joints in the case of dissimilar metal friction stir welding. In general, there is a critical volume fraction of the intermetallic compounds in the mix zone of the friction stir welding-joint at which the mechanical properties of the joint are maximized. That is, insufficient inter-material mixing and the accompanying sub-critical volume fraction of the intermetallic compounds results in insufficient inter-material bonding and inferior joint strength. Conversely, super-critical volume fraction of the intermetallic compounds typically gives rise to the joint embrittlement. To address the problem of the effect of the friction stir welding process parameters on the extent of intermetallic compound formation, a multi-physics computational framework has been developed and applied to the case of dissimilar metal friction stir welding involving commercially pure (CP) aluminum and AISI 1005 low-carbon steel. The multi-physics framework comprises the following main modules: (a) finite-element-based friction stir welding-process modeling; (b) quantum-mechanics, atomistic and CALPHAD-type continuum material thermodynamics analyses of the intermetallic compound-nucleation process; (c) a continuum-type analysis of multi-component diffusion-controlled growth of the intermetallic compounds; and (d) Kolmogorov–Johnson–Mehl–Avrami type analysis of the evolution of the intermetallic compound volume fraction within the friction stir welding joint as a function of the friction stir welding process parameters. The results obtained revealed that: (i) the extent and the spatial distribution of the intermetallic compounds is a sensitive function of the friction stir welding-process parameters; and (ii) among the six potential Al-Fe intermetallic compounds, FeAl and Fe3Al are associated with the largest volume fractions and, hence, play a key role in both attaining the required joint strength and in the potential loss of the joint fracture toughness.

Rheological Characterization of Aqueous ZrO2-Suspension for Additive Manufacturing

Water-based suspensions from commercial Tetragonal stabilized zirconia (3Y-TZP) were produced and characterized with different contents of solids and two different dispersants. According to zeta potential measurements, 3Y-TZP particles showed basic surface characteristics and IEP of around 9 when in aqueous media. The critical volume fraction of solids was about 79.6 wt%, which hindered the processing of more concentrated slurries. Rheological measurements confirmed that well dispersed slurries could be obtained with solid content as high as 79.6 wt.%. The results showed that Triton X-114 was an effective dispersant for preparing well stabilized 3Y-TZP suspensions for the layer-wise slurry deposition process.

Wear and Mechanical Behaviour of Hypo-Eutectic Al-7%Si-0.5%Mg Alloy (A357) Reinforced with Al2O3 Particles

In this study, A357 (Al-7%Si-0.5%Mg) alloy/Al2O3 composites with various volume fractions (4%, 8%, 10%) were prepared by using permanent mould casting. In addition, A357 alloys were cast for comparison purposes. The alloys and composites were given a T6 heat treatment process (solution treatment and artificial ageing), Also microstructure, hardness and tensile properties of these composites were evaluated and compared. In addition, tribological properties of these composites were evaluated using a Pin-on-Disc apparatus at a constant sliding velocity of 1m/s and pressure of 0.35 MPa. The microstructure of the composites shows homogenous distribution of Al2O3 plate-like particles in the Al matrix except in the A357/10%Al2O3 composite. The wear and mechanical properties of composites improve with increasing the volume fraction of Al2O3 upto 8% and then decreases. Particularly, mechanical properties of the A357/10%Al2O3 composite are lower than the alloy indicating that the critical volume fraction of Al2O3 reinforcement in the A357 alloy is 8%. Wear morphology studies show that abrasive and delamination wear are extensive in the alloy whereas the slight delamination wear with some abrasive grooves are found in the composites.