Attractive Van Der Waals Forces Research Articles

Thermodynamic Properties of Ferrofluid: Preparation, Stability and Statistical Mechanics

Ferrofluids are known as magnetic liquids that are colloidal suspensions of ultrafine, single domain magnetic particles in either aqueous or non-aqueous liquids. For such fluids, the problem arises in calculating thermal conductivity, viscosity, and thermodynamic properties on nanoparticles and ferrofluids. Thus, the main objective is to determine thermal conductivity and viscosity for ferro-nanoparticles and ferrofluids. For this study, the ZnO and Fe3O4 are checked for mechanical properties such as SEM, TEM and XRD. Then, being suspended into the diesel engine oil SAE-50 as base fluid and surfactant, Triton-100, in preparation of two-step method. Ferrofluids are prepared for 0.1%, 0.4% & 0.7% w/v and stability of nanofluids are being observed for 5 days. From the results obtained experimentally, the nanoparticles were found to be in good stability as no coagulate occur. This is because the EDLRF acts as the opposite to Van der Waals attractive force which separates the particles from each other. Finally, the thermal conductivity and viscosity for ferro-nanoparticles and ferrofluids were successfully obtained and demonstrated. Statistical mechanics are then discussed to calculate the properties of ferrofluids. The analytical results from statistical mechanics are potentially be used to compare with the experiment data.

Internal Force Mechanism of Pisha Sandstone as a Soil Amendment to Improve Sandy Soil Structural Stability in Mu Us Sandy Land

Compounding Pisha sandstone (PSS) with sandy soil in Mu Us Sandy Land is a viable agronomical measure to effectively reduce soil erosion and improve soil quality due to the complementary characters and structures of the two materials. Aggregate stability is an important indicator to assess sandy soil erosion resistance and quality, which could be largely affected by soil surface electrochemical properties and particle interaction forces. However, the effect of the compound ratio and particle interaction forces on the aggregate stability of compound soils with Pisha sandstone and sandy soil is still unclear. Therefore, in this study, the electrochemical properties, particle interaction forces, and their effects on the aggregate stability of PSS and sandy soil at five volume ratios (0:1, 1:5, 1:2, 1:1, and 1:0) were determined to clarify the internal force mechanism of PSS to increase sandy soil structural stability in a 10-year field experiment. Experiments were measured by a combined method for the determination of surface properties and aggregate water stability. A ten-year field study revealed that the incorporation of Pisha sandstone significantly enhanced the soil organic carbon (SOC) and cation exchange capacity (CEC) (p < 0.05), while the CEC value notably increased from 4.68 to 13.76 cmol·kg−1 (p < 0.05). The soil surface potential (absolute value) and the electric field intensity gradually decreased with the increase in the Pisha sandstone content. For the compound soil particle interaction force, the addition of Pisha sandstone enhanced the van der Waals attraction force, reduced the net repulsive force between compound soil particles, and promoted the agglomeration of aeolian sandy soil. The overall trend of the aggregate breaking strength of compound soils under different addition ratios of PSS was 1:0 > 1:1 > 0:1 > 1:5 > 1:2. When the Pisha sandstone content in the compound soils was <50%, the aggregate stability was mainly influenced by compound soil particle interaction forces, and the interaction force increase was the key reason for the aggregate breakdown. When the Pisha sandstone content in the compound soils was ≥50%, the aggregate stability was affected by the combined effects of the compound soil particle composition and particle interaction forces. These results indicate that PSS addition ratios and particle interaction force are important factors affecting the structural stability of compound soils, in which the volume ratio of PSS to sandy soil of 1:2 is the appropriate ratio. Our study provides some theoretical references for further understanding of the compound soil structure improvement and sandy soil erosion control in Mu Us Sandy Land.

Influence of Defects and Charges on the Colloidal Stabilization of Graphene in Water.

Mastering graphene preparation is an essential step to its integration into practical applications. For large-scale purposes, full graphite exfoliation appears as a suitable route for graphene production. However, it requires overpowering attractive van der Waals forces demanding large energy input, with the risk of introducing defects in the material. This difficulty can be overcome by using graphite intercalation compounds (GICs) as starting material. The greater inter-sheet separation in GICs (compared with graphite) allows the gentler exfoliation of soluble graphenide (reduced graphene) flakes. A solvent exchange strategy, accompanied by the oxidation of graphenide to graphene, can be implemented to produce stable aqueous graphene dispersions (Eau de graphene, EdG), which can be readily incorporated into many processes or materials. In this work, we prove that electrostatic forces are responsible for the stability of fully exfoliated graphene in water, and explore the influence of the oxidation and solvent exchange procedures on the quality and stability of EdG. We show that the amount of defects in graphene is limited if graphenide oxidation is carried out before exposing the material to water, and that gas removal of water before the incorporation of pre-oxidized graphene is advantageous for the long-term stability of EdG.

A micro-mechanical insight into the thermo-mechanical behaviour of clays

The response of fine-grained soils to the combined effects of stress and temperature is a problem of growing concern in geoenvironmental engineering. Unlike most materials, fine-grained soils subjected to heating under drained conditions can exhibit either reversible expansion or irreversible contraction, depending on their loading history. This clay complex thermo-mechanical behaviour is widely reported in the literature, but its origin is still unknown. This paper explores the particle-scale origin of clay thermo-mechanical behaviour and helps to inform constitutive thermo-mechanical models. Clay particle interactions include non-contact forces, which are electrochemical in nature and prevail in face-to-face configuration and contact forces, which are mechanical forces transferred from one particle to another through a contact surface, typical of edge-to-face configuration. Non-contact forces include electrostatic Coulombic forces and van der Waals attractive forces. This paper proposes a combined numerical and analytical approach to quantify the elementary interactions between clay particles. The results are used to interpret typical stress-thermal paths, such as compression tests at different temperatures and heating-cooling cycles at constant mechanical stress. It is concluded that the electrochemical interactions governing the face-to-face particle configuration can only explain the elastic volumetric response of over-consolidated clays subjected to heating. The thermo-plastic behaviour associated with the reduction of the pre-consolidation pressure with temperature and the volumetric plastic compressive strain in response to heating in normally-consolidated clays is attributed to the edge-to-face particle configurations.

Elevated temperature effects (T > 100 °C) on the interfacial water and microstructure swelling of Na-montmorillonite

Montmorillonite-based barriers are key elements of the engineered barrier systems (EBS) in geological disposal facilities (GDF). Their performance at temperatures above 100 °C is not sufficiently understood to assess the possibility of raising the temperature limits in GDF designs that could reduce construction costs and CO2 footprint. The present work provides new fundamental insights through molecular dynamics (MD) simulations of Na-montmorillonite's water-clay interactions and swelling pressure at temperatures 298–500 K and basal spacings of 1.5–3.5 nm. At temperatures above 100 °C, the swelling behaviour is governed by the attractive van der Waals force and the repulsive hydration force instead of the repulsive electrostatic (double layer) force. The swelling pressure reduction with increasing temperature is related to the weakened hydration repulsion and electric double layer repulsion, which result from the deterioration of the interlayer water layer structure and the shrinkage of the electric double layer. The applicability and breakdown of the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory at elevated temperatures are examined. By excluding the osmotic contribution in the DLVO theory, the summation of the van der Waals interaction in DLVO and an additional non-DLVO hydration interaction can predict our MD system's swelling under high temperatures. The findings of this study provide a fundamental understanding of the swelling behaviour and the underlying molecular-level mechanisms of the clay microstructure under extreme conditions.

Experimental In-Situ Observatory on Brownian Motion Behavior of 105 nm Sized Silica Particles During Chemical Mechanical Polishing of 4H-SiC by an Evanescent Field

The experimentally observing optical systems for on-machine measurement have been developed to study on nano-polishing phenomena during the chemical mechanical polishing process, which is a wet process in semiconductor manufacturing. The developed optical system employs an evanescent field to selectively enhance exclusively the observatory of phenomena occurring on the surface being polished, offering a lateral resolving power of approximately 400 nm, in the slurry concentration of up to 5 wt% based on the numerical aperture of the objective lens. In addition, there is also the observability of 105 nm and down to 55 nm-sized silica particles without requiring additive fluorescence agents in or around the nano-particles, even when these particles are moving on surfaces such as silica glass or hard materials (silicon carbide: 4H-SiC). Consequently, the motion behavior of nano-particles disjoining with polishing pad asperity was explored and discussed, in this paper. Experimental results revealed that the polishing pad spatially constrains the movement of particles between the pad and the substrate surface, guiding them toward the surface being polished. During pad sliding, fluidically dragged nano-particles exhibit slower movement than the polishing pad sliding speed while retaining the Brownian motion. Furthermore, 105 nm-sized silica particles did not continuously approach to attach onto the SiC surface; the nano-particles approached in steps with reduced Brownian motion in all directions before attaching. This behavior can be attributed to the effects of van der Waals attraction and electrostatic repulsion forces between the particle and the substrate surfaces.

Small Molecule Additives to Suppress Bundling in Dimensional‐Limited Self‐Alignment Method for High‐Density Aligned Carbon Nanotube Array

AbstractSemiconducting single‐walled carbon nanotube (CNT) is a promising candidate as a channel material for advanced logic transistors, attributed to the ultra‐thin 1‐nm cylindrical geometry, high mobility, and high carrier injection velocity. However, the presence of undesired CNT bundles in the CNT arrays for wafer‐scale device fabrication, even when utilizing the state‐of‐the‐art dimension‐limited self‐alignment (DLSA) method, poses challenges. These CNT bundles degrade the transistor gate's efficiency in controlling the flow of charge carriers in the CNT channel, leading to pronounced device‐to‐device variability. Here, a novel method is introduced to alleviate bundling in CNT arrays assembled via DLSA, by involving small molecule additive to screen the attractive van der Waals force between neighboring CNTs during the DLSA process, resulting in over 50% reduction in CNT bundling. Furthermore, a pioneering methodology for quantifying CNT bundles is presented and employed experimentally to assess bundles in dense CNT arrays assembled by DLSA using transmission electron microscopy. Both experimental data and molecular dynamics simulation reveal that CNT bundling originates from van der Waals attraction between CNTs, and the disturbed liquid‐liquid interface by accumulating excess polar molecules. These findings illuminate new pathways for realizing dense, bundle‐free CNT arrays.

Universal Pairwise Interatomic van der Waals Potentials Based on Quantum Drude Oscillators.

Repulsive short-range and attractive long-range van der Waals (vdW) forces play an appreciable role in the behavior of extended molecular systems. When using empirical force fields, the most popular computational methods applied to such systems, vdW forces are typically described by Lennard-Jones-like potentials, which unfortunately have a limited predictive power. Here, we present a universal parameterization of a quantum-mechanical vdW potential, which requires only two free-atom properties─the static dipole polarizability α1 and the dipole-dipole C6 dispersion coefficient. This is achieved by deriving the functional form of the potential from the quantum Drude oscillator (QDO) model, employing scaling laws for the equilibrium distance and the binding energy, and applying the microscopic law of corresponding states. The vdW-QDO potential is shown to be accurate for vdW binding energy curves, as demonstrated by comparing to the ab initio binding curves of 21 noble-gas dimers. The functional form of the vdW-QDO potential has the correct asymptotic behavior at both zero and infinite distances. In addition, it is shown that the damped vdW-QDO potential can accurately describe vdW interactions in dimers consisting of group II elements. Finally, we demonstrate the applicability of the atom-in-molecule vdW-QDO model for predicting accurate dispersion energies for molecular systems. The present work makes an important step toward constructing universal vdW potentials, which could benefit (bio)molecular computational studies.

A new method for estimating zeta potential of carboxylic acids’ functionalised particles

Zeta potential is an important colloid parameter that dictates many intriguing phenomena such as colloid stability/aggregation, electrophoretic deposition and particle separation technology. Zeta potential is commonly used to characterise colloid particles’ electrostatic interactions coupled with other forces such as van der Waals attraction, hydration and steric forces. However, the measurement of zeta potential involves complicated sample preparation and instrument/theory selection, often resulting in inaccurate measurement. Here, we developed a simple method that combines Stern–Grahame and Gouy–Chapman theories, for estimating zeta potential using parameters such as acid site pKa, acid site density and particle size. The method is applied to a wide range of carboxylic acids’ functionalised colloid particles with various pKa. Results show that the new method is capable of capturing zeta potential dependence on pKa and pH. The new method can be applied to particles with complicated or multiple acid/base sites. Without the need for sample preparation/instrument, this new method is believed to save efforts for estimating zeta potential with good accuracy.

Componential and molecular-weight-dependent effects of natural organic matter on the colloidal behavior, transformation, and toxicity of MoS2 nanoflakes

The potential widespread applications in water processing have rendered the necessity for investigations of the fate and hazard of molybdenum disulfide (MoS2) nanosheets. Herein, it was found that humic acid (HA) had better performances toward stabilizing pure 2H phase MoS2 and chemical-exfoliated MoS2 (ce-MoS2) in electrolyte solutions than fulvic acid (FA), and molecular weight (MW)-dependent manners were disclosed due to steric repulsions. Compared with darkness, the extent to which the aggregation and sedimentation of ce-MoS2 facilitated by visible light irradiation was greater in the presence of HA and FA fractions, likely due to the introduction of stronger plasmonic dipole-dipole interaction and Van der Waals attraction forces. HA-triggered structural disintegration of nanosheets was performed after irradiation and it was observed to be more significant with the increase in MWs, whereas the MW-dependent dissolution of MoS2 caused by FA was much quicker than that by HA owing to the higher generation of singlet oxygen. Moreover, FA lowered the bioavailability of MoS2 and relieved its toxicity to zebrafish more effectively than HA. Our findings boost the insights into the effects of organic molecules on the fates and hazards of MoS2, providing guidance for the MoS2-based nanotechnological development on environment.

Micro‐mechanical analysis of one‐dimensional compression of clay with DEM

AbstractIn order to clarify the micro‐mechanics of clay during compression, the behavior of clay subjected to one‐dimensional compression is investigated at the particle scale using discrete element method (DEM). The flaky clay particles in the simulation are approximated by clumps made of spheres. A new contact model is implemented to account for the double‐layer repulsive force, the van der Waals attractive force and the mechanical contact force. The effect of sphere arrangement in the particle clump is discussed. The DEM model is validated against experimental observations in terms of macroscopic compressibility, particle dip angle as well as the over consolidated behavior. The e‐logσv curve shows a concave‐to‐linear shape. The evolution of dip angle of clay particles indicates that particles tend to have an anisotropy with a preferential orientation towards horizontal direction. The increase of preconsolidation pressure decreases the initial compressibility due to the increase the number of mechanical contacts. The evolution of average coordination and sphere‐sphere contact shows that the majority of mechanical contacts are generated before the compressive stress reaches 100 kPa. Evolution of soil fabric is presented and discussed.

Effects of the Changes of Particle Surface Electric Field and Interaction Force on the Reclaimed Soil Aggregate Structural Stability under the Application of Different Soil Conditioners

Aggregate stability is a key factor in the evaluation of soil structure and erosion resistance, which is largely influenced by soil electric field and particle interaction. However, there are few studies on how different organic and inorganic soil conditioners change the surface electric field and interaction force of reclaimed soil to improve the aggregate stability. Therefore, a five-year field experiment was conducted to quantitatively study the effects of FeSO4 (TM), organic fertilizer (TO), fly ash (TF), maturing agent + organic fertilizer (TMO) and fly ash + organic fertilizer (TFO), compared with control (CK) treatment, on the reclaimed soil internal force and the aggregate crushing strength. The results showed that the reclaimed soil surface potential and electric field intensity increased after 5 years of application of organic and inorganic soil conditioners. Under the same electrolyte concentration and electric field conditions, the crushing strength of aggregates (<5 μm) treated with TFO, TMO, TO, TF and TM decreased by 43.70%, 35.51%, 25.97%, 8.28% and 5.49%, respectively, compared with the control treatment, and the combination of organic and inorganic treatment (TFO and TMO) had a better effect on improving the aggregate crushing resistance. With the application of soil conditioners, the reclaimed soil DLVO force and net resultant force gradually decreased, and the order of magnitude was TFO < TMO < TO < TF < TM < CK, indicating that the application of organic and inorganic soil conditioners enhanced the van der Waals attractive force and net attractive force between reclaimed soil particles, and reduced the net repulsive force between particles. The theoretical calculation results of the reclaimed soil internal force well explain the experimental results of aggregate stability against crushing, and the relationship between aggregate crushing strength and net resultant force is exponential (p < 0.01). Generally speaking, the soil conditioners increase the net attractive force between particles, reduce the possibility of violent crushing of aggregates due to the increase of electric field intensity and improve the aggregate structural stability, among which the combined application of organic and inorganic soil conditioners has a better improvement effect. The results of this study will lay a theoretical foundation for clarifying the improvement of different soil conditioners on the reclaimed soil structural stability and erosion resistance.

Interaction force mechanism for the improvement of reclaimed soil aggregate stability in abandoned homestead by different organic-inorganic soil conditioners

Reasonable application of organic-inorganic soil conditioners can effectively improve the structure and fertility of reclaimed soil in abandoned homestead. Aggregate stability is an important indicator to evaluate soil structure and fertility, and is largely influenced by soil internal forces (van der Waals attractive force, electrostatic repulsive force, hydration repulsive force) and particle surface properties. However, there are few studies on the influence of different soil conditioners on the reclaimed soil internal forces and its relationship with the aggregate stability. Therefore, we selected six different treatments of organic fertilizer (TO), fly ash (TF), maturing agent (TM), maturing agent + organic fertilizer (TMO), fly ash + organic fertilizer (TFO) and control (CK) to conduct a 5-year field experiment to study the effects of reclaimed soil particle interaction forces and surface characteristics on aggregate stability under the treatment of different soil conditioners. The results showed that with the application of soil conditioners, the soil organic matter (SOM), specific surface area (SSA), surface charge (σ0), cation exchange capacity (CEC), aggregate mean weight diameter (MWD) and Hamaker constant increased gradually, while the pH value decreased slightly. In particular, the MWD under the treatments of TFO and TMO increased by 150.3% and 65.6% respectively compared with that under the CK treatment. With the increasing application of soil conditioners, the electrostatic repulsive force and van der Waals attractive force between reclaimed soil particles increased constantly, but the net resultant force between particles decreased and the net attractive force increased continuously, thus improving the aggregate stability. Therefore, there is a significant negative correlation between the net resultant force among reclaimed soil particles and MWD and CEC. In addition, 10−2 mol L-1 is the critical concentration that affects the reclaimed soil internal force, and the organic-inorganic treatments of TFO and TMO can improve the net resultant force better. In a word, the particle interaction forces are important factors affecting the reclaimed soil structural stability, and this study provides a scientific reference for the rational selection of soil conditioners and its interaction force mechanism in the reclaimed soil improvement.

MoS2 nanosheets based label-free colorimetric aptasensor for Escherichia coli O157: H7 detection

The aggregation behavior of large-scale two-dimensional molybdenum disulfide (MoS2) nanosheets prepared by sonication-assisted exfoliation in environmental friendly 45% ethanol/water mixture under different conditions (e.g., salt concentration, cation valence and nanosheets size) had been examined to make them more appropriate for biological sensing application. Adjustment of sonication time and centrifuging speed could be utilized to select MoS2 nanosheets with various concentrations and sizes. Higher concentrations of salt and cations with higher valence were more effective to aggregate MoS2 nanosheets and settle them than their counterparts, which could be attributed to the perturbation of attractive van der Waals forces and repulsive Coulombic interactions. Moreover, the ethanol in mixture was capable of assisting MoS2 nanosheets to resist this aggregation initiated by salt but it would disturb the stability of aptamer functionalized MoS2 nanosheets in salt solution. The interplay of Escherichia coli O157: H7 (E. coli O157:H7) aptamer functionalized MoS2 nanosheets and salt was then inspired to develop a high sensitive detection method of E. coli O157:H7. The introduction of target bacteria induced MoS2 nanosheets to be exposed to cations, and promoted the aggregation and sedimentation behavior of MoS2 nanosheets. The change in extinction of MoS2 nanosheets had a linear relationship with E. coli O157:H7 concentration in a range of 500–5000 CFU/mL with a detection limit of 116 CFU/mL. This proposed colorimetric sensor expands the application scope of MoS2 nanosheets and shows its promising potential as an alternative tool for bacteria detection in food and water quality monitoring.

Impact of bending stiffness on ground-state conformations for semiflexible polymers.

Many variants of RNA, DNA, and even proteins can be considered semiflexible polymers, where bending stiffness, as a type of energetic penalty, competes with attractive van der Waals forces in structure formation processes. Here, we systematically investigate the effect of the bending stiffness on ground-state conformations of a generic coarse-grained model for semiflexible polymers. This model possesses multiple transition barriers. Therefore, we employ advanced generalized-ensemble Monte Carlo methods to search for the lowest-energy conformations. As the formation of distinct versatile ground-state conformations, including compact globules, rod-like bundles, and toroids, strongly depends on the strength of the bending restraint, we also performed a detailed analysis of contact and distance maps.

Nanoparticle-Imprinted Silica Gel for the Size-Selective Capture of Silver Ultrafine Nanoparticles from Water.

A synthetic approach has been developed to prepare silica gel monoliths that embed well separated silver or gold spherical nanoparticles (NP), with diameters of 8, 18 and 115 nm. Fe3+, O2/cysteine and HNO3 were all successfully used to oxidize and remove silver NP from silica, while aqua regia was necessary for gold NP. In all cases, NP-imprinted silica gel materials were obtained, with spherical voids of the same dimensions of the dissolved particles. By grinding the monoliths, we prepared NP-imprinted silica powders that were able to efficiently reuptake silver ultrafine NP (Ag-ufNP, d = 8 nm) from aqueous solutions. Moreover, the NP-imprinted silica powders showed a remarkable size selectivity, based on the best match between NP radius and the curvature radius of the cavities, driven by the optimization of attractive Van der Waals forces between SiO2 and NP. Ag-ufNP are increasingly used in products, goods, medical devices, disinfectants, and their consequent diffusion in the environment is of rising concern. Although limited here to a proof-of-concept level, the materials and methods described in this paper may be an efficient solution for capturing Ag-ufNP from environmental waters and to safely dispose them.

A Novel Plastic‐Crystal Electrolyte with Fast Ion‐Transport Channels for Solid Zinc‐Ion Batteries

AbstractMiniaturized solid zinc‐ion batteries that are safe, environmentally friendly, and low‐cost are ideal candidates for powering emerging microelectronics. However, sluggish Zn2+ mobility in solid phases hampers the viability of solid Zn2+ electrolytes and hence their practicability. Here, nanoscale Zn2+ channels are successfully engineered in a plastic‐crystal electrolyte, thus activating fast Zn2+ solid‐state transport. The ion‐dipole interaction exerted by water molecules orients amphiphilic anions in bilayers, further forming a layered architecture backed by long‐range van der Waals attractive forces. In the interlayer, the heteroleptic coordination contributed by the water molecule and anion frees the Zn2+ from anionic traps, leading to a high Zn2+ conductivity of 2.2 × 10−3 S cm−1. This elaborately tailored texture confers a combination of robust mechanical characteristics and outstanding electrochemical performance upon the resultant electrolyte. The applicability is demonstrated by the high Zn2+ platting/stripping efficiency (99.6%), durable longevity of symmetric Zn‐Zn and Zn‐MnO2 cells, as well as the engineering of versatile micro batteries (MBs). This work provides new perspectives for developing super multivalent ion conductors through the innovative design of ion‐conducting nanochannels.

Influence of Surface Roughness, Nanostructure, and Wetting on Bacterial Adhesion.

Bacterial fouling is a persistent problem causing the deterioration and failure of functional surfaces for industrial equipment/components; numerous human, animal, and plant infections/diseases; and energy waste due to the inefficiencies at internal and external geometries of transport systems. This work gains new insights into the effect of surface roughness on bacterial fouling by systematically studying bacterial adhesion on model hydrophobic (methyl-terminated) surfaces with roughness scales spanning from ∼2 nm to ∼390 nm. Additionally, a surface energy integration framework is developed to elucidate the role of surface roughness on the energetics of bacteria and substrate interactions. For a given bacteria type and surface chemistry; the extent of bacterial fouling was found to demonstrate up to a 75-fold variation with surface roughness. For the cases showing hydrophobic wetting behavior, both increased effective surface area with increasing roughness and decreased activation energy with increased surface roughness was concluded to enhance the extent of bacterial adhesion. For the cases of superhydrophobic surfaces, the combination of factors including (i) the surpassing of Laplace pressure force of interstitial air over bacterial adhesive force, (ii) the reduced effective substrate area for bacteria wall due to air gaps to have direct/solid contact, and (iii) the reduction of attractive van der Waals force that holds adhering bacteria on the substrate were summarized to weaken the bacterial adhesion. Overall, this study is significant in the context of designing antifouling coatings and systems as well as explaining variations in bacterial contamination and biofilm formation processes on functional surfaces.

Elucidating the particle concentration-dependent flow behavior of aqueous TiO2 suspensions based on polymer dispersant structures and interparticle surface distances

Flowing behavior of concentrated aqueous TiO2 suspensions was evaluated in relation to the structure of polymeric dispersants, their adlayer thickness on particle surface, and particle concentrations. Comb-type polymeric dispersants comprising polyethylene glycol-based side chains with different combinations of unit number and side chain length were investigated. Based on particle concentration–apparent viscosity curves of the suspensions with TiO2 nanoparticles saturated with dispersants, maximum packing fraction and polymer adlayer thickness were estimated through the Krieger–Dougherty model. When the steric repulsive force of polymer dispersant dominated van der Waals attractive forces, the flow curves of the suspension exhibited hysteresis characteristics as the average particle surface distance approached the adlayer thickness of polymer dispersants. Additionally, by introducing the concept of relative surface distance, which is the average particle surface distance divided by the adlayer thickness, the particle concentration dependency of the suspension viscosities with different dispersants followed a unified trend.

The role of coal gasification slag in cement paste with and without polycarboxylate superplasticizer and its rheology

Coal gasification slag (CGS) is the main by-product of coal gasification technology, and the utilization of CGS as mineral admixture is environmentally sound. In this paper, the effect and mechanisms of CGS on the workability (i.e., fluidity and rheological behaviors) of ordinary Portland cement (OPC) paste with and without polycarboxylate superplasticizer (PCE) were studied. The zeta potential and surface free energies of OPC and CGS were tested to calculate the electrostatic force and Van der Waals force variations due to the addition of CGS particles. The results revealed that CGS mainly decreases the van der Waals attraction force between binder particles, enhancing the fluidity and reducing cement pastes’ yield stress and plastic viscosity. When blended with PCE, the dissolution of CGS mainly increased the ionic concentrations of Si(OH)x(4-x), which promoted the aggregation of PCE and decreased its adsorption, thus decreasing the fluidity and increasing the rheological parameters.