Repulsive Interparticle Forces Research Articles

Investigation and analysis of the macro- and micro-responses of bentonite-sand mixtures to temperature

Bentonite-sand mixture has been proposed as a buffer material of high-level radioactive waste (HLW) repositories in many countries. The elevated temperature in HLW repositories significantly influences the properties and behaviour of the surrounding buffers. However, to date the mechanism of temperature effects on the behaviour of the bentonite buffer is not well understood. This study is aimed at clarifying the macro- and micro-responses of bentonite-sand mixtures by conducting cone penetration test, rheometer test, flask volumetric test, scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) at different temperatures. The results from macro-experiments show that the liquid limit and yield stress increased while bound water content decreased with increasing temperature. The normalized relationships disclose the sand content dramatically affects the degree of temperature influence on the macro-behaviour. SEM and MIP results present that the contact manner between particles converted from edge-to-face to the edge-to-edge association and some intra-aggregate pores merged to form inter-aggregate pores as temperature increases. The mechanisms of the increasing temperature influence on the responses of bentonite-sand mixtures can be inferred that: 1) the diffuse double layer is supposed to decrease since more ions were electrolyzed from montmorillonite particles, thereby, increasing the ion concentration and changing the ion valence; 2) the slight shrinkage of diffuse double layer produced nano-fissures, causing water-hold capacity to increase; 3) the temperature-induced transition from bound water into free water results in an increase of liquid volume; 4) increasing temperature led to increased inter-particle repulsive force. Furthermore, an empirical model was proposed to predict the yield stress of bentonite dispersion incorporating the combined effects of sand content and temperature.

Oversaturating Liquid Interfaces with Nanoparticle‐Surfactants

AbstractAssemblies of nanoparticles at liquid interfaces hold promise as dynamic “active” systems when there are convenient methods to drive the system out of equilibrium via crowding. To this end, we show that oversaturated assemblies of charged nanoparticles can be realized and held in that state with an external electric field. Upon removal of the field, strong interparticle repulsive forces cause a high in‐plane electrostatic pressure that is released in an explosive emulsification. We quantify the packing of the assembly as it is driven into the oversaturated state under an applied electric field. Physiochemical conditions substantially affect the intensity of the induced explosive emulsification, underscoring the crucial role of interparticle electrostatic repulsion.

Oversaturating Liquid Interfaces with Nanoparticle-Surfactants.

Assemblies of nanoparticles at liquid interfaces hold promise as dynamic "active" systems when there are convenient methods to drive the system out of equilibrium via crowding. To this end, we show that oversaturated assemblies of charged nanoparticles can be realized and held in that state with an external electric field. Upon removal of the field, strong interparticle repulsive forces cause a high in-plane electrostatic pressure that is released in an explosive emulsification. We quantify the packing of the assembly as it is driven into the oversaturated state under an applied electric field. Physiochemical conditions substantially affect the intensity of the induced explosive emulsification, underscoring the crucial role of interparticle electrostatic repulsion.

Colloidal Stability of PFSA-Ionomer Dispersions. Part I. Single-Ion Electrostatic Interaction Potential Energies.

Charged colloidal particles neutralized by a single counterion are increasingly important for many emerging technologies. Attention here is paid specifically to hydrogen fuel cells and water electrolyzers whose catalyst layers are manufactured from a perfluorinated sulfonic acid polymer (PFSA) suspended in aqueous/alcohol solutions. Partially dissolved PFSA aggregates, known collectively as ionomers, are stabilized by the electrostatic repulsion of overlapping diffuse double layers consisting of only protons dissociated from the suspended polymer. We denote such double layers containing no added electrolyte as "single ion". Size-distribution predictions build upon interparticle interaction potential energies from the Derjaguin-Landau-Verwey-Overbeek (DLVO) formalism. However, when only a single counterion is present in solution, classical DLVO electrostatic potential energies no longer apply. Accordingly, here a new formulation is proposed to describe how single-counterion diffuse double layers interact in colloidal suspensions. Part II (Srivastav, H.; Weber, A. Z.; Radke, C. J. Langmuir 2024 DOI: 10.1021/acs.langmuir.3c03904) of this contribution uses the new single-ion interaction energies to predict aggregated size distributions and the resulting solution pH of PFSA in mixtures of n-propanol and water. A single-counterion diffuse layer cannot reach an electrically neutral concentration far from a charged particle. Consequently, nowhere in the dispersion is the solvent neutral, and the diffuse layer emanating from one particle always experiences the presence of other particles (or walls). Thus, in addition to an intervening interparticle repulsive force, a backside osmotic force is always present. With this new construction, we establish that single-ion repulsive pair interaction energies are much larger than those of classical DLVO electrostatic potentials. The proposed single-ion electrostatic pair potential governs dramatic new dispersion behavior, including dispersions that are stable at a low volume fraction but unstable at a high volume fraction and finite volume-fraction dispersions that are unstable with fine particles but stable with coarse particles. The proposed single-counterion electrostatic pair potential provides a general expression for predicting colloidal behavior for any charged particle dispersion in ionizing solvents with no added electrolyte.

Emerging investigator series: suspended air nanobubbles in water can shuttle polystyrene nanoplastics to the air–water interface

Suspended nanoplastics can be removed from the water column with nanobubbles if interparticle repulsive forces are overcome by pH adjustment.

Linking Multicomponent Interactions of Catalyst Ink and Catalyst Layer Fabrication with Electrochemical CO2 Reduction Performance

The controllable fabrication of catalyst layers (CL) by tuning the multiscale structure formation is complex but vital to achieving optimum CO2 reduction (CO2R) performance. The CL formation is deeply influenced by catalyst ink. An in-depth understanding on the role of each catalyst ink component and how multicomponent interactions affect ink status, catalyst layer structure, and CO2R performance is crucial.In this work, the roles of various ingredients of catalyst ink were systematically investigated from simple binary inks to complete catalyst inks. Our results showed Ag agglomerates can be broken down more efficiently in water than in alcohols due to stronger inter-particle repulsive forces induced by water disassociation. Ag particles-Nafion networks were found to play a decisive role in stabilizing catalyst ink, mitigating agglomeration and particle sintering. The catalyst ink was comprehensively characterized and reported by static multiple light scattering (SMLS) for the first time in this study. The evolution of catalyst ink was identified in three stages: stable, flocculation and sedimentation. Isopropanol (IPA)-rich solvents were demonstrated to be more effective in stabilizing catalyst ink due to better dispersed Nafion aggregates and further enhanced Ag particle-Nafion interactions.Subsequently, catalyst layer structure and CO2R performance were correlated with multi-component interactions in catalyst ink. Strong Ag particle-Nafion interactions were proven to promote not only ink stability, but also catalyst layer homogeneity and reaction site distribution. Water-rich inks helped improve the porosity and durability of GDEs. The cathodic potential of GDEs made by 70%-water inks (-0.75 V vs. NHE) was 30% lower than zero-water inks (-1.1 V vs. NHE), and the highest CO selectivity was boosted to 97% at an industrial meaningful current density of 200 mA/cm2 by enhancing Ag particle-Nafion interactions through rational design of ink formulation, dispersing and fabrication processes.Simultaneously, a scalable manufacturing methodology of robust GDE was developed and validated to achieve optimal CO2R performance. It will not only provide a meaningful reference for lab applications (fast and reproducible GDE fabrication aiming at new catalysts, ionomers, membranes or operation conditions development), but also provide a steppingstone to industrial applications (GDE fabrication aiming at large scale, good durability and quality of conformance). Figure 1

Improvement in geotechnical properties of soft filter cake stabilized with autoclaved aerated concrete powder: Experimental evidence and micro-mechanism

Filter cake is a type of engineering waste soil composed of fine-grained particles, typically characterized by its high initial saturation and poor engineering performance. In this study, autoclaved aerated concrete powder (AACP) was used as an admixture to improve the mechanical properties of filter cake. The effects of AACP content and curing time on the unconfined compressive strength (UCS) and volume change behavior of compacted specimens were investigated. The test results showed that the UCS of compacted AACP/filter cake mixtures initially increased with increasing AACP content, reaching a peak value at 40 % AACP content, and subsequently decreased. The sample containing 40 % AACP (cured for 28 days) exhibited a constrained modulus comparable to that of conventional embankment filling materials, but with the added advantage of a lower dry density. Expansion of the parent soil, when exposed to water, occurred through interparticle expansion. The addition of AACP resulted in a reduction in the thickness of the diffuse double layer (DDL) of clay particles, as well as a decrease in the interparticle repulsive force. This allowed soil particles to approach each other more closely and facilitated the formation of aggregated soil particles. AACP incorporation further altered the particle size distribution and soil structure, thereby contributing to the improvement in mechanical properties of the filter cake. The physicochemical and microstructural observations, such as SEM, XRD, and MIP analyses, and zeta potential tests, were in good agreement with the changes in the geotechnical properties of the samples. These experimental results provide technical references for the utilization of AACP and filter cake in embankment engineering.

Dual functionality of ferrocene-based metallopolymers as radical scavengers and nanoparticle stabilizing agents.

The beneficial redox properties of ferrocene-based polymers have been utilized during in situ preparation of metallic nanoparticles, while such redox features also indicate a great promise in applications as free radical scavengers. Here, colloidal dispersions of an antioxidant nanozyme composed of amidine-functionalized polystyrene latex (AL) nanoparticles, negatively charged poly(ferrocenylsilane) (PFS(-)) organometallic polyions, and ascorbic acid (AA) were formulated. The AL was first functionalized with PFS(-). Increasing the polymer dose resulted in charge neutralization and subsequent charge reversal of the particles. The strength of repulsive interparticle forces of electrostatic nature was significant at low and high doses leading to stable colloids, while attractive forces dominated near the charge neutralization point giving rise to unstable dispersions. The saturated PFS(-) layer adsorbed on the surface of the AL (p-AL nanozyme) enhanced the colloidal stability against salt-induced aggregation without affecting the pH-dependent charge and size of the particles. The joint effect of PFS(-) and the AA in radical decomposition was observed indicating the antioxidant potential of the system. The immobilization of PFS(-) deteriorated its scavenging activity, yet the combination with AA improved this feature. The results indicate that p-AL-AA is a promising radical scavenger since the high colloidal stability of the particles allows application in heterogeneous systems, such as in industrial manufacturing processes, where antioxidants are required to maintain acceptable product quality.

Direct Measurement of Surfactant-Mediated Picoforces among Nanoparticles in a Quasi-Two-Dimensional Environment.

The lack of methodologies which enable us to measure forces acting between nanomaterials is one of the factors limiting the full comprehension of their behavior and their more effective exploitation in new devices. Here we exploit the irreversible adsorption of surfactant-decorated nanoparticles at the air/water interface to investigate interparticle forces and the effect of the surfactant structure on them. We measured the interparticle repulsive forces as a function of the modulation of the interparticle distance by simultaneously performing compression isotherms and the grazing incidence small-angle X-ray scattering (GISAXS) structural characterization of the monolayers at water–vapor interfaces. Our results demonstrate that the short-range interparticle forces are strongly affected by the presence of the organic ligands, which are shown to be able to influence the interparticle repulsions even when added in micromolar amounts. In particular, we demonstrate the predominant steric nature of short-range forces, which are accounted for in terms of the compression-induced stretched-to-coiled conformational transition of the ligand hydrophobic tail.

Discontinuous shear thickening in dense suspensions: Mechanisms, force networks, and fluctuations

<h2>Abstract</h2> Dense suspensions of particles in a liquid, with industrial examples including coatings or precursors to solid ceramics and cements, can be quite difficult to process because their flow properties are very sensitive to particle surface interactions. We focus on the extreme rate dependence known as "discontinuous shear thickening" (DST) where the viscosity undergoes a finite and typically large discontinuous jump in viscosity at some shear rate. Simultaneous with DST, there is a large increase in the normal stress, including the nonequilibrium osmotic pressure, or ‘particle pressure', leading to the historical name of `dilatancy' for shear thickening. Our computational simulations inclusive of the three ingredients of i) lubrication hydrodynamics, ii) repulsive interparticle forces (e.g. due to surface charge) and iii) contact with friction have been shown to reproduce the primary features of DST found experimentally; this is called lubricated-to-frictional (LF) rheology. We describe the main features of the shear thickening transition in the LF scenario, including the observation of extreme fluctuations. Using our simulation results, we explore the microscopic basis for the LF transition in the force network developed under flow.

Effect of interparticle forces on the stability and droplet diameter of Pickering emulsions stabilized by PEG-coated silica nanoparticles

HypothesisAttractive and repulsive interparticle forces influence the stability and structure of Pickering emulsions. The effect these forces have on emulsion behavior must be better understood to improve Pickering emulsions for subsurface applications, including enhanced oil recovery and aquifer decontamination. Past work demonstrates improved emulsion stability with increasing salinity and reduced electrostatic repulsion, possibly because of interparticle networks. We hypothesize that emulsion stability is similarly improved by reducing interparticle steric repulsion. ExperimentsWe assessed the effect of interparticle forces on emulsion stability by generating decane-in-water emulsions. We used polyethylene glycol (PEG)-coated silica nanoparticles with different diameters, surface modification, and salinities to modify either vdW, steric, or electrostatic interactions. We measured emulsion stability using centrifugation, imaged emulsion droplets with optical microscopy, and analyzed images with ImageJ to calculate droplet diameters. FindingsMildly aggregated particles with 0.5–1.0 μmol/m2 surface PEG exhibit the highest emulsion stability. This optimal surface concentration maximizes a trade-off between particle repulsion and aggregation. Droplet diameters are well explained by an energy balance limited coalescence model, generated by solving DLVO equations. We find that while emulsion stability is influenced by interparticle forces, droplet size is dominated by particle-droplet interactions. These results demonstrate the potential of surface modification to significantly improve emulsion stability.

Spray dried hydroxyapatite-based supraparticles with uniform and controllable size and morphology

This work aims to prepare uniform spray dried hydroxyapatite-based (SD HAP-based) supraparticles with controllable morphology via micro-fluidic spray drying. Sodium polyacrylate (PAAS) and sodium chloride (NaCl) were used to prepare the precursor suspensions by regulating the inter-particle repulsive forces and electrostatic shielding effect, respectively. The particle size (D50) and zeta potential of the suspension were highly associated with the mass ratio of HAP to PAAS (mH/mP) and the NaCl concentration (CNaCl), which further had significant effect on the permeability (k) of the droplet shell formed during spray drying and ultimately the supraparticle morphology. D50 ˂ 2 µm and absolute zeta potential ˃ 20 mV, obtained when mH/mP ˂ 100 under low CNaCl, rendered ultralow k and consequently deformed supraparticles; Whereas D50 ˃ 2 µm and absolute zeta potential ˂ 20 mV, achieved by decreasing PAAS amount, i.e. mH/mP ≥ 100 or improving CNaCl to efficiently screen surface net charge of HAP, high k and spherical supraparticles were thus preferentially formed.

Organics-Coated Nanoclays Further Promote Hydrate Formation Kinetics.

A deeper understanding of the kinetics of CO2 hydrate formation in the complicated natural environment is required for its enhanced sequestration. Here we found that the organics-coated nanoclays enriched in the natural sediments could contribute to a 92% decline of the induction time of hydrate formation. This can be ascribed to the negative charges carried by the organics and the resulting ordered arrangement of the surrounding water molecules. It was, for the first time, proposed that the abundant functional groups from the coating organics could function as a protecting crust enabling the system more resistant to the acidification potentially upon the CO2 sequestration; besides, the negative charges could help prevent the deposition of the nanoclays via interparticle repulsive forces. These would consequently secure their sustainable promoting effect on hydrate formation. The findings suggest the deposits of gas hydrate a kinetically promising geological setting for the CO2 sequestration via forming hydrates.

Nonlinear harmonic generation in two-dimensional lattices of repulsive magnets.

In this work, we provide experimental evidence of nonlinear wave propagation in a triangular lattice of repulsive magnets supported by an elastic foundation of thin pillars, and we interpret all the individual features of the nonlinear wave field through the lens of a phonon band calculation that precisely accounts for the interparticle repulsive forces. We confirm the coexistence of two spectrally distinct components (homogeneous and forced) in the wave response that is induced via second harmonic generation (SHG) as a result of the quadratic nonlinearity embedded in the magnetic interaction. The detection of the forced component, specifically, allows us to attribute unequivocally the generation of harmonics to the nonlinear mechanisms germane to the lattice. We show that the spatial characteristics of the second harmonic components are markedly different from those exhibited by the fundamental harmonic. This endows the lattice with a functionality enrichment capability, whereby additional modal characteristics and directivity patterns can be triggered and tuned by merely increasing the amplitude of excitation.

Montmorillonite and phosphorus enrichment in sediments as the causative factor for mud bank formation along the southwest coast of India

Mud banks of Kerala (southwest coast of India) are renowned for immense fish harvesting during the southwest monsoon season. Although inclement weather and turbulent waves during monsoon prevent vessels sailing into the sea, the tranquil mud banks provide a natural platform for artisanal fishing. Despite several attempts over the past 6 decades, the formation and sustenance of these mud banks remain scientifically unexplained. In this study, we analyzed the geochemical properties of sediments and fluid mud collected from Alappuzha mud banks. The sediments were mostly silty clay (relative abundance of kaolinite [35%–67%] and montmorillonite [25%–45%]), whereas the fluid mud was purely fine clay (montmorillonite [47%–67%] and kaolinite [29%–45%]). Phosphorus content was exceptionally high in the fluid mud (2240–2634 μg/g) and sediments (1559–3013 μg/g). Laboratory experiments showed an increase in volume and a decrease in the settling rate of sediments spiked with varying proportions of montmorillonite and phosphorus. Natural conditions such as winds, waves, currents, or terrestrial factors dislodged the sediments into the water column. Natural sedimentation of clay particles results in the rapid flocculation of large particles (kaolinite and illite), whereas light particles (montmorillonite) remain suspended in the water column for a longer time. During this period, phosphate anions (or any oxyanions) geochemically interact with montmorillonite as well as with its interlayer cations in the following ways: (i) the ligand exchange reaction between the edge hydroxyl groups of mineral with phosphate anions increase the size and negative charge of the clay particles and (ii) phosphate anions effectively adsorb to the interlayer cations. The resultant strong interparticle repulsive force stabilizes the clay suspension, and thereafter, (iii) the intercalation of organic moieties stably converts the hydrophilic clay suspension into a hydrophobic suspension. Results of bulk geochemical parameters along the southwest coast of India show that montmorillonite and phosphorus-rich sediments are the unique properties of Alappuzha mud banks, which lead to their recurrent formation.

Rheological analysis and EOR potential of surfactant treated single-step silica nanofluid at high temperature and salinity

Single-step nanofluids have shown better stability and size control properties than conventional two-step nanofluids under similar conditions. However, for wide-spread oilfield acceptance, there is a need to investigate the role of oilfield conditions viz., temperature, salt and pH on stability of single-step nanofluids. Thus, in this study, single-step silica nanofluids were synthesized in base fluid (1000 ppm polyacrylamide, PAM) and their stability was investigated using methods such as dynamic light scattering (DLS) and rheological analysis to establish their viability as suitable enhanced oil recovery (EOR) agents. PAM is a widely used oilfield practically applicable polymer. Primarily, the single-step silica nanofluids were found to destabilize at higher temperatures (≥90 °C) due to thermal stability issues of PAM at high temperatures. This was also understood by PAM rheology. The inclusion of salt reduced the stability of nanofluids due to the suppression of inter-particle repulsive forces. The variation in pH also influenced nanofluid stability and pH range of 8–10 was observed for the stable behavior of nanofluids. The addition of an anionic surfactant (SDS) improved nanofluid stability by reducing salt-induced NP agglomeration; increasing surfactant concentration initially improved nanofluid resistance to salt induced agglomeration and at high surfactant concentrations, the nanofluids exhibited greater NP agglomeration even in the absence of salt. The oil recovery results also showed that surfactant use in the synthesis of silica nanofluid for oil recovery applications may provide better results than sole silica nanofluid. Based on the observations, surfactant treated single-step silica nanofluid use was found favorable for oilfield practices where conventional nanofluids may show challenges.

Universal physics of bound states of a few charged particles

We study few-body bound states of charged particles subject to attractive zero-range/short-range plus repulsive Coulomb interparticle forces. The characteristic length scales of the system at zero energy are set by the Coulomb length scale D and the Coulomb-modified effective range reff. We study shallow bound states of charged particles with D≫reff and show that these systems obey universal scaling laws different from neutral particles. An accurate description of these states requires both the Coulomb-modified scattering length and the effective range unless the Coulomb interaction is very weak (D→∞). Our findings are relevant for bound states whose spatial extent is significantly larger than the range of the attractive potential. These states enjoy universality – their character is independent of the shape of the short-range potential.

On the decay of the pair correlation function and the line of vanishing excess isothermal compressibility in simple fluids.

We revisit the competition between attractive and repulsive interparticle forces in simple fluids and how this governs and connects the macroscopic phase behavior and structural properties, as manifested in pair correlation functions. We focus on the asymptotic decay of the total correlation function h(r) which is, in turn, controlled by the form of the pair direct correlation function c(r). The decay of rh(r) to zero can be exponential (monotonic) if attraction dominates repulsion and exponentially damped oscillatory otherwise. The Fisher-Widom (FW) line separates the phase diagram into two regions characterized by the two different types of asymptotic decays. We show that there is a new and physically intuitive thermodynamic criterion which approximates well the actual FW line. This new criterion defines a line where the isothermal compressibility takes its ideal gas value χT=χT id. We test our hypothesis by considering four commonly used models for simple fluids. In all cases, the new criterion yields a line in the phase diagram that is close to the actual FW line for the thermodynamic state points that are most relevant. We also investigate (Widom) lines of maximal correlation length, emphasizing the importance of distinguishing between the true and Ornstein-Zernike correlation lengths.

Quantification of shear induced agglomeration in chemical mechanical polishing slurries under different chemical environments

The impact of shear on agglomeration in CMP slurries needs to be studied to reduce the defectivity resulting from large agglomerates (>0.5 μm) during Chemical Mechanical Planarization/Polishing (CMP) process. In this work the impact of the change in the pH of CMP slurries on their agglomeration behavior at different quantified shear rates are studied. The threshold value of Camp number (equal to shear rate x time) which represents total shear that is required for causing agglomeration in CMP slurries for different pH values (pH 2, 7 and 10) are measured. The value of the threshold Camp number required to cause agglomeration in a slurry was lowest for acidic pH conditions (Camp number 1E5), highest for basic pH conditions (Camp number 1.5E6) and value of threshold Camp number for neutral pH conditions (Camp number 1.5E5) was between acidic and basic conditions. It was concluded that the value of the threshold Camp number is dependent on the inter-particle forces or surface charges on silica particles in the slurry, and higher inter-particle repulsive forces increases the threshold value of Camp number. Good co-relations between Camp number and the extent of agglomeration in different CMP slurry samples are demonstrated. This method can be used for designing better slurry delivery systems for different slurry chemistries, to reduce the formation of the shear induced agglomerates during slurry handling and in turn reducing the defects during CMP process.

Effect of Polyelectrolyte Mono- and Bilayer Formation on the Colloidal Stability of Layered Double Hydroxide Nanoparticles.

Sequential adsorption of polyelectrolytes on nanoparticles is a popular method to obtain thin films after deposition. However, the effect of polyelectrolyte multilayer formation on the colloidal stability of the nanoparticles has not been studied in detail. In the present work, layered double hydroxides (LDH) were synthesized and interaction with oppositely and like-charged polyelectrolytes was investigated. Electrophoretic and light scattering measurements revealed that colloidal stability of LDH can be tuned by adsorption of poly(styrene sulfonate) (PSS) on the oppositely charged LDH surface in appropriate doses and thus, unstable or stable dispersions can be designed. Negatively charged LDH of adsorbed PSS monolayer was obtained and a poly(diallyldimethyl ammonium chloride) (PDADMAC) second layer was systematically built on the particles. The obtained polyelectrolyte bilayer provided high colloidal stability for the LDH-PSS-PDADMAC dispersions due to the presence of repulsive interparticle forces of electrostatic and steric origin. The results provide crucial quantitative information on designing highly stable particle-polyelectrolyte systems for the preparation of thin films or immobilization of guest substances between the layers for delivery processes.