Electrostatic Strength Research Articles

Preparation of spherical HMX@PDA-based PBX by co-axial droplet microfluidic technology: Enhancing the interfacial effect and safety performance of composite microspheres

Surface engineering plays a crucial role in improving the performance of high energy materials, and polydopamine (PDA) is widely used in the field of energetic materials for surface modification and functionalization. In order to obtain high-quality HMX@PDA-based PBX explosives with high sphericity and a narrow particle size distribution, composite microspheres were prepared using co-axial droplet microfluidic technology. The formation mechanism, thermal behavior, mechanical sensitivity, electrostatic spark sensitivity, compressive strength, and combustion performance of the microspheres were investigated. The results show that PDA can effectively enhance the interfacial interaction between the explosive particles and the binder under the synergistic effect of chemical bonds and the physical "mechanical interlocking" structure. Interface reinforcement causes the thermal decomposition temperature of the sample microspheres to move to a higher temperature, with the sensitivity to impact, friction, and electrostatic sparks (for S-1) increasing by 12.5%, 31.3%, and 81.5% respectively, and the compressive strength also increased by 30.7%, effectively enhancing the safety performance of the microspheres. Therefore, this study provides an effective and universal strategy for preparing high-quality functional explosives, and also provides some reference for the safe use of energetic materials in practical applications.

Discontinuous Transition in Electrolyte Flow through Charge-Patterned Nanochannels.

We investigate the flow of an electrolyte through a rigid nanochannel decorated with a surface charge pattern. Employing lattice Boltzmann and dissipative particle dynamics methods, as well as analytical theory, we show that the electrohydrodynamic coupling leads to two distinct flow regimes. The accompanying discontinuous transition between slow, ionic, and fast, Poiseuille flows is observed at intermediate ion concentrations, channel widths, and electrostatic coupling strengths. These findings indicate routes to design nanochannels containing a typical aqueous electrolyte that exhibit a digital on-off flux response, which could be useful for nanofluidics and ionotronic applications.

Highly 002-Oriented Dendrite-Free Anode Achieved by Enhanced Interfacial Electrostatic Adsorption for Aqueous Zinc-Ion Batteries.

Rechargeable aqueous zinc-ion batteries (AZIBs) are gaining recognition as promising next-generation energy storage solution, due to their intrinsic safety and low cost. Nevertheless, the advancement of AZIBs is greatly limited by the abnormal growth of zinc dendrites during cycling. Electrolyte additives are effective at suppressing zinc dendrites, but there is currently no effective additive screening criterion. Herein, we propose employing the interfacial electrostatic adsorption strength of zinc ions for the initial screening of additives. Subsequently, dendrite-free plating is achieved by employing the anionic surfactant sodium dodecyl benzenesulfonate (SDBS) to enhance electrostatic adsorption. The cycled zinc anode exhibited a dense plating morphology and a high (002) orientation (I002/I101 = 22). The Zn||MnO2 full cell with SDBS exhibited a capacity retention of 85% after 1000 cycles at 1 A g-1. Furthermore, an instantaneous nucleation model and continuous nucleation model (CNM) are constructed to reveal the microscale plating/stripping dynamics under the scenarios of weak adsorption and strong adsorption. The CNM accurately explains the self-optimizing reconstruction of electrodes resulting from enhanced electrostatic adsorption. Our exploration was extended to other anionic surfactants (sodium dodecyl sulfate and disodium laureiminodipropionate), confirming the effectiveness of strong electrostatic adsorption in the screening of electrolyte additives.

Urea-formaldehyde resin room temperature phosphorescent material with ultra-long afterglow and adjustable phosphorescence performance

Organic room-temperature phosphorescence materials have attracted extensive attention, but their development is limited by the stability and processibility. Herein, based on the on-line derivatization strategy, we report the urea-formaldehyde room-temperature phosphorescence materials which are constructed by polycondensation of aromatic diamines with urea and formaldehyde. Excitingly, urea-formaldehyde room-temperature phosphorescence materials achieve phosphor lifetime up to 3326 ms. There may be two ways to enhance phosphorescence performance, one is that the polycondensation of aromatic diamine with urea and formaldehyde promotes spin-orbit coupling, and another is that the imidazole derivatives derived from the condensation of aromatic o-diamine with formaldehyde maintains low levels of energy level difference and spin-orbit coupling, thus achieving ultra-long afterglow. Surprisingly, urea-formaldehyde room-temperature phosphorescence materials exhibit tunable phosphorescence emission in electrostatic field. Accordingly, 1,4-phenylenediamine, urea, and formaldehyde are copolymerized and self-assembled into phosphorescence microspheres with different electrostatic potential strengths. By mixing 1 wt% 1,4-phenylenediamine polycondensation microspheres with 1,4-phenylenediamine free microspheres, phosphor lifetime of the composite could be regulated from 27 ms to 123 ms. Moreover, vulcanization process enables precise shaping of urea-formaldehyde room-temperature phosphorescence materials. This work not only demonstrates that urea-formaldehyde room-temperature phosphorescence materials are promising candidates for organic phosphors, but also exhibits the phenomenon of electrostatically regulated phosphorescence.

Responses of assembled structures of block polyelectrolytes to electrostatic interaction strength.

In this paper, the responses of assembled behaviors of block polyelectrolytes (PEs) to the strength of electrostatic interactions are studied through molecular dynamic simulations. The results show that the assembled structures closely depend on the electrostatic strength. It should be noted that PE coacervation can outweigh the nucleation of hydrophobic blocks and invert the micelle structures at strong electrostatic strengths, leading to the formation of inverted micelles of PE cores and hydrophobic coronas. In the poor solvent condition for neutral block, diverse anisotropic micelles are presented; candy-like conventional micelles of hydrophobic cores and PE patches coexist with inverted candy-like micelles of PE cores and hydrophobic patches and with Janus micelles of semi-neutral aggregate and semi-PE cluster in the presence of divalent and trivalent counterions. The formation of conventional or inverted micelle is largely determined by the type of micellar fusion, which results from the nucleation competition between electrostatic correlation and hydrophobic interaction. The merge of micelles mediated by hydrophobic attraction leads to conventional hydrophobic cores, and the fusion induced by electrostatic correlations results in PE cores micelles. At strong electrostatic strengths, the PE chains exhibit rich conformations at trivalent counterions, ranging from a fully collapsed state to a rod-like state, and parallel alignment of PE chains is found.

Tailoring the high-protein texture-modified foods for the dysphagia elderly by heating whey protein isolate-pectin complexes

Adequate dietary protein intake is an effective way to combat muscle wasting disorders in the elderly, who are highly susceptible to dysphagia due to declining physiological functions. Herein, whey protein isolate (WPI) and pectin electrostatic complexes were chosen to prepare texture-modified foods with high protein (15%, w/v) for dysphagia elderly. Firstly, the region of soluble complex formation was initially identified as pH 4.2–5.5 by determination of the zeta potential of both biopolymers. Following this, it was found that the stability of WPI-pectin complexes was significantly dependent on the increase in the amount of pectin (from 1.0 to 2.0 %, w/v). However, the viscoelasticity and the degree of WPI aggregation of these complexes after heat treatment (90 °C, 20 min) both showed the lowest level at pH 4.6 (it was fluid state) regardless of the pectin content, and the degree of protein aggregation weakened with the increase of pectin content. Additionally, the shear viscosity, yield stress, and tribological properties of the thermal complexes were also positively correlated with the degree of protein thermal aggregation. Moreover, based on the dietary texture classes developed by the International Dysphagia Diet Standardisation Initiative (IDDSI), unlike pure WPI thermally-induced gels that are attributed to level 6, the WPI-pectin thermal complexes can achieve texture class coverage from level 3 to level 6. These findings suggest that by modulating the electrostatic binding strength and positive-negative charge balance between WPI and pectin, tailored design of high-protein diets for elderly people with varying degrees of dysphagia may be achieved.

Dual enzyme self-assembly cluster for high efficient asymmetric reduction of ethyl 6-oxo-8-chlorooctanoate

(R)-ECHO is synthesized through the asymmetric reduction of ethyl 6-oxo-8-chlorooctanoate (ECOO) using carbonyl reductase(CR2) as a catalyst and co-enzyme NADPH as a hydrogen donor with addition of glucose dehydrogenase (GDH) for NADPH regeneration, thereby enhancing biotransformation efficiency. To improve the reaction efficiency further, a dual enzyme self-assembly cluster EutM-SC-ST-CR2(GDH) was developed specifically for this purpose. This co-immobilised system demonstrated a 50% increase in the conversion of ECOO compared to when SpyTag-CR2(ST-CR2) and SpyTag-GDH(ST-GDH) were co-catalysts. The optimal conditions for this increase were observed to be at a pH of 8.0, 30°C, when concentrations of 250 mM ECOO, 270 mM glucose and 0.1 mM NADPH, and a molar ratio of ST-CR2 to ST-GDH to EutM-SpyCatcher(EutM-SC) of 1:1:2 (molecular concentrations of ST-CR2, ST-GDH and EutM-SC were 3.5 mM, 3.5 mM and 7 mM). Under these conditions, the conversion of ECOO reached up to 95% and the enantiomeric excess (e.e.) of (R)-ECHO achieved 99.9%. Moreover, the EutM-SC-ST-CR2(GDH) construct displayed enhanced enzyme activity, stability, and kinetics, as well as improvements in electrostatic and ionic strengths. In conclusion, this study presents the development of a novel self-assembled protein scaffold, EutM-SC, for the co-immobilisation of ST-CR2 and ST-GDH, thus optimizing the biological reaction conditions and offering potential for the industrial production of (R)-α-lipoic acid.

Effect of counterion size on polyelectrolyte conformations and thermodynamics.

We present a theoretical model to study the effect of counterion size on the effective charge, size, and thermodynamic behavior of a single, isolated, and flexible polyelectrolyte (PE) chain. We analyze how altering counterion size modifies the energy and entropy contributions to the system, including the ion-pair free energy, excluded volume interactions, entropy of free and condensed ions, and dipolar attraction among monomer-counterion pairs, which result in competing effects challenging intuitive predictions. The PE self-energy is calculated using the Edwards-Muthukumar Hamiltonian, considering a Gaussian monomer distribution for the PE. The condensed ions are assumed to be confined within a cylindrical volume around the PE backbone. The dipolar and excluded volume interactions are described by the second and third virial coefficients. The assumption of freely rotating dipoles results in a first-order coil-globule transition of the PE chain. A more realistic, weaker dipolar attraction, parameterized in our theory, shifts it to a second-order continuous transition. We calculate the size scaling-exponent of the PE and find exponents according to the relative dominance of the electrostatic, excluded volume, or dipolar effects. We further identify the entropy- and energy-driven regimes of the effective charge and conformation of the PE, highlighting the interplay of free ion entropy and ion-pair energy with varying electrostatic strengths. The crossover strength, dependent on the counterion size, indicates that diminishing sizes favor counterion condensation at the expense of free ion entropy. The predictions of the model are consistent with trends in simulations and generalize the findings of the point-like counterion theories.

Moderated ionic bonding for water-free recyclable polyelectrolyte complex materials.

While nature extensively uses electrostatic bonding between oppositely charged polymers to assemble and stabilize materials, harnessing these interactions in synthetic systems has been challenging. Synthetic materials cross-linked with a high density of ionic bonds, such as polyelectrolyte complexes, only function properly when their charge interactions are attenuated in the presence of ample amounts of water; dehydrating these materials creates such strong Coulombic bonding that they become brittle, non-thermoplastic, and virtually impossible to process. We present a strategy to intrinsically moderate the electrostatic bond strengths in apolar polymeric solids by the covalent grafting of attenuator spacers to the charge carrying moieties. This produces a class of polyelectrolyte materials that have a charge density of 100%, are processable and malleable without requiring water, are highly solvent- and water-resistant, and are fully recyclable. These materials, which we coin "compleximers," marry the properties of thermoplastics and thermosets using tailored ionic bonding alone.

Increasing the accuracy of electrostatic fields strength measurement by using an improved differential transimpedance amplifier circuit

An electrostatic field mill (EFM) is widely used to measure the strength of electrostatic fields, the main drawback of which is the occurrence of large measurement errors (up to 15 % in the range from 0 to 1 kV/m). This paper examines the aspects of using transimpedance amplifiers (TIAs) for the tasks of converting the current received from the EFM sensor into voltage, which will make it possible to reduce the instrumental error and ensure the linearity of the atmospheric electrostatic field strength measurement. In the general case, for the functional circuits of the electrostatic field mill, which include a differential transimpedance amplifier, there is the use of two TIA circuits, which are connected in parallel. Despite the simplicity of implementation, such a configuration contains a number of disadvantages and is not optimal. In the paper, a comparative analysis of a typical circuit of a differential TIA and a circuit of an ungrounded differential transimpedance amplifier with zero voltage drop proposed by the authors is carried out. As a result of the analysis, it was established that the designed authentic circuit of the ungrounded differential transimpedance amplifier with zero voltage drop has better parameters of linearity and interference resistance, in contrast to the generally accepted one. The value of the signal-to-noise ratio for the proposed scheme improved by 42 % on average compared to the typical one. The main difference of the proposed scheme is that the stability of the amplification factor is ensured, the influence of the bias parameters of the operational amplifier is leveled, and the overall noise level is reduced. The use of the designed scheme of an ungrounded differential transimpedance amplifier with zero voltage drop could make it possible to increase the accuracy of the measurement of the electrostatic field strength

Underlying features for the enhanced electrostatic strength of the extremophilic malate dehydrogenase interface salt-bridge compared to the mesophilic one

Malate dehydrogenase (MDH) exists in multimeric form in normal and extreme solvent conditions where residues of the interface are involved in specific interactions. The interface salt-bridge (ISB) and its microenvironment (ME) residues may have a crucial role in the stability and specificity of the interface. To gain insight into this, we have analyzed 218 ISBs from 42 interfaces of 15 crystal structures along with their sequences. Comparative analyses demonstrate that the ISB strength is ∼30 times greater in extremophilic cases than that of the normal one. To this end, the interface residue propensity, ISB design and pair selection, and ME-residue’s types, i.e., type-I and type-II, are seen to be intrinsically involved. Although Type-I is a common type, Type-II appears to be extremophile-specific, where the net ME-residue count is much lower with an excessive net ME-energy contribution, which seems to be a novel interface compaction strategy. Furthermore, the interface strength can be enhanced by selecting the desired mutant from the net-energy profile of all possible mutations of an unfavorable ME-residue. The study that applies to other similar systems finds applications in protein–protein interaction and protein engineering. Communicated by Ramaswamy H. Sarma

Charge Characteristics of Dielectric Particle Swarm Involving Comprehensive Electrostatic Information.

The triboelectrification effect caused by dynamic contact between particles is an issue for explosions caused by electrostatic discharging (ESD) in the triboelectric nanogenerators (TENGs) for powering the flexible and wearable sensors. The electrostatic strength of dielectric particles (surface charge density, surface potential, electric field, etc.) is essential to evaluate the level of ESD risk. Those differential electrostatic characteristics concerned with unhomogenized swarmed particles cannot be offered via in-current employed-joint COMSOL 6.1 simulation, in which the discrete charged dielectric particles are mistakenly regarded as continuous ones. In this paper, the hybrid discrete element method (EDEM tool) associated with programming in COMSOL Multiphysics 6.1 with MATLAB R2023a was employed to obtain the electrostatic information of the triboelectric dielectric particle swarm. We revealed that the high-accuracy strengths of electric potential and electric field inside particle warm are crucial to evaluating ESD risk. The calculated electrostatic characteristics differ from the grid method and continuous method in the surface potential and electric field. This EDEM-based simulation method is significant for microcosmic understanding and the assessment of the ESD risk in TENGs.

Impact of the inner solute structure on the electrostatic mean-field and strong-coupling regimes of macromolecular interactions.

The structural diversity of the solute molecules involved in biomolecular processes necessitates the characterization of the forces between charged macromolecules beyond the point-ion description. From the field-theoretic partition function of an electrolyte confined between two anionic membranes, we derive a contact-value identity valid for general intramolecular solute structure and electrostatic coupling strength. In the electrostatic mean-field regime, the inner charge spread of the solute particles is shown to induce the twofold enhancement of the short-range Poisson-Boltzmann level membrane repulsion and a longer-range depletion attraction. Our contact theorem indicates that the twofold repulsion enhancement by solute size is equally present in the opposite strong-coupling regime of linear and spherical solute molecules. Upon the inclusion of the dielectric contrast between the electrolyte and the interacting membranes, the emerging polarization forces substantially amplify the solute specificity of the macromolecular interactions. Namely, the finite size of the dumbbell-like solute particles composed of similar terminal charges weakens the intermembrane repulsion. However, the extended structure of the solute molecules carrying opposite elementary charges such as ionized atoms and zwitterionic molecules enhances the membrane repulsion by several factors. We also show that these polarization forces can extend the range of the solute structure effects up to intermembrane distances exceeding the solute size by an order of magnitude. This radical alteration of the intermembrane interactions by the salt structure identifies the solute specificity as a key ingredient of the thermodynamic stability in colloidal systems.

Polymer complexation: Partially ionizable asymmetric polyelectrolytes.

Theories of bulk coacervation of oppositely charged polyelectrolytes (PE) obscure single molecule level thermodynamic details, considered significant for coacervate equilibrium, whereas simulations account for only pairwise Coulomb interaction. Also, studies of effects of asymmetry on PE complexation are rare compared to symmetric PEs. We develop a theoretical model, accounting for all entropic and enthalpic contributions at the molecular level, and the mutual segmental screened Coulomb and excluded volume interactions between two asymmetric PEs, by constructing a Hamiltonian following Edwards and Muthukumar. Assuming maximal ion-pairing in the complex, the system free energy comprising configurational entropy of the polyions and free-ion entropy of the small ions is minimized. The effective charge and size of the complex, larger than sub-Gaussian globules as for symmetric chains, increase with asymmetry in polyion length and charge density. The thermodynamic drive for complexation is found to increase with ionizability of symmetric polyions and with a decrease in asymmetry in length for equally ionizable polyions. The crossover Coulomb strength demarcating the ion-pair enthalpy-driven (low strength) and counterion release entropy-driven (high strength) is marginally dependent on the charge density, because so is the degree of counterion condensation, and strongly dependent on the dielectric environment and salt. The key results match the trends in simulations. The framework may provide a direct way to calculate thermodynamic dependencies of complexation on experimental parameters such as electrostatic strength and salt, thus to better analyze and predict observed phenomena for different sets of polymer pairs.

Effect of the counterion size on microphase separation in charged-neutral diblock copolymers.

In this work, the question of the influence of the counterion size on the self-assembly in melts of diblock copolymers with one charged block was studied using coarse-grained molecular dynamics simulations. It was assumed that the blocks were fully compatible, i.e., the Flory-Huggins parameter χ between them was equal to 0. Due to the presence of correlation attraction (electrostatic cohesion) between the charged species, the systems with all types of counterions underwent transitions to ordered states, forming various morphologies, including lamellae, perforated lamellae, and hexagonally packed cylinders. Phase diagrams were constructed by varying the chain composition fc and locating the order-disorder transition positions in terms of the electrostatic strength parameter λ (dimensionless Bjerrum length). Despite having a rather large ion size mismatch, the systems with smaller counterions demonstrated an even better tendency to form microphase separated states than the systems with larger ones. It was found that the differences between the phase diagrams of the systems with different counterions can be roughly rationalized by using coordinates (volume fraction of the charged block φc-modified interaction parameter λ*). The latter parameter assumes that the electrostatic energy is simply inversely proportional to the characteristic distance between the ions of different signs. Such an approach appeared to be rather effective and allowed the diagrams obtained for different counterion sizes to almost coincide. The results of this work suggest that the counterion size can be used as a tool to control the system morphology as well as the effective incompatibility between the blocks.

Driving force and pathway in polyelectrolyte complex coacervation

There is notable discrepancy between experiments and coarse-grained model studies regarding the thermodynamic driving force in polyelectrolyte complex coacervation: experiments find the free energy change to be dominated by entropy, while simulations using coarse-grained models with implicit solvent usually report a large, even dominant energetic contribution in systems with weak to intermediate electrostatic strength. Here, using coarse-grained, implicit-solvent molecular dynamics simulation combined with thermodynamic analysis, we study the potential of mean force (PMF) in the two key stages on the coacervation pathway for symmetric polyelectrolyte mixtures: polycation-polyanion complexation and polyion pair-pair condensation. We show that the temperature dependence in the dielectric constant of water gives rise to a substantial entropic contribution in the electrostatic interaction. By accounting for this electrostatic entropy, which is due to solvent reorganization, we find that under common conditions (monovalent ions, room temperature) for aqueous systems, both stages are strongly entropy-driven with negligible or even unfavorable energetic contributions, consistent with experimental results. Furthermore, for weak to intermediate electrostatic strengths, this electrostatic entropy, rather than the counterion-release entropy, is the primary entropy contribution. From the calculated PMF, we find that the supernatant phase consists predominantly of polyion pairs with vanishingly small concentration of bare polyelectrolytes, and we provide an estimate of the spinodal of the supernatant phase. Finally, we show that prior to contact, two neutral polyion pairs weakly attract each other by mutually induced polarization, providing the initial driving force for the fusion of the pairs.

Impact of Charge Regulation on Self-Assembly of Zwitterionic Nanoparticles.

Zwitterionic modification of colloids with weak acids and bases represents a promising strategy in creating functional materials with tunable properties and modeling the self-organization of charged proteins. However, accurate incorporation of the dynamic dissociation or association of ionization groups known as charge regulation (CR) is often intractable in theoretical and computational investigations since charge redistribution and configuration need to be evolved self-consistently. Using hybrid MonteCarlo and molecular dynamics simulations, we demonstrate that a dilute suspension of overall charge-neutral zwitterionic Janus nanoparticles shows a conformational transition from an open assembly of string or bundle to compact cluster along with the variation in pH. The behavior under CR is qualitatively different from the commonly employed constant charge condition where the transition is absent. The CR-induced clustering is due to the inhomogeneous and fluctuating charges localized near the equatorial boundary of the Janus particle. These features are enhanced particularly at low salt concentration and high electrostatic coupling strength. Our results indicate the critical role of charge regulation in the spatial self-organization of zwitterionic nanoparticles.

Magnetic responsive mesoporous alginate/β-cyclodextrin polymer beads enhance selectivity and adsorption of heavy metal ions

Mesoporous (~7–8 nm) biopolymer hydrogel beads (HNTs-FeNPs@Alg/β-CD) were synthesised via ionic polymerisation route to separate heavy metal ions. The adsorption capacity of HNTs-FeNPs@Alg/β-CD was higher than that of raw halloysite nano tubes (HNTs), iron nanoparticles (FeNPs), and bare alginate beads. FeNPs induce the magnetic properties of adsorbent and metal-based functional groups in and around the hydrogel beads. The mesoporous surface of the adsorbent permits access of heavy metal ions onto the polymer beads to interact with internal active sites and the mesoporous polymer network. Maximum adsorption capacities of lead (Pb), copper (Cu), cadmium (Cd), and nickel (Ni) were 21.09 mg/g, 15.54 mg/g, 2.47 mg/g, and 2.68 mg/g, respectively. HNTs-FeNPs@Alg/β-CD was able to adsorb heavy metals efficiently (75–99%) under environment-relevant concentrations (200 μg/L) from mixed metal contaminants. The adsorption and selectivity trends of heavy metals were Pb > Cu > Cd > Ni, despite electrostatic binding strength of Cd > Cu > Pb > Ni and covalent binding strength of Pb > Ni > Cu > Cd. It demonstrated that not only chemosorption but also physisorption acts as the sorption mechanism. The reduction in surface area, porosity, and pore volume of the expended adsorbent, along with sorption study results, confirmed that pore filling and intra-particle diffusion played a considerable role in removing heavy metals.

Molecular mechanisms of cardiac actomyosin transforming from rigor state to post-rigor state.

Sudden cardiac death contributed to half of all deaths from cardiovascular diseases. The mechanism of the kinetic cycle of cardiac myosin is crucial for heart protection and drug development. The state change in the myosin kinetic cycle from the rigor state to the post-rigor state is fundamental to explain binding and dissociation. Here, we used β-cardiac myosin in the rigor and post-rigor states to model the actomyosin complexes. Molecular dynamics simulations, electrostatic analysis, and energetic analysis of actomyosin complexes were performed in this work. The results showed that there are fewer interactions and lower electrostatic binding strength in the post-rigor state than in the rigor state. In the post-rigor state, there were higher free binding energy, fewer salt bridges, and fewer hydrogen bonds. The results showed a lower binding affinity in the post-rigor state than in the rigor state. The decrease in the binding affinity provided important conditions for dissociation of the myosin from the actin filament. Although previous studies focused mostly on the binding process, this study provides evidence of dissociation, which is even more important in the myosin kinetic cycle. This research on the mechanism of myosin kinetic cycles provides a novel direction for future genetic disease studies.

Effect of salinity on the characteristics, pH-triggered demulsification and rheology of crude oil/water nanoemulsions

The interest in utilizing nanoemulsions in a number of industrial applications is growing rapidly because of their superiority over conventional emulsions. Therefore, the formulation of highly stable crude oil-in-water nanoemulsions with different salinity (i.e., NaCl) levels is preseented in this study. Despite the observed extreme emulsion stability, zeta potential of the nanoemulsions decreased with increasing the salt concentration as a result of the charge screening effect induced by NaCl addition. Charge screening effect and, accordingly, the weakening of the electrostatic repulsion range and strength resulted in an increase in the average droplet size and also in a wider size distribution as the salinity level in the nanoemulsions increased. Additionally, the nanoemulsion viscosity also increased with increasing the salt concentration, however, the increase was marginal (except at 20 g/L NaCl). One interesting and unprecedented observation reported herein is the change in the nanoemulsion flow behavior from shear-thinning to Newtonian and then to shear-thickening as the applied shear rate increased. Nonetheless, at a salt concentration of 20 g/L NaCl, the shear-thickening behavior disappeared. Another important finding is that the presence of NaCl made the on-purpose destabilization of these stable nanoemulsions through the addition of NaOH or HCl (i.e., pH-alteration induced demulsification) more effective.