Dilute Electrolyte Research Articles

Analytical treatment of ion-exchange permselectivity and transport number measurements for high accuracy

We analyse electromotive force measurements of concentration cells using non-equilibrium thermodynamics, and determine the transference coefficients of ion-exchange membranes in aqueous KCl solutions. By taking advantage of the analytical expression for the permselectivity, we extract transport coefficients with high accuracy. The transport number of K+ and the transference coefficient of water in the Selemion CMVN cation-exchange membrane are found to be 100tK+=99.59±0.56 and tw=3.69±0.40 respectively, while for the Selemion AMVN anion-exchange membrane they are 100tCl−=100.21±0.37 and tw=−3.75±0.27. These results suggest that the membranes are perfectly selective to the target ion, and that each ion carries 3-4 water molecules through the membrane, which reduces the membrane permselectivity. In these concentration cells, the electrical potential contribution of the membrane alone was more easily isolated with bare Ag/AgCl electrodes without reference solutions and liquid junction plugs. Additionally, we find a large contribution to the measured concentration cell voltage from concentration gradients across the porous plug of the reference electrode, which cannot be explained by Henderson’s equation alone. For most of the concentration range, the transport number of the porous plug is determined to be 100tK+=49.43±0.78 with negligible water transport, similar to literature values for bulk electrolyte. In dilute electrolyte solutions with concentrations below 0.1 mol kg−1, the plug shows anomalous behaviour consistent with an increase in K+ selectivity and water co-transport.

A low-cost dilute aqueous hybrid electrolyte for low-temperature supercapacitors

A low-cost dilute aqueous hybrid electrolyte for low-temperature supercapacitors

Fast formation of a black inner α‐Al2O3 layer doped with CuO on Al–Cu–Li alloy by soft sparking PEO process

AbstractForming high‐temperature α‐Al2O3 phase under soft sparking is an intriguing phenomenon in plasma electrolytic oxidation (PEO) of Al alloys, which contradicts the low energy input of the process. In this study, α‐Al2O3 doped with black CuO is formed beneath an amorphous white outer layer on Al–Cu–Li alloy by PEO in a dilute silicate electrolyte under soft sparking. In comparison, reddish coatings with dominating γ‐Al2O3 are formed under the conventional plasma discharges, although blackish inner layer with α‐Al2O3 can also be exposed by heavily polishing the samples. In order to know the underlying mechanism, temperatures at the coating surface and the underlying substrate have been monitored by a thermocouple under the conventional and soft sparking PEO regimes, respectively. Interestingly, high temperatures are detected in the case of soft sparking rather than PEO with strong discharges. The formation of CuO, quartz, and cristobalite within the soft sparking coating also supports the existence of high temperature. Hence, the formation of α‐Al2O3 under soft sparking can be resolved to the conventional thermal activation mechanism, without the need of seeking other plausible explanations. Thermal condition evaluation for soft sparking PEO suggests that values of the effective thermal conductivity during PEO process for the outer layer and the barrier layer at the coating/substrate interface might be lower than ∼0.05 and ∼0.0017 W m−1 K−1, respectively. It is believed that the amorphous structure of the outer and barrier layers effectively blocks the heat dissipation, facilitating the formation of a highly wear‐resistant inner layer with α‐Al2O3, CuO, and the other high‐temperature species under soft sparking.

A low-concentration 2-step synthesized spiroquaternary ammonium salt electrolyte for commercially stable pouch-type supercapacitors

Currently, non-aqueous, stable supercapacitors manufactured for commercial use require an environmentally benign and economically viable electrolyte synthesis technique. Spiro-based salts dissolved in organic solvents are known to have smaller ion-size, which facilitate charge transport during storage at varying temperatures and preserve storage efficiency over time. Previously, the synthesis of spirobased salt syntheses via complex multistep procedures involving toxic chemical solvents and low yields have been reported. The current work proposes a modified water-based ion-exchange process coupled with an innovative purification step that results in improved yield. In addition, the synthesized spiro-(1,1′)-bipyrrolidinium tetrafluoroborate (SBPBF4) salt mixed in an optimized organic solvent blend produced a dilute (0.2 M) electrolyte with its ionic conductivity comparable to commercially recognized, higher concentrated ionic salt electrolytes (3 M). Using the dilute SBPBF4 electrolyte, the pouch-type (PoC-SBF4) devices were operated up to 3 V.An average rated capacitance of 300 F was demonstrated with up to 43 W h kg−1 specific energy and 1 kW kg−1 of maximum deliverable power. After 10,000 continuous charge-discharge cycles, the device retained 97 % of its capacitance at an applied current of 5 A.Notably, the extreme temperature shock tests at −70 °C also demonstrated ~60 % capacitance retention after subjecting the device to cycling at 5 A for 72 h (3 days) to simulate extreme weather conditions for potential integration with renewable energy, mobility, or deep space applications.The water-based ion exchange step and the use of dilute electrolytes reduces the overall cost of manufacturing supercapacitor when scaling up the production process. The results presented provides a critical evaluation of the criteria for developing robust, stable, and low-cost supercapacitors from laboratory to large-scale manufacturing.

Cu(InGa)(SeS)2 Electrodeposition from a Single Bath Using Pulsing Current Technique

Cu(In,Ga)(S,Se)2 (CIGSS) due to its greater band gap, has potential advantages over CuInGaSe2 (CIGS) as a photovoltaic film. Due to its lower capital cost and relatively high productivity, electrodeposition is a particularly appealing method for producing such solar materials (1-5). However, none describes the full production of such a molecule without the necessity for extra sulfur addition from the vapor phase4. Several recent articles disclose CIGSS electrodeposition. We introduce here the pulsing current method to dilute electrolytes used in previous work (6-7). Because of the diluted electrolyte composition, CIGSS can be directly electrodeposited from a single bath with a pulsing technique. The bath composition is 0.45 mM CuCl2-H2O; 0.4 mM InCl3; 0.77 mM H2SeO3; 0.51 mM GaCl3; and 0.3 mM Na2S2O3. PHydrion is applied to buffer the electrolyte to pH=2, and 0.7 M LiCl is applied as a supporting electrolyte. The flow was quantitatively characterized by agitation electrodeposition, which was done at room temperature onto a revolving disk electrode. Mass transport's impacts on deposit composition and substrate adherence are examined in various electrode rotation speeds and are represented by sample polarization curves. There was no requirement for the inclusion of metals from the gas phase during the subsequent annealing stage, which was carried out in an argon atmosphere. Two separate samples of absorber were evaluated for final sulfur atomic ratios of 5% and 15%. Utilizing the Energy-dispersive X-ray spectroscopy method, the final composition was calculated (EDS). CIGSS crystallography was analyzed using the XRD method.

The Dramatic Effect of Water Structure on Hydration Forces and the Electrical Double Layer

Forces between hydrophilic surfaces mediated by water are important in various systems from lipid membranes and solid surfaces to colloids and macromolecules, first discovered as a significant addition to DLVO forces at the nanoscale. These “hydration forces” have been studied in great detail experimentally using osmotic stress measurements, surface force apparatus, and AFM, and they have also been the subject of multiple theories and simulations. One spectacular feature observed in experimental and simulation studies was the nonmonotonic, oscillatory decay in the forces between atomically smooth surfaces. Forces between “rougher” surfaces exhibit only quasi-exponential, monotonic decay. Here we revisit this hydration force problem by exploring the consequences of an extended phenomenological Landau–Ginzburg approach that describes nonlocal correlations in water, linking them with the key features of the wave-number k-dependent nonlocal dielectric function of water. With corresponding boundary conditions, this theory predicts the observed oscillatory decay in hydration force between ideally flat surfaces, the oscillatory mode disappearing with just a tiny roughness of the surfaces (of mean height ca. of the size of a water molecule). This study also brings an important side message. Explanation of these observations appears only possible under an assumption of two modes of polarization in water, consistent with the behavior of the response function, i.e., Lorentzian at small k and resonance-like at higher k. This resolves the “force oscillation–non-oscillation” paradigm, which is a strong, although indirect indication of the existence of these two modes. We also consider other important subjects, such as how the distribution of ions near a charged surface reacts to the propensity for overscreening oscillations due to polarized water. This is important not only for the interactions between charged surfaces but also for the fundamental understanding of the structure of the electrical double layer at electrochemical interfaces. We show that even in dilute electrolytes, the distribution of ions in the vicinity of the polarized interface follows, although not literally, preferential positions corresponding to the potential wells caused by “resonance” water layering. For a sharp interface, the theory predicts that the decaying spatial oscillation profiles extend over a 1 to 2 nm distance from the interface. With the smearing of the interface and the corresponding suppression of the resonance water layering, oscillations in the spatial distribution of ions subside, resulting in a familiar Gouy–Chapman–Stern picture. At longer distances from the interface, whether smeared or not, the ion distribution profiles become Gouy–Chapman-like. The effect of the boundary conditions on water polarization at the interface goes beyond a trivial shift of the potential of zero charge. We show that they can dramatically affect the ion distribution near the charged surface. Last, but not least, we study how the interfacial water layering influences the double layer capacitance and show the effect of the boundary conditions on the slopes of Parsons–Zobel plots, resolving some recently discussed puzzles.

Bidirectional activation technology towards foam-like carbon nanosheets and its coupling with oxygen-deficient α‐MnO2 for ammonium-ion hybrid supercapacitors

BackgroundAqueous non-metallic ammonium ions (NH4+) have newly been developed as a promising charge carrier for electrochemical energy storage owing to their high safety, abundance, and tiny hydrated ionic size. Producing reliable electrode materials with excellent electrochemical performance, however, remains a significant issue. Methodswe proposed a bidirectional chemical activation strategy, which effective coupling “in to out” and “out to in” etching manner, to synthesize foam-like porous carbon nanosheets (FCNSs) with the surface area much larger than that samples obtained from the unidirectional mode. Meanwhile, oxygen-deficient α‐MnO2 nanorods can be rationally obtained through mild redox reaction, both of which display excellent capacitive performance in dilute (NH4)2SO4 electrolyte (0.5 M). Significant findingsthe as-synthesized FCNSs and oxygen-deficient α‐MnO2 nanorods can deliver a specific capacitance of 257.5 F g−1 and 525.1 F g−1, respectively, demonstrating their huge potential to assemble ammonium-ion hybrid supercapacitor (A-HSC). Benefitting from the feasible electrochemical performance for both anode and cathode, the resulting A-HSC displays a specific capacitance of 180.8 F g−1 (calculated based on both anode and cathode) within 0–1.6 V, and a low self-discharge rate, which outperforms the state-of-the-art A-HSC devices. Importantly, the energy storage mechanism has been elucidated from several ex-situ characterizations.

On the Transition-State theory approach to the Jones-Dole’s viscosity B-coefficient: A novel molecular-based interpretation, assessment of its implications, and experimental evidence

We report a novel statistical mechanics interpretation of the frequently invoked Feakins’ transition-state theory approach to the Jones − Dole’s Bi- coefficient, and its temperature–pressure derivatives, in the context of their suitability as structure-making/breaking markers for the behavior of solutes in dilute electrolyte solutions. We provide additional rigorous molecular-based thermodynamic evidence to highlight the non-uniqueness of the Bi- and ∂Bi/∂TP- responses to the solute–solvent intermolecular asymmetries in these systems, and to illustrate the resulting outcomes according to a fundamental structure-making/breaking function involving the available experimental data for aqueous electrolyte solutions. Finally, we discuss the implications of our findings while providing a cautionary outlook on the pervasive use of the viscosity-based structural markers.

Design of Localized High-Concentration Electrolytes via Donor Number

Salt-concentrated electrolytes offer properties beyond conventional dilute electrolytes yet suffer from high cost and viscosity which hinder their practical applications. Introducing a secondary solvent as a diluent could reduce the salt content while maintaining the local solution structure of salt-concentrated electrolytes, giving rise to localized high-concentration electrolytes (LHCEs). Through a comprehensive investigation involving over 500 samples, we find that the dielectric constant of solvent, a widely used parameter for electrolyte design, does not serve as a useful screening criterion for diluents; instead, donor number (DN) is an effective design parameter to achieve LHCE structure─i.e., the primary solvent must have DN > 10 and the diluent must have DN ≤ 10. Based on this simple rule, a new LHCE using low-cost m-fluorotoluene diluent is formulated, enabling high-voltage (>4.6 V) and wide-temperature (−40–100 °C) operation of lithium batteries.

Lithium Salt Dissociation Promoted by 18‐Crown‐6 Ether Additive toward Dilute Electrolytes for High Performance Lithium Oxygen Batteries

AbstractLithium‐oxygen batteries (LOBs) are well known for their high energy density. However, their reversibility and rate performance are challenged due to the sluggish oxygen reduction/evolution reactions (ORR/OER) kinetics, serious side reactions and uncontrollable Li dendrite growth. The electrolyte plays a key role in transport of Li+ and reactive oxygen species in LOBs. Here, we tailored a dilute electrolyte by screening suitable crown ether additives to promote lithium salt dissociation and Li+ solvation through electrostatic interaction. The electrolyte containing 100 mM 18‐crown‐6 ether (100‐18C6) exhibits enhanced electrochemical stability and triggers a solution‐mediated Li2O2 growth pathway in LOBs, showing high discharge capacity of 10 828.8 mAh gcarbon−1. Moreover, optimized electrode/electrolyte interfaces promote ORR/OER kinetics on cathode and achieve dendrite‐free Li anode, which enhances the cycle life. This work casts new lights on the design of low‐cost dilute electrolytes for high performance LOBs.

Lithium Salt Dissociation Promoted by 18-Crown-6 Ether Additive toward Dilute Electrolytes for High Performance Lithium Oxygen Batteries.

Lithium-oxygen batteries (LOBs) are well known for their high energy density. However, their reversibility and rate performance are challenged due to the sluggish oxygen reduction/evolution reactions (ORR/OER) kinetics, serious side reactions and uncontrollable Li dendrite growth. The electrolyte plays a key role in transport of Li+ and reactive oxygen species in LOBs. Here, we tailored a dilute electrolyte by screening suitable crown ether additives to promote lithium salt dissociation and Li+ solvation through electrostatic interaction. The electrolyte containing 100 mM 18-crown-6 ether (100-18C6) exhibits enhanced electrochemical stability and triggers a solution-mediated Li2 O2 growth pathway in LOBs, showing high discharge capacity of 10 828.8 mAh gcarbon -1 . Moreover, optimized electrode/electrolyte interfaces promote ORR/OER kinetics on cathode and achieve dendrite-free Li anode, which enhances the cycle life. This work casts new lights on the design of low-cost dilute electrolytes for high performance LOBs.

Non-polar ether-based electrolyte solutions for stable high-voltage non-aqueous lithium metal batteries

The electrochemical instability of ether-based electrolyte solutions hinders their practical applications in high-voltage Li metal batteries. To circumvent this issue, here, we propose a dilution strategy to lose the Li+/solvent interaction and use the dilute non-aqueous electrolyte solution in high-voltage lithium metal batteries. We demonstrate that in a non-polar dipropyl ether (DPE)-based electrolyte solution with lithium bis(fluorosulfonyl) imide salt, the decomposition order of solvated species can be adjusted to promote the Li+/salt-derived anion clusters decomposition over free ether solvent molecules. This selective mechanism favors the formation of a robust cathode electrolyte interphase (CEI) and a solvent-deficient electric double-layer structure at the positive electrode interface. When the DPE-based electrolyte is tested in combination with a Li metal negative electrode (50 μm thick) and a LiNi0.8Co0.1Mn0.1O2-based positive electrode (3.3 mAh/cm2) in pouch cell configuration at 25 °C, a specific discharge capacity retention of about 74% after 150 cycles (0.33 and 1 mA/cm2 charge and discharge, respectively) is obtained.

Dilute Aqueous Hybrid Electrolyte with Regulated Core‐Shell‐Solvation Structure Endows Safe and Low‐Cost Potassium‐Ion Energy Storage Devices

AbstractHigh‐concentration “water‐in‐salt” (WIS) electrolytes with the wider electrochemical stability window (ESW) can give rise to safe, non‐flammable, and high‐energy aqueous potassium‐ion energy storage devices, thus highlighting the prospect for applications in grid‐scale energy storage. However, WIS electrolytes usually depend on highly concentrated salts, leading to serious concerns about cost and sustainability. Here, an aqueous low‐concentration‐based potassium‐ion hybrid electrolyte is demonstrated with the regulated core‐shell‐solvation structure by using an aprotic solvent, i.e., trimethyl phosphate, to limit the water activity. This aqueous hybrid electrolyte has a low salt concentration (1.6 mol L−1) of potassium trifluoromethanesulfonate but with an expanded ESW up to 3.4 V and the nonflammable property. Based on this dilute aqueous hybrid electrolyte, electrochemical double‐layer capacitors are capable of working within a large voltage range (0–2.4 V) at a wide range of temperatures from −20 to 60 °C. An aqueous potassium‐ion battery consisting of an organic 3,4,9,10‐perylenetetracarboxylic diimide anode, Prussian blue K1.5Mn0.61Fe0.39[Fe(CN)6]0.77·H2O cathode and this dilute aqueous hybrid electrolyte can operate well at rates between 0.2 and 4.0 C and deliver a high energy density of 66.5 Wh kg−1 as well as a durable cycling stability with a capacity retention of 84.5% after 600 cycles at 0.8 C.

Hydrogen-Bond Restructuring of Water-in-Salt Electrolyte Confined in Ti3C2Tx MXene Monitored by Operando Infrared Spectroscopy.

Highly concentrated water-in-salt aqueous electrolytes exhibit a wider potential window compared to conventional, dilute aqueous electrolytes. Coupled with MXenes, a family of two-dimensional transition metal carbides and nitrides with impressive charge storage capabilities, water-in-salt electrolytes present a potential candidate to replace flammable and toxic organic solvents in electrochemical energy storage devices. A new charge storage mechanism was recently discovered during electrochemical cycling of Ti3C2Tx MXene electrodes in lithium-based water-in-salt electrolytes, attributed to intercalation and deintercalation of solvated Li+ ions at anodic potentials. Nevertheless, direct evidence of the state of Li+ solvation during cycling is still missing. Here, we investigate the hydrogen bonding of water intercalated between MXene layers during electrochemical cycling in a water-in-salt electrolyte with operando infrared spectroscopy. The hydrogen-bonding state of the confined water was found to change significantly as a function of potential and the concentration of Li+ ions in the interlayer space. This study provides fundamentally new insights into the electrolyte structural changes while intercalating Li+ in the MXene interlayer space.

Weakening Li+ De-solvation Barrier for Cryogenic Li-S Pouch Cells.

Li-S batteries hold promise for pushing cell-level energy densities beyond 300Wh kg-1 while operating at low temperatures (LTs, below 0°C). However, the capacity release of existing Li-S batteries at LTs is still barely satisfactory, and there is almost no verification of the practicability of Li-S batteries at LTs in the Ah-level pouch cell. Here, antecedent molecular dynamics (MDs) combined with density functional theory analysis are used to systematically investigate Li+ solvation structure in conventional Li-S batteries at LTs, which unprecedentedly reveals the positive correlation between lithium salt concentration and Li+ de-solvation barrier, indicating dilute electrolytes can enhance the Li+ de-solvation kinetics and thus improve the capacity performance of cryogenic Li-S batteries. These insights derived from theoretical simulations invested Li-S batteries with a 67.34% capacity retention at -40°C compared to their room temperature performance. In particular, an Ah-level Li-S pouch cell using dilute electrolytes with a high sulfur loading (5.6mg cm-2 ) and lean electrolyte condition is fabricated, which delivers a discharge capacity of about 1000 mAh g-1 and ultra-high energy density of 350Wh kg-1 at 0°C, offering a promising route toward a practical high-energy cryogenic Li-S battery.

Low-Temperature Aqueous Na-Ion Batteries: Strategies and Challenges of Electrolyte Design

Aqueous Na-ion batteries (ANIBs) are considered to be promising secondary battery systems for grid-scale energy storage applications and have attracted widespread attention due to their unique merits of rich resources of Na, as well as the inherent safety and low cost of aqueous electrolytes. However, the narrow electrochemical stability widow and high freezing point of traditional dilute aqueous electrolytes restrict their multi-scenario applications. Considering the charge-storage mechanism of ANIBs, the optimization and design of aqueous Na-based electrolytes dominate their low-temperature performance, which is also hot off the press in this field. In this review, we first systematically comb the research progress of the novel electrolytes and point out their remaining challenges in ANIBs. Then our perspectives on how to further improve the low-temperature performance of ANIBs will also be discussed. Finally, this review briefly sheds light on the potential direction of low-temperature ANIBs, which would guide the future design of high-performance aqueous rechargeable batteries.

Effect of a Weak Coordination Solvent on a Kinetically Favorable Electrode Reaction in Concentrated Lithium-Ion Battery Electrolytes

We present highly concentrated electrolytes prepared with a fluorinated acetate solvent that has much weaker coordination power, allowing for a kinetically favorable electrode reaction in lithium (Li)-ion batteries (LIBs). Among the concentrated electrolytes using conventional organic solvents, the concentrated electrolyte containing a 2,2,2-trifluoroethyl acetate (TFEAc) solvent and 3.2 mol dm–3 LiFSA salt (FSA: bis(fluorosulfonyl)amide) had the lowest ionic conductivity but a wide electrochemical window (∼5 V), allowing for a LIB electrode reaction. Compared to an analogous electrolyte containing LiTFSA salt (TFSA: bis(trifluoromethanesulfonyl)amide), the concentrated LiFSA/TFEAc electrolyte demonstrated significantly improved charge–discharge behavior with a high C-rate performance on the graphite negative electrode. The activation energy (Ea) of the graphite electrode reaction (i.e., Li+-insertion reaction) was determined experimentally to be Ea = 19.9 kJ mol–1 in the concentrated LiFSA/TFEAc electrolyte, which was significantly lower than that reported previously for dilute carbonate-based electrolytes. Furthermore, a combination of high-energy X-ray total scattering experiments and all-atom molecular dynamics simulations revealed that Li ions are co-coordinated with TFEAc molecules and FSA anions to form intricate ion-ordered complexes in the bulk solution with no free solvent and counteranion. From a structural viewpoint, we discussed the characteristic Ea in the current concentrated electrolyte system and concluded that the weak interaction between Li-ion and TFEAc remaining in the activation state plays a key role in triggering energetically easier decoordination during the charge transfer process, achieving a kinetically unique graphite electrode reaction.

Durable semi-crystalline interphase engineering to stabilize high voltage Ni-rich cathode in dilute ether electrolyte

Ethers are promising electrolyte solvents for secondary Li metal batteries because of their excellent reduction stability. However, their oxidation stability has been mostly relying on the high concentration approach, and limited progress has been made on building effective interphase to protect the cathode from the corrosion of the electrolyte. In this work, we construct a semi-crystalline interfacial layer on the surface of Li(Ni0.8Co0.1Mn0.1)O2 cathode that can achieve improved electrochemical stability in the highly corrosive chemical environment formed by the decomposition of ether molecules. Different from traditional brittle crystalline interphases, the optimized semi-crystalline layer with low modulus and high ionic conductivity can effectively relieve electrode strain and maintain the integrity of the interface layer. Due to this design, the continuous oxidation decomposition of ether-based electrolytes could be significantly suppressed and the battery shows outstanding cycling stability (84% capacity retention after 300 cycles). This article provides a solution to address the oxidation instability issue of ether-based electrolytes.

Unveiling the dynamic Li+-solvent interaction evolution in lithium metal batteries.

The interfacial chemistry during plating/stripping between electrolytes with different concentrations and Li metal is firstly in situ visualized by in situ Fourier transform infrared spectroscopy (FTIR) and simulated by density functional theory (DFT) calculations. It is verified that different Li+-solvent interaction evolutions at interfaces during the Li+ stripping and plating processes result in different interfacial stability. This work uncovers the critical role of Li+-solvent interaction evolution for the stability of the interface between the solvent and Li metal anode.

Colloid thermophoresis in the dilute electrolyte concentration regime: from theory to experiment.

Colloid thermophoresis in aqueous media is vital for numerous applications in nanoscience and life sciences. To date, a general description of colloid thermophoresis in DI water has not been determined. Here, we describe a theoretical model within the framework of the Fokker-Planck formalism and the flickering cluster concept to describe the hydration entropy effect on the thermophoretic behaviour of colloids suspended in DI water and compare this to new experimental results. We built an experimental platform to allow for rapid and robust temperature control and investigate the thermophoretic behaviour of silica microspheres with different sizes at various background temperatures for comparison. In this work, the ionic shielding effect is accounted for by using the well-known Duhr-Dhont's model, and the hydration layer effect is determined using the developed theoretical model. For the latter, our model reveals that the sign of the Soret coefficient is governed by the interplay between the binding energy and the chemical potential of water molecules, which were found to be in the same order of magnitude. We show that our analysis accurately describes the experimental behaviour of colloidal particles that opens a new avenue for developing versatile trapping and separation techniques for various colloidal particles in aqueous systems according to their size and background temperature.