Evaluation of Four Measurement Operation Modes of Streaming Potential for Microfiltration and Ultrafiltration Membranes

Surface charge characteristics of a membrane can be determined by the streaming potential. In order to obtain more accurate streaming potential value during the measurement, four measurement operation modes were investigated in this study, and among the four modes, the steady mode with pressure stepped downward was considered the best one. Experimental results showed that the effects of compaction on the streaming potential measurement for a microfiltration membrane was more obvious than that for a ultrafiltration membrane. Both feed pH and presoaking could affect the measurement of streaming potential.

Hierarchical model for strain generalized streaming potential induced by the canalicular fluid flow of an osteon

A hierarchical model is developed to predict the streaming potential （SP） in the canaliculi of a loaded os teon. Canaliculi are assumed to run straight across the os teon annular cylinder wall, while disregarding the effect of lacuna. SP is generalized by the canalicular fluid flow. Ana lytical solutions are obtained for the canalicular fluid veloc ity, pressure, and SP. Results demonstrate that SP amplitude （SPA） is proportional to the pressure difference, strain am plitude, frequency, and strain rate amplitude. However, the key loading factor governing SP is the strain rate, which is a representative loading parameter under the specific phys iological state. Moreover, SPA is independent of canalicu lar length. This model links external loads to the canalicu lar fluid pressure, velocity, and SP, which can facilitate fur ther understanding of the mechanotransduction and electro mechanotransduction mechanisms of bones.

Characterization of polysulfone hollow-fiber ultrafiltration membrane and its cleaning efficiency by streaming potential and flux method

Polysulfone(PS)hollow-fiber ultrafiltration membrane was characterized combined with flux and streaming potential in single electrolyte solutions.The effects of trans-membrane pressure,electrolyte concentration,ion valence and pH value of electrolyte solution on the streaming potential(SP)of the membrane were investigated.The zeta potential and surface charge density of the membrane were calculated on the basis of Helmholtz-Smoluchowski equation and Gouy-Chapmann theory.The results indicate that the valence and concentration of cation have a greater influence on the SP and surface charge density of PS membrane than those of anion,and the pH value of electrolyte solution has great effects on the SP and zeta potential of the membrane surface. Both the absolute value of the streaming potential and water flux of the adsorbed membrane decrease,compared with those of the clean membrane.The streaming potential and flux of the cleaned membrane can be completely recovered by cleaning with the mass fraction of 0.8%EDTA at pH=10.

Mechanism of water-evaporation-induced electricity beyond streaming potential

Since its first discovery in 2017,evaporation-induced electricity has attracted extensive attention and shown significant advantages in green energy conversion.While the streaming potential-related electrokinetic effect has been intensively explored and widely recognized as the underlying mechanism,the role of coupling between water molecules and charge carriers in the material remains elusive.Here we show through carefully designed experiments that the streaming potential effect indeed plays a role but can only contribute about half to the total water-evaporation-induced voltage occurring within the partially-wetted region of the carbon black film where the solid-liquid-gas three-phase interface exists.It is also shown that water evaporation from carboxyl and amino-functionalized carbon black films produces opposite voltage signals.Detailed first-principles calculations unveil that the adsorption of water molecules can lead to reversed charge transfer in the carboxyl and amino-functionalized carbon substrates.Finally,an evaporation-driven charge transport mechanism is proposed for the induced electricity mediated by the coupling between water molecules and charge carriers in the material.The results reveal the important role of direct interaction between water molecules and materials,deepening our understanding of the mechanism for evaporation-induced hydrovoltaic effect beyond streaming potential.

Investigation of pressure loading rates on streaming potentials in bone

When load is applied to bone,it deforms and causes fluid pressure to build up in bone.The pressure gradient between different portions of the bone microcnannels drives fluid flow through them.This kind of bone fluid flow can induces the streaming potentials which are considered to play a role for bone remodeling.Aimed to determine the impact of ribbed rough inner surfaces of the microchannels on the streaming potentials,streaming potentials were measured as bone fluid flowed through the mcrospaces of thin cylinder bone samples under different pressure loading rates.The results show that the streaming potentials decrease with the increase of the pressure loading rates.A digital simulation calculation was performed and the results demonstrated that there were turbulent flows near the inner wall surfaces,which making the streaming potentials smaller in bone microchannels.

Discontinuous streaming potential via liquid gate

Streaming potential is mainly related to electrokinetic energy conversion,which has been considered to show promising potential for advanced technologies,especially sensing.The inherent property of streaming potential is that the energy conversion process is always a continuous state.However,practical applications include many cases of discontinuous states,such as nonlinear sensing.Here,we report a discontinuous streaming potential electrokinetic energy conversion fluid system.Experiments and theoretical calculations reveal that this system exhibits a discontinuous electrokinetic effect and provides a gating liquid slip in micropores,offering the advantages of gating liquid charge coupling and interfacial drag reduction.Moreover,the system is demonstrated in a wearable fall-down alert application.We expect this liquid gating energy conversion system to open up a platform for the design and application of autonomous health monitoring devices,seismic sea wave warning systems,and beyond.

Influence of Electric Double Layer on Lubrication

A mathematical model of lubrication with the electric double layer (EDL) was put forward in order to study the influence of EDL.The lubrication tests with a composite sliding block and a disk were carried out with oleic acid used as an additive to strengthen EDL.The streaming potential and friction force were measured. The experimental results show that the EDL has an apparent effect on the frictional force, which increases the ability of forming lubrication film.

Electrokinetic energy conversion of electro-magneto-hydro-dynamic nanofluids through a microannulus under the time-periodic excitation

In this work,the effects of externally applied axial pressure gradients and transverse magnetic fields on the electrokinetic energy conversion(EKEC)efficiency and the streaming potential of nanofluids through a microannulus are studied.The analytical solution for electro-magneto-hydro-dynamic(EMHD)flow is obtained under the condition of the Debye-Huuckel linearization.Especially,Green’s function method is used to obtain the analytical solutions of the velocity field.The result shows that the velocity distribution is characterized by the dimensionless frequency?,the Hartmann number Ha,the volume fraction of the nanoparticlesφ,the geometric radius ratio a,and the wallζpotential ratio b.Moreover,the effects of three kinds of periodic excitations are compared and discussed.The results also show that the periodic excitation of the square waveform is more effective in increasing the streaming potential and the EKEC efficiency.It is worth noting that adjusting the wallζpotential ratio and the geometric radius ratio can affect the streaming potential and the EKEC efficiency.

On the energy conversion in electrokinetic transports

Energy conversion in micro/nano-systems is a subject of current research,among which the electrokinetic energy conversion has attracted extensive attention.However,there exist two different definitions on the electrokinetic energy conversion efficiency in literature.A few researchers defined the efficiency using the pure pressure-driven flow rate,while other groups defined the efficiency based on the flow rate with the inclusion of the effect of the streaming potential field.In this work,both definitions are investigated for different fluid types under the periodic electrokinetic flow condition.For Newtonian fluids,the two definitions give similar results.However,for viscoelastic fluids,these two definitions lead to significant difference.The efficiency defined by the pure pressure-driven flow rate even exceeds 100%in a certain range of the parameters.The result shows that in the case of viscoelastic flow,it is incorrect to define the energy conversion efficiency by pure pressure-driven flow rate.At the same time,the reason for this problem is clarified through comprehensive analysis.

Electrokinetic flow and energy conversion in a curved microtube

Curved channels are ubiquitous in microfluidic systems.The pressure-driven electrokinetic flow and energy conversion in a curved microtube are investigated analytically by using a perturbation analysis method under the assumptions of the small curvature ratio and the Reynolds number.The results indicate that the curvature of the microtube leads to a skewed pattern in the distribution of the electrical double layer(EDL)potential.The EDL potential at the outer side of the bend is larger than that at the inner side of the bend.The curvature shows an inhibitory effect on the magnitude of the streaming potential field induced by the pressure-driven flow.Since the spanwise pressure gradient is dominant over the inertial force,the resulting axial velocity profile is skewed into the inner region of the curved channel.Furthermore,the flow rate in a curved microtube could be larger than that in a straight one with the same pressure gradient and shape of cross section.The asymptotic solutions of the axial velocity and flow rate in the absence of the electrokinetic effect are in agreement with the classical results for low Reynolds number flows.Remarkably,the curved geometry could be beneficial to improving the electrokinetic energy conversion(EKEC)efficiency.

Electrokinetic phenomena of poly(vinyl butyral) hollow fiber membranes in different electrolyte solutions

The streaming potential of poly（vinyl butyral） （PVB） hollow fiber membrane was studied in different electrolyte solutions （including NaCl, KCl, CaCl2 and MgCl2）, the effects of ionic strength, ion valence and pH value on the streaming potential （SP） of the membrane were investigated. The zeta potentials and surface charge densities of the membrane were estimated on the basis of Helmholtz-Smoluchowski equation and Gouy-Chapmann theory. The results show that the PVB membrane has a weak negative charge due to the specific adsorption of ions. Moreover, the streaming potential, the zeta potential and the surface charge density of the membrane depend strongly on the salt concentration and the type and valence of ions. The iso-electric point （IEP） of the PVB membrane is arotmd 3.0 in the monovalent media （NaC1 and KC1） and 3.5 in divalent electrolytes （CaCl2 and MgCl2）. A few retentions were obtained for PVB membrane in low concentration solutions. This result verifies that the negative charged membrane surface can reject inorganic solutes by means of electrostatic repulsion effect even though the size of membrane pores is much larger than the size of salts.

The Upstream ＂Strong Signals＂ of the Water Vapor Transport over the Tibetan Plateau during a Heavy Rainfall Event in the Yangtze River Basin

A heavy rainfall event that occurred over the middle and lower reaches of the Yangtze River Basin （YRB） during July 11-13 2000 is explored in this study. The potential/stream function is used to analyze the upstream ＂strong signals＂ of the water vapor transport in the Tibetan Plateau （TP）. The studied time period covers from 2000 LST 5 July to 2000 LST 15 July （temporal resolution： 6 hours）. By analyzing the three-dimensional structure of the water vapor flux, vorticity and divergence prior to and during the heavy rainfall event, the upstream ＂strong signals＂ related to this heavy rainfall event are revealed. A strong correlation exists between the heavy rainfall event in the YRB and the convective clouds over the TE The ＂convergence zone＂ of the water vapor transport is also identified, based on correlation analysis of the water vapor flux two days and one day prior to, and on the day of, the heavy rainfall. And this ＂convergence zone＂ coincides with the migration of the maximum rainfall over the YRB. This specific coupled structure actually plays a key role in generating heavy rainfall over the YRB. The eastward movement of the coupled system with a divergence]convergence center of the potential function at the upper/lower level resembles the spatiotemporal evolution of the heavy rainfall event over the YRB. These upstream ＂strong signals＂ are clearly traced in this study through analyzing the three-dimensional structure of the potential/stream function of upstream water vapor transport.

A UNIFORMLY VALID ASYMPTOTIC SOLUTION OF THE NAVIER-STOKES EQUATIONS

In this paper, problems of the flow over a fat plate in the large Reynolds numbercase are studied by using the method of multiple scales￣[1,2].We have obtained N-orderuniformly valid asymptotic solutions of the Naver-Stodes equations.

Emerging design principles,materials,and applications for moisture-enabled electric generation

Smart generators that collect energy from the ambient environment are a new approach for meeting growing global energy needs.Moisture is one of the most abundant resources in the ambient environment,and using it to generate electricity has aroused great interest in recent years.In this review,we first summarize the emerging design principles of moisture power generation,including ion diffusion,streaming potential,and charged surface potential.Then,based on these fundamental principles,we systematically summarize the materials thus far known to be suitable for moisture power generation.Finally,we highlight the application of moisture energy generators in various fields,such as thermoelectricity,solar thermal evaporation,capacitors,strain sensors,and information storage,and discuss current challenges and future prospects for the development of moisture energy generators.

Effects of operating conditions on membrane charge property and nanofiltration

The effects of the operating pressure,crossflow velocity,feed concentration,and temperature on the streaming and Zeta potential of the membranes were studied.The permeateflux and the retention rate under different nanofiltration operating conditions were also investigated.The results show that the higher pressure,feed concentration,temperature,and lower crossflow velocity lead to the higher absolute value of streaming and Zeta potential.The permeateflux of the nanofiltration decreases with the feed concentration and increases with not only the pressure but also the crossflow velocity and temperature.The higher the pressure and the crossflow velocity,the higher the retention rate.The lower feed concentration and higher temperature leads to lower retention rate.The effects of the operating conditions on the permeateflux and the retention rate were explained by the variation of the membrane charge property.