Interfacial Surface Charge Research Articles

A green recyclable Li3VO4-pectin electrode exhibiting pseudocapacitive effect as an advanced anode for lithium-ion battery

Battery system design and development is prioritizing environmentally friendly recycling processes to ensure a sustainable future for our planet. The reuse of active materials in Li-ion batteries is critical for this goal. Herein, we investigated the electrochemical performance of Li3VO4 (LVO) anode with pectin as a binder. Our Li-ion half-cells showed stable capacity of 230 mAh g−1 at a current density of 0.02 A g−1 after 100 cycles. In addition, we observed a novel enhanced specific capacity of 400 mAh g−1 during delithiation at a high current density of 1 A g−1, which did not occur during lithiation. This higher capacity was can be attributed to the pseudocapacitive lithium storage behavior in the LVO-pectin electrode, as identified by CV and EIS analyses. The heterostructure of LVO-pectin resulted in an interfacial surface charge that contributed to the capacity, as demonstrated by impedance spectroscopy in conjunction with the distribution of relaxation times. The utilization of pectin as an eco-friendly binder demonstrated nearly 90 % material recovery and 100 % capability for subsequent re-lithiation, indicating recyclability. Furthermore, the pseudocapacitive effect becomes increasingly dominant in regenerated LVO-pectin cells. These results exemplify a promising approach towards the development of environmentally friendly Li-ion batteries with high energy and power density.

Chemically bonded BiVO4/Bi19Cl3S27 heterojunction with fast hole extraction dynamics for continuous CO2 photoreduction

Surface charge localization and inferior charge transfer efficiency seriously restrict the supply of reactive hydrogen and the reaction dynamics of CO2 photoreduction performance of photocatalysts. Herein, chemically bonded BiVO4/Bi19Cl3S27 (BVO/BCS) S-scheme heterojunction with a strong internal electric field is designed. Experimental and density function theory calculation results confirm that the elaborated heterojunction accelerates the vectorial migration of photogenerated charges from BiVO4 to Bi19Cl3S27 via the interfacial chemical bonding interactions (i.e., Bi-O and Bi-S bonds) between Bi atoms of BVO and S atoms of BCS or Bi atoms of BCS and O atoms of BVO under light irradiation, breaking the interfacial barrier and surface charge localization of Bi19Cl3S27, and further decreasing the energy of reactive hydrogen generation, CO2 absorption and activation. The separation efficiency of photogenerated carriers is much more efficient than that counterpart individual in BVO/BCS S-scheme heterojunction system. As a result, BVO/BCS heterojunction exhibits a significantly improved continuous photocatalytic performance for CO2 reduction and the 24 ​h CO yield reaches 678.27 ​μmol·g−1. This work provides an atomic-level insight into charge transfer kinetics and CO2 reduction mechanism in S-scheme heterojunction.

On the role of surface charge and surface tension tuned by surfactant in stabilizing bulk nanobubbles

The abnormal stability of bulk nanobubbles has attracted substantial attention from academia and industry since classical Epstein–Plesset theory predicts that gas bubbles cannot keep stable thermodynamic equilibrium spontaneously. The dual nature of ionic surfactants, acting simultaneously as charge carriers and attenuators of surface tension at the gas–liquid interface, enables them to play a unique role in bulk nanobubble stabilization. Herein the stability of bulk nanobubbles in anionic, cationic and nonionic surfactant solutions over a wide range of concentration is studied. Experimental results show that different kinds of surfactant molecules are involved in the nucleation and stabilization of bulk nanobubbles in different ways. We demonstrate that the accumulation of net charges carried by surfactant ions at the interface is predominantly responsible for stabilizing nanobubbles, instead of the reduction of surface tension. With theoretical calculations, we further quantify the coupling action of interfacial tension and surface charge on the stable equilibrium state of bulk nanobubbles. The result illustrates that the interfacial tension and the degree of gas saturation together determine the upper limit of the bubble size that can exist stably. Our study identifies a route to explore the intrinsic mechanism of bulk nanobubble’s stability.

Surface Potential Dynamics of Polyimide Under DC Corona Based on Noninvasive Measurement

To explore the surface charge behavior of polyimide films under corona discharge, the surface potential at both high-voltage (HV) stage and short-circuit (SC) stage is measured by a noninvasive method. DC HVs with different magnitudes, polarities, and durations are applied to a needle electrode to generate corona discharge. The surface potential without corona discharge exhibits a homopolar pulse at the HV stage and a heteropolar pulse at the SC stage because of interfacial polarization and depolarization. This article proposes a three-region model (including corona region, homopolar-charge region, and sample surface region) to explain the surface potential evolution with corona discharge. Surface potential under corona discharge shows a large fluctuation followed by decay with oscillation during the HV stage. The combined effect of interfacial depolarization and surface charge leakage explains the “backtracking” phenomenon at the SC stage. From the comparison under different polarities, it is found that negative corona produces more charge deposition than the positive case, and the leakage rate of negative charge is faster than that of positive charge. Moreover, both a lower applied voltage and a longer duration lead to a smaller amount of residual surface charge and a more obvious “backtracking” phenomenon. It is expected that this article will help to understand the surface charge behavior under dc corona in future studies.

(Invited) DNA-Directed High-Precision Assembly of High-Performance CNT FETs

Precise fabrication of semiconducting channel materials into densely-aligned uniform arrays is one prerequisite towards the high-performance ultra-scaled technology nodes, in particular for carbon nanotubes (CNTs). Traditional thin-film approaches generally yield CNTs in irregularly-spaced bundles or with wide orientation distribution, and lack a mechanism to effectively eliminate the mis-aligned CNTs from the ultra-scaled channel area. Therefore, the averaged pitch value and precision of CNT arrays, the key parameters defining lateral CNT spacing, fail to simultaneously meet all of the patterning requirements for the ultra-scaled technology nodes. Bio-fabrication is promising for patterning CNTls at a resolution beyond the existing lithographic limit. However, impacted by surface charges and sub-micron dimensions of typical bio-templates, current bio-templated electronics exhibit both poor transport performance and array uniformity smaller than 1 micron.We report precise scaling of inter-CNT pitch using a supramolecular assembly method called Spatially Hindered Integration of Nanowire Electronics (SHINE). Specifically, by using nano-trenches to align CNTs and DNA hybridization to stabilize them in place, we constructed parallel CNT arrays with uniform pitch as small as 10.4 nm, at an assembly yield over 95%. The pitch precision improves on that prepared from conventional thin-film approaches by more than two orders of magnitude. Compared to the lithography-patterned Si channels at 10 nm technology node, SHINE simultaneously provides both 70% smaller averaged pitch value and molecular-scale pitch precision in the channel area. By engineering the interfacial compositions, metal ions and surface charges that are destructive to FET performance have been excluded from the channel area without degrading CNT alignment. Under a source-to-drain voltage of -0.5 V, we demonstrate both transconductance more than 0.6 mS/μm with fast on/off switching. And the key FET performance metrics are improved by more than one order of magnitude than previous bio-templated FETs. Furthermore, we demonstrate centimeter-scale alignment of fixed-width CNT arrays. At the interface of high-performance electronics and bio-molecular self-assembly, precise bio-fabrication could provide ultra-scaled devices or circuits compatible with or sensitive to local biological environments.

Modeling Lithium Transport and Electrodeposition in Ionic-Liquid Based Electrolytes

Purely ionic electrolytes—wherein ionic liquids replace neutral solvents—have been proposed to improve lithium-ion-battery performance, on the basis that the unique microscopic characteristics of polarized ionic-liquid/electrode interfaces may improve the selectivity and kinetics of interfacial lithium-exchange reactions. Here we model a “three-ion” ionic-liquid electrolyte, composed of a traditional ionic liquid and a lithium salt with a common anion. Newman's concentrated-solution theory is extended to account for space charging and chemomechanical coupling. We simulate electrolytes in equilibrium and under steady currents. We find that the local conductivity and lithium transference number in the diffuse double layers near interfaces differ considerably from their bulk values. The mechanical coupling causes ion size to play a crucial role in the interface's electrical response. Interfacial kinetics and surface charge on the electrodes both affect the apparent transport properties of purely ionic electrolytes near interfaces. Larger ionic-liquid cations and anions may facilitate interfacial lithium-exchange kinetics.

(Invited) DNA-Directed High-Precision Assembly of CNT FETs

Precise fabrication of semiconducting channel materials into densely-aligned uniformly parallel arrays is one prerequisite to the high-performance ultra-scaled technology nodes, in particular for carbon nanotubes (CNTs). Traditional thin-film-based approaches generally yield CNTs in irregularly-spaced bundles or with wide orientation distribution, and lack a mechanism to effectively eliminate mis-aligned CNTs from the ultra-scaled channel area. Therefore, the averaged pitch value and precision of CNT arrays, the key parameters defining lateral CNT spacing, fail to simultaneously meet all of the patterning requirements for the ultra-scaled technology nodes. Bio-fabrication is promising for patterning CNTls at a resolution beyond the existing lithographic limit. However, impacted by surface charges and sub-micron dimensions of typical bio-templates, current bio-templated electronics exhibit both poor transport performance and array uniformity smaller than 1 micron.We report precise scaling of inter-CNT pitch using a supramolecular assembly method called Spatially Hindered Integration of Nanowire Electronics (SHINE). Specifically, by using nano-trenches to align CNTs and DNA hybridization to stabilize them in place, we constructed parallel CNT arrays with uniform pitch as small as 10.4 nm, at an assembly yield over 95%. The pitch precision improves on that prepared from conventional thin-film approaches by more than two orders of magnitude. Compared to the lithography-patterned Si channels at 10 nm technology node, SHINE simultaneously provides both 70% smaller averaged pitch value and molecular-scale pitch precision in the channel area. By engineering the interfacial compositions, metal ions and surface charges that are destructive to FET performance have been excluded from the channel area without degrading CNT alignment. Under a source-to-drain voltage of -0.5 V, we demonstrate both transconductance more than 0.6 mS/μm with fast on/off switching. And the key FET performance metrics are improved by more than one order of magnitude than previous bio-templated FETs. Furthermore, we demonstrate centimeter-scale alignment of fixed-width CNT arrays. At the interface of high-performance electronics and bio-molecular self-assembly, precise bio-fabrication could provide ultra-scaled devices or circuits compatible with or sensitive to local biological environments.

Two-liquid electroosmotic thrusters for micro propulsion applications

We investigate analytically the thruster performances and power consumption rates of a two-liquid electroosmotic thruster based on slit microchannels with hydrodynamic slip walls. The two electrolytes are considered to have different material properties and are arranged in the configuration of a core liquid layer surrounded by immiscible outer liquid layers with the outer layers in contact with the microchannel solid walls, thus forming electrical double layers at the solid-liquid interface. Interfacial potential jumps and surface charge densities are included to model the liquid-liquid interfacial double layers. Results reveal that, with the properties of both liquids being identical, nonzero liquid-liquid interfacial electrostatics only slightly increase the thrust but noticeably reduce the thruster efficiency and thrust-to-power ratio due to the enhanced Joule heating and viscous dissipation caused by the increased charge distributions and distorted velocity profiles. Moreover, the thrust and efficiency can be substantially increased as the dynamic viscosity ratio is decreased with the density ratio fixed at one, whereas the thrust, efficiency, and thrust-to-power ratio are all significantly enhanced by increasing the dynamic viscosity ratio when the kinematic viscosity ratio equals to one. The bulk electrolyte concentration/conductivity ratio is identified as a key parameter capable of simultaneously maximizing one or more thruster performances. While improving upon the performances of the single-liquid electroosmotic thruster previously reported, the two-liquid results and modeling presented herein may likely relax the limitations on the choice of electroosmotic propellants, increase the operational flexibility of electrokinetic thrusters, and be further applied in space or underwater micropropulsion applications.

High Electromechanical Deformation Based on Structural Beta-Phase Content and Electrostrictive Properties of Electrospun Poly(vinylidene fluoride- hexafluoropropylene) Nanofibers.

The poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) polymer based on electrostrictive polymers is essential in smart materials applications such as actuators, transducers, microelectromechanical systems, storage memory devices, energy harvesting, and biomedical sensors. The key factors for increasing the capability of electrostrictive materials are stronger dielectric properties and an increased electroactive β-phase and crystallinity of the material. In this work, the dielectric properties and microstructural β-phase in the P(VDF-HFP) polymer were improved by electrospinning conditions and thermal compression. The P(VDF-HFP) fibers from the single-step electrospinning process had a self-induced orientation and electrical poling which increased both the electroactive β-crystal phase and the spontaneous dipolar orientation simultaneously. Moreover, the P(VDF-HFP) fibers from the combined electrospinning and thermal compression achieved significantly enhanced dielectric properties and microstructural β-phase. Thermal compression clearly induced interfacial polarization by the accumulation of interfacial surface charges among two β-phase regions in the P(VDF-HFP) fibers. The grain boundaries of nanofibers frequently have high interfacial polarization, as they can trap charges migrating in an applied field. This work showed that the combination of electrospinning and thermal compression for electrostrictive P(VDF-HFP) polymers can potentially offer improved electrostriction behavior based on the dielectric permittivity and interfacial surface charge distributions for application in actuator devices, textile sensors, and nanogenerators.

Detection and amplification of capacitance- and charge-based signals using printed electrolyte gated transistors with floating gates

The electrolyte gated transistor with a floating gate (FGT) is a promising sensing platform for both chemical and biodetection applications due to its fast, label-free response, low voltage operation, and simple fabrication by printing and conventional lithography. We present here a unified framework for understanding how FGTs measure changes in interfacial capacitance and surface charge, using self-assembled monolayers (SAMs) on the FGT detection area as model systems. The capacitance measurements take advantage of alkyl thiol SAMs with different chain lengths, while the charge experiments deprotonate 11-mercaptoundecanoic acid by changing solution pH. The effects of capacitance and surface charge are identified readily by analysis of the changes in the quasi-static current–voltage (ID–VG) characteristics of a stand-alone FGT in response to changes in the surface properties; changes in capacitance produce changes in slope, whereas changes in surface charge cause horizontal shifts in the transfer curves. For sensing applications, it is preferable to integrate the FGT into a resistor-loaded inverter to take advantage of the amplified voltage output relative to a stand-alone FGT. For inverters, changes in capacitance lead to changes in inverter gain, whereas changes in surface charge produce horizontal shifts in the inverter curves. A capacitance sensitivity of 70 mV/(μF/cm2) and a charge sensitivity of 40 mV/(μC/cm2) are obtained from the inverter output voltages. The ability to sense both capacitance and charge, and to distinguish between them, makes FGTs attractive for the detection of a wide variety of targets in chemical and biological sensing applications.

Structural, thermal, dielectric and optical behaviour investigations of water-free ZnO/lyotropic liquid crystal nanocolloids

ABSTRACTZinc oxide (ZnO) nanoparticles of spherical symmetry (average size of ≈ 20 nm) have been synthesised via a non-aqueous lyotropic liquid crystalline (LLC) templating process. Lyotropic liquid crystalline nanocolloids are prepared via dispersing 0.05, 0.1 and 0.5 wt.% ZnO nanoparticles in non-aqueous lyotropic phase. No structural phase change has been seen with the doping of nanoparticles as stable lamellar phases are observed in all the cases. Stability of the lamellar structure and orientation of the ZnO nanoparticles in the liquid crystalline matrix may be attributed to the interfacial surface charge interactions. A significant increase and pronounced dispersion in dielectric permittivity of the ZnO/LLC nanocolloids could be the result of parallel coupling among guest/host, higher dipole- moment of the ZnO nanoparticles and Maxwell-Wagner polarisation. The variation of relaxation parameters has also been discussed and correlated with the dielectric and structural parameters. ZnO/lyotropic nanocolloids devices exhibit dc conductivity of the order of 10−5S/m owing to the increase in the number of ions (of the order of 1019m−3) in the doped systems. Nanocolloids exhibits, the refractive index of range 1.40 to 1.45 and the wide bandgap of the range 4.1–4.5 eV.

A model of two viscoelastic liquid films traveling down in an inclined electrified channel

This study addresses the stability of two immiscible, viscoelastic electrified fluids for two films, each has a finite depth in porous media. The system is subjected to both an interfacial insoluble surfactant and surface charge accumulated at the interface. We study both the cases of small Reynolds and wave numbers, where stability process and numerical calculations are performed to describe the linear stage of the interface evolution. The surface tension is allowed to vary linearly with surfactants and temperature. The governing equations and the corresponding conditions led to three evaluation equations for the stream function, temperature, and the electric potential. In dealing with this system we assumed two cases of both small Reynolds and wave numbers. The stability pictures are illustrated, in which regions of stability and instability are identified. For small Reynolds number, numerical computations show that the surfactants through the elasticity number can be used to either suppress or enhance the interface stability depending on the thickness ratio of the channel. Weber number can be either stabilizing or destabilizing depending on the selected parameters, in particular, the viscosity ratio. Comparing the present results with that available in the literature, our results are in good agreement. In the long-wave limit, both the Darcy number and permeability ratio have a stabilizing influence on the movement of the interface.

Calorimetric study of alkali and alkaline-earth cation adsorption and exchange at the quartz-solution interface

Cations in natural solutions significantly impact interfacial processes, particularly dissolution and surface charge measurements for quartz and silica, which are amongst the most naturally abundant and technologically important solids. Thermodynamic parameters for cation-specific interfacial reactions have heretofore been mostly derived instead of directly measured experimentally. This work investigates the energetics of adsorption and exchange reactions of alkali metal (M+) and alkaline earth (M2+) cations with the quartz surface by flow adsorption microcalorimetry, in tandem with in-situ pH measurements. The magnitudes of the heats of adsorption and exchange were found to increase along the Hofmeister series i.e., Li+<Na+<K+<Rb+<Cs+ and Mg2+<Ca2+<Sr2+<Ba2+, and exhibited strong correlations to bulk cation hydration enthalpies (ΔHhyd). These results suggest inner-sphere adsorption for all studied cations and highlight the role ΔHhyd plays in rationalizing these reactions and controlling their net overall enthalpy. pH measurements demonstrate that quartz surface charge will vary depending on the cation present, as is well known for amorphous forms of silica. Along with calorimetric signals, pH data revealed kinetic differences between the adsorption and desorption reactions of M+ and M2+, and individual cations within each group.

Ultrafiltration of saline oil-in-water emulsions stabilized by an anionic surfactant: Effect of surfactant concentration and divalent counterions

The paper presents results of a direct visualization study of membrane fouling by hexadecane-in-water emulsions (0.1% v/v) stabilized by sodium dodecyl sulfate (SDS; 0.1mM or 3mM) in the presence of divalent counterions (Mg2+; 0mM, 6.7mM, or 42.6mM). Direct Observation Through the Membrane (DOTM) tests were performed using an ultrafiltration membrane (Anopore; dpore =0.02µm) and low wettability by hexadecane (contact angle, θ, in 3mM aqueous solution of SDS is ~164°). Three emulsions employed in DOTM tests had different values of interfacial tension and surface charge and exhibited distinctly different behaviors of oil droplets on the membrane surface. In addition to decreasing the solubility of SDS, MgSO4 had two opposing effects on emulsion stability wherein both interfacial tension and ζ-potential of oil droplets decreased; the overall effect of MgSO4 was a more facile droplet coalescence that was further promoted by permeate flux and concentration polarization of oil. The dominant fouling mechanism was cake filtration with multilayer and sub-monolayer coverages observed for different conditions. Because of the relative oleophobicity of the membrane, the attached oil did not form contiguous oil films. Under conditions of extensive coalescence (high MgSO4), oil droplets reached a critical size and were then removed by the crossflow resulting in minimal membrane fouling.

Vibrational Sum Frequency Generation Spectroscopy of Fullerene at Dielectric Interfaces

Vibrational sum frequency generation (VSFG) spectroscopy was used to measure the interfacial spectra of fullerene thin films on dielectric substrates that are commonly used in IR spectroscopy. The VSFG spectra on SiO2 and CaF2 exhibit notably different intensities for the F1u and Ag vibrational modes. This difference is attributed to different interfacial surface charges and C60/surface interactions. DFT calculations were performed to model the influence of a unidirectional electrostatic perturbation on the IR and Raman activities. The VSFG activities were then calculated for comparison to the interfacial second-order susceptibilities obtained from multilayer interference fitting of the experimental spectra. We find that the negative surface charge of CaF2 substrates causes a larger perturbation of fullerene than native silica surfaces, which leads to a stronger influence on the VSFG spectra.

Charge Transport Analysis in Two-Phase Composite Dielectric Systems

Analyses of unipolar charge transport phenomena in series, two-region composite dielectric systems are presented for planar, coaxial cylindrical, and concentric spherical electrode geometries. Space charge limited condition is applied at the charge emitting electrode for steady state and transient. Method of characteristics is used to convert the governing partial differential equations into a set of ordinary differential equations that allow analytical solutions as functions of time and space for volume and interfacial surface charge densities, charge trajectories, electric field intensity, and voltage drop across the electrodes. Solutions given in this paper can be used in design of high-voltage capacitors, pulsed-power transmission lines, and other apparatus. These solutions have also been used as a way of gaining confidence in the correctness and accuracy of our charge transport and prebreakdown models in two-phase insulation systems.

Grain boundary melting in ice

We describe an optical scattering study of grain boundary premelting in water ice. Ubiquitous long ranged attractive polarization forces act to suppress grain boundary melting whereas repulsive forces originating in screened Coulomb interactions and classical colligative effects enhance it. The liquid enhancing effects can be manipulated by adding dopant ions to the system. For all measured grain boundaries this leads to increasing premelted film thickness with increasing electrolyte concentration. Although we understand that the interfacial surface charge densities qs and solute concentrations can potentially dominate the film thickness, we cannot directly measure them within a given grain boundary. Therefore, as a framework for interpreting the data we consider two appropriate qs dependent limits; one is dominated by the colligative effect and other is dominated by electrostatic interactions.

Gas–liquid mass transfer in the presence of ionic surfactant: effect of counter‐ions and interfacial turbulence

This work investigated the effect of counter‐ions and interfacial turbulence on oxygen transfer from gas to liquid phase containing ionic surfactant, and experiments were performed in a mechanically stirred reactor with flat gas–liquid interface. Counter‐ions in terms of hydration ability and polarizability influence the interfacial coverage of ionic surfactants (i.e. cetytrimethylammonium bromide (CTAB) and cetytrimethylammonium chloride) with the same hydrocarbon chain length, producing hindrance but in different extent on oxygen transfer. The addition of electrolyte (NH4Br) substantially reduced the interfacial tension and surface charge of micelles (zeta potential) in CTAB system, and this salt effect greatly compressed interfacial double layer leading to gas transfer inhibition. The surface charge, aggregation number as well as stability of micelles formed above the critical micelle concentration could also alter interfacial configuration of surfactant layer reflected by gas absorption rate. Liquid turbulence was analyzed to decide the role of surfactant present in water on gas–liquid mass transfer, since Marangoni instability effect playing positive role should be taken into consideration under moderate liquid flow, while in turbulent system, contribution of Marangoni effect became overshadowed and consequently surfactant pose ‘barrier’ effect on gas transfer due to its surface active nature. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Linear instability of the electrified free interface between two cylindrical shells of viscoelastic fluids through porous media

In this paper, we have discussed the linear stability analysis of the electrified surface separating two coaxial Oldroyd-B fluid layers confined between two impermeable rigid cylinders in the presence of both interfacial insoluble surfactant and surface charge through porous media. The case of long waves interfacial stability has been studied. The dispersion relation is solved numerically and hence the effects of various parameters are illustrated graphically. Our results reveal that the influence of the physicochemical parameter β is to shrink the instability region of the surface and reduce the growth rate of the unstable normal modes. Such important effects of the surfactant on the shape of interfacial structures are more sensitive to the variation of the β corresponding to non-Newtonian fluids-model compared with the Newtonian fluids model. In the case of long wave limit, it is demonstrated that increasing β, has a dual role in-fluence (de-stabilizing effects) depending on the viscosity of the core fluid. It has a destabilizing effect at the large values of the core fluid viscosity coefficient, while this role is exchanged to a regularly stabilizing influence at small values of such coefficient.

Critical polyelectrolyte adsorption under confinement: Planar slit, cylindrical pore, and spherical cavity

We explore the properties of adsorption of flexible polyelectrolyte chains in confined spaces between the oppositely charged surfaces in three basic geometries. A method of approximate uniformly valid solutions for the Green function equation for the eigenfunctions of polymer density distributions is developed to rationalize the critical adsorption conditions. The same approach was implemented in our recent study for the "inverse" problem of polyelectrolyte adsorption onto a planar surface, and on the outer surface of rod-like and spherical obstacles. For the three adsorption geometries investigated, the theory yields simple scaling relations for the minimal surface charge density that triggers the chain adsorption, as a function of the Debye screening length and surface curvature. The encapsulation of polyelectrolytes is governed by interplay of the electrostatic attraction energy toward the adsorbing surface and entropic repulsion of the chain squeezed into a thin slit or small cavities. Under the conditions of surface-mediated confinement, substantially larger polymer linear charge densities are required to adsorb a polyelectrolyte inside a charged spherical cavity, relative to a cylindrical pore and to a planar slit (at the same interfacial surface charge density). Possible biological implications are discussed briefly in the end.