Strong Electrostatic Coupling Research Articles

Toward Modeling the Structure of Electrolytes at Charged Mineral Interfaces Using Classical Density Functional Theory.

The organization of water molecules and ions between charged mineral surfaces determines the stability of colloidal suspensions and the strength of phase-separated particulate gels. In this article, we assemble a density functional that measures the free energy due to the interaction of water molecules and ions in electric double layers. The model accounts for the finite size of the particles using fundamental measure theory, hydrogen-bonding between water molecules using Wertheim's statistical association theory, long-range dispersion interactions using Barker and Henderson's high-temperature expansion, electrostatic correlations using a functionalized mean-spherical approximation, and Coulomb forces through the Poisson equation. These contributions are shown to produce highly correlated structures, aptly rendering the layering of counterions and co-ions at highly charged surfaces and permitting the solvation of ions and surfaces to be measured by a combination of short-range associations and long-ranged attractions. The model is tested in a planar geometry near soft, charged surfaces to reproduce the structure of water near graphene and mica. For mica surfaces, explicitly representing the density of the outer oxygen layer of the exposed silica tetrahedra allows water molecules to hydrogen-bond to the solid. When electrostatic interactions are included, water molecules assume a hybrid character, being accounted for implicitly in the dielectric constant but explicitly otherwise. The disjoining pressure between approaching like-charged surfaces is calculated, demonstrating the model's ability to probe pressure oscillations that arise during the expulsion of ions and water layers from the interfacial gap and predict strong interattractive stresses that form at narrow interfacial spacing when the surface charge is overscreened. This interattractive stress arises not due to in-plane correlations under strong electrostatic coupling but due to the out-of-plane structuring of associating ions and water molecules.

Ferroelectric-programmed photonic computing in monolayer WS2

Photonic computing has the potential to significantly improve energy efficiency and data processing speed beyond that of von Neumann architecture. Although various optical processing techniques have been developed during recent two decades, the photonic manipulation is still a big challenging due to the bosonic nature of photons. Herein, we propose a ferroelectric field-controlled photonic computing based on the heterostructure of ferroelectric/van der Waals semiconductor. The strong and tunable electrostatic coupling of ferroelectric (PMN-PT) with monolayer WS2 results in a multi-level (24 bits) photoluminescence (PL) output. Furthermore, combining device modeling with experiments, we find that the multi-level PL output is because of the regulation of ferroelectric polarization on the net recombination rate of WS2. The ferroelectric field-controlled multi-level PL output enables us to design an optical arithmetic operation in the PMN-PT/WS2 heterostructure, which provides an attractive solution for photonic information computing.

Colloid Electrolyte with Weakly Solvated Structure and Optimized Electrode/Electrolyte Interface for Zinc Metal Batteries

Aqueous zinc batteries are considered as a viable candidate for cost-effective and environmentally sustainable energy storage technology but are severely hampered by the notorious dendrite growth and parasitic reactions at the zinc anode side. Herein, we propose a bifunctional colloidal electrolyte design that utilizes upconversion nanocrystals, i.e., NaErF4@NaYF4, as a solid additive to provide the sustained release of functional metal and fluoride ions, which can effectively improve the reversibility of the Zn anode to inhibit dendrite growth and hydrogen evolution through forming an electrostatic shielding layer and in situ constructing a ZnF2-enriched protective interface. Experimental characterization and molecular dynamics simulation jointly confirm that the NaErF4@NaYF4 additive could modify the Zn2+ solvation environment in the vicinity of the NaErF4@NaYF4 surface via the strong electrostatic coupling with Zn2+ ions. As a consequence, the modified electrolyte enables stable zinc plating/stripping over 2100 h at a current density of 3 mA cm–2 and a capacity of 1 mAh cm–2 in symmetric cells. The assembled Zn||MnO2 full cells with a modified electrolyte can operate stably for 1600 cycles at 2 A g–1. This work thereby has great potential for the exploration of multifunctional electrolyte additives toward long-lasting aqueous Zn metal batteries.

Highly Efficient, Non-Covalent Functionalization of CVD-Graphene via Novel Pyrene-Based Supporter Construct

Ultra-thin two-dimensional (2D) materials have attained huge interest for biosensing applications because of their strong electrostatic coupling with target molecules such as spike proteins and DNA. One such 2D material is graphene, which is extremely thin and flexible and has a strong non-covalent interaction with the supporting constructs needed to detect biomolecules. This work aimed to develop a way to efficiently functionalize the surface of 2D material using a pyrene-based supporter construct to detect the target protein. For this purpose, high-quality, pristine graphene was grown via the chemical vapor deposition (CVD) method and transferred over the Si/SiO2 substrate for its functionalization using our engineered pyrene–lysine-based supporter construct (PLB). The construct was synthesized using the solid-phase peptide synthesis (SPPS) method and utilized to functionalize the graphene-channel-based field-effect transistor (FET) device via non-covalent π−π stacking interaction. The optimum concentration of the functionalized PLB was evaluated via atomic force microscopy (AFM), Raman spectroscopy, and real-time electrical measurements. The characterization techniques successfully provide an overview of the effect of the concentration of PLB used for functionalization. Moreover, the performance was tested and compared in terms of the percentage response of the device generated after the detection of various concentrations of the streptavidin protein. This research could be useful in determining how to functionalize any 2D material by designing a supporter construct without material degradation and owing to over-stacking or bypassing surface screening effects.

Diverse Defects in Alkali Niobate Thin Films: Understanding at Atomic Scales and Their Implications on Properties.

Defects in ferroelectric materials have many implications on the material properties which, in most cases, are detrimental. However, engineering these defects can also create opportunities for property enhancement as well as for tailoring novel functionalities. To purposely manipulate these defects, a thorough knowledge of their spatial atomic arrangement, as well as elastic and electrostatic interactions with the surrounding lattice, is highly crucial. In this work, analytical scanning transmission electron microscopy (STEM) is used to reveal a diverse range of multidimensional crystalline defects (point, line, planar, and secondary phase) in (K,Na)NbO3 (KNN) ferroelectric thin films. The atomic-scale analyses of the defect-lattice interactions suggest strong elastic and electrostatic couplings which vary among the individual defects and correspondingly affect the electric polarization. In particular, the observed polarization orientations are correlated with lattice relaxations as well as strain gradients and can strongly impact the properties of the ferroelectric films. The knowledge and understanding obtained in this study open a new avenue for the improvement of properties as well as the discovery of defect-based functionalities in alkali niobate thin films.

Self-Assembly of Miktoarm Star Polyelectrolytes in Solutions with Various Ionic Strengths

We studied the self-assembly of miktoarm star polyelectrolytes with different numbers of arms in solutions with various ionic strengths using coarse-grained molecular dynamic simulations. Spherical micelles are obtained for star polyelectrolytes with fewer arms, whereas wormlike clusters are obtained for star polyelectrolytes with more arms at a low ionic strength environment, with hydrophilic arms showing a stretched conformation. The number of clusters shows an overall decreasing tendency with increasing the number of arms in star polyelectrolytes due to strong electrostatic coupling between polycations and polyanions. The formation of wormlike clusters follows an overall stepwise pathway with an intermittent association–dissociation process for star polyelectrolytes with weak electrostatic coupling. These computational results can provide relevant physical insights to understand the self-assembly mechanism of star polyelectrolytes in solvents with various ionic strengths and to design star polyelectrolytes with functional groups that can fine-tune self-assembled structures for specific applications.

Optically Induced Picosecond Lattice Compression in the Dielectric Component of a Strongly Coupled Ferroelectric/Dielectric Superlattice

AbstractAbove‐bandgap femtosecond optical excitation of a ferroelectric/dielectric BaTiO3/CaTiO3 superlattice leads to structural responses that are a consequence of the screening of the strong electrostatic coupling between the component layers. Time‐resolved X‐ray free‐electron laser diffraction shows that the structural response to optical excitation includes a net lattice expansion of the superlattice consistent with depolarization‐field screening driven by the photoexcited charge carriers. The depolarization‐field‐screening‐driven expansion is separate from a photoacoustic pulse launched from the bottom electrode on which the superlattice is epitaxially grown. The distribution of diffracted intensity of superlattice X‐ray reflections indicates that the depolarization‐field‐screening‐induced strain includes a photoinduced expansion in the ferroelectric BaTiO3 and a contraction in CaTiO3. The magnitude of expansion in BaTiO3 layers is larger than the contraction in CaTiO3. The difference in the magnitude of depolarization‐field‐screening‐driven strain in the BaTiO3 and CaTiO3 components can arise from the contribution of the oxygen octahedral rotation patterns at the BaTiO3/CaTiO3 interfaces to the polarization of CaTiO3. The depolarization‐field‐screening‐driven polarization reduction in the CaTiO3 layers points to a new direction for the manipulation of polarization in the component layers of a strongly coupled ferroelectric/dielectric superlattice.

Analysis of the charging kinetics in silver nanoparticles-silica nanocomposite dielectrics at different temperatures

Dielectric nanocomposite materials are now involved in a large panel of electrical engineering applications ranging from micro-/nano-electronics to power devices. The performances of all these systems are critically dependent on the evolution of the electrical properties of the dielectric parts, especially under temperature increase. In this study we investigate the impact of a single plane of silver nanoparticles (AgNPs), embedded near the surface of a thin silica (SiO2) layer, on the electric field distribution, the charge injection and the charge dynamic processes for different AgNPs-based nanocomposites and various temperatures in the range 25°C–110°C. The electrical charges are injected locally by using an Atomic Force Microscopy (AFM) tip and the related surface potential profile is probed by Kelvin Probe Force Microscopy (KPFM). To get deeper in the understanding of the physical phenomena, the electric field distribution in the AgNPs-based nanocomposites is computed by using a Finite Element Modeling (FEM). The results show a strong electrostatic coupling between the AFM tip and the AgNPs, as well as between the AgNPs when the AgNPs-plane is embedded in the vicinity of the SiO2-layer surface. At low temperature (25°C) the presence of an AgNPs-plane close to the surface, i.e., at a distance of 7 nm, limits the amount of injected charges. Besides, the AgNPs retain the injected charges and prevent from charge lateral spreading after injection. When the temperature is relatively high (110°C) the amount of injected charges is increased in the nanocomposites compared to low temperatures. Moreover, the speed of lateral charge spreading is increased for the AgNPs-based nanocomposites. All these findings imply that the lateral charge transport in the nanocomposite structures is favored by the closely situated AgNPs because of the strong electrostatic coupling between them, additionally activated by the temperature increase.

Spatial segregation of mixed-sized counterions in dendritic polyelectrolytes

Langevin dynamics simulations are utilized to study the structure of a dendritic polyelectrolyte embedded in two component mixtures comprised of conventional (small) and bulky counterions. We vary two parameters that trigger conformational properties of the dendrimer: the reduced Bjerrum length, lambda _B^*, which controls the strength of electrostatic interactions and the number fraction of the bulky counterions, f_b, which impacts on their steric repulsion. We find that the interplay between the electrostatic and the counterion excluded volume interactions affects the swelling behavior of the molecule. As compared to its neutral counterpart, for weak electrostatic couplings the charged dendrimer exists in swollen conformations whose size remains unaffected by f_b. For intermediate couplings, the absorption of counterions into the pervaded volume of the dendrimer starts to influence its conformation. Here, the swelling factor exhibits a maximum which can be shifted by increasing f_b. For strong electrostatic couplings the dendrimer deswells correspondingly to f_b. In this regime a spatial separation of the counterions into core–shell microstructures is observed. The core of the dendrimer cage is preferentially occupied by the conventional ions, whereas its periphery contains the bulky counterions.

Visible-light driven photo-catalytic performance of novel composite of TiO2 and fluorinated hexagonal boron nitride nanosheets

This article presents a novel synthesis of fluorinated hexagonal boron nitride (F-BN)/Titanium di-oxide (TiO2) hybrid nano-composite by sol-gel method. The prepared nano-composite has shown remarkable photo-catalytic activity under visible light illumination. Our results revealed a strong electrostatic coupling between TiO2 nanoparticles, while the reduced band gap of F-BN makes F-BN/TiO2 highly responsive to visible light. It is also observed that the hybridization of F-BN (with TiO2) not only increases the surface absorption but also enhances the electron–hole separation efficiency. The reduced charge carriers’ recombination rate of TiO2 nanoparticles leads to visible light driven photo-catalytic activity. Furthermore, the proposed nanocomposite display an excellent cycling stability for up to 5 cycles. Our results would motivate the applications of F-BN/metal oxide nanostructures in multidisciplinary fields especially in water splitting and photo-catalysis.

Nanofluidic Charge Transport under Strong Electrostatic Coupling Conditions

The comprehensive depiction of the many-body effects governing nanoconfined electrolytes is an essential step for the conception of nanofluidic devices with optimized performance. By incorporating self-consistently multivalent charges into the Poisson-Boltzmann equation dressed by a background monovalent salt, we investigate the impact of strong-coupling electrostatics on the nanofluidic transport of electrolyte mixtures. We find that the experimentally observed negative streaming currents in anionic nanochannels originate from the collective effect of Cl- attraction by the interfacially adsorbed multivalent cations and the no-slip layer reducing the hydrodynamic contribution of these cations to the net current. The like-charge current condition emerging from this collective mechanism is shown to be the reversal of the average potential within the no-slip zone. Applying the formalism to surface-coated membrane nanoslits located in the giant dielectric permittivity regime, we reveal a new type of streaming current activated by attractive polarization forces. Under the effect of these forces, multivalent ions added to the KCl solution set a charge separation and generate a counterion current between the neutral slit walls where the pure KCl conductivity vanishes. The adjustability of the current characteristics solely via the valency and amount of the added multivalent ions identifies the underlying process as a promising mechanism for nanofluidic ion separation purposes.

Condensation of Rodlike Counterions on a Charged Cylinder

We study the condensations of dumbbell-like counterions onto an oppositely charged cylinder at weak and strong electrostatic coupling strengths. Performing extensive Monte Carlo simulations, we show that the condensation characteristics of the dumbbell ions can be understood by viewing dumbbell ions of length d as point ions with an effective valency depending on the radial distance r from the cylinder’s axis. In terms of the condensation behavior, dumbbell ions behave as two independent point ions if r ≪ d, but act as a single point ion with twofold valency when r ≫ d. Such a distance-dependent effective valency as a characteristic of ions of extended structures explains a unique feature in the condensed counterion fraction and heat capacity at both weak and strong coupling strengths.

Strong-coupling theory of counterions with hard cores between symmetrically charged walls.

By a combination of Monte Carlo simulations and analytical calculations, we investigate the effective interactions between highly charged planar interfaces, neutralized by mobile counterions (salt-free system). While most previous analysis have focused on pointlike counterions, we treat them as charged hard spheres. We thus work out the fate of like-charge attraction when steric effects are at work. The analytical approach partitions counterions in two subpopulations, one for each plate, and integrates out one subpopulation to derive an effective Hamiltonian for the remaining one. The effective Hamiltonian features plaquette four-particle interactions, and it is worked out by computing a Gibbs-Bogoliubov inequality for the free energy. At the root of the treatment is the fact that under strong electrostatic coupling, the system of charges forms an ordered arrangement, that can be affected by steric interactions. Fluctuations around the reference positions are accounted for. To dominant order at high coupling, it is found that steric effects do not significantly affect the interplate effective pressure, apart at small distances where hard-sphere overlap are unavoidable, and thus rule out configurations.

Charged Dendrimers with Finite-Size Counterions.

We report on the structure of dendritic polyelectrolytes accompanied by counterions in a good, salt-free, implicit solvent using Langevin dynamics simulations and a Flory-type approach. Our focus is on the modification of charged dendrimer conformations via the strength of electrostatic interactions and the counterion excluded volume. We study the effects caused by charges by varying the reduced Bjerrum length, λB*, between the extremes of weak and strong electrostatic interactions. The counterion excluded volume was controlled by the size of ions. We investigate counterions ranging from conventional ones, with the size comparable to the monomer size, to bulky ions. Our results indicate that, as compared to neutral dendrimers, dendritic polyelectrolytes exist in swollen conformations, and the degree of swelling changes non-monotonically with increasing λB*. For weak electrostatic couplings, counterion density within dendrimers is minor and their radius of gyration subtly exceeds the size of neutral dendrimers. For intermediate electrostatic couplings, Coulomb attraction between opposite charges promotes absorption of ions into dendrimers' pervaded volume and counterion condensation on charged monomers. As a result, counterion density inside dendrimers abruptly increases and the ionic size starts to play a crucial role. In this regime, we observe that swelling of dendrimers reaches its maximum and is more pronounced for bulky counterions. For strong electrostatic couplings, complete condensation of conventional counterions proceeds, whereas for bulky ions condensation remains partial. In this regime, dendrimers deswell. In particular, in the presence of conventional ions, dendrimers collapse into globules, while, for bulky counterions, deswelling is suppressed.

Beyond Nernst Sensitivity of Ion Sensitive Field Effect Transistor based on Ultra-Thin Body Box FDSOI

This paper reports an ultrahigh-sensitive ISFET sensor that is developed using TCAD model of the industrial 22-nm ultrathin body and buried oxide (UTBB) fully depleted silicon-on-insulator (FDSOI) transistors. The modeling method is exploited by changing the potential surface charge depending on the electrolyte pH change and investigating how will it cause the threshold voltage shift of ISFET device and other transfer characteristic parameters. The properties of a user-defined material offered by Silvaco are exploited to simulate the electrolyte behavior. The parameters of silicon semiconductor material (i.e., energy bandgap, permittivity, affinity, and density of states) are set to reconstruct an electrolyte solution. The electrostatic solution of the electrolyte area is investigated by giving a numerical solution for the semiconductor equation inside this area. On the other hand, the strong electrostatic coupling between the front gate and the back gate of FDSOI devices provide an intrinsic signal amplification feature for sensing applications. Utilizing a layer deposited Titanium dioxide (TiO2) as a pH sensing film, pH sensors having a sensitivity ∼1250 mV/pH is reported. The small sensing area and the FDSOI-based technology of the device make the sensors ideal for the IoT market.

Absence of Interlayer Tunnel Coupling of K-Valley Electrons in Bilayer MoS_{2}.

In Bernal stacked bilayer graphene interlayer coupling significantly affects the electronic band structure compared to monolayer graphene. Here we present magnetotransport experiments on high-quality n-doped bilayer MoS_{2}. By measuring the evolution of the Landau levels as a function of electron density and applied magnetic field we are able to investigate the occupation of conduction band states, the interlayer coupling in pristine bilayer MoS_{2}, and how these effects are governed by electron-electron interactions. We find that the two layers of the bilayer MoS_{2} behave as two independent electronic systems where a twofold Landau level's degeneracy is observed for each MoS_{2} layer. At the onset of the population of the bottom MoS_{2} layer we observe a large negative compressibility caused by the exchange interaction. These observations, enabled by the high electronic quality of our samples, demonstrate weak interlayer tunnel coupling but strong interlayer electrostatic coupling in pristine bilayer MoS_{2}. The conclusions from the experiments may be relevant also to other transition metal dichalcogenide materials.

Charged nanorods at heterogeneously charged surfaces.

We study the spatial and orientational distribution of charged nanorods (rodlike counterions) as well as the effective interaction mediated by them between two plane-parallel surfaces that carry fixed (quenched) heterogeneous charge distributions. The nanorods are assumed to have an internal charge distribution, specified by a multivalent monopolar moment and a finite quadrupolar moment, and the quenched surface charge is assumed to be randomly distributed with equal mean and variance on the two surfaces. While equally charged surfaces are known to repel within the traditional mean-field theories, the presence of multivalent counterions has been shown to cause attractive interactions between uniformly charged surfaces due to the prevalence of strong electrostatic couplings that grow rapidly with the counterion valency. We show that the combined effects due to electrostatic correlations (caused by the coupling between the mean surface field and the multivalent, monopolar, charge valency of counterions) as well as the disorder-induced interactions (caused by the coupling between the surface disorder field and the quadrupolar moment of counterions) lead to much stronger attractive interactions between two randomly charged surfaces. The interaction profile turns out to be a nonmonotonic function of the intersurface separation, displaying an attractive minimum at relatively small separations, where the ensuing attraction can exceed the maximum strong-coupling attraction (produced by multivalent monopolar counterions between uniformly charged surfaces) by more than an order of magnitude.

Piezo-Potential Generation in Capacitive Flexible Sensors Based on GaN Horizontal Wires.

We report an example of the realization of a flexible capacitive piezoelectric sensor based on the assembly of horizontal -polar long Gallium nitride (GaN) wires grown by metal organic vapour phase epitaxy (MOVPE) with the Boostream® technique spreading wires on a moving liquid before their transfer on large areas. The measured signal (<0.6 V) obtained by a punctual compression/release of the device shows a large variability attributed to the dimensions of the wires and their in-plane orientations. The cause of this variability and the general operating mechanisms of this flexible capacitive device are explained by finite element modelling simulations. This method allows considering the full device composed of a metal/dielectric/wires/dielectric/metal stacking. We first clarify the mechanisms involved in the piezo-potential generation by mapping the charge and piezo-potential in a single wire and studying the time-dependent evolution of this phenomenon. GaN wires have equivalent dipoles that generate a tension between metallic electrodes only when they have a non-zero in-plane projection. This is obtained in practice by the conical shape occurring spontaneously during the MOVPE growth. The optimal aspect ratio in terms of length and conicity (for the usual MOVPE wire diameter) is determined for a bending mechanical loading. It is suggested to use 60–120 µm long wires (i.e., growth time less than 1 h). To study further the role of these dipoles, we consider model systems with in-plane 1D and 2D regular arrays of horizontal wires. It is shown that a strong electrostatic coupling and screening occur between neighbouring horizontal wires depending on polarity and shape. This effect, highlighted here only from calculations, should be taken into account to improve device performance.

Ultrahigh-Sensitive CMOS pH Sensor Developed in the BEOL of Standard 28 nm UTBB FDSOI

This paper reports ultrahigh-sensitive and ultralow-power CMOS compatible pH sensors that are developed in the back-end-of-line (BEOL) of industrial 28-nm ultrathin body and buried oxide (UTBB) fully depleted silicon-on-insulator (FDSOI) transistors. Fabricating the sensing gate and the control gate of the sensors in a capacitive divider circuit, CMOS compatible pH sensors are demonstrated where the front gate bias is applied through a control gate rather than a bulky reference electrode. On the other hand, the strong electrostatic coupling between the front gate and the back gate of FDSOI devices provide an intrinsic signal amplification feature for sensing applications. Utilizing an atomic layer deposited aluminum oxide (Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) as a pH sensing film, pH sensors having a sensitivity of 475 mV/pH and 730 mV/pH in the extended gate and BEOL configuration, respectively, are reported. Sensitivities of both configurations are superior to state-of-the-art low power ion-sensitive field-effect transistors. The small sensing area and the FDSOI-based low power technology of the device make the sensors ideal for the IoT market. The proposed approach has been validated by TCAD simulation, and demonstrated through experimental measurements on proof-of-concept extended gate pH sensors and on sensors that are developed in the BEOL of industrial UTBB FDSOI devices.

Distinct Effects of Multivalent Macroion and Simple Ion on the Structure and Local Electric Environment of a Weak Polyelectrolyte in Aqueous Solution.

Adding ionic species can critically affect the structure of weak polyelectrolyte (PE) chains, whose charge density in aqueous solution can be greatly regulated by bathing solution conditions such as pH and added ions. Distinct from simple ions that can be treated as point charges, multivalent macroions of finite size, including many charged nanoparticles and biopolymers, could show strong electrostatic coupling with PEs and effectively modify the conformation and assembly of PEs in aqueous solution. In this work, we have compared the effects of hydrophilic multivalent macroion of finite size and simple divalent ion on the conformational transition of a model weak polybase, poly(2-vinylpyridine) (P2VP), in dilute aqueous solution. By using fluorescence correlation spectroscopy combined with photon counting histogram analysis, we have examined the swollen-to-collapsed conformational transition and local electric potential of a P2VP chain in ionic aqueous solution at a single-molecule level. Adding inorganic polytungstate ([W12]) macroion bearing eight negative charges per [W12] of ∼0.8 nm in diameter at increased concentration from 10-9 to 10-5 mM can lead to a shift of the critical conformational transition pH, pHcr, of P2VP to lower pH values, in an opposite trend to the previously reported effect of adding simple monovalent anion. Conversely, adding simple divalent sulfate anion can lead to a nonmonotonic change of pHcr when increasing its concentration from 0.03 to 15 mM. Additionally, at pH < pHcr where P2VP is highly protonated and adopts a swollen conformation, a monotonic decrease of P2VP size is observed with increased sulfate ionic concentration, exhibiting the typical ionic screening effect. In contrast, the size of the P2VP chain shows little change with increasing [W12] concentration before the precipitation of P2VP from water. To investigate the distinct effects of multivalent ion and macroion on the conformational transition of P2VP in aqueous solution, we have also measured the local proton concentration in the vicinity to a P2VP chain by an attached pH-sensitive fluorescence probe. In both cases, we have observed the monotonic reduction of the local electric potential of a swollen P2VP chain with increased ionic concentration, despite the increased protonation degree of P2VP. The results suggest that counterion condensation of multivalent ion and macroion can modify the effective net charge density of P2VP chains in dilute aqueous solution. However, possibly due to its high multivalency and finite size, multivalent [W12] macroion is much more effective in modifying the local electric environment and structure of P2VP chains at 3-7 orders of magnitude lower concentrations than simple sulfate counterion.