Scaling Theory of Polyelectrolyte Adsorption on Repulsive Charged Surface

We studied polyelectrolyte adsorption on a repulsive charged surface by scaling analysis. At low ionic strength and low surface charge density in which a single polyelectrolyte is able to be adsorbed onto the surface, different regimes in the phase diagram are identified. The possibility of multi-layer structure formed by polyelectrolytes of like charge is also investigated.Comment: 4 pages, 2 figure

Development of Polymer-Based In-Plane Nanopore for DNA Sequencing

Mechanically robust solid-state nanopores have the potential to be the next generation DNA sensing platforms. However, mass production and limited base-calling accuracy are the hurdles for solid-state nanopore based DNA sensing. In order to solve these problems, a polymer dual-nanopore device fabricated via high throughput nanoimprint lithography (NIL) was proposed to sequence DNA by time-of-flight (ToF) measurement. As a proof of concept, this study presents mononucleotides discrimination via ToF measurement using polymer in-plane dual-nanopore device. First, fabrication of polymer in-plane nanopore with controllable dimensions was studied in consideration of experimental conditions and materials selection. Then, surface charge density effect on DNA translocation through in-plane nanopore was studied numerically and experimentally using fabricated nanopore devices on PEGDA, PMMA and COC. λ-DNA sensing was only observed in PEGDA device with a surface charge density lower than the threshold surface charge density predicted by COMSOL simulation. With demonstrated single molecule sensing ability, mononucleotides were introduced to PEGDA dual-nanopore with 500 nm flight tube and discriminated under various conditions. At pH 8.0, mononucleotides were driven by eletrophoretic motion and their ToF was in a decreasing order of dGMP \u3e dAMP \u3e dCMP \u3e dTMP. At pH 10.0, mononucleotides were driven by electroosmotic flow (EOF) due to a higher surface charge density on nanochannel walls and ToF was in the same order as pH 8.0 with an average identification accuracy of 55%. Dual-nanopore device with 1 μm flight tube was then used to improve the average identification accuracy to 75%. Finally, dGMP and dTMP in a mix solution were dicriminated by their ToF difference

Poisson-Boltzmann Theory of Charged Colloids: Limits of the Cell Model for Salty Suspensions

Thermodynamic properties of charge-stabilised colloidal suspensions are commonly modeled by implementing the mean-field Poisson-Boltzmann (PB) theory within a cell model. This approach models a bulk system by a single macroion, together with counterions and salt ions, confined to a symmetrically shaped, electroneutral cell. While easing solution of the nonlinear PB equation, the cell model neglects microion-induced correlations between macroions, precluding modeling of macroion ordering phenomena. An alternative approach, avoiding artificial constraints of cell geometry, maps a macroion-microion mixture onto a one-component model of pseudo-macroions governed by effective interactions. In practice, effective-interaction models are usually based on linear screening approximations, which can accurately describe nonlinear screening only by incorporating an effective (renormalized) macroion charge. Combining charge renormalization and linearized PB theories, in both the cell model and an effective-interaction (cell-free) model, we compute osmotic pressures of highly charged colloids and monovalent microions over a range of concentrations. By comparing predictions with primitive model simulation data for salt-free suspensions, and with predictions of nonlinear PB theory for salty suspensions, we chart the limits of both the cell model and linear-screening approximations in modeling bulk thermodynamic properties. Up to moderately strong electrostatic couplings, the cell model proves accurate in predicting osmotic pressures of deionized suspensions. With increasing salt concentration, however, the relative contribution of macroion interactions grows, leading predictions of the cell and effective-interaction models to deviate. No evidence is found for a liquid-vapour phase instability driven by monovalent microions. These results may guide applications of PB theory to soft materials.Comment: 27 pages, 5 figures, special issue of Journal of Physics: Condensed Matter on "Classical density functional theory methods in soft and hard matter

Nanogenerators from Electrical Discharge

Electrical discharge is generally considered as a negative effect in the electronic industry and often causes electrostatic discharge (ESD) and thus failure of electronic components and integrated circuits (IC). However, this effect was recently used to develop a new energy-harvesting technology, direct-current triboelectric nanogenerator (DC-TENG). In this chapter, its fundamental mechanism and the working modes of the nanogenerator will be presented. They are different from the general alternating current TENG (AC-TENG) invented in 2012, which is based on triboelectrification and electrostatic induction. Taking advantage of the electrostatic discharge, it can not only promote the miniaturization trend of TENG and self-powered systems, but also provide a paradigm shifting technique to in situ gain electrical energy

Statics and Dynamics of Strongly Charged Soft Matter

Soft matter materials, such as polymers, membranes, proteins, are often electrically charged. This makes them water soluble, which is of great importance in technological application and a prerequisite for biological function. We discuss a few static and dynamic systems that are dominated by charge effects. One class comprises complexation between oppositely charged objects, for example the adsorption of charged ions or charged polymers (such as DNA) on oppositely charged substrates of different geometry. The second class comprises effective interactions between similarly charged objects. Here the main theme is to understand the experimental finding that similarly and highly charged bodies attract each other in the presence of multi-valent counterions. This is demonstrated using field-theoretic arguments as well as Monte-Carlo simulations for the case of two homogeneously charged bodies. Realistic surfaces, on the other hand, are corrugated and also exhibit modulated charge distributions, which is important for static properties such as the counterion-density distribution, but has even more pronounced consequences for dynamic properties such as the counterion mobility. More pronounced dynamic effects are obtained with highly condensed charged systems in strong electric fields. Likewise, an electrostatically collapsed highly charged polymer is unfolded and oriented in strong electric fields. At the end of this review, we give a very brief account of the behavior of water at planar surfaces and demonstrate using ab-initio methods that specific interactions between oppositely charged groups cause ion-specific effects that have recently moved into the focus of interest.Comment: 61 pages, 31 figures, Physics Reports (2005)-in press (high quality figures available from authors

Neutral and Charged Polymers at Interfaces

Chain-like macromolecules (polymers) show characteristic adsorption properties due to their flexibility and internal degrees of freedom, when attracted to surfaces and interfaces. In this review we discuss concepts and features that are relevant to the adsorption of neutral and charged polymers at equilibrium, including the type of polymer/surface interaction, the solvent quality, the characteristics of the surface, and the polymer structure. We pay special attention to the case of charged polymers (polyelectrolytes) that have a special importance due to their water solubility. We present a summary of recent progress in this rapidly evolving field. Because many experimental studies are performed with rather stiff biopolymers, we discuss in detail the case of semi-flexible polymers in addition to flexible ones. We first review the behavior of neutral and charged chains in solution. Then, the adsorption of a single polymer chain is considered. Next, the adsorption and depletion processes in the many-chain case are reviewed. Profiles, changes in the surface tension and polymer surface excess are presented. Mean-field and corrections due to fluctuations and lateral correlations are discussed. The force of interaction between two adsorbed layers, which is important in understanding colloidal stability, is characterized. The behavior of grafted polymers is also reviewed, both for neutral and charged polymer brushes.Comment: a review: 130 pages, 30 ps figures; final form, added reference

A theory for viral capsid assembly around electrostatic cores

We develop equilibrium and kinetic theories that describe the assembly of viral capsid proteins on a charged central core, as seen in recent experiments in which brome mosaic virus (BMV) capsids assemble around nanoparticles functionalized with polyelectrolyte. We model interactions between capsid proteins and nanoparticle surfaces as the interaction of polyelectrolyte brushes with opposite charge, using the nonlinear Poisson Boltzmann equation. The models predict that there is a threshold density of functionalized charge, above which capsids efficiently assemble around nanoparticles, and that light scatter intensity increases rapidly at early times, without the lag phase characteristic of empty capsid assembly. These predictions are consistent with, and enable interpretation of, preliminary experimental data. However, the models predict a stronger dependence of nanoparticle incorporation efficiency on functionalized charge density than measured in experiments, and do not completely capture a logarithmic growth phase seen in experimental light scatter. These discrepancies may suggest the presence of metastable disordered states in the experimental system. In addition to discussing future experiments for nanoparticle-capsid systems, we discuss broader implications for understanding assembly around charged cores such as nucleic acids.Comment: This version has been updated from v1 as follows. The calculation accounts for curvature, explicitly represents the polymeric nature of surface functionalization molecules, and determines the dissociation equilibrium of the functionalized carboxylate groups. 13 pages main text, 4 pages appendix, 14 figure

Controlling static on an unwinding roll

Excessive static charges on insulating webs are the root cause for a number of problems in roll-to-roll manufacturing operations. Static charges attract contaminants and cause discharges that can ignite flammable vapors, shock operators, damage machine control systems, and change the surface chemistry of carefully formulated products. Webs are commonly unwound and wound several times in a manufacturing operation. For example, webs formed by an extrusion process are wound. The roll may be unwound in a coating, slitting, or converting process and wound a second time in a customer roll. Finally, the roll may be unwound a third time in a customer application such as printing or in a label application process.Static charges on the web are stored in each wound roll. Each time a roll is unwound is a unique opportunity to neutralize static. Proposed here is a new method for neutralizing static on unwinding rolls. The static control method has three key elements. First, a high performance static bar must be located to neutralize the outside surface of the unwinding roll. Second, a static bar must be located downstream of the first conveyance roller to neutralize the inside surface of the web. Third, the first conveyance roller after the unwinding roll must contact the inside surface of the web.The method to neutralize static on an unwinding roll is analyzed to show that static charge separated at the unwinding nip by tribocharging may be substantially reduced. The same method also reduces static charges wound into the roll from previous operations.Finally, the effect of the first conveyance roller on static control is discussed. The web exiting the unwinding roll is likely to have a high level of static that will cause a static discharge known as pre-nip ionization that occurs in the gap between the charged web and the surface of the first roller prior to contact. Pre-nip ionization requires that the first conveyance roller contact the inside surface of the web. Otherwise, the charge neutralization performance of this method is compromised and the web will remain highly charged through the production operation resulting in high static in the winding roll

Electrostatic Discharge

As we enter the nanoelectronics era, electrostatic discharge (ESD) phenomena is an important issue for everything from micro-electronics to nanostructures. This book provides insight into the operation and design of micro-gaps and nanogenerators with chapters on low capacitance ESD design in advanced technologies, electrical breakdown in micro-gaps, nanogenerators from ESD, and theoretical prediction and optimization of triboelectric nanogenerators. The information contained herein will prove useful for for engineers and scientists that have an interest in ESD physics and design