Browsing by Subject "Electrostatics"

Now showing 1 - 12 of 12

Open Access
Beyond Poisson-Boltzmann : fluctuations and fluid structure in a self-consistent theory
(Institute of Physics Publishing, 2016) Büyükdağlı, Şahin; Blossey, Ralf
Poisson-Boltzmann (PB) theory is the classic approach to soft matter electrostatics and has been applied to numerous physical chemistry and biophysics problems. Its essential limitations are in its neglect of correlation effects and fluid structure. Recently, several theoretical insights have allowed the formulation of approaches that go beyond PB theory in a systematic way. In this topical review, we provide an update on the developments achieved in the self-consistent formulations of correlation-corrected Poisson-Boltzmann theory. We introduce a corresponding system of coupled non-linear equations for both continuum electrostatics with a uniform dielectric constant, and a structured solvent - a dipolar Coulomb fluid - including non-local effects. While the approach is only approximate and also limited to corrections in the so-called weak fluctuation regime, it allows us to include physically relevant effects, as we show for a range of applications of these equations.
Open Access
Counterflow in Bose gas bilayers: collective modes and dissipationless drag
(American Institute of Physics, 2020) Abedinpour, S. H.; Tanatar, Bilal
We investigate the collective density oscillations and dissipationless drag effect in bilayer structures of ultra-cold bosons in the presence of counterflow. We consider different types of inter-particle interactions and obtain the drag coefficient and effect of counterflow on the sound velocity. We observe that counterflow enhances (suppresses) the energy of symmetric (asymmetric) density mode and drives the homogeneous system towards instability. The dependence of the drag coefficient on the spacing between two layers is determined by the form of particle-particle interaction.
Open Access
Electrostatic effects on nanofiber formation of self-assembling peptide amphiphiles
(Elsevier, 2011) Toksoz, S.; Mammadov R.; Tekinay, A. B.; Güler, Mustafa O.
Self-assembling peptide amphiphile molecules have been of interest to various tissue engineering studies. These molecules self-assemble into nanofibers which organize into three-dimensional networks to form hydrocolloid systems mimicking the extracellular matrix. The formation of nanofibers is affected by the electrostatic interactions among the peptides. In this work, we studied the effect of charged groups on the peptides on nanofiber formation. The self-assembly process was studied by pH and zeta potential measurements, FT-IR, circular dichroism, rheology, atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The aggregation of the peptides was triggered upon neutralization of the charged residues by pH change or addition of electrolyte or biomacromolecules. Understanding the controlled formation of the hydrocolloid gels composed of peptide amphiphile nanofibers can lead us to develop in situ gel forming bioactive collagen mimetic nanofibers for various tissue engineering studies including bioactive surface coatings. © 2010 Elsevier Inc.
Open Access
Electrostatic force spectroscopy of near surface localized states
(Institute of Physics Publishing Ltd., 2005) Dâna, A.; Yamamoto, Y.
Electrostatic force microscopy at cryogenic temperatures is used to probe the electrostatic interaction of a conductive atomic force microscopy tip and electronic charges trapped in localized states in an insulating layer on a semiconductor. Measurement of the frequency shift of the cantilever as a function of tip-sample bias voltage shows discrete peaks at certain voltages when the tip is located near trap centres. These discrete changes in frequency are attributed to one by one filling of individual electronic states when the quantized energies traverse the substrate conduction band Fermi energy as the tip-sample voltage is increased. Theoretical analysis of the experiment suggests that such a measurement of the cantilever frequency shift as a function of bias voltage can be interpreted as an AC force measurement, from which spectroscopic information about the location and energy of localized states can be deduced. Experimental results from the study of a sample with InAs quantum dots as trap centres are presented.
Open Access
Electrostatic interactions in charged nanoslits within an explicit solvent theory
(Institute of Physics Publishing, 2015) Buyukdagli, S.
Within a dipolar Poisson-Boltzmann theory including electrostatic correlations, we consider the effect of explicit solvent structure on solvent and ion partition confined to charged nanopores. We develop a relaxation scheme for the solution of this highly non-linear integro-differential equation for the electrostatic potential. The scheme is an extension of the approach previously introduced for simple planes (Buyukdagli and Blossey 2014 J. Chem. Phys. 140 234903) to nanoslit geometry. We show that the reduced dielectric response of solvent molecules at the membrane walls gives rise to an electric field significantly stronger than the field of the classical Poisson-Boltzmann equation. This peculiarity associated with non-local electrostatic interactions results in turn in an interfacial counterion adsorption layer absent in continuum theories. The observation of this enhanced counterion affinity in the very close vicinity of the interface may have important impacts on nanofluidic transport through charged nanopores. Our results indicate the quantitative inaccuracy of solvent implicit nanofiltration theories in predicting the ionic selectivity of membrane nanopores.
Open Access
Experimental and computational analyses of electroabsorption in polar InGaN/GaN quantum zigzag heterostructures
(IEEE, 2008-11) Sarı, Emre; Özel, Tuncay; Koç, Aslı; Ju, J.-W.; Ahn, H.-K.; Lee, I.-H.; Baek, J. H.; Demir, Hilmi Volkan
Traditional quantum confined Stark effect is well known to lead to strong electroabsorption in multiple quantum well (MQW) structures, yielding only red-shift of the absorption edge with the externally applied electric field, independent of the direction of the applied field. However, a little is known the electroabsorption behavior in III nitride quantum structures grown on c-plane of their wurtzite crystal structure, which is substantially different than the electroabsorption of conventional quantum structures. Such III-N heterostructures exhibit strong polarization fields and discontinuity of such polarization fields at their heterointerfaces causes stimulation of large electrostatic fields in alternating directions for their wells and barriers. Consequently, their energy band diagrams form a zigzag potential profile in conduction and valence bands, instead of those with square profiles. A natural and suitable approach for understanding these polarization fields and also developing insight to design related devices (e.g., electroabsorption modulators) is to study electroabsorption behavior as a function of the polarization field in such polar structures. To this end, we present a comparative, computational and experimental study of electroabsorption in our different designs of c-plane grown polar InGaN/GaN quantum structures with varying levels of polarization.
Open Access
Independent parallel lithography using the atomic force microscope
(A I P Publishing LLC, 1996-05) Minne, S. C.; Manalis, S. R.; Atalar, Abdullah; Quate, C. F.
Independent parallel features have been lithographically patterned with a 2×1 array of individually controlled cantilevers using an atomic force microscope. Control of the individual cantilevers was achieved with an integrated piezoelectric actuator in feedback with a piezoresistive sensor. Patterns were formed on 〈100〉 single crystal silicon by using a computer controlled tip voltage to locally enhance the oxidation of the silicon. Using the piezoresistor directly as a force sensor, parallel images can be simultaneously acquired in the constant force mode. A discussion of electrostatic forces due to applied tip voltages, hysteresis characteristics of the actuator, and the cantilever system is also presented.
Open Access
Ionic current inversion in pressure-driven polymer translocation through nanopores
(American Physical Society, 2015) Buyukdagli, S.; Blossey, R.; Ala-Nissila, T.
We predict streaming current inversion with multivalent counterions in hydrodynamically driven polymer translocation events from a correlation-corrected charge transport theory including charge fluctuations around mean-field electrostatics. In the presence of multivalent counterions, electrostatic many-body effects result in the reversal of the DNA charge. The attraction of anions to the charge-inverted DNA molecule reverses the sign of the ionic current through the pore. Our theory allows for a comprehensive understanding of the complex features of the resulting streaming currents. The underlying mechanism is an efficient way to detect DNA charge reversal in pressure-driven translocation experiments with multivalent cations. © 2015 American Physical Society.
Unknown
Like-Charge Attraction And Opposite-Charge Decomplexation Between Polymers and DNA Molecules
(American Physical Society, 2017) Buyukdagli, S.
We scrutinize the effect of polyvalent ions on polymer-DNA interactions. We extend a recently developed test-charge theory [S. Buyukdagli, Phys. Rev. E 94, 042502 (2016)1539-375510.1103/PhysRevE.94.042502] to the case of a stiff polymer interacting with a DNA molecule in an electrolyte mixture. The theory accounts for one-loop level electrostatic correlation effects such as the ionic cloud deformation around the strongly charged DNA molecule as well as image-charge forces induced by the low DNA permittivity. Our model can reproduce and explain various characteristics of the experimental phase diagrams for polymer solutions. First, the addition of polyvalent cations to the electrolyte solution results in the attraction of the negatively charged polymer by the DNA molecule. The glue of the like-charge attraction is the enhanced shielding of the polymer charges by the dense counterion layer at the DNA surface. Second, through the shielding of the DNA-induced electrostatic potential, mono- and polyvalent cations of large concentration both suppress the like-charge attraction. Within the same formalism, we also predict a new opposite-charge repulsion effect between the DNA molecule and a positively charged polymer. In the presence of polyvalent anions such as sulfate or phosphate, their repulsion by the DNA charges leads to the charge screening deficiency of the region around the DNA molecule. This translates into a repulsive force that results in the decomplexation of the polymer from DNA. This opposite-charge repulsion phenomenon can be verified by current experiments and the underlying mechanism can be beneficial to gene therapeutic applications where the control over polymer-DNA interactions is the key factor.
Open Access
Pulling a DNA molecule through a nanopore embedded in an anionic membrane: tension propagation coupled to electrostatics
(Institute of Physics Publishing, 2020) Sarabadani, J.; Büyükdağlı, Şahin; Ala-Nissila, T.
We consider the influence of electrostatic forces on driven translocation dynamics of a flexible polyelectrolyte being pulled through a nanopore by an external force on the head monomer. To this end, we augment the iso-flux tension propagation theory with electrostatics for a negatively charged biopolymer pulled through a nanopore embedded in a similarly charged anionic membrane. We show that in the realistic case of a single-stranded DNA molecule, dilute salt conditions characterized by weak charge screening, and a negatively charged membrane, the translocation dynamics is unexpectedly accelerated despite the presence of large repulsive electrostatic interactions between the polymer coil on the cis side and the charged membrane. This is due to the rapid release of the electrostatic potential energy of the coil during translocation, leading to an effectively attractive force that assists end-driven translocation. The speedup results in non-monotonic polymer length and membrane charge dependence of the exponent α characterizing the translocation time τ ∝ Nα 0 of the polymer with length N0. In the regime of long polymers N0 500, the translocation exponent exceeds its upper limit α = 2 previously observed for the same system without electrostatic interactions.
Open Access
Reducing anchor loss in micromechanical extensional Mode resonators
(IEEE, 2010-02) Tas, V.; Olcum, S.; Aksoy, M. D.; Atalar, Abdullah
In this work, we propose a novel method to increase the quality factor of extensional mode micromechanical resonators. The proposed resonator topology is suitable for integration in a silicon-based process to fabricate micromechanical filters and oscillators. It is a half-wavelength-long strip excited longitudinally by electrostatic forces, and it is isolated from the substrate by alternating with bars of a quarter wavelength long. This structure causes a large impedance mismatch between the resonator and the substrate and hence reduces the anchor loss considerably. The performance of the resonator is determined by finite element simulations. We introduce an equivalent electrical circuit to predict the performance of the resonator. The electrical model gives results consistent with the finite element simulations. The proposed resonator is expected to have a very small anchor loss resulting in a very high Q.
Open Access
Sensing translocating polymers via induced magnetic fields
(TÜBİTAK, 2023) Büyükdağlı, Şahin
The requirement to boost the resolution of nanopore-based biosequencing devices necessitates the integration of novel biosensing techniques with reduced sensitivity to background noise. In this article, we probe the signatures of translocating polymers in magnetic fields induced by ionic currents through membrane nanopores. Within the framework of a previously introduced charge transport theory, we evaluate the magnetic field signals generated by voltage- and pressure-driven DNA translocation events in monovalent salt solutions. Our formalism reveals that in voltage-driven transport, the translocating polymer suppresses the induced magnetic field via the steric blockage of the ion current through the midpore. In the case of pressure-driven transport, the magnetic field reduction by translocation originates from the negative electrokinetic contribution of the anionic DNA surface charges to the streaming current predominantly composed of salt cations. The magnitude of the corresponding field signals is located in the nano-Tesla range covered by the resolution of the magnetoelectric sensors able to detect magnetic fields down to the pico-Tesla range. This suggests that the integration of magnetic field detection techniques into the current biosequencing approaches can complement efficiently the conventional biosensing strategies employing ionic current readouts with high susceptibility to background noise.