Sample-to-sample fluctuations of electrostatic forces generated by quenched charge disorder (original) (raw)
Related papers
Electromagnetic fluctuation-induced interactions in randomly charged slabs
The Journal of Chemical Physics, 2012
Randomly charged net-neutral dielectric slabs are shown to interact across a featureless dielectric continuum with long-range electrostatic interaction forces that scale with the statistical variance of their quenched random charge distribution and inversely with the distance between the bounding surfaces of the slabs. By accounting for the whole spectrum of electromagnetic field fluctuations, we show that this disorder-generated long-range interaction extends well into the retarded regime where higher-order Matsubara frequencies contribute significantly. This occurs even for highly clean samples with only a trace amount of charge disorder and shows that disorder effects can be important down to the nano scale. As a result, the previously predicted non-monotonic behavior for the total force between two dissimilar (plane-parallel) slabs as a function of their separation distance is substantially modified by higher-order contributions, and in almost all cases of interest, we find that the equilibrium inter-surface separation is shifted to substantially larger values compared to predictions based solely on the zero-frequency component. This suggests that the ensuing non-monotonic interaction is more easily amenable to experimental detection. The presence of charge disorder in the intervening dielectric medium between the two slabs is shown to lead to an additional force that can be repulsive or attractive depending on the system parameters and can, for instance, wash out the non-monotonic behavior of the total force when the intervening slab contains a sufficiently large amount of disordered charges.
Sample-to-sample torque fluctuations in a system of coaxial randomly charged surfaces
The European Physical Journal E, 2012
Polarizable randomly charged dielectric objects have been recently shown to exhibit long-range lateral and normal interaction forces even when they are effectively net neutral. These forces stem from an interplay between the quenched statistics of random charges and the induced dielectric image charges. This type of interaction has recently been evoked to interpret measurements of Casimir forces in vacuo, where a precise analysis of such disorder-induced effects appears to be necessary. Here we consider the torque acting on a randomly charged dielectric surface (or a sphere) mounted on a central axle next to another randomly charged surface and show that although the resultant mean torque is zero, its sample-to-sample fluctuation exhibits a long-range behavior with the separation distance between the juxtaposed surfaces and that, in particular, its root-mean-square value scales with the total area of the surfaces. Therefore, the disorder-induced torque between two randomly charged surfaces is expected to be much more pronounced than the disorder-induced lateral force and may provide an effective way to determine possible disorder effects in experiments, in a manner that is independent of the usual normal force measurement. (a) Corresponding author -Email: a.naji@damtp.cam.ac.uk Randomly charged surfaces are equally abundant in colloidal and soft matter systems [5-7], examples arise in surfactant coated surfaces [8], unstructured proteins and random polyelectrolytes and polyampholytes [9].
Nonmonotoic fluctuation-induced interactions between dielectric slabs carrying charge disorder
The Journal of Chemical Physics, 2010
We investigate the effect of monopolar charge disorder on the classical fluctuation-induced interactions between randomly charged net-neutral dielectric slabs and discuss various generalizations of recent results (A. Naji et al., Phys. Rev. Lett. 104, 060601 (2010)) to highly inhomogeneous dielectric systems with and without statistical disorder correlations. We shall focus on the specific case of two generally dissimilar plane-parallel slabs, which interact across vacuum or an arbitrary intervening dielectric medium. Monopolar charge disorder is considered to be present on the bounding surfaces and/or in the bulk of the slabs, may be in general quenched or annealed and may possess a finite lateral correlation length reflecting possible 'patchiness' of the random charge distribution. In the case of quenched disorder, the bulk disorder is shown to give rise to an additive long-range contribution to the total force, which decays as the inverse distance between the slabs and may be attractive or repulsive depending on the dielectric constants of the slabs. By contrast, the force induced by annealed disorder in general combines with the underlying van der Waals forces in a non-additive fashion and the net force decays as an inverse cube law at large separations. We show however that in the case of two dissimilar slabs the net effect due to the interplay between the disorder-induced and the pure van der Waals interactions can lead to a variety of unusual non-monotonic interaction profiles between the dielectric slabs. In particular, when the intervening medium has a larger dielectric constant than the two slabs, we find that the net interaction can become repulsive and exhibit a potential barrier, while the underlying van der Waals force is attractive. On the contrary, when the intervening medium has a dielectric constant in between that of the two slabs, the net interaction can become attractive and exhibit a free energy minimum, while the pure van der Waals force is repulsive. Therefore, the charge disorder, if present, can drastically alter the effective interaction between net-neutral objects.
We study the effective interaction mediated by strongly coupled Coulomb fluids between dielectric surfaces carrying quenched, random monopolar charges with equal mean and variance, both when the Coulomb fluid consists only of mobile multivalent counterions and when it consists of an asymmetric ionic mixture containing multivalent and monovalent (salt) ions in equilibrium with an aqueous bulk reservoir. We analyze the consequences that follow from the interplay between surface charge disorder, dielectric and salt image effects, and the strong electrostatic coupling that results from multivalent counterions on the distribution of these ions and the effective interaction pressure they mediate between the surfaces. In a dielectrically homogeneous system, we show that the multivalent counterions are attracted towards the surfaces with a singular, disorder-induced potential that diverges logarithmically on approach to the surfaces, creating a singular but integrable counterion density profile that exhibits an algebraic divergence at the surfaces with an exponent that depends on the surface charge (disorder) variance. This effect drives the system towards a state of lower thermal `disorder', one that can be described by a renormalized temperature, exhibiting thus a remarkable antifragility. In the presence of an interfacial dielectric discontinuity, the singular behavior of counterion density at the surfaces is removed but multivalent counterions are still accumulated much more strongly close to randomly charged surfaces as compared with uniformly charged ones. The interaction pressure acting on the surfaces displays in general a highly non-monotonic behavior as a function of the inter-surface separation with a prominent regime of attraction at small to intermediate separations. This attraction is caused directly by the combined effects from charge disorder and strong coupling electrostatics of multivalent counterions, which dominate the surface-surface repulsion due to the (equal) mean charges on the two surfaces and the osmotic pressure of monovalent ions residing between them. These effects can be quite significant even with a small degree of surface charge disorder relative to the mean surface charge. The strong coupling, disorder-induced attraction is typically much stronger than the van der Waals interaction between the surfaces, especially within a range of several nanometers for the inter-surface separation, where such effects are predicted to be most pronounced.
Quenched charge disorder and Coulomb interactions
Physical Review E, 2005
We develop a general formalism to investigate the effect of quenched fixed charge disorder on effective electrostatic interactions between charged surfaces in a one-component ͑counterion-only͒ Coulomb fluid. Analytical results are explicitly derived for two asymptotic and complementary cases: ͑i͒ mean-field or Poisson-Boltzmann limit ͑including Gaussian-fluctuations correction͒, which is valid for small electrostatic coupling, and ͑ii͒ strong-coupling limit, where electrostatic correlations mediated by counterions become significantly large as, for instance, realized in systems with high-valency counterions. In the particular case of two apposed and ideally polarizable planar surfaces with equal mean surface charge, we find that the effect of the disorder is nil on the mean-field level and thus the plates repel. In the strong-coupling limit, however, the effect of charge disorder turns out to be additive in the free energy and leads to an enhanced long-range attraction between the two surfaces. We show that the equilibrium interplate distance between the surfaces decreases for elevated disorder strength ͑i.e., for increasing mean-square deviation around the mean surface charge͒, and eventually tends to zero, suggesting a disorder-driven collapse transition.
Fluctuation-Induced Interaction between Randomly Charged Dielectrics
Physical Review Letters, 2010
Monopolar charge disorder effects are studied in the context of fluctuation-induced interactions between neutral dielectric slabs. It is shown that quenched bulk charge disorder gives rise to an additive contribution to the net interaction force which decays as the inverse distance between the slabs and may thus completely mask the standard Casimir-van der Waals force at large separations. By contrast, annealed (bulk or surface) charge disorder leads to a net interaction force whose largedistance behavior coincides with the universal Casimir force between perfect conductors, which scales as inverse cubic distance, and the dielectric properties enter only in subleading corrections.
Interaction between random heterogeneously charged surfaces in an electrolyte solution
The Journal of Chemical Physics, 2015
We study, using Monte Carlo simulations, the interaction between infinite heterogeneously charged surfaces inside an electrolyte solution. The surfaces are overall neutral with quenched charged domains. An average over the quenched disorder is performed to obtain the net force. We find that the interaction between the surfaces is repulsive at short distances and is attractive for larger separations.
Long-ranged attraction between disordered heterogeneous surfaces
2011
Graham some 150 years ago, hinges on the balance between attractive and repulsive surface forces(1). In aqueous media the electrostatic double-layer repulsion between likecharged surfaces plays the dominant role in the stabilization, keeping particles from aggregating under van der Waals attraction(1-3). Such forces have been studied for decades(3-6): but while nearly all understanding of the interactions relate to uniformlycharged surfaces, most real surfaces are in fact heterogeneous and disordered. Here we demonstrate that two surfaces covered with random charge patches experience a longranged attraction across water that is orders of magnitude stronger than van der Waals forces, and which persists, remarkably, even in the complete absence of any correlations between opposing positive and negative domains (so-called 'quenched disorder'). The origin of this attraction is, as we show, in the counter-intuitive observation that two oppositely-charged surfaces attract each other across water (or other ion-containing liquids) much more strongly than equally-charged surfaces repel, for identical surface separations and charge densities. This striking asymmetry may result in strong, longranged attraction between randomly charged surfaces even when they are overall-
Novel Electrostatic Attraction from Plasmon Fluctuations
Physical Review Letters, 2000
In this Letter, we show that at low temperatures, zero-point fluctuations of the plasmon modes of two mutually coupled 2-D planar Wigner crystals give rise to a novel long-range attractive force. For the case where the distance d between two planar surfaces is large, this attractive force has an unusual power-law decay, which scales as d −7/2 , unlike other fluctuation-induced forces. Specifically, we note that its range is longer than the "standard" zero-temperature van der Waals interaction. This result may in principle be observed in bilayer electronic systems and provides insight into the nature of correlation effects for highly charged surfaces. 61.20.Qg, 63.22.+m Fluctuation-induced forces are ubiquitous in nature (for a recent review, see ) and constitute an important contribution to the interactions of many condensed matter systems . The classic example is the Casimir effect in which quantum fluctuations of the electromagnetic field between two parallel conducting plates lead to an attractive force between them. In the context of statistical physics, Fisher and de Gennes [4] have suggested that a similar effect also exists at or near the critical point of a system which is confined between two planes. Other examples include colloid particles immersed in a critical fluid [5], superfluid films [6], liquid crystals [7], and protein inclusions in fluctuating membranes . In general, fluctuation-induced forces arise because external constraints modify the fluctuations of a correlated medium. These interactions, which are usually longranged, are controlled by thermal fluctuations at finite temperature or quantum fluctuations at low temperature. In this Letter, we present arguments for a longrange attraction, derived from the zero-point fluctuations of the plasmon modes associated with two 2-D Wigner crystals .