Pseudo-Casimir interactions across nematic films with disordered anchoring axis

Haddadan, Fahimeh Karimi Pour; Naji, Ali; Seifi, A Khame; Podgornik, Rudolf

doi:10.1088/0953-8984/26/7/075103

Cited by 13 publications

(21 citation statements)

References 40 publications

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“…[37]). In contrast to the case of simple fluids or binary liquid mixtures, for complex fluids surface disorder effects on Casimir-like interactions can be dominant as shown recently for nematic liquid-crystalline films [38].…”

Section: Introductionmentioning

confidence: 86%

Fluctuation induced forces in critical films with disorder at their surfaces

et al. 2017

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We investigate the effect of quenched surface disorder on effective interactions between two planar surfaces immersed in fluids which are near criticality and belong to the Ising bulk universality class.We consider the case that, in the absence of random surface fields, the surfaces of the film belong to the surface universality class of the so-called ordinary transition. We find analytically that in the linear weak-coupling regime, i.e., upon including the mean-field contribution and Gaussian fluctuations, the presence of random surface fields with zero mean leads to an attractive, disorderinduced contribution to the critical Casimir interactions between the two confining surfaces. Our analytical, field-theoretic results are compared with corresponding Monte Carlo simulation data.

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Section: Introductionmentioning

confidence: 86%

Fluctuation induced forces in critical films with disorder at their surfaces

et al. 2017

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“…We have also taken e = z on both surfaces including the disordered one (see Eq. (2)); assuming other components for e makes the analysis of the fluctuation-induced force more complicated in this context as we have discussed elsewhere [34].…”

Section: The Modelmentioning

confidence: 99%

“…Structural inhomogeneities may modify locally all the parameters entering this anchoring energy: the strength of the surface anchoring energy W (x), the preferred anchoring axis (easy direction) e(x) [34], and/or the (rough) geometry of the surface S in contact with the LC film [31]. These inhomogeneities may be annealed, partially annealed or quenched, depending on whether the degrees of freedom associated with them are fully thermalized with the medium (director field) or not.…”

Section: Introductionmentioning

confidence: 99%

“…In a previous publication [34], we analyzed the effects of both quenched and annealed disorder in the distribution of the easy direction on the fluctuation-induced interaction mediated by a nematic film between two plane-parallel surfaces, one of which imposes a strong homeotropic anchoring (in order to ensure a uniform mean director field across the LC film), whereas the other surface imposes a random distribution of the easy direction. It was shown that in the quenched case, the disorder effects appear additively in the total interaction, while in the annealed case, the disorder effects turn out to be nonadditive in the total inter-surface interaction.…”

Section: Introductionmentioning

confidence: 99%

“…1). Furthermore, the disorder in W (x) is considered to be annealed (the case of quenched anchoring will be studied elsewhere [35]). While we assume a specific type of surface disorder we nevertheless confine ourselves to the case where the easy direction remains on average homeotropic even on the "disordered" surface at all separations between the two bounding surfaces of the cell.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Fluctuation-induced interactions in nematics with disordered anchoring energy

Haddadan¹,

Naji²,

Shirzadiani³

et al. 2014

J. Phys.: Condens. Matter

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We examine fluctuation-induced (pseudo-Casimir) interactions in nematic liquid-crystalline films confined between two surfaces, where one of the surfaces imposes a strong homeotropic anchoring (ensuring a uniform mean director profile), while the other one is assumed to be a chemically disordered substrate exhibiting an annealed, random distribution of anchoring energies. We employ a saddle-point approximation to evaluate the free energy of interaction mediated between the two surfaces and investigate how the interaction force is influenced by the presence of disordered surface anchoring energy. It is shown that the disorder results in a renormalization of the effective surface anchoring parameter in a way that it leads to quantitative and qualitative changes (including a change of sign at intermediate inter-surface separations) in the pseudo-Casimir interaction force when compared with the interaction force in the absence of disorder.

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Pseudo-Casimir stresses and elasticity of a confined elastomer film

Naji

Podgornik

2016

Soft Matter

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Investigations of the elastic behavior of bulk elastomers have traditionally proceeded on the basis of classical rubber elasticity, which regards chains as thermally fluctuating but disregards the thermal fluctuations of the cross-links. Herein, we consider an incompressible and flat elastomer film of an axisymmetric shape confined between two large hard co-planar substrates, with the axis of the film perpendicular to the substrates. We address the impact that thermal fluctuations of the cross-links have on the free energy of elastic deformation of the system, subject to the requirement that the fluctuating elastomer cannot detach from the substrates. We examine the behavior of the deformation free energy for one case where a rigid pinning boundary condition is applied to a class of elastic fluctuations at the confining surfaces, and another case where the same elastic fluctuations are subjected to soft "gluing" potentials. We find that there can be significant departures (both quantitative and qualitative) from the prediction of classical rubber elasticity theory when elastic fluctuations are included. Finally, we compare the character of the attractive part of the elastic fluctuation-induced, or pseudo-Casimir, stress with the standard thermal Casimir stress in confined but non-elastomeric systems, finding the same power law decay behavior when a rigid pinning boundary condition is applied; for the case of the gluing potential, we find that the leading order correction to the attractive part of the fluctuation stress decays inversely with the inter-substrate separation.

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Pseudo-Casimir interactions across nematic films with disordered anchoring axis

Cited by 13 publications

References 40 publications

Fluctuation induced forces in critical films with disorder at their surfaces

Fluctuation induced forces in critical films with disorder at their surfaces

Fluctuation-induced interactions in nematics with disordered anchoring energy

Pseudo-Casimir stresses and elasticity of a confined elastomer film

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