Landau<i>–</i>de Gennes theory of wetting and orientational transitions at a nematic-liquid<i>–</i>substrate interface

Sen, Asok K.; Sullivan, D. E.

doi:10.1103/physreva.35.1391

Cited by 155 publications

(76 citation statements)

References 64 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As remarked earlier, it is important to aScount for the large magnitude (e.g., up to several hundred A (1 1)) of the bulk coherence length SNI, which in turn results from the weakly first-order nature of the nematic-isotropic transition. The effects of this can be analyzed in the framework of Landau -de Gennes type theories (15,22,23) for the spatial variation of orientational order parameters. As also found in Landau theories of wetting by ordinary liquids (7)(8)(9)(10)24), the exponentially decaying tails of the order-parameter profiles yield a contribution to V(1) of the form where a -O(1) is a numerical coefficient.…”

Section: Now Givesmentioning

confidence: 99%

“…Furthermore, we conjecture that distortion-induced corrections of 0 ( t 2 ) to the leading-order result in [4] may result from other mechanisms besides that based on the anchoring energies of the separate a -N and N-I interfaces. Model calculations, for example, based on a Landau -de Gennes theory allowing for director tilt (22), are needed to elucidate this point.…”

Section: Now Givesmentioning

confidence: 99%

See 1 more Smart Citation

On the free energy of nematic wetting layers

Sullivan¹,

Lipowsky²

1988

Can. J. Chem.

View full text Add to dashboard Cite

. J. Chem. 66,553 (1988).The contributions to the free energy of a nematic wetting layer as a function of its thickness 1 are analyzed. The longest-range contribution is due to distortion of the nematic director across the film, resulting from different preferred molecular orientations at the two interfaces bounding the film. Van der Waals forces as well as the decaying tails of the interfacial order-parameter profiles yield contributions to the free energy of successively shorter range. These effects lead to crossovers between different scaling rtgimes for variation of the mean wetting-layer thickness with temperature. Experimental implications of the results are described. DONALD E. SULLIVAN, et REINHARD LIPOWSKY. Can. J. Chem. 66,553 (1988).On a ttudit l'influence de l'tpaisseur (I) de couches ntmatiques mouillantes sur l'tnergie libre. La contribution qui se fait sentir a la plus grande distance est d i e a une distorsion du directeur ntmatique a travers le film; cette distorsion rtsulte elle-m&me d'orientations moltculaires prtftrentielles difftrentes aux deux interfaces qui lient le film. Utilisant les forces de van der Waals ainsi que les profils de l'ordre interfaciallparam2tres, on a pu dtduire les contributions a l'tnergie libre pour des distances de plus en plus courtes. Ces effets conduisent a des croisements entre divers rCgimes dlCchelles pou la variation de l'tpaisseur moyenne de la couche mouillante avec la temperature. On dtcrit les implications exptrimentales de ces rtsultats.[Traduit par la revue]Consider a liquid crystalline material at a temperature T slightly above the transition temperature TNI for the onset of nematic (N) ordering. While the bulk of the material then exists as an isotropic (I) liquid phase with no long-range orientational order, some degree of local nematic order may be spontaneously induced at the interface with another phase a such as a solid substrate or the vapour in coexistence with the liquid. If, on lowering the temperature, the mean thickness i of that nematic layer diverges over microscopic length scales as T + TNI, then we say that the nematic phase completely wets the a-I interface. Experimental evidence of this effect has been seen for a number of nematic substances, at both solid-liquid (1-3) and liquidvapour (3-5) interface^.^ Entirely analogous wetting phenomena involving three distinct thermodynamic phases have recently come under extensive study for a variety of physical systems (7).In this note we draw attention to some novel critical properties characterizing the approach to complete wetting in the case of a nematic layer. In particular, we focus on the asymptotic scaling laws describing the divergence of the mean wetting-layer thickness in the limit that t = (T -TNI)/TNI goes to zero. Our approach is similar to ones used successfully to describe wetting in other systems (7-lo), based on analysis of the free energy u(1) per unit area of the layer as a function of its thickness 1, when the latter is viewed as a thermodynamic order parameter. This approac...

show abstract

Section: Now Givesmentioning

confidence: 99%

Section: Now Givesmentioning

confidence: 99%

On the free energy of nematic wetting layers

Sullivan¹,

Lipowsky²

1988

Can. J. Chem.

View full text Add to dashboard Cite

show abstract

“…To our knowledge, this has not been done before. Actually, there is some confusion in the literature, since a number of papers dealing with "degenerate planar anchoring" describe in fact homeotropic anchoring with negative S [8][9][10][11]. The confusion arises from the fact that the molecules themselves are planar and randomly oriented in this homeotropic situation.…”

mentioning

confidence: 99%

Modeling planar degenerate wetting and anchoring in nematic liquid crystals

2005

View full text Add to dashboard Cite

Abstract. -We propose a simple surface potential describing the planar degenerate anchoring of nematic liquid crystals, i.e., the tendency of the molecules to align parallel to one another along any direction parallel to the surface. We show that, at lowest order in the tensorial Landau-de Gennes order-parameter, fourth-order terms must be included. We analyze the anchoring and wetting properties of this surface potential. In the nematic phase, we find the desired degenerate planar anchoring, with positive scalar order-parameter and some surface biaxiality. In the isotropic phase, we find, in agreement with experiments, that the wetting layer may exhibit a uniaxial ordering with negative scalar order-parameter. For large enough anchoring strength, this negative ordering transits towards the planar degenerate state.Introduction. -Nematic liquid crystals are non-polar liquids consisting of elongated molecules aligned, on the average, parallel to a common direction ±n [1]. The unit vector n is called the director. Exceptionally, in the case of "negative order," the molecules may be distributed perpendicularly to n. The nematic order is quantified by a symmetric traceless tensor Q, of Cartesian components Q ij (i, j = 1, 2, 3). Microscopically, calling m a unit vector parallel to the long axis of the molecules, the tensor order-parameter can be defined as Q ij = m i m j −

show abstract

“…The expression for the anchoring energy with the positive fourth order coefficient w 4 coming from the quadrupole-quadrupole interactions and short-range anisotropic repulsive and attractive forces [42,43,44] was originally derived by Sen and Sullivan [28]. The non-polar azimuthally degenerated anchoring energy (1) with the quartic term (w 1 = 0 and w 4 = 0) was recently used to analyze temperature-driven transitions between the conical, planar and anticonical anchorings observed on a grafted polymer brush [45].…”

Section: Discussionmentioning

confidence: 99%

“…III and, in Sec. IV, discuss how they can be interpreted theoretically using the phenomenological model of two competing easy axes with the anchoring potential taken in the Sen-Sullivan form [28]. Concluding remarks are given in Sec.…”

Section: Introductionmentioning

confidence: 99%

Liquid-crystal anchoring transitions on aligning substrates processed by a plasma beam

2008

View full text Add to dashboard Cite

We observe a sequence of the anchoring transitions in nematic liquid crystals (NLC) sandwiched between the hydrophobic polyimide substrates treated with the plasma beam. There is a pronounced continuous transition from homeotropic to low tilted (nearly planar) alignment with the easy axis parallel to the incidence plane of the plasma beam (the zenithal transition) that takes place as the exposure dose increases. In NLC with positive dielectric anisotropy, a further increase in the exposure dose results in in-plane reorientation of the easy axis by 90 • (the azimuthal transition). This transition occurs through the two-fold degenerated alignment characteristic for the second order anchoring transitions. In contrast to critical behavior of anchoring, the contact angle of NLC and water on the treated substrates monotonically declines with the exposure dose. It follows that the surface concentration of hydrophobic chains decreases continuously. The anchoring transitions under consideration are qualitatively interpreted by using a simple phenomenological model of competing easy axes which is studied by analyzing anchoring diagrams of the generalized polar and non-polar anchoring models.

show abstract

Landau–de Gennes theory of wetting and orientational transitions at a nematic-liquid–substrate interface

Cited by 155 publications

References 64 publications

On the free energy of nematic wetting layers

On the free energy of nematic wetting layers

Modeling planar degenerate wetting and anchoring in nematic liquid crystals

Liquid-crystal anchoring transitions on aligning substrates processed by a plasma beam

Contact Info

Product

Resources

About