Systematics of wetting and layering phenomena in smectic materials

Pawlowska, Z.; Sluckin, T. J.; Kventsel, G. F.

doi:10.1103/physreva.38.5342

Cited by 48 publications

(15 citation statements)

References 35 publications

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“…Our surface phase diagram closely resembles a theoretical (V, T) surface phase diagram obtained by Pawlowska et al [16] as far as the locations of the triple points and the relative positions of the different layer transitions are con-cerned. As observed by us experimentally, the model of [16] predicts with decreasing temperature either a sequence of single-layer transitions or a multiple-layer transition followed by one or more single-layer transitions.…”

supporting

confidence: 87%

Surface Triple Points and Multiple-Layer Transitions Observed by Tuning the Surface Field at Smectic Liquid-Crystal–Water Interfaces

Bahr

2007

Phys. Rev. Lett.

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We present an ellipsometric study of the interface between a smectic liquid crystal and water in the presence of a nonionic surfactant. The surfactant concentration serves as a handle to tune the surface field. For sufficiently large surfactant concentrations, a smectic phase is present at the interface in the temperature range above the smectic-A-isotropic bulk transition; when the bulk transition is approached, the thickness of this surface phase grows via a series of layer-by-layer transitions at which single smectic layers are formed. At lower surfactant concentrations, transitions appear at which the thickness of the surface phase jumps by multiple smectic layers, thereby implying the existence of triple points at which surface phases with different smectic layer numbers coexist. This is the first experimental demonstration of such surface triple points which are predicted by theoretical models.

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supporting

confidence: 87%

Surface Triple Points and Multiple-Layer Transitions Observed by Tuning the Surface Field at Smectic Liquid-Crystal–Water Interfaces

Bahr

2007

Phys. Rev. Lett.

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“…Several theoretical studies [27][28][29][30] are concerned with the behavior near an interface above isotropic-Sm-A transitions. Especially suited for a free surface is the study by Mederos and Sullivan [29] who use a density functional model which yields the surface self-consistently between coexisting liquid and vapor phases without introducing external surface fields.…”

Section: R Lucht and Ch Bahrmentioning

confidence: 99%

Wetting Phenomena at the Free Surface of the Isotropic Phase of a Smectic Liquid Crystal

Lucht

Bahr

1997

Phys. Rev. Lett.

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We report an ellipsometric study of the free surface of a smectic liquid crystal possessing a smectic-A-to-isotropic phase transition. Approaching the transition from above, an ordered surface layer appears at a discontinuous transition one degree above the bulk transition temperature. With decreasing temperature the thickness of the surface layer increases continuously, indicating a possible logarithmic divergence at the bulk transition. The behavior may be described as complete wetting accompanied by a prewetting transition. [S0031-9007(97)03114-1] PACS numbers: 64.70.Md, 68.45.Gd The free surface of thermotropic liquid crystals exerts a pronounced ordering effect to the molecules close to the surface which becomes apparent even above the transition to the isotropic liquid phase: Beaglehole [1] has reported an ellipsometric study of the free surface of the liquid crystal 5CB [2] above its isotropic-nematic transition. The results showed the presence of a nematic layer interposing the isotropic liquid-vapor interface; the nematic coverage was found to diverge logarithmically at the bulk nematic-isotropic transition temperature thereby indicating complete wetting. Since then, a number of nematic compounds were found to show essentially the same behavior [3,4].Whereas in the nematic phase only a long-range orientational order of the rodlike molecules exists, smectic phases show in addition a quasi-long-range positional order leading to a layered structure. Thus, above a nematicsmectic [5][6][7][8][9] or isotropic-smectic transition [10][11][12][13] usually the formation of smectic layers at the free surface is observed. In particular, above the isotropicsmectic-A ͑Sm-A͒ transition of the compound 12CB [14] a sequence of five successive layering transitions was observed [10,13]; since the number of surface-induced smectic layers was finite, this behavior corresponds to partial wetting of the isotropic liquid-vapor interface by the smectic phase.In this Letter, we report a new wetting behavior above an isotropic-Sm-A phase transition. Compared to the behavior of 12CB there are two main differences: first, the thickness of the ordered surface domain grows continuously with decreasing temperature and possibly diverges at the bulk transition; second, the first appearance of an ordered surface layer on the isotropic liquid is characterized by a sharp, discontinuous transition. The corresponding layer thickness just below this transition is not that of a single smectic layer but about twice as large. Thus, our results may be described by complete wetting accompanied by a prewetting transition.We have studied the 4-hexyloxyphenylester of 4dodecyloxybenzoic acid, labeled in the following as 12.O.6 (cf. Fig. 1), the Sm-A-isotropic transition temperature T AI of the bulk sample is 89.1 ± C. The compound was purified by chromatography and several recrystallizations. The temperature width of the two-phase region at the Sm-A-isotropic transition, observed in a polarization micoscope, was found to be smaller than the resoluti...

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“…This discrete layering phenomenon was, however, not observed for 10CB [17,19]. Also, theoretical work, using a lattice-gas model, suggests that the discrete layering transition is continuous only for the first layer, the rest being first order [20]. Both X-ray measurements, as well as theoretical work, indicate that only a few layers form before the transition extends throughout the sample.…”

Section: Resultsmentioning

confidence: 66%

Interface influenced phase transitions of alkylcyanobiphenyl liquid crystals A calorimetric study

1993

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Using an AC-calorimetry technique, we report measurements of the heat capacity and the phase shift between the applied heating power and the resulting thermal oscillations on the thermotropic liquid crystal series of alkylcyanobiphenyl (nCB) above the tricritical point. Specifically, we studied the first order phase transition smectic A to isotropic as a function of substrate, under atmospheric pressure. Different combinations of sapphire, Kapton type 200H polyimide film and air, are used to vary systematically the interfaces encountered by a liquid crystal. The calorimeter uses a sapphire disk, 10 mm in diameter and 013 mm thick, above which the samples are placed. A second sapphire disk, or a disk-shaped Kapton film, are used to sandwich the liquid crystal. Air interface samples are droplets allowed to spread naturally on the chosen substrate. The chosen geometry is such that interface effects appear to be maximized. Striking features found in the heat capacity and the phase shift studies with lOCB and 12CB will be presented for the different interfaces.

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Systematics of wetting and layering phenomena in smectic materials

Cited by 48 publications

References 35 publications

Surface Triple Points and Multiple-Layer Transitions Observed by Tuning the Surface Field at Smectic Liquid-Crystal–Water Interfaces

Surface Triple Points and Multiple-Layer Transitions Observed by Tuning the Surface Field at Smectic Liquid-Crystal–Water Interfaces

Wetting Phenomena at the Free Surface of the Isotropic Phase of a Smectic Liquid Crystal

Interface influenced phase transitions of alkylcyanobiphenyl liquid crystals A calorimetric study

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