Wetting and prewetting transition in metallic fluid K–KCl solutions studied by second harmonic generation

Tostmann, H.; Nattland, D.; Freyland, W.

doi:10.1063/1.471567

Cited by 38 publications

(22 citation statements)

References 45 publications

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“…16,17 Here we list only the information which is relevant to the results of this study. To generate the SHG and PG signals at the alloy-vapor interface, a Q-switched Nd-YAG laser ͑ϭ1064 nm͒ with a pulse duration of 4 ns, an irradiance of about 1 W/m 2 , a beam diameter of about 2 mm and a repetition rate of 5 Hz is used as a light source at an angle of incidence of about 70 degrees.…”

Section: Methodsmentioning

confidence: 98%

Oscillatory wetting instability induced by liquid–liquid decomposition in a Ga–Pb alloy

Turchanin

Tsekov

Freyland

2004

The Journal of Chemical Physics

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We present the first experimental investigation and pertinent theoretical modeling of an interfacial oscillatory instability in a binary fluid alloy, the Ga-Pb system. It is characterized by spinodal decomposition at elevated temperatures and by a complete wetting transition at liquid-liquid coexistence. For the alloy Ga(0.95)Pb(0.05) the fluid interface has been probed by second harmonic generation (SHG) under UHV conditions at temperatures between 740 and 550 K. At conditions inside the miscibility gap clear oscillations of the SHG-intensity with a period of approximately 30 min are found for different cooling cycles and also at constant temperatures. These interfacial oscillatory instabilities simultaneously induce temperature oscillations in the bulk fluid with the same period. This phenomenon can be explained by a periodic variation of the fluid interfacial emissivity. A model has been developed which describes the wetting-dewetting dynamics by hydrodynamic equations within the Reynolds approximation. It is found that the interfacial oscillatory instability is determined by capillary-gravitation instability. The model quantitatively describes the time evolution of the interfacial and temperature oscillations and gives the correct value of the oscillation period. A detailed comparison of the experimental and model results is given.

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Section: Methodsmentioning

confidence: 98%

Oscillatory wetting instability induced by liquid–liquid decomposition in a Ga–Pb alloy

Turchanin

Tsekov

Freyland

2004

The Journal of Chemical Physics

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“…Experimental evidence for this assumption has been found for the similar systems Ga-Pb 12 and K-KCl. 13 The discussion of the data is divided into two parts: (i) T < T w ≃ T mono (110…”

Section: Resultsmentioning

confidence: 99%

Microscopic Structure of the Wetting Film at the Surface of Liquid Ga-Bi Alloys

et al. 2000

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X-ray reflectivity measurements of the binary liquid Ga-Bi alloy reveal a dramatically different surface structure above and below the monotectic temperature Tmono = 222• C. A Gibbs-adsorbed Bi monolayer resides at the surface at both regimes. However, a 30Å thick, Bi-rich wetting film intrudes between the Bi monolayer and the Ga-rich bulk for T > Tmono. The internal structure of the wetting film is determined withÅ resolution, showing a theoretically unexpected concentration gradient and a highly diffuse interface with the bulk phase.

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“…Experimentally, prewetting transitions are seldom observed [23][24][25][26] and, to our knowledge, no experimental observations of prewetting phenomena have been reported for liquid crystals. The behavior observed here at the free surface of 12.O.6 may be thus the first example of a prewetting transition in liquid crystals.…”

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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Wetting and prewetting transition in metallic fluid K–KCl solutions studied by second harmonic generation

Cited by 38 publications

References 45 publications

Oscillatory wetting instability induced by liquid–liquid decomposition in a Ga–Pb alloy

Oscillatory wetting instability induced by liquid–liquid decomposition in a Ga–Pb alloy

Microscopic Structure of the Wetting Film at the Surface of Liquid Ga-Bi Alloys

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

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