Shear-induced molecular precession in a hexatic Langmuir monolayer

被引:46
作者
Ignés-Mullol, J [1 ]
Schwartz, DK [1 ]
机构
[1] Tulane Univ, Dept Chem, New Orleans, LA 70118 USA
关键词
D O I
10.1038/35066539
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
Liquid crystalline behaviour is generally limited to a select group of specially designed bulk substances. By contrast, it is a common feature of simple molecular monolayers and other quasi-two-dimensional systems(1), which often possess a type of in-plane ordering that results from unbinding of dislocations-a 'hexatic' liquid crystalline phase. The flow of monolayers is closely related to molecular transport in biological membranes, affects foam and emulsion stability and is relevant to microfluidics research. For liquid crystalline phases, it is important to understand the coupling of the molecular orientation to the flow. Orientationally ordered (nematic) phases in bulk liquid crystals exhibit 'shear aligning' or 'tumbling' behaviour under shear, and are described quantitatively by Leslie-Ericksen theory(2). For hexatic monolayers, the effects of flow have been inferred from textures of Langmuir-Blodgett films(3-5) and directly observed at the macroscopic level(6-10). However, there is no accepted model of hexatic flow at the molecular level. Here we report observations of a hexatic Langmuir monolayer that reveal continuous, shear-induced molecular precession, interrupted by occasional jump discontinuities. Although superficially similar to tumbling in a bulk nematic phase, the kinematic details are quite different and provide a possible mechanism for domain coarsening and eventual molecular alignment in monolayers. We explain the precession and jumps within a quantitative framework that involves coupling of molecular orientation to the local molecular hexatic 'lattice', which is continuously deformed by shear.
引用
收藏
页码:348 / 351
页数:5
相关论文
共 25 条
[1]   IMAGING OF THE LATERAL STRUCTURE OF LANGMUIR-BLODGETT-FILMS BY METAL DECORATION AND POLARIZATION MICROSCOPY [J].
BUBECK, C .
THIN SOLID FILMS, 1992, 210 (1-2) :674-677
[2]  
Chandrasekhar S., 1992, LIQUID CRYSTALS
[3]   Shear-induced optical anisotropy in a Langmuir monolayer: A Brewster angle reflectivity study [J].
Cuvillier, N ;
Mingotaud, C ;
Ikegami, K .
JOURNAL OF CHEMICAL PHYSICS, 1999, 111 (15) :6982-6990
[4]  
Edwards D., 1991, INTERFACIAL TRANSPOR
[5]   Direct visualization of flow-induced anisotropy in a fatty acid monolayer [J].
Friedenberg, MC ;
Fuller, GG ;
Frank, CW ;
Robertson, CR .
LANGMUIR, 1996, 12 (06) :1594-1599
[6]   Nonlinear shear response and anomalous pressure dependence of viscosity in a Langmuir monolayer [J].
Ghaskadvi, RS ;
Ketterson, JB ;
Dutta, P .
LANGMUIR, 1997, 13 (19) :5137-5140
[7]   Effect of subphase Ca++ ions on the viscoelastic properties of Langmuir monolayers [J].
Ghaskadvi, RS ;
Carr, S ;
Dennin, M .
JOURNAL OF CHEMICAL PHYSICS, 1999, 111 (08) :3675-3678
[8]   Shear response of Langmuir monolayers of heneicosanoic (C-21) acid studied using a torsion pendulum [J].
Ghaskadvi, RS ;
Bohanon, TM ;
Dutta, P ;
Ketterson, JB .
PHYSICAL REVIEW E, 1996, 54 (02) :1770-1773
[9]   THEORY OF 2-DIMENSIONAL MELTING [J].
HALPERIN, BI ;
NELSON, DR .
PHYSICAL REVIEW LETTERS, 1978, 41 (02) :121-124
[10]   Alignment of hexatic Langmuir monolayers under shear [J].
Ignés-Mullol, J ;
Schwartz, DK .
PHYSICAL REVIEW LETTERS, 2000, 85 (07) :1476-1479