Chiral-symmetry selection in soft monolayers under vortical flow

摘要

Herein, we report and interpret a new chiral-selection phenomenon in the orientational ordering of soft-assembled domains that arise spontaneously in Langmuir monolayers of an azobenzene derivative at the air/water interface. The orientational chirality of isolated sub-millimeter domains was unambiguously assessed by optical microscopy. The selection process, quantified by using an enantiomeric excess parameter, was controlled by stirring the aqueous subphase. We have studied the dependence of this process on stirring rate and handedness, stirring time, temperature, and on the initial state of the monolayer. The influence of the concomitant cis/trans isomerization on the reported chiral-selection process is also discussed. En aquest article presentem i interpretem un nou fenomen de selecci? quiral de l'ordre orientacional en monocapes de Langmuir de derivats azobenzènics mitjan?ant l'agitaci? (vòrtex) de la subfase que suporta la monocapa. A partir de l'observaci? de les estructures amb microscòpia òptica podem quantificar l′excés enantiomeric sense cap ambigüitat. Estudiem l'efecte dels diferents paràmetres de control sobre aquest fenomen i discutim la influència de la isomeritzaci? cis-trans sobre el procés de selecci? quiral. A swirl of surfactants: The orientational chirality of sub-millimeter domains that arise spontaneously in Langmuir monolayers of achiral surfactants was selected by using a vortical flow under the surface. The enantiomeric excess was directly assessed by polarizing optical microscopy, and depended on the forcing conditions and on the initial monolayer state (see figure).