Title:	Novel mesogenic azobenzene dimer at air-water and air-solid interfaces
Authors:	Kumar, Bharat Prajapati, A.K. Varia, M.C. Suresh, K.A.
Issue Date:	22-Dec-2008
Publisher:	American Chemical Society
Citation:	Langmuir, 2008, Vol.25, p839
Abstract:	We have synthesized a novel mesogenic azobenzene molecule and studied its monolayer film properties at air−water interface (Langmuir film) and air−solid interface (Langmuir−Blodgett film). The material, H-shaped dimer bis[5-(4′-n-dodecyloxy benzoyloxy)-2-(4′′-methylphenylazo)phenyl] adipate (12D1H) exhibits a smectic C phase between 51 and 48 °C on cooling. Surface manometry studies showed the formation of a stable monolayer at the air−water interface. Brewster angle microscopy (BAM) showed that liquid domains coexisting with the gas region at large area transformed to a uniform liquid phase with increasing surface density and finally to a collapsed state. We have carried out atomic force microscope (AFM) studies on Langmuir−Blodgett (LB) films transferred onto freshly cleaved hydrophilic mica substrate. The AFM images showed domains of height of about 3.8 nm, which corresponds to the estimated height of the molecule confirming the formation of monomolecular film. On a hydrophobic silicon substrate, the LB transfer yields a bilayer film, which dewets to form uniform nanodroplets of diameter of about 100 nm and height in the range 10−50 nm. Our analysis indicated that the mechanism involved in the formation of nanodroplets can be attributed to spinodal dewetting. The 12D1H molecule containing an azobenzene group undergoes a trans to cis transformation in the presence of ultraviolet light. Our surface manometry studies showed that the monolayer in the presence of ultraviolet light was more stable with a collapse pressure three times that of the monolayer in the dark.
Description:	Restricted Access.
URI:	http://hdl.handle.net/2289/3695
ISSN:	0743-7463 (Print) 1520-5827 (Online)
Alternative Location:	http://dx.doi.org/10.1021/la8030733
Copyright:	2008 American Chemical Society
Appears in Collections:	Research Papers (SCM)

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