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    STUDIA CHEMIA - Issue no. 2 / 2004  
         
  Article:   ATOMIC FORCE MICROSCOPY STUDIES OF LANGMUIR-BLODGETT FILMS. I. STRUCTURES OF COLLAPSED STEARIC ACID MONOLAYERS.

Authors:  MARIA TOMOAIA-COTISEL, GHEORGHE TOMOAIA, AURORA MOCANU, VASILICA-DANIELA POP, NECULAI APETROAEI, GHEORGHE POPA. 		 
       
         
  Abstract:  Our previous theoretical studies on the collapse mechanism of stearic acid monolayers at the air/aqueous solution of pH 2 interface have suggested that the collapse mechanism can be described by a nucleation process subsequently followed by a growth of the nuclei. In the present work we will provide more evidence on the collapse mechanism and on collapsed structures of stearic acid monolayers by using atomic force microscopy (AFM) on Langmuir-Blodgett (LB) films of stearic acid transferred from monolayers, at the air/water interface, on hydrophilic substrates. Topographic and phase AFM images have shown several types of collapsed structures identified by us as straight bilayer ridges and buckling areas, three layered collapsed fragments, and multilayered colloidal particles. By using cross section profiles through the topographic images, the said collapsed structures were found in equilibrium with condensed stearic acid monolayer domains. These results are in substantial agreement with our earlier theory on collapse mechanism of Langmuir monolayers and with similar reported data in the literature. Finally, they confirm that AFM provides an accurate analysis on the packing of the molecules in monolayers and in collapsed structures and on the formation of LB film domains at the nanometer scale.  
         
     
         
         
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