SURFACE MOLECULAR STRUCTURE DETERMINATION OF LITHIUM SALT OF 10,12-NONACOSADIYNOIC ACID MONOMER AND POLYMER LANGMUIR-BLODGETT FILMS BY SCANNING FORCE MICROSCOPY COMPARED TO ELECTRON DIFFRACTION RESULTS

Abstract

Langmuir-Blodgett films of lithium salts of 10,12-nonacosadiynoic acid monomer (Li/16-8 DA) and polymer (Li/16-8 PDA) were characterized by scanning force microscopy (SFM or AFM) to study their surface molecular structure. Based on analysis of these images, a two-dimensional oblique unit mesh is assigned for Li/16-8 DA monomer LB film with unit mesh parameter c = 0.549 ± 0.040 nm and b = 0.541 ± 0.060 nm with an angle of 113°. A hexagonal unit mesh is assigned for Li/16-8 PDA with unit mesh parameter c = 0.497 ± 0.052 nm and b = 0.497 ± 0.060 nm. We then report the comparison of two-dimensional, fast Fourier transform (FFT) of SFM images to the electron diffraction images. From the viewpoint of a three-dimensional structure projected onto a plane, centered rectangular nets can be assigned for both Li/16-8 DA and Li/16-8 PDA. The monomer unit cell parameters are c = 0.460 ± 0.040 nm and b = 1.020 ± 0.060 nm. The polymer cell parameters are c = 0.485 ± 0.080 nm and b = 0.820 ± 0.010 nm. The correlation between the two very different methods of surface structure determination is excellent. However, care must be taken in assigning the unit net (two-dimensional representation) and the projected unit cell (three-dimensional) vectors.