Atomic force microscopy on polymers and polymer related compounds

Abstract

Atomic Force Microscopy (AFM) images have been recorded from the surfaces of platelet type monocrystals of linear alkanes, n-tritriacontane, C₃₃H₆₈, and n-hexatriacontane, C₃₆H₇₄. Structural details have been revealed in the range from several hundreds of nanometers down to the atomic scale. High resolution AFM micrographs of the linear alkanes show a regular pattern of elevations characterized by two main periodicities: a_AFM=.70±.02 nm, b_AFM=.52±.05 nm, $\gamma _{AFM} = 88 \pm 3^\circ ,$, and a_AFM=.79±.05 nm, b_AFM=.61±.05 nm, $\gamma _{AFM} = 87 \pm 3^\circ$, for C₃₃H₆₈ and C₃₆H₇₄ respectively. This structure is in fair agreement with the orthorhombic subcell of the bulk structure as confirmed by electron diffraction. Further, AFM results are in accordance with an orthorhombic unit cell for C₃₃H₆₈, and a monoclinic one for C₃₆H₇₄ under investigation. Consequently, the elevations in the AFM images can be assigned to individual methyl groups, which form the surface layer of a paraffine crystal. A regular surface structure has also been observed in AFM images of platelet crystals of cyclic alkanes, cyclooctatetracontane (CH₂)₄₈, and cyclodoheptacontane (CH₂)₇₂. In these cases, the periodicities are characterized by a_AFM=1.10±.01 nm, b_AFM=.85±.01 nm, y_AFM=89±1^o, and a_AFM=1.11±.06 nm, b_AFM=.91±.05, and $\gamma _{AFM} = 90 \pm 3^\circ$, for (CH₂)₄₈ and (CH₂)₇₂, respectively. The images are consistent with the arrangement of the adjacent reentry folds obtained from crystallographic data.