Lamellar surface

Precise thickness measurements by TEM require sections transverse to the basal lamellar surface. Conversely, only lamellae that can be identified as untilted "edge-on" or "flat-on" in AFM images are suitable for thickness analysis. The average thickness obtained by these techniques is based on sampling microscopic areas and will only be correct if the morphology is uniform in the sample. Micrographs taken from different areas of the specimen are usually studied, and statistical analysis of histograms used for quantitative analysis [255,256]. 

The small ratio of lamellar thickness to the contour length of a polymer molecule clearly implies that chains must fold back and forth into stems with chain direction essentially perpendicular to the lamellar surface, as originally declared by Storks. The large surfaces of the lamellae containing the chain folds are called fold surfaces, and the thin surfaces are called lateral surfaces. 

Near-field scanning techniques are relative newcomers, and the basis for their interpretation is less well established. However, AFM has opened up new perspectives for morphological studies, particularly given that excessive surface damage in soft specimens can be avoided by use of non-contact or intermittent contact modes. Its sensitivity to surface topography nevertheless makes AFM prone to artefacts when used to observe surfaces prepared by microtoming, and its effective depth of field is limited compared with SEM. On the other hand, if lamellar surfaces can be prepared such that the surface relief (or hardness, friction variations) is representative of the bulk texture, very striking detail can be recorded at the nanometre scale in deformed polyolefins [11]. 

Conventional bright-field TEM observations of polyolefins often require contrast enhancement, usually by staining with Ru04 or other suitable markers [17]. These accumulate in the amorphous phase, at lamellar surfaces and in cavities, and differential staining can reveal the phase distribution in blends. Staining also hardens the specimens, facilitating preparation of thin sections at room temperature (cryo-sectioning is required for unfixed polyolefins). 

The melt-crystallised sample skipped Process 1 due to the limited relaxation of its entangled molecules on the lamellar surfaces, rather than the adjacent re-entry folding for the solution-crystallised sample. 

The evidence for more specific physical and chemical influences of substrate composition is less clear. Chemically, molybdenum disulphide is very inert. The sulphur atoms which form the surface layer of a lamella are strongly bonded to the molybdenum atoms, and their valency electrons are fully occupied in those bonds. Although molybdenum disulphide is highly polarised in its hexagonal crystals, the free energy at the lamellar surfaces is very small. 

Using atomic force microscopy (AFM), lamellar surface of normal and cyclic alkanes C33H68, C36H74, (CH2)48, and (CH2)72 was examined to atomic scale.114 In the cycloalkanes, the observed images are consistent with adjacent re-entry 100 folds in a monoclinic crystal structure. 

Because the length difference of the two miscible components is small, the disorder is considered mainly in terms of site occupancies close to the lamellar surface.159 163 Thus, alkane solid solutions provide good models of surface disorder, which has been studied by infrared and Raman spectros-... 

For example, vinyl monomer-montmorillonite intercalate (VM-MMT), able to swell and disperse in organic solvents, was prepared by exchanging the mineral cations of MMT by vinylbenzyltrimethylammonium chloride. The resulting VM-MMT material rendered the mineral organophilic and having polymerizable moieties directly bonded to the lamellar surface of the mineral. Radical polymerization of S between the interlayers of 5,10,25, and 50 wt % of VM-MMT... 

Moller M, Cantow H-J, Drottloff H, Emeis D, Lee K-S, Wegner G (1986) Phase transitions and defect structures in the lamellar surface of pdyethylene and n-alkane crystallites. Magic angle spinning C NMR studies. Makromol. Chem. 1S7 1237... 

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