| Abstract
| - The results of visualization of morphology and nanostructure of polydiethylsiloxane (PDES)are presented. The study was performed in a temperature range, which covers melting, crystallization,mesophase formation, and isotropization of PDES, on polymer samples of different molecular weightsand different thicknesses. The morphological identification of α2- and β2-polymorphs of PDES was furtherextended by demonstrating, for the first time, that the α2- and β2-crystalline polymorphs transform totwo morphologically incompatible α-mesophase and β-mesophase. Domains, which are several micronsin size, are typical morphologic patterns for the α-phase material, whereas large lamellae (from a few totens of microns in length and several hundreds of nanometers in width) are typical structures of theβ-phase PDES. The above polymorphs and amorphous polymers have appeared in different ratios in thesamples depending on their preparation (deposition way, thermal history) and thickness. Shearing ofPDES into thin film on Si substrate induced the formation of the mesomorphic β-phase structures, whichare embedded in amorphous material. Crystallization of the amorphous PDES occurred at much lowertemperatures due to its constrained geometry. The width of the β-phase lamellae in the crystalline andmesomorphic state as measured from AFM images correlates with the length of the extended PDES chainsin the crystalline state. Sublamellae structures were revealed by AFM imaging the mesomorphic lamellaewith different tip−sample forces. Each lamella has a skeleton formed of 10−15 nm thick linear structures,which are separated by 40−50 nm and tapered at the ends to form a single entity. This skeleton is wrappedwith numerous 0.8 nm thick layers, which are most likely formed of partially ordered domains of extendedchains. Crystallization of the β-mesomorphic lamellae leads to more ordered and stiffer top layers oflamellae. In some cases individual lamellae are broken into small crystalline blocks, and in other casescrystalline blocks incorporate two neighboring lamellae. The domains of the mesomorphic α-phase areless organized, and upon crystallization large domains are broken into smaller blocks due to shrinkage.This is accompanied by surface roughening. Some of the blocks exhibit periodic surface structures witha repeat distance of 50−60 nm. At least partial chain extension in the α-phase PDES is suggested.
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