This article reviews and discusses some open problems concerning polymer materials of reduced sizes and dimensions. Such objects exhibit exceptional physical properties when compared with their macroscopic counterparts. More specifically, abrupt increases in polymer nanofiber elastic modulus have been observed when diameters drop below a certain value. In addition, temperature dependence of elastic modulus is highly influenced by fiber diameter. Mechanical (macroscopic) analyses have failed to provide satisfactory explanations for the mechanisms ruling such features, calling for detailed microscopic examination of the systems in question. A hypothesis bridging the current knowledge gaps is presented. The key element of this hypothesis is based on confinement of the supermolecular microstructure of polymer nanofibers and its dominant role in the deformation process. This suggestion challenges the commonly held view suggesting that surface effects are the most significant parameters impacting mechanical and thermodynamic nanofiber behaviors. The review will focus on the mechanical and thermodynamic properties of electrospun polymer nanofibers, selected as representatives of nanoscale polymer objects. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Tungsten disulfide inorganic nanotubes (WS₂ INTs), which are available now in large amounts, were embedded into a poly methyl methacrylate (PMMA) nanofiber matrix. The PMMA solution and PMMA–WS₂ INT suspensions were electrospun to form aligned nanofiber meshes. TEM analysis revealed that WS₂ INTs are well dispersed within the PMMA fiber matrix and aligned along the fiber axes. Characteristic Raman signatures of WS₂ INTs were observed for the composite fiber meshes. The characteristic optical absorption band of WS₂ INTs shifted to the blue wavelength region in the presence of PMMA, a shift indicating a significant interaction between WS₂ INTs and PMMA. The thermal stability of WS₂ INT-embedded PMMA meshes was increased by 23 °C, in comparison to PMMA. The elastic modulus of PMMA fiber meshes was increased 10 times and 22 times, when WS₂ INTs were embedded and aligned along the fiber axes, for 1 wt% and 2 wt% respectively, and without compromising the tensile strength of the PMMA fiber mesh. Respective 35% and 30% increases in the tensile strength and toughness of the composite fibers were recorded. In addition, the dielectric constant of composite fiber meshes was 61% higher than that of PMMA fiber meshes. The developed PMMA–WS₂ INT organic–inorganic composites featuring enhanced stiffness and toughness may have potential applications as transparent high energy absorption materials.