The synthetic routes and materials properties of polypropylene/montmorillonite nanocomposites are reviewed. The nanocomposite formation is achieved in two ways: either by using functionalized polypropylenes and common organo-montmorillonites, or by using neat/ unmodified polypropylene and a semi-fluorinated organic modification for the silicates. All the hybrids can be formed by solventless melt-intercalation or extrusion, and the resulting polymer/inorganic structures are characterized by a coexistence of intercalated and exfoliated montmorillonite layers. Small additionsstypically less than 6 wt %sof these nanoscale inorganic fillers promote concurrently several of the polypropylene materials properties, including improved tensile characteristics, higher heat deflection temperature, retained optical clarity, high barrier properties, better scratch resistance, and increased flame retardancy.

Poly(vinyl alcohol)/sodium montmorillonite nanocomposites of various compositions were created by casting from a polymer/silicate water suspension. The composite structure study revealed a coexistence of exfoliated and intercalated MMT layers, especially for low and moderate silicate loadings. The inorganic layers promote a new crystalline phase different than the one of the respective neat PVA, characterized by higher melting temperature and a different crystal structure. This new crystal phase reflects on the composite materials properties. Namely, the hybrid polymer/silicate systems have mechanical, thermal, and water vapor transmission properties, which are superior to that of the neat polymer and its conventionally filled composites. For example, for a 5 wt % MMT exfoliated composite, the softening temperature increases by 25 °C and the Young's modulus triples with a decrease of only 20% in toughness, whereas there is also a 60% reduction in the water permeability. Furthermore, due to the nanoscale dispersion of filler, the nanocomposites retain their optical clarity.

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The crystallization behavior of poly(ethylene oxide) (PEO) was studied in the presence of an inorganic filler surface (sodium montmorillonite) with DSC, as well as isothermal crosspolarization optical microscopy. Crystallization of PEO is found to be inhibited, exhibiting a decrease of spherulite growth rate and crystallization temperature. However, the overall crystallization rate increases with silicate loading as a result of extra nucleation sites, which occur in the bulk PEO matrix (i.e., far from the silicate surfaces). PEO differs from other systems, where crystallinity is typically enhanced next to such surfaces, in that the polymer is amorphized near the montmorillonite surfaces. This behavior is attributed to the specific way that PEO interacts with Na + montmorillonite, where strong coordination of PEO to the surface Na + cations promotes noncrystalline (ether crown) PEO conformations.

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Crystallization of poly (vinyl alcohol) in the presence of an inorganic filler surface (sodium montmorillonite, MMT) was observed and compared to the crystallization of the neat polymer. For this purpose, several atomic force microscopy modes, providing spatial resolution between amorphous and crystalline polymer, are employed to observe filled and unfilled PVA films. The various AFM modes utilized are detailed, with the emphasis on how they can contrast stiff (crystalline) and softer (amorphous) domains on a polymer surface. The study revealed changes in the PVA crystal morphology, with bulk crystallites growing to sizes of more than 5 µm, whereas next to the inorganic surfaces grow to only 1-2 µm in size. Moreover, complementary X-ray diffraction and DSC investigations indicate a new crystal structure formed next to the MMT surfaces, at the expense of the bulklike crystal.

Using electron beam lithography, amorphous Si (a-Si) nanopillars were fabricated with a height of 100 nm and diameters of 100, 200, 300, 500, and 1000 nm. The nanopillars were electrochemically cycled in a 1 M lithium trifluoromethanesulfonate in propylene carbonate electrolyte. In situ atomic force microscopy (AFM) was used to qualitatively and quantitatively examine the morphology evolution of the nanopillars including volume and height changes versus voltage in real-time. In the first cycle, an obvious hysteresis of volume change versus voltage during lithiation and delithiation was measured. The pillars did not crack in the first cycle, but a permanent volume expansion was observed. During subsequent cycles the a-Si roughened and deformed from the initial geometry, and eventually pillars with diameters >200 nm fractured. Furthermore, a degradation of mechanical properties is suggested as the 100 and 200 nm pillars were mechanically eroded by the small contact forces under the AFM probe. Ex situ scanning electron microscopy (SEM) images, combined with analysis of the damage caused by in situ AFM imaging, demonstrate that during cycling, the silicon became porous and structurally unstable compared to as-fabricated pillars. This research highlights that even nanoscale a-Si suffers irreversible mechanical damage during cycling in organic electrolytes.

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