Nanocomposites crystallization

Most of the time, metal/dielectric nanocomposites are studied in the form of solutions or thin solid films on a substrate Colloids, doped and annealed glasses, sol-gels, surfactant-stabilized nanoparticles, micelles, two- or three-dimension self-assembled nanocomposites, self-organized mesoporous oxides filled with metals, electrochemically-loaded template membranes, metal-ion implanted crystals, nanocomposite films elaborated by laser ablation, cluster-beam deposition, radio-frequency sputtering, or nanolithography. 

Based on their dimensions, which are in the nanometre range, three types of fillers can be distinguished. Isodimensional nanoparticles (NP), such as spherical silica NP have three nanometric dimensions. Nanotubes or whiskers are stretched constructions in which two dimensions are in the nanometre range and the other dimension is larger. When only one dimension is in the nanometre range, the composites are termed polymer-layered crystal nanocomposites, and are obtained by the complete intercalation of the polymer inside the galleries of layered host crystals [2]. 

Fig. 3.13 X-ray analysis data of chitosan/chitin crystal nanocomposites...

Very recently Mathew et al. [79] reported on the crystal studies of chitosan/ chitin crystal nanocomposites. The chitosan (a) exhibits a highly amorphous nature with broad and ill-dehned signals at 29 = 9-10° and 18-20° (Fig. 3.13). The chitin nanocrystals (b) show a strong peak at 29 = 8.8 and 19° and shoulders at 29 = 20 and 22°, conhrming its crystalline structure as a-chitin. 

They are attractive for various applications such as liquid crystals, nanocomposites, CVD coatings, and photoresists in lithographic technologies, based on their high temperature and oxidation resistance properties compared to non-POSS containing polymers [210]. 

Winiarz JG, Prasad PN (2002) Photorefractive inorganic-organic polymer-dispersed liquid-crystal nanocomposites photosensitized with cadmium sulfide quantum dots. Opt Lett 27 1330-1332... 

This is a highly polar polymer and crystalline due to the presence of amide linkages. To achieve effective intercalation and exfoliation, the nanoclay has to be modified with some functional polar group. Most commonly, amino acid treatment is done for the nanoclays. Nanocomposites have been prepared using in situ polymerization [85] and melt-intercalation methods [113-117]. Crystallization behavior [118-122], mechanical [123,124], thermal, and barrier properties, and kinetic study [125,126] have been carried out. Nylon-based nanocomposites are now being produced commercially. 

PP is probably the most thoroughly investigated system in the nanocomposite field next to nylon [127-132]. In most of the cases isotactic/syndiotactic-PP-based nanocomposites have been prepared with various clays using maleic anhydride as the compatibilizer. Sometimes maleic anhydride-grafted PP has also been used [127]. Nanocomposites have shown dramatic improvement over the pristine polymer in mechanical, rheological, thermal, and barrier properties [132-138]. Crystallization [139,140], thermodynamic behavior, and kinetic study [141] have also been done. 

Fig. 5.6 (A) TEM micrograph of alginate-Ni50Co5o nanocomposites (B) correlation between alginate-NiCo solid solution composition and face-centered cubic crystal parameters. (Adapted from [50]).

Fig. 9.14 (A) Photographs of biodegradability of neat PLA and PLA-based nanocomposite recovered from compost with time. Initial size of the crystallized samples was 3 x 10 x 0.1 cm3.

Nanoclay particles by virtue of their particulate nature are emerging as effective heterogeneous nucleating agents for polyesters. The nanoclay particles in PET/montmorillonite nanocomposites impart to PET a higher crystallization rate without the need for expensive nucleating agents. 

F. J. Medellin-Rodriguez, C. Burguer, B. S. Flsiao, B. Chu, R. Vaia, S. Phillips, Time-resolved shear behavior of end tethered nylon 6-clay nanocomposites followed by non-isothermal crystallization, Polymer, vol. 42, pp. 9015-2023, 2001. 

Wax Crystal Control Nanocomposites Stimuli-Responsive Polymers... 

Cheng Q (2010) Green nanocomposites reinforced with cellulosic crystals isolated from juvenile poplar. In Proceedings International Convention of Society of Wood Science and Technology and United Nations Economic Commission for Europe - Timber Committee October 11-14, Geneva, Switzerland, Paper NT-6 1... 

In rubber-plastic blends, clay reportedly disrupted the ordered crystallization of isotactic polypropylene (iPP) and had a key role in shaping the distribution of iPP and ethylene propylene rubber (EPR) phases larger filler contents brought about smaller, less coalesced and more homogeneous rubber domains [22]. Clays, by virtue of their selective residence in the continuous phase and not in the rubber domains, exhibited a significant effect on mechanical properties by controlling the size of rubber domains in the heterophasic matrix. This resulted in nanocomposites with increased stiffness, impact strength, and thermal stability. 

For both EPDM-LDH and XNBR-LDH nanocomposites, the various tensile properties are summarized in Table 13 and their typical stress-strain plots are shown in Fig. 58 [104]. In Fig. 58a, the gum vulcanizates of both rubber systems showed typical NR-like stress-strain behavior with a sharp upturn in the stress-strain plot after an apparent plateau region, indicating strain-induced crystallization. With the addition of LDH-C10 in the XNBR matrix, the stress value at all strains increased significantly, indicating that the matrix undergoes further curing (Fig. 58b). 

---