Polymer materials are commonly reinforced with organic or inorganic fillers to improve their mechanical properties and to reduce the cost. Such reinforcement strongly depends on the characteristics of fillers (e.g. size, shape, aspect ratio and surface feature) and their dispersion in polymer matrix. The use of inorganic fillers exploits the synergistic effect of high mechanical strength and heat durability of fillers and processing ease of polymers. However, it often causes interfacial incompatibility and an increase in density and a loss of tenacity and opacity. Because layered clays possess rich intercalation chemistry and can be delaminated into disk-like nanopartciles, we investigate the possibility of developing polymer nanocomposites from montmorillonite (MMT). As a result, two nanomaterials, intercalated polyaniline (PANI) nanocomposites and exfoliated PS nanocomposites, have been fabricated via in situ polymerization. Morevoer, experimental work shows that the surface modification of clays and the dispersion of organically modified clays (i.e. organoclays) are crucial to the success of fabricating polymer nanocomposites. Therefore, molecular dynamics (MD) simulations are used to investigate such fundamental aspects on the structure and dynamics of organoclays and the interfacial interactions and structure of diblock copolymer (i.e. PU) nanocomposites. The simulated results are in good agreement with the available experimental data. For organoclays, the results indicate that the alkyl chains exhibit strong layered structures in the interlayer space of clays. Such layering behaviors strongly depend on the chain length and layer charge. More importantly, a pseudo-quadrilayer structure is observed for organoclays modified with dioctadecyldimethyl ammoniums in which the alkyl chains do not lie flat within a single layer but interlace and spread into the adjacent layers. Finally, different orientaion of chain segments is found in the middle and end segments, and within and out of the layer structure. For polyurethane (PU) nanocomposites, van der Waals interaction between apolar alkyl chains and PU soft segments dominates the interactions between organoclay and PU. In addition, hydrogen bonding can form between the siloxane oxygen of clay surface and nitrogen (hard segment) or oxygen (soft segments) of PU. Furthermore, there is no distinct phase-separated structure for PU in the nanocomposites, which is attributed to the results of competitive interactions among PU, alkyl ammonium and clay surface.
| Identifer | oai:union.ndltd.org:ADTP/187922 |
| Date | January 2004 |
| Creators | Zeng, Qinghua, Materials Science & Engineering, Faculty of Science, UNSW |
| Publisher | Awarded by:University of New South Wales. School of Materials Science and Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Qinghua Zeng, http://unsworks.unsw.edu.au/copyright |
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