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Nanomaterials 2015, 5(1), 366-375; doi:10.3390/nano5010366

On the Mass Fractal Character of Si-Based Structural Networks in Amorphous Polymer Derived Ceramics

Department of Materials Science, University of California at Davis, Davis, CA 95616, USA
Present address: Department of Chemical Engineering, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
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Author to whom correspondence should be addressed.
Academic Editor: Emanuel Ionescu
Received: 6 February 2015 / Revised: 7 March 2015 / Accepted: 9 March 2015 / Published: 17 March 2015
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Abstract

The intermediate-range packing of SiNxC4−x (0 ≤ x ≤ 4) tetrahedra in polysilycarbodiimide and polysilazane-derived amorphous SiCN ceramics is investigated using 29Si spin-lattice relaxation nuclear magnetic resonance (SLR NMR) spectroscopy. The SiCN network in the polysilylcarbodiimide-derived ceramic consists predominantly of SiN4 tetrahedra that are characterized by a 3-dimensional spatial distribution signifying compact packing of such units to form amorphous Si3N4 clusters. On the other hand, the SiCN network of the polysilazane-derived ceramic is characterized by mixed bonded SiNxC4−x tetrahedra that are inefficiently packed with a mass fractal dimension of Df ~2.5 that is significantly lower than the embedding Euclidean dimension (D = 3). This result unequivocally confirms the hypothesis that the presence of dissimilar atoms, namely, 4-coordinated C and 3-coordinated N, in the nearest neighbor environment of Si along with some exclusion in connectivity between SiCxN4−x tetrahedra with widely different N:C ratios and the absence of bonding between C and N result in steric hindrance to an efficient packing of these structural units. It is noted that similar inefficiencies in packing are observed in polymer-derived amorphous SiOC ceramics as well as in proteins and binary hard sphere systems. View Full-Text
Keywords: polymer derived ceramics; mass fractal; nuclear magnetic resonance (NMR); structural packing polymer derived ceramics; mass fractal; nuclear magnetic resonance (NMR); structural packing
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Sen, S.; Widgeon, S. On the Mass Fractal Character of Si-Based Structural Networks in Amorphous Polymer Derived Ceramics. Nanomaterials 2015, 5, 366-375.

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