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Open AccessArticle

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
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Author to whom correspondence should be addressed.
Present address: Department of Chemical Engineering, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
Academic Editor: Emanuel Ionescu
Nanomaterials 2015, 5(1), 366-375; https://doi.org/10.3390/nano5010366
Received: 6 February 2015 / Revised: 7 March 2015 / Accepted: 9 March 2015 / Published: 17 March 2015
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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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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