Conductive Composite Fibers with a Rigid-Rod Matrix
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CONDUCTIVE COMPOSITE FIBERS WITH A RIGID-ROD MATRIX
KONSTANTINOS BELTSIOS AND S. H. CARR Engineering Science and Materials 60208 University, Evanston, IL
Department,
Northwestern
ABSTRACT Conductive composite fibers are prepared by dry-jet wet-spinning of a strong-acid solution of rod-like polymers and phthalocyanine(Pc) A model yielding a hierarchical structure for a pure compounds. The inclusion of NiPc in the rigid-rod fiber is described first. spinning dope leads upon coagulation to isolated NiPc domains that are predicted to correspond to body centered cells (exhibiting The observed dependence of fiber various degrees of disorder). conductivity of composition is explained in terms of tunneling and percolation processes. STRUCTURE OF RIGID ROD FIBERS Reports on neat rigid rod fibers document the presence of a hierarchy of solid domain widths: 3-10Mm, 50-60Mm, 0.5-0.6Mm, 5Mm. in the In addition, axial (i.e. [1-4, 8 and references therein] fiber length direction) characteristic dimensions are found in a variety of size scales, at least in some of the neat rigid rod report for poly(p(1983) fibers. For example, Panar, et al. phenyleneterephthalamide) (PPTA) a 30 to 40nm length (described as 'defect spacing'), a 250 nm spacing ('defect zone') and also 'tie points', occurring at every 2 to 3Mm (along the fiber direction). The study of composite fibers resulting from the precipitation of phthalocyanines (NiPc, (SiPcO)n, H2 Pc, etc.) and rigid rods from the same strong acid solution have indicated that the phthalocyanines tend to occupy elongated pockets parallel to fiber axis, with aspect ratios such as 5:1 and widths such as 40-50nm (NiPc), 300nm 51-2Mm ((SiPcO)n), (H 2Pc and possibly similar for (SiPcO),, [5-12]. Finally early rigid fiber literature 20Mm((SiPCO)n) indicated the presence of elongated microvoids of typical widths of 4-5 nm and corresponding axial lengths 4 to 5 times larger. The above information taken together may be considered as evidence that for almost every level of rigid fiber hierarchical along with each solid lateral width, there is the structure, potential for a corresponding axial spacing and also for a "Aspect ratios" complementary pair of characteristic openings. (axial length divided by corresponding width) of the order of 5 and scaling factors such as 10, are found. in a fiber of One possible cause for the generation the density upon solid formation is suprastructural 'spacings' in the presence of volume change (and need for adjustment) If such constraints are present over more than one constraints. size scale during the course of structure formation, then multiple The fates of the dimensions may evolve. characteristic
Mat. Res. Soc. Symp. Proc. Vol. 255. 01992 Materials Research Society
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characteristic spacings of the openings are not necessarily the same as those of the spacings of corresponding solid domains. For example, a fiber may increase its bulk density through rearrangement and better packing of the largest of the structural units, thus causing a reduction in the size
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