university of bayreuth

DMM

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PC M2200 - 2.0 % MWCNT

compression moulded sample - good dispersion

s = 2.7 x 10E-9 S/m

PC M2200 - 2.0 % MWCNT

after 1 h at 250 ˚C - agglomaration

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(i) (ii)

(iii)

(i)� Agglomeration & Clustering� --> Formation of percolated networks(ii)�Destruction and interruption of

electrically conductive pathways(iii)�Oscillations in s with increasing

amplitude� --> Deformations of clusters

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Based on our experimental data, the existing models [1-3] can be extended.

This model illustrates the development of electri-cal conductivity by the incorporation of MWCNT into Polycarbonate.Partially bent nanotubes (black), forming agg-glomerates (circles) through entanglements and bonds. These clusters are embedded in the poly-mer matrix. The clustering of agglomerates, lea-ding to electrical conductivity, is highlighted by the contacting circles.

Observations in terms of electrical conductivity are interpreted as the superpositi-on of three contributing phenomena:(i) Formation and reformation of percolated electrically conductive networks through agglomeration and clustering of nanotubes.(ii) Destruction / interrruption of pathways of clusters leading to decreasing electri cal conductivity at high shear amplitudes.(iii)Deformation of clusters / MWCNT-MWCNT bonds emerging in oscillations in electrical conductivity.

PC / MWCnt - nanoCoMPosites

University of Bayreuth - Polymer Engineering Universitaetsstr. 30 - 95447 Bayreuth - Germany

Contact person: Dipl.-Ing. Rico ZeilerEmail: rico.zeiler@uni-bayreuth.de www.polymer-engineering.de

Abstract Motivation and ObjectivesInfluence of molar mass (using a high-viscosity and a low-viscosity poly-carbonate) on the formation of networks of multiwalled carbon nanotu-bes (MWCNTs) in shear was investigated.The formation of electrical and rheological networks proceeds more ra-pidly at higher temperatures and thereby a lower-viscosity matrix.Lower temperatures cause a larger stress-transfer and the breakup of the electrical network intensifies.Sinusoidal shear deformations give rise to oscillations in electrical con-ductivity.

Formation of electrical networks of multiwalled carbon nanotubes (MWCNT) in a polycarbonate (PC) matrix in oscillatory shear flows Rico Zeiler, Ulrich A. Handge, Dirk J. Dijkstra, Helmut Meyer, Volker Altstädt

Materials

References and Notes[1] F. Du et al. Polym. Sci. B Polym. Phys. 41(24) (2003) 3333-3338[2] P. Pötschke et al. Polymer 45(26) (2004) 8863-8870[3] I. Alig et al. Phys. Status Solidi B 244(11) (2007) 4223-4226 and in Polymer 49 (16) (2008) 3524-3532[4] R. Zeiler et al. Polymer 52(2) (2011) 430-442[5] U.A. Handge et al. Rheol. Acta, published online 12 June 2011

Strain amplitude dependent behaviour

Especially in the field of conductive polymer composites, CNTs are ideal candidates for use as filler materials; due to their high length-to-diameter ratio in the 100-1000 range they can form percolated struc-tures at very low filler concentrations.Electrical measurements can reveal the existence of a percolated net-work of conductive fillers in an isolating matrix [1-3].Oscillatory melt rheology is a sensitive tool to probe the structure of polymer melts.Simultaneous rheological and electrical investigations of polycarbo-nate composites are the focus of this study [4-5].

Two different batches of neat polycarbonate (PC) with different molecular weight distributions: Makrolon® M2200 and M2800.Composites containing 0.5, 1.0, 1.5, 2.0, 3.0 and 5.0 wt% Baytu-bes® (MWCNTs from Bayer MaterialScience AG).Simultaneous rheological and elecrical measurements were performed using a plate-plate geometry with electrically isola-ted tools.

Dynamic mechanical analysisDynamic mechanical analysis in the melt was performed at a frequency of 1 Hz and a deformation amplitude of 5 % at 280 °C.

Results and discussion

Strain sweeps with increasing shear amplitude were conducted.Strain amplitude ranged from 0.4 to 300 % at a frequency of 0.1 rad/s.

Summary and conclusions

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The addition of MWCNT leads to an increase in G‘ for temperatures above Tg and particular for higher temperatures, solid-like behaviour is exhibited.The percolation threshold is situated between 0.5 wt% and 1.0 wt% for the PC M2200 composites and between 1.0 wt% and 1.5 wt% for the PC M2800 composites.According to frequency sweep (not shown) and strain amplitude sweep experi-ments, a lower matrix viscosity yields a lower percolation threshold for electrical conductivity.The electrically conductive networks persist below the glass transition temperature and thereby maintain in the glassy state of the PC composites.The formation of electrical conductivity is a degressive process facilitated by high temperature and low matrix viscosity and proceeds faster with higher filler content.

(i) Agglomeration & Clustering--> Formation of percolated networks

(ii) Destruction and interruption of electrically conductive pathways

(iii)Oscillations in s with increasing amplitude--> Deformations of clusters