S4.1
Polymer Nanocomposites for Enhanced Electrical and Shape
Memory Functionality
P D Coates1, B R Whiteside1, C Tuinea-Bobe1,
P Spencer 1, G Fei2, D Li2, G Li2 & H Xia2
2
1
Polymer IRC, University of Bradford, Bradford BD7 1DP, UK, and
State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065, China.
Abstract
Microinjection molding has emerged as an efficient way to manufacture devices which
contain surface micro-features using a wide range of polymers with high accuracy.
In our initial research [1], polyurethane -carbon nanotube (CNT) composites were
micromoulded, and the electrical conductivity studied, including the use of postmoulding annealing to optimize conductivity. Quantification of the structures obtained,
including in-situ TEM with detailed statistical analysis of the images, and computer
modeling of conductivity have been undertaken. It has been found that the electrical
conductivity of microinjection molded parts is relatively low due to the high shear rates
prevalent in the process. An annealing treatment improves the electrical conductivity
by several orders of magnitude, although there are only nanoscale changes in the
CNTs network (most probable nearest neighbour distance only decreases by several
nanometres on annealing). A mechanism of residual stress release in the polymer at the
CNT interface is proposed, and supported by Raman band shifts (the G+ band, 1590 cm -1,
is sensitive to strain) [2, 3].
Secondly, shape memory polyurethane-carbon nanotube composites were prepared by
twin-screw melt extrusion and subsequently processed using microinjection molding
to obtain components with surface micropatterns (a circular Fresnel lens). An electroactivated surface micropattern tuning system was developed which could recover the
original micropatterned surface of the components after a thermal deformation had
been imposed. This was achieved by applying a current which heats the component by
resistive heating. In order to optimize the technique, three key areas were investigated
in this work: conductivity of the microinjection molded microparts, the retention of
shape memory micropatterns on the surface of microparts during annealing treatment,
and the macroscopic area shrinkage of microparts after thermal treatment.
The required annealing treatment to improve electrical conductivity can be detrimental
to the dimensional stability of the micropatterns, which depends significantly on
particular micro-injection molding parameters, especially the mould temperature.
Increasing the mould temperature, melt temperature, injection speed and injection
pressure all result in better retention of the micropattern and improved dimensional
stability after annealing [4].
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Our research demonstrates the potential of electro-activated surface micropattern
control for microinjection molded electrically conductive shape memory polymer
composites, which could be a promising technology for a range of application areas
including: electro-adjustable adherence, information storage, and anti-counterfeiting
technology.
References
1. H. S. Xia, P. Coates, D. X. Li, G. X. Fei and Q. C. Gong, 2012, Parts. WO 2012/089998 A2.
2. Lucas M, Young RJ. Effect of residual stresses upon the Raman radial breathing modes of nanotubes in epoxy
composites. Composites Science and Technology 2007;67(5):840-3.
3. Tishkova V, Raynal P-I, Puech P, Lonjon A, Fournier ML, Demont P, et al. Electrical conductivity and Raman imaging
of double wall carbon nanotubes in a polymer matrix. Composites Science and Technology 2011;71(10):1326-30
4. G Fei, C Tuinea-Bobe, D Li, G Li, B Whiteside, P Coates, H Xia, RSC Adv., 2013, 3, 24132–24139.
Keywords: conductivity, shape memory, polymer nanocomposite, micromoulding
Short Biography
Professor Phil Coates FREng is Professor of Polymer Engineering at the University of
Bradford, UK and Associate Director of the internationally recognised Interdisciplinary
Research Centre (IRC) in Polymer Science and Technology, with some 30 researchers.
He has published extensively - some 300 papers, in scientific journals and international
conferences, co-authored 5 books, and edited 11 books. His research is internationally
recognised, with many keynote addresses and worldwide collaborations (particularly
Europe, N America, China, Australia and Japan), and he has developed the UK centre
for in-process measurements. His research interests include; (i) analysis/modelling of
polymer processing mechanics, involving experimental characterisations of the solid
and fluid phase rheology of polymers, with novel rheo-optical, ultrasound techniques
and in-process spectroscopy; (ii) processing machinery design and control of processing,
especially in the fields of injection moulding, extrusion and reactive processing encompassing determination of process dynamic responses to the de-convolution
of machine and raw material variables for real time closed loop process control; (iii)
computer modelling of solid and melt phase processing - used in process design and
control (with a licensed polymer orientation process), and for insight into deformation
and flow mechanisms - his new computer modelling research centre adjoins the
experimental laboratory. He holds honorary Professor positions at Sichuan University
and Beijing University of Chemical Technology.
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