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MIT World Peace University

School of Polymer Engineering

The formation and electrical properties of vapour phase polymerised polypyrrole films on dip-coated polyethylene oxide (PEO)-cupric chloride substrates have been studied with respect to different deposition parameters. The substrate speed (U) during the dip-coating process affects the film thickness (d) and a relationship of the type da Un with n = 0.27 is followed. The X-ray diffraction studies reveal a distinct formation of ordered polypyrrole moieties but these are very small in size/number. The conductivity of the films increases very rapidly with the exposure time to pyrrole vapours as well as the concentration of the cupric chloride used in the complex. A sharp variation of conductivity with film thickness is also observed for thicknesses lower than 5 μm. These various results have been explained on the basis of formation of conducting polypyrrole domains in the crystalline regions of the polyethylene oxide complex giving rise to a composite type material in which the concentration and packing of the conducting moieties depend on the different deposition parameters used. © 1997 Elsevier Science S.A.

World University root node

Engineering and Technology

Thin Solid Films

Application of dip-coating process for depositing conducting polypyrrole films

The aging behaviour of conductivity in vapour phase deposited polypyrrole films has been investigated after storage in dry ambient temperature conditions. The decrease of conductivity with time is found to be complex suggesting a two-stage process. The rate of decrease of conductivity is also found to be dependent on the concentration of the dopant. Studies on changes in anisotropy and the X-ray photoelectron spectra suggest that morphological features and displacement of the dopant ions could be important factors governing the aging behaviour of these films. © 1997 Elsevier Science Limited.

Polymer Degradation and Stability

Long-term aging and stability of conductivity in vapour phase deposited polypyrrole films

The effect of CaCO3 on the crystallization behaviour and the modification of structure in polypropylene (PP) has been investigated using X-ray diffraction and optical microscopy. The crystallization half time deduced from spherulitic growth rate was found to vary sharply and decreased considerably from 5-6 min for pure polymer to less than 2 min in the presence of CaCO3. The ultimate spherulite size also decreased considerably for PP containing CaCO3. Its dependance on composition however, showed a plateau region at about 10-15 wt % of additive. The intensities of certain reflections especially the 130 and 040 of the α phase were greatly affected by the presence of CaCO3 and large variations in the crystallinity (Ci) values were observed with composition. The ratio of intensities of 130 and 040 reflections and the Ci revealed a maximum at a certain concentration of CaCO3. The above results can be explained on the basis of nucleation and preferential growth of the α phase of PP crystallites. © 1996 Chapman &amp; Hall.

Journal of Materials Science

Effect of CaCO3 on the crystallization behaviour of polypropylene

The structure and morphology of para-nitroaniline dispersed in various polymers such as polymethyl methacrylate, polyvinyl alcohol, polvinyl acetate and polyethylene oxide were investigated by X-ray diffraction and optical polarizing microscopy as a function of composition. At low concentrations the material showed little structure but at concentrations above 40% high crystallinity was observed. Although in all cases the crystal structure conformed to the monoclinic one with a = 12.33 Å, b = 6.07 Å, c = 8.59 Å and β = 91.45°, the intensities of different peaks especially the 101 and 012 reflections as well as the type of growth habit and morphology were strongly dependent on the polymer used.

Materials Letters

Matrix mediated control of morphology in para-nitroaniline dispersed polymeric composites

Polypyrrole molecular composites were prepared by in situ deposition in poly(ethylene oxide) complexes with copper chloride blended with polystyrene. The electrical conductivity of these materials showed some peculiar features such as anisotropy, sharp change with temperature and nonlinear I-V characteristics which were enhanced at a particular composition or certain deposition condition. These various results have been explained on the basis of phase-segregated morphology and a Poole-Frenkel type of conduction process, and are confirmed by detailed studies of the I-V characteristics.

Synthetic Metals

Charge transport processes in polypyrrole nanoscale composites

The crystallization in polyethylene oxide/polymethyl methacrylate (PEO/PMMA) blends was investigated with respect to composition and different casting solvents. Sharp changes in the intensities of the major reflections (120 and 112/004 from PEO) were observed in their X-ray diffraction scans when these blends were cast from different solvents. Large deviations were noted in the crystallinity values as well as the intensities of the peaks from those expected from simple rules of mixture or dilution law. The various results could be explained on the basis of restricted growth of the PEO crystallites along certain directions in the presence of PMMA. Copyright © 1996 Elsevier Science Ltd.

Polymer

Effect of casting solvent on the crystallization in PEO/PMMA blends

A conducting polymer-based chemical sensor was fabricated by depositing a film containing polyaniline blended with polyethylene oxide and doped with copper chloride onto interdigitated electrodes in a surface cell configuration. It was found to be very sensitive to alcoholic vapours, especially methanol. Its characteristics such as response time (tr), recovery time (td), sensitivity factor (σmax/σ0), etc. have been studied with respect to film composition, chemical vapour dosage, etc. It was found that the sensitivity was maximum and tr minimum at a certain concentration of polyaniline in the film matrix. Although the response was quite fast (tr&lt; 10 s), the recovery was slow and in many cases followed a two-step process. The two components in the recovery were clearly delineated in log-log plots, from which one could be associated with diffusion and the other with selective residual adsorption of the chemical vapour by the conducting polymer moieties. These results have been discussed in the light of the charge transport mechanism and the formation of interfacial barriers between polyaniline domains.

Advanced Materials for Optics and Electronics

Conducting polymer-based chemical sensor: Characteristics and evaluation of polyaniline composite films

The electrical properties of poly(ethylene oxide) gels incorporated with CuCl2 and polypyrrole were investigated with respect to temperature, concentration of CuCl2 and the degree of crosslinking. Highly conducting gels were obtained even at low concentrations of CuCl2 and polypyrrole. The activation energy for conduction and effect of crosslinking and swelling in methanol on the electrical properties strongly indicate the hybrid nature of these materials. The conduction process was predominantly of the electronic semimetallic type with some contribution from ionic mobility. © 1995.

Polypyrrole in poly(ethylene oxide) gels with copper(ii) chloride: a hybrid conducting polymer

The crystallization behavior, modification of crystalline form, and orientation in polypropylene processed by blow film extrusion was studied as a function of processing parameters as well as different types of additives. The isothermal crystallization rate was greatly enhanced in the presence of certain additives, especially CaCO3. The crystalline form was predominantly α type in both compression molded or blow extruded films. However, there was an unusually large intensity of the α040 peak in the X‐ray diffraction of the latter case films. The variation of the peak intensities and the increase of birefringence with increase of take‐up speed has been explained on the basis of orientation induced by uniaxial stress in the machine direction. This orientation contained two components, namely the orientation of the b axis of the crystallites and the orientation of loosely bound polymer chains in the amorphous regions. © 1995 John Wiley &amp; Sons, Inc. Copyright © 1995 John Wiley &amp; Sons, Inc.

Journal of Applied Polymer Science

Structure development in processing of polypropylene films with additives

Dielectric and rheological measurements are reported for the cure in a series of mixtures of an epoxy‐acrylate with n‐butyl methacrylate. The level of the initiator and properties of the epoxy acrylate and n‐butyl methacrylate influence the cure characteristics and morphology of the film formed. Analysis of the rheological data indicates that during the curing process, microphase separation occurs within the mixture. The changes in the dielectric relaxation behavior with composition of the completely cured material is also consistent with microphase separation occurring in these resins while they are cured. Copyright © 1995 Society of Plastics Engineers