Structure and dynamics of electroactive polymers
By “electroactive polymers” it is meant electronic conducting polymers, ionic conducting
polymers and mixed conducting polymers. Structures and microstructures are more
particularly studied. In addition, molecular dynamics is also investigated by using incoherent
inelastic and quasielastic neutron scattering techniques.
In more details
Our favorite experimental tools mainly consist in X-ray and neutrons diffraction and
scattering techniques. By this way, the molecular arrangement can be explored at different
length scales. The molecular dynamics is investigated on different energy scales (typically
from the intramolecular vibrational domain with 10-14 – 10-15 s as characteristic times towards
diffusive motions of big molecular fragments whose characteristic times lie in the 10 -11- 10-9 s
range). All these measurements are possible only by using several different instruments. In
addition to home made X-ray diffractometers in the lab, small angle X-ray and neutron
scattering experiments are also carried out ( D24 at LURE – Orsay – France and D11 at ILL –
Grenoble – France). For molecular dynamics measurements, time of flight spectrometers (IN6
at ILL and IRIS at RAL – Chilton – Great Britain) and backscattering spectrometers (IN10,
IN13 and IN16 at ILL) are mainly used.
During these three last years, we have mainly studied two families of electroactive polymers:
1- PEO (polyethylene oxide) and azobenzene based “rod-coil ” molecules (see figure
below) that are designated as PEGAZOH and DiAZOH. The azobenzene entity is well
known for its trans-cis isomerization property when it is irradiated by UV light. If
these molecules are mixed with a high mass PEO and a perchlorate lithium salt, the
C6H13 NN O(CH2CH2O)nCH3
O N N C6H13
C6H13 N N O O
ionic conductivity of the obtained polymer electrolyte can be reversibly modulated as
much as 70 to 90 % when UV light is turned on and off in a temperature range from
room temperature to 90°C. These molecules were studied in the pure state and when
mixed with the electrolyte by using in situ SAXS measurements in order to understand
their structural evolution from dark to illuminated state. We found the impact on the
electrical properties is essentially due to a release of additional charge carriers via the
individual conformational changes of the active molecules. These conclusions could
be obtained because we could measure the different involved kinetics in these
structural changes and we could do the comparison with the kinetics of the
corresponding changes of the ionic conductivity.
2- conducting polyaniline (PANI) doped by organic sulfonic acids.
In the electronic conducting polymers family, polyaniline is of most importance. It is
first one of the most chemically stable once prepared in its conducting state. More
recently, US scientists succeeded to prepare one solution containing the polymer and
the camphor sulfonic acid (figure 1), from this moment it has been much more easier
to obtain conducting free standing films and fibers. Moreover, PANi doped with these
Figure 1 : polyaniline fragment
in interaction with a CSA ion.
CH3 Camphor Sulfonic Acid
O S O
O C O H
Figure 2 : Main sulfonated organic
C SO3H acids with which metallic polyaniline
based films are prepared
1,2-benzenedicarboxylic acid, 4-sulfo-1,2-
1,2-benzenedicarboxylic acid 4-sulfo-1,2-di(2-
sulfonic organic acids give metallic samples in a 300 down to 250 or 200 K depending on the
used counter-ion. At these latter temperatures is always occurring a broad electrical transition
leading to a semi-conducting state. The main acids we used are shown in the figure 2. The
molecules having aliphatic tails can not only dope the polymer but also play the role of a
plasticizing agent. These molecules have especially designed at the CEA in a research
program aiming to the achievement of a true “conducting plastic”. In addition to the structural
study of these compounds we have brought our attention to the study of the molecular
dynamical disorder existing in these materials by using quasielastic neutron scattering
techniques. We could show first that, in the explored energy domain, the polyaniline chains
could be considered as very stiff objects whose dynamics is only vibrational in nature. The
whole information obtained in these experiments was thus coming from localized diffusive
motions of the counter-ions. Second, we always found the existence of a dynamical transition
of the counter-ions precisely in the temperature range in which the metal-insulator transition
is also occurring. In other words, we found a microscopic probe whose the messages can be
recovered at a macroscopic level when considering the electrical conductivity of the sample
itself. Additional work is in progress in order to try to understand these results in more details.
David Djurado : Chargé de Recherche au CNRS
Marc Bée : University of Grenoble and Institut Laue Langevin - Grenoble (France).
Jérôme Combet : Institut Charles Sadron - Strasbourg (France).
Patrice Rannou, Adam Pron, Jean Pierre Travers : CEA Grenoble (France).
Didier Delabouglise: LEPMI, ENSEEG, INP Grenoble;
Emil Samuelsen : University of Trondheim (Norway).
Wojciech Luzny : University of Mining and Metallurgy of Krakow (Poland).
Miguel Angel Gonzalez : Institut Laue Langevin - Grenoble (France).
DJURADO D., NICOLAU Y.F., RANNOU P., LUZNY W., SAMUELSEN E., TERECH P.,
BEE M., SAUVAJOL J.L.
An overall view of the structure of an heterogeneous medium :the conducting polyaniline
Synthetic Metals, vol. 101, p. 764-767 (1999).
Abstract : The structures of free standing films of polyaniline (PAni) protonated by camphor
sulfonic acid (CSA) are characterized by different scattering techniques :WAXD, IINS,SANS,
and SEM. In this way, we could investigate the complex structural arrangement of these films
at different length scales. It is shown that a unique description of structure and microstructure
of such films is not realistic since they tightly depend on the conditions of preparation and
processing. This contribution gives an account of the most important structural data obtained
on films prepared in Grenoble during the four last years.
D. DJURADO, J. COMBET, M. BÉE, P. RANNOU, A. PRON.
Molecular Dynamics in PANI/CSA as seen by quasielastic neutron scattering
Synth. Metals, vol.. 119, p. 411- 412 (2001).
Abstract: Molecular dynamics has been measure in fully hydrogenated (PANI-h5/CSA) and
partially deuterated (PANI-d4/CSA) samples. Quasielastic neutron scattering (QENS)
measurements have been performed on time of flight (IN6 at ILL – Grenoble – France),
backscattering (IN16 at IL° and on time –of-flight inverted geometry (IRIS at RAL – Chilton
– Great Britain) spectrometers. The obtained results suggest that the polymer chains are very
stiff objects giving none quasielastic contribution and that all the counter-ions are not
dynamically equivalent. The so-called rotation rate distribution model can satisfactorily
describe the motion of methyl groups of CSA ions. This rotation can be considered as a quasi-
free one at high tempeartures (270<T<330K) while for T<270K the inter-molecular effects
turn more effective to broaden the correlation times distribution. Finally, an overall motion of
the CSA ion itself has been detected on IN16 and on IRIS at high temperature. Thus dynamics
also experiences a transition around 280K. It is noticeable that all these changes of dynamics
exactly occur in the temperature range in which a metal-insulator electrical transition is also
M. BÉE, D. DJURADO, J. COMBET, M. TELLING, P. RANNOU, A. PRON,
Dynamics of Camphor Sulfonic Acid in Polyaniline (PAni-CSA) : A Quasielastic Neutron
Physica B, vol.301, p. 49 – 53 (2001).
Abstract: PolyAniline (PANI) doped by camphor sulfonic acid (CSA) exhibits an electronic
conductivity of several hundreds of S/cm. All the authors agree to invoke in various extents
the role of disorder in the evolution of the transport properties as a function of the
temperature. The IRIS spectrometer at the Rutherford-Appleton-Laboratory was used to
remove uncertainties of previous IN6-IN16 experiments at Institut Laue langevin. The rigidity
of the PANI chains was confirmed, in both a conducting and a partially doped samples. All
the observable quasielastic scattering occurs from the CSA dynamics. However, this
contribution is too weak in the case of the partially doped specimen to conclude about the
coupling of the counter-ion disorder with the electronic transport properties.
D. DJURADO, M. BÉE, J. COMBET, B. DUFOUR, P. RANNOU, A. PRON, J.P.
Is the dynamics of counter-ions a probe of the microscopic mechanisms of the electronic
transport in conducting polyaniline ?
ILL Annual Report 2000 – Scientific highlights p. 62 – 63.
Abstract: Polyaniline, protonated by an organic sulfonic acid, is a new generation of
electronic conducting polymers. Stable, conducting, flexible films (conductivity = 150 to
500 S/cm at room temperature) can be cast from a solution. In general, these films exhibit a
broad transition from a metal-like regime to an insulating one when the temperature is
lowered. The origin of this transition is still debated. Lattice disorder is generally thought to
be responsible of this behaviour but the respective role played by polymer chains and
counter-ions in this transitio remain unclear. Incoherent neutron scattering techniques have
been used in order tostudy the lattice dynamics without being obscured by the presence of
mobile electronic charges. The results suggest that the dynamical disorder of the counter-
ions and the metal-like conduction regime are related.