The dielectric and mechanical relaxation of two
different polyelectrolyte−lipid complexes with a stack-of-bilayer morphology is characterized by broad band dielectric
spectroscopy in the frequency range between
10-2 and 107 Hz and by dynamic shear
relaxation experiments. With these experiments, we compare
a
synthetic model system consisting of polyacrylic acid and
didodecyldimethylammonium counterions (PAA−C12
2) with the complex of a fraction of soybean
lecithine and a cationic polyelectrolyte (PDADMAC−Lec).
The lamellar morphologies consisting of stacks of bilayers are
characterized by quantitative small angle
X-ray scattering measurements. PAA−C12
2
shows in the mechanical experiment two β-relaxation
processes
and exhibits at room temperature a storage modulus of G‘ ≈
200 MPa which isconsidering the observed
good deformabilityvery high. The whole behavior is similar to
high-performance loaded rubbers and
reflects the extraordinary mechanical response of the lamellar
superstructure. For PDADMAC−Lec, a
less structured relaxation behavior and lower moduli are found.
Above the glass transition, a transition
zone is observed which is followed by a rubbery plateau with
G‘ being still on the order of 1 MPa.
Considering
the very high deformability of this material, the natural
polyelectrolyte lipid complex turned out to be an
excellent rubbery material. In the dielectric relaxation
experiment, both systems show a very similar
behavior which is regarded to be typical for a stack-of-bilayer order.
At low temperatures, localized
β-relaxations are described which are tentatively assigned to lipid
motions. In addition, both systems
exhibit a transition from a nonohmic to an ohmic conductivity which
occurs close to the softening point
of the polyelectrolyte layers.