No abstract

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 isconsidering the observed good deformabilityvery 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.

The dielectric and conductivity behavior of some selected solid polyelectrolyte-surfactant complexes (PE-surf) is characterized by broadband dielectric spectroscopy in the frequency range 10-*-107 Hz. Depending on phase-morphology and volume fraction of alkyl-tails, electrical conductivities at room temperature of up to lo4 S/cm are found. In addition, the behavior at low temperatures is characterized by two distinct p-relaxations which show an Arrhenius-like activation, and their relaxation strength depends on temperature, in contrast to the standard behavior of dielectric media. The relaxations are assigned to surfactant movements, the number or strength of which increase with temperature, which are obviously important already well below the glass transition temperature of the ionic layers. Doping of a selected complex showing a rather high basic conductivity with LiC104 results in a decrease of the conductivity, which is explained by an increase in the glass transition temperature of the ionic layer.

Ultrathin layers of organic materials have great potential in advanced electronic and electro‐optical applications. Little is, however, known about the dielectric properties and molecular dynamics of Langmuir‐Blodgett film‐forming materials. Here, thin LB films of the title compound have been studied and their properties compared with those of the corresponding bulk materials.