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Free-standing polyelectrolyte multilayer membranes have been formed by the layer-by-layer technique using a dip-coating apparatus. The polymer-chain mobility has been studied by 1H relaxation in the rotating frame T 1rho NMR with 13C chemical shift resolution. For each of the individual polymers a single relaxation component has been observed for all resolved signals. In the multilayer a significantly different relaxation time T 1rho has been observed with a minor second component. The interaction between the oppositely charged polyelectrolytes influences the molecular mobility.

The dynamics of spin-labeled poly(acrylic acid) (PAA) in polyelectrolyte complexes (PECs) has been studied by EPR. It has been found that the segmental mobility of the PAA in the PECs is nearly constant in the pH range 10 to 5 but decreases dramatically for pH < 5. Recently, we have studied the dynamics of spin-labeled poly(ethylene-alt-maleic acid) (P(E-alt-MA)) in PECs. The rotational mobility of the P(E-alt-MA) has been observed to depend on pH, which has been related to the formation of hydrogen bonds of the maleic acid units at low pH [Macromolecules 2015, 48, 3577]. To test this hypothesis, in the present study, P(E-alt-MA) has been replaced with PAA, which is a structural isomer of P(E-alt-MA). Now with the results for PAA at hand, we can conclude that the low mobility of the P(E-alt-MA) at low pH cannot be exclusively attributed to the presence of maleic acid units. Nevertheless, it has been confirmed that the dynamics in the PECs is strongly influenced by the degree of dissociation of the weak po...

A nitroxide spin label has been covalently linked to the weak polyacid poly(ethylene-alt-maleic acid) (P(E-alt-MA)) to study the rotational mobility of the polyacid backbone in polyelectrolyte complexes (PEC) formed with the oppositely charged strong polycation poly(diallyldimethylammonium chloride) (PDADMAC) in dependence on the pH of the dispersion and the temperature. The rotational mobility of the polyacid chain segments has been determined by simulation of the line shape of the continuous wave (CW) electron paramagnetic resonance (EPR) spectra using the microscopic order/macroscopic disorder (MOMD) model of restricted rotational diffusion. The study has shown that the diffusion coefficient characterizing the rotational motions of the polyacid backbone is significantly smaller at low degree of dissociation at pH 4 than at high degree of dissociation at pH 7 and pH 10.

The local dynamics in polymer melts and the impact of external shear in a Couette geometry have been investigated using rheological nuclear magnetic resonance (NMR). The spin-spin relaxation time, T2, which is sensitive to chain-segment motion, has been measured as a function of shear rate for two samples of poly(dimethylsiloxane). For the low-molecular-weight sample, a mono-exponential decay is observed, which becomes slightly faster with shear, indicating restrictions of the polymer chain motion. For the high-weight sample, a much faster bi-exponential decay is observed, indicative of entanglements. Both components in this decay become longer with shear. This implies that the free polymer segments between entanglements become effectively longer as a result of shear.

A nitroxide spin label has been covalently attached to the polyelectrolyte poly(ethylene-alt-maleic acid) (P(E-alt-MA)) to study the interaction between this weak polyanion, the oppositely charged strong polycation poly(diallyldimethylammonium chloride) (PDADMAC) and water in swollen polyelectrolyte multilayers (PEM) by electron paramagnetic resonance (EPR) spectroscopy. If the spin-labeled polyanion has been used for the preparation of every double layer, the growth of the PEM film can be monitored by quantitative EPR. On the other hand, if the spin-labeled polyanion has been selectively placed in different layers in the PEM film the influence of the environment such as pH of the swelling medium of the mobility of the polyelectrolyte molecules positioned in the selected layer can be investigated.

The influence of maltose-modified poly(propylene imine) (PPI) dendrimers on dimyristoylphosphatidylcholine (DMPC) or dimyristoylphosphatidylcholine/dimyristoylphosphatidylglycerol (DMPC/DMPG) (3%) liposomes was studied. Fourth generation (G4) PPI dendrimers with primary amino surface groups were partially (open shell glycodendrimers — OS) or completely (dense shell glycodendrimers — DS) modified with maltose residues. As a model membrane, two types of 100nm diameter liposomes were used to observe differences in the interactions between neutral DMPC and negatively charged DMPC/DMPG bilayers. Interactions were studied using fluorescence spectroscopy to evaluate the membrane fluidity of both the hydrophobic and hydrophilic parts of the lipid bilayer and using differential scanning calorimetry to investigate thermodynamic parameter changes. Pulsed-filed gradient NMR experiments were carried out to evaluate common diffusion coefficient of DMPG and DS PPI in D2O when using below critical micelle concentration of DMPG. Both OS and DS PPI G4 dendrimers show interactions with liposomes. Neutral DS dendrimers exhibit stronger changes in membrane fluidity compared to OS dendrimers. The bilayer structure seems more rigid in the case of anionic DMPC/DMPG liposomes in comparison to pure and neutral DMPC liposomes. Generally, interactions of dendrimers with anionic DMPC/DMPG and neutral DMPC liposomes were at the same level. Higher concentrations of positively charged OS dendrimers induced the aggregation process with negatively charged liposomes. For all types of experiments, the presence of NaCl decreased the strength of the interactions between glycodendrimers and liposomes. Based on NMR diffusion experiments we suggest that apart from electrostatic interactions for OS PPI hydrogen bonds play a major role in maltose-modified PPI dendrimer interactions with anionic and neutral model membranes where a contact surface is needed for undergoing multiple H-bond interactions between maltose shell of glycodendrimers and surface membrane of liposome.