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Surface-attached architectures of p(MEO2MA-co-OEGMA) copolymers are thermoresponsive PEG analogues with potential applications in biotechnology and medicine. In this respect, structure and dynamics of polymer brushes made of these copolymers are of great interest. In this work, the near surface dynamics of a p(MEO2MA-co-OEGMA) brush with a height of 250 nm was investigated with neutron spin echo spectroscopy under grazing incidence (GINSES) conditions. The brush dynamics was studied at two penetration depths of the neutrons. An influence of the distance from the confining surface on the collective diffusion was found. For the first time, the experiment demonstrates the feasibility of studying thermal fluctuations of macromolecules at a single planar liquid/solid interface by neutron spin echo spectroscopy under grazing incidence.

This paper addresses the relation between gold nanoparticle (AuNP) distribution in thermoresponsive polymer brushes and the thermally induced color change of the polymer brush/AuNP hybrids. Therefore, we report on the effect of AuNP surface functionalization on the structure and optical response of the nanoparticles in thermoresponsive poly(N- isopropylacrylamide) (PNIPAM) brushes. Two different types of gold nanoparticles are attached to the PNIPAM brushes: (1) AuNPs that are coated with citrate anions (AuNP-citrate), and (2) AuNPs stabilized with 12-mercaptododecanoic acid ligands (AuNP-MDA). Neutron reflectivity (NR) measurements indicate that the spatial structure of the hybrid depends on the particle type. A strong increase in thickness is observed after attachment of AuNP-citrate; this is not the case for AuNP-MDA. The thermoinduced color change of the PNIPAM/AuNP hybrids depends strongly on the particle type. While a red-shift of the surface plasmon band occurs in case of AuNP-citrate, a blue-shift is found for AuNP-MDA when the temperature is increased above the PNIPAM's volume phase transition temperature. This blue-shift vanishes after a certain number of heating/cooling cycles, indicating a rearrangement of the AuNPs in the brush. The different behavior of AuNP-citrate as compared to AuNP-MDA can be explained by the hydrophobic nature of the 12-mercaptododecanoic acid ligands.

Linearly assembled polyelectrolyte multilayers (PEMs) are prepared by sequential adsorption of polyanions and polycations from 0.1 mol/L NaCl. The internal structure of PEMs is investigated with neutron reflectivity. The films are made from poly(ethylenimine) (PEI), poly(diallyldimethylammonium) (PDADMA) and poly(styrenesulfonate) (PSS or deuterated PSS-d). Each film consists of a protonated and a deuterated block, built from m protonated and n deuterated polycation/polyanion layer pairs, respectively. Annealing in salt solution (1 mol/L NaCl) allows the polyelectrolytes to gain entropy by adopting a more coiled conformation and by intermixing. During annealing the internal interface between the two blocks broadens due to interdiffusion; thus, the PSS diffusion coefficient is measured. Eventually the annealing leads to a uniform distribution of protonated and deuterated PSS throughout the film. Yet, if one polycation layer in the film center is branched PEI, then this PEI layer serves as a diffusion barri...

We have investigated the interactions between cationic poly(amidoamine) (PAMAM) dendrimers of generation 4 (G4), a potential gene transfection vector, with net-anionic model biomembranes composed of different ratios of zwitterionic phosphocholine (PC) and anionic phospho-L-serine (PS) phospholipids. Two types of model membranes were used: solid-supported bilayers, prepared with lipids carrying palmitoyl-oleoyl (PO) and diphytanoyl (DPh) acyl chains, and free-standing bilayers, formed at the interface between two aqueous droplets in oil (droplet interface bilayers, DIBs) using the DPh-based lipids. G4 dendrimers were found to translocate through POPC:POPS bilayers deposited on silica surfaces. The charge density of the bilayer affects translocation, which is reduced when the ionic strength increases. This shows that the dendrimer-bilayer interactions are largely controlled by their electrostatic attraction. The structure of the solid-supported bilayers remains intact upon translocation of the dendrimer. However, the amount of lipids in the bilayer decreases and dendrimer/lipid aggregates are formed in bulk solution, which can be deposited on the interfacial layers upon dilution of the system with dendrimer-free solvent. Electrophysiology measurements on DIBs confirm that G4 dendrimers cross the lipid membranes containing PS, which then become more permeable to ions. The obtained results have implications for PAMAM dendrimers as delivery vehicles to cells.

The structure and dynamics of nanostructure films formed by mixtures of soy phosphatidylcholine and glycerol dioleate at the silicon–aqueous interface were studied by grazing incidence neutron spin echo spectroscopy (GINSES), specular and off-specular neutron reflectometry, and small-angle X-ray diffraction. Reverse hexagonal (HII) and micellar cubic phase (Fd3m) layers at the solid–liquid interface have been identified with neutron reflectometry measurements. A preferred orientation of the liquid crystalline (LC) domains was observed only for the anisotropic HII phase. The size of the LC domains was found to be about 1 micrometer as estimated from the width of the diffraction peaks. GINSES revealed that the cubic phase forms rather rigid films. In comparison, the HII film was more flexible, appearing as a modified undulation spectrum of the cylinders due to the interaction with the substrate.

A common feature of ionic liquids composed of cations with long aliphatic side chains is structural heterogeneities on the nanometer length scale. This so-called microphase separation arises from the clustering of aliphatic moieties. The temperature dependence of the liquid bulk structure was studied by small-angle X-ray and neutron scattering for a set of methylimidazolium ([C18C1im]+, [C22C1im]+) based ionic liquids with tris(pentafluoroethyl)trifluorophosphate ([FAP]−), bis(trifluoromethylsulfonyl)imide ([NTf2]−), and bis(nonafluorobutylsulfonyl)imide ([NNf2]−) anions. The experimental data is quantitatively analyzed using a generalized Teubner–Strey model. Discussion of the resulting periodicity d and correlation length ξ shows that the structural heterogeneities are governed by the interplay between the alkyl chain length, the geometry of the anion, and entropic effects. Connections between the mesoscopic correlation functions, density, and entropy of fusion are discussed in comparison to alcohols. T...

The internal interfaces of polyelectrolyte multilayers are investigated with neutron reflectivity. The films are made from poly(diallyldimethylammonium) (PDADMA), poly(styrenesulfonate) (PSS), and deuterated PSS-d. Each film consists of a protonated and a deuterated block. The internal roughness is smallest next to the film/air interface and increases with the number of layer pairs away from the film/air interface until a metastable state is reached. Both the final internal roughness and the interdiffusion constant increase with the salt concentration in the deposition solution and with PDADMA polymer weight. The increased mobility found with high molecular weight PDADMA is attributed to residual stresses occurring during film formation. The experiments suggest that PSS and PDADMA move partly as a complex. Postpreparation immersion in 1 M NaCl salt solutions has little effect if the multilayer is prepared from low salt solution and with high molecular weight PDADMA. However, almost complete intermixing is...

Using neutron reflectivity, the internal structure of polyelectrolyte multilayers is described on the nanoscale. Each film consists of a protonated and a deuterated block, built from x protonated and y deuterated polycation/polyanion bilayers, respectively. The number of bilayers N = x + y is kept constant; the position of the interface between the blocks is varied systematically. The polyanion is poly(styrenesulfonate) (PSS), and the polycation is poly(allylamine hydrochloride) (PAH) or poly(diallyldimethylammonium chloride) (PDADMAC). Always, the first four to five bilayers are thinner than the average bilayer thickness, but the three terminating bilayers are sometimes thicker. In the core zone, the bilayer thickness is constant. The internal roughness is smallest next to the film/air interface and increases with the number of bilayers away from the film/air interface. This suggests that each deposition step promotes the interdiffusion of the supporting layers. At the selected preparation conditions, th...

To describe the swelling of polyelectrolyte multilayers (PEMs) on a molecular scale, the PEM architecture is varied. The polyanion is poly(styrenesulfonate) (PSS) and the polycation poly(allylamine...