Functionalized scanning force microscope (SFM) probes were used to investigate and to mimic the interaction between fibrinogen and self-assembled monolayers (SAMs) of methoxytri(ethylene glycol) undecanethiolates −S(CH2)11(OCH2CH2)3OCH3 (EG3-OMe) on gold and silver surfaces. The SAMs on gold are resistant to protein adsorption, whereas the films on silver adsorb variable amounts of fibrinogen. Experiments were performed with both charged and hydrophobic tips as models for local protein structures to determine the influence of these parameters on the interaction with the SAMs. A striking difference between the two monolayers was established when the forces were measured in an aqueous environment with hydrophobic probes. While a long-range attractive hydrophobic interaction was observed for the EG3-OMe on silver, a repulsive force was measured for EG3-OMe on gold. The strong dependence of the repulsive force for the EG3-OMe-gold system upon the solution ionic strength suggests that this interaction has a significant electrostatic contribution. The observed differences are attributed to the distinct molecular conformations of the oligo(ethylene glycol) tails on the gold-supported (helical) and silver-supported (“all-trans”) monolayers. A comparison of the force/distance curves for the EG3-OMe SAMs with those measured under identical conditions on end-grafted poly(ethylene glycol) (PEG 2000) on gold further emphasizes that the nature of the repulsive forces originating from the short-chain oligomers is unique and not related to a “steric repulsion” effect.

Octadecylphosphoric acid ester is shown to self-assemble on amorphous/nanocrystalline tantalum oxide (Ta2O5) layers deposited by physical vapor deposition onto glass substrates. Three complementary surfaceanalytical techniques (angle-dependent X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and atomic force microscopy in lateral force mode), showed that a 2.2 nm thick, "tailsup"-oriented adlayer is formed, which displays local near-hexagonal order, strong P-O-Ta bonding, and the presence of (-P-O-)2Ta species. A model for the binding and the structural organization of the octadecyl phosphate molecules on the tantalum oxide surface is proposed involving direct coordination of the terminal phosphate headgroup to Ta(V) cations forming a strong complexation bond, two types of bonding of the octadecyl phosphate with both monodentate and bidentate phosphate-Ta(V) coordinative interactions, and, locally, the formation of a coincidence lattice of approximately hexagonal structure defined by both the location of Ta(V) cation sites and an intermolecular spacing between the octadecyl phosphate ligands of approximately 0.5 nm. This is very similar to the self-assembled monolayer structure of long-chain alkanethiols on gold. The use of phosphoric acid ester derivatives is believed to have potential for designing specific interface architectures in sensor technology, in surface modification of oxide-passivated metallic biomaterials, and in composite metal (oxide)-polymer interfaces.

The efficient synthesis of high molar mass, first-(G1) and second-generation (G2) dendronized polymethacrylate derivatives PG1 and PG2, respectively, and their thermoresponsive properties in aqueous solution are described. All dendrons are branched 3-fold and were synthesized on the multigram scale using gallic acid as branching point and tri(ethylene glycol) (TEG) units as linker. The corresponding macromonomers carry methoxy groups in the periphery and are water-soluble, which allows polymerizing in aqueous medium. For comparison, PG1 and PG2 were also prepared in DMF solution and in bulk. These polymers are fully soluble in water at room temperature and turn turbid at elevated temperatures (approximately 62-65°C), a phenomenon that is typically referred to as thermoresponsiveness. This phase transition was investigated by 1 H NMR spectroscopy and turbidity measurements using UV/vis spectroscopy. The effect of molar mass and concentration on this transition was examined. In accordance with the normal usage, this transition temperature is referred to as lower critical solution temperature (LCST). Aggregates with sizes in the range of a few micrometers were observed above the LCSTs by conventional optical microscopy. Finally, the thermally induced aggregation and deaggregation processes were video-taped in high resolution.

Microcontact printing (µCP) is a simple and cost-effective method to create micrometer-scale chemical patterns on surfaces. By careful modification of the conventionally used stamping material (poly-(dimethylsiloxane) (PDMS)) and the stamping technique (e.g., "thin stamp µCP"), one can create surface chemical structures down to the submicrometer size range. In the present paper we report on the application of a new class of materialsspolyolefin plastomers (POPs) for µCP applications. We show that the POP stamps are well suited to print proteins or block copolymers. Comparative studies on reproducibility, homogeneity, and quality of printing between POP and conventional PDMS stamps were also performed. The results show a superior performance of the POP stamps in the nanometer range and an identical performance in the micrometer range compared to PDMS. Further advantages of the POP-based µCP are faster stamp production, the lack of monomeric contamination (typical for PDMS stamps), and the possibility of recycling the POP stamps. We believe that POPs offer a useful alternative to PDMS for µCP and open new possibilities in submicrometer-range printing.

We have investigated the ferroelectric phase diagram of poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA). The binary nonequilibrium temperature composition diagram was determined and melting of αand β-phase PVDF was identified. Ferroelectric β-PVDF:PMMA blend films were made by melting, ice quenching, and subsequent annealing above the glass transition temperature of PMMA, close to the melting temperature of PVDF. Addition of PMMA suppresses the crystallization of PVDF and, as a consequence, the roughness of blend films was found to decrease with increasing PMMA content. Using timedependent 2D numerical simulations based on a phase−field model, we qualitatively reproduced the effect of PMMA on the crystallization rate and the spherulite shape of PVDF. The remnant polarization scaled with the degree of crystallinity of PVDF. The thermal stability of the polarization is directly related to the Curie temperature. We show that, at high temperature, the commodity ferroelectric PVDF:PMMA blends outperform the commonly employed specialty copolymer poly(vinylidene fluoride−trifluoroethylene) (P(VDF−TrFE)).

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Novel first (G1) and second (G2) generation dendrimers based on three-fold branched oligoethylene glycol dendrons are efficiently synthesized which show characteristic thermoresponsive behavior and negligible cytotoxicity (for G2).

The adhesional forces between a series of polymer film surfaces and chemically well-defined atomic force microscopy tips have been measured and found to depend strongly on the chemical nature of both probe and sample surfaces. For a given series of polymers, the ranking in adhesion strength was markedly different for polar and nonpolar probes, irrespective of the precise chemical composition of those probes. In the case of nonpolar polymers, a correlation of adhesion force with calculations based on the Lifshitz theory of Van der Waals interactions was found. In the case of polar polymers, a reasonable correlation with water-contact angle was observed. The adhesional differences between different probe tips translate into reversals of chemical contrast in high-spatial-resolution lateral force images, when examining polymer blends using chemically different tips, demonstrating the potential of this approach for the nanometer-scale, friction-mediated surface-chemical imaging of polymers. Central to these experiments has been the use of perfluorodecalin as a medium for measuring interactions. Employment of this liquid greatly facilitates measurement of the forces between the probe tip and the polymer surface.