Direkte Messung supramolekularer Bindungskräfte in Polymeren

Wo hohe Kräfte sinnvoll walten: Die Abrisskräfte supramolekularer Bindungen und die Dissoziationsdynamik kovalent angebundener Polymere wurden durch kraftmikroskopische Einzelmolekül-Kraftspektroskopie (AFM-SMFS) untersucht. Die Studien führten zum ersten quantitativen Vergleich der Bindungsdissoziationsdynamiken aus unabhängigen AFM-SMFS- und NMR-Daten

Chemical Composition of Polymer Surfaces Imaged by Atomic ForceMicroscopy and Complementary Approaches

In this article we review the recent developments in the field of high resolution lateral mapping of the surface chemical composition of polymers by atomic force microscopy (AFM) and other complementary imaging techniques. The different AFM approaches toward nanometer scale mapping with chemical sensitivity based on chemical force microscopy (CFM) are discussed as a means to unravel, for instance, the lateral distribution of surface chemistry, the stability of various types of functional groups in various environments, or the interactions with controlled functional groups at the tip surface. The applicability and current limitations of CFM, which allows one to image chemical functional group distributions with a resolution in principle down to the 10–20 nm scale, are critically discussed. In addition, complementary imaging techniques are briefly reviewed and compared to the AFM-based techniques. The complementary approaches comprise various spectroscopies (infrared and Raman), secondary ion mass spectrometry (SIMS), matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), X-ray photoelectron spectroscopy (XPS or ESCA), and near-field optical techniques used for imaging

Elastic Modulus Profiles in the Cross Sections of Drying Alkyd Coating Films: Modelling and Experiments

The temporal development of the modulus of elasticity and its profile were studied in water-borne alkyd coatings during the drying process of the coating films. Values of the Young’s moduli of elasticity of free coating films were measured using tensile tests. Since the elastic modulus is related to cross-link density, the values of the moduli give information on the advancement of the drying process. A mathematical model was developed to predict the degree of effective cross-linking and the mechanical behaviour of the drying coating films with different thicknesses. This model is based on trends observed by confocal Raman microspectroscopy, which exhibit the profile of the consumption of double bonds and thus can be used to monitor the development of cross-link density as a function of depth from the film surface. The average values of the Young’s measured moduli were successfully described by the numerical model as a function of drying time

Self-Complementary Recognition of Supramolecular Urea - Aminotriazines in Solution and on Surfaces

The recognition of self-complementary quadruple urea–aminotriazine (UAT)-based hydrogen-bonded arrays was investigated in solution and at surfaces. For this purpose, an UAT-based donor–acceptor–donor–acceptor (DADA) array and complementary receptors were synthesized. Two-dimensional proton nuclear magnetic resonance (1H NMR) measurements in CDCl3 pointed at an intramolecular hydrogen-bond stabilization of the UAT, which promotes a planar molecular geometry and, thereby, results in a significant stabilization of the dimeric complex. The bond strength of the UAT dimers at surfaces was determined by atomic force microscopy-based single molecule force spectroscopy (AFM–SMFS) in hexadecane. The UAT receptor was immobilized on gold surfaces using an ultrathin layer of ethylene glycol terminated lipoic acid and isocyanate chemistry. The layers obtained and the reversible self-complementary recognition were thoroughly characterized with contact angle measurements, grazing angle Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and AFM. Loading rate-dependent SMFS measurements yielded a barrier width xβ and a bond lifetime at zero force toff(0) of 0.29 ± 0.02 nm and 100 ± 80 ms, respectively. The value of the corresponding off-rate constant koff suggests a substantially larger value of the dimerization constant compared to theoretical predictions, which is fully in line with the additional intramolecular hydrogen-bond stabilization detected in solution by 1H NMR spectroscopy

Pattern transfer fidelity in capillary force lithography with poly(ferrocenylsilane) plasma etch resists

The influence of processing conditions and polymer architecture on pattern transfer in capillary force lithography (CFL) using poly(ferrocenylsilane) etch resists is investigated. Zero-shear-rate viscosities measured at different temperatures and for polymers with different molar masses are related to the quality of CFL patterns, assessed based on atomic force microscopy experiments. An optimal range of viscosities corresponding to appropriate molar masses and processing temperatures is established. In this range, polymers possess enough mobility allowing for reasonably quick surface pattern formation. Yet, the polymers are not too mobile and preserve their shape when quenched to below Tg prior to serving as etch resist masks

Patterns of Surface Immobilized Block Copolymer Vesicle Nanoreactors

The immobilization and positioning of ultra small reaction vessels on solid supports open new pathways in applications such as lab-on-a-chip, sensors, microanalyses and microreactors. In our work block copolymer vesicles made from polystyrene-block-polyacrylic acid (PS-b-PAA) were immobilized from aqueous medium onto 3-amino propyl trimethoxysilane functionalized silicon surfaces exploiting electrostatic interactions. The immobilization of the vesicles was investigated by Fourier transform infrared (FTIR) spectroscopy, as well as fluorescence optical and atomic force microscopy (AFM). In addition, the influence of pH and ionic strength on the surface coverage of vesicles bound to the surface was elucidated. Finally micro-molding in capillaries (MIMIC) was utilized to create line patterns of the vesicles containing the enzyme trypsin and the fluorogenic substrate rhodamine 110 bisamide. The selective positioning of vesicle nanoreactors in conjunction with electrostatic immobilization serves as a proof of principle for potential applications in real-time observation of confined chemical reaction inside vesicles as nanocontainers and for the fabrication of integrated microarray systems