Holger Schönherr

Enhanced Removal of Methylene Blue and Methyl Violet Dyes from Aqueous Solution Using a Nanocomposite of Hydrolyzed Polyacrylamide Grafted Xanthan Gum and Incorporated Nanosilica

The synthesis and characterization of a novel nanocomposite is reported that was developed as an efficient adsorbent for the removal of toxic methylene blue (MB) and methyl violet (MV) from aqueous solution. The nanocomposite comprises hydrolyzed polyacrylamide grafted onto xanthan gum as well as incorporated nanosilica. The synthesis exploits the saponification of the grafted polyacrylamide and the in situ formation of nanoscale SiO2 by a sol-gel reaction, in which the biopolymer matrix promotes the silica polymerization and therefore acts as a novel template for nanosilica formation. The detailed investigation of the kinetics and the adsorption isotherms of MB and MV from aqueous solution showed that the dyes adsorb rapidly, in accordance with a pseudo-second-order kinetics and a Langmuir adsorption isotherm. The entropy driven process was furthermore found to strongly depend on the point of zero charge (pzc) of the adsorbent. The remarkably high adsorption capacity of dyes on the nanocomposites (efficiency of MB removal, 99.4%; maximum specific removal Qmax, 497.5 mg g(-1); and efficiency of MV removal, 99.1%; Qmax, 378.8 mg g(-1)) is rationalized on the basis of H-bonding interactions as well as dipole-dipole and electrostatic interactions between anionic adsorbent and cationic dye molecules. Because of the excellent regeneration capacity the nanocomposites are considered interesting materials for the uptake of, for instance, toxic dyes from wastewater.

Surface design : applications in bioscience and nanotechnology

1. Tutorial Reviews 1.1 Coupling Chemistries for the Modification and Functionalization of Surfaces to Create Advanced Bio-interfaces, H. Schonherr 1.2 Surface Plasmon Resonance-Based Biosensors, J. Dostalek, Chun Jen Huang and W. Knoll 1.3 Surface Modification and Adhesion, R. Forch 1.4 Modern Biological Sensors, A.T.A. Jenkins 2. Functional Thin Film Architectures and Platforms Based on Polymers 2.1 Controlled Block Copolymer Thin Film Architectures, M. Roerdink, M. A. Hempenius, G. J. Vancso 2.2 Stimuli Responsive Polymer Brushes, E. Benetti, M. Navarro, S. Zapotoczny, G. J. Vancso 2.3 Cyanate Ester Resins as Thermally Stable Adhesives for PEEK, B. Yameen, M. Tamm, N. Vogel, A. Echler, R. Forch, U. Jonas and W. Knoll 2.4 Structured and Functionalized Polymer Thin Film Architectures, H. Schonherr, C. L. Feng, A. Embrechts, G. J. Vancso 3. Biointerfaces, Biosensing, and Molecular Interactions 3.1 Surface Chemistry in Forensics, K. Bender 3.2 Modification of Surfaces by Photosensitive Silanes, X.S. Li, S. Pradhan-Kadam, M. Alvarez-Chamorro, U. Jonas 3.3 Solid Supported Bilayer Lipid Membranes, I. Koper, I. Vockenroth 3.4 Interaction of Structured and Functionalized Polymers with Cancer Cells, A. Embrechts, C. L. Feng, I. Bredebusch, J. Schnekenburger, Wolfram Domschke, G. J. Vancso, and H. Schonherr 3.5 Fabrication and Application of Surface Tethered Vesicles, A.T.A. Jenkins and T. L. Williams 3.6 Plasma Polymerized Allylamine Thin Films for DNA Sensing, L. Q. Chu, W. Knoll, R. Forch 4. Nanoparticles and -containers 4.1 Defined Colloidal 3D Architectures, N. V. Dziomkina, M. A. Hempenius, G. J. Vancso 4.2 Nanoparticles at the Interface: The Properties of Nanoparticles Assembled into 2-D and 3-D Structures at Planar Electrode Surfaces, P. J. Cameron 4.3 Surface Engineering of Quantum Dots with Designer Ligands, N. Tomczak, D. Janczewsk, O. Tagit, M. Y. Han, G. J. Vancso 4.4 Stimuli Responsive Capsules, Y. Ma, M. A. Hempenius, E. S. Kooij, W.-F. Dong, H. Mohwald, and G. J. Vancso 4.5 Nanoporous Thin Films as Highly Versatile and Sensitive Waveguide Biosensors, K.H. Aaron Lau, P. J. Cameron, H. Duran, A. I. Abou-Kandil, W. Knoll 5. Surface and Interface Analysis 5.1 Stretching and Rupturing Single Covalent and Associating Macromolecules by AFM-based Single Molecule Force Spectroscopy, M. I. Giannotti, W. Q. Shi, S. Zou, H. Schonherr, G. J. Vancso 5.2 Quantitative Lateral Force Microscopy, H. Schonherr, E. Tocha, J. Song, G. J. Vancso 5.3 Long Range Surface Plasmon-enhanced Fluorescence Spectroscopy as a Platform for Biosensors, A. Kasry, J. Dostalek, W. Knoll 6. Glossary of Surface Analytical Tools, R. Forch, H. Schonherr, and A. T. A. Jenkins 6.1 Atomic Force Microscopy 6.2 Contact Angle Goniometry 6.3 Ellipsometry 6.4 Infra Red Spectroscopy 6.5 Impedance Spectroscopy 6.6 Scanning Electron Microscopy 6.7 Surface Plasmon Resonance Spectroscopy 6.8 Optical Waveguide Mode Spectroscopy (OWS) 6.9 Waveguide Mode Spectroscopy (WaMS) 6.10 X-Ray Photoelectron Spectroscopy

Block-Copolymer Vesicles as Nanoreactors for Enzymatic Reactions

The impact of the spatial confinement of polystyrene-block-poly(acrylic acid) (PS-b-PAA) block copolymer (BCP) vesicles on the reactivity of encapsulated bovine pancreas trypsin is studied. Enzymes, as well as small molecules, are encapsulated with loading efficiencies up to 30% in BCP vesicles with variable internal volumes between 0.014 aL (internal vesicle diameter, d(in) = 30 nm) and 8 aL (d(in) = 250 nm), obtained by manipulating the vesicle preparation conditions. The kinetics of the trypsin-catalyzed reaction of a fluorogenic substrate inside and outside the vesicles is quantitatively estimated using fluorescence spectroscopic analyses in conjunction with the use of NaNO(2) as selective quencher for non-encapsulated fluorophores. The values of the catalytic turnover number obtained for reactions in differently sized nanoscale reactors show a significant increase (up to approximately 5x) with decreasing BCP vesicle volume, while the values of the Michaelis-Menten constant decrease. The observed increase in enzyme efficiency by two orders of magnitude compared to bulk solution is attributed to an enhanced rate of enzyme-substrate and molecule-wall collisions inside the nanosized reactors, as predicted in the literature on the basis of Monte Carlo simulations.

Host-Guest Interactions at Self-Assembled Monolayers of Cyclodextrins on Gold

We have developed synthesis routes for the introduction of short and long dialkylsulfides onto the primary side of alpha-, beta-, and gamma-cyclodextrins. Monolayers of these cyclodextrin adsorbates were characterized by electrochemistry, wettability studies, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and atomic force microscopy (AFM). The differences in thickness and polarity of the outerface of the monolayers were measured by electro-chemistry and wettability studies. On average about 70% of the sulfide moieties were used for binding to the gold, as measured by XPS. Tof-SIMS measurements showed that the cyclodextrin adsorbates adsorb without any bond breakage. AFM measurements revealed for beta-cyclodextrin monolayers a quasi-hexagonal lattice with a lattice constant of 20.6 A, which matches the geometrical size of the adsorbate. The alpha-cyclodextrin and gamma-cyclodextrin monolayers are less ordered. Interactions of the anionic guests 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS) and 2-(p-toluidinyl)naphthalene-6-sulfonic acid (2,6-TNS) and the highly ordered monolayers of heptapodant beta-cyclodextrin adsorbates were studied by surface plasmon resonance (SPR) and electrochemical impedance spectroscopy. The SPR measurements clearly showed interactions between a beta-cyclodextrin monolayer and 1,8-ANS. Electrochemical impedance spectroscopy measurements gave high responses even at low guest concentrations (< or = 5 microM). The association constant for the binding of 1,8-ANS (K = 289,000 +/- 13,000M-1) is considerably higher than the corresponding value in solution. (Partial) methylation of the secondary side of the beta-cyclodextrin strongly decreases the binding.

Enzyme degradable polymersomes from hyaluronic acid-block-poly(ε-caprolactone) copolymers for the detection of enzymes of pathogenic bacteria.

We introduce a new hyaluronidase-responsive amphiphilic block copolymer system, based on hyaluronic acid (HYA) and polycaprolactone (PCL), that can be assembled into polymersomes by an inversed solvent shift method. By exploiting the triggered release of encapsulated dye molecules, these HYA-block-PCL polymersomes lend themselves as an autonomous sensing system for the detection of the presence of hyaluronidase, which is produced among others by the pathogenic bacterium Staphylococcus aureus. The synthesis of the enzyme-responsive HYA-block-PCL block copolymers was carried out by copper-catalyzed Huisgen 1,3-dipolar cycloaddition of ω-azide-terminated PCL and ω-alkyne-functionalized HYA. The structure of the HYA-block-PCL assemblies and their enzyme-triggered degradation and concomitant cargo release were investigated by dynamic light scattering, fluorescence spectroscopy, confocal laser-scanning microscopy, scanning and transmission electron, and atomic force microscopy. As shown, a wide range of reporter dye molecules as well as antimicrobials can be encapsulated into the vesicles during formation and are released upon the addition of hyaluronidase.

Scanning force microscopy of polymers

Introduction (Vancso) Part I: Principles: Theory and Practice 1. Physical Principles of Scanning Probe Microscopy Imaging (Vancso) 2. Atomic Force Microscopy in Practice (Schonherr) 2.1 Assembling of AFMs for operation 2.1.1 Scanned sample AFM (contact mode) 2.1.2 Stand alone AFM (contact mode) 2.1.3 Intermittent contact (tapping) mode 2.2 Practical issues of AFM operation 2.2.1 AFM cantilevers, tips and their characteristics 2.2.2 Sample preparation 2.2.3 Choice of operation modes and suitable imaging environments 2.2.4 Tip handling modification procedures 2.2.5 Calibration issues 2.2.6 General guidelines for AFM laboratories 2.2.7 Data evaluation 2.2.8 Typical AFM artefacts 2.3 References / further reading Part II. Case Studies: Macromolecules, Polymer Morphology and Polymer Surface Properties by AFM 3 Visualization of Macromolecules and Polymer Morphology 3.1 Structural Hierarchy in Polymers (Vancso) 3.2 Single Component Systems (Schonherr) 3.2.1 Visualization of Single Macromolecules 3.2.1.1 Visualization of Poly(ethylene imine) (PEI) Adsorbed on Mica 3.2.1.2 Visualization of Poly(amidoamine) Dendrimers Adsorbed on Mica 3.2.2 Lattice Visualization of Crystallized Homopolymers 3.2.2.1 Lattice Visualization of Poly(tetrafluoro ethylene) (PTFE) by CM-AFM 3.2.2.2 Lattice Visualization of Poly(oxy methylene) (POM) by CM-AFM 3.2.3 Amorphous Polymers 3.2.3.1 Imaging of the Surface Morphology of Poly(ethylene terephthalate) (PET) by TM-AFM 3.2.3.2 Imaging of Dewetted Perfluoropolyether Lubricant on Hard Disc Surfaces by TM-AFM 3.2.4 Lamellar Crystals (Crystallized from Solution or Melt) 3.2.4.1 Solution-Grown Lamellae of POM and PE by CM-AFM 3.2.4.2 Lamellae inIsotactic Polypropylene (iPP) by TM-AFM 3.2.4.3 Lamellae in Spin-Coated Films of Poly(ethylene oxide) (PEO) by TM- AFM 3.2.5 Extended Chain Crystals and Shish-Kebob Structures 3.2.5.1 CM-AFM on Extended Chain Crystals of Cold-Drawn PET 3.2.5.2 TM-AFM on Shish-Kebob Morphology in Drawn Polyethylene Copolymers 3.2.6 Hedrites and Spherulites 3.2.6.1 Sample Preparation: Melt Crystallization Followed by Etching 3.2.6.2 CM-AFM on Thin Films of Isotactic Polypropylene (iPP) - a-iPP 3.2.7 References 3.3 Biopolymers (Schonherr) 3.3.1 Imaging of Biological and Biopolymer Specimens under Liquid 3.3.1.1 AFM under liquid 3.3.1.2 Mounting the liquid cell (dry sample) 3.3.1.3 CM-AFM operation under liquid 3.3.1.4 TM-AFM operation under liquid 3.3.2 Hand-on examples 3.3.2.1 Visualization of Adsorbed Lipid Vesicles and Bilayers 3.3.2.2 Visualization of Polymerizable Lipid Bilayers 3.3.2.3 Visualization of the Tobacco Mosaic Virus 3.3.2.4 Cellulose Fibers in Pulp 3.3.2.5 Cellulose Microcrystals 3.3.2.6 Polysaccharides: Xanthan gum 3.3.2.7 Collagen 3.3.2.8 Crystallized Protein Layers : Streptavidin 3.3.2.9 Lambda DNA 3.3.2.10 Biocompatible Polymers 3.3.3 References 3.4 Multi Component Systems (Schonherr) 3.4.1 Materials Contrast in AFM Imaging of Multi Component Systems 3.4.2 Block Copolymers 3.4.2.1 Visualization of Microphase Separated Morphology of Films of Polystyrene-b-polyisoprene-b-polystyrene 3.4.2.2 Visualization of Microphase Separated Morphology of Hydrolyzed Films of polystyrene-b-poly(tert-butyl acrylate) 3.4.3 Polymer Blends 3.4.3.1 Identification of Phases in Blend of PMMA and PB 3.4.3.2 Identification of Phases in Blends of Impact Polymers by FMM 3.4.4 Filled Polymer Systems 3.4.4.1 Distribution of

Free-Standing 3 D Supramolecular Hybrid Particle Structures†

Make a stand: The formation of stable and ordered free-standing particle bridges and hollow capsule structures with controllable sizes and geometries is demonstrated by combining the directed assembly of submicrometer particles, transfer printing, and supramolecular layer-by-layer assembly.

Nanoscale Thermal AFM of Polymers: Transient Heat Flow Effects

Thermal transport around the nanoscale contact area between the heated atomic force microscopy (AFM) probe tip and the specimen under investigation is a central issue in scanning thermal microscopy (SThM). Polarized light microscopy and AFM imaging of the temperature-induced crystallization of poly(ethylene terephthalate) (PET) films in the region near the tip were used in this study to unveil the lateral heat transport. The radius of the observed lateral surface isotherm at 133 °C ranged from 2.2 ± 0.5 to 18.7 ± 0.5 μm for tip-polymer interface temperatures between 200 and 300 °C with contact times varying from 20 to 120 s, respectively. In addition, the heat transport into polymer films was assessed by measurements of the thermal expansion of poly(dimethyl siloxane) (PDMS) films with variable thickness on silicon supports. Our data showed that heat transport in the specimen normal (z) direction occurred to depths exceeding 1000 μm using representative non-steady-state SThM conditions (i.e., heating from 40 to 180 °C at a rate of 10 °C s(-1)). On the basis of the experimental results, a 1D steady-state model for heat transport was developed, which shows the temperature profile close to the tip-polymer contact. The model also indicates that ≤1% of the total power generated in the heater area, which is embedded in the cantilever end, is transported into the polymer through the tip-polymer contact interface. Our results complement recent efforts in the evaluation and improvement of existing theoretical models for thermal AFM, as well as advance further developments of SThM for nanoscale thermal materials characterization and/or manipulation via scanning thermal lithography (SThL).

Mechanical properties of block copolymer vesicle membranes by atomic force microscopy

The mechanical properties of polystyrene-block-poly(acrylic acid) (PS-b-PAA) vesicles prepared with different block copolymer chain lengths and block length ratios were studied under ambient conditions using atomic force microscopy (AFM). The deformation δ, as well as the spring constant of the membranes kmem, of individual vesicles with external diameter of ∼150 nm and systematically varied membrane thicknesses between 22 nm and 40 nm were calculated from the captured AFM force-displacement data. The application of the shell deformation model provided estimates of the apparent Youngs moduli E of the vesicle membranes. While the values of kmem increased with increasing membrane thickness, the values of E were found to decrease. This observed decrease in E with increasing shell thickness coincides with the reduced degree of chain stretching reported in the literature for longer polymer chains.

Factors affecting the preparation of permanently end-grafted polystyrene layers

Deuterated and protonated end-functionalized polystyrenes of low and high molecular weight were grafted onto silicon substrates by solution-spincasting, followed by annealing and removal of ungrafted chains. The remaining layers were characterised by spectroscopic ellipsometry and atomic force microscopy. The effect of a variation of the initial film thickness, the annealing temperature and time on the resulting grafted layers was investigated. It was found that only the initial film thickness and deuteration had a marked effect on the layer morphology and thickness. Further improvement in reproducibility is needed to achieve real process control.