Dieter Pleul

Polypropylene surface functionalization with chitosan

Chitosan coatings on oxygen-plasma pre-treated polypropylene (PP) surfaces were formed to improve their wettability, dyeing behavior and reactivity without altering material bulk properties. XPS, electrokinetic potential and contact angle measurements as well as dye uptake tests were carried out for surface characterization of modified PP, evaluation of chitosan coatings stability, and the effects of temperature and pH on coatings formation. About 20–30% of the total amount of chitosan immobilized on PP was found to be covalently bonded to the plasma pre-treated surface through the heat induced reactions with oxygen-containing functional groups at T > 80°C that corresponded to 47% of surface coverage. Subsequent cross-linking reaction with epichlorohydrin proved to be an efficient way to reduce the susceptibility of chitosan coatings to acidic hydrolysis.

A study of paint adhesion to polymeric substrates

In order to explore the fundamental mechanism of paint adhesion to polymer substrates the surface of polypropylene- ethylene propylene rubber (PP-EPR) blends was modified by flame or plasma treatments. The changes in surface composition and properties were investigated and discussed in light of the results of simple adhesion tests. The topography and surface properties of the PP-EPR samples were studied by employing various surface sensitive techniques. Additionally, the surface properties of the pre-treated PP-EPR were compared with the model polymers poly(methyl methacrylate) (PMMA) and polycarbonate (PC) displaying a poor and an excellent paint adhesion, respectively. Differential scanning calorimetry (DSC) measurements showed that the miscibility of the polymer substrate with paint components was an essential factor for the understanding of the adhesion mechanism. A general model of paint adhesion to polymer surfaces is proposed, where the degree of interdiffusion of the polymer chains of the substrate and paint in the interphase determines the adhesion strength.

Plasma assisted immobilization of poly(ethylene oxide) onto fluorocarbon surfaces

Different plasma-assisted procedures were compared with respect to the immobilization of poly(ethylene oxide) (PEO) and poly(ethylene-block-propylene) triblock copolymers (PEO-PPO-PEO) on top of thin plasma-deposited fluorocarbon layers. The fluorocarbon substrate was used as a model system for the common poly(tetrafluoroethylene) as it provides several advantages to apply surface-selective analytical methods. The fixation of pre-adsorbed PEO-PPO-PEO by argon plasma treatments on the fluorocarbon surface was found to produce less homogeneous coatings probably due to the insufficient adsorption of the triblock-copolymers on the substrate. More effective PEO coverage of the fluorocarbon surface was achieved by O2-plasma initiated graft polymerization of PEO-dimethacrylate (Mw = 400 g/mol) and PEO-monoacrylate (Mw = 1000 g/mol) from solutions or melts. X-ray photoelectron spectroscopy (XPS) and contact angle measurements were utilized for a detailed study of the modified surfaces. The efficiency of PEO-coatings with respect to the reduction of protein adsorption onto the hydrophobic fluorocarbon layer was demonstrated with the example of the adsorption of fibrinogen. The adsorbed amount of this protein was determined based on spectroscopic ellipsometry.

X-Ray Photoelectron Spectroscopy

X-Ray photoelectron spectroscopy is a highly surface sensitive technique, which can provide information on composition, binding and functionality of polymers at the surface. The aspect of information depth and surface charging is discussed as well as quantification and data interpretation.

Plasma modification of diamond surfaces

Because of its extreme hardness, diamond is a very interesting material for many industrial applications. One way to extend the field of diamond application and optimize the process conditions in diamond tool production is to enhance its surface reactivity. Low-pressure oxygen-plasma treatments were applied to equip the diamond surfaces with chemically reactive groups to improve their adhesion properties. XPS and DRIFT spectroscopy investigations showed that oxygen plasmas were suitable to oxidize the diamond surface. Combining derivatization reactions and solvatochromic dye adsorption studies, the introduction of alcoholic groups was confirmed. Besides the surface oxidation, the plasma treatment initiates decomposition of the diamond lattice which is followed by a re-arrangement of the carbon atoms in a graphite-like structure. The planar graphite structure supports the formation of carbonyl groups.

Surface chemistry of polyethylene grafted with hydrophilic monomers: XPS and ToF-SIMS studies

Polyethylene (PE) powders were grafted by acrylic acid or maleic anhydride/styrene monomers. The elemental surface composition was determined by means of X-ray photoelectron spectroscopy (XPS). Time-of-flight secondary ion mass spectrometry (TOF-SIMS) investigations were carried out to obtain information about the molecular build-up of the grafted polymers. XPS measurements showed the presence of oxygen-containing functional groups on the PE particle surface. The TOF-SIMS spectra gave evidence for polymer chains with alternating maleic anhydride and styrene units. In addition, fragments of polystyrene block segments were found.

The chemical structure and stability of plasma-deposited thin hydrocarbon layers on polyethylene

AbThe surfaces of polyethylene (PE) films were modified by deposition of layers from acetylene/ethylene monomer gases in a low-pressure radio-frequency plasma. The chemical structure of the plasma-deposited layers and their long-term stability were studied by X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, and contact angle measurements. These studies have shown that the plasma-deposited layers consist mainly of amorphous, short-chain, functional CxHy structures with aryl units. As the reactive radical centers formed during the plasma process are susceptible to further reaction with atmospheric oxygen and water, the chemical stability of these layers was investigated. This stability is ensured over the long-term, although an increase in the number of functional groups is obtained over time. It was demonstrated that the post-reactions reach a state of equilibrium after a few weeks.

Time-of-Flight Secondary Ion Mass Spectrometry

Static secondary ion mass spectrometry provides information on the molecular composition of the topmost layer of a sample. It is mostly used as a complementary technique to determine surface composition, surface contamination or surface segregation of components. The time-of-flight technique enables high mass resolution also at the higher mass values needed for polymers.

Surface Characterization of Electron Irradiated Polymer Brushes

Abstract Polymer brushes are representing a versatile tool to adjust and control surface phenomena like wetting, adsorption and adhesion. Moreover, certain complementary surface modification methods can support improving their intended applications. A promising strategy is the combination of the grafting-to method under initiator and solvent free conditions with an additional electron-beam irradiation step which can lead to polymer brushes with high-selective properties. The experiments were focused on the investigation of the surface reactions taking place during the dose-dependent irradiation of the thin polymer brush layers with the aim to modify their properties. A comprehensive and detailed study of the initiated functionalization reactions associated with their influence on the alteration of surface properties of different homo and binary polymer brush layers was performed using sensitive surface characterization techniques such as XPS, contact angle measurements, and ellipsometry.