Polymer coatings are frequently utilized to control and modify substrate properties. The performance of the coatings is often determined by the first polymer layers between the substrate and the bulk ...polymer material, which are termed interphase. Standard methods have failed to completely characterize this interphase, because its properties change significantly over a few nanometers. Here we determine the spatially resolved adhesion properties of the interphase in polyelectrolyte multilayers (PEMs) by desorbing a single polymer covalently bound to an atomic force microscope cantilever tip from PEMs with varying thickness. We show that the adhesion properties of the first few layers (up to three double layers) is dominated by the surface potential of the substrate, while thicker PEMs are controlled by cohesion in between the PEM polymers. For cohesion, the local film conformation is the crucial parameter. This finding is generalized by utilizing oligoelectrolyte multilayer (OEM) as coatings and both hydrophilic and hydrophobic polymers as polymeric force sensors.
A novel method for the preparation of transparent Al2O3 coatings of polymers is presented. An environmental‐friendly sol–gel method is employed, which implies mild conditions and low costs. A ...thermoresponsive brush is chosen as a model surface. X‐ray photoelectron spectroscopy is used to characterize the samples during the conversion of the precursor Al(OH)3 into oxide and to prove the mildness of the protocol. The study evidences a relation between lateral homogeneity of alumina and the wettability of the polymer surface by the precursor solution, while morphology and elasticity are dominated by the polymer properties. The study of the swelling behavior of the underneath brush reveals the absence of water uptake, proving the impermeability of the alumina layer. The broad chemical and structural variety of polymers, combined with the robustness of transparent alumina films, makes these composites promising as biomedical implants, protective sheets and components for electric and optical devices.
Waterproof and transparent: A method for the preparation of transparent Al2O3 coatings of polymer brushes is presented. Layer composition, morphology, and mechanical properties were characterized by a combination of XPS, SEM, and AFM. The presence of the alumina layer preserved the underneath brush from swelling in water.
The thesis presents the preparation and characterization of smart coatings based on polymer brushes, polyelectrolyte multilayers (PEMs), aluminium oxide and their combination as multicompartment ...systems. The latter are highly relevant, as they extend the properties of each subsystem. For instance, they carry multiple sensitivity to external stimuli, hierarchical structures which can be selectively activated, enhanced robustness and thermal stability. However, the interaction between the constituent parts might alter their individual responsiveness to the surrounding environment, therefore nature and strength of such a synergy is a crucial knowledge to achieve the desired structure and properties of multicompartment coatings. The combination of optical methods and scanning probe techniques allowed to characterize structure, morphology and responsiveness of the systems. In addition, these studies provided information on the interaction and the consequent mutual effects governing the behavior of the composites. The first part of the thesis presents the successful assembly of short-chain polyelectrolytes into multilayers. The development of an appropriate preparation protocol is fundamental to achieve a systematic layer-by-layer growth from the balance between the characteristic layer instability, leading to degradation, and enhanced mass uptake. In the second part, the interaction between polymer brushes and osmolytes is analyzed for different co-solute concentration and temperature. In particular, the synergistic use of experiments and simulations clarify direct and indirect effects on the conformational behavior of the polymer chain. In the third part, multicompartment systems are presented, in which homo- and block copolymer brushes are used as substrates for the deposition of PEMs and aluminium oxide films. In the first case, strong interactions in the brush/PEM composites is observed, leading to stable complexes in the inner part of the brush which alter but not suppress the responsive properties of the system towards humidity and temperature. The results suggest a crucial role of brush thickness and charge density on the diffusion and interaction of the polyelectrolytes, which represents a fundamental tool to tune the properties of the resulting composites. Finally, a novel procedure allows to coat a polymer brush with aluminum oxide, where the quality of the coating is determined by the wettability of the polymer substrate. Significant mutual effects on morphological, mechanical and swelling properties of the films are found, meaning that brush/alumina composites can successfully exploit the properties of both organic and inorganic materials. This thesis analyzes fundamental aspects for the design of complex smart coatings, where the interaction between the constituent parts govern their structure and responsive behavior under different conditions.
For the first time, the combination of experimental preparation and results of fully atomistic simulations of an oligoelectrolyte multilayer (OEM) made of poly(diallyl dimethyl ammonium ...chloride)/poly(styrene sulfonate sodium salt) (PDADMAC/PSS) is presented. The layer-by-layer growth was carried out by dipping silica substrates in oligoelectrolyte solutions and was modeled by means of atomistic molecular dynamics simulations with a protocol that mimics the experimental procedure up to the assembly of four layers. Measurements of OEM thickness, surface roughness and amount of adsorbed oligoelectrolyte chains obtained from both approaches are compared. A good agreement between simulated and experimental results was found, with some deviations due to intrinsic limitations of both methods. However, the combination of information extracted from simulations to support the analysis of experimental data can overcome such restrictions and improve the interpretation of experimental results. On the other hand, processes dominated by slower kinetics, such as the destabilization of adsorbed layers upon equilibration with the surrounding environment, are out of reach for the simulation modeling approach, but they can be investigated by monitoring in situ the oligoelectrolyte adsorption during the assembly process. This demonstrates how the synergistic use of simulation and experiments improves the knowledge of OEM properties down to the molecular scale.
A novel method for the preparation of transparent Al2O3 coatings of polymers is presented. An environmental‐friendly sol–gel method is employed, which implies mild conditions and low costs. A ...thermoresponsive brush is chosen as a model surface. X‐ray photoelectron spectroscopy is used to characterize the samples during the conversion of the precursor Al(OH)3 into oxide and to prove the mildness of the protocol. The study evidences a relation between lateral homogeneity of alumina and the wettability of the polymer surface by the precursor solution, while morphology and elasticity are dominated by the polymer properties. The study of the swelling behavior of the underneath brush reveals the absence of water uptake, proving the impermeability of the alumina layer. The broad chemical and structural variety of polymers, combined with the robustness of transparent alumina films, makes these composites promising as biomedical implants, protective sheets and components for electric and optical devices.
Durchsichtig und wasserdicht: Eine Methode zur Herstellung von transparenten Al2O3‐Beschichtungen auf Polymerbürsten wird vorgestellt. Zusammensetzung, Morphologie und mechanische Eigenschaften wurden mit XPS, SEM und AFM charakterisiert. Die Al2O3‐Schicht schützt das darunterliegende Polymer gegen das Aufquellen in Wasser.
For the first time, the combination of experimental preparation and results of fully atomistic simulations of an oligoelectrolyte multilayer (OEM) made of poly(diallyl dimethyl ammonium ...chloride)/poly(styrene sulfonate sodium salt) (PDADMAC/PSS) is presented. The layer-by-layer growth was carried out by dipping silica substrates in oligoelectrolyte solutions and was modeled by means of atomistic molecular dynamics simulations with a protocol that mimics the experimental procedure up to the assembly of four layers. Measurements of OEM thickness, surface roughness and amount of adsorbed oligoelectrolyte chains obtained from both approaches are compared. A good agreement between simulated and experimental results was found, with some deviations due to intrinsic limitations of both methods. However, the combination of information extracted from simulations to support the analysis of experimental data can overcome such restrictions and improve the interpretation of experimental results. On the other hand, processes dominated by slower kinetics, like the destabilization of adsorbed layers upon equilibration with the surrounding environment, are out of reach for the simulation modeling approach, but they can be investigated by monitoring in situ the oligoelectrolyte adsorption during the assembly process. This demonstrates how the synergistic use of simulation and experiments improves the knowledge of OEM properties down to the molecular scale.
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