Understanding
the impact of the intricate morphology and surface
chemistry of ZnO nanorod arrays on their interactions with polyelectrolyte
polymers is crucial for the development of nascent ZnO-based adhesion-promoting
materials. AFM-based single molecule force spectroscopy was applied
for the analysis of the adsorption of poly(acrylic acid) (PAA) on
zinc oxide (ZnO) film covered stainless steel substrates in aqueous
electrolytes at pH 7. Based on the electrodeposition process, the
morphology of zinc oxide films could be varied ranging from platelet-like
crystals to nanorods. This approach allowed for the morphology dependent
analysis of macromolecular adsorption processes on complex ZnO nanostructures
which have diverse applications in the field of adhesion-promoting
thin films. The surface chemical composition, as determined by X-ray
photoelectron spectroscopy, could be correlated to the AFM-based desorption
studies. Only equilibrium desorption events (plateaus), centered at
42 pN, were observed on mirror polished, preconditioned stainless
steel. However, for platelet-like ZnO films, the poly(acrylic acid)
desorption showed a mixture of rupture events (mean rupture forces
of about 350 pN) and equilibrium desorption, while ZnO nanorod structures
showed solely rupture events with mean rupture forces of about 1300
pN. These results indicate that simultaneous multiple ruptures of
carboxylate–zinc bonds occur due to the macromolecular coordination
of poly(acrylic acid) to the ZnO nanorods. The analysis of the interfacial
adhesion processes is further supported by the dwell time dependence
of desorption processes.
Deposit formation and fouling in reactors for polymer production and processing especially in microreactors is a well-known phenomenon. Despite the flow and pressure loss optimized static mixers, fouling occurs on the surfaces of the mixer elements. To improve the performance of such parts even further, stainless steel substrates are coated with ultra-thin films which have low surface energy, good adhesion, and high durability. Perfluorinated organosilane (FOTS) films deposited via chemical vapor deposition (CVD) are compared with FOTS containing zirconium oxide sol-gel films regarding the prevention of deposit formation and fouling during polymerization processes in microreactors. Both film structures led to anti-adhesive properties of microreactor component surfaces during aqueous poly(vinylpyrrolidone) (PVP) synthesis. To determine the morphology and surface chemistry of the coatings, different characterization methods such as X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy as well as microscopic methods such as field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) are applied. The surface free energy and wetting properties are analyzed by means of contact angle measurements. The application of thin film-coated mixing elements in a microreactor demonstrates a significant lowering in pressure increase caused by a reduced deposit formation.
Bacterial colonization of abiotic surfaces such as those
of medical
implants, membrane filters, and everyday household items is a process
of tremendous importance for public health. Bacteria use adhesive
cell surface structures called adhesins to establish contact with
abiotic surfaces. Among them, protein filaments called type IV pili
are particularly important and found in many Gram-negative pathogens
such as
Pseudomonas aeruginosa
. Understanding
the interaction of such adhesin proteins with different abiotic surfaces
at the molecular level thus represents a fundamental prerequisite
for impeding bacterial colonization and preventing the spread of infectious
diseases. In this work, we investigate the interaction of a synthetic
adhesin-like peptide, PAK128-144ox, derived from the type IV pilus
of
P. aeruginosa
with hydrophilic and
hydrophobic self-assembled monolayers (SAMs). Using a combination
of molecular dynamics (MD) simulations, quartz crystal microbalance
with dissipation monitoring (QCM-D), and spectroscopic investigations,
we find that PAK128-144ox has a higher affinity for hydrophobic than
for hydrophilic surfaces. Additionally, PAK128-144ox adsorption on
the hydrophobic SAM is furthermore accompanied by a strong increase
in α-helix content. Our results show a clear influence of surface
hydrophobicity and further indicate that PAK128-144ox adsorption on
the hydrophobic surface is enthalpically favored, while on the hydrophilic
surface, entropic contributions are more significant. However, our
spectroscopic investigations also suggest aggregation of the peptide
under the employed experimental conditions, which is not considered
in the MD simulations and should be addressed in more detail in future
studies.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.