Ingenieurwissenschaften und zugeordnete Tätigkeiten
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The aim of this study is to develop polymeric thin films for corrosion protection of magnesium alloy AZ31. As polymer matrix, poly(4-vinyl pyridine) (P4VP) is selected due to its semiconducting properties and protonic conductivity. Polyacrylic acid is tested as crosslinking layers to improve interfacial adhesion. The macroscopic corrosion properties of the multilayer coatings are investigated by means of electrochemical methods, such as linear sweep voltammetry and electrochemical impedance spectroscopy (EIS), in corrosive media simulating technical and biomedical applications. It is demonstrated that thin multilayer coatings can suppress the corrosion rates of magnesium alloys. To our best knowledge, this is the first demonstration of the use of P4VP as a conducting polymer film with protonic conductivity for corrosion protection of magnesium alloys.
Spherical lignin nanoparticles (LNPs) fabricated via nanoprecipitation of dissolved lignin are among the most attractive biomass-derived nanomaterials. Despite various studies exploring the methods to improve the uniformity of LNPs or seeking more application opportunities for LNPs, little attention has been given to the fundamental aspects of the solvent effects on the intrinsic properties of LNPs. In this study, we employed a variety of experimental techniques and molecular dynamics (MD) simulations to investigate the solvent effects on the intrinsic properties of LNPs. The LNPs were prepared from softwood Kraft lignin (SKL) using the binary solvents of aqueous acetone or aqueous tetrahydrofuran (THF) via nanoprecipitation. The internal morphology, porosity, and mechanical properties of the LNPs were analyzed with electron tomography (ET), small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), and intermodulation AFM (ImAFM). We found that aqueous acetone resulted in smaller LNPs with higher uniformity compared to aqueous THF, mainly ascribing to stronger solvent−lignin interactions as suggested by MD simulation results and confirmed with aqueous 1,4-dioxane (DXN) and aqueous dimethyl sulfoxide (DMSO).
More importantly, we report that both LNPs were compact particles with relatively homogeneous density distribution and very low porosity in the internal structure. The stiffness of the particles was independent of the size, and the Young’s modulus was in the range of 0.3−4 GPa. Overall, the fundamental understandings of LNPs gained in this study are essential for the design of LNPs with optimal performance in applications.
Carbamazepine Dihydroxybenzoic Acid Cocrystals: Exploring Packing Interactions and Reaction Kinetics
(2021)
Herein, we present the mechanochemical formation of three new cocrystals containing the active pharmaceutical ingredient carbamazepine and dihydroxybenzoic acids as coformers (CBZ:2,4-DHBA 1:1, CBZ:2,5-DHBA 1:1, and CBZ:2,6-DHBA 1:1). Rietveld methods were used for three different purposes: (i) refining all structures solved using powder X-ray diffraction, (ii) performing a quantitative phase analysis of the diffraction data collected from ex situ mechanochemical reactions at different milling times, and (iii) determining the cocrystallization kinetic profiles. The rate of cocrystallization was found to be higher for the formation of CBZ:2,4-DHBA and CBZ:2,6-DHBA, reaching an equilibrium after 600 s of milling. In the case of CBZ:2,5-DHBA a short induction period of 20 s was detected prior to the start of the reaction and an equilibrium was reached after 1200 s. An empirical trend between the rate of cocrystallization and the structural complexity of the cocrystal product was found. The slowest cocrystallization rate observed for CBZ:2,5-DHBA corresponds to the crystal structure deviating substantially from the hydrogen-bonding motif found in the reactants.
We obtained concomitant dimorphic forms of Anthracene Schiffbase (N-(anthracen-9-yl methylene)-2,5- dichloroaniline) from hexane solvent. Two polymorphs can be differentiated by their morphology and mechanical properties. One form is long acicular type and elastically bendable while another form is block shaped and brittle in nature. Mechanical property is attributed to underlying crystal packing. Hirsh- feld analysis and energy framework calculations were done to corroborate structure-property correlation of two forms.
Superalloy inspired Al10Co25Cr8Fe15Ni36Ti6 compositionally complex alloy is known for its gamma-gamma' microstructure and the third Heusler phase. Variations of this alloy, gained by replacing 0.5 or 1 at. pct Al by the equivalent amount of Mo, W, Zr, Hf or B, can show more phases in addition to this three-phase morphology. When the homogenization temperature is chosen too high, a eutectic phase formation can take place at the grain boundaries, depending on the trace elements: Mo and W do not form eutectics while Hf, Zr and B do. In order to avoid the eutectic formation and the potential implied grain boundary weakening, the homogenization temperature must be chosen carefully by differential scanning calorimetry measurements. A too low homogenization temperature, however, could impede the misorientation alignment of the dendrites in the grain. The influence of grain boundary phases and incomplete dendrite re-orientation are compared and discussed.
Long-time behavior of surface properties of microstructures fabricated by multiphoton lithography
(2021)
The multiphoton lithography (MPL) technique represents the future of 3D microprinting, enabling the production of complex microscale objects with high precision. Although the MPL fabrication parameters are widely evaluated and discussed, not much attention has been given to the microscopic properties of 3D objects with respect to their surface properties and time-dependent stability. These properties are of crucial importance when it comes to the safe and durable use of these structures in biomedical applications. In this work, we investigate the surface properties of the MPL-produced SZ2080 polymeric microstructures with regard to the physical aging processes during the post-production stage. The influence of aging on the polymeric microstructures was investigated by means of Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). As a result, a time-dependent change in Young’s Modulus, plastic deformation, and adhesion and their correlation to the development in chemical composition of the surface of MPL-microstructures are evaluated. The results presented here are valuable for the application of MPL-fabricated 3D objects in general, but especially in medical technology as they give detailed information of the physical and chemical time-dependent dynamic behavior of MPL-printed surfaces and thus their suitability and performance in biological systems.
In contrast to other cyclic tin bisphenoxides, polymerizations of glycolide and l-lactide with the spirocyclic tin(IV) bis-1,1′-bisnapthoxide yield linear chains having a 1,1′-bisnapthol end group and no cycles. In the case of l-lactide, LA/Cat ratio and temperature are varied and at 160 °C or below, all polylactides mainly consist of even-numbered chains. A total predominance of even-numbered chains is also found for homopolymerization of glycolide, or the copolymerization of glycolide and l-lactide, when conducted <120 °C.
Linear chains having a bisnaphthol end group are again the main reaction products of ring-expansion polymerizations (REP) of 𝝐-caprolactone, but above 150 °C cycles are also formed.
1-Propyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide (Solarpur®), an ionic liquid was purchased from Merck (formerly Sigma Aldrich), was analyzed using hard x-ray photoelectron spectroscopy (HAXPES). The liquid is UHV stable, vertically and laterally homogeneous, and is easy to clean; thus, it can be used as a reference material. The HAXPES spectra of Solarpur® obtained using monochromatic Cr Kα radiation at 5414.8 eV include a survey scan, high-resolution spectra of C 1s, O 1s, N 1s, S 2p, S 1s, S 2s, F 1s, and S KLL.
Superhydrophobic surfaces can be quickly formed with supramolecular materials. Incorporating low-molecular-weight gelators (LMWGs) with perfluorinated chains generates xerogel coatings with low surface energies and high roughness. Here, we examine and compare the properties of the xerogel coatings formed with eight different LMWGs. These LMWGs all have a trans-1,2-diamidocyclohexane core and two perfluorinated ponytails, whose lengths vary from three to ten carbon atoms (CF3 to CF10). Investigation of the xerogels aims to provide in-depth information on the chain length effect. LMWGs with a higher degree of fluorination (CF7 to CF10) form superhydrophobic xerogel coatings with very low surface energies. Scanning electron microscopy images of the coatings show that the aggregates of CF5 and CF7 are fibrous, while the others are crystal-like. Aggregates of CF10 are particularly small and further assemble into a porous structure on the micrometer scale. To test their stabilities, the xerogel coatings were flushed multiple times with a standardized water flush test. The removal of material from the surface in these flushes was monitored by a combination of the water contact angle, contact angle hysteresis, and coating thickness measurements. A new method based on image processing techniques was developed to reliably determine the change of the coating thickness. The CF7, CF9, and CF10 surfaces show consistent hydrophobicity and coating durability after repetitive flushing tests. The length of the perfluorinated side chains thus has a significant effect on the morphology of the deposited xerogel coatings, their roughness, and, in consequence, their hydrophobicity and mechanical durability.
Effect of the Anchoring Layer and Transport Type on the Adsorption Kinetics of Lambda Carrageenan
(2021)
The kinetics of lambda carrageenan (λ-car) adsorption/desorption on/from anchoring layers under diffusion- and convection-controlled transport conditions were investigated. The eighth generation of poly(amidoamine) dendrimers and branched polyethyleneimine possessing different shapes and polydispersity indexes were used for anchoring layer formation. Dynamic light scattering, electrophoresis, streaming potential measurements, optical waveguide lightmode spectroscopy, and quartz crystal microbalance were applied to characterize the formation of mono- and bilayers. The unique combination of the employed techniques enabled detailed insights into the mechanism of the λ-car adsorption mainly controlled by electrostatic interactions. The results show that the macroion adsorption efficiency is strictly correlated with the value of the final zeta potentials of the anchoring layers, the transport type, and the initial bulk concentration of the macroions. The type of the macroion forming the anchoring layer had a minor impact on the kinetics of λ-car adsorption. Besides significance to basic science, the results presented in this paper can be used for the development of biocompatible and stable macroion multilayers of well-defined electrokinetic properties and structure.