Designing stainless steel surfaces with anti-pitting properties applying laser ablation and organofluorine coatings

Long-lasting and superhydrophobic stainless steel with anti-pitting properties is achieved by modifying conventional AISI 304L through a two-step strategy: 1) application of a femtosecond surface laser ablation treatment to generate micro-nano structures on the surface; and 2) deposition of organofluorine nanometric coating. Samples with two different patterns, namely paraboloid- and cauliflower-like, are approached and investigated by means of contact angle hysteresis, X-ray photoelectron spectroscopy, and electrochemical techniques. Results indicate that the stainless steel surface acquires efficient anticorrosive properties due to the homogenization and refinement of the patterned microstructure into a magnetite rich phase, in combination with the formation of a carbonaceous and sol–gel layer. The adherent semiconducting oxide layer is stable over time in presence of an aggressive chloride environment. The prepared superhydrophobic surfaces prevent the steel substrates from getting wet with water, protecting them from the pitting corrosion caused by the electrolyte intrusion. The corrosion resistance is explained by a mechanism in which, in addition of the silane coating, the air trapped into the micro-nano patterned surfaces plays an important role.Peer ReviewedPostprint (author's final draft

Mechanical Characterization of Arteries: Comparison of Square and Cruciform Biaxial Tests Using Inverse Modeling Technique

Peer reviewed: NoNRC publication: Ye

Synthesis and Rheological Characterization of Star-Shaped and Linear Poly(hydroxybutyrate)

Indium and zinc complexes, [(NNO_tBu)­InCl]₂(μ-Cl)­(μ-OTHMB) (<b>2</b>) and (NN_iO_tBu)­Zn­(CH₂CH₃) (<b>3</b>), were used to produce monodispersed three- and six-armed star-shaped PHBs using tris­(hydroxymethyl)­benzene (THMB) and dipentaerythritol as the chain transfer agents. Reactions catalyzed by complex <b>2</b> were highly controlled, with THMB:catalyst ratios of up to 590:1, resulting in star-shaped PHBs with predictable molecular weights (<i>M</i>_n = 1.25–219 kDa) and narrow dispersities (<i>Đ</i> = 1.02–1.08). The zinc-based catalyst, <b>3</b>, was less controlled than the indium analogue but nevertheless generated moderately syndiotactic PHBs with maximum <i>M</i>_n values of ∼100 kDa. Importantly, <b>3</b> allowed the formation of previously unknown 6-armed star PHBs, allowing us to compare the effects of the different PHB architectures on the rheological behavior of the materials. High molecular weight linear and star polymers were characterized using solution and melt viscoelastic studies. Zero-shear viscosity of linear PHBs exhibited a power law relationship with the span molecular weight; however, it scaled exponentially for star polymers with slightly higher values for the 6-armed star PHBs. This was attributed to the moderately syndiotactic microstructure of these polymers. The absence of a district arm retraction relaxation in the dynamic master curves, and overshoot in the transient viscosity for the 6-armed star PHBs, are due to the lower entanglement density and slightly broader molecular weight distribution of these polymers

A Comparison of the Rheological and Mechanical Properties of Isotactic, Syndiotactic, and Heterotactic Poly(lactide)

A series of poly­(lactide) (PLA) samples, exhibiting various levels of syndiotactic enrichment, were formed via the ring-opening polymerization of <i>meso</i>-lactide using two families of dinuclear indium catalysts: (<i>RR</i>/<i>RR</i>)-[(NNO)­InCl]₂(μ-Cl)­(μ-OEt) (<b>1</b>) and (<i>RR</i>/<i>RR</i>)-[(ONNO)­In­(μ-OEt)]₂ (<b>2</b>). Isotactic and heterotactic PLAs were also synthesized using known methodologies, and the thermal and rheological behaviors of these PLAs with different microstructures were compared. Solution rheological studies showed that the values of intrinsic viscosities and hydrodynamic radii as functions of molecular weight (<i>M</i>_w) were highest for iso-PLAs, followed by hetero and then syndio-PLAs. The viscosities of the heterotactically enriched PLAs were in agreement with literature values reported for atactic PLAs. The molecular weight between entanglements (<i>M</i>_e) was greatest for the syndiotactically enriched PLAs, giving rise to the lowest zero-shear viscosity. In addition, hetero- and isotactically enriched PLA had higher flow activation energies (<i>E</i>_a,flow) than syndiotactic variants, implying the inclusion of transient aggregate regions within these polymers due to enhanced L- and D-interactions. Although strain hardening was observed for all types of PLAs, it was more dominant for isotactic PLAs due to stronger L- and D-interactions possibly leading to a small degree of stereocomplex microcrystallites