Hierarchically structured polymer blends based on silsesquioxane hybrid nanocomposites with quaternary ammonium units for antimicrobial coatings

The paper reports the first study on hierarchical assemblies (nanofibrillar micelles confined within semi-cylindrical shells) with silsesquioxane and quaternary ammonium units obtained through polymer blending intended for antimicrobial/antifungal stone coatings. The formation of hierarchical structures on solid surfaces is due to the multiple intermolecular ionic interactions, intermolecular Van der Waals and hydrophobic interactions acting among the component molecules. Their antimicrobial/antifungal properties toward the Gram-negative bacteria, Escherichia coli, Gram-positive bacteria, Staphylococcus aureus, and Candida albicans fungus were determined in aqueous solution and were found to be strongly dependent of the topographical features of the coating.     

Synthesis and characterization of side-chain poly(methacrylate)s bearing new azo-moieties

New side-chain poly(methacrylate)s with azo moieties were prepared by free radical copolymerization, starting from methyl methacrylate (MMA) and some original azo-monomers. The chromophore content was evaluated from ¹H-NMR spectroscopy and elemental analyses; all structures exhibited a high content of azobenzene units. UV–Vis measurements have also supported this fact. Reactivity ratios for the methacrylate systems and their corresponding Q–e values were calculated based on several initial feed compositions (MMA and the newly synthesized azo-monomers) using an integral method with its appropriate software. The polymers were also characterized by FTIR, SEC and DSC-TGA techniques. The coloured poly(methacrylate)s exhibited glass transition temperatures between 141 and 168 °C and thermal stabilities up to 306 °C.     

Atmospheric Pressure Plasma Activation of Hydroxyapatite to Improve Fluoride Incorporation and Modulate Bacterial Biofilm

Despite the technological progress of the last decade, dental caries is still the most frequent oral health threat in children and adults alike. Such a condition has multiple triggers and is caused mainly by enamel degradation under the acidic attack of microbial cells, which compose the biofilm of the dental plaque. The biofilm of the dental plaque is a multispecific microbial consortium that periodically develops on mammalian teeth. It can be partially removed through mechanical forces by individual brushing or in specialized oral care facilities. Inhibition of microbial attachment and biofilm formation, as well as methods to strengthen dental enamel to microbial attack, represent the key factors in caries prevention. The purpose of this study was to elaborate a cold plasma-based method in order to modulate microbial attachment and biofilm formation and to improve the retention of fluoride (F⁻) in an enamel-like hydroxyapatite (HAP) model sample. Our results showed improved F retention in the HAP model, which correlated with an increased antimicrobial and antibiofilm effect. The obtained cold plasma with a dual effect exhibited through biofilm modulation and enamel strengthening through fluoridation is intended for dental application, such as preventing and treating dental caries and enamel deterioration.     

Synthesis of a new oxazoline macromonomer for dispersion polymerization

We synthesized new macromonomers containing vinylsilane moiety by cationic ring-opening polymerization of 2-ethyl-2-oxazoline. Kinetic studies proved that initiation with vinylsilane derivative, bearing chloride counterion, is a fast process followed by a slow propagation and absence of termination. We used the dispersion polymerization of styrene as test for the stabilizing efficiency of the newly synthesized macromonomer. The dispersion polymerization tests allowed the investigation of the effect of the macromonomer concentration on the number average diameter of the prepared polystyrene microspheres and its polydispersity index. In addition, we compared the stabilizing efficiency of commercial poly(N-vinylpyrollidone) with that of our macromonomer. Copolymerization of styrene with 10 wt% oxazoline macromonomer yielded stable and monodisperse microspheres, having the number average diameter of 1.8 μm and a good size polydispersity index of 1.05.     

BiFeO3-synthesis,characterization and its photocatalytic activity towards doxorubicin degradation from water

Pure bismuth ferrite was successfully obtained through the thermolysis of new bismuth ferrioxalate coordination compound, namely BiFe(C₂O₄)₃·3H₂O. The synthesized precursor was characterized by chemical analysis, infrared spectroscopy and thermal analysis. The bismuth ferrite obtained after a heating treatment of the precursor for at 450–800?°C/1?h was investigated by X-ray diffraction, FE-SEM, TEM and HRTEM. The obtained pure bismuth ferrite nanoparticles (480?°C) was tested as photocatalyst towards the degradation of doxorubicin (DOX), a well-known anti-cancer drug commonly used for the treatment of various cancer types, which has been detected in hospital effluent water. The comparative results of DOX degradation through photolysis and photocatalysis under UV irradiation showed a great photocatalytic activity of bismuth ferrite towards DOX degradation and mineralization from water. The kinetics aspects were discussed based on the first-order kinetics model that fitted the best the experimental photocatalysis results.     

Corrosion behaviour in alkaline medium of zinc phosphate coated steel obtained by cathodic electrochemical treatment

The present work evaluated the ability of zinc phosphate coating, obtained by cathodic electrochemical treatment, to protect mild steel rebar against the localized attack generated by chloride ions in alkaline medium. The corrosion behaviour of coated steel was assessed by open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy. The chemical composition and the morphology of the coated surfaces were evaluated by X-ray diffraction and scanning electron microscopy. Cathodically phosphated mild steel rebar have been studied in alkaline solution with and without chloride simulating the concrete pore solution. For these conditions, the results showed that the slow dissolution of the coating generates the formation of calcium hydroxyzincate (Ca(Zn(OH)₃)₂·2H₂O). After a long immersion time in alkaline solution with and without Cl⁻, the coating is dense and provides an effective corrosion resistance compared to mild steel rebar.     

Covalent Poly(2‐Isopropenyl‐2‐Oxazoline) Hydrogels with Ultrahigh Mechanical Strength and Toughness through Secondary Terpyridine Metal‐Coordination Crosslinks

The present study reports the synthesis of poly(2‐isopropenyl‐2‐oxazoline) (PiPOx) dual‐crosslinked hydrogels by both covalent and physical (i.e., metal–ligand coordination) interactions. First, chemical crosslinking of a modified PiPOx polymer containing terpyridine (TPy) unit is achieved by reacting with azelaic acid (non‐anedioic acid). Transient crosslinks are subsequently introduced by complexation of the TPy units with different divalent transition metal ions. This strategy provides access to hydrogels with superior mechanical properties compared to the pure covalently crosslinked PiPOx hydrogels. The mechanical properties and water uptake of the hydrogels could be easily controlled by swelling in different aqueous metal ion solutions. PiPOx hydrogels swollen in Zn²⁺ solution are found to possess ultrahigh compression strength (9 MPa), remarkable toughness (99 MJ m^?3) and outstanding self‐recoverability (98% toughness recovery after swelling for 60 min without external stimuli), which are among the highest reported in literature to date. These remarkable properties are assigned to the thermodynamically stable, but kinetically labile Zn²⁺‐TPy complexes that produce a dynamic network with fewer imperfections and better adaptive properties under mechanical stress compared to those with other metal ions.     

Synthesis and characterization of side-chain oxazoline–methyl methacrylate copolymers bearing azo-dye

We synthesized new polymeric structures by attaching a side-chain azo-moiety on poly(oxazoline) and poly(oxazoline-co-methyl methacrylate)s. For the polymer analogous transformation, we took advantage of the highly effective ring-opening addition of carboxyl group to the oxazoline cycle. The comonomers feed ratio allowed us to control the composition of the products while the kinetic treatment, employing an integral method, revealed a statistical copolymerization tendency of 2-isopropenyl-2-oxazoline with methyl methacrylate in acetonitrile at 70 °C. The elemental analysis and ¹H NMR spectroscopy provided almost identical composition data for both the substrates and the side-chain copolymers. The UV spectroscopy sustained the quantitative addition of 4-(4-hydroxy-3,5-dimethylphenylazo)benzoic acid to the oxazoline rings. Both the unmodified copolymers and the coloured ones exhibited good thermal stabilities, up to 371 °C and 302 °C, respectively. The glass transition temperatures ranged from 141.5 to 177.5 °C and from 153.8 to 200.9 °C for the substrates and for the modified copolymers, respectively. Preliminary investigations showed fluorescence activity for all copolymers bearing azo-moieties.