Chitosan nanocomposite coatings with enhanced corrosion inhibition effects for copper.

A biopolymer coating on copper was prepared based on chitosan nanocomposite and its corrosion inhibition efficiency was investigated. Inclusion of silica nanoparticles substantially reduces swelling ratio of chitosan coating while enhancing its thermal stability. The corrosion resistance of chitosan-based coatings is improved by introducing 2-mercaptobenzothiazole and silica in the matrix. It is found that upon crosslinking the chitosan coatings, a higher corrosion resistance could be achieved and the highest inhibition efficiency for chitosan nanocomposite coatings is calculated as 85%. The corrosion mechanism is found closely related to mass transition and diffusion process, and also the polarization resistance contributes to the impedance. Calculated impedance using Kramers-Kronig transformation shows good agreement with experimental values, thus validating the impedance measurements. This study exhibits the enhanced efficiency of nanocomposite and potential of chitosan coatings in corrosion prevention for copper.

A novel method for rapid estimation of lactic acid bacterial concentration in fermented milk based on superhydrophobic surface wettability.

A novel and facile method is developed for rapid estimation of lactic acid bacterial concentration in fermented milk. Growth of bacteria in a liquid changes physicochemical property of the medium and its behavior at solid-liquid interface. Wettability determines characteristic of solid-liquid interface. Nano-rod, helical tetragonal and L-shaped morphologies were designed and fabricated. Hydrophobicity and zeta potential were measured for dried surfaces of 5 dairy bacterial strains. Relationship between microbial population and changes in solid-liquid interface was studied by wettability and surface free energy measurements. Due to hydrophobic surface property of conventional dairy strains, they strongly affect solid-liquid and liquid-vapor surface tensions when dispersed in a liquid, which are dependent on the bacterial concentration. Response surface methodology results showed that type and concentration of bacteria, droplet volume and solid-surface morphology affect wettability significantly. Higher hydrophobicity resulted in higher ∆θ (absolute value of the difference between the pure physiological saline and the bacterial suspension contact angles) dependence on the bacterial concentration. Probiotic bacteria concentration in fermented milk was estimated using the proposed method. A direct relationship was obtained between milk contact angle and bacterial concentration. Results show that this physical method can be applied for rapid estimation of bacterial concentration.

Application of Mn-Cu Helical Star-Shaped (Pine-Tree-Like) Sculpted Thin Films with Different Symmetries Using Surface-Enhanced Raman Spectroscopy (SERS).

In this work, the surface engineering method is used to produce Mn helical star-shaped (pine-tree-like) nanosculptured thin films with three-, four-, and fivefold symmetries on Cu substrates using an oblique angle deposition technique together with rotation of the sample holder at certain angles. Nano structure and morphologies of the produced samples were obtained by means of atomic force microscope and field emission scanning electron microscope. Raman spectroscopy of the Mn/Cu samples impregnated by 4,4'-bipyridine (C10H8N2) solution with different concentrations, zidovudine (C10H13N5O4), and L-histidine (C6H9N3O2) was performed using 532 nm laser wavelength. A high degree of enhancement is achieved on Raman spectroscopy of all of these specimens. Comparison of the surface-enhanced Raman spectroscopy (SERS) results for 4,4' bipyridine (bipy) obtained in this work with the published literature using Ag and Au substrates in different shapes showed a significant enhancement improvement by using Mn sculptured structures. Reduction of the bipy concentration changed the enhancement factor. Enhancement factors of 107 and 105 were obtained for threefold symmetry sample using 2.885 × 10-2 and 10-3 mol L-1 bipy concentrations, respectively. Surface-enhanced Raman spectroscopy results of this work show that Mn nanostructures designed and engineered in this work can not only replace Ag and Au materials, but also provide a much higher enhancement factor.