Tõnis Arroval

Oxygen Barrier Properties of Al2O3- and TiO2-coated LDPE Films

Current work focuses on establishing optimal growth conditions for covering commercial grade polymer blown films with a gas barrier oxide layer. As opposed to regular solid state substrates, low density polymers host an abundance of free space in the form of pores and voids between large polymer chains (MW > 1000) and a heterogeneous crystallized phase. In the following we will show how the structural peculiarities of the polymer matrix influence the ALD process for growing TiO2 and Al2O3 gas blocking layers on top of the LDPE substrate. Possible causes of low gas barrier performance, thermal expansion coefficient differences, are proposed and commercial process additives, such as slip or antioxidants, are suggested. GRAPHICAL ABSTRACT

Enhanced flexibility and electron-beam-controlled shape recovery in alumina-coated Au and Ag core–shell nanowires

The proper choice of coating materials and methods in core-shell nanowire (NW) engineering is crucial to assuring improved characteristics or even new functionalities of the resulting composite structures. In this paper, we have reported electron-beam-induced reversible elastic-to-plastic transition in Ag/Al2O3 and Au/Al2O3 NWs prepared by the coating of Ag and Au NWs with Al2O3 by low-temperature atomic layer deposition. The observed phenomenon enabled freezing the bent core-shell NW at any arbitrary curvature below the yield strength of the materials and later restoring its initially straight profile by irradiating the NW with electrons. In addition, we demonstrated that the coating efficiently protects the core material from fracture and plastic yield, allowing it to withstand significantly higher deformations and stresses in comparison to uncoated NW.