Comparison of experimental methods to characterize Young’s modulus of ultrathin coatings on polymer films

• The combination of metal thin coating with polymer films have been studied extensively in e.g. the field of food packing, medical and aerospace application. In such applications the mechanical performance and structural integrity of the coated films are frequently of interest. Depending on the purpose of the coating, there are various characterization methods, for example the peel test, scratch test, indentation test, fragmentation test as well as simulation methods to predict the mechanical performance based on material properties identified by such tests. The first and perhaps most common parameter to characterize is the stiffness of the coating and substrate, which are important input parameters in predictive finite element simulations of failure of brittle coatings, affecting the barrier function. The relatively thick polymer films can be characterized by conventional tensile testing. However, stiffness characterization for the ultrathin coating (nanometer scale) is much more challenging. In this research, three independent experimental test modes have been used to estimate the thickness of thin brittle coatings. The various methods are complementary with different advantages and drawbacks. They are based on (i) Nanoindentation, (ii) strain induced elastic buckling instability, and (iii) AFM peak force measurements. The samples were prepared by atomic layer deposition in 4 types of coating: TiO2 (titanium oxide) of 20 and 6 nm thick and MOX (mixed oxide, TiO2 and Al2O3) of 20 and 4 nm thick. The differences in estimated Young’s moduli are interpreted in terms of the underlying assumptions and test conditions. Their specific advantages and drawbacks are also compared and discussed.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Teknisk mekanik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Applied Mechanics (hsv//eng)

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