M.E. Dokukin, I. Sokolov
Keywords: AFM, new modes of operation, quantitative material properties, material properties at the nanoscale, compositional contrast
Summary:Dynamic mechanical spectroscopy (DMS), which allows measuring frequency-dependent viscoelastic properties, is important to study soft materials, tissues, biomaterials, polymers. However, the existing DMS techniques (nanoindentation) have limited resolution when used on soft materials, preventing them from being used to study mechanics at the nanoscale. The nanoindenters are not capable of measuring cells, nanointerfaces of composite materials. Here we present a highly accurate dynamic mechanical spectroscopy mode, which is a combination of three different methods: quantitative DMS (nanoDMA), gentle force and fast response of atomic force microscopy (AFM), and Fourier transform (FT) spectroscopy. This new spectroscopy (which we suggest to call FT-nanoDMA) is fast and sensitive enough to allow DMS imaging of nanointerfaces and single cells, while attaining about 100x improvements on polymers in both spatial (down to 10nm) and temporal resolution (down to 0.7 sec/pixel, multiple frequencies are measured simultaneously) compared to the current art. The uses of 10 simultaneous frequencies are demonstrated in both ambient conditions and liquid environment. The frequency range is up to 300Hz which is a rather relevant range for biological materials and polymers. The method is quantitatively verified on known polymers and demonstrated on cells. Analysis shows that FT-nanoDMA is highly quantitative.