Sum frequency generation imaging for semi-crystalline polymers

Sum-frequency generation (SFG) spectroscopy is a powerful tool to study the molecular orientation in confined systems such as interfaces on the basis of the second-order nonlinear optical effect. We herein demonstrated SFG imaging for films of uniaxially oriented poly(vinylidene fluoride) and spin-coated isotactic polypropylene and successfully identified the orientational difference of lamellar fibrils in the two films. SFG chemical mapping was finally performed by taking advantage of the different absorption wavelengths for methylene groups in the two samples. To the best of our knowledge, this is the first report dealing with SFG mapping for synthetic polymers.