Imaging the Molecular Structure of Polyethylene Blends with Broadband Coherent Raman Microscopy.

Polyethylene (PE) has been widely used in a myriad of consumer products and critical infrastructure products such as underground gas and water pipes. These products are often made of blends of multiple types of PE with different molecular architectures. Although the long-term performance of these products is largely dictated by their local molecular structure, it has been studied mostly by indirect and bulk-averaging methods such as calorimetry and neutron scattering due to lack of chemical contrast for conventional imaging techniques. We demonstrate that broadband coherent anti-Stokes Raman scattering (CARS) microscopy can acquire images of the chemical composition and molecular orientation of a miscible semicrystalline PE blend with two different molecular architectures. We discuss the detailed crystal structure observed at different length scales and new insights it provides into polymer crystal morphology.