Precise Control over Polymer Semiconducting Films by Tuning the Thermal Behavior of the Thin-Film State's Crystalline and Morphological Structures

Lamellar orientation at the surface of isotactic polystyrene thin films analyzed by sum frequency generation spectroscopy

Analyzing the orientation of polymeric crystalline lamella at the surface of thin films can be challenging. Even though atomic force microscopy (AFM) is often sufficient for this analysis, there are cases when imaging is not sufficient to confidently determine lamellar orientation. Here, we used sum frequency generation (SFG) spectroscopy to analyze the lamellar orientation at the surface of semi-crystalline isotactic polystyrene (iPS) thin films. The SFG orientation analysis indicated that the iPS chains are oriented perpendicular to the substrate (flat-on lamellar orientation), which was confirmed by AFM. By analyzing the evolution of the SFG spectral features with the progress of crystallization, we demonstrated that the ratios of the SFG intensities of the phenyl ring resonances are a good indication of the surface crystallinity. Furthermore, we explored the challenges associated with SFG measurements of heterogeneous surfaces, which is commonly present in many semi-crystalline polymeric films. To the best of our knowledge, this is the first time that the surface lamellar orientation of semi-crystalline polymeric thin films was determined by SFG. Also, this work pioneers in reporting the surface conformation of semi-crystalline and amorphous iPS thin films by SFG and in linking the SFG intensity ratios to the progress of the crystallization and the surface crystallinity. This study demonstrates the potential applicability of SFG spectroscopy in the conformational analysis of polymeric crystalline structures at interfaces and opens the way to the investigation of more complex polymeric structures and crystalline arrangements, especially for the case of buried interfaces, where AFM imaging is not an option.

Low Ice Adhesion Surfaces Based on Flexible Fluorinated Polymers with a Polynorbornene Backbone

Realizing icephobic surfaces with low ice adhesion and durability continues to be fascinating as well as challenging. Herein, a norbornene-based fluorinated polymer (NFP) with high flexibility and high tensile strength is designed and fabricated using a fluorinated side chain and a norbornene backbone, displaying low ice shear strength less than 20 kPa and excellent durability. Experimental and theoretical analyses show that the flexibility of the polymer chains and the synergistic macromolecular aggregation of the fluorinated side groups and the norbornene backbone play key roles in the excellent surface icephobic properties of the NFP films. Moreover, we also develop a facile approach to the design of durable icephobic slippery surfaces, which possess remarkable icephobic performance. This study not only sheds light on the relationship between the polymer molecular structure and surface icephobic properties but also provides a new avenue to conveniently realize anti-icing coatings.