Chemical reactions are the most important phenomena in chemistry. However, chemical reactions at buried solid/solid interfaces are very difficult to study in situ. In this research, the chemical reaction between two solid polymer materials, a nylon film and a maleic anhydride (MAH) grafted poly(ethylene-octene) (MAHgEO) sample, was directly analyzed at the buried nylon/MAHgEO interface at the molecular level in real time and in situ, using surface and interface sensitive sum-frequency generation (SFG) vibrational spectroscopy. Disappearance of nylon signals indicated a chemical reaction between amine and hydrolyzed amide groups of nylon and MAH groups on the MAHgEO at the buried interface. The appearance of SFG signals from reaction products was also observed at the buried nylon/MAHgEO interface. The mechanism of the observed interfacial reaction was further analyzed. Temperature-dependent SFG experiments were performed to measure the activation energy of the interfacial reaction, enabling a comparison with that reported for the bulk materials. The interfacial chemical reaction between nylon and MAHgEO greatly improved the adhesion of these dissimilar materials. The detailed analysis of a chemical reaction between two polymers at the polymer/polymer buried interface underscores the utility of SFG as a powerful analytical tool to build understanding of buried interfaces and to accelerate the design of interfacial structures with desired properties.

Nylon and maleic anhydride (MAH)-grafted polyolefin-based thin co-extruded multilayer films are widely used in packaging applications encountered in daily life. The molecular structure of the nylon/MAH-grafted polyolefin buried interface and molecular bonding between these two chemically dissimilar layers are thought to play an important role in achieving packaging structures with good adhesion. Here, the molecular bonds present at a nylon/maleic anhydride (MAH)grafted polyethylene buried interface were systematically examined in situ for the first time using sum frequency generation (SFG) vibrational spectroscopy. The carbonyl stretching frequency region of the SFG spectra of a nylon/MAH-grafted polyethylene buried interface showed the presence of hydrolyzed MAH groups grafted to the polyethylene chain and very low levels of unreacted MAH enriched at the buried interface. The ability of SFG to detect these molecular species at the buried interface yields important understanding of the interfacial molecular structure and provides the basis for subsequent in situ studies of the bonding reaction between the grafted MAH and nylon directly at the interface. This understanding may guide the design of multilayer films with improved properties such as enhanced adhesion between polymer layers. The approach used in this study is general and is applicable to study the molecular characteristics of other buried interfaces of significance, such as buried interfaces involving polymers in solar cells, polymer semiconductors, and batteries. Nylon impact modification is another area of interest where the interaction between the MAH-grafted elastomer and the continuous phase of nylon is important.

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Modulating terahertz (THz) waves actively and smartly through an external field is highly desired in the development of THz spectroscopic devices. Here, we demonstrate an active and smart electro-optic THz modulator based on a strongly correlated electron oxide vanadium dioxide (VO2). With milliampere current excitation on the VO2 thin film, the transmission, reflection, absorption, and phase of THz waves can be modulated efficiently. In particular, the antireflection condition can be actively achieved and the modulation depth reaches 99.9%, accompanied by a 180° phase switching. Repeated and current scanning experiments confirm the high stability and multibit modulation of this electro-optic modulation. Most strikingly, by utilizing a feedback loop of “THz-electro-THz” geometry, a smart electro-optic THz control is realized. For instance, the antireflection condition can be stabilized precisely no matter what the initial condition is and how the external environment changes. The proposed electro-optic THz modulation method, taking advantage of strongly correlated electron material, opens up avenues for the realization of THz smart devices.