This review provides detailed fundamental principles of X-ray-based characterization methods, i.e., X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, and near-edge X-ray absorption fine structure, and the development of different techniques based on the principles to gain deeper understandings of chemical structures in polymeric materials. Qualitative and quantitative analyses enable obtaining chemical compositions including the relative and absolute concentrations of specific elements and chemical bonds near the surface of or deep inside the material of interest. More importantly, these techniques help us to access the interface of a polymer and a solid material at a molecular level in a polymer nanocomposite. The collective interpretation of all this information leads us to a better understanding of why specific material properties can be modulated in composite geometry. Finally, we will highlight the impacts of the use of these spectroscopic methods in recent advances in polymer nanocomposite materials for various nano- and bio-applications.

We report the use of phenolic functional groups of lignosulfonate to impart antioxidant properties and the cell binding domains of gelatin to enhance cell adhesion for poly(ethylene glycol) (PEG)-based scaffolds. Chemoselective thiol–ene chemistry was utilized to form composites with thiolated lignosulfonate (TLS) and methacrylated fish gelatin (fGelMA). Antioxidant properties of TLS were not altered after thiolation and the levels of antioxidation were comparable to those of L -ascorbic acid. PEG-fGelMA-TLS composites significantly reduced the difference in COL1A1 , ACTA2 , TGFB1 , and HIF1A genes between high-scarring and low-scarring hdFBs, providing the potential utility of TLS to attenuate fibrotic responses.

We employed imaging rotational fluorescence correlation microscopy to directly observe the segmental dynamics of the polymer near the polymer−substrate interface using a probe-tethered polymer brush buried in bulk polymer films. The probetethered polymers grafted onto the polymer−substrate interface provide spatial selectivity to probe only the segmental dynamics of polymer near the polymer−substrate interface. The perturbation caused by the grafted polymer chains on the segmental dynamics of the polymer film near the interface was minimized by reducing the molecular weight of the polymer brush compared with the critical entanglement molecular weight of the polymer and grafted with a low grafting density (≈0.1 chains/nm 2 ) using a "grafting-to" method, which allows precisely controlled and fully characterized polymer brush structures. In addition, the molecular weight of the brush polymer was further controlled to ≈10 kg/mol with the root-mean-square end-to-end distance of ≈5 nm to probe dynamics within 10 nm of the polymer−substrate interface. Polystyrene and poly(methyl methacrylate) films carrying rather unfavorable and similar surface energies, respectively, with the silane-modified silicon wafer substrates were investigated. The polymer dynamics near the interface characterized by the degrees of non-Arrhenius temperature dependence and nonexponential relaxation were not altered in both systems compared with those of the bulk, suggesting that the polymer dynamics is not sensitive to moderate differences in enthalpic interaction between the polymer and the substrate.

Planar metal–insulator–metal (MIM) optical cavities are attractive for biochemical and environmental sensing applications, as they offer a cost-effective cavity platform with acceptable performances. However, localized detection and scope of expansion of applicable analytes are still challenging. Here, we report a stimuli-responsive color display board that can exhibit local spectral footprints, for locally applied heat and alcohol presence. A thermoresponsive, optically applicable, and patternable copolymer, poly­(N-isopropylacrylamide-r-glycidyl methacrylate), is synthesized and used with a photosensitive cross-linker to produce a responsive insulating layer. This layer is then sandwiched between two nanoporous silver membranes to yield a thermoresponsive MIM cavity. The resonant spectral peak is blue-shifted as the environmental temperature increases, and the dynamic range of the resonant peak is largely affected by the composition and structure of the cross-linker and the copolymer. The localized temperature increase of silk particles with gold nanoparticles by laser heating can be measured by reading the spectral shift. In addition, a free-standing color board can be transferred onto a curved biological tissue sample, allowing us to simultaneously read the temperature of the tissue sample and the concentration of ethanol. The stimuli-responsive MIM provides a new way to optically sense localized environmental temperature and ethanol concentration fluctuations.

The approach of utilizing polymer-tethered fluorescent molecules in probing segmental dynamics of polymers near the glass transition was validated by the examination of the rotational dynamics of the probes that were randomly dispersed in the same polymer hosts as the tethered polymers. Poly(alkyl methacrylate)-and polystyrene-tethered fluorescent probes, located either at the end or in the middle of a polymer chain, were tethered either with flexible dodecyl or hexyl alkyl chains by atom transfer radical polymerization and post-polymerization modification, respectively. Different polymeric systems with different glass transition temperature and fragility differing by ≈100 K and ≈80, respectively, were studied. Although the polymer-tethered probes report increased average rotational relaxation times compared to segmental dynamics of polymers, the temperature dependence of the polymer dynamics reported by the probe was not altered as confirmed by the goodness-of-fit test of the Vogel−Fulcher−Tammann (VFT) equation. Through the comparison of β reported by a bigger untethered probe in the same system, the origin of the vertical shift of VFT was interpreted as the result of an increased restriction of probes upon tethering, which was not associated with an increase in the probing length scale. To summarize, the rotational dynamics of the tethered probe accurately captures the degree of non-Arrhenius temperature dependence and nonexponential relaxation of the host polymers regardless of T g and fragility of the system or the tethering condition.