The molecular level details of the displacement of surface adsorbed fibrinogen from silica substrates were studied by atomic force microscopy, immunochemical assays, fluorescence microscopy, and vibrational sum frequency spectroscopy. The results showed that human plasma fibrinogen (HPF) can be readily displaced from the interface by other plasma proteins near neutral pH because the positively charged alpha C domains on HPF sit between the rest of the macromolecule and the underlying surface. The alpha C domains make weak electrostatic contact with the substrate, which is manifest by a high degree of alignment of Lys and Arg residues. Upon cycling through acidic pH, however, the alpha C domains are irreversibly removed from this position and the rest of the macromolecule is free to engage in stronger hydrogen bonding, van der Waals, and hydrophobic interactions with the surface. This results in a 170-fold decrease in the rate at which HPF can be displaced from the interface by other proteins in human plasma.

In this study, we developed a simple and powerful method to fabricate flexible and lightweight graphene-based composites that provide high electromagnetic interference (EMI) shielding performance. Electrospun waterborne polyurethane (WPU) that featured sulfonate functional groups was used as the polymer matrix, which was light and flexible. First, graphene oxide (GO)/WPU composites were prepared through layer-by-layer (L-b-L) assembly of two oppositely charged suspensions of GO, the cationic surfactant (didodecyldimethylammonium bromide, DDAB)-adsorbed GO and intrinsic negatively charged GO, depositing on the negatively charged WPU fibers. After the L-b-L assembly cycles, the GO bilayers wrapped the WPU fiber matrix completely and revealed fine connections guided by the electrospun WPU fibers. Then, we used hydroiodic acid (HI) to obtain highly reduced GO (r-GO)/WPU composites, which exhibited substantially enhanced electrical conductivity (approximately 16.8 S/m) and, moreover, showed a high EMI-shielding effectiveness (approximately 34 dB) over the frequency range from 8.2 to 12.4 GHz.

TiO2 thin films coated on SiO2 substrates were prepared for the investigation of water structure at the TiO2/aqueous interface by vibrational sum-frequency spectroscopy (VSFS). The films were first characterized by X-ray photoelectron spectroscopy, ellipsometry, and atomic force microscopy. Film thickness could be readily varied between 0.9 and 5.9 nm with the thinnest film displaying the least degree of surface roughness. The 0.9 nm films were employed in the VSFS investigations and showed characteristic 3200 and 3400 cm -1 OH stretch frequencies of highly aligned interfacial water. Such peaks were reminiscent of those known from SiO2/aqueous interfaces; however, the chemistry at TiO2/aqueous interfaces was significantly richer. In the presence of Cl anions, the surface had an isoelectric point near pH 5.5 and showed the least degree of water organization near this pH. Almost equally strong 3200 cm -1 features could be produced at pH 2.0 and 12.0. On the other hand, the spectra were dramatically altered in the presence of phosphate-buffered saline. The phosphate ions specifically bound to the substrate surface and shifted the isoelectric point of the interface to pH 2.0. In this case, the intensity of the 3400 cm -1 peak was significantly increased in comparison with the Cl ion data at both neutral and acidic pH values. This is presumably because of a lack of sites directly adjacent to the oxide for forming tetrahedrally coordinated water when phosphate ions are present.

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Flexible and lightweight graphene nanosheet (GN)/waterborne polyurethane (WPU) composites which exhibit high electrical conductivity and electromagnetic shielding performance were prepared. Covalently modifying GNs with aminoethyl methacrylate (AEMA; AEMA-GNs) through free radical polymerization effectively inhibited the restacking and aggregation of the GNs because of the -NH3(+) functional groups grafted on the AEMA-GNs. Moreover, the AEMA-GNs exhibited high compatibility with a WPU matrix with grafted sulfonated functional groups because of the electrostatic attraction, which caused the AEMA-GNs to homogeneously disperse in the WPU matrix. This homogeneous distribution enabled the GNs to form electrically conductive networks. Furthermore, AEMA-GNs with different amounts of AEMA segments were introduced into the WPU matrix, and the effects of the surface chemistry of the GNs on the electrical conductivity and EMI shielding performance of composites were investigated. AEMA-GN/WPU composites with a GN loading of 5 vol % exhibited remarkable electrical conductivity (approximately 43.64 S/m) and EMI shielding effectiveness (38 dB) over the frequency of 8.2 to 12.4 GHz.