Carolina C. Ilie

Water Interactions with Crystalline Polymers with Large Dipoles

We compare the interactions of water with the ferroelectric copolymer poly(vinylidene fluoride (PVDF) – trifluoroethylene (TrFE)) and poly(methylvinylidenecyanide) (PMCV), a strongly dipole ordered polymer. At the microscopic scale, dipole interactions matter and affect the surface chemistry at these polymer surfaces, as does lattice strain caused by water absorption. Light polarization dependent photo-assisted thermal desorption helps demonstrate that water desorption from surface and bulk can be influenced by the formation of electronic metastable states. Changes in local dipole orientation and the formation of long lived metastable states affect the strength of the coupling between the dipoles of water molecules and the dipoles of the copolymer poly(vinylidene fluoride – trifluoroethylene) but these effects were not observed for poly(methylvinylidenecyanide).

Water Absorption and Subsequent Lattice Changes in the Crystalline Poly(Methyl Vinylidene Cyanide) and in the Ferroelectric Poly(Vinylidene Fluoride with Trifluoroethylene)

Water absorption on surfaces has been a major part of surface science for decades [1, 2], but there is not yet a corresponding level of understanding in how water (or indeed any adsorbate) interacts with polymer surfaces [3]. Unlike single-crystal metal surfaces, polymers are typically not very good electrical or thermal conductors and are notorious for having very heterogeneous surfaces [3], adding considerable impediments to the undertaking of otherwise standard surface science techniques. For example, segregation of one component [4–10] complicates attempts to prepare a reproducible surface. Yet, water absorption by polymers is not only a subject of considerable research, but also an issue with considerable industrial applications, such as gels, in vivo implants, and water-resistant coatings. Despite the complexities of polymer surface characterization, water has been identified as a cause of reorientation at polymer surfaces [11–14], including the surface structure of fluorinated polymers [15, 16]. Due to water’s strong dipole, it is not surprising that water absorption is also known to change the dielectric properties of polymers, including the ferroelectric copolymer poly(vinylidene fluoride with trifluoroethylene) [17–19]. Water adsorption and absorption on crystalline poly(methyl vinylidene cyanide) and polyvinylidene fluoride with 30% trifluoroethylene, P(VDFTrFE, 70:30), was examined by thermal desorption spectroscopy [20–22]. Two distinctly different water adsorption sites are identified: one adsorbed species that resembles ice and another species that interacts more strongly with the polymer thin film. The existence of the latter species is consistent with Xray diffraction studies of water absorbed into the bulk of copolymers of polyvinylidene fluoride with trifluoroethylene crystalline thin films poly(vinylidene fluoride-trifluoroethylene) (70:30), P(VDF-TrFE), have been previously investigated as water adsorption systems

Angle resolved thermal desorption studies for poly(methylvinylidene cyanide) and poly(vinylidenefluoride trifluoroethylene)

We compare water adsorption and desorption on ferroelectric copolymer poly(vinylidene fluoride-trifluoroethylene), and the dipole ordered polymer poly(methylvinylidene cyanide). The angle-resolved thermal desorption spectra prove that the absorbed water species interacts more strongly with poly(vinylidene fluoride-trifluoroethylene) than with poly(methylvinylidene cyanide). The angle resolved thermal desorption spectra shows large deviations from the cos θ distribution for light illuminated poly(vinylidene fluoride-trifluoroethylene). Water desorption from poly(methylvinylidene cyanide) deviates from the cos θ distribution without illumination.

Inkjet printable-photoactive all inorganic perovskite films with long effective photocarrier lifetimes

Photoactive perovskite quantum dot films, deposited via an inkjet printer, have been characterized by x-ray diffraction and x-ray photoelectron spectroscopy. The crystal structure and bonding environment are consistent with CsPbBr3 perovskite quantum dots. The current-voltage (I-V) and capacitance-voltage (C-V) transport measurements indicate that the photo-carrier drift lifetime can exceed 1 ms for some printed perovskite films. This far exceeds the dark drift carrier lifetime, which is below 50 ns. The printed films show a photocarrier density 109 greater than the dark carrier density, making these printed films ideal candidates for application in photodetectors. The successful printing of photoactive-perovskite quantum dot films of CsPbBr3, indicates that the rapid prototyping of various perovskite inks and multilayers is realizable.

Molecular Adsorption and Fragmentation of Bromoform on Polyvinylidene Fluoride with Trifluoroethylene

Bromoform absorption on crystalline polyvinylidene fluoride with 30% of trifluoroethylene, P(VDF-TrFE 70:30) was investigated by photoemission and inverse photoemission and found to be associative and reversible. Molecular bromoform adsorption appears to be an activated process at 120 K with enhanced adsorption following the initial adsorption of bromoform. Strong intermolecular interactions are also implicated in the presence of a weak shake off or screened photoemission final state.

Mercury and C 2 B 10 Icosahedra Interaction

We contrast the interaction of mercury with adsorbed orthocarborane films and semiconducting (dehydrogenated) boron carbide. Photoemission spectra reveal small shifts in orthocarborane (C2B10H12) molecular orbital binding energies as well as the shift in mercury 5d5/2 shallow core level binding energies, suggesting only small interaction between mercury and the molecular film. Mercury does, however, interact with decomposed orthocarboranes i.e. semiconducting boron carbide.