Sze C. Yang

Double-strand polyaniline

We report the synthesis and the characterization of molecular complexes between polyaniline and a polymeric anion dopant. The molecular complex is advantageous in several respects: (1) It offers good stability of the conductive state. (2) The second strand allows for functionalization to improve material processability and for adjustment of properties to satisfy demands in applications. Evidence for supporting the structures of a molecular complex is outlined.

Corrosion protection of aluminum alloys by double-strand polyaniline

Abstract Corrosion protection of aluminum alloys was achieved by using a double-strand polyaniline as a surface conversion coating. The effectiveness of the coating was tested by salt-spray, and immersions in salt and acidic salt solutions. Electrochemical impedance spectroscopy measurements show that the conducting polymer coated AA7075 alloy is highly resistant to corrosion. Mechanistic studies indicate that the conducting polymer is not a barrier polymer coating, but it chemically converts the surface of the alloy to form a passive layer that protects the metal from corrosion. The use of double-strand polyaniline facilitates a paintable formulation for coating and provides good adhesion to the metal surface

Spectroscopy and Structure of the Alkali Hydride Diatomic Molecules and their Ions

All significant experimental measurements and theoretical calculations of the spectroscopy and structure of the alkali hydrides NaH, KH, RbH, and CsH, and the corresponding alkali deuterides, are identified and reviewed. Published molecular constant determinations from conventional and laser spectroscopy are evaluated; recommended spectroscopic constants for X 1Σ+ and A 1Σ+ states are tabulated. RKR and hybrid potential energy curves are evaluated; recommended RKR curves for X 1Σ+ and A 1Σ+ states are tabulated. Ground state dissociation energy (De) estimates are evaluated; recommended X 1Σ+ and A 1Σ+ state De and D0 values are tabulated. Accurate electronic structure calculations (Hartree–Fock or better) are listed and described briefly; all excited electron states considered are included. Experimental and theoretical radiative and dipole properties are noted and discussed. Calculations on the positive and negative ions of the four diatomic alkali hydrides are also listed and described briefly.

Morphological modification of polyaniline using polyelectrolyte template molecules

Abstract We report modification of polymer morphology for polyaniline by using different electrolytes to dissolve the aniline monomer before polymerization. Aqueous HCl, poly(vinylsulfonic acid), poly(acrylic acid), and poly(styrenesulfonic acid) were used as electrolytes for electrochemical polymerization of aniline. We found the morphology is strongly modified by using these polymer acids a electrolytes to replace the conventional aqueous HCl electrolyte. The observed variation in morphology among different polyelectrolytes is consistent with variation in binding of aniline to different polymer acids. The polymer acids appear to serve as a templates for polymerization.

Conducting polymer as electrochromic material: polyaniline

The first conducting polymer was reported in 1977 when Shirakawa, MacDiarmid, Heeger and other coworkers1 discovered that polyacetylene (Fig. 1), an organic polymer and electrical insulator, could be converted into an electrical conductor by absorbing a small amount of iodine. Since then, active research has led to the synthesis of new conducting polymers. Examples are: polyphenylene2, polypyrrole3, polythiophene4, poly-(phenylenesulfide)2 and polyaniline5. Their chemical structures are shown in Fig. 1.

Sensitivity and dynamic electrical response of CNT-reinforced nanocomposites

A series of dynamic compressive experiments were performed to experimentally investigate the electrical response of multi-wall carbon nanotube (CNT)-reinforced epoxy nanocomposites subjected to split Hopkinson pressure bar (SHPB) loading. Low-resistance CNT/epoxy specimens were fabricated using a combination of shear mixing and ultrasonication. Utilizing the CNT network within, the electrical resistance of the nanocomposite was monitored using a high-resolution four-point probe method during each compressive loading event. In addition, real-time deformation images were captured using high-speed photography. The percent change in resistance was correlated to both strain and real-time damage. The results were then compared to previous work conducted by the authors (quasi-static and drop weight impact) in order to elucidate the strain rate sensitivity on the electrical behavior of the material. Furthermore, the percent change in conductivity was determined using a Taylor expansion model to investigate the electrical response based on both dimensional change as well as resistivity change during mechanical loading within the elastic regime. Experimental findings indicate that the electrical resistance is a function of both the strain and deformation mechanisms induced by the loading. The bulk electrical resistance of the nanocomposites exhibited an overall decrease of 40–65% and 115–120% during quasi-static/drop weight and SHPB experiments, respectively.

The avoided crossing region of the CsH X 1Σ+ potential energy curve

Measurements of the laser induced fluorescence spectrum of CsH from the B 1Σ+ state to the X 1Σ+ state are reported. The Rydberg–Klein–Rees potential of the X 1Σ+ state is determined up to v″ = 24, a vibrational level very close to the dissociation limit. The dissociation energy of the X 1Σ+ state is estimated to be D0 = 14 360±30 cm−1 or De = 14 805±30 cm−1. The highest energy level of X 1Σ+ state observed in this experiment is v″ = 24, J″ = 16. It is found to be quasibound by 14 cm−1±30 cm−1. Both the vibrational spacings and the rotational constants show anomalous behavior as a function of the vibrational quantum number v″. This behavior is explainable in terms of the ionic–covalent avoided crossing. The Rydberg–Klein–Rees potential curve shows a sharp change of slope at v″≃20, and gives detailed information on the avoided crossing region. The avoided crossing point is determined to be Rc=5.33 A and the energy gap of the A 1Σ+ and X 1Σ+ adiabatic potentials at RC is found to be ΔV(Rc)=5020±30 cm−1. Com...

The dissociation energies of the diatomic alkali hydrides

A new method for estimating the dissociation energies for the alkali hydride molecules is reported. It involves extrapolating the known Rydberg–Klein–Rees potential curve of the A 1Σ+ state to the ionic–covalent avoided crossing point. The estimate dissociation energies De(X) are 16 000±400 cm−1 for NaH, 15 020±400 cm−1 for KH, and 14 580±600 cm−1 for RbH.

Anti-Corrosion Studies of Novel Conductive Polymer Coatings on Aluminum Alloys

We report the corrosion protection properties of a novel conductive polymer coating on aluminum alloys. The conductive polymer coating is a double strand molecular complex of polyaniline and a polyelectrolyte. The double strand polyaniline offers advantages in stability and processability over other forms of conductive polymers. The coated aluminum alloys (AA7075- T6) were evaluated for corrosion protection in an aggressive salt environment of.5N NaCl solutions using cyclic polarization and electrochemical impedance spectroscopy. Corrosion current densities were calculated for uncoated alloy samples and alloys coated with the conductive and non-conductive derivative of the double strand polymer. The conductive form of the double strand polyaniline coating shows a two order of magnitude lowering of the corrosion current over the uncoated samples and a one order magnitude lowering over the non-conductive form of the polymer coated samples. The shape of the cyclic polarization data closely resembles results of sulfuric acid anodized aluminum. This data indicates that the conductive state of the polymer is required for improved corrosion protection and an anodized type protection is occurring.

Experimentally determined PH-potential phase diagram for polyaniline; clues for optically distinguishable sub-phase in the conductor form

Abstract In this article we introduce an experimentally determined pH-potential phase diagram to correlate the structure of polyaniline with its properties. We illustrate that such a diagram is helpful and necessary for organizing and understanding the finer details of the properties of polyaniline. Using the pH-potential phase diagram to discuss patterns observed in in-situ optical absorption spectra, we show that there is a strong clue for the existence of two optically distinguishable sub-phases of the conductor form. It is speculated that these sub-phases of the conductor form may be related to the Curie and the Pauli spin phases previously reported by Epstein and MacDiarmid.