F. J. Boerio

RAMAN SCATTERING IN CRYSTALLINE POLYETHYLENE.

The Raman scattering in crystalline polyethylene, deuterated polyethylene, and n‐paraffins has been investigated as a function of temperature. Crystal‐field splitting of the A1G methylene bending mode observed at room temperature increases at − 160°C in both polyethylene and deuterated polyethylene. No splitting of the B2G skeletal stretching mode and the B3G methylene twisting modes in polyethylene is observed at room temperature, but the two components of the space group fundamental are resolved at − 160°C. Similarly, splitting of the B2G methylene wagging mode in deuterated polyethylene is observed at − 160°C but not at room temperature. The observed crystal‐field splittings are discussed in terms of splittings calculated from repulsive forces between hydrogen atoms on neighboring chains in the polyethylene crystal.

Vibrational Analysis of Polytetrafluoroethylene

With the aid of newly obtained Raman data, a normal coordinate analysis has been performed on the polytetrafluoroethylene (PTFE) molecule. Calculations were made for three different helix models including the 13/6, 15/7, and planar zigzag. The frequencies corresponding to the 15/7 helix were fitted by adjusting the force field. The conformation was changed, and the changes in the frequencies for the 13/6 helix and the planar zigzag were calculated using the same force field. Changes predicted for the 13/6 helix from the normal coordinate calculations are not in agreement with those actually observed at the 19°C transition. It was therefore hypothesized that the changes in the infrared and Raman spectra at this transition were due to Raman thermal defects as suggested by Brown. The potential‐energy distribution was obtained for the optically active modes of the 15/7 helix, and the eigenvectors were presented for the motions of the A modes. The dispersion curve for the 15/7 helix is presented, and the coupl...

Raman Scattering and Band Assignments in Polytetrafluoroethylene

The laser‐excited Raman spectrum of polytetrafluoroethylene (PTFE) is reported. A new band, an E1 mode at 198 cm−1, is observed. Additional bands, which are apparently E2 modes, are observed at 308 and 676 cm−1 at a sample temperature of − 50°C and at 389 and 741 cm−1 at a sample temperature of − 130°C that are not observed in samples at room temperature. Bands at 575 and 595 cm−1 are found to change in intensity as a function of temperature. Band assignments in PTFE are discussed utilizing the Raman spectra of n‐C5F12, n‐C6F14, C14F30, and C18F38, which are reported here for the first time.

The structure of γ-aminopropyltriethoxysilane films on iron mirrors

Abstract The structure of γ-aminopropyltriethoxysilane (γ-APS) films deposited on mechanically polished iron mirrors from aqueous solutions has been investigated using reflection-absorption infrared spectroscopy. Films formed at the natural pH of 1% aqueous solutions of γ-APS (∼10.5) were about 120 A in thickness and were composed of highly hydrolyzed oligomers characterized by infrared bands near 1550 and 1480 cm −1 . These bands were assigned to NH 2 deformation modes in amino groups that were very strongly hydrogen bonded with silanol groups to form cyclic structures. Films formed at pH = 12 were characterized by infrared bands near 1580 and 1488 cm −1 that were assigned to deformation modes of NH + 3 groups obtained by essentially complete proton transfer from silanol groups to amino groups. In all cases the as-formed films were stable in a dry environment but exposure to atmospheric humidity disrupted the strong hydrogen bonding, enabling the oligomers to condense to form polysiloxanes.

An XPS investigation of the adsorption of aminosilanes onto metal substrates

Spectroscopic evidence has been obtained showing that γ-aminopropyltriethoxysilane (γ-APS) is partially adsorbed onto the oxidized surfaces of certain metals through the amino group. Results obtained from X-ray photoelectron spectroscopy (XPS) indicate that the amino groups on γ-APS are protonated by interaction with hydroxyl groups on the surfaces of silicon, iron, titanium, aluminum, nickel, and magnesium. The extent of protonation is greatest on silicon, aluminum, and titanium; intermediate on iron and nickel; and least on magnesium; and thus correlates well with the predicted isoelectric points of the oxides. The extent of protonation also depends on the pretreatment of the substrate. Thus, the extent of protonation of the amino groups is greater on aluminum surfaces that have been treated by the Forest Products Laboratory (FPL) etching process than on aluminum surfaces that have been mechanically polished. γ-APS interacts with the oxidized surface of copper by formation of complexes in which the lone...

Surface‐enhanced Raman scattering from p‐nitrobenzoic acid

The surface‐enhanced Raman scattering (SERS) from thin films formed by p‐nitrobenzoic acid (PNBA) adsorbed onto silver island films has been investigated. SERS spectra obtained using low laser powers were very similar to the normal Raman spectra of the sodium salt of PNBA and were characterized by strong bands near 1600 and 1355 cm−1 and by weaker bands near 1395, 1115, and 875 cm−1. The band near 1395 cm−1 was assigned to the symmetric stretching mode of carboxylate groups, indicating that PNBA was adsorbed as a metal salt. When PNBA films were irradiated at high laser powers, a rapid reaction occurred. The bands near 1355 and 1115 cm−1 gradually decreased in intensity and a strong band near 1460 cm−1 and a strong doublet near 1150 cm−1 gradually appeared. The band near 1460 cm−1 and the doublet near 1150 cm−1 were attributed to azodibenzoate formed by the reductive coupling of PNBA molecules at the silver surface during laser irradiation. When adsorbed PNBA films were irradiated at low laser powers, the...

Development of novel single-wall carbon nanotube?epoxy composite ply actuators

This paper describes a carbon nanotube epoxy ply material that has electrochemical actuation properties. The material was formed by dispersing single-wall carbon nanotubes in a solvent and then solution casting a thin paper using a mold and vacuum oven. In order to take advantage of the high elastic modulus of carbon nanotubes for actuation, epoxy as a chemically inert polymer is considered. An epoxy layer was cast on the surface of the nanotube paper to make a two-layer ply. A wet electrochemical actuator was formed by placing the nanotube epoxy ply in a 2 M NaCl electrolyte solution. Electrochemical impedance spectroscopy and cyclic voltammetry were carried out to characterize the electrochemical properties of the actuator. The voltage–current relationship and power to drive the actuator material were also determined. Compared to previous single-wall carbon nanotube buckypaper tape actuators, which had poor adhesion between the nanotubes and tape, and other nanotube–thermal plastic polymer actuators, which could not provide high strength, the epoxy based actuator has a higher elastic modulus and strength, which will be useful for future structural applications. This demonstrates that a polymer layer can reinforce nanotube paper, which is an important step in building a new structural material that actuates. Further work is under way to develop a solid electrolyte to allow dry actuation. Finally, these actuator plies will be laminated to build a carbon nanocomposite material. This smart structural material will have potential applications that range from use in robotic surgical tools to use as structures that change shape.

Interphase Composition in Aluminum/Epoxy Adhesive Joints

Abstract Model epoxy/aluminum adhesive joints were constructed with a geometry that allowed cracks to be propagated extremely close to the adhesive/adherend interface. The joints were fractured in air and the fracture surfaces analyzed using angle resolved X-ray photoelectron spectroscopy. Fracture occurred in a manner that left a significant amount of aluminum oxide on the epoxy side of the fracture surface and very little epoxy on the aluminum side. Aliphatic amine curing agent found associated with the aluminum oxide on both the adhesive and the adherend sides of the fracture surface was protonated by the acidic hydroxyls present in the aluminum hydroxide. Moreover, catalysis of the curing reaction by these hydroxyls resulted in an increased degree of crosslinking in the regions of the adhesive very close to the oxide surface. Thus, the aluminum oxide surface modified the structure of the adhesive in the near surface regions and resulted in the formation of a distinct interphase region with a compositi...

Structure and properties of organosilane primers for adhesive bonding

Abstract Reflection—absorption infrared spectroscopy was used to determine the structure of films formed by the adsorption of γ-aminopropyltriethoxysilane (γ-APS) onto iron mirrors from aqueous solutions. Films formed at the natural pH of 1% aqueous solutions were composed of oligomers characterized by infrared bands near 1550, 1470 and 1130 cm-1 while films formed at pH values less than about 9.0 were composed of polysiloxanes characterized by bands near 1600, 1500 and 1135 cm-1. The polysiloxanes formed at low pH values were much more effective as primers for improving the hydrothermal stability of iron/epoxy lap joints than the oligomers obtained at high pH values. Joints prepared from substrates primed with γ-APS at pH = 8.0 retained about 70% of their strength after immersion for 60 days in water at 60°C while those prepared from substrates primed at pH = 10.4 retained only about 50% of their strength. By comparison, joints prepared from unprimed substrates retained only about 25% of their strength after such exposure.

Analysis of Thin Films on Metal Surfaces

Abstract External reflection infrared spectroscopy was used in combination with other surface analysis techniques such as ellipsometry, Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS) to determine the structure of organofunctional silanes adsorbed onto 2024 aluminum and titanium-6 Al, 4V mirrors. The results obtained indicated that the adsorption of γ-aminopropyltriethoxysilane (γ-APS) onto aluminum was a strong function of pH and adsorption time. Films formed by adsorption of γ-APS at pH = 8.5 were composed of polysiloxanes containing amine hydrochlorides. The structure of films formed by adsorption of γ-APS at pH-10.4 depended on time. Films obtained after one minute were composed of polysiloxanes that did not interact strongly with the oxide but during 15 minutes adsorption the air-formed oxide was dissolved and copper accumulated near the surface of the mirrors. Films formed by the adsorption of γ-glycidoxypropyltrimethoxysilane (γ-GPS) onto aluminum were composed of poly...