Harold Schonhorn

Kinetics of Wetting of Surfaces by Polymer Melts

The kinetics of wetting of both high‐energy (aluminum, mica) and low‐energy (FEP Teflon) surfaces by thermostated polyethylene and ethylene‐vinyl acetate copolymer melts in air were followed by the rate of approach of the apparent contact angle θ to its final value θ∞ and the change of the radius of the base of the polymer melt drop, r, with time. The volume of the drops studied varied from 0.006 cm3 to 0.028 cm3 and θ could be studied in the interval from about 100°>θ≥θ∞. The melted polymer drops maintain the shape of a spherical segment. The reduced dimension r/r0, where r0 is the value of r when the contact angle is 90°, is a universal function of the reduced time aTt, a dimensionless quantity. The reduced contact angle cosθ/cosθ∞, where cosθ∞ is the value of cosθ at infinite time, can be represented by a function of the same variable aTt. The shift factor aT is given by γ/Lwη, where γ is the surface tension of the liquid, η is the viscosity, and Lw is a length characteristic of the polymer‐substrate s...

Dynamic Mechanical Properties of the Transcrystalline Regions in Two Polyolefins

The dynamic Youngs moduli E of molded films of a polyethylene and a polypropylene were found to decrease with increasing thickness t. An upper limit of E appears to exist when the film thickness is reduced to less than 1 mil. For thicker films, E is inversely proportional to t. Finally, the modulus approaches a lower asymptotic value when t is in excess of 20 mil. The results can be represented quantitatively by a model in which the surface transcrystalline region and the bulk phase of the polymer respond in a parallel combination to the applied stress. The modulus of the transcrystalline region in each polymer is higher than that of the bulk phase. The thickness of a surface region is about 12 μ in polypropylene and 15 μ in polyethylene. The effects of thermal history and the nature of the molded surface were examined briefly.

Surface Treatment of Polypropylene for Adhesive Bonding

ABSTRACT The CASING (crosslinking by activated species of inert gases) treatment of polypropylene film in both oxygen and nitrous oxide is shown to be an effective surface treatment for conventional adhesive bonding. A crosslinked surface extending to a depth of about 300 A, apparently independent of exposure time, is produced in both excited oxygen and nitrous oxide.

Kinetics of spreading of glass on fernico metal

Abstract The spreading of drops of glass on Fernico metal at 1000°C was studied. Scanning electron microscopy confirmed the existence in this system of a precursor, microscopic foot (ahead of the advancing glass drop) whose height is of the order of 1 μg. The kinetics of spreading did not appear to exhibit a droplet mass effect. We comment on the relationships between the spreading phenomena encountered in this complex system and other recent studies of spreading of polymer melts.

Structural and chemical analysis of ion beam produced conductive regions on highly resistive organic films

Thin films of both polymeric and nonpolymeric organic solids turn optically dense and electrically conductive on irradiation with high energy ion beams (e.g., 2 MeV Ar+). The structural and chemical properties of these films were investigated by ultraviolet (UV) visible, infrared (IR), Raman spectroscopic techniques, electron spin resonance (ESR), electron spectroscopy for chemical analysis (ESCA), and Rutherford backscattering (RBS) measurements. Specifically, in the case of 3,4,9,10‐perylenetetracarboxylic dianhydride (PTCDA) and nickel phthalocyanine (NiPc), and UV visible, IR, and Raman spectra show the loss of the initial molecular structure at low irradiation doses (1013–1014 cm−2) followed by the appearance, at high doses, of a spectrum similar to that observed for amorphous carbon. The Raman spectra indicate the absence of any long range graphitic microcrystalline structure and suggest that the films are nearly amorphous at higher doses. The RBS spectra indicate gradual loss of oxygen in PTCDA with increasing irradiation dose. There is negligible oxygen left in the film at high doses and a maximum loss of ∼35% (∼15%) of the carbon atoms in PTCDA (NiPc) is observed. The resistivity of the films decreases with increasing dose, reaching a minimum of ∼5×10−4 Ω cm at a dose of ∼1017 Ar+/cm2. Surprisingly, the resistivity of these films at high doses (∼1017 Ar+/cm2) is considerably lower than that of any amorphous phase of carbon. In the case of NiPc, such a low resistivity is obtained even though 60% of the N and 100% of the Ni originally contained in the films are retained. In situ measurements of the evolution rate of molecular fragments during the bombardment indicate a decrease with dose, suggestive of an irreversible modification of the material with ion bombardment.Thin films of both polymeric and nonpolymeric organic solids turn optically dense and electrically conductive on irradiation with high energy ion beams (e.g., 2 MeV Ar+). The structural and chemical properties of these films were investigated by ultraviolet (UV) visible, infrared (IR), Raman spectroscopic techniques, electron spin resonance (ESR), electron spectroscopy for chemical analysis (ESCA), and Rutherford backscattering (RBS) measurements. Specifically, in the case of 3,4,9,10‐perylenetetracarboxylic dianhydride (PTCDA) and nickel phthalocyanine (NiPc), and UV visible, IR, and Raman spectra show the loss of the initial molecular structure at low irradiation doses (1013–1014 cm−2) followed by the appearance, at high doses, of a spectrum similar to that observed for amorphous carbon. The Raman spectra indicate the absence of any long range graphitic microcrystalline structure and suggest that the films are nearly amorphous at higher doses. The RBS spectra indicate gradual loss of oxygen in PTCDA wit...

Kinetics of wetting of surfaces by polymer mealts

Abstract We review previous work on the kinetics of wetting of surfaces by polymer melts. We then show that glycerol also exhibits the same anomalous behavior, satisfying the same scaling laws independent of the initial mass of the spreading drop as we had previously established for polymer melt drops. The limiting radial velocity of wetting vanishes as l − 5 6 and the cosine of the apparent contact angle attains its final value according to apparent second-order kinetics.

Adhesion of Polytetrafluoroethylene

Abstract Nucleation and crystallization of polytetrafluoroethylene in contact with gold produces a surface region of high mechanical strength in the polymer as evidenced from the strong adhesive joints prepared with a conventional epoxy adhesive. In addition, the wettability of the gold-nucleated polytetrafluoroethylene, after dissolution of the gold, is vastly improved. The critical surface tension of wetting increases from 18.5 dynes/cm to 40 dynes/cm, indicating an increase in the surface density of the gold-nucleated polymer. We conclude from this study, that the occurrence of the normal weak boundary layer on polytetrafluoroethylene is a consequence of the morphology of the surface region and is therefore influenced by the method of preparation.

Comment on ’’Thermal oxidation of InP and properties of oxide film’’

In a recent paper, Yamaguchi and Ando [J. Appl. Phys. 51, 5007 (1980)] discussed the composition of thermally grown oxide films on InP. Reanalysis of their infrared absorption data in conjunction with Raman data shows that their assignments of oxide products are in error. The dominant product at T≳620 °C is indium orthophosphate.

Effect on Wettability of FEP Teflon Surface Morphology

ABSTRACT Wettability of FEP Teflon® (a perfluorinated ethylene-propylene copolymer) is vastly improved by heterogeneous nucleation and crystallization in contact with gold, a high surface free energy substrate. The critical surface tension of wetting (γe) increases from 18.8 dynes/cm to 40.4 dynes/cm. We compute that this rise in γe results from a 20 percent increase in the surface density of gold-nucleated FEP Teflon®. The increase in critical surface tension from 18.8 dynes/cm to 20.6 dynes/cm, for as received FEP Teflon which had been crosslinked by helium in a glow discharge (CASING technique), suggests an increase of the surface density with crosslinking. The critical surface tension of the gold-nucleated FEP Teflon® is sharply decreased from 40.4 dynes/cm to 22.0 dynes/cm by short exposure to the CASING treatment in helium. The results of ATR infrared spectroscopy show that in the surface region of the polymer there are no chemical changes such as the presence of unsaturated groups or the introducti...

Relationship between Fiber Tension and Drawing Velocity and Their Influence on the Ultimate Strength of Laser-Drawn Silica Fibers,

The ultimate strength of laser‐drawn silica fibers has been found to be related to the velocity of drawing and the tension in the fiber required to maintain it. We find that when the uncoated pristine fiber tension during drawing exceeds about 80 g for a 110‐μm fiber there is a dramatic decrease in strength (coated fiber). Dimensional analysis of the laser‐drawing process indicates that for this particular system the fiber tension should be proportional to the cube of the drawing velocity. This is confirmed experimentally for fibers drawn at a variety of tensions and speeds of 0.4 and 1.0 m/s.