Search

Contact angles are the characteristic angles made between the surface of a liquid and a solid surface. The measurement of contact angles can be done with multiple methods. However, because there ar...

Surface topography and surface chemistry heterogeneity are widely accepted as causes of contact angle hysteresis. Contact angle hysteresis occurs on essentially all industrial polymer films. Four u...

Advancing and receding contact angle measurements on polymer surfaces can be performed using a number of different methods. Ballistic deposition is a new method for both rapidly and accurately measuring the receding contact angle of water. In the ballistic deposition method, a pulsed stream of 0.15-μL water droplets is impinged upon a surface. The water spreads across the surface and then coalesces into a single 1.8-μL drop. High-speed video imaging shows that, on most surfaces, the water retracts from previously wetted material, thereby forming receding contact angles that agree with the receding angles measured by the Wilhelmy plate technique. The ballistic deposition method measures the receding angle within one second after the water first contacts the surface. This rapid measurement enables the investigation of polymer surface properties that are not easily probed by other wettability measurement methods. For example, meaningful contact angles of water can be obtained on the water-soluble low-molecul...

The effects of low-molecular-weight oxidized materials generated by corona treatment on the adhesion properties of polypropylene (PP) film were investigated by adhering four different materials to the modified PP: a polyamide printing ink, vapor-coated aluminum, a synthetic-rubber pressure-sensitive adhesive, and an acrylate-based pressure-sensitive adhesive. The low-molecularweight materials enhanced the adhesion of the ink and acrylate-based material, but hindered the adhesion of the metal and the rubber-based adhesive. This seemingly contradictory adhesion behavior can be readily explained using the principles outlined by Brewis and Briggs in the 1980s.

Contact-angle measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize flame-treated biaxially oriented polypropylene (PP) films. While the surface of PP treated in a fuel-lean flame is highly oxidized, no watersoluble low-molecular-weight oxidized material (LMWOM) is formed by the flame treatment. A new computational model, SPIN, was used to determine the chemical composition of the impinging flames used to modify the PP. The SPIN model indicates that the species primarily responsible for the surface oxidation of the PP are OH, HO2, H2O2, and O2. Because the concentration of atomic O in the flame is low, there is little scission of the PP chains and no formation of LMWOM. AFM indicates that a 'nodular' surface topography is generated during the flame oxidation of the PP. The surface topographical features generated by flame treatment are probably the result of the agglomeration of intermediate-molecular-weight materials.

Contact-angle measurements, the ASTM standard wetting test for polyolefin films, and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize flame-treated polypropylene (PP) films. Two combustion models, STANJAN and PREMIX, were then used to determine the chemical and physical properties of the flames used to treat the PP films. Both the flame equivalence ratio and the position of the PP film in the flame are important variables in determining the extent of oxidation and improvement in wettability obtained by flame treating. The optimal equivalence ratio for the flame treatment of PP is 0.93, while the optimal luminous flame-to-film distance is 0-2 mm. Modeling of the combustion processes occurring in the flame provides evidence that the extent of treatment correlates closely with the concentrations of H, O, and OH radicals present in the flame. The extent of surface modification of the flame-treated PP does not appear to correlate with either the flame temperature or the concentraion of ...

Oxidation is the most common surface modification of polymers. This paper presents a comparison of five gas-phase surface oxidation processes: corona discharge, flame, remote air plasma, ozone, and combined UV/ozone treatments. Well-characterized biaxially oriented films of polypropylene and poly(ethylene terephthalate) were treated by each of the five techniques. The surface-treated films were then analyzed by X-ray photoelectron spectroscopy (XPS or ESCA), contact-angle measurements, and Fourier-transform IR (FTIR) spectroscopy. Corona, flame, and remote-plasma processes rapidly oxidize polymer surfaces, attaining XPS O/C atomic ratios on polypropylene of greater than 0.10 in less than 0.5 s. In contrast, the various UV/ozone treatments require orders of magnitude greater exposure time to reach the same levels of surface oxidation. While corona treatment and flame treatment are well known as efficient means of oxidizing polymer surfaces, the ability of plasma treatments to rapidly oxidize polymers is no...

Contact-angle measurements in air and water environments and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface properties of air-corona-treated polypropylene (PP) and poly(ethylene terephthalate) (PET) films. Surface properties were examined as a function of the storage time at various temperatures. Corona treatment forms water-soluble, low-molecular-weight oxidized materials on both polymer films. Corona-treated PP and corona-treated PET films have markedly different responses to aging. For corona-treated PP stored at ambient temperatures, only a slight decrease in wettability was observed. This decrease was attributed to the reorientation of oxidized functionalities within the surface region. At elevated storage temperatures, migration of oxidized species out of the surface region occurred under some conditions. For corona-treated PET, extensive migration and reorientation of oxidized groups occurred even at ambient temperatures, leading to significant decreases in wettability...

X-ray photoelectron spectroscopy (ESCA), wettability measurements, and an ink adhesion test were used to characterize changes in the surface properties of air-corona-treated polypropylene (PP) films upon aging under a variety of storage conditions. No changes in ESCA O/C atomic ratios as a function of aging were observed for corona-treated PP films. The wettability data indicated a slight decrease in wettability upon aging. Aging did not affect ink adhesion for the particular PP and ink studied. The responses obtained were independent of the various film storage conditions employed. The slight decrease in wettability observed upon aging was attributed to reorientation of oxidized functionalities within the surface region.

The surface chemical modification of polypropylene by CF3Cl plasma treatment was studied by ESCA, wettability measurements, and pressure-sensitive-adhesive performance tests. Improved adhesion was observed on polypropylene treated under CF3Cl plasma conditions that maximized Cl and minimized F and O incorporation. Polypropylene treated using CF3Cl plasmas had a high dispersive component of surface energy, as indicated by low diiodomethane contact angles. High dispersive energy is characteristic of chlorinated surfaces, and may contribute to the improved adhesion.

—ESCA, wettability measurements, SEM, weight-loss determinations, and an ink adhesion test were used to characterize low-molecular-weight oxidized materials (LMWOM) formed during the corona-discharge treatment of polypropylene film. Water-soluble LMWOM is readily formed by scission processes occurring during corona treatment. The presence of water-soluble LMWOM complicates the interpretation of wettability-based measurements of corona effectiveness. Surface roughening on corona-treated polypropylene is caused by the interaction of LMWOM and water in a high-relative-humidity environment. LMWOM does not necessarily form a weak boundary layer that hinders subsequent adhesion of ink to the corona-treated film.