Surface free energy

Most industrially applied polymer resins and composites have low surface free energy and lack polar functional groups on their surface, resulting in inherently poor adhesion properties. A strong research momentum to understand polymer adhesion in the last decade has been motivated by the growing needs of the automotive and aerospace industries for better adhesion of components and surface coatings. This paper reviews the recent research efforts on polymer adhesion with a special focus on adhesion mechanisms. It starts with an introduction to adhesion with explanatory notes on adhesion phenomena. Recent research on the adhesion mechanisms of mechanical coupling, chemical bonding and thermodynamic adhesion is then discussed. The area of adhesion promoters is reviewed with the focus on plasma and chemical treatments, along with direct methods for adhesion measurement. The topics of polymer blends and reactive polymerization are considered and the interactions with adhesion mechanisms are reported. The concluding section provides recommendations regarding future research on the contentious aspects of currently accepted adhesion mechanisms and on strategies for enhancing polymer adhesion strength.

A unified mechanistic model for slug liquid holdup is developed based on a balance between the turbulent kinetic energy of the liquid phase and the surface free energy of dispersed spherical gas bubbles. The turbulent kinetic energy is estimated by use of the shear stress at the ...

The acid-base approach to the calculation of solid surface free energy and liquid-liquid interfacial tensions is a practical example of application of correlation analysis, and thus it is an approximate approach. In these limits, and provided that wide and well-obtained sets of contact angles or interfacial tension data are used for their computation, surface tension components can be considered as material properties. Although their numerical value depends on the characteristics of the chosen reference material, their chemical meaning is independent on the selected scale. Contact angles contain accessible information about intermolecular forces; using surface tension component (STC) acid-base theory, one can extract this information only making very careful use of the mathematical apparatus of correlation analysis. The specific mathematical methods used to obtain these results are illustrated by using as an example a base of data obtained by the supporters of the equation-of-state theory (EQS). The achievements are appreciably good and the agreement between STC and EQS is discussed.

The mechanical and surface properties of chitosan, poly(vinyl pyrrolidone) (PVP) and chitosan/PVP blends before and after UV irradiation have been investigated by mechanical testing (Instron) and by contact angle measurements. Air-dried specimens were submitted to treatment with UV irradiation (wavelength 254nm) for different time intervals. The changes in mechanical properties, such as breaking strength, percentage elongation and Young's modulus have

Adherend surface treatment prior to bonding is pivotal for efficient assembly or repair of carbon fiber reinforced polymer (CFRP) composites. The effect of CFRP surface treatment has gathered much attention in the literature but reported test results on fatigue performance are less prevalent. The effect of surface treatment was extended in this work to cover the static and also fatigue strength of single-lap bonded joints. Surface treatments of manual sanding, grit blasting, and peel-ply plus grit blasting were produced and their surface roughness and energy were measured. The sanding treatment produced the lowest static strength but the best static strength retention at one million cycles with 55.4%, compared to 50.3% for peel-ply plus grit blasting, and 47.5% for grit blasting. The failure surfaces of the fatigued sanding specimens were the most uniform, mostly of cohesive failure mode for static and low-cycle fatigue, progressing to thin-layer cohesive for high-cycle fatigue.

Organo-modified fluorohectorite (OFH) clay filled polysulfone (PSf) nanocomposite films were prepared by solution casting method. The morphology of the nanocomposites was investigated using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The surface properties assessed by contact angle measurements showed significant increase in hydrophobicity of the nanocomposites relative to the virgin polymer. The relationship between contact angle, surface roughness, and surface chemistry was discussed. From the measured contact angle values, various surface parameters such as total surface free energy, interfacial free energy, work of adhesion, spreading coefficient, and Girifalco-Good's interaction parameter were calculated. The mechanical properties like tensile strength and elongation at break were increased considerably upon increasing the organoclay content to 3 wt%. But further increase in the clay content decreased the properties to some extent. The dielectric investigation carried out in room temperature indicated that dielectric constant of PSf/OFH clay nanocomposite films decreases with the increase of the clay content. This work describes the preparation of PSf nanocomposite with desired hydrophobic, dielectric, and mechanical properties for water repellent and electronic applications.