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Physical Properties of Polymeric Solids
Published in Richard A. Pethrick, Gennadi E. Zaikov, Teiji Tsuruta, Naoyuki Koide, Polymer Yearbook 13, 2019
Tisato Kajiyama, Atsushi Takahara
Chemical force microscopy or molecular force microscopy can carry out by using a standard AFM which has a cantilever tip modified with some functional group. T. Nakagawa (3927, E1361) measured the chemical force acting between a chemically modified cantilever tip and a chemically modified silicone wafer. The chemically modified cantilever tip and the silicone wafer were prepared by the chemisorption of organosilane from a solution. Using the chemically modified tips, the monolayer consisting of hydrocarbon chains could be discriminated from that consisting of perfluorocarbon chains by measuring the adhesive force in ethanol. If the solid surface and cantilever tip has the same chemical structure, the largest adhesive force was observed. The origin of interaction between the chemically modified tips and the sample surface depended on the chemical structure of the monolayers and the environmental liquids where the interactions were measured. If the interaction between monolayer and environmental liquid was strong, the adhesion force became small due to the weak aggregation of hydrocarbon or fluorocarbon chains.
Surfaces
Published in Gerald L. Schneberger, Adhesives in Manufacturing, 2018
With ionic crystalline solids, surface charging can occur due to unequal vacancy energies. Near-surface vacancies in these solids may be either positively or negatively charged. The energy associated with the formation of these vacancies varies, and an excess of one or the other type of vacancy occurs. This excess causes a voltage between the surface and the interior of the solid. The overall energy of the system is decreased when there is an excess of positively charged ion vacancies in the solid, and these migrate toward the surface. When in the bulk (Fig. 10a), they will bring about an internal arrangement of vacancy charges (Fig. 10b) such that the positive charge exists near the surface, and the Debye charged layer will form. This layer will have no effect on the behavior of the solid surface, as in, for example, its interaction with an adhesive.
Hybrid materials and surfaces
Published in Chang-Sik Ha, Saravanan Nagappan, Hydrophobic and Superhydrophobic Organic-Inorganic Nanohybrids, 2018
Chang-Sik Ha, Saravanan Nagappan
The wettability of a solid surface is determined by two forces: cohesive force and adhesive interactions between the solid surface and the liquid drop. In general, most natural and synthetic materials and surfaces exhibit hydrophilic or hydrophobic surface properties [62]. The term “hydrophilic” also refers to the “water loving” nature. Hydrophilic surfaces are wetted easily by water droplets (but not dissolved) due to the penetration of the water droplet at the surface [62]. The hydrophilicity is also due to the presence of oxygen or nitrogen atoms in their structure, polar molecules, high surface energy and surface tension, and smooth surface. These properties can allow the water droplet to penetrate into surface of the substrate (e.g., salt, textile, wood, concrete, and leather). The polar nature of the hydrophilic surface can attract a water droplet through strong hydrogen bonding and shows a CA below 90°, whereas the water droplet completely penetrates the surface when the surface has more polar groups. This property is called superhydrophilicity, and the surface CA is generally below 10° [63].
Effect of surface texture on the mechanical performance of bonded joints: a review
Published in The Journal of Adhesion, 2023
Nidhal Naat, Yasmina Boutar, Sami Naïmi, Salah Mezlini, Lucas Filipe Martins Da Silva
Interatomic and intermolecular forces magnitude can commonly be linked to fundamental thermodynamic quantities, such as, surface free energies of both adherend and adhesive. Therefore, good wetting criteria is essential for good adhesion. Figure 5 illustrates that poor wetting causes interfacial defects and a reduction in the contact area between the adherend and the adhesive, thereby lowering bond strength. On the other hand, complete wetting provides the highest joint strength. Therefore, for an adhesive to well wet a solid surface, the surface energy of the adherend should be higher than the surface energy of the adhesive.[53] This theory has led to the development of adhesives with lower surface energy than those of adherends. According to this theory, organic adhesives such as epoxies wet and have good adhesion to metals, while they show poor wettability and weak adhesion to untreated polymeric substrates such as polyethylene, polypropylene and fluoroplastics.[54]
Performance Enhancement Using Porous Slabs in a Jet Impingement Microchannel Heat Sink
Published in Heat Transfer Engineering, 2022
Jyoti Pandey, Mohd. Zahid Ansari, Afzal Husain
Several parameters are analyzed using numerical modeling in this study to demonstrate fluid flow and heat exchange behavior. Variation of the characteristic parameters is observed for different flow and geometric conditions, i.e., jet Reynolds number (200 ≤ Re ≤ 500) and porous media size. The Reynolds number is defined as Tw,max determines the proficiency of the MJI-P-MCHS. Similarly, Rth determines the overall magnitude of hindrance offered by the heat sink in the process of heat transfer. where, ΔTmax= Tw,max ̶̶ Tin is the maximum temperature rise that is equal to the difference between Tw,maxand Tin. Additionally, havg indicates heat exchange occurred between the solid surface and fluid within the heat sink, which is expressed as [11]
Study on film effects during isothermal drying of square capillary tube using Lattice Boltzmann method
Published in Drying Technology, 2022
Supriya Bhaskaran, Divyansh Pandey, Debashis Panda, Shubhani Paliwal, Nicole Vorhauer, Evangelos Tsotsas, Vikranth Kumar Surasani
For the study of film formation, a fully saturated single capillary tube is considered for a convective drying phenomenon. During drying, the phase change instigates the invasion process by the counter diffusion of vapor and air. The molecular forces between and within the gas, liquid and solid phases, govern the invasion. The existence of adhesive forces between the liquid-solid interfaces makes the wetting phase stick to the solid surface. The combined effects of adhesive forces, cohesive forces within the gas and liquid phases and counter diffusion due to phase change phenomena make the invasion a non-uniform process in the square cross-section of the capillary tube. As the invasion progresses, the bulk meniscus recedes while a thick non-uniform liquid layer (film) remains attached to the corners of the tube, see Figure 1. At micro-scale, the molecular forces induce macro-scale pressure gradient within the wetting phase. The developed pressure gradient along the thick corner films facilitates liquid transport and existence of the film for a prolonged period even when the phase change occurs along with the film interface. Thus, the film formation process is multicomponent and multiphase in nature involving air and water (in liquid and vapor phases).