Adhesion physical adsorption/wetting

Equilibrium and dynamic wetting and spreading processes, adhesion, physical adsorption, chemisorption and heterogeneous catalysis, spectroscopic and optical studies of surfaces, flow through porous media... 

Several mechanisms by which mucoadhesives adhere to biological surface have been suggested, including the electronic, adsorption, wetting, diffusion, and fracture theories. It is likely that water movement from the mucosa to the polymer and physical entanglement of the adhesive polymer in the mucus glycoprotein chains are important in obtaining adherence. 

Eriekson and Plueddemann suggest that particularly in filled systems, complete wetting of the mineral surface will improve adhesion by physical adsorption that would exceed the cohesive strength of the polymer. However, it is difficult to see how physical adsorption provides bond reinforcement when the polymer is in competition with water and possibly other weakly bonded surface layers, and where chemical bonding is also present [12],... 

As stated in the Introduction, physical adsorption is common to all three types of adhesion systems. For good adsorption, wetting is necessary and essential. Wetting and wettability of polymers have been reviewed by Zisman, " ) Mittal,etc. In the past, efforts have been focused on the thermodynamic aspects of wetting because wetting is the only way to achieve maximum thermodynamic (Lifshitz-van der Waals) work of adhesion according to Dupree s... 

Immiscible Planar Substrates. Consider the simplest case in which a liquid adhesive is placed on a molecularly smooth solid substrate with which it is totally immiscible. The time-dependent process whereby the adhesive and substrate come into intimate contact is called wetting. The interface is a plane across which molecular forces of attraction, also denoted intrinsic adhesion, exist between the liquid and solid. These forces range in magnitude from strong covalent or ionic chemical bonds to weaker physical adsorption, e.g., H-bonding, dipole-dipole, and van der Waals interactions. 

Thus, protein adsorption and cell adhesion occur for various reasons and in different appearances. When surfaces of living systems are involved, specific recognition mechanisms undoubtedly play crucial roles. Nevertheless, since we are dealing with a rather general phenomenon, it is likely that these specific interactions are superimposed on a generic interaction mechanism. Bioadhesion and adsorption is very complicated from a physical chemical point of view. Interfacial tensions, wetting and electrical properties of the surfaces are prominently involved. 

Adsorption of polymers on a solid flat substrate is an important physical chemistry issue in many applications of polymers, such as composites, coatings, adhesion, lubricates, gel chromatography, wetting, colloidal stability, piping transportation. 

Adsorption on Planar Substrates. The simplest type of adhesive bond occurs when a liquid is contacted with a planar solid with which it is totally immiscible and into which it cannot diffuse. Bonding is limited to physical and/or chemical adsorption at specific sites on the substrate surface. A sharp and planar interface is formed. This is the usual situation when an organic adhesive adheres to a very smooth inorganic substrate. The time-dependent process during which interfacial bonds form is called wetting. In general, it involves an increase in the... 

Superhydrophobic materials have surfaces that are extremely difficult to wet, with water contact angles in excess of 150° or even greater, see Fig. 20.6 shows that surfaces with ultrahydrophobicity have aroused much interest with their potential applications in self-cleaning coatings, microfluidics, and biocompatible materials and so on. Many physical-chemical processes, such as adsorption, lubrication, adhesion, dispersion, friction, etc., are closely related to the wettability of materials surfaces [52, 53]. Examples of hydrophobic molecules include alkanes, oils, fats, wax, and greasy and organic substances with C, N, O, or F as the key constituent element. 

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