Rheology adhesive force

AFM can also be used to probe local mechanical properties of thin films of food biopolymers, which are difficult to measure using traditional rheological methods. Several mechanical models have been developed to analyze the Young s modulus of food systems. One of the simplest models, the Hertz model, assumes that only the elastic deformation exists in a surface with spherical contacts, and the adhesion force can be neglected (Hugel and Seitz 2001). Equation (8.2) describes the relationship between the loading force, F and the penetration depth, d, where a is the radius of contact area, R the curvature of the tip radius, Vi and the Poisson s ratios of the two contact materials that have Young s modulus, Ei and E2. ... 

The presence of an oil film on the surface causes adhesion as a result of surface tackiness. In this case the adhesive forces of the particles depend on the rheological properties and thickness of the oil film. 

Fig. 13. Correlation in time scale dependence between adhesion and linear rheology, a) Adhesion energy (blue points) and peak adhesive force (red points) as a function of separation velocity for a polymer gel with an equilibrium modulus of 470 Pa b) tan(6) as a function of oscillation frequency.

Based on the arguments presented thus far, it would seem that, for a given PSA, the work of adhesion, and thus the peel force, should decrease systematically as the surface energy of the release coating is decreased. Therefore, fluorochemical containing polymers should provide the lowest release forces. In practice, these generalities often do not hold, due to other factors, such as interfacial dynamics and rheological considerations. 

The dependence of release force on the flexibility of the release layers is noted in systems other than silicones. Recent work in olefin release shows that release is a strong function of the density or crystallinity of the layer [44], At a density above 0.9 g/cm release for an acrylate PSA is greater than 270 g/cm. However, when the density of PE is dropped to 0.865 g/cm-, the release force of the same adhesive construction drops to 35 g/cm. An investigation of interfacial friction and slip in these systems has not yet been reported, but again the manipulation of release rheology greatly impacts the measured peel force. 

One of the most common rubber adhesives are the contact adhesives. These adhesives are bonded by a diffusion process in which the adhesive is applied to both surfaces to be joined. To achieve optimum diffusion of polymer chains, two requirements are necessary (1) a high wettability of the adhesive by the smooth or rough substrate surfaces (2) adequate viscosity (in general rheological properties) of the adhesive to penetrate into the voids and roughness of the substrate surfaces. Both requirements can be easily achieved in liquid adhesives. Once the adhesive solution is applied on the surface of the substrate, spontaneous or forced evaporation of the solvent or water must be produced to obtain a dry adhesive film. In most cases, the dry-contact adhesive film contains residual solvent (about 5-10 wt%), which usually acts as a plasticizer. The time necessary... 

The surface force apparatus (SFA) is a device that detects the variations of normal and tangential forces resulting from the molecule interactions, as a function of normal distance between two curved surfaces in relative motion. SFA has been successfully used over the past years for investigating various surface phenomena, such as adhesion, rheology of confined liquid and polymers, colloid stability, and boundary friction. The first SFA was invented in 1969 by Tabor and Winterton [23] and was further developed in 1972 by Israela-chivili and Tabor [24]. The device was employed for direct measurement of the van der Waals forces in the air or vacuum between molecularly smooth mica surfaces in the distance range of 1.5-130 nm. The results confirmed the prediction of the Lifshitz theory on van der Waals interactions down to the separations as small as 1.5 nm. 

Rheology is the study of flow and deformation of materials under the influence of external forces. It involves the viscosity characteristics of powders, liquids, and semisolids. Rheological studies are also important in the industrial manufacture and applications of plastic materials, lubricating materials, coatings, inks, adhesives, and food products. Flow properties of pharmaceutical disperse systems can be of particular importance, especially for topical products. Such systems often exhibit rather complex rheological properties, and pharmaceutical scientists have conducted fundamental investigations in this area [58-64],... 

Texture is a key component of the quality and palatability of potato products. Texture is generally quantified by measuring the resistance of a product to an applied force. A number of different rheological parameters can be used to evaluate a range of tuber characteristics such as firmness, hardness, softness, adhesiveness, fracturability, etc. There is a considerable amount... 

Other Thixotropic Additives. Microcellular fillers such as glass and plastic are also used to provide nonsag properties to adhesives and sealants. However, their mode of operation is very much different from that of the rheological modifiers mentioned above. Microcellular fillers work because they drastically reduce the specific gravity of the product. Thus, because the adhesive or sealant is lighter, there is less stress on the adhesive or sealant due to the forces of gravity. 

Fundamental mechanisms of adhesion. All classical adhesion tests involve a rheological component, in the deformation of the near-interface material, and a surface chemical component. With the recent availability of microscopic techniques to study surface forces, one can possibly go after the surface chemical component, separately from the rheological component. More generally, the configurational and dynamic behavior of macromolecular interfacial regions remains a very rich area. 

Food rheology is mainly concerned with forces and deformations. In addition, time is an important factor many rheological phenomena are time-dependent. Temperature is another important variable. Many products show important changes in rheological behavior as a result of changes in temperature. In addition to flow and deformation of cohesive bodies, food rheology includes such phenomena as the breakup or rupture of solid materials and surface phenomena such as stickiness (adhesion). 

The mechanical troweling apparatus for preparation of adhesion test specimen of plastering materials to concrete substrate has been proposed by R.NANIWA. Workability of PLCM were estimated by 3 rheological characteristics horizontal reaction force Ftr, vertical reaction force Fnr and reaction moment Mr at the grip (supporting point) were measured. Fig. 5 shows the schema of troweling motion and the apparatus in this test method. Some examples of test... 

Adhesives have very broad range of performance requirements. The performance spectrum ranges from pressure sensitive products where almost minimal adhesion is required, to extremely high performance adhesives with strength equivalent to that of metals. But the scope of the adhesive s performance goes well beyond adhesive strength. Flowability, force to adhere and mechanical, thermal, electrical, barrier, and optical properties as well as chemical and weather resistance and rheological behavior all must be considered in adhesive formulations. These essential parameters are discussed below from the point of view of the influence of fillers. 

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