Polymers desorption

Figure 5. Molecular weight dependence on the polymer desorption at y = 7800 sec-1 ( ) PS-4 ...

When the multilayer is formed the question of adsorption reversibility of polycation is very important. It was determined experimentally that the polymer desorption is a very slow process and only very small amount can be desorbed. There are only structural changes if the adsorbed amount is fixed [13,14],... 

Recent experimental data [28] indeed show that a weak interface can be created by lowering the surface energy with an fluorocarbon elastomer coating. On such a weakly adsorbing die wall, a macroscopic slip occurs in linear polyeth-ylenes during capillary die extrusion. However, the same surface fails to produce any observable wall slip at low stresses that can be reliably generated in a parallel-plate flow cell. This contrast emphasizes that massive polymer desorption and interfacial slip occur only beyond a critical wall stress. 

It was thought in the past that the only mechanism for wall slip would be polymer desorption, i.e., an adhesive breakdown [25, 53]. However, lack of a strong temperature dependence would be inconsistent with an activation process of chain desorption. Since the onset of the flow discontinuity (i.e., stick-slip) transition was found to occur at about the same stress over a range of experimental temperatures, it was concluded from the outset [9] that the phenomena could not possibly have an interfacial origin. Thus, the idea of regarding the flow discontinuity as interfacial did not receive sufficient and convincing theoretical and experimental support in the past, not only because the transition was often accompanied by severe extrudate distortion and hysteresis, but also because the molecular mechanism for such an interfacial transition involving wall slip was elusive. 

De Gennes originally assumed that polymer adsorption would be absent at any stress. It is more realistic to assert that polymer desorption would occur only beyond a certain level of wall stress... 

Energy required for complete polymer desorption E nyE where... 

Paturej J, Dubbeldam JLA, Rostiashvili VG, Milchev A, Vilgis TA (2014) Force spectroscopy of polymer desorption theory and molecular dynamics simulation. Soft Matter 10 2785-2799... 

This paper proposes a phenomenological analysis, based on laboratory experimental work, of the effects of adsorption properties on pol3nner slug propagation. The adsorption properties studied include kinetic aspects, i.e. instantaneous adsorption, reorganization of macromolecules inside adsorbed layer, exchanges between free and adsorbed polymer, desorption as well as properties at thermodynamic equilibrium which can be described by a partially reversible adsorption isotherm. The conditions for hydro-dynamic retention are also discussed. In addition, an analysis of the effects of polymer polydispersity on each of these adsorption phenomena shows that these effects cannot be neglected in a predictive simulator. 

Calculation of the density of monomer links of the polymer in the adsorption layer showed [72] that it is lower than in the bulk polymer and decreases when the number of macromolecules on the unit surface area decreases. This is evidence concerning the influence of polymer desorption on polymer concentration in the absorption layer. 

When the maeromolecule is flexible, its deformation takes place at adsorption. One ean observe the change in the number of chain links bound with the surface (Fig. 29) and the surfaee area blockaded by one macromolecule. The rate of ehange of the fraction of bound links is close to the rate of polymer adsorption at the slow stage and the rate of polymer desorption. Therefore, these three processes are boimd to one another and their rates are limited by the rate of macromolecule deformation in the adsorption layer or its flexibility [72]. 

The adsorption isotherm for the adsorption of poly(ethylenhnine) on the copper(II) oxide powder is the same as for the adsorption of the saturated complex of copper(II) ions with poly(ethylenimine). Therefore, the equilibrium concentration of adsorbed polymer is reached very quickly and the polymer desorption is the stage limiting an appearance of the complex... 

The rate of a ehange of the complex of copper(II) ions with poly(ethylenimine) in solution is proportional to the rate of polymer desorption. At the first approximation, we considered that... 

Some of these processes can possibly be reversible, resulting in polymer desorption from fibers and colloids, break-up of fiber fiocs and colloidal aggregates and detachment of colloids from fibers. Which of these processes actually occurs depends on the characteristic times of these processes. To be able to make estimates of these times, we will discuss some of these processes in more detail. 

The single-polymer desorption experiments do allow to determine not only interactions between polymers and substrates but also binding parameters of cosolutes onto polymers as recendy demonstrated. Cosolutes such as ions, ligands, or other small molecules can strongly influence adhesion properties of polymers and even their stmcture. In such an AFM-based... 

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