Adsorption of polymer

For polymer adsorption the first requirement is that the pol5mier must be soluble within certain limits in the solvent. The second requirement is that it adsorbs at the ceramic powder surface. 

Solubility Polymer solubility can be predicted by the Hildebrand solubility parameter. The Hildebrand solubility parameter, 8, is defined as the square root of the molar energy of vaporization, LE = AH - R,  

This equation holds for all but the very high polymer volume fractions. 

It should be noted that a similaiily between two solubility parameters alone is an indication, but by no means an assurance, of solute solubility. That is because the total solubility parameter, 8, is the result of many types of interaction principally, nonpolar interactions caused by dispersional forces, 8, polar interactions, 8, and hydrogen bonding, 8  

For true compatability of solute and solvent, matching of all these partial solubility parameters (i.e., 8, Bp, 8 ) is necessary. The total solubility parameter can be easily calculated [1, p. 307] finm the material s enthalpy of vaporization, vapor pressure as a function of temperature, surface tension, thermal expansion coefficient, critical pressure, and second virial coefficient of its vapor, as well as by calculating its value for the chemical structure of the material. For the calculation of the Hildebrand solubility parameter fi om chemical structure, we use Small s [58] equation  

The adsorption of high-molar-mass compounds onto solid interfaces differs characteristically from that of low-molar-mass compounds. To a first approximation, low-molar-mass compounds are more or less spherical each molecule has only one contact point with the surface and the number of contacts per unit surface area determines the coverage. Thus, it is sufficient to 

Layer thickness and polymer concentration is obtained directly by ellipsometry, that is, the change in elliptically polarized light after reflection from a surface covered by an adsorbed layer. The number of adsorbed segments is accessible via infrared spectroscopic studies as well as via calorimetric adsorption enthalpy measurements. 

Adsorption is stronger when adsorption occurs for a polymer in a poorer solvent. Poly(styrene) does not adsorb at all on chromium from the good 

Danielli, K. G. A. Parthurst, and A. C. Biddiford, Surface Phenomena in Chemistry and Biology, Pergamon Press, New York, 1958. 

Miller and D. Bach, Biopolymers at interfaces. Surf Colloid Sci. 6, 185 (1973). 

The adsorption of polymers and other solutes from solutions on to solid surfaces is important in many practical situations  

Many (co-)polymers protecf (used as st ilizers for colloidal systems) 

Natural polymers like the protein casein in milk and many synthetic polymers like PEG and surfactants are used for stabilizing emulsions and colloidal dispersions. Many block copolymers like poly(ethylene oxide) surfactants are also used. Block and graft co-polymers are effective steric stabilizers when one type of block is soluble in the dispersion medium and the other is insoluble so that it attaches to the colloid particles. 

Adsorption of a Novozymes lipase towards a hydrophobic surface 

The adsorption of polymers typically increases with polymer molecular weight and is higher and best (e.g. thicker, denser adsorbed layers) from a solution containing a poor solvent. For these reasons, block-copolymers are excellent steric stabihzers. Block copolymers like poly(ethylene oxide) surfactants are suitable as one part of the stabilizer has a high tendency to adsorb onto the particle surface and the other has a high affinity for the solvent. 

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Polymers have so far been used comparatively less than the common surfactants to stabilize emulsions in spite of the fact that excellent stabilization by them can be achieved (18—20). AppHcation probably has been limited because the adsorption of polymers to emulsion droplets has displayed some intricate phenomena small changes in polymer stmcture or in solvent properties may lead to drastic changes in adsorption. 

The simplest model of polymers comprises random and self-avoiding walks on lattices [11,45,46]. These models are used in analytical studies [2,4], in particular in the numerical implementation of the self-consistent field theory [4] and in studies of adsorption of polymers [35,47-50] and melts confined between walls [24,51,52]. 

In contrast, 7 always stays much smaller and even turns negative for the strongly adsorbing case, indicating that spontaneous adsorption of polymers from the bulk of the film to the attractive wall occurs. 

E. Eisenriegler, K. Kremer, K. Binder. Adsorption of polymer chains at surfaces Scaling and Monte Carlo analysis. J Chem Phys 77 6296-6320, 1982. 

It was found that [5-7] the rate of flocculation of particles produced by the bridging action of polymer is the slower process and, consequently, the rate-determining step. The primary adsorption of polymer is fairly rapid, but the slow attainment of the adsorption equilibrium under agitation arises at least in part from the breakdown of floes offering new surfaces for adsorption. Thus, the bridging step is slow because a polymer adsorbed on one particle must find another particle having a free surface available to complete the bridge. 

Selected Structural Data on Physical Adsorption of Polymers. . 140... 

This exchangeability of adsorbed layers should be considered for better understanding of the irreversible adsorption of polymers. Apparently, penetration by the macromolecules adsorbed later through the layer of the initially adsorbed ones will include a slow exchange between the positions of segments and take a longer time. 

Chromatographic Packings Prepared by Physical Adsorption of Polymers on Silica or Porous Glass... 

Lipatov YuS, Sergeeva LN (1972) Adsorption of polymers, Naukova Dumka, Kiev... 

Lipotov YS, Sergeeva LM (1974) Adsorption of polymers, J Wiley, New York... 

It has been well established that wear resistance of filled rubber is essentially determined by filler loading, filler morphology, and polymer-filler interaction. For fillers having similar morphologies, an increase in polymer-filler interaction, either through enhancement of physical adsorption of polymer chains on the filler surface, or via creation of chemical linkages between filler and polymer, is crucial to the enhancement of wear resistance. In addition, filler dispersion is also essential as it is directly related to the contact area of polymer with filler, hence polymer-filler interaction. 

For the adsorption of polymers, the number of segments per molecule n is large which allows further simplification of the relationships. If the quantity Ks(l-6) 1,... 

Numerous statistical treatments of the adsorption of polymers at solid-liquid interfaces have been described in the literature. 

The equilibrium model for the adsorption of polymers at solid-liquid interfaces recently presented by Hogg and Mirville (1) has been evaluated at some length. It has been shown that, for polymers consisting of a reasonably large number of segments, the adsorption isotherms can be closely approximated by an expression of the form ... 

Lipatov, Y. S. "Adsorption of Polymers" Keter Publishing House, Ltd. Jerusalem, 1974. 

Such displacement effects, although often very pronounced, have not yet been studied systematically. They will be the subject of the present paper. We will discuss the adsorption of polymer from a mixture of two solvents and we will see that in some cases drastic effects occur as a function of the mixture composition. Also, we explore some consequences and practical applications of displacement. It turns out that displacement studies not only increase our insight on the role of the solvent in polymer adsorption but can also be used to determine the segmental adsorption energy. So far, experimental data for this quantity were very scarce. Some illustrative experiments will be discussed briefly. 

Other applications. Displacement must also have its impact on colloidal stability. The relation between the adsorption of polymers on colloidal particles and the resultant steric stability... 

If we consider multilayer formation to be the result only of sequential desorption (adsorption) of polymers one on top of the other at each surface site, we can write the following partition function for one such "chain"... 

The variation of refractive index n(D) of the medium separating the mica surfaces is shown in figure 6b (for PE02), both before and after adsorption of polymer, as well as following replacement of the polymer solution by pure electrolyte after adsorption. The results show that adsorption of the PEO is essentially irreversible, and that little polymer appears to desorb either following compression/decompression cycles, or in pure solvent. The value of the adsorbance T estimated from the n(D) profiles is 4 1.5 mg m-2 for both polymers. 

As will be discussed in Chapter 7, the adsorption of polymers may either increase or decrease colloid stability. 

Fleer, G. J., and J. Lyklema (1983), "Adsorption of Polymers", in G. D. Parfitt and C. H. Rochester, Eds., Adsorption from Solution at the Solid/Liquid Interface, Chapter 4, Academic Press, London. 

Figure 2.13 (a) Adsorption of terminal hydrophobic group giving no additional network links (b) adsorption of polymer chain giving an additional network link for each chain adsorbed... 

The presence of pre-adsorbed polyacrylic acid significantly reduces the adsorption of sodium dodecylsulfonate on hematite from dilute acidic solutions. Nonionic polyacrylamide was found to have a much lesser effect on the adsorption of sulfonate. The isotherm for sulfonate adsorption in absence of polymer on positively charged hematite exhibits the typical three regions characteristic of physical adsorption in aqueous surfactant systems. Adsorption behavior of the sulfonate and polymer is related to electrokinetic potentials in this system. Contact angle measurements on a hematite disk in sulfonate solutions revealed that pre-adsorption of polymer resulted in reduced surface hydrophobicity. 

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