Poly macromolecules, adsorption

Rebar VA, Santore MM. Molecular weight effects and the sequential dynamic nature of poly(ethyleneoxide) adsorption on silica from polydisperse aqueous solution. Macromolecules 1996 29 6273—6283. 

Biomaterials with Low Thrombogenicity. Poly(ethylene oxide) exhibits extraordinary inertness toward most proteins and biological macromolecules. The polymer is therefore used in bulk and surface modification of biomaterials to develop antithrombogenic surfaces for blood contacting materials. Such modified surfaces result in reduced concentrations of ceU adhesion and protein adsorption when compared to the nonmodifted surfaces. 

It has been outlined by several authors that the single macromolecule may be irreversibly bound because of the large number of weakly interacting segments. The first papers on the construction of polymer-coated silica adsorbents involved the physical adsorption of water-soluble polymers. Polyethylene oxides [28, 29] and poly-/V-vinylpyrrolidone [30] are examples of the stationary phases of this type. 

Zhang W, Shi L, An Y, Wu K, Gao L, Liu Z, Ma R, Meng Q, Zhao C, He B. Adsorption of poly(4-vinyl pyridine) unimers into polystyrene-Wocfe-poly(acrylic acid) micelles in ethanol due to hydrogen bonding. Macromolecules 2004 37 2924-2929. 

In the case of poly(methacrylates) mentioned above there is a decreasing in the X values when the aromatic ring has alkyl groups as substituents. This behavior was explained taken into account at least two factors. If the model accepted to explain the preferential adsorption is that which consider that this phenomenon occurs along the polymer chain, the rigidity of the macromolecule must influence the amount of the adsorbed solvent. 

Bioactive macromolecules like peptides, proteins, and nucleic acids have been successfully embedded in planar LbL films. An important question is the retention of the bioactivity of the film-embedded biomolecules. The structural properties and stability of the LbL films formed from synthesized polypeptides of various amino acid sequences were recently reported [50]. The authors showed that control over the amino acid sequence enables control over non-covalent interpolypeptide interaction in the film, which determines the film properties. Haynie and coworkers showed by circular dichroism spectroscopy that the extent of adsorption of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) in the LbL films scales with the extent of secondary structure of the polypeptides in solution [51]. Boulmedais demonstrated that the secondary structure of the film composed of these polypeptides is the same as the peptide structure in the complex formed in solution [52], as found by Fourier transform IR spectroscopy (FUR). 

Gan D, Lyon LA (2002) Synthesis and protein adsorption resistance of PEG-modified poly(/V-isopropylacrylamide) core/shell microgels. Macromolecules 35 9634—9639... 

The ability of some macromolecules to adsorb at interfaces is made use of in suspension and emulsion stabilisation (see Chapter 7). Gelatin, acacia, poly(vinyl alcohol) and proteins adsorb at interfaces. Sometimes such adsorption is unwanted, as in the case of insulin adsorption onto glass infusion bottles and poly(vinyl chloride) infusion containers and tubing used in giving sets. Adsorption of insulin to glass bottles and plastic i.v. tubing at slow rates of infusion is well documented. It... 

Polymers are also essential for the stabilisation of nonaqueous dispersions, since in this case electrostatic stabilisation is not possible (due to the low dielectric constant of the medium). In order to understand the role of nonionic surfactants and polymers in dispersion stability, it is essential to consider the adsorption and conformation of the surfactant and macromolecule at the solid/liquid interface (this point was discussed in detail in Chapters 5 and 6). With nonionic surfactants of the alcohol ethoxylate-type (which may be represented as A-B stmctures), the hydrophobic chain B (the alkyl group) becomes adsorbed onto the hydrophobic particle or droplet surface so as to leave the strongly hydrated poly(ethylene oxide) (PEO) chain A dangling in solution The latter provides not only the steric repulsion but also a hydrodynamic thickness 5 that is determined by the number of ethylene oxide (EO) units present. The polymeric surfactants used for steric stabilisation are mostly of the A-B-A type, with the hydrophobic B chain [e.g., poly (propylene oxide)] forming the anchor as a result of its being strongly adsorbed onto the hydrophobic particle or oil droplet The A chains consist of hydrophilic components (e.g., EO groups), and these provide the effective steric repulsion. 

In combination with adsorption measurements, electro-optics is proved to be a powerful technique for studying the structure of adsorbed polyelectrolyte layers. Our data show flat conformation of the adsorbed macromolecules, which slightly depends on the polyelectrolyte charge density in accordance with the theory for weak poly electrolytes. Counterion condensation is also suggested on the surface of weakly charged poly electrolytes, which has not been predicted from the theory. 

Blaakmeer J, Bohmer MR, Cohen Stuart MA, Fleer GJ. Adsorption of weak polyelectrolytes on highly charged surfaces. Poly(acrylic acid) on polystyrene latex with strong cationic groups. Macromolecules 1990 23 2301-2309. 

Pefferkorn E, Elaissari A. Adsorption—desorption processes in charged poly-mer/colloid systems structural relaxation of adsorbed macromolecules. J Colloid Interface Sci 1990 138 187-194. 

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