Adsorption of polyelectrolytes

Adsorption of polyelectrolytes onto solid surfaces are not yet explored as extensively as that of non-ionic polymers, and most studies are limited to adsorbance measurements. 

The adsorption of sodium polyacrylate on kaolinite was investigated by Michaels and Morelos1105 in the pH range 5-8. Adsorbance was found to decrease with rising pH and to increase in proportion to M0 05. Schmidt and Eiriehm) dealt with a series of vinyl aeetate-crotonic acid copolymers adsorbed on anatase as a function of the charge density of copolymer and the pH of solution. Adsorbance largely increased as the crotonic add content was raised and also as the pH was lowered. 

The adsorption of ionized poly(4-vinylpyridine) onto a glass surface was investigated by Peyser and Ullmanm), who found that adsorbance decreased with increasing ioniza- 

Recently, Bartels and Arends113 studied the adsorption of poly(4-vinylpyridinium fluoride) with different hexadecyl group content on hydroxyapatite. Adsorbance decreased as the hexadecyl content, i.e. the charge density, was increased. Desorption experiments showed that the adsorption of this polyelectrolyte in water is essentially irreversible. However, the polymer partially desorbed when excess calcium ions were added. Bartels and Arends concluded that adsorption of poly(4-vinylpyridinum fluoride) occurs as a result of the uptake of fluoride ions by hydroxyapatite which releases phosphate ions into water. They also suggested that this adsorption phenomenon can be interpreted in terms of an ion-exchange mechanism. 

The first ellipsometric measurement of the thickness of the adsorbed layer and the adsorbance of a polyelectrolyte and a negative adsorbance of salt onto a solid surface was reported by Takahashi et al.U4) They measured the adsorption of sodium poly(acrylate) (M = 950 x 103) onto a platinum plate as a function of the concentration of added sodium bromide. In an aqueous polyelectrolyte solution with an added simple salt, the bulk phase is a three-component system which consists of a polyelectrolyte, a simple salt, and water. The adsorbed layer on the solid surface is a three-component phase as well. The adsorbance of polyelectrolytes thus cannot easily be determined from measurements of the refractive index nf of the adsorbed phase. Hence, it was assumed that the adsorbed layer is a homogeneous layer of thickness t and further that nf is represented by the Lorenz-Lorentz equation as follows  

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IV. ADSORPTION OF POLYELECTROLYTES ONTO OPPOSITELY CHARGED SURFACES... 

The process of adsorption of polyelectrolytes on solid surfaces has been intensively studied because of its importance in technology, including steric stabilization of colloid particles [3,4]. This process has attracted increasing attention because of the recently developed, sophisticated use of polyelectrolyte adsorption alternate layer-by-layer adsorption [7] and stabilization of surfactant monolayers at the air-water interface [26], Surface forces measurement has been performed to study the adsorption process of a negatively charged polymer, poly(styrene sulfonate) (PSS), on a cationic monolayer of fluorocarbon ammonium amphiphilic 1 (Fig. 7) [27],... 

Ellipsometric Study of Adsorption of Polyelectrolyte onto a Metal Surface... 

Adsorption of polyelectrolyte on interfaces is concerned with various applications such as flocculation and steric-stabilization of colloidal particles in an aqueous phase, oil recovery, and soil conditioning. In these cases, both the adsorbance of polyelectrolytes and the conformation of the adsorbed polymer, which is connected with the thickness of the adsorbed layer, are very important. 

Experimental studies of the adsorption of polyelectrolyte have been reported by several authors Pefferkom, Dejardin, and Varoqui (3) measured the hydrodynamic thickness of an alternating copolymer of maleic acid and ethyl vinyl ether adsorbed on the pore walls in cellulose ester filter as a function of the molecular weight and the concentration of NaCl. Robb et al. (4) studied the adsorption of carboxy methyl cellulose and poly (acrylic acid) onto surfaces of insoluble inorganic salts. However, their studies are limited to the measurements of adsorbance and the fraction of adsorbed segments. 

A.V. (1997) Adsorption of a corticoid on colloidal hematite particles of different geometries. J. Colloid Interface Sd. 187 429-434 Verdonck, L. Hoste, S. Roelandt, F.F. Van der Kelen, G.P. (1982) Normal coordinate analysis of a-FeOOH - a molecular approach. J. Molecular Structure 79 273-279 Vermilyea, D.A. (1966) The dissolution of ionic compounds in aqueous media. J. Electro-chem. Soc. 113 1067-1070 Vermohlen, K. Lewandowski, H. Narres, H-D. Schwager, M.S. (2000) Adsorption of polyelectrolytes onto oxides - the influence of ionic strength, molar mass and Ca " ions. Coll. Surf. A 163 45-53... 

The influence of adsorption of polyelectrolytes on bimolecular phospholipid leaflets was studied. All polyelectrolytes studied were adsorbed on the surface of the film, as demonstrated by greatly increased drainage times. Only some of the polyelectrolytes investigated are able to decrease the d.c. resistance, notably a protein derived from ox erythrocyte ghosts and a Na-K polyphosphate. The combination of these latter substances proved particularly effective. It is concluded that the decrease of d.c. resistance is caused by adsorption and penetration of the polyelectrolytes into the membrane, resulting in the formation of pores or water channels, and not by the possibility of transport of charged macromolecules through the membrane. 

In his second paper, Hesselink57 developed a new theory for the adsorption of polyelectrolyte by assuming loop-train conformations but neglecting tail formation. The partition function for Na polyelectrolytes adsorbed on the surface with an area S from the solution of volume V is still given by Eq. (B-21), but AF is now the sum of the following five contributions. 

Some interesting conclusions can be drawn from this theoretical treatment of the adsorption of polyelectrolyte. The calculated isotherms are of the high-affinity type as is... 

Existing theories of the adsorption of polyelectrolyte allow effects of the polymer charge density, the surface charge density, and the ionic strength on the adsorption behavior to be predicted. The predicted adsorption behavior resembles that of nonionic polymers if the ionic strength is high or the polymer charge density is very low. 

For the adsorption of polyelectrolytes, the existing theories predict only qualitatively the observed behavior, and more theoretical improvements remain to be made. 

Membrane fouling due to adsorption of polyelectrolytes (such as humic acids, surfactants, and proteins) may severely reduce ion permeability, especially in the anion-exchange membranes. However, exhausted anion-exchange membranes used in the ED of molasses, whey, citric acid, or sodium dodecyl-benzenesulfonate can be reactivated by circulating simultaneously an acidic solution in one compartment and an alkaline solution in the other one, both solutions at titres greater than 0.1 kmol/m3 (Tokuyama Soda Co., 1983). 

Balabushevitch NG, Sukhorukov GB, Moroz NA et al (2001) Encapsulation of proteins by layer-by-layer adsorption of polyelectrolytes onto protein aggregates. Biotechnol Bioeng 76 207-213... 

Larionova NI, Volodkin DV, Balabushevitch NG et al (2001) Microcapsules responsive to physiological pH fabricated by layer-by-layer adsorption of polyelectrolytes on protein aggregates. Sci Pharm 69 175-176... 

Borukhov et al. [11] investigated the effect of polyelectrolyte adsorption on the intercolloidal forces. They assume that the adsorption of polyelectrolyte molecules on the surface of the plates was solely due to the electrostatic interactions between the negatively charged plates and the positively charged polyelectrolyte segments. However, there are additional interactions between the surfaces of the plates and the segments, such as the van der Waals interactions. 

Kinetics of Layer-by-Layer Adsorption of Polyelectrolyte and Surfactant... 

The adsorption of polyelectrolytes at charged surfaces is used frequently for both charge neutralization and charge reversal. Polyelectrolyte multilayers formed by polycation-polyanion pairs provide additional opportunities to control surface morphology and film thickness [24],... 

Fig. 4 Zetapotential-pH-profiles of PMBQ and PSS monolayers and multilayers of PMBQ/PSS on glass, Adsorption of polyelectrolytes in water...

Fig. 5 Reflectivity in dependence on angle for 15 double layer PMBQ/PSS, Adsorption of polyelectrolytes in water and 0.01 M KC1...

Rojas OJ (2002) Adsorption of Polyelectrolytes on Mica. In Hubbard A (ed) Encyclopedia of Surface and Colloid Science. Marcel Dekker, Inc, New York 1 517... 

The electrostatic repulsion between the colloids can also be strengthened by adsorption of polyelectrolytes with the same net charge as the colloids. Such adsorption has been observed experimentally by several groups [55,56]. Another example is adsorption of polyelectrolytes on clay particles and in Fig. 13 it is shown that more salt must be added to coagulate the clay particles when the polyelectrolyte concentration has been increased (except for very low concentrations of polyelectrolytes, which has been described above). The polyelectrolytes only adsorb on equally charged clay particles in the presence of salt [51]. There are many explanations to this phenomenon and one theory is that the adsorption preferentially takes place at edges of the clay particles and it has been found that the probability for adsorption is higher for short polymers [56]. 

A variety of applications will be presented in the present Volume. To start with, chapter 4 on electrokinetics, builds directly on chapter 3. particularly on sec. 3.13, but also on the sections describing double layer structures at rest, because they differ only slightly from those in applied fields. Double layers also play an Inportant role in the adsorption of polyelectrolytes (chapter 5). 

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