Reload Index (ZRiChK UMCS)

THE INFLUENCE OF IONIC STRENGTH ON ADSORPTION AND ELECTROKINETIC PROPERTIES OF DISPERSED ALUMINIUM OXIDE IN A PRESENCE OF POLYACRYLIC ACID

 

Stanisław CHIBOWSKI, Jacek PATKOWSKI, Małgorzata PASZKIEWICZ and Małgorzata WIŚNIEWSKA

DEPARTMENT OF RADIOCHEMISTRY AND COLLOID CHEMISTRY

 

 

Behaviour of solids dispersed in polymer solutions is a very important issue. Researches are conducted as well in a practical aspect as a theoretical one
[[1], [2]]. The practical meaning of the polymer adsorption on solids is connected with the usage of polymers in stabilization and flocculation processes.

An influence of ionic strength, pH of solution and molecular weight of polyacrilic acid (PAA) on adsorption and the properties of electrical double layer (Al2O3/polyelectrolyte solution) were examined.

Our measurements show, that the adsorption increases with the increase of ionic strength and molecular weight of polymer, whereas the increase of pH lowers the adsorption.

A comparison between surface charge and  charge of diffusion layer leads to a conclusion, that these two are the major factors, which cause changes in zeta potential of Al2O3 (depending on ionic strength, pH of solution, molecular weight and polymer concentration).

Thicknesses of PAA layers adsorbed on aluminium oxide and corresponding expansion coefficient (a) were also calculated. It was shown that the increase of ionic strength, pH of solution and molecular weight of polymer cause the increase of both thickness of adsorption layer and expansion coefficient (a) of PAA.

 

References



[[1]] G.J. Fleer, M.A. Cohen Stuart, J.M.H.M. Scheutjens, T. Cosgrove, B. Vincent, Polymers at Interfaces, Chapman & Hall, London, 1993.

[[2]] G.J. Fleer, J.M.H.M. Scheutjens in: B.Dobias (Ed.), Coagulation and Floculation; Theory and Applications, Chapter 5, Marcel Dekker, New York, 1993.

 

 

STUDY ON THE INFLUENCE OF SURFACTANT (CTAB) ON THE ADSORPTION BEHAVIOR OF POLYETHYLENE GLYCOL AT AL2O3 SURFACE

 

An introduction of surface active substance - surfactant to a polymer - solid system is interesting from both theoretical and practical points of view. A typical example of such systems application is process of the stabilization of colloid suspensions, and emulgation or flocculation. For this reason many polymer- surfactant systems are used in various branches of industry (cosmetics, chemicals, food and medicaments production) [1-2].

In this context, the studies on the influence of cationic surfactant, CTAB (hexadecylotrimethyloammonium bromide) on the adsorption properties of the polyethylene glycol (PEG) on surface of alumina seems to be interesting. Observed increase of the polymer adsorption in the presence of the surfactant (Tab. 1) results from the formation of the polymer-surfactant complex. The PEG – CTAB mutual interactions in aqueous solutions were used to explanation of adsorption equilibrium in Al2O3 polymer solution system in presence of the surfactant (CTAB).

 

Table 1. The size of PEG adsorption on the surface of Al2O3 in the presence and absence of CTAB and thickness of the adsorption layer of the polyethylene glycol from the pure solutions of the polymer and mixed polymer-CTAB ones (CPEG=1x10-4g/ml).

 

CCTAB
[M/dm3]

MW PEG

2 000

10 000

20 000

35 000

δ[nm]

without CTAB

4,3

5.9

6.6

7.7

CTAB 1x10-4

4.3

5,9

6,6

7.7

CTAB 5x10-4

4.7

6,4

7,1

8,3

CTAB 1x10-3

5.1

6.9

8,0

9,1

Γ[g/m2]

without CTAB

7,5

14,25

17,8

23,7

CTAB 1x10-4

7.7

14,3

17.75

23.65

CTAB 5x10-4

12.0

17.0

21,5

27.1

CTAB 1x10-3

13.0

20.1

24.8

31,5

The viscimetric measurements proved that CTAB presence influences the structure of adsorbed polymer layers by increasing thickness of the adsorption layer  (d) of the polymer (Tab. 1). Occurring interactions between the polymer and CTAB generate the structure changes of the macromolecule in the solution and at the surface of the solid. Due to these interactions, the macromolecule increases its linear dimensions that increase its adsorption affinity and thickness of the adsorbed polymer layers.

 

References:

[1]  Ghodbane J., Denoyel R., Colloids Surfaces, 127 (1997) 97.

[2]  Nusink J. and Koopal L.K., Talanta, 29 (1982) 495.