Reload Index (ZRiChK UMCS)

 

 

AN INFLUENCE OF THE TEMPERATURE ON THE CONFORMATION OF POLYACRYLIC ACID (PAA) MACROMOLECULES AT THE ZrO2 –  POLYMER SOLUTION INTERFACE.

 

Stanisław CHIBOWSKI, Małgorzata WIŚNIEWSKA, Małgorzata PASZKIEWICZ

DEPARTMENT OF RADIOCHEMISTRY AND COLLOID CHEMISTRY

 

 

Temperature q is one of the most important parameter characterizing the polymer – solution system. In the temperature q the polymer chains, dissolved in particular solvent, attain the same conformation as in their own solution, i.e. they are coiled maximally. Such conditions are called undisturbed state and solvent in

Pole tekstowe:  
Fig.1. Adsorption of PAA 2 000 on surface of ZrO2 as a function of the temperature of the system, CNaCl=1´10-2mol/dm3.

such condition is called ideal bad quality solvent. For most solvents, their quality improves with temperature, that reflects in more developed conformation of macromolecules. Considering above information the adsorption, electrokinetic and viscometric measurements were arranged in  ZrO2‑NaCl‑PAA system in the temperatures ranged 15‑40oC. The choice of the temperatures was imposed by temperature q for polyacrylic acid equal to 14oC [1, 2].

The measurements revealed adsorption minimum at 25-30oC (Fig. 1) caused by changes of conformation of the polymer chains.  In examined range of temperatures (15‑40oC) the structure of adsorbed macromolecules change from polymer coils at 15oC to developed conformation, perpendicular to the surface of the solid at 40oC. Interactions between PAA chains and the surface of ZrO2 in temperature 15oC are of dispersed type and when temperature rises contribution of the hydrogen bridge type interactions increases.

To confirm proposed mechanism of the polyacrylic acid adsorption on the surface of zirconium oxide the expansion coefficients (a) of the polymer in water solution were calculated. Their value rises with the increase of the temperature that corresponds more developed conformation of PAA chains in solution and at the surface of zirconium oxide.

Studies of the mechanism of polyethylene oxide (PEO) adsorption on the surface of Al2O3 in the presence of sodium dodecylsulfate (SDS).

 

Pole tekstowe:  
Fig. 1.	Adsorption isotherm of PEO of various molecular weights on the surface of Al2O3 with and without SDS (CSDS = 10-3 M/dm3) as a function of the equilibrium concentration of the polymer in the NaCl solution (CNaCl = 10-3 M/dm3).

Studies aimed on the influence of sodium dodecylsulfate (SDS) on the adsorption behavior of polyethylene oxide on the surface of Al2O3.

Observed increase of the adsorption of polyethylene oxide is connected with polymer-surfactant complex formation (Fig.1).

Concentration of the polymer and the surfactant increases considerably at the interface in comparison to the bulk that favors SDS-PEO interaction. Creating PEO-SDS complexes produce well-marked increase of the polymer adsorption.

Studies of the thickness of adsorbed polymer layers (d) in the presence and absence of the surfactant (Table 1), confirm polymer‑surfactant interaction.

 

            Table 1. Thickness of the adsorption layer of the polyethylene glycol formed on the surface of Al2O3 from the pure solutions of the polymer and mixed PEO-SDS ones.

Mcz PEO

CPEO [ppm]

d [nm]

G [mg/m2]

d[nm]
PEO‑SDS

G[mg/m2] PEO‑SDS

100 000

100

11.1

0.08

12

0.089

300 000

100

12.6

0.086

13.5

0.093

 

            Introduction of the surfactant to Al2O3 - PEO system results in the increase of the thickness of adsorption layers of the polymer. This increase (d) may be caused by increase of the PEO adsorption in the presence of SDS (Fig. 1), as well as by PEO‑SDS complexes formed at the interface. Occurring interactions between PEO and SDS led to changes of the structure of the macromolecules in bulk and at the oxide surface alike. Macromolecule, during interaction with the surfactant develops is linear size that led to the increase of its adsorption affinity and increase of the thickness of the polymer adsorption layers.

 

References:

[1] D. H. Napper, J. Colloid Interface Sci., 58 (1977) 390.

[2] A.Silberberg, J. Eliassaf and A. Katchalsky, J. Polym. Sci., 23 (1957) 259.