Polymer ordering at surfaces
PEO has an “inverse” water solubility – it becomes less soluble at higher temperatures.
A general principle:
The less soluble the adsorbed polymer – the less stable the dispersion.
PEO has a nonpolar part but also an oxygen atom that allows for hydrogen bonding. Thus, at lower temperatures, these molecules can interact with water, but as temperature increases, hydrogen bonding weakens, and the nonpolar part of the polymer chain begins to dominate. The molecules become more hydrophobic. And when molecules are hydrophobic and not soluble, they want to form clumps and come closer together. That is why the equilibrium energy decreases with temperature.
MW and temperature effects
Polystyrene polymers on mica.
(a) End-grafted in toluene, (b) Adsorbed from cyclohexane.
Both solubility and bridging effects are possible in (b)
Polymers at surfaces
- (a) In solution
- (b) End-grafted
- (c) Adsorbed
- (d) Adsorbed at low &thetha;
- (e) Adsorbed at high &thetha;
- (f) Bridging
- Bäkker, G. Kapillarität und oberflächenspannung; Akademische Verlagsgesellschaft: Leipzig. 1928.
- de Gennes, P.-G.; Brochard-Wyart, F.; Quéré, D. Capillarity and wetting phenomena. Springer: New York; 2002.
- Derjaguin, B.V.; Churaev, N.V.; Muller, V.M. Surface forces; * Consultants Bureau: New York; 1987.
- Gaines, Jr., G.L. Insoluble monolayers at liquid-gas interfaces. John Wiley & Sons: New York; 1966.
- Hirschfelder, J.O.; Curtiss, C.F.; Bird, R.B. Molecular theory of gases and liquids. John Wiley & Sons: New York; 1954.
- Israelachvili, J.N. Intermolecular and surface forces, 2nd ed.; Academic Press: New York; 1992.
- Jones, A.L. Soft condensed matter. Oxford University Press: New York; 2002.
- Parsegian, V.A. van der Waals forces. Cambridge University Press: New York; 2006.
- Tanford, C. The hydrophobic effect: Formation of micelles and biological materials. John Wiley & Sons: New York; 1980.
- van der Waals, J.D. On the continuity of the gaseous and liquid states. Rowlinson, J.D., Ed.; Dover Publications: Mineola, NY; 1988.