Adsorption and Conformation of Polymers at Interfaces

Consider the case of the PEO-PPO-PEO block copolymer at the interface (represented by a simple flat surface). The PPO chain adsorbs on the surface with many attachment points, forming small loops , whereas the A chains (sometimes referred to as tails ) extend to some distance (few nm) from the surface [11-13], The chain segments in direct contact with the surface are termed trains . A 

Adsorption of polymers at interfaces differs significantly from that of simple surfactant molecules (described in Chapter 5) The adsorption isotherm is of the high affinity type, i.e. the first added molecules are virtually completely adsorbed and the plateau adsorption is reached at low equilibrium concentration. Adsorption is practically irreversible because the molecule is attached with several segments to the surface. 

The isotherm depends on the structure, molecular weight and environment (temperature, electrolyte) of the chains. To fidly characterise polymer adsorption, one needs to obtain information on the following parameters The amount of ad- 

The most important parameter for steric stabilisation is the strong anchoring of the B chain to the surface and the extension of the A chains (adsorbed layer thickness, (Jh) and its solvation by the molecules of the medium. 

---

Several experimental methods can be applied to study adsorption and conformation of polymers at interfaces. The amount of polymer adsorbed, F, can be directly determined by equilibrating a known amount of the disperse phase (particles or droplets) with a polymer solution of known concentration, Cj. When the system reaches equilibrium (that may take hours or even days with high-molecular weight polymers), the disperse phase is separated (by filtration or centrifugation), and the equilibrium concentration of the polymer, C, is determined using a suitable analytical method. From Cj and C2 and the amount of disperse phase m and its surface area A (m /g, which may be obtained from a knowledge of the particle size distribution), F can be calculated, that is. 

Several experimental methods can be applied to study adsorption and conformation of polymers at interfaces. The amount of polymer adsorbed, T, can be directly determined by equilibrating a known amount of the disperse phase (particles or droplets) with a poly-... 

---