Agents for Formulation of Suspensions

4-12%). -(CH2-CH-OH) -(CH2-CH(OCOCH3)-OH)y-(CH2-CH-OH) -. Block copolymers of ethylene oxide-propylene oxide (ABA block of PEO-PPO-PEO), Pluronics (BASF), Synperonic PE (ICI), H-(0-CH2-CH2) -(CH2-CH (CH3)-0) ,-(CH2-CH2-0) -H. Graft copolymers, for example a poly(methyhnethacrylate) (PMMA) backbone (with some polymethacryhc add) with grafted PEO chains (Atlox4913, Hypermer CG6 ICI). 

As this subject was covered in detail in Chapter 5, only a summary will be provided at this point. Surfactant adsorption is usually reversible, and hence thermodynamics can be applied for deriving the adsorption isotherm. Eor example, the adsorption of ionic surfactants onto hydrophobic surfaces may be represented by the Stern-Langmuir isotherm [13]. Consider a substrate containing sites (molm ) on which F molm of surfactant ions are adsorbed. The surface coverage 0 is (F/NJ and the fraction of uncovered surface is (1 — 0). The Stern-Langmuir 

Equation (9.31) applies only at low surface coverage (6 0.1) where lateral interaction between the surfactant ions can be neglected. At high surface coverage [9 0.1) one should take the lateral interaction between the chains into account, by introducing a constant A, for example using the Erumkin-Eowler-Guggenheim equation [13], 

Various authors [14] have used the Stern-Langmuir equation in a simple form to describe the adsorption of surfactant ions on mineral surfaces, 

Various contributions to the adsorption free energy may be envisaged. To a first approximation, these contributions may be considered to be additive. In the first instance, may be taken to consist of two main contributions, that is 

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