Surfactant adsorption poloxamers

This topic is dealt with in great detail by Uno and Tanaka [45-47]. Apart from the energies of repulsion and attraction due to adsorption of surfactants, adhesion may result from crystallization under the special conditions that obtain when particles are left behind after drainage of the bulk phase. Particles will be trapped by the surface tension of the liquid film (Fig. 9.18). As the particle dissolves there is supersaturation followed by deposition of the solid around the particle. According to Uno and Tanaka the solubility of the suspension particle increases at the particle-wall contact point due to the pressure exerted on the particle by the surface tension forces. Following deposition, evaporation of the continuous phase occurs as depicted in Fig. 9.18 [46]. Deposition due to cooling, to medium evaporation and to the adhesiveness of additives in the formulation can occur. The effect of polysorbate 80, benzethonium chloride, some anionic surfactants and poloxamers on the adhesion of chloramphenicol suspensions has... 

If has been observed fhaf by adsorbing surfactants onto the crystal surfaces of poorly water-soluble drugs, dissolution rate can be enhanced. Chen et al. " showed that the dissolution rate of Cl-1041, a poorly water-soluble compound, in 0.1 N HCl may be affected by the surfactant Tween 80. The effects of surfactant are complicated, and many factors are involved. Above the CMC of Tween 80, the adsorption of the surfactant onto the crystal surface may inhibit crystal nucleation on the surface, and causes the dissolution rate to increase. By adsorbing a very small amount of poloxamer onto the hydrophobic drug particle surface. 

Surface modification by polymer adsorption is an alternative to surface modification by polymer grafting. For example, polystyrene nanospheres coated by Poloxamer or Poloxamine (Ilium and Davis, 1983 Muller, 1991) or poly(methyl methacrylate) colloidal carriers coated by Poloxamer (Trds-ter and Kreuter, 1988) circulate longer in blood. This family of surfactants consist of poly(propylene glycol) (PPG) blocks, which adsorb on the hydrophobic polystyrene surface, and of more hydrophilic PEG blocks, which stick out of the surface in aqueous solutions and prevent opsonin adsorption. In spite of the increase in blood circulation time, particle coating by polymer adsorption was found to have several drawbacks (Petrak, 1993) ... 

One of the earliest polymeric surfactants used is the A-B-A block copolymer of poly(ethylene oxide) (PEO,A) and propylene oxide (PPO,B) - Pluronics or Poloxamers. These are not ideal since adsorption by the PPO chain is not strong. 

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