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Amphipathic polymers, steric stabilization

Steric Stabilization. A third stabilization mechanism that is normally achieved by amphipathic polymers or by nonionic surfactants is steric stabilization. To be a candidate for steric stabilization, the polymers must consist of long segments, which are soluble in the liquid medium, interspersed by short segments, usually called anchors which are strongly adsorbed at the oil-water interface (Figure 17). [Pg.135]

The best steric stabilizers are found empirically to be amphipathic block or graft copolymers. One of the comonomers should generate a homopolymer that is nominally insoluble in the dispersion medium whereas the other should polymerize to form a polymer that is soluble in the dispersion medium. [Pg.28]

Figure 2.2 portrays the reason why amphipathic molecules are such effective steric stabilizers. It would be expected that the polymer that was nominally insoluble in the dispersion medium would attach itself to the particle. This attachment to a colloidal particle could occur by physical adsorption on to a preformed colloidal particle, or by physical and/or chemical adsorption on to (or even incorporation into) a growing particle. Whatever the mechanism of attachment, the nominally insoluble polymer serves to anchor the soluble moieties to the colloidal particles. Such polymer is accordingly referred to as the anchor polymer. The role of the soluble polymer is to impart steric stabilization and, for this reason, such chains are termed the stabilizing moieties. [Pg.28]

The effectiveness of amphipathic polymer molecules in imparting steric stabilization can be understo< if a second identical particle is imagined to approach the one portrayed in Fig. 2.2. The stabilizing moieties must be mutually repulsive if the polymer is to impart stability. In these circumstances, the Brownian collision stresses the stabUizing molecules, which endeavour to escape from the stress zone. This escape can be effected either by desorption from the particle surface or by laterd movement over the particle surface... [Pg.28]

Due to the relatively weak adsorption of homopolymers at the L/L interface, and in some cases at the S/L interface, homopolymers are seldom used as emulsifiers or dispersants. For this purpose, the molecule is modified to include some specific units that have strong adsorption to the surface. A good example is partially hydrolysed poly (vinyl acetate), which is commercially referred to as poly(vinyl alcohol) (PVA). The polymer contains 4-12% acetate groups (i.e. 96-88% hydrolysed) and these groups impart an amphipathic character to the chain. The polymer becomes surface-active at the L/L interface and hence it can be used as an emulsifier. In addition, on a hydrophobic surface such as polystyrene, the acetate groups become preferentially adsorbed on the surface of the particles, thus leaving the PVA units dangling in solution as loops and tails . The latter provide the required steric stabilization. [Pg.373]


See other pages where Amphipathic polymers, steric stabilization is mentioned: [Pg.30]    [Pg.161]    [Pg.791]    [Pg.780]    [Pg.194]    [Pg.100]   
See also in sourсe #XX -- [ Pg.135 ]




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Amphipathic

Amphipathic polymer

Amphipathicity

Amphipaths

Polymer stabilization

Polymer stabilization stabilizers

Stability steric

Stabilizer polymer

Stabilizing polymers

Steric stabilization

Steric stabilizer

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