Grafted PEO chains

Figure 10 shows a schematic of the formation of a single chain core-shell nanostructure. It is known that the short grafted PEO chains have an average... 

Fig. 17 Dependence of the average PEO brush height ((Jj)brush) on the surface area per grafted chain (s), where (/i)brush was calculated by two different methods. The squares represent (h)brush from the difference between the average radii of the PNIPAM microgels with and without the grafted PEO chains and the circles from the ratio of / [70]...

When calculating the theoretical force curves shown in Fig. 9 we used the XPS results to obtain the value of s and twice the length of the polymer brush was set to 23 nm. The anchoring points for the grafted PEO-chains were set at a distance 1.5 nm away from the mica surface. This value was chosen to be equal to the undisturbed layer thickness of the adsorbed chitosan polymer without grafted side-chains. When the prefactor is set equal to 1, the lower curve in Fig. 9 is obtained, and when a prefactor equal to two is used the upper curve is obtained. 

Despite these excellent in vitro results, little progress has been made in vivo. For instance, under clinical conditions, blood proteins have been demonstrated to adsorb extensively to a PEO coated polymer, in contrast to in vitro results [69], Also, in vivo research on PEO coatings in the oral cavity showed poor results [70], despite excellent in vitro reductions in salivary protein adsorption and oral bacterial adhesion to PEO coatings on glass and hydroxyapatite [70,71], Possibly, the durability of the thin layer of grafted PEO chains in the oral cavity was not sufficient over a clinically relevant time scale. 

Figure 3.97. Surface pressure isotherms for end-grafted PEO chains. SF lattice theory, iV = 700, t = 0.35 nm, two values of X (indicated).

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). 

It is clear from the above discussion that the interaction between suspension particles and emulsion droplets depends on the nature of the stabiliser used for the particles and droplets. For that reason, model systems were investigated whereby the latex particles contained grafted PEO chains (with no possible desorption) and the emulsion was based on hexadecane stabilised with Pluronic PE L92 (containing 20% PEO). The particle and droplet radii were very similar (315 and 280nm, respectively) in order to avoid complications arising from the change in particle size distribution on mixing the suspension and emulsion. 

The effect of droplet size and its distribution on the adsorbed layer thickness may be inferred from a comparison of the results obtained with the o/w emulsions with those recently obtained using polystyrene latex dispersions containing grafted PEO chains of (molecular weight 2000) (49). As discussed earlier, the viscoelastic behavior of the system (which reflects the steric interaction) is determined by the ratio of the adsorbed layer thickness to the particle radius (8/R). The larger this ratio, the lower the volume fraction at which the system changes from predominantly viscous to predominantly elastic response. With relatively polydisperse systems, ( )cr shifts to higher values when compared to monodisperse systems with the same mean size. 

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