Thickness hydrodynamic

Dhinojwala A and Granick S 1997 Surface forces In the tapping mode solvent permeability and hydrodynamic thickness of adsorbed polymer brushes Macromoiecuies 30 1079-85... 

Filter properties Equality of the hydrodynamics Thickness Pore diameter... 

Experimental studies of the adsorption of polyelectrolyte have been reported by several authors Pefferkom, Dejardin, and Varoqui (3) measured the hydrodynamic thickness of an alternating copolymer of maleic acid and ethyl vinyl ether adsorbed on the pore walls in cellulose ester filter as a function of the molecular weight and the concentration of NaCl. Robb et al. (4) studied the adsorption of carboxy methyl cellulose and poly (acrylic acid) onto surfaces of insoluble inorganic salts. However, their studies are limited to the measurements of adsorbance and the fraction of adsorbed segments. 

In this paper we present results for a series of PEO fractions physically adsorbed on per-deutero polystyrene latex (PSL) in the plateau region of the adsorption isotherm. Hydro-dynamic and adsorption measurements have also been made on this system. Using a porous layer theory developed recently by Cohen Stuart (10) we have calculated the hydrodynamic thickness of these adsorbed polymers directly from the experimental density profiles. The results are then compared with model calculations based on density profiles obtained from the Scheutjens and Fleer (SF) layer model of polymer adsorption (11). 

For the calculation of the hydrodynamic thickness we divide the profile artificially into elementary layers, the result being independent of the division chosen provided it is sufficiently fine. The s.a.n.s. data is obtained as a function of Q, the wave vector (4it/A sin(0/2), where X is the neutron wavelength and 0 the scattering angle. The Q resolution corresponds in real space to a fraction of a bond length which is small enough for defining an elementary layer. 

In principle, using the porous layer theory, it is possible to obtain the hydrodynamic thickness of an adsorbed layer using the experimental density profile and the permeability function. The results of this calculation are given in Table I. In figure 2 it can be seen that the calculated 6jjsans values fall within the tail of the s.a.n.s. density profiles. However, comparison with the results obtained by p.c.s. (Table I) show a large systematic discrepancy. 

Figure 3. P.C.S. values of the hydrodynamic thickness ( ). "Steric thickness results ( ) of Klein and Luckham. +, 2Rg (calculated), against molecular weight.

Figure 4. Hydrodynamic thickness ( ) and 2Rg (+) as a function of chain length calculated on the basis of theoretical density profiles using the SF theory.

This must cast some doubt on the hydrodynamic thickness calculated from the s.a.n.s. profile. From Table I we can see that the values of 6 cs are considerably larger than and... 

A simple procedure to demonstrate this effect of sensitivity is to truncate the theoretical profiles at different layers. In Figure 5 values of the hydrodynamic thickness are shown when the profile is truncated at 1% and at 2%. This clearly shows the effect that reducing the sensitivity dramatically reduces the hydrodynamic thickness as it eliminates segments at the extremity of the adsorbed layer. 

Segment density profiles and hydrodynamic thickness measurements have been made for polyethylene oxides adsorbed on polystyrene latex. Comparison with theoretical models shows that the hydro-dynamic thickness is determined by polymer segments (tails) at the extremity of the distribution. It is also concluded that the sensitivity of the s.a.n.s. experiment precludes the measurement of segments in this region and that the experimental segment density profiles are essentially dominated by loops and trains. 

The other major casein monomer in bovine milk is asi-casein. The SCF theory suggests that a loop-like protein conformation is favoured for adsorbed asi-casein (see Figure 8.1a) (Dickinson et al., 1997 Home, 1998). This implies a reduced hydrodynamic thickness of the adsorbed layer for as]-casein as compared with p-casein. 

The most convenient of these methods is viscosity measurement of a liquid in which particles coated with a polymer are dispersed, or measurement of the flow rate of a liquid through a capillary coated with a polymer. Measurement of diffusion coefficients by photon correlation spectroscopy as well as measurement of sedimentation velocity have also been used. Hydrodynamically estimated thicknesses are usually considered to represent the correct thicknesses of the adsorbed polymer layers, but it is worth noting that recent theoretical calculations52, have shown that the hydrodynamic thickness is much greater than the average thickness of loops. 

Fig. 19. Hydrodynamic thickness at high surface coverage as a function of intrinsic viscosity81 ...

Fig. 23. Variation of surface layer thickness with molecular weight of the stabilizing polydimethylsiloxane (PDMS) chain. Hydrodynamic thickness <5109) PMMA particles (O), PS particles ( ), micellar dispersions (A) from viscosity data x, thickness h from surface coverage data of PMMA particles assuming a prolate ellipsoid model for the...

Measurements of hydrodynamic thickness LH have been performed by many investigators and, in most cases, the measured LH were almost twice the radii of gyration of polymer coils in bulk solution. It is desirable to clarify the theoretical relationship between LH and the root-mean-square thickness of the adsorbed polymer layer. Some progress in this direction has been made recently. 

The hydrodynamic thickness of graft chains both in nonsolvated and solvated states was experimentally quantified by Webber et al. [110]. When a poly(2-... 

Liquid lubrication mechanism. There are four defined regimes of liquid lubrication hydrodynamic (thickness of lubricant film (h), h > 0.25 pm), elastohydrodynamic (h 0.025 to 2.5 pm), boundary (h 0.0025 pm), and mixed. These regimes are dependent on oil viscosity (Z) and relative velocity (V) and are inversely proportional to the load (L), (ZV/L). Fig. 5.1, known as the Stribeck-Hersey curve, depicts these regimes in terms of friction coefficient versus viscosity, velocity, and load (ZV/L) (Fusaro, 1995). 

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