Polymer layer thickness

Encouraged by the X-ray and contact angle results, we performed some preliminary gas-permeation measurements. Here, a self-supporting film is required and only the longer block copolymers were used. Fluoro-PSB-II and Fluoro-triblock were coated on porous Celgard 2400 membranes the measurements were taken at room temperature at a driving pressure of 5 bars. Since no absolute polymer layer thickness has been determined, only relative values of the permeability are given (Table 10.6). In the case of the separation of C02 from... 

Recently, Quirk and Mathers [264] performed LASIP of isoprene on silicon wafers. A chlorodimethylsilane-functionalized diphenylefhene (DPE) was coupled onto the surface and lithiated with n-BuLi to form the initiating species. The living poly(isoprene) (PI) was end- functionalized with ethylene oxide. A brush thickness of 5 nm after two days of polymerization (9.5 nm after four days) was obtained in contrast to a polymer layer thickness of 1.9 nm by the grafting onto method using a telechelic silane functionahzed PI. 

Figure 9 Schematic representation of model used for estimation of polymer layer thickness...

Fig. 28 Cell density versus distance histogram at 3 days after incubation on item a non-grafted photoreactive copolymer surface, and graft-polymer-layer-thickness gradient surfaces of a polyDMAPAAmMel, b polyMA, c polyDMAAm. The number of cells per unit area (0.225 mm ) is plotted against the unit distance (500 jim) from the edge of the photomask...

Polymer layer thickness -10 pm Number of feed channels 7... 

The concentration profile of fixed oxidized and reduced sites within the film depends on the dimensionless parameter Dcjr/d2, where r is the experimental timescale, i.e. RT/Fv in cyclic voltammetry, and d is the polymer layer thickness. When Dcix/d2 1, all electroactive sites within the film are in equilibrium with the electrode potential, and the surface-type behavior described previously is observed. In contrast, Dcjx/d2 <3C 1 when the oxidizing scan direction is switched before the reduced sites at the film s outer boundary are completely oxidized. The wave will exhibit distinctive diffusional tailing where these conditions prevail. At intermediate values of Dcjr/d2, an intermediate ip versus v dependence occurs, and a less pronounced diffusional tail appears. 

Samples were made in the following way. The bottom copper electrode in the form of a strip is deposited on a glass substrate by the vacuum thermal evaporation through a shadow mask with area of 1 x 10 mm. The thin polymer films were prepared by the spin coating from 5% polymer solution, in cyclohexanone. Immediately after spinning the samples were thermally dried for 3-4 h at 150°C before deposition of the electrode. Middle and upper copper electrodes were prepared in the same way. The middle polymer layer was placed between the second and third electrodes and was made similar to the first polymer layer. Thickness of the polymer layers was about 500 nm, the thickness of metal electrodes did not exceed 100 nm. The active area between three electrodes was 0.01 cm ... 

We argue that the above features of star dynamics are generic for soft systems of the core-shell type for which stars serve as prototype. Support for this comes from the dynamic light scattering (DLS) investigation of large block copolymer micelles, where all three relaxation modes, i.e., cooperative, structural and selfdiffusion are observed [188]. In particular, the star model discussed above applies to core-shell particles with a small spherical core relative to the chain (shell) dimensions. For a surface number density a = f / (47i r ) the polymer layer thickness under good solvent conditions is L ... 

IV. These and similar reactions produce polymer structures (not brushes), which are, in fact, bonded silicone oils known as polysiloxanes. Any cross- linked polymer layer thickness can be chosen. Multifarious methods of synthesis are known. Very advantageous is the shielding of the silica backbone by the polymeric layer, leading to a good pH stability. 

Figure 14 shows the variation of the steady shear relative viscosity at the high shear limit with the effective volume fraction as defined by equation 46 for poly(methyl methacrylate) (PMMA) suspensions of different sizes in decalin sterically stabilized by means of grafted poly (12-hydroxy stearic acid) chains with a degree of polymerization of 5. The stabilizing polymer layer thickness is 9 1 nm, in particular, A = 9 nm... 

For sterically stabilized suspensions, the polymer thickness A changes with the medium temperature and shear rate. It can be said that the effective polymer thickness decreases with compression pressure exerted on the polymer chain. In other words, for the same suspension, when the volume fraction is low, the polymer layer thickness is likely to have more effect on the steady shear viscosity than when the volume fraction is high. However, when the ratio of the polymer thickness to the particle diameter is large, the suspending fluid inside the polymer layer can reduce the effect of the attached polymer. 

Figure 2. Theoretical calculation of the dependence of the steric interaction energy Ester (a) and the total interaction energy Et (b) on interparticle distance for different values of polymer layer thickness. Reproduced from Ref [32] with kind permission of Elsevier.

R = MWNT radius b = crystalline polymer layer thickness /nt = MWNT length... 

Applying this model to MWNT/PVA composites resulted in a predicted interfacial shear strength, t, of 348 231 MPa, about an order of magnitude higher than expected. Thus, Eq. (35.5) was modified to allow for the observed interfacial failure at the boundary between the bulk polymer and the ciystalline polymer layer (thickness = b) adhering to the MWNT surface. 

Figure 6. a.Time dependence of polymer layer thickness 8h (logarithmic time scale) during desorption into pure solvent for 6 different PEO samples. Molecular weights are indicated in the figure. At t = 0 injection of pure solvent on a polymer layer initially saturated at c= 100 m starts. Initial parts of these curves are dashed since they are affected by instrumental artifacts (dead volume). 

At the other composition, with saturated surfaces, the pressure rises much earlier with volume fraction. Denses packing may be defined as the volume fraction for which the pressure curves becomes nearly verticad. This is obtained at a volume fraction of 0.05 for saturated layers, and 0.2 for unsaturated layers. This shows that the effective hard core which has to be considered in the dense packing is the sum of the hard core of the particle plus the polymer layer thickness. This is in good agreement with the idea that a polymer layer is essentially incompressible. A saturated layer is thicker than an unsaturated one and this leads to a lower concentration in the case of floe compared to nearly saturated particles. 

By knowing T and we can determine the particle radius. The polymer layer thickness, h, can then be readily determined by the following relation ... 

Bridging flocculation of charged particles is enhanced by iuCTeasing the ionic strength (i.e., reducing k ). In the aggregates thus formed, the particles are not in direct contact with each other. Their separation compares with the polymer layer thickness because closer separation would be detrimental to the polymer conformational entropy and, hence, causes Gbr(/t) to become less negative. 

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