Diffusion polystyrenes

The resolution of infra-red densitometry (IR-D) is on the other hand more in the region of some micrometers even with the use of IR-microscopes. The interface is also viewed from the side (Fig. 4d) and the density profile is obtained mostly between deuterated and protonated polymers. The strength of specific IR-bands is monitored during a scan across the interface to yield a concentration profile of species. While in the initial experiments on polyethylene diffusion the resolution was of the order of 60 pm [69] it has been improved e.g. in polystyrene diffusion experiments [70] to 10 pm by the application of a Fourier transform-IR-microscope. This technique is nicely suited to measure profiles on a micrometer scale as well as interdiffusion coefficients of polymers but it is far from reaching molecular resolution. 

Figure 2.20 Permeant diffusion coefficient as a function of permeant molecular weight in water, natural rubber, silicone rubber and polystyrene. Diffusion coefficients of solutes in polymers usually lie between the value in natural rubber, an extremely permeable polymer, and the value in polystyrene, an extremely impermeable material [28]...

Here, if ris known in advance, D can be directly obtained from Eq. (15). If it is unknown, x and D are determined fix)m the measurements with varied A. As the striation period can be as narrow as 1 pm, even slight movement and slow diffrision can be measured. The measurement area can also be small. For measurement purposes, a molecule that can be excited by a laser light as a probe or a probe that is tagged by a chromophore must be used. Studies on polystyrene diffusion partially labeled by 4-bromomethyl-azobenzene in gelatin [22] and spiropyrane in polystyrene gel [23] have been reported. 

Fig. 3. Infrared spectra of polystyrene (a) transmission of a 33-p.m thick polystyrene film (b) diffuse reflection of polystyrene powder at a concentration of...

The spreading rate of a polymer droplet on a surface has been measured (363,364). The diffusion constant was at least an order of magnitude smaller than that of the bulk. The monomer—surface friction coefficient for polystyrene has been measured on a number of surfaces and excellent... 

TABLE 16-8 Self Diffusion Coefficients in Polystyrene-divinylbenzene Ion Exchangers... 

Except where the foam is surrounded by a skin of relatively impermeable material, it would be expected that the blowing gas would diffuse out and be replaced by air and that the thermal conductivities of the foams would increase until they approached that of expanded polystyrene of similar density. Whilst this... 

Fig. 6. The ripple experiment at the interface between a bilayer of HDH- and DHD-labeled polystyrene, showing the interdifussion behavior of matching chains. The protonated sections of the chain are marked by filled circles. The D concentration profiles are shown on the right. Top the initial interface at / = 0. The D concentration profile is flat, since there is 50% deuteration on each side of the interface. Middle the interface after the chain ends have diffused across (x < / g). The deuterated chains from Que side enrich the deuterated centers on the other side, vice ver.sa for the protonated sections, and the ripple in the depth profile of D results. A ripple of opposite sign occurs for the H profile. Bottom the interface when the molecules have fully diffused across. The D profile becomes flat [20,56].

The non-bonded interaction energy, the van-der-Waals and electrostatic part of the interaction Hamiltonian are best determined by parametrizing a molecular liquid that contains the same chemical groups as the polymers against the experimentally measured thermodynamical and dynamical data, e.g., enthalpy of vaporization, diffusion coefficient, or viscosity. The parameters can then be transferred to polymers, as was done in our case, for instance in polystyrene (from benzene) [19] or poly (vinyl alcohol) (from ethanol) [20,21]. 

FIQ. 3 Diffusion coefficient of benzene molecules in benzene-polystyrene mixtures normalized by the diffusion coefficient of neat benzene molecular dynamics results, NMR measurements and prediction by the Mackie-Meares model [26]. 

D. S. Cannel, F. Rondelez. Diffusion of polystyrene through microporous membranes. Macromolecules 75 1599-1602, 1980. 

H. Kim, T. Chang, J. M. Yohanan, L. Wang, H. Yu. Polymer diffusion in linear matrices Polystyrene in toluene. Macromolecules 19 2121-21AA, 1986. 

N. Nemoto, M. Kishine, T. Inoue, T. Osaki. Tracer diffusion of linear polystyrene in entanglement networks. Macromolecules 22 659-664, 1990. 

N. A. Rotstein, T. P. Lodge. Tracer diffusion of linear polystyrenes in poly-(vinyl methyl ether) gels. Macromolecules 25.T 316-1325, 1992. 

It is easy to measure the potential of this system and it has been found that membranes of polystyrene, linseed oil and a tung oil varnish yielded diffusion potentials of 43-53 mV, the dilute solution being always positive to the concentrated. Similar results have been obtained with films of nitrocellulose, cellulose acetate , alkyd resin and polyvinyl chloride . 

A very similar effect of the surface concentration on the conformation of adsorbed macromolecules was observed by Cohen Stuart et al. [25] who studied the diffusion of the polystyrene latex particles in aqueous solutions of PEO by photon-correlation spectroscopy. The thickness of the hydrodynamic layer 8 (nm) calculated from the loss of the particle diffusivity was low at low coverage but showed a steep increase as the adsorbed amount exceeded a certain threshold. Concretely, 8 increased from 40 to 170 nm when the surface concentration of PEO rose from 1.0 to 1.5 mg/m2. This character of the dependence is consistent with the calculations made by the authors [25] according to the theory developed by Scheutjens and Fleer [10,12] which predicts a similar variation of the hydrodynamic layer thickness of adsorbed polymer with coverage. The dominant contribution to this thickness comes from long tails which extend far into the solution. 

Measurements of diffusion of tracer polymers in ordered block copolymer fluids is another potentially informative activity, since molecular diffusion is one of the most basic dynamic characteristics of a molecule. Balsara, et al. have measured the retardation of diffusion due to ordering in the diffusion of polystyrene tracer homopolymers in polystyrene-polyisoprene matrices of various domain sizes [167]. Measurement of the tracer diffusion of block copolymer molecules will also be important. Several interesting issues are directly addressable via measurements... 

In a number of experimental studies of polymer diffusion, molar mass exponents close to 2 have been found, though always with some deviations. For example, using radio-labelled molecules, the diffusion coefficient of polystyrene in dibutyl phthalate was found to follow the relationship... 

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