Solvent concentration profile of poly

Solvent Concentration Profile of Poly(methyl methacrylate) Dissolving in Methyl Ethyl Ketone... 

UMMETAL. Solvent Concentration Profile of Poly (methyl methacrylate) 387... 

Figure 9.10 (a) Normalised velocity profiles for different concentration solutions of polyfethylene oxide) in water obtained using dynamic NMR microscopy. The concentrations increase in equal steps from 0.5% (w/v) ( ) to 4.5% (w/v) ( ). (b) The polymer self-diffusion profile for the highest concentration solution in units of 10 m s" Note that this was obtained in a separate experiment so that the capillary wall does not fall at precisely the same pixel as in (a), (c) Water solvent velocity and (d) diffusion maps for the 4.5% (w/v) poly(ethylene oxide) solution. (From Y. Xia and P.T. Callaghan [18] and reproduced by permission of the American Chemical Society.)... 

These latter studies were done in low salt at very low concentrations of poly I poly C (ca 5.0 x 10 M) and poly-L-lysine (ca 2.25 x 10 M). The complex was formed at room temperature. The poly-L-lysine used in these complexes was of a high molecular weight (60-90,000). These investigators reported the binding reaction of poly-L-lysine to polynucleotide to be quantitative, irreversible and with a definite stoichiometric ratio. The poly-L-lysine to poly I poly C ratio at these concentrations was 0.5 NH PO. The thermal de-naturation profile of this complex was found to be a one-step transition with a T at about 89°C in a solvent which contained 0.05 M-NaCl + 0.001 M-9a Citrate ( " 0.3X SSC). Complexes formed between poly I-poly C and poly-L-lysine with less poly-L-lysine than the 1P 0 5 NH ratio gave two-step thermal denaturation profiles with T s at 5rC and 89 C. The lower temperature (T ) indicated that tSere was still free poly I poly C. 

At this point, it is instructive to examine the contact method (Fig. 6). When a solvent is brought into contact with a polymer film, it diffuses into the polymer. If the film is constrained between two IR transparent substrates and the liquid is forced into the gap by capillary action, the contact and subsequent diffusion of the liquid can be easily monitored by means of chemical imaging using light transmitted in the perpendicular direction. After contact, diffusion between the two materials starts. The absorbance (concentration) profile can be measured with accuracy to yield diffusion profiles [83]. However, for hquids, where capUlary acdion is facilitated, the examination of concentration profiles in-situ is difficult. If the concentration profiles developed at higher temperatures are examined at a temperature that prevents further diffusion, the profiles are frozen-in. The diffusion of E7 into poly(butyl methacrylate) (PBMA) w is studied [84] in this manner and compo-... 

Polymer solutions were prepared with deoxygenated, spectral-grade tetrahydrofuran and placed in air-tight glass cuvettes with 2-mm pathlengths. Films were cast from concentrated solutions of the poly-ynes in either tetrahydrofuran or methylene chloride onto glass substrates. Solvent was usually removed under vacuum. The resultant films were removed from the glass and stored in film holders. Film thicknesses were measured with a Tencor Alpha-Step 200 surface profiler. 

Polymers can adsorb spontaneously from solution on to surfaces if the interaction between the polymer and the surface is more favorable than that of the solvent with the surface. For example, a polymer like poly(ethylene oxide) (PEO) is soluble in water but will adsorb on various hydrophobic surfaces and on the water/air interface. This is the case of equilibrium adsorption where the concentration of the polymer monomers increases close to the surface with respect to their concentration in the bulk solution. We discuss this phenomenon at length both on the level of a single polymer chain (valid only for extremely dilute polymer solutions), see Section II, and for polymers adsorbing from (semidilute) solutions, see Section III. In Fig. 2a we schematically show the volume fraction profile (p(z) of monomers as a function of the distance z from the adsorbing substrate. In the bulk, i.e., far away from the substrate surface, the volume fraction of the monomers is (p], whereas, at the surface, the corresponding value is (p > (p]. The theoretical models address questions in relation to the polymer conformations at the interface, the local concentration of polymer in the vicinity of the surface, and the total amount of adsorbing polymer chains. In turn, the knowledge of the polymer interfacial behavior is used to calcu-... 

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