Solvent Accelerated Polymer Diffusion in Thin Films

Abstract

We have investigated the absorption of cyclohexane vapor into polystyrene films and the resulting polymer interdiffusion that is enabled by this process. The swelling of films due to solvent absorption was relatively insensitive to the film thickness or polymer molecular weight but increased with increasing temperature. The interdiffusion enabled by absorbed solvent was examined in multilayered films comprising alternating layers of deuteriopolystyrene (dPS) and hydrogenous polystyrene (hPS). Deuterium concentration gradients were measured in dry films following exposure to cyclohexane vapor at controlled temperatures and times to establish the relationship between the coefficient of solvent accelerated interdiffusion, D*, and (i) M w of hPS, (ii) Mw of both hPS and dPS, (iii) temperature, and (iv) film thickness. Scaling relationships were established for D* as a function of molecular weight. D* ∼ Mw -1 for increasing hPS molecular weight for Mw(hPS) < Mw(dPS) and was independent of Mw(hPS) for Mw(hPS) > Mw(dPS). This indicates that the lower molecular weight polymer, in keeping with predictions of "fast-mode" diffusion theory, dominates the rate of interdiffusion. When both dPS and hPS molecular weights were increased simultaneously, the interdiffusion coefficient scaled with Mw -1.8 . A marked increase in D* with increasing solvent temperature was observed, consistent with the temperature dependence of film swelling. A strong and unexpected correlation between D* and total film thickness was found. This effect was attributed to prolonged solvent retention in thicker films following exposure to solvent vapor.

Surface Modification of Polyethylene with Multi-End-Functional Polyethylene Additives

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Particle-Induced X-Ray Emission Analysis

“…This was used by Tosaki (2006) [36] to distinguish different forms of carbon. It is the behaviour of the EBS resonance for 12 C(p,p) 12 C at 1734 keV that allows us to prove the presence not only of carbon but also of SiO 2 precipitates in these inclusions.…”

“…µPIXE ( Figure 13) shows that the samples are very heterogeneous, and EBS analysis unequivocally demonstrated them to be carbonaceous from the 12 C(p,p) 12 C resonance at 1734 keV ( Figure 14). This result initially baffled the geologists, for whom such a sample was unprecedented.…”

“…If the layer of the diffusing species is initially extremely small then it effectively becomes diluted as soon as diffusion begins, and under these circumstances the tracer diffusion this component is independent of the thermodynamics of mixing. Deuterium labelling has commonly been applied to determine the diffusion of one organic material into another [4,[10][11][12]. Here, some or all of the hydrogen atoms of one component in the mixture are substituted for deuterium, which has minimal impact on the chemical and physical properties, but enables direct determination by elastic recoil detection and nuclear reaction analysis.…”

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