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| - Measuring the Mutual Diffusion Coefficient for Dodecyl Acrylate in Low Molecular WeightPoly(dodecyl acrylate) with Laser Line Deflection (Wiener's Method) and the Fluorescenceof Pyrene
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| - Diffusion of small molecules into glassy polymers is quite complicated and almost always non-Fickian. Littlework has been done with the diffusion of low molecular weight polymers that are liquids at room temperature(such as poly(dodecyl acrylate)) into their miscible monomers. We have studied three molecular weightsunder 20 000 to determine if poly(dodecyl acrylate) diffusion into dodecyl acrylate could be treated withFick's law and if so to determine the values of the diffusion coefficients. We compare two methods formeasuring the diffusion of dodecyl acrylate into poly(dodecyl acrylate): We used laser line deflection (Wiener'smethod) and improved upon the method from published reports. We also used the dependence of pyrene'sfluorescence on the viscosity to measure the concentration distribution, and thus to extract the diffusioncoefficient. After an initial relaxation period, diffusion in all cases followed Fick's law with a singleconcentration-independent diffusion coefficient. Comparison of the diffusion coefficients obtained by bothmethods yielded the same order of magnitude for the diffusion coefficients (10-7 cm2/s) and showed thesame trend in the dependence on the average molecular weight of the polymer (a decrease in the diffusioncoefficient with an increase in the molecular weight).
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