The mutual diffusion coefficient for (meth)acrylate monomers as determined with a nuclear microprobe

The value of the mutual diffusion coeff. DV of two acrylic monomers is detd. with nuclear microprobe measurements on a set of polymer films. These films have been prepd. by allowing the monomers to diffuse into each other for a certain time and subsequently applying fast UV photo-polymn., which freezes the concn. profile. The monomer diffusion profiles are studied with a scanning 2.1 MeV proton microprobe. Each monomer contains a marker element, e.g., Cl and Si, which are easily detected with proton induced x-ray emission. From the diffusion profiles, it is possible to det. the mutual diffusion coeff. The mutual diffusion coeff. is dependent of concn., which is concluded from the asymmetry in the Cl- and Si-profiles. A linear dependence of the mutual diffusion coeff. on the compn. is used as a first order approxn. The best fits are obtained for a value of b=(0.38+-0.15), which is the ratio of the diffusion coeff. of 1,3-bis(3-methacryloxypropyl)-1, 1,3,3-tetramethyldisiloxane in pure 2-chloroethyl acrylate and the diffusion coeff. of 2-chloroethyl acrylate in pure 1,3-bis(3-methacryloxypropyl)-1,1,3,3-tetramethyldisiloxane. Under the assumption of a linear dependence of the mutual diffusion coeff. DV on monomer compn., it follows that DV=(2.9+-0.6).10-10 m2/s at a 1:1 monomer ratio. With Flory-Huggins expressions for the monomer chem. potentials, one can derive approx. values for the individual monomer diffusion coeffs