Effect of pore characteristics on carrier-facilitated transport of Am(III)across track-etched membranes

Track-etched membranes (TEMs) with well-defined pore characteristics were p repared by bombarding polycarbonate plastics with Dy-161 ions of 13.0 MeV p er nucleon energy and by bombarding polycarbonate plastics with fission fra gments from a Cf-252 source, In order to optimise the properties of TEMs fo r their applications as model supports in supported liquid membrane (SLM) s tudies, the transport of Am(III) across the SLM with TRUEX extracrants (0.2 M n-octylphenyl (N,N-diisobutyl carbamoyl methyl) phosphine oxide (CMPO) 1.2 M tributyl phosphate (TBP) in dodecane) as carrier has been examined. The latent tracks formed by heavy-ions in the plastics were enlarged into w ell-defined pores by chemical etching. The geometry of the pores formed in the plastics was obtained by the track-etched model, based on the dynamics of pore etching. The TEMs were converted as supports for SLM studies by imp regnating them with the carrier (0.2 M CMPO + 1.2 M TBP in dodecane). The S LMs with different supports were used for studying the facilitated transpor t of Am(III). The permeation across the SLM formed by using TEM with 17% po rosity was found to be comparable to those SLMs formed by using commercial membranes with much higher porosities. The comparison of permeability coeff icients (P) obtained by using TEMs with 29-30 mum and 10 mum thickness indi cated that P decreases linearly with thickness and hence transport of Am(II I) is diffusion controlled, and reaction kinetics of extraction and strippi ng steps are fast. The variation of P as a function of porosity of the TEM support indicated t hat P decreased with increase in porosity upto 10% and thereafter it remain ed constant. The data on variation of P as a function of porosity were used to obtain the thickness of the aqueous diffusion layer and the membrane di ffusion coefficient of the SLM system studied in the present work. The TEMs with very small pore size (0.07 mum) and very large pore size (3 mum) were found to deviate from the expected trend and gave anomalously low P values . Such low P values were also reported elsewhere with membranes of small po re size. The low P values with small pore size support may be due to hinder ed diffusion due to aggregation of the permeant (Am-CMPO complex in this ca se), but no satisfactory explanation was found for low P values in the case of supports with large pore size. (C) 2001 Elsevier Science B.V. All right s reserved.