Table 2. Comparison of Calculated Perineation Rates lrom Weight Galn Assays wlth Those Observed in Permeation Cell Experiments Permeant 1.1.2-hIchi0r0~thane 1.2dichloroethane benzene
toluene
Pemeatim Rates (g/cm2/h)10' Calc. Obs. 6.0 5.3 12.0 26.0
9.4
1.3 12.0
13.0
tween when the chemicals are detected and establishment of steady-state conditions where the plots are linear. The slopes of the steady-state portion of the plots represent the permeation rates. The permeation cell experiments served three useful purposes. First, they were an empirical validation of the results from the immersionlweight-gain experiments. Second, if "failure" of the HDPE material had occurred, changes in permeation rates, indicative of failure, would easily have been detected. Third, the experiments examined the possibility of synergistic action of chemicals on HDPE. That is, if no synergistic action occurred, the permeation rates of each of the mixed chemicals in the permeation cells would be the same as those calculated from the immersionlweight-gain assays using single chemicals. Comparison of Results of Immersion/Weight-Gain Assays with the Permeation-Cell Experiments The predicted permeation rates of each of the five chemicals in an equimolar solution, as in the permeation cell experiments, were calculated based on data from the immersionlweight-gain assays. These values are compared in Tahle 2 with the observed permeation rates from the permeationcell experiments. There is fair agreement (i.e., all values in the same order of magnitude) between the values suggesting that the predicted permeation rates given in Tahle 2 are reasonable. This also suggests that there were no changes in permeation rates in HDPE due to mixtures of chemicals (i.e., synergistic effects).
Often highly sophisticated experimental techniques are being used in most advanced research laboratories to measurediffusion characteristics ofpolymers, yet both the complexity and the cost of even simple equipment prevents the inclusion of these methods in undereraduate teaching lahoratories. Hence, many graduates areleaving the schooiwith little experience in practical aspects of these problems. The immersion/weight-gain method presented here is relatively straiehtforward both exoerimentallv and conce~tuallv,and thusvprovides an ideal kxperiment-by which &dents can gain experience with practical systems in the laboratory. Although a detailed understanding of the theory of diffusion is somewhat difficult, the method can he used with greater safety and ease to evaluate solvent diffusion through polymer films. Preliminary results with other materials indicate that the method is convenient and supplements data obtained from permeation cell experiments (6). Acknowledgment The authors (PEC and TMA) thank the Robert A. Welch Foundation (Grant AI-5241, Houston, Texas, for its financial support; T.M.A also thanks the administrators of Karnatak University for the sanction of leave and Texas Research Institute for a Faculty Summer Fellowship for 1986.
Literature Cited 1. Casnidy, P. E.:Aminabhavi, T. M.; Thornpaon, C. M. Rubber Chem. Tochn. 1983.56,
2723. 6. Brittm,L.N.;l\lihman,RH.:Arninsbhavi.T. M. J.Appl.Poiym.Sci.subrnitted. 7. Jmt. W. Diffwion in Solids,Liquids and Gosea. Academic: New York, 1852.
15. Corbin, G.A : Cohen, R. E.:Baddo'ur, R.F. d. Appl. Poiym. Sci. 1%
Storage of PolyacrylamideGels Polyacrylamidegel elecfrophoresis has hem widely accepted as a separation techniqut in biochemisrry. Pnrteins can heseparated becauseof differingmobiliries in their nativestateor as denatured suhunits in the presence of sodium dodecyl sulfate and 3-mercaproethanol.Typically, staining is accomplished using Ccmnassie hlue or silver mtrate, and the gcl is ~then dried. It is time consuming M dry and stare a large number of gels. Furthermore, a commercial slab gel dryer requires the use of a vacuum pump, dry ice, and a heating unit. Usually only one gel can he dried at a time. A unit designed for the storage of food can be used to save polyacrylamidegels. The Dazey Micro-Seal 11, Model MS2 is ideal for this purpose. After staining, the gel is slid into an appropriate length of Micro-Seal material designed for making food storage bags. Type #6010 is most convenient since it comes in a roll 10cm X 20 ft with 2 mil thickness. One of the ends is then sealed off using the Model MS2 unit. This is followed by the removal of excess solvent from the gel by gently stroking the bag to farce liquid toward the open end. Finally, that side is sealed using the Model MS2 unit. The storage of gels in a Micro-Seal hag can be done quickly and with minimum cost (approximately $13 for the sealing unit and $4 for a rdll of plastic). Gels can be viewed days or months after sealing in the food storage bag. Thus, it is ideally ' suited for meeting the requirements of a large classroom situation. ~
Salvatore F. Russo Western Washington University Beliingham, WA 98225
370
Journal of Chemical Education
