HYDROGEN DEUTERIUM ISOTOPE EFFECTS ON MICROPHASE SEPARATION IN UNSTABLE CRYSTALLINE MIXTURES OF BINARY N-ALKANES/

We have observed large hydrogen-deuterium isotope effects on the micro phase separation that occurs in unstable crystalline binary mixtures o f n-alkanes rapidly quenched from the malt. These effects were studied in C-30/C-36 mixtures at room temperature, mainly by infrared spectro scopy and electron diffraction. The isotope effects are manifest in a number of different ways: (i) immediately after the quench, the D/H (C -30(D)/C-36(H)) mixture is significantly more demixed than the H/D (C- 30(H)/C-36(D)) mixture; (ii) the spontaneous demixing, which begins im mediately after the quench to room temperature, is faster for D/H by a factor of about 3; (iii) the C-36(H) domains in the D/H mixture grow at a notably faster rate than those of C-30(D) and at a faster rate th an the domains of either component in the H/D mixture. These effects c an be largely accounted for in terms of molar volume differences betwe en the hydrogenated and deuterated n-alkanes that constitute the mixtu res. Similar isotope effects are found to occur in other binary n-alka ne mixtures.