MECHANISM OF UNILATERAL DISTRIBUTION OF TWO SOLVENT PHASES IN THE ROTATING COIL

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A simple rotary device was fabricated to study motion and distribution of two immiscible solvent phases in a rotating coil. Experiments were performed by glass coils of 1 to 2 cm i.d., with helical diameters ranging from 2.5 cm to 20 cm. The results obtained with various two-phase solvent pairs are summarized below on the basis of interplay between the two major physical factors, i.e., solvent-wall interaction and Achimedean screw force. 1. Effect of solvent-wall interaction: High interfacial tension of some binary solvent systems causes plug of phase segments in a narrow-bore coil to interfere with movement of the two phases in the rotating coil. 2. Combined Effects: In this transitional case, one phase with wall-surface affinity passes through segments of the other phase affected by Archimedean screw force and unilaterally distributed in the head side of the coil. 3. Archimedean screw effect: In the rest of the cases, two phases display characteristic distribution consisting of 4 stage according to the applied rotational speed. Stage I: Slow coil rotation distributes two phases evenly in the coil. Stage II: At critical rotational speed, two phases from unilateral distribution. Except for chloroform/water, the heavier phase occupies the head side of the coil. Stage III: Unilateral distribution returns to even distribution through a variety of distribution patterns. Stage IV: Finally, high rotational speed establishes hydrostatic phase distribution.