Free Vertical Growth of Myelin Figures

Abstract

Myelin figures which grow from a floating egg-yolk lecithin lump on a surface of water/glycerin mixture have been found to grow only vertically towards the bottom of a glass cell and never to grow horizontally along the medium surface nor radially. The structure of the growing myelin figures is basically simple rod-like or a bundle of a few simple rods. Helixing, twisting or coiling myelin figures were never observed under the present experimental condition.

Taking the results obtained from the reported growth behaviour of myelin figures into consideration, it is proposed that one of the driving forces of helixing. coiling and twisting growth of myelin figures is thought to be due to a chemical potential difference caused by a concentration gradient along the radial direction perpendicular to the long axis of a myelin figure. The hydrocarbon chains in the fully hydrated stacked bilayer of myelin figures are proposed to be in a more ordered state than reported so far. The arrangement of hydrocarbon chains, both in myelin figures and in an egg-yolk lecithin/water complex, and the density of them also will be discussed.

Key Words:

• myelin figures
• vertical growth
• egg-yolk lecithin
• density
• X-ray diffraction
• morphology