Monolayer crystals grown from solutions

Well defined lath-shaped lamellar crystals of isotactic polypropylene were grown from solution [163]. The thickness of these lamellae, as determined by small-angle X-ray diffraction of crystal aggregates, is 125 A. The crystals were mainly monolayer with the shorter and larger dimensions, respectively, of about 0.2 and 1 pm. Similar lamellar crystals were observed by Sauer et al. [164], Morrow et al. [165], Kojima [166], and Lotz and Wittmann [167]. Fibrils parallel to the longitudinal direction of the lamella were often observed. According to Kojima [166] these fibrils connect the planes of fracture and cleavage that are parallel to the a axis. This is an indication that the 010 planes are the most probable fold planes. Lotz and... 

Figure 3.1 Monolayer crystals of polyethylene grown from 0.1% tetrachloroethylene solution by free cooling from about 120°C. The pleats were formed when the hollow pyramid shape crystals collapsed. A small spiral growth is evident on the largest crystal. Transmission electron micrograph from Reneker and Geil [2] with permission from the American Institute of Physics.

Figure 3.7 Dark-field electron micrograph of a monolayer crystal of poly(4-methylpentene-l) grown from a 0.1% solution in equivolume xylene and amyl acetate solution at 90°C. Each of the four sectors has a 100 growth face contrast is described in the text. From Khoury and Barnes [7] contribution of the National Institute of Standards and Technology.

While the majority of monolayer polymer crystals grown in dilute solution are planar or nearly so, some three-dimensional aspects are worthy of mention. Sec-torization that accompanies the growth of facets can lead to modest departures from planarity as follows. Bassett [15] first noticed that folding leads to subtly different interplanar spacings in different sectors. Consider... 

Figure 3.12 (a) TEM of monolayer crystals of polyethylene, M = 10 kDa, grown at 80°C from 0.01 % xylene solution. There are no pleats or creases that indicate a nonplanar shape, (b) Exactly as in (a), except that the polyethylene has M = 120 kDa. The pleat along the b-axis (small diagonal) indicates that the crystal was a hollow pyramid in solution. Note also the spiral growths. From Holland and Lindenmeyer [16] with permission from John Wiley Sons, Inc. 

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