Lozenge-shaped single crystal

Characteristic lozenge shaped lamellar crystals ca. 40 pm long and 10 nm thick were observed. The results indicated that, for the low molecular mass, the surface of the HDPE single crystals is formed of sharp and regular folds, whereas for the high the surface has switchboard-like random loose loops. The surface structure of the intermediate molecular mass is also intermediate. 

Fig. 2.15 Several lozenge-shaped polyethylene single crystals grown from xylene solution (from Geil (1963) courtesy of Geil).

Poly(L-lactic acid) is reported to crystallize into lozenge-Uke [37,112-114] and hexagonal-like [37, 114] single crystals in dilute solutions. In contrast, single crystals of the stereocomplex of PLLA and PDLA have a peculiar triangular shape when they are formed in p-xylene at solution concentrations as low as 0.04% [33, 115]. 

Careful examination of single crystals grown from solution at 70 °C in xylene indicated that they are lozenge shaped and have surfaces that are 110 planes. 

Figure 5.3 Transmission electron micrograph of a solution-grown single crystal of linear polyethylene showing lozenge-shaped crystals.

Generally in regime I the habit of single crystals is lenticular, whereas the habit of the polycrystallite aggregates is axialitic. In regime II the lamellae have truncated lozenges shape, whereas the superstructure is spherulitic. 

Figure 5.3 Morphologies of polyethylene single crystals (a) lozenge-shaped tent type, (b) truncated-lozenge-shaped tent type, (c) two halves of truncated lozenge-shaped chair type, and (d) truncated lozenge-shaped chair type with spiral terraces from screw dislocations [11].

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