Scanning Transmission Electron Microscopy of Polyethylene Crystals

Abstract

The lateral growth habits and non-planar conformations of polyethylene crystals grown from dilute solutions (<0.1% wt./vol.) are known to vary depending on the crystallization temperature. 1-3 With the notable exception of a study by Keith 2 , most previous studies have been limited to crystals grown at <95°C. The trend in the change of the lateral growth habit of the crystals with increasing crystallization temperature (other factors remaining equal, i.e. polymer mol. wt. and concentration, solvent) is illustrated in Fig.l. The lateral growth faces in the lozenge shaped type of crystal (Fig.la) which is formed at lower temperatures are {110}. Crystals formed at higher temperatures exhibit 'truncated' profiles (Figs. lb,c) and are bound laterally by (110) and (200} growth faces. In addition, the shape of the latter crystals is all the more truncated (Fig.lc), and hence all the more elongated parallel to the b-axis, the higher the crystallization temperature.