Observation Of Banded Spherulites And Lamellar Structures By Atomic Force Microscopy

Polarized optical microscopy and phase-contrast microscopy were used to observe the banded spherulites of poly(e-caprolactone)/ poly(vinyl chloride) (PCL/PVC) blends. The ring spacing and regularity of the banded spherulites decreased with the decrease of the crystallizing temperature. The thickness had some influence on the development of the banded spherulites: When the thickness reduced to some degree, PCL would develop chrysanthemum-like spherulites, which had no extinction rings or the Maltese cross pattern under the crossed polarized optical microscopy. The results of the phase-contrast microscopy showed that growth speed of the chrysanthemum-like spherulites along the radius was not constant. PCL could form banded spherulites through blending with Poly(bisphenol A-co-decane)Lamellar structures of banded spherulites of poly(s-caprolactone)/poly(vinyl chloride) (PCL/PVC) blends were observed using tapping mode atomic force microscopy (AFM). The surface of the PCL/PVC banded spherulites presented to be concentric periodic ups and downs. The period of the bands corresponded to the extinction rings under the polarized optical microscopy observation. The lamellae with edge-on orientation in the ridges and the flat-on lamellae in the valleys of the banded spherulites were observed clearly. The twisting between the edge-on and flat-on lamellae was also observed.The growth of lamellae at the interface of the banded spherulites was studied in situ using atomic force microscopy (AFM) with a hot-stage. The lamellae with edge-on and the flat-on orientation alternated to form the banded spherulites. The growth speed was forced to decreased by the spatial hindrance and limitationof the crystalline chain segment during the closing up of the two spherulites. It was easy to see that the lamellae from different spherulites could penetrate each other and form "lamellar bridges" when the growth directions of lamellae were nearly parallel. The lamellae in different directions could join and stop growing by each other at the interface of spherulites, which lead the formation of defects.