Spherulites in crystalline polymers

It was therefore suggested that there is a possible aggregation of the domains into superdomains , similarly with the growth of spherulites in crystalline polymers, inducing formation of lamellar and fibrillar crystals (a model proposed by Kabanov [694]). Such a quasi-crystalline structure may have a characteristic period of ordering of 1 pm. 

Haze is generally caused by the scattering of light in crystalline polymers. Optical inhomogenities with dimensions in the wavelength range of visible light cause haze. The latter often corresponds to the spherulite volume fraction, spherulite size and crystallinity. An increased size of spherulites results in... 

The formation of shear bands under compression is found in crystalline polymers when loaded at temperatures lower than 0.75 T. Under such a condition the shear bands interact with certain morphological features such as spherulite boundaries or lamellar arrangements inside the spherulites. The band initiation stress, ct, increases and the strain at break, Cp, decreases with decreasing temperature and increasing stiffness of the tested polymer, i.e. increasing degree of crystallinity. 

Cast films exhibit a range of morphologies due to the effect of solvents, substrates and orientation. In the case of block copolymers the choice of solvent is quite important to the final structure. Spherulites, a common textural structure observed in crystalline polymers, are formed in many industrial processes where the polymer is melted prior to forming the article of interest. Films produced by these industrial processes differ from films used in model studies as the former are usually not thin in the microscopic sense. In true thin films, the spherulitic texture is two dimensional, whereas in these thicker film materials the spherulites are three dimensional. 

To some polymer scientists the word morphology means the assembly and relative arrangement of crystals or of second phase particles, while others use supermolecular structure to describe the same thing. Whatever the name, optical and electron microscopy and the complementary techniques of light and x-ray scattering are used to determine such structure. Common arrangements in crystalline polymers solidified frpm the melt are spherulites, row structures, stacks or bundles of lamellae, rods and fibrils. Poorly ordered materials may have... 

The lack of fibrils bridging the walls of cavities results from the mechanism of their formation within spherulitic structure in crystalline polymers above... 

The degree of crystallinity has an important effect upon the physical properties of a polymer. If a polymer melt is allowed to crystallize the crystallinity clearly increases as the spherulites form and grow and so the analysis of the crystallization of a polymer is of profound importance in understanding structure/property relationships in polymers. The nucle-ation and growth of spherulites in a polymer liquid can be readily analysed if a series of assumptions is made. 

Figure 5.27. Diagram showing the detail of the lamellar structure of a spherulite in a polymer with a high degree of crystallinity.

Thomas, C., Seguela, R., Detrez, R, Miri, V., Vanmansart, C. Plastic deformation of spherulitic semi-crystalline polymers an in-situ AFM study of polybutene under tensile drawing. Polymer 50, 3714-3723 (2009)... 

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