Preparation and Self‐Repairing of Highly Oriented Structures of Ultrathin Polymer Films

Abstract

Thin and ultrathin polymer films play an important role in a variety of applications, such as electronics, liquid crystal alignment, adhesion, and so on. It is well established that the properties of semicrystalline polymeric materials depend remarkably on their multiscale structures; for example, an increase of more than a factor of 100 has been reported for the electrical conductivity of doped and aligned conjugated macromolecules compared with their nonoriented counterparts. Consequently, sophisticated methods have been developed for preparing highly oriented polymer ultrathin films. It should be pointed out that the highly oriented crystalline structure of polymers can be maintained only at temperatures below their melting points. Otherwise, structure rearrangement will result in the loss of orientation and therefore the properties. Therefore, self‐repairing of highly oriented polymer structures is of great significance for the long‐term application of polymer thin films in some specific fields. In this review paper, the preparation and self‐repair of the highly oriented structure of polymer thin films is described in the hopes that this will afford useful information for further development of polymeric materials for advanced applications.

Orientation of Poly(ε-caprolactone) in Its Poly(vinyl chloride) Blends Crystallized under Strain: The Role of Strain Rate

“…This kind of orientation has been referred to as ring-fiber orientation, as schematically presented in Figure 4 b, by Kakudo and Kasai [ 55 ] and also observed for a PCL/PVC (80/20) blend crystallized at room temperature under a draw ratio of λ = 3.6 at a strain rate of 20 mm/min [ 51 ]. For the stretched blends, the vertical c -axis orientation with respect to the strain direction is unusual, since the crystallization of stretched PCL is expected to start from the chains oriented by stretching, similar to the structure of melt-draw induced crystallization of polymers, where the c -axis is always aligned along the stretching direction [ 11 , 12 , 13 , 14 , 15 , 16 ]. This demonstrates the influence of PVC on the crystal orientation of the PCL.…”

“…This stimulates the extensive studies of crystallization from oriented (amorphous) chains for different polymeric materials, including individual polymers and polymer blends. The studies on the crystallization from elongated chains of individual polymers demonstrated the formation of a uniaxial (or fiber) orientation of them with the c -axis aligned in the stretching direction, while the a- and b -axes were arranged randomly about the c -axis [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. However, the orientation of miscible crystalline/crystalline polymer blends crystallized under strain can be quite different from the uniaxial fiber orientation.…”

Tacticity-Dependent Epitaxial Crystallization of Poly(l-lactic acid) on an Oriented Polyethylene Substrate

“…Highly oriented PE thin films were prepared according to a melt-draw technique introduced by Petermann and Gohil . The details of the procedure can be found in the early publication . The thus-prepared ultrathin films with a thickness of ca.…”

“…Therefore, many techniques have been employed to control the multiscale structure of polymers. − Among them, epitaxy offers a simple and effective way to simultaneously control the crystal structure, orientation, and spatial arrangement of the backbone chain. Therefore, epitaxial crystallization of polymers on a variety of substrates has widely been studied. − …”

“…36 The details of the procedure can be found in the early publication. 25 The thus-prepared ultrathin films with a thickness of ca. 50 nm have been frequently used as a substrate.…”