Mediating polymer crystal orientation using nanotemplates from block copolymer microdomains and anodic aluminium oxide nanochannels

Crystals formed by polymers are typically nanoscale in at least one dimension. The directional control of properties via precise control of the orientations of polymer nanocrystals has strong relevance to technical applications in various areas. Polymer crystals may exhibit preferential orientation when they are formed inside nanoscale domains or pores. Such a confinement-mediated orientation behavior has been a subject of extensive investigation over the past two decades, where a block copolymer in which two or more chemically different sub-chains form a single molecule template system that has received the most attention. In this article, we focus on an overview of the orientation behavior of polymer crystals under the influence of one-dimensional (1-D) and two-dimensional (2-D) confinement templated by the lamellar and cylindrical microdomains of block copolymers, respectively. In the case of lamellae-forming diblock copolymers, both the crystalline-amorphous system (which is composed of one type of nanocrystals) and the more complex double-crystalline diblock (which consists of two types of nanocrystals) are considered. In addition to the templates offered by block copolymers, the preferential orientation of polymer crystals confined in the inorganic anodic aluminium oxide (AAO) nanochannels has also been critically reviewed due to strong relevance to the 2-D confinement effect. Moreover, the significant thermodynamic and kinetic factors governing the crystal orientation behavior have been summarized, which may allow one to understand the strategy for tuning the preferential orientation of polymer nanocrystals under the spatial confinement of different dimensionalities.