Confined crystallization in polymer nanolayered films: A review
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Confined crystallization in polymer nanolayered films: A review Joel M. Carr, Deepak S. Langhe, Michael T. Ponting, Anne Hiltner, and Eric Baera) Department of Macromolecular Science and Engineering, Center for Layered Polymeric Systems, Case Western Reserve University, Cleveland, Ohio 44106-7202 (Received 8 November 2011; accepted 29 December 2011)
Recent advances utilizing forced assembly multilayer coextrusion have led to the development of a new approach to study the structure–property relationships of confined polymer crystallization. Confinement of crystalline polymer materials in layer thicknesses ranging from hundreds to tens of nanometers thick, resulted in multilayer films possessing enhanced gas barrier properties. The enhanced gas barrier has been attributed to nanolayer confinement of the crystalline polymer resulting in a highly ordered intralayer lamellae orientation extending over micron or larger scale areas. Research into the confined crystallization mechanism of the multilayered polymer films has resulted in several material case studies as well as an understanding of the chemical and thermodynamic parameters that control the degree and rate of the confinement in multilayer polymer systems. This review highlights our recent studies on the confinement of poly(ethylene oxide), poly(e-caprolactone), polypropylene, and poly(vinylidene fluoride) polymers in multilayered films.
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.17
temperature, film thickness, chain mobility, and substrate/ polymer interactions.26 Polymer crystallization under one-dimensional (1D) confinement is conventionally studied with a spin-coated thin polymer layer on a substrate,27 with a block copolymer that contains at least one crystallizable block,18 with a deformation of immiscible blends,28 or with a patterned substrate.29 Each of these techniques has specific limitations. Spin-coating and patterned substrates require a solvent during processing, which can limit the choice of polymer. The process itself also produces a small amount of material that contains a free surface, which is known to affect the properties of the polymer thin layer.26,30 Selfassembly of block copolymers requires specific synthesis, which limits the polymers available for study. The final phase separated block copolymer morphology may not possess long-range order and can require the use of shear alignment to produce a uniformly oriented phase structure.31 Blending is limited by miscibility of the blended components. Layer-multiplying “forced assembly” coextrusion offers a new approach to study confined crystallization of polymers.32 This process can be used to combine two or three polymers into a continuous alternating layered structure with hundreds or thousands of layers with individual layer thicknesses down to 10 nm. This process allows for long range, almost defect-free confinement to study confined polymer crystallization. In recent years, our interest in confined crystallization in micro- and nanolayered films has led to an exc
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