Stacks of correlated polymer lamellar crystals as platform for functional assemblies

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Polymer lamellar crystals can be considered as part of the family of quasi-two-dimensional nano-sheets with tunable thickness and (functional) surface properties. Besides single-layer crystals, correlated stacks of multi-lamellar polymer crystals with unique orientation can be generated from solution or melt. It is generally accepted that the formation of new crystalline layers on top of the amorphous fold surface of a basal lamella requires a nucleation process. However, the mechanism responsible for stack formation and how the stacked layers are mutually connected is not yet clear. In this joint proposal, we aim to produce stacks of correlated polymer lamellar crystals, both from homopolymers and block copolymers. The thickness of the lamellar core and the interfacial layer, the number of lamellar layers and the areal density of connecting tie chains in the stacks will be tuned via systematic variation of characteristic polymer chain parameters and crystallization conditions. The effect of self-induced nucleation on the fold surface will be examined methodically and in detail. For the formation of stacks of correlated lamellae, a model accounting for the competition of nucleation, growth and diffusion will be developed. Furthermore, we will employ stacks of correlated polymer lamellar crystals as platform for functional anisotropic assemblies yielding composite materials exhibiting features of single crystals. For instance, we will synthesize end-functionalized polymer chains (e.g., using tetraphenylethylene) which emit light when the end-groups aggregate at high areal densities, leading to aggregation-induced emission. After crystallization of such end-functionalized polymers, the functional groups are confined within amorphous interlayers between crystalline lamellae. We will also attempt to incorporate quantum dots or small dyes molecules within the amorphous interlayers. The fluorescence behavior (orientation and polarization dependence) of the stacked lamellar crystals will be investigated in detail. In addition, lithium salts will be inserted into amorphous interlayers and the electric (transport) properties will be measured. We expect that the outcome of the joint project will not only deepen our understanding of the central mechanism of self-induced nucleation in polymer crystals leading to the formation of (high) stacks of correlated polymer lamellar crystals, but also provide new concepts for designing functional materials based on correlated stacks of two-dimensional polymer lamellar crystals.