2D hybrid substrates for functional polymer-based materials

Polymer nanocomposites (PNC) with 2D nanostructured fillers (i.e., layered silicates, layered double hydroxides, graphene etc.) have emerged in the past decades as a promising class of materials with improved mechanical, thermal and barrier performance [1]. Final material properties depend not only on the size of particles but also on the properties of the interphase and interfacial interactions, which govern the matrix chain mobility, filler dispersion and distribution [2]. Much work has been done on the modification of both filler and matrix in order to tune and optimize the reciprocal interactions and to create a co-continuous organic/inorganic phase necessary for improving the thermo-mechanical properties. Recently, in addition to the optimization of PNC structural features, emphasis is given to the introduction of new functional properties (i.e. optical, electrical, sensing, bioactive, etc.) by dispersing 2D hybrid heterostructures, used as "nanocarriers" of specific active moieties [3]. In particular, the 2D structure of layered double hydroxides (LDHs) can accommodate functional organic molecules (i.e. dyes, biomolecules, oligomers, stabilizers, etc.), which are firmly anchored by anionic bond to the layer surfaces. These hybrid host-guest systems can be used as fillers for polymers thus obtaining PNC where the structural properties are ruled by the organic/inorganic polymer network, and the functional properties are related to the chemical nature of the substances incorporated into the filler. In this way, PNC can be endowed with interesting optical, sensing and bioactive properties by simply transferring the targeted property from the 2D hybrid system to the polymer matrix through the nanocomposite preparation. This lecture reviews the results obtained in our laboratory about the preparation of PNC obtained by dispersing 2D hybrid materials modified with functional molecules, such as dyes, antioxidant and antibacterial agents [4-7] for possible packaging and sensor applications. The role of the 2D substrate functionalization and of the chemistry at the interface for the optimization of morphology and final properties of PNC will be discussed.