Bio-inspired Highly Scattering Networks via Polymer Phase Separation

A common strategy to optimize whiteness in living organisms consists in using three-dimensional random networks with dense and polydisperse scattering elements constituted by relatively low-refractive index materials. Inspired by these natural architectures, we developed a fast and scalable method to produce highly scattering porous polymer films via phase separation. By varying the molecular weight of the polymer, we modified the morphology of the porous films and therefore tuned their scattering properties. The achieved transport mean free paths are in the micrometer range, improving the scattering strength of analogous low-refractive index systems, e.g. standard white paper, by an order of magnitude. The produced porous films show a broadband reflectivity of approximately 75 % whilst only 4 m thick. In addition, the films are flexible and can be readily index-matched with water (i.e. they become transparent when wet), allowing for various applications such as coatings with tunable transmittance and responsive paints

Bio-inspired Highly Scattering Networks via Polymer Phase Separation

A common strategy to optimize whiteness in living organisms consists in using three-dimensional random networks with dense and polydisperse scattering elements constituted by relatively low-refractive index materials. Inspired by these natural architectures, we developed a fast and scalable method to produce highly scattering porous polymer films via phase separation. By varying the molecular weight of the polymer, we modified the morphology of the porous films and therefore tuned their scattering properties. The achieved transport mean free paths are in the micrometer range, improving the scattering strength of analogous low-refractive index systems, e.g. standard white paper, by an order of magnitude. The produced porous films show a broadband reflectivity of approximately 75 % whilst only 4 m thick. In addition, the films are flexible and can be readily index-matched with water (i.e. they become transparent when wet), allowing for various applications such as coatings with tunable transmittance and responsive paints

Graphene network organisation in conductive polymer composites

A latex technique is used to prepare graphene/polystyrene and graphene/poly(propylene) composites with varying GR loadings. Their electrical properties and the corresponding volume organisation of GR networks are studied. Percolation thresholds for conduction are found to be about 0.9 and 0.4 wt% for GR/PS and GR/PP with maximum obtained conductivities of 12 and 0.4 S m -1 for GR loadings of 2 wt%, respectively. Investigations using SEM and electrical conductivity measurements show that for the preparation conditions used GR forms an isotropic 3D network in the PS matrix, but GR forms a 2D network in the PP matrix. The different GR network organisations are possibly forced by the different melt flow behaviour of the matrix polymers during processing and the subsequent crystallisation of PP

Graphene network organisation in conductive polymer composites

A latex technique is used to prepare graphene/polystyrene and graphene/poly(propylene) composites with varying GR loadings. Their electrical properties and the corresponding volume organisation of GR networks are studied. Percolation thresholds for conduction are found to be about 0.9 and 0.4 wt% for GR/PS and GR/PP with maximum obtained conductivities of 12 and 0.4 S m -1 for GR loadings of 2 wt%, respectively. Investigations using SEM and electrical conductivity measurements show that for the preparation conditions used GR forms an isotropic 3D network in the PS matrix, but GR forms a 2D network in the PP matrix. The different GR network organisations are possibly forced by the different melt flow behaviour of the matrix polymers during processing and the subsequent crystallisation of PP

Local organization of graphene network inside graphene / polymer composites

The local electrical properties of a conductive graphene/polystyrene (PS) composite sample are studied by scanning probe microscopy (SPM) applying various methods for electrical properties investigation. We show that the conductive graphene network can be separated from electrically isolated graphene sheets (GS) by analyzing the same area with electrostatic force microscopy (EFM) and conductive atomic force microscopy (C-AFM). EFM is able to detect the graphene sheets below the sample surface with the maximal depth of graphene detection up to ˜100 nm for a tip-sample potential difference of 3 V. To evaluate depth sensing capability of EFM, the novel technique based on a combination of SPM and microtomy is utilized. Such a technique provides 3D data of the GS distribution in the polymer matrix with z-resolution on the order of ˜10 nm. Finally, we introduce a new method for data correction for more precise 3D reconstruction, which takes into account the height variations