André Espinha

One-Step-Process Composite Colloidal Monolayers and Further Processing Aiming at Porous Membranes

Composite materials consisting of a monolayer of polystyrene spheres (diameters of 430 and 520 nm) and porous silica, filling in the interstices, have been fabricated and characterized. The proposed growth method introduces some novelties as far as the fabrication of this kind of monolayers is concerned, as it probes the compatibility of coassembly (in which a silica precursor, tetraethyl orthosilicate (TEOS), is added to the base colloid) with confined growth in a wedge-shaped cell, while profiting from the advantages of both techniques. Using this method, it is possible to fabricate the composite monolayer in a single growth step. A systematic study of the influence of TEOS concentration in the initial colloid was performed in order to improve the quality of the two-dimensional crystals produced. Thus, it was demonstrated that the two methods are compatible. Furthermore, the composites were then subjected to thermal treatment so that the polymer is removed to reveal the inverse structure. After the calcination the membranes still present very good quality and so the proposed approach is effective for the fabrication of porous membranes. A comparison of reflectance spectra, between composite monolayers fabricated using this method and composites achieved by infiltrating polystyrene bare opals with silica chemical vapor deposition, is also established. The procedure presented is expected to establish the route for an easier and quicker fabrication of inverse monolayers of high refractive index materials with applications in light control.

Research data supporting "Shape Memory Cellulose-based Photonic Reflectors"

Summary of available data Original or unprocessed data is provided in support of the article “Shape Memory Cellulose-based Photonic Reflectors”. The data is structured into two folders, each correlating to a specific data type presented in the published article. Folder 1: Polarised optical microscopy (POM) The polarised optical microscopy images (.png) used in Figures 1 and in Figure 2 of the Manuscript are provided into their corresponding folders. The scale bar is included in each folder for reference together with an image of the fiber used to collect the spectra. Both folder contain also the reflectivity spectra (.mat) used to plot the graph in Figure 1 and in Figure 2. The films were imaged under with polarizing filters, as described in the Experimental section of the Manuscript. Folder 2: Scanning electron microscopy (SEM) Micrographs cellulose films cross-sections showing the chiral nematic arrangement of cellulose nanocrystals retained after the shape memory polymer infiltration (.tif). The folder ‘Figure 3’ contains high and low magnification images, used for Figure 3 of the Manuscript, the folder ‘Figure S2’ contains the low magnification images, used for Figure S2 of the Supplementary Information. The folder ‘Table 2’ contains the low and high micrographs used to extrapolate the data presented in Table 2 of the Manuscript.

Shape-memory effect for self-healing and biodegradable photonic systems

Photonic systems with the capability to respond to different stimuli are more and more desirable for achieving multifunctionality and higher levels of performance. They demand materials with responsivity that may eventually be used for integrating sensing and actuating functions, a feature highly pursued in technological applications. A notable property which is being gradually incorporated in this kind of multifunctional materials is the shape memory effect (SME). In this work, a material system consisting of a two-dimensional photonic crystal (PC) imprinted in the surface of a shape memory polymer (SMP) is reported. It integrates several interesting features such as elasticity, thermoresponsivity and shape memory. The referred PC is composed of a hexagonal lattice of nanobowls, transferred to the SMP surface using replica molding. Good quality and large extensions of PC were achieved. Differential scanning calorimetry studies confirmed a melting transition responsible for the SME in these materials. From the structural point of view, their surfaces were characterized by atomic force and scanning electron microscopies. From the optical point of view, the characterization of the first order Bragg diffraction angle was carried out. A full programmable character of the structures, derived from the SME, was demonstrated. The reported material system presents some interesting additional features. In particular, the SMP selected for replicating the PC belongs to the family of polydiolcitrates, which are known to be biocompat- ible and biodegradable elastomers. The PC described herein is thus attractive for the development of disposable devices or for temporal usage in biomedicine or biophotonics.