Enhanced mechanical performance of a DGEBA epoxy resin‐based shape memory polymer by introducing graphene oxide via covalent linking

Electron delocalization in defect-containing graphene and its influence on tetrel bond formation

Using the advanced analyses of electron density and fermionic potential, we show how electron delocalization influences the ability of defect-containing graphene to form tetrel bonds. The Cg atoms of a vacancy defect can produce one nonpolar interaction, alongside a peculiar polar Cg⋯Cg bond. The latter stems from the presence of a localized electron pair on a vacancy defect Cg atom and the local depletion of electron localization on another Cg atom. This interaction is an example of intralayer tetrel bond. In the presence of an absorbed molecule of bisphenol A diglycidyl ether (DGEBA), graphene is able to form incipient tetrel Cg⋯O bonds with an ether group oxygen. In contrast to an epoxy group oxygen, the disposition of the ether oxygen often causes the orientation of electron-rich π-domains of graphene carbon on the weakly expressed electrophilic region of the oxygen. In the case of graphene with a point Si defect, the Si atom can form quite strong Si⋯C interactions with the DGEBA aryl carbons. In contrast to other noncovalent bonds, this interaction significantly alters the electron (de)localization on the Si atom and in the aryl ring. The reliability of the obtained results is enhanced by the use of multiple 2D periodic models with defects located at different positions along the DGEBA skeleton.

Using Thermomechanical Properties to Reassess Particles' Dispersion in Nanostructured Polymers: Size vs. Content

Nanoparticle-filled polymers (i.e., nanocomposites) can exhibit characteristics unattainable by the unfilled polymer, making them attractive to engineer structural composites. However, the transition of particulate fillers from the micron to the nanoscale requires a comprehensive understanding of how particle downsizing influences molecular interactions and organization across multiple length scales, ranging from chemical bonding to microstructural evolution. This work outlines the advancements described in the literature that have become relevant and have shaped today's understanding of the processing-structure-property relationships in polymer nanocomposites. The main inorganic and organic particles that have been incorporated into polymers are examined first. The commonly practiced methods for nanoparticle incorporation are then highlighted. The development in mechanical properties-such as tensile strength, storage modulus and glass transition temperature-in the selected epoxy matrix nanocomposites described in the literature was specifically reviewed and discussed. The significant effect of particle content, dispersion, size, and mean free path on thermomechanical properties, commonly expressed as a function of weight percentage (wt.%) of added particles, was found to be better explained as a function of particle crowding (number of particles and distance among them). From this work, it was possible to conclude that the dramatic effect of particle size for the same tiny amount of very small and well-dispersed particles brings evidence that particle size and the particle weight content should be downscaled together.

Surface modification and characterization of waste derived carbon particles to reinforce photo-cured shape memory composites

Carbon fillers have been a source of inspiration to accommodate a range of surface chemistries for different applications. In this study different surface chemistries have been compared for shape memory effect on polymeric composites. Sugar industry waste (fly ash) has been utilized to prepare carbon particles named FCB. Surface modification of FCB has been done in two steps, oxidation and thiolation, respectively. In the first step, different reagents have been used to anchor the surface of FCB with oxygenated functionalities. In the second step, oxygenated FCB has been treated with a thiolating agent to covalently link thio groups on its surface. Polymeric composites have been photo cured with both types of particles, separately. A thermal actuation study has been carried out to check the shape recovery behavior of the composites. A quick shape recovery has been observed for thiolated FCB composites, due to thio linkages in the polymeric network. Samples have been characterized by scanning electron microscopy (SEM), attenuated total reflectance (ATR), dynamic light scattering (DLS), thermal gravimetric analysis (TGA), pH, conductivity, acid content particle dispersion, and composite gel content.

Carbon fillers have been a source of inspiration to accommodate a range of surface chemistries for different applications.