Thermoelectric Nanocomposite Foams Using Non-Conducting Polymers with Hybrid 1D and 2D Nanofillers

Characteristics of Epoxy Composites Containing Carbon Nanotubes/Graphene Mixtures

The paper considers the development of fillers representing mixtures of carbon nanotubes and graphene materials (graphene oxide and graphene nanoplatelets) in different mass ratios to modify epoxy resin. The effect of graphene type and content on the dispersed phase particle effective sizes—both in aqueous suspensions and the resin—was analyzed. Hybrid particles were characterized by Raman spectroscopy and electron microscopy. The composites containing 0.15–1.00 wt.% CNTs/GO and CNTs/GNPs were thermogravimetrically analyzed, and their mechanical characteristics were determined. SEM images of the composite fracture surfaces were acquired. Optimal dispersions containing 75–100 nm particles were obtained at the CNTs:GO mass ratio of 1:4. It was shown that the CNTs can be located between the GO layers and on the GNP’s surface. The samples containing up to 0.2 wt.% CNTs/GO (at 1:1 and 1:4 ratios) were stable when heated in air up to 300 °C. For 0.15–0.20 wt.% CNTs/GO (at 1:1 ratio), the tensile strength and modulus of the composite increased by 84–88 and 40%, respectively. The increase in the strength characteristics was found to occur due to the interaction of the filler layered structure with the polymer matrix. The obtained composites can be used as structural materials in different fields of engineering.

Highly Flexible and Durable Thermoelectric Power Generator Using CNT/PDMS Foam by Rapid Solvent Evaporation

Using a simple, rapid solvent evaporation process, the authors produced 3D carbon nanotube (CNT)/polydimethylsiloxane (PDMS) foams with both high thermoelectric (TE) and good mechanical performance and used them to fabricate highly flexible and durable TE generators. The numerous pores and interfaces in the CNT/PDMS foams, which have porosities exceeding 87%, afford very low thermal conductivity of 0.13 W m^-1 K^-1 . The foam has a zT value of 6.6 × 10^-3 , which is twice as high as that of pristine CNT foam. Importantly, the CNT/PDMS foam exhibits good tensile strength of 0.78 MPa, elongation greater than 20%, and excellent resilience even at compressive strain of 80%. This foam is used to fabricate a highly flexible TE foam generator that exhibits a moderate output power of 1.9 µW generated from the large temperature gradient of 18.1 K produced by applied heat. The authors also demonstrate a practical TE foam generator that produces sustainable output power of 3.1 µW under a compressive strain of 80% and 38.2 nW under the continuous vibrational stress produced by a car engine. The TE foam generator also exhibits excellent stability and durability under cyclic bending and harsh vibrational stress.

Nanoclay Intercalation During Foaming of Polymeric Nanocomposites Studied in-Situ by Synchrotron X-Ray Diffraction

The intercalation degree of nanoclays in polymeric foamed nanocomposites containing clays is a key parameter determining the final properties of the material, but how intercalation occurs is not fully understood. In this work, energy dispersive X-ray diffraction (ED-XRD) of synchrotron radiation was used as an in-situ technique to deepen into the intercalation process of polymer/nanoclay nanocomposites during foaming. Foamable nanocomposites were prepared by the melt blending route using low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS) with surface treated nanoclays and azodicarbonamide (ADC) as the blowing agent. Foaming was induced by heating at atmospheric pressure. The time and temperature evolution of the interlamellar distance of the clay platelets in the expanding nanocomposites was followed. Upon foaming, interlamellar distances of the nanocomposites based on LDPE and PP increase by 18% and 16% compared to the bulk foamable nanocomposite. Therefore, the foaming process enhances the nanoclay intercalation degree in these systems. This effect is not strongly affected by the type of nanoclay used in LDPE, but by the type of polymer used. Besides, the addition of nanoclays to PP and PS has a catalytic effect on the decomposition of ADC, i.e., the decomposition temperature is reduced, and the amount of gas released increases. This effect was previously proved for LDPE.