Composites Part A | Engineering foam skeletons with multilayered graphene oxide coatings for enhanced energy dissipation

author:系统管理员time:2020-10-01views:903

Abstract

This work shows how to improve the energy dissipation of open-cell polyurethane (PU) foams by creating multilayered graphene oxide (GO) nano-architectures onto the struts via a modified dip-coating process. Pristine PU foams are alternately dip-coated with GO coatings and water-based polyurethane dispersions (PUD) for a given number of times. The GO coating morphologies are carefully adjusted and the inner energy dissipation mechanisms reach the optimized interfacial frictions of GO-PU and GO-GO. Along with the synergistic effect of the multiple interpenetrating structure of GO/PU coating phases, these engineered composite foams with extremely low GO content (~0.12 wt%) afford a significant increase of quasi-static energy dissipation (52%) and dynamic damping (76%) when compared with counterpart foams coated with the same number of pure PUD layers. The specific Young’s modulus and strength of the designed foams also show remarkable enhancements of 310% and 490% respectively compared with those of pristine PU foams.

Keywords

Graphene oxide

Interfacial friction

Nanocomposite foams

Energy dissipation

Fig. 1. (a) Schematic diagram of the preparation process of PU composite foams with skeletons of multi-layer sandwich structure. (b) AFM image of the as-prepared GO nanoplatelets and (c) height profile pattern derived from line 1, revealing that the nanoplatelets are ~ 10 μm in lateral size and ~ 6 nm in thickness. (d) SEM image showing the cellular macrostructure of the pristine PU foams, the inset image shows the cross-section of one foam strut.

Fig. 2. SEM images of (a) PU foam struts coated with GO inks of different concentrations, (a₁) pristine PU, (a₂) 0.05 wt%, (a₃) 0.1 wt%, (a₄) 0.2 wt%, (a₅) 0.3 wt% and (a₆) 0.4 wt%, the rougher surfaces with the increasing concentrations of coating inks demonstrate more GO nanoplatelets attached on the surface. The surface morphologies of the struts coated with 0.2 wt%GO-ink under (b) low and (c) high magnifications, showing that the unfolded GO nanoplatelets are quasi-uniformly coated on the whole struts of the foams and form an entangled coating network with some sparsely uncovered PU areas.

Fig. 3. SEM images of the sandwich structure of the foam struts. (a) The smooth surface of the PUD coating and (b) cross-section of PU + PUD samples brittlely fractured by an external force after liquid nitrogen treatment. Cross-sections of PU + 0.2 wt%GO + PUD samples (c, d) brittlely fractured after liquid nitrogen treatment and (e, f) gradually fractured at room temperature.

Fig. 4. The mechanical, quasi-static energy dissipation and dynamic damping properties of the sandwich structural foams coated with GO inks of various concentrations. (a) Stress–strain curves from compression tests and the derived (b) Young’s modulus (E) at 2%~3% strain and (c) strength () at 10% strain. (d) Energy dissipations (ΔW) and loss factors (η) obtained from quasi-static cyclic compression tests. (e) Storage modulus (E’) and (f) damping loss factor (tan δ) obtained by DMA under different frequencies.

Fig. 5. The schematic of the evolution of interfacial friction mechanisms with the increase of GO coating contents (ink concentrations). The GO nanoplatelets are sandwiched by the PU matrix (PUD is the polyurethane dispersion), and the interfacial friction can be activated for the foam skeletons under the vibration (cyclic) microscale deformations.

Fig. 6. Cross-sections of (a) a ligament of 5(PU + GO + PUD) samples with brittle failure after liquid nitrogen treatment and the zoomed-in image showing the obvious five-layer sandwich structure. (b) Micrograph showing the measured length and diameter of a ligament. (c) Curves of lengths, diameters and length/diameters ratios of the ligaments versus coating layers (the data are the averages with error bars based on 50–60 measurements). (d) Density variation of the foams with the increase of number of coating layers n.

Fig. 7. Stress–strain curves of (a) n(PU + GO + PUD) and (b) n(PU + PUD) samples under compression. The inserted figure is the enlarged stress–strain curve of pristine PU foams under large compression rate, containing three distinct and typical deformation regions. (c) Young’s modulus E at 2 ~ 3% strain and (d) strength

at 10% strain of the multi-layer coated foams. The insets are the corresponding specific Young’s modulus and strength divided by the density. Linear fittings for the relationships of (e) the Young’s modulus E versus

and (f) the strength

versus

. The fitting lines are derived from the four data of samples with 0–3 coating layers because the values of Adj. R² are almost 1 (0.97–0.99). The data points for samples with 4 and 5 coating layers do deviate significantly from the linear fitting.

Fig. 8. SEM images of n(PU + GO + PUD) foams with different coating layers at 10% compression strain as (a) pristine, (b) one, (c) two, (d) three, (e) four and (f) five coating layers. Red circles show the observable deformations of the struts as the bending and buckling. The deformation schematics of supporting cell-bars under the applied compression for (g) the slender structs and (h) the stubby struts, and their derived loading and deforming forms of GO nanoplatelets.

Conclusions

In this work, PU foam skeletons with multi-layer sandwich GO coatings are successfully designed and fabricated by using a modified dip-coating method. The GO coatings work as the core layers of the sandwich architecture covering the whole surfaces of the foam skeleton and provide a satisfying energy dissipation mechanism of the GO-GO and GO-PU interfacial micro sliding under cyclic deformation. When compared with the counterpart foams without GO layers, the energy dissipations (loss factors) of composite foams with only ~ 0.12 wt% GO content increase by 52% and 76%, respectively, from quasi-static cyclic compression tests and DMA tests. These enhancements are atributed to the inner energy dissipation mechanisms performed by the optimized interfacial frictions of GO-PU and GO-GO and the synergistic effect of the multiple interpenetrating structure of GO/PU coating phases. Besides, the introduction of the PUD coating layers significantly enhances the Young’s modulus (310%) and strength (490%) of the foams compared with the pristine PU foams. This work provides an effective route to design and manufacture graphene nanocomposite foams for damping applications and affords insightful analyses for the structural mechanisms of this material under static and dynamic load.

Title：Engineering foam skeletons with multilayered graphene oxide coatings for enhanced energy dissipation

Website：https://www.sciencedirect.com/science/article/pii/S1359835X20302748#f0005

Work Group ：https://person.zju.edu.cn/hxpengwork

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