A novel nanocomposite foam with microcellular structures based on poly(vinylidene fluoride) (PVDF) and titanium dioxide (TiO2) was fabricated by the combination of melt compounding and supercritical carbon dioxide (scCO2) foaming. To improve its dielectric performance, silane modified and unmodified titanium dioxide nanoparticles were added as reinforcing fillers at low weight percentages (0.5, 1, and 5 wt%) during the melt blending process. It was found that the incorporation of nanoparticles had a strong influence on cell morphology. As a result, the foaming process significantly altered the dielectric, and mechanical properties of the composite foams. The dielectric constants of the composite foams were no longer frequency dependent while tan delta was lowered at least by a factor of 10. Furthermore, the porous structure generated by foaming also assisted the α-to-β phase transformation of the PVDF matrix in a way similar to mechanical stretching. Such method is superior to other phase transformation techniques since β-phase PVDF can be produced in bulk geometries instead of a thin film configuration.
ZengWShuLLiQ, et al. Fiber‐based wearable electronics: a review of materials, fabrication, devices, and applications. Adv Mater Weinheim2014; 26: 5310–5336.
4.
MartinsPCaparrosCGonçalvesR, et al. Role of nanoparticle surface charge on the nucleation of the electroactive β-poly (vinylidene fluoride) nanocomposites for sensor and actuator applications. J Phys Chem C2012; 116: 15790–15794.
5.
FanFRTangWWangZL.Flexible nanogenerators for energy harvesting and self‐powered electronics. Adv Mater Weinheim2016; 28: 4283–4305.
6.
AntonSRSodanoHA.A review of power harvesting using piezoelectric materials (2003–2006). Smart Mater Struct2007; 16: R1–R21.
7.
WangZLSongJ.Piezoelectric nanogenerators based on zinc oxide nanowire arrays. Science2006; 312: 242–246.
8.
SodanoHAInmanDJParkG.A review of power harvesting from vibration using piezoelectric materials. Shock Vib Digest2004; 36: 197–206.
9.
BhavanasiVKumarVParidaK, et al. Enhanced piezoelectric energy harvesting performance of flexible PVDF-TrFE bilayer films with graphene oxide. ACS Appl Mater Interfaces2016; 8: 521–529.
10.
ChangCTranVHWangJ, et al. Direct-write piezoelectric polymeric nanogenerator with high energy conversion efficiency. Nano Lett2010; 10: 726–731.
11.
GregorioJRCestariM.Effect of crystallization temperature on the crystalline phase content and morphology of poly(vinylidene fluoride). J Polym Sci B Polym Phys1994; 32: 859–870.
12.
GregorioRJrandUenoEM.Effect of crystalline phase, orientation and temperature on the dielectric properties of poly (vinylidene fluoride) (PVDF). J Mater Sci1999; 34: 4489–4500.
13.
SunLLiBZhangZ, et al. Achieving very high fraction of β-crystal PVDF and PVDF/CNF composites and their effect on AC conductivity and microstructure through a stretching process. Eur Polym J2010; 46: 2112–2119.
14.
BhartiVKauraTNathR.Ferroelectric hysteresis in simultaneously stretched and corona-poled PVDF films. IEEE Trans Dielect Electr Insul1997; 4: 738–741.
15.
CostaPSilvaJSencadasV, et al. The effect of fibre concentration on the α to β-phase transformation, degree of crystallinity and electrical properties of vapour grown carbon nanofibre/poly (vinylidene fluoride) composites. Carbon2009; 47: 2590–2599.
16.
HuangXJiangPKimC, et al. Influence of aspect ratio of carbon nanotubes on crystalline phases and dielectric properties of poly (vinylidene fluoride). Eur Polym J2009; 45: 377–386.
17.
SuiGJanaSZhongW, et al. Dielectric properties and conductivity of carbon nanofiber/semi-crystalline polymer composites. Acta Materialia2008; 56: 2381–2388.
18.
WangLDangZ-M.Carbon nanotube composites with high dielectric constant at low percolation threshold. Appl Phys Lett2005; 87: 042903.
19.
ShahDMaitiPGunnE, et al. Dramatic enhancements in toughness of polyvinylidene fluoride nanocomposites via nanoclay‐directed crystal structure and morphology. Adv Mater2004; 16: 1173–1177.
20.
PatroTUMhalgiMVKhakharD, et al. Studies on poly (vinylidene fluoride)–clay nanocomposites: effect of different clay modifiers. Polymer2008; 49: 3486–3499.
21.
DangZ-MWangH-YXuH-P.Influence of silane coupling agent on morphology and dielectric property in BaTiO3/polyvinylidene fluoride composites. Appl Phys Lett2006; 89: 112902.
22.
ZhangYZhangYXueX, et al. PVDF–PZT nanocomposite film based self-charging power cell. Nanotechnology2014; 25: 105401.
23.
SauceauMFagesJCommonA, et al. New challenges in polymer foaming: a review of extrusion processes assisted by supercritical carbon dioxide. Progr Polym Sci2011; 36: 749–766.
24.
DemoriRBischoffEde AzeredoAP, et al. Morphological, thermo-mechanical, and thermal conductivity properties of halloysite nanotube-filled polypropylene nanocomposite foam. J Cell Plast2018; 54: 217–233.
25.
LeeJELeungSN.Multi-stage crystallization mechanism of electroactive phase polyvinylidene fluoride induced by thermal and supercritical carbon dioxide processing. Cryst Eng Comm2018; 20: 4080–4089.
26.
ZhaoBZhaoCWangC, et al. Poly (vinylidene fluoride) foams: a promising low-k dielectric and heat-insulating material. J Mater Chem C2018; 6: 3065–3073.
27.
DorigatoABianiABonaniW, et al. Thermo-electrical behaviour of cyclic olefin copolymer/exfoliated graphite nanoplatelets nanocomposites foamed through supercritical carbon dioxide. J Cell Plast2019; 55: 263–282.
28.
AroraKALesserAJMcCarthyTJ.Preparation and characterization of microcellular polystyrene foams processed in supercritical carbon dioxide. Macromolecules1998; 31: 4614–4620.
29.
NaguibHRizviRCochraneB, et al. Fabrication and characterization of melt-blended polylactide-chitin composites and their foams. J Cell Plast2011; 47: 283–300.
30.
JoCNaguibHE.Effect of nanoclay and foaming conditions on the mechanical properties of HDPE–clay nanocomposite foams. J Cell Plast2007; 43: 111–121.
31.
RichardsERizviRChowA, et al. Biodegradable composite foams of PLA and PHBV using subcritical CO2. J Polym Environ2008; 16: 258–266.
32.
SunY-CTerakitaDTsengAC, et al. Study on the thermoelectric properties of PVDF/MWCNT and PVDF/GNP composite foam. Smart Mater Struct2015; 24: 085034.
33.
NelsonJKFothergillJC.Internal charge behaviour of nanocomposites. Nanotech2004; 15: 586–595.
34.
RoyMNelsonJKMacCroneRK, et al. Polymer nanocomposite dielectrics-the role of the interface. IEEE Trans Dielect Electr Insul2005; 12: 629–643.
35.
KhodaparastPOunaiesZ.On the impact of functionalization and thermal treatment on dielectric behavior of low content TiO2 PVDF nanocomposites. IEEE Trans Dielect Electr Insul2013; 20: 166–176.
36.
MatuanaLMParkCBBalatineczJJ.Processing and cell morphology relationships for microcellular foamed PVC/wood‐fiber composites. Polym Eng Sci1997; 37: 1137–1147.
37.
ZhaiWYuJWuL, et al. Heterogeneous nucleation uniformizing cell size distribution in microcellular nanocomposites foams. Polymer2006; 47: 7580–7589.
38.
ShenJZengCLeeLJ.Synthesis of polystyrene–carbon nanofibers nanocomposite foams. Polymer2005; 46: 5218–5224.
39.
PapageorgiouGZAchiliasDSBikiarisDN, et al. Crystallization kinetics and nucleation activity of filler in polypropylene/surface-treated SiO2 nanocomposites. Thermochimica Acta2005; 427: 117–128.
40.
SeoM-KLeeJ-RParkS-J.Crystallization kinetics and interfacial behaviors of polypropylene composites reinforced with multi-walled carbon nanotubes. Mater Sci Eng: A2005; 404: 79–84.
41.
ZhaoBParkCB.Tunable electromagnetic shielding properties of conductive poly (vinylidene fluoride)/Ni chain composite films with negative permittivity. J Mater Chem C2017; 5: 6954–6961.
42.
HamidinejadMZhaoBChuRK, et al. Ultralight microcellular polymer–graphene nanoplatelet foams with enhanced dielectric performance. ACS Appl Mater Interfaces2018; 10: 19987–19998.
43.
ZhaoBZhaoCHamidinejadM, et al. Incorporating a microcellular structure into PVDF/graphene–nanoplatelet composites to tune their electrical conductivity and electromagnetic interference shielding properties. J Mater Chem C2018; 6: 10292–10300.
44.
TangC-WLiBSunL, et al. The effects of nanofillers, stretching and recrystallization on microstructure, phase transformation and dielectric properties in PVDF nanocomposites. Eur Polym J2012; 48: 1062–1072.
45.
HeFLauSChanHL, et al. High dielectric permittivity and low percolation threshold in nanocomposites based on poly (vinylidene fluoride) and exfoliated graphite nanoplates. Adv Mater2009; 21: 710–715.
46.
XuNHuLZhangQ, et al. Significantly enhanced dielectric performance of poly (vinylidene fluoride-co-hexafluoropylene)-based composites filled with hierarchical flower-like TiO2 particles. ACS Appl Mater Interfaces2015; 7: 27373–27381.
47.
FengYMiaoBGongH, et al. High dielectric and mechanical properties achieved in Cross-Linked PVDF/α-SiC nanocomposites with elevated compatibility and induced polarization at the interface. ACS Appl Mater Interfaces2016; 8: 19054–19065.
48.
ZhaoBHamidinejadMZhaoC, et al. A versatile foaming platform to fabricate polymer/carbon composites with high dielectric permittivity and ultra-low dielectric loss. J Mater Chem A2019; 7: 133–140.
49.
MartinsPLopesALanceros-MendezS.Electroactive phases of poly (vinylidene fluoride): determination, processing and applications. Progress in Polymer Science2014; 39: 683–706.
50.
ScheinbeimJNakafukuCNewmanB, et al. High‐pressure crystallization of poly (vinylidene fluoride). J Appl Phys1979; 50: 4399–4405.
51.
MatsushigeKNagataKTakemuraT.Direct observation of crystal transformation process of poly (vinylidene fluoride) under high pressure by PSPC X-ray system. Jpn J Appl Phys1978; 17: 467–472.
Supplementary Material
Please find the following supplemental material available below.
For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.
For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.
