ABSTRACT
To meet the growing demand for rapid heat dissipation in electronic devices to ensure their reliable performance with a high level of safety, many polymer composites with thermally conductive but electrically insulating 2D boron nitride nanosheets (BNNSs) are being developed. Here we present an efficient way to enhance the thermal conductivity (TC) of a polymer composite by means of "grafting-from" polymerization of a poly(caprolactone) (PCL) onto BNNSs. The BNNSs, which were exfoliated from bulk BN by means of ultra-sonication, were prepared by means of radical oxidation. These oxidized BNNSs (oxi-BNNSs) were employed as initiators for subsequent ring-opening polymerization of PCL, which successfully resulted in PCL chemically grafted onto BNNSs (PCL-g-BNNSs). The excellent dispersion of PCL-g-BNNSs in common solvents allowed us to readily fabricate a polymer composite that contained PCL-g-BNNSs embedded in a PCL matrix, and the composite showed TC values that were five and nine times greater in the out-of-plane and in-plane mode, respectively, than those of pristine PCL.
ABSTRACT
We have developed multifunctional nanohybrids of poly(vinylidene fluoride-co-chlorotrifluoroethylene) (CTFE) with a small percentage of surface modified inorganic layered silicate showing dramatic improvement in toughness, radiation resistant and piezoelectric properties vis-à-vis pristine polymer. Massive intercalation (d(001) 1.8 â 3.9 nm) of polymer inside the nanoclay galleries and unique crystallization behavior of the fluoropolymer on the surface of individual silicate layer has been reported. Toughness in the nanohybrid increases more than three orders of magnitude as compared to pure CTFE. High energy radiation (80 MeV Si(+7)) causes chain session, amorphization and creates olefinic bonds in the pure polymer while the nanohybrids are radiation resistant at a similar dose. Nanoclay induces the metastable piezoelectric ß-phase in CTFE, suitable for sensor and actuator application. Molecular level changes after irradiation and controlled morphology for smart membrane have been confirmed by using spectroscopy, sol-gel technique, surface morphology studies and in situ residual gas analysis.
ABSTRACT
Ion flux dependent swift heavy ions (SHI) induced structural changes have been reported for pristine poly(vinylidene fluoride) (PVDF). Ordering phenomena has been observed first followed by its transformation from α to ß-form (polar metastable piezoelectric phase). The ordering of (020) plane become prominent at higher ion flux SHI irradiation and its further increase induces structural change from α to ß phase as revealed by XRD and FTIR analyses. Structural changes are also supported by morphological evidence and thermal studies before and after SHI irradiation.
ABSTRACT
Poly(vinylidene fluoride-co-hexafluoropropylene) (HFP) nanocomposites with layered silicate have been synthesized via the melt extrusion route. The intriguing nanostructure, crystalline structure, morphology, and thermal and mechanical properties of the nanocomposites have been studied and compared critically with pristine polymer. HFP forms intercalated or partially exfoliated nanostructure (or both) in the presence of nanoclay, depending on its concentration. The bombardment of high-energy swift, heavy ions (SHI) on HFP and its nanocomposites has been explored in a wide range of fluence. The nanoclay induces the piezoelectric beta-phase in bulk HFP, and the structure remains intact upon SHI irradiation. SHI irradiation degrades pure polymer, but the degradation is suppressed radically in nanocomposites. The heat of fusion of pristine HFP has drastically been reduced upon SHI irradiation, whereas there are relatively minute changes in nanocomposites. The coarsening on the surface and bulk of HFP and its nanocomposite films upon SHI irradiation has been measured quantitatively by using atomic force microscopy. The degradation has been considerably suppressed in nanocomposites through cross-linking of polymer chains, providing a suitable high-energy, radiation-resistant polymeric material. A mechanism for this behavior originating from the swelling test and gel fraction (chemical cross-linking) as a result of SHI irradiation has been illustrated.
Subject(s)
Ions/chemistry , Nanostructures/chemistry , Polyvinyls/chemistry , Silicates/chemistry , Crystallography, X-Ray , Fullerenes/chemistry , Models, Molecular , Particle Size , Polyvinyls/chemical synthesis , Surface PropertiesABSTRACT
Poly(vinylidene fluoride) (PVDF) has been made radiation-resistant through a nanocomposite (NC) route. The bombardment of high-energy swift heavy ions (SHI) on PVDF and its NCs with layered silicate has been studied in a range of fluences. The degradation of PVDF after SHI irradiation is suppressed radically in NCs. PVDF forms an intercalated nanostructure in the presence of nanoclay and, further, the ion fluence raises the extent of intercalation. The crystallinity and the heat of fusion of pristine PVDF have drastically been reduced after SHI irradiation, while there are relatively small changes in NCs even at higher fluences. The metastable piezoelectric beta form of PVDF gets stabilized by the presence of layered silicate, and the structure is retained upon SHI irradiation. The clay platelets act as nucleating agents, and SHI irradiation causes two crystallization temperatures for the samples exposed to high fluences. The damages created on the surface and bulk of PVDF and its NC films upon SHI irradiation have been measured quantitatively by using atomic force microscopy. The pitting dimensions and degradation are enhanced significantly beyond 10(11) ions/cm(2) fluence for pristine PVDF, which limits the use of PVDF for any ion irradiation application. The degradation is considerably suppressed in NCs, providing a suitable high-energy radiation-resistant thermoplastic polymer.
