Electromagnetic interference (EMI) shielding properties in the 1–18 GHz frequency range for multi-walled carbon nanotube (MWNT)–poly(vinylidene fluoride) (PVDF) composites are reported. A simple and gentle acid-treatment of MWNT showed a percolation threshold (PT) of 0.15 wt% in the PVDF matrix as against 0.35 wt% for unfunctionalized MWNT. Acid-treatment of MWNT significantly improves dispersion, interfacial adhesion with the matrix and the EMI shielding properties of PVDF composites. Further, the EMI shielding properties are correlated with the electrical properties. Using composite films of 0.3 mm thickness, the maximum shielding effectiveness (SE_T) values for 4 wt% unfunctionalized MWNT composites are found to be about 110, 45, 30, 26, and 58 dB for L (1–2 GHz), S (2–4 GHz), C (4–5.8 GHz), J (5.8–8 GHz), and X (8–12 GHz) bands, while the corresponding values for only 0.5 wt% acid functionalized MWNT composites are about 98, 45, 26, 19, and 47 dB, respectively. The electrical conductivity for both the cases is ∼10⁻³ S cm⁻¹ and the weight contents of CNTs are higher than the PT for the respective composites. The comparable EMI SE and electrical conductivity values for both the composites at different weight fractions of CNTs suggest that there is a critical electrical conductivity above which the composites attain improved EMI shielding properties. Further, the shielding mechanism was found to be dominated by absorption loss. Therefore, the composites may also serve as a radar absorbing material.

Structural arrangements of nanoplatelets in a polymer matrix play an important role in determining their properties. In the present study, multilayered composite films of poly(vinyl alcohol) (PVA) with Laponite clay are assembled by layer-by-layer (LBL) deposition. The LBL films are found to be hydrated, flexible and transparent. A facile and solvent-free method-by depositing self-assembled monolayers (SMA) of a functional silane on substrates-is demonstrated for preparing free-standing LBL films. Evolution of nanostructures in LBL films is correlated with thermal and mechanical properties. A well-dispersed solvent-cast PVA/Laponite composite film is also studied for comparison. We found that structurally ordered LBL films with an intercalated nanoclay system exhibits tensile strength, modulus and toughness, which are significantly higher than that of the conventional nanocomposites with well-dispersed clay particles and that of pure PVA. This indicates that clay platelets are oriented in the applied stress direction, leading to efficient interfacial stress transfer. In addition, various grades of composite LBL films are prepared by chemical crosslinking and their mechanical properties are assessed. On account of these excellent properties, the LBL films may find potential use as optical and structural elements, and as humidity sensors.

In this study, poly(ε-caprolactone) (PCL) has been blended with a more hydrophilic poly(ethylene glycol) (PEG) and with a biocompatible block-co-polymer: poly(L-lactide-co-ε-caprolactone-co-glycolide) (PLCG) in order to improve hydrophilicity, biocompatibility and biodegradability of PCL. PCL and the blend solutions were subjected to electrospinning to produce nanofiber scaffolds by the addition of only 1wt% of PEG and PLCG either singly or in combination in PCL to retain the mechanical properties of the scaffolds. PCL-PEG-PLCG ternary and two binary (PCL-PEG and PCL-PLCG) blend nanofiber scaffolds have been prepared for comparison. The resulting nanofibers showed a smooth and flaw-free surface and the diameter of the nanofibers displayed a normal distribution. The PCL-PEG nanofiber scaffold showed improved hydrophilicity [water contact angle (WCA) ∼84°] over pristine PCL (WCA ∼127°); while PCL-PLCG and PCL-PEG-PLCG scaffolds exhibited absolute wetting by water, likely due to high porosity. In vitro biocompatibility studies using gingival mesenchymal stem cells (gMSCs) suggested that, both the PCL and the blend scaffolds were biocompatible supporting cell-viability and growth of gMSCs following their seeding on these scaffolds. Biodegradation studies in phosphate buffer solution showed that the addition of PEG and PLCG in PCL increased the weight loss of scaffolds with time, indicating higher extent of biodegradation in the blend scaffolds and the weight loss followed the power law curve with time.