High aspect ratio, processable coordination polymer gel nanotubes based on an AIE-active LMWG with tunable emission

A new TPE based low molecular weight gelator (LMWG) which displays both AIE and MCIE phenomena in gel state has been synthesized. LMWG self-assembles to form 1D nanofibers which undergo morphology transformation to coordination polymer gel (CPG) nanotubes upon metal ion coordination. CPG shows enhanced mechanical stability along with tunable emission properties.

Ultra-small sulphur nanoparticles configured inside a flexible organic mixed conducting network as a cathode for lithium-sulphur batteries

The major challenges in Li-S batteries are the formation of soluble polysulphides during the reversible conversion of S-8 <-> Li2S, large changes in sulphur particle volume during lithiation and extremely poor charge transport in sulphur. We demonstrate here a novel and simple strategy to overcome these challenges towards practical realization of a stable high performance Li-S battery. For the first time, a strategy is developed which does away with the necessity of pre-fabricated high surface area hollow-structured adsorbates and also multiple nontrivial synthesis steps related to sulphur loading inside such adsorbates. A lithiated polyethylene glycol (PEG) based surfactant tethered on ultra-small sulphur nanoparticles and wrapped up with polyaniline (PAni) (abbreviated as S-MIEC) is demonstrated here as an exceptional cathode for Li-S batteries. The PEG and PAni network around the sulphur nanoparticles serves as an efficient flexible trap for sulphur and polysulphides and also provides distinct pathways for electrons (through PAni) and ions (through PEG) during battery operation. Contrary to the cathodes demonstrated based on various carbon-sulphur composites, the mixed conducting S-MIEC showed an extremely high loading of 75%. The S-MIEC exhibited a stable capacity of nearly 900 mA h g(-1) at the end of 100 cycles at a 1C current rate.

Attenuating microwave radiation by absorption through controlled nanoparticle localization in PC/PVDF blends

Nanoscale ordering in a polymer blend structure is indispensable to obtain materials with tailored properties. It was established here that controlling the arrangement of nanoparticles, with different characteristics, in co-continuous PC/PVDF (polycarbonate/poly(vinylidene fluoride)) blends can result in outstanding microwave absorption (ca. 90%). An excellent reflection loss (RL) of ca. -71 dB was obtained for a model blend structure wherein the conducting (multiwall carbon nanotubes, MWNTs) and the magnetic inclusions (Fe3O4) are localized in PVDF and the dielectric inclusion (barium titanate, BT) is in PC. The MWNTs were modified using polyaniline, which facilitates better charge transport in the blends. Furthermore, by introducing surface active groups on BT nanoparticles and changing the macroscopic processing conditions, the localization of BT nanoparticles can be tailored, otherwise BT nanoparticles would localize in the preferred phase (PVDF). In this study, we have shown that by ordered arrangement of nanoparticles, the incoming EM radiation can be attenuated. For instance, when PANI-MWNTs were localized in PVDF, the shielding was mainly through reflection. Now by localizing the conducting inclusion and the magnetic lossy materials in PVDF and the dielectric materials in PC, an outstanding shielding effectiveness of ca. -37 dB was achieved where shielding was mainly through absorption (ca. 90%). Thus, this study clearly demonstrates that lightweight microwave absorbers can be designed using polymer blends as a tool.

Interplay of Substrate Conductivity, Cellular Microenvironment, and Pulsatile Electrical Stimulation toward Osteogenesis of Human Mesenchymal Stem Cells in Vitro

The influences of physical stimuli such as surface elasticity, topography, and chemistry over mesenchymal stem cell proliferation and differentiation are well investigated. In this context, a fundamentally different approach was adopted, and we have demonstrated the interplay of inherent substrate conductivity, defined chemical composition of cellular microenvironment, and intermittent delivery of electric pulses to drive mesenchymal stem cell differentiation toward osteogenesis. For this, conducting polyaniline (PANI) substrates were coated with collagen type 1 (Coll) alone or in association with sulfated hyaluronan (sHya) to form artificial extracellular matrix (aECM), which mimics the native microenvironment of bone tissue. Further, bone marrow derived human mesenchymal stem cells (hMSCs) were cultured on these moderately conductive (10(-4)10(-3) S/cm) aECM coated PANI substrates and exposed intermittently to pulsed electric field (PEF) generated through transformer-like coupling (TLC) approach over 28 days. On the basis of critical analysis over an array of end points, it was inferred that Coll/sHya coated PANI (PANI/Coll/sHya) substrates had enhanced proliferative capacity of hMSCs up to 28 days in culture, even in the absence of PEF stimulation. On the contrary, the adopted PEF stimulation protocol (7 ms rectangular pulses, 3.6 mV/cm, 10 Hz) is shown to enhance osteogenic differentiation potential of hMSCs. Additionally, PEF stimulated hMSCs had also displayed different morphological characteristics as their nonstimulated counterparts. Concomitantly, earlier onset of ALP activity was also observed on PANI/Coll/sHya substrates and resulted in more calcium deposition. Moreover, real-time polymerase chain reaction results indicated higher mRNA levels of alkaline phosphatase and osteocalcin, whereas the expression of other osteogenic markers such as Runt-related transcription factor 2, Col1A, and osteopontin exhibited a dynamic pattern similar to control cells that are cultured in osteogenic medium. Taken together, our experimental results illustrate the interplay of multiple parameters such as substrate conductivity, electric field stimulation, and aECM coating on the modulation of hMSC proliferation and differentiation in vitro.

Electromagnetic Shielding Properties of Nano Carbon Filled Silicone Rubber Composites

Electromagnetic shielding has become important for various electrical systems because of the electromagnetic pollution caused by the large scale use of electronic devices operating at different frequencies and power levels. Traditionally used metallic shields lack flexibility and hence may not be the right choice for certain applications. In such situations, filled polymer composites provide a good alternative for electromagnetic shielding applications. Being polymer based, they are easy to manufacture and can be molded into the required geometry and shape. In this study, the shielding properties of multiwalled carbon nanotubes and carbon nanofibers filled silicone rubber are studied. The conductivity and the shielding effectiveness of the composites were measured at different filler loadings. Both the fillers are able to make the base polymer conducting even at very low filler loadings. The conductivity and the shielding effectiveness improved when the filler loading was above the percolation threshold.