Mechanical,Tribological, and Thermal Properties of Hot‐Pressed ZrB2‐B4C Composite

The effect of addition of submicrometer‐sized B₄C (5,10 and 15 wt%) on microstructure, phase composition, hardness, fracture toughness, scratch resistance, wear resistance, and thermal behavior of hot‐pressed ZrB₂‐B₄C composites is reported. ZrB₂‐B₄C (10 wt%) composite has V_H1 of 20.81 GPa and fracture toughness of 3.93 at 1 kgf, scratch resistance coefficient of 0.40, wear resistance coefficient of 0.01, and ware rate of 0.49 × 10^?3 mm³/Nm at 10N. Crack deflection by homogeneously dispersed submicrometer‐sized B₄C in ZrB₂ matrix can improve the mechanical and tribological properties. Thermal conductivity of ZrB₂‐B₄C composites varied from 70.13 to 45.30 W/m K between 100°C and 1000°C which is encouraging for making ultra‐high temperature ceramics (UHTC) component.     

Grafting of N,N′‐methylenebisacrylamide onto cellulose using Co(III)‐acetylacetonate complex in aqueous medium

The grafting of N,N′‐methylenebisacrylamide (N,N′‐MBA) onto cellulose is carried out using the cobaltacetylacetonate complex (Co(acac)₃) under nitrogen atmosphere at 40°C. The rate of graft copolymerization has been studied as a function of [N,N′‐MBA], [Co(acac)₃], and temperature. The activation energy of grafting is found to be 156.0 k J mol⁻¹ within the temperature range of 30–60°C. The effect of perchloric acid, methanol, and surfactants on graft yield has also been studied and results are suitably explained. The higher efficiency of the metal chelate in initiation of graft copolymerization has been assumed due to the coordination of the π electrons of the N,N′‐MBA with the metal chelate, which facilitated the formation of the radicals through homolytic cleavage of metal–oxygen bond of the cobalt acetylacetonate complex. On the basis of the results, a suitable kinetic scheme for graft copolymerization is presented and rate expression is derived. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 906–912, 2000     

Effects of Thermal and Cryogenic Conditionings on Flexural Behavior of Thermally Shocked Cu-Al2O3 Micro and NanoComposites

This investigation has used flexural test to explore the effects of thermal treatments, i.e., high-temperature and cryogenic environments on the mechanical property of Al₂O₃ particulate-reinforced Cu metal matrix micro and nanocomposites in ex-situ and in-situ conditions. Cu-5 vol. pct Al₂O₃ micro (10 μm)- and nanocomposites (<50 nm) fabricated by powder metallurgy route were subjected to up-thermal shock cycle [193 K to 353 K (?80 °C to 80 °C)] and down-thermal shock cycle [353 K to 193 K (from 80 °C to ?80 °C)] for different time periods followed by 3-point bend test. One batch of specimens (micro and nanocomposites) was conditioned at 353 K and 193 K (80 °C and ?80 °C) separately followed by 3-point flexural test. High-temperature flexural test was performed at 373 K and 523 K (80 °C and 250 °C) on the micro and nanocomposites. All the fractured samples obtained after various thermal treatments were studied under scanning electron microscope (SEM). The development of thermal stresses quite often results in concentration of residual stresses at the particle/matrix interface eventually weakening it. Enhancement of flexural strength was recorded for down- as well as for up-thermal shock in microcomposites. The high-temperature flexural strengths of micro and nanocomposites are lower than those at ambient temperature. The amelioration and declination in mechanical properties as a consequence of thermal shock, thermal conditioning, and high-temperature flexural testing have been discussed in the light of fractography.     

Molecular Origin of Strain-Induced Chain Alignment in PDPP-Based Semiconducting Polymeric Thin Films

Donor–acceptor (D–A) type semiconducting polymers have shown great potential for the application of deformable and stretchable electronics in recent decades. However, due to their heterogeneous structure with rigid backbones and long solubilizing side chains, the fundamental understanding of their molecular picture upon mechanical deformation still lacks investigation. Here, the molecular orientation of diketopyrrolopyrrole (DPP)-based D–A polymer thin films is probed under tensile deformation via both experimental measurements and molecular modeling. The detailed morphological analysis demonstrates highly aligned polymer crystallites upon deformation, while the degree of backbone alignment is limited within the crystalline domain. Besides, the aromatic ring on polymer backbones rotates parallel to the strain direction despite the relatively low overall chain anisotropy. The effect of side-chain length on the DPP chain alignment is observed to be less noticeable. These observations are distinct from traditional linear-chain semicrystalline polymers like polyethylene due to distinct characteristics of backbone/side-chain combination and the crystallographic characteristics in DPP polymers. Furthermore, a stable and isotropic charge carrier mobility is obtained from fabricated organic field-effect transistors. This study deconvolutes the alignment of different components within the thin-film microstructure and highlights that crystallite rotation and chain slippage are the primary deformation mechanisms for semiconducting polymers.     

An In-depth Analysis of the Mechanical,Electrical, and Drug Release Properties of Gelatin–Starch Phase-Separated Hydrogels

Gelatin–starch-based phase-separated hydrogels were prepared in this study. Corn starch, soluble starch, and hydrated starch were used as the representative starches for the preparation of the hydrogels. Bright field microscopy suggested the formation of phase-separated hydrogels. An increase in the hydrophilic nature of the starch molecules resulted in decrease in the agglomeration of the starch particles within the gelatin matrices. Fourier transform infrared study confirmed the presence of starch particles within the hydrogels. X-ray diffraction studies suggested that the higher degree of crystallinity of corn starch and soluble starch was responsible for the comparative hydrophobic nature of these starch particles. Hydrated starch was found to be amorphous in nature and can be explained by the destruction of the intramolecular associative forces. Stress relaxation and creep recovery studies indicated predominant elastic nature of the hydrogels. Hydrated starch-containing hydrogels were firmer than corn starch and soluble starch because of the better miscibility of the hydrated starch particles within the gelatin matrices. The bulk resistance of the starch-containing hydrogels was higher. This was because of the capability of the starch particles to behave as dielectric medium. Incorporation of starch particles within the gelatin matrix was found to increase the polymer relaxation-mediated drug diffusion. Metronidazole-loaded hydrogels were found to have good antimicrobial activity.     

Ion‐conductivity study and anomalous diffusion analysis of plasticized gelatin films

In this article, we report a study on ion conduction in gelatin films with different concentrations of glycerol as a plasticizer; these films might be a candidate for electrolyte materials in solid polymer batteries. The ion conductivity was appreciable, showing a maximum of about 9.14 × 10^?3 S/m at room temperature without the addition of any ionic salt. Analysis of the impedance measurements was done with a model based on material properties instead of the usual equivalent circuit formalism, where circuit elements are difficult to interpret. Generalized calculus was used to model the anomalous diffusion in the system. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3018–3024, 2013     

PLA-TiO2 nanocomposites: Thermal,morphological, structural,and humidity sensing properties

In this paper, the effect of TiO₂ ceramic nanoparticles on the thermal stability, morphology, molecular mass, structure and electrical properties of the polylactic acid-Titanium dioxide (PLA-TiO₂) composites, aimed for relative humidity (RH) sensing have been reported. PLA-TiO₂ nanocomposites films were developed through a spin coating process. The developed films were characterized by X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and electrochemical impedance spectroscopy analysis (EIS). To investigate the RH-dependent characteristics, the devices were prepared on pre-patterned ITO substrates. The capacitive and resistive response of the nanocomposite films were studied under RH levels ranging from 20–90%. The PLA-TiO₂ nano-sensing films, having modified surface by acetone etching, exhibited superior morphological and electrical performance when compared to PLA-TiO₂ pristine samples.