Vikram Sarabhai Space Centre

About: Vikram Sarabhai Space Centre is a facility organization based out in Thiruvananthapuram, India. It is known for research contribution in the topics: Aerosol & Ultimate tensile strength. The organization has 2092 authors who have published 3058 publications receiving 47975 citations. The organization is also known as: VSSC.

High transition temperature shape memory polymers (SMPs) by telechelic oligomer approach

Abstract: This work describes the synthesis and comparative shape memory properties of cross-linked networks derived from epoxy and cyanate ester monomers containing polyether oligomers as reactive shape memory segments. The hydroxy telechelic oligomers viz. polyethyleneglycol (PEG), polypropyleneglycol (PPG), and polytetramethyleneglycol (PTG) are reacted with epoxy–cyanate ester matrix resulting in shape memory polymers with high transition temperatures. The soft oligomer segments act as flexible linker unit which interconnect oxazolidone, isocyanurate and triazine ring structures in the cross-linked polymer. The resultant cyclomatrix SMPs exhibit high transition temperatures 132, 178 and 161 °C respectively for PEG, PPG and PTG integrated SMPs. The Eg/Er ratios are increased in the order PEG 98% with recovery time <100 s. All the SMPs display good thermal stabilities (both inert and oxidative) above 275 °C.

Long-living, stress- and pH-tolerant superhydrophobic silica particles via fast and efficient urethane chemistry; facile preparation of self-recoverable SH coatings

Abstract: Superhydrophobic (SH) and water-rolling oligomer wrapped silica particles (OWS) were synthesized using a one-step method by employing the quick and efficient silanol–isocyanate surface reaction. The presence of urethane/allophanate linkages and oligomer formation over the silica surface was confirmed using FTIR and MALDI-TOF-MS analyses. The thin coating of the particles displayed a static contact angle of >160°, a roll-off angle of ∼3° and exhibited a micro-nano structure as shown in the FESEM images. The OWS particles are tolerant to variations in pH either side of the pH scale, from 1 to 13, exhibiting water roll-off properties when exposed to harsh acidic and basic conditions. The pH tolerance was observed after mechanical damage. The rapidity and efficiency of the method was demonstrated with a low extent of grafting also. The superhydrophobic particles are long-living as they retained SH properties in different pH conditions even after one year of continuous exposure to ambient conditions. Furthermore, the SH particles with an incorporated cross-linked poly(dimethylsiloxane) coating displayed excellent pH and stress resistance. Surprisingly, the SH coating exhibits self-recoverable superhydrophobicity without an external stimulus (under ambient conditions) or heat treatment after water impalement, pH, boiling water and stress tests.

Diglycidyl ether of bisphenol-A epoxy resin–polyether sulfone/polyether sulfone ether ketone blends: phase morphology, fracture toughness and thermo-mechanical properties

Abstract: The properties of diglycidyl ether of bisphenol-A epoxy resin toughened with poly(ether sulfone ether ketone) (PESEK) and poly(ether sulfone) (PES) polymers were investigated. PESEK was synthesised by the nucleophilic substitution reaction of 4,4’-difluorobenzophenone with dihydroxydiphenylsulfone using sulfolane as solvent and potassium carbonate as catalyst at 230 °C. The T g–composition behaviour of the homogeneous epoxy resin/PESEK blend was modelled using Fox, Gordon–Taylor and Kelley–Bueche equations. A single relaxation near the glass transition of epoxy resin was observed in all the blend systems. From dynamic mechanical analysis, the crosslink density of the blends was found to decrease with increase in the thermoplastic concentration. The storage modulus of the epoxy/PESEK blends was lower than that of neat resin, whilst it is higher for epoxy/PES blends up to glass transition temperature, thereafter it decreases. Scanning electron microscopic studies of the blends revealed a homogeneous morphology. The homogeneity of the blends was attributed to the similarity in chemical structure of the modifier and the cured epoxy network and due to the H-bonding interactions between the blend components. The fracture toughness of epoxy resin increased on blending with PESEK and PES. The increase in fracture toughness was due to the increase in ductility of the matrix. The thermal stability of the blends was comparable to that of neat epoxy resin.