K.S. Santhosh Kumar
Vikram Sarabhai Space Centre
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Featured researches published by K.S. Santhosh Kumar.
Journal of Materials Chemistry | 2015
S. Ramakrishna; K.S. Santhosh Kumar; Dona Mathew; C. P. Reghunadhan Nair
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.
Journal of Materials Chemistry | 2015
M. Ragin Ramdas; K.S. Santhosh Kumar; C. P. Reghunadhan Nair
Thermally induced shape memory polymers (SMPs) are capable of storage, release of energy and shape recovery on the macro-scale. In this work, cross-linked SMPs were synthesized from the monomers tris(4-(1-azido 3-oxy propan-2-ol)phenyl) methane (A3), and 1,4-bis(propargyloxy) benzene (B2), and the propargyl functionalized novolac oligomer (B3). The A3B2 polymer exhibited a low trigger temperature of 92 °C, whereas A3B3 registered a higher trigger temperature of 125° C. The extent of shape recovery of both the SMPs was above 95% and it was repeatable for at least 10 times. On repeating the shape memory cycles, the response time for shape recovery increased, but nearly a complete shape recovery was observed in both polymers. In addition, a polymer with dual trigger temperature (83 and 113 °C) was synthesized by click polymerization between the A3 monomer and stoichiometric equivalence of B2 and B3 monomers. The polytriazole networks bearing monophenyl and oligomer structures in tandem enabled both low and high trigger temperature in a single polymeric structure. The SMP possesses a shape recovery to an extent as high as 98% at both the trigger points even on the 10th shape memory cycle. These polymers exhibited hydrophobicity with a static water contact angle of about 90° and very low water absorption ( 230 °C) and are suitable for actuator applications.
RSC Advances | 2014
K.S. Santhosh Kumar; C. P. Reghunadhan Nair
Shape memory cyclomatrix network polymers comprising oxazolidone and triazine groups linked by a shape memory segment of polycaprolactone are synthesised by co-reacting a cyanate ester with an epoxy monomer in the presence of a polycaprolactone diol (PCLD). These systems possess transition temperatures (Ttrans) between 127 and 180 °C and are tunable by the PCLD concentration. The cross-linked polymers exhibit 100% shape fixity and near complete shape recovery in a short span of time. The high Ttrans and low propensity for moisture absorption provide a stable fixed shape. Water repellency is reflected in the contact angles of 82–86°, which are higher than that for typical epoxy systems.
Journal of Materials Chemistry | 2014
K.S. Santhosh Kumar; Vijendra Kumar; C. P. Reghunadhan Nair
A promising method for constructing ‘bulk’ level superhydrophobicity on CaCO3 microparticles has been developed by employing silane and urethane chemistries in sequence. Silanol-terminated short-chain polydimethyl siloxane (PDMS) segments were grafted onto a CaCO3 surface. The particles were characterised by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and GPC analyses. By the reaction of silanol groups on the surface of CaCO3 particles with isocyanate functionalities, the crosslinking of particles was accomplished. The resultant coating exhibited a water contact angle >150° with a sliding angle approximately 5–8° on the entire material. The bulk level SH behaviour is attributed to both inter- and intraparticle hydrogen bonding, which was substantiated by FTIR. The rod-shaped morphology of the bulk material was evidenced in SEM images and resulted due to the encasing of well-connected microparticles by PDMS chains.
RSC Advances | 2016
M. Ragin Ramdas; K.S. Santhosh Kumar; C. P. Reghunadhan Nair
Shape memory polytriazole actuatable by both heat and solvents is presented. Hydrogen bonding solvents exhibit strong influence on shape recovery. In this work, a dual-stimuli responsive (both temperature and solvents) polymer is synthesized from propargylated bisphenol-F (PF) and a tris azide (TA) monomer via an azide–alkyne polycycloaddition reaction in the presence of a copper catalyst. The polytriazole exhibits a trigger temperature at 103 °C and displays cyclic shape memory properties. The SMP shows a storage modulus >2 GPa with a cross-link density of 6.9 × 103 mol m−3. The SMP possesses shape memory features in different solvents. Highly polar solvents lead to shape recovery with cracks whereas hydrogen bonding solvents like ethanol supported crack-free shape recovery. A two-step kinetic profile is seen in the shape recovery sequence of SMP in hydrogen bonding solvents. The SMP is hydrophobic and no recovery in water is observed.
Journal of Materials Chemistry | 2017
S. Ramakrishna; Dona Mathew; K.S. Santhosh Kumar
Superhydrophobic (SH) particles and coatings with high mechanical resistance get widespread attention due to their versatile performance in applications such as self-cleaning, moisture protection and so on. In this work, superhydrophobic particles with excellent repellency to highly viscous and low surface tension liquids are synthesized via a two-step method. The grafting of soft and elastomeric polydimethyl siloxane segments onto silica surfaces confers the capacity for the absorption/distribution of mechanical impacts to SH particles. Thus, these particles can withstand high mechanical impact (∼8000 kg cm−2) and maintain a water contact angle (WCA) of around 150°. When SH particle incorporated PVDF-co-HFP is coated on substrates, the coating exhibits water roll-off properties with a sliding angle of 160°. This coating is tolerant to water hammer pressures of 1.33 MPa and sand impingement energies of 3.6 × 10−7 J per grain, and the coating restores SH properties under ambient conditions after these tests. Additionally, the surfaces damaged by impalement/impingement undergo self-reconstruction to hold their super-repellent nature. A fibrous and porous structure morphology is evident in field emission scanning electron microscope images which is attributed to the heat treatment and subsequent solvent evaporation process. Moreover, the coating displays super-repellency to different liquids and shows good adhesion on various substrates such as aluminium, polyimide, chloroprene rubber and stainless steel.
Handbook of Thermoset Plastics (Third Edition) | 2014
K.S. Santhosh Kumar; C. P. Reghunadhan Nair
Polybenzoxazines (PBz) belong to the family of new generation phenolic resins. They have emerged as addition-curable polymers. This feature obviates many of the shortcomings associated with conventional phenolic resins. They are endowed with excellent thermal, physical, and thermo-physical properties, and surpass the features of many conventional and state-of-the-art polymers. These unique materials offer extraordinary characteristics: near zero shrinkage, no release of volatiles during cure, high Tg, low flammability, and high UV and chemical stabilities. Given the breadth of molecular design flexibility, a wide variety of polybenzoxazines can be developed. PBz equipped with additional curing groups can generally enhance the overall thermal and mechanical properties. Blends with epoxy resins, cyanate esters, and bismaleimides offer other opportunities for fine-tuning properties. This chapter gives an account of the developments of PBz materials from their inception to the current level of application in engineering areas.
Journal of Materials Chemistry | 2017
S. Anitha; K. P. Vijayalakshmi; G. Unnikrishnan; K.S. Santhosh Kumar
A green and supramolecular approach is demonstrated to enhance the transparency/toughness/adhesive strength of epoxy cross-linked networks. A monocyclic carbonate (MCC) was synthesized by a reaction between CO2 and an epoxy monomer under moderate pressure. By incorporating the one-end reactive MCC into an epoxy network (composed of triamino oligoetheramine and digylcidyl ether bisphenol A), elongation up to 67% was achieved. The epoxy network containing 10 wt% MCC displayed >100% increase in toughness vis-a-vis the pristine network. In addition, two segmental motions were exhibited by the toughened networks, where the lower Tg orients at 55–60 °C and the higher Tg at 73–93 °C. The second Tg is attributed to additional hydrogen bonded regions of the epoxy network (because of the hydrogen bonding spacer unit) as recognized by FTIR studies. Furthermore, studies using density functional theory (DFT) substantiated the existence of two different regions that are responsible for the two Tgs (the second Tg is induced by MCC units via additional hydrogen bonding). The FESEM and AFM investigations further established that no phase separation is present in the networks. The adhesive strengths (LSS) of the epoxy networks increased from ∼17 to 22 MPa due to H-bonding interactions. The networks can perform as self-standing films due to their flexible nature. The networks are transparent (visible transparency increased to >80% by addition of MCC from 68% of the neat epoxy network) and are thermally stable (T10% > 250 °C).
Reactive & Functional Polymers | 2013
K.S. Santhosh Kumar; R. Biju; C. P. Reghunadhan Nair
European Polymer Journal | 2007
K.S. Santhosh Kumar; C. P. Reghunadhan Nair; T.S. Radhakrishnan; K. N. Ninan