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R Dhamodharan
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R Dhamodharan
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R Dhamodharan
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Dhamodharan, Raghavachari
Raghavachari, Dhamodharan
Dhamodharan, R.
Iyengar, Dhamodharan R.
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48 results
Now showing 1 - 10 of 48
- PublicationFacile, shear-induced, rapid formation of stable gels of chitosan through in situ generation of colloidal metal salts(01-01-2018)
;Ravishankar, Kartik ;Kanniyappan, Hemalatha ;Shelly, K. M.; A novel method of preparing chitosan gels using in situ generated negatively-charged colloidal salts of a variety of metal ions is described. Their potential as scaffolds for tissue-engineering and as recoverable catalysts in aza-Michael addition is demonstrated here. Given their wide range of properties, they have broad scope for applications. - PublicationControlled polymerization of carbazole-based vinyl and methacrylate monomers at ambient temperature: A comparative study through ATRP, SET, and SET-RAFT polymerizations(15-02-2011)
;Haridharan, NeelameganThe polymerization of N-vinylcarbazole (NVK) and carbazole methacrylate (CMA) was carried out using controlled radical polymerization methods such as atom transfer radical polymerization (ATRP), single electron transfer (SET)-LRP, and single electron transfer initiation followed by reversible addition fragmentation chain transfer (SET-RAFT). Well-controlled polymerization with narrow molecular weight distribution (Mw/Mn) < 1.25 was achieved in the case of NVK by high-temperature ATRP while ambient temperature SET-RAFT polymerization was relatively slow and controlled. In the case of CMA, SET-RAFT is found to be more suitable for the ambient temperature polymerization. The polymerization rate followed first order kinetics with respect to monomer conversion and the molecular weight of the polymer increased linearly with conversion. The controlled nature of the polymerization is further demonstrated by the synthesis of diblock copolymers from PNVK and PCMA macroinitiators using a new flavanone-based methacrylate (FMA) as the second monomer. All the polymers exhibited fluorescence. The excimer bands in the homopolymers of PNVK and PCMA were very broad, which may be attributed to the carbazole-carbazole overlap interaction. The scanning electron microscopy analysis of the block copolymer reveals interesting morphological features. © 2010 Wiley Periodicals, Inc. - PublicationEpoxidized natural rubber-magnetite nanocomposites for oil spill recovery(21-01-2013)
;Venkatanarasimhan, SwarnalathaNew, eco-friendly nanocomposite materials have been synthesized from natural rubber (NR) and magnetite nanoparticles for the first time. The poor oil resistance of natural rubber is exploited for the removal of oil spills. Towards this purpose, mildly epoxidized natural rubber (ENR)-magnetite nanoparticle (MN) nanocomposites are prepared and the absorption of petrol (gasoline) is studied. The extent of epoxidation is controlled in such a manner that the NR does not lose its elasticity while retaining to a significant degree its oil absorbing property. Epoxidation also serves as a means for binding sufficient quantity of MNs so that the composite can be recovered using a magnetic field. ENR with 5 mol% of epoxidation served as the best absorbent among all the absorbents studied as it was stable in petrol even after many days of immersion. It is observed that the ENR-MN nanocomposite absorbs 7 g of petrol per gram without any mass loss. The material was reused for several cycles without much loss in the capacity. The petrol uptake of ENR-MN is greater than that of butyl rubber which is the most commercially used rubber for oil spill removal. Porous rubber was also synthesized for the first time as oil uptake is facilitated not only by the hydrophobicity but also by the capillary absorption. Porous ENR absorbed a relatively larger amount of oil and exhibited the highest stability in oil. All the sorbents have quite high absorption capacities to be applied practically with a very low water uptake and a few of the absorbents could be satisfactorily reused. The model studies promise their potential use in the environmental field. © 2013 The Royal Society of Chemistry. - PublicationKinetic studies on star polymerization of styrene, MA and MMA using new three and four arm Chain Transfer Agents (CTAs): The role of R-Group structure present in the CTA on RAFT polymerization(01-09-2011)
;Kannan, MukundamurthyPolystyrene, poly(methylacrylate) and poly(methyl methacrylate) four and three-arm stars were synthesized by Reversible Addition Fragmentation chain-Transfer (RAFT) polymerization by using two new dithioester-derived chain transfer agents [CTA or R-S-(C = S)Z]), CTA-1 and CTA-2. CTA-1 is a four arm CTA while CTA-2 is a three-arm CTA. These were easily synthesized from commercially available reagents and were characterized by spectroscopic techniques such as 1H-NMR, 13C-NMR, IR and mass spectrometry. It is demonstrated that the two new CTAs enable the growth of arms away from the core (i.e., core first approach). An attempt has been made to study the effect of the structure of the R-group, which is present as the core in the CTA, on the polymerization, by analyzing the detailed kinetics. This study suggests that CTA-2, with a benzylic R group, enables the controlled star polymerization of styrene while CTA-1, with a R group similar in structure to the propagating radical derived from the polymerization of methyl acrylate (MA), enables the controlled polymerization of MA although to a lesser extent. This study also reveals that the temperature of free radical initiated RAFT (star) polymerization should be chosen in such a way that it is a compromise between reasonable rate of homolysis of the initiator and the CTA (R-group). © Taylor & Francis Group, LLC. - PublicationSynthesis of fluorescent, dansyl end-functionalized PMMA and poly(methyl methacrylate-b-phenanthren-1-yl-methacrylate) diblock copolymers, at ambient temperature(15-04-2012)
;Haridharan, Neelamegan ;Bhandary, Rajesh ;Ponnusamy, K.The polymerization of MMA, at ambient temperature, mediated by dansyl chloride is investigated using controlled radical polymerization methods. The solution ATRP results in reasonably controlled polymerization with PDI < 1.3. The SET-LRP polymerization is less controlled while SET-RAFT polymerization is controlled producing poly(methyl methacrylate) (PMMA) with the PDI < 1.3. In all the cases, the polymerization rate followed first order kinetics with respect to monomer conversion and the molecular weight of the polymer increased linearly with conversion. The R group in the CTAs do not appear to play a key role in controlling the propagation rate. SET-RAFT method appears to be a simpler tool to produce methacrylate polymers, under ambient conditions, in comparison with ATRP and SET-LRP. Fluorescent diblock copolymers, P(MMA-b-PhMA), were synthesized. These were highly fluorescent with two distinguishable emission signatures from the dansyl group and the phenanthren-1-yl methacrylate block. The fluorescence emission spectra reveal interesting features such as large red shift when compared to the small molecule. © 2012 Wiley Periodicals, Inc. - PublicationControlled polymerization of methacrylates at ambient temperature using trithiocarbonate chain transfer agents via SET-RAFT-cyclohexyl methacrylate: A model study(01-12-2010)
;Haridharan, N. ;Ponnusamy, K.Controlled radical polymerization of cyclohexyl methacrylate (CHMA), at ambient temperature, using various chain transfer agents (CTAs) is successfully demonstrated via single electron transfer-radical addition fragmentation chain transfer (SET-RAFT). Well-controlled polymerization with narrow molecular weight distribution (Mw/Mn) < 1.25 was achieved. The polymerization rate followed first-order kinetics with respect to monomer conversion, and the molecular weight of the polymer increased linearly up to high conversion. A novel, fluorescein-based initiator, a novel fluorescent CTA and two other CTAs comprising of butane thiol trithiocarbonate with cyano (CTA 1) and carboxylic acid (CTA 3) as the end group were synthesized and characterized. The polymerization is observed to be uncontrolled under SET and less controlled under atom transfer radical polymerization (ATRP) condition. CTA 2 and 3 produces better control in propagation compared with CTA 1, which may be attributed to the presence of R group that undergoes ready fragmentation to radicals, at ambient temperature. The poly(cyclohexyl methacrylate) [P(CHMA)] prepared through ATRP have higher fluorescence intensity compared with those from SET-RAFT, which may be attributed to the quenching of fluorescence by the trithiocarbonate and the long hydrocarbon chain. It is observed that block copolymers P(CHMA-b-t-BMA) produced from P(CHMA) macroinitiators synthesized via SET-RAFT result in lower polydispersity index in comparison with those synthesized via ATRP. © 2010 Wiley Periodicals, Inc. - PublicationSuper water-absorbing new material from chitosan, EDTA and urea(10-12-2015)
;Narayanan, AbathodharananA new, super water-absorbing, material is synthesized by the reaction between chitosan, EDTA and urea and named as CHEDUR. CHEDUR is probably formed through the crosslinking of chitosan molecules (CH) with the EDTA-urea (EDUR) adduct that is formed during the reaction. CHEDUR as well as the other products formed in control reactions are characterized extensively. CHEDUR exhibits a very high water uptake capacity when compared with chitosan, chitosan-EDTA adduct, as well as a commercial diaper material. A systematic study was done to find the optimum composition as well as reaction conditions for maximum water absorbing capacity. CHEDUR can play a vital role in applications that demand the rapid absorption and slow release of water such as agriculture, as a three in one new material for the slow release of urea, water and other metal ions that can be attached through the EDTA component. The other potential advantage of CHEDUR is that it can be expected to degrade in soil based on its chitosan backbone. The new material with rapid and high water uptake could also find potential applications as biodegradable active ingredient of the diaper material. - PublicationTetrakis(trialkylsilylethynylphenyl)ethenes: Mechanofluorochromism arising from steric considerations with an unusual crystal structure(01-01-2017)
;Ramachandran, ElumalaiMechanofluorochromism (MFC) arising from extended partial planarization of a conjugated molecular framework through the transfer of mechanical stress by terminal bulky groups is demonstrated. Thus the tetrakis(triisopropylsilyl-4-ethynylphenyl)ethene [TPE-(TIPS)4] luminophore, synthesized for the first time, is shown to exhibit MFC when the threshold pressure exceeds about 1.3 MPa. An analogous luminophore, tetra(trimethylsilyl-4-ethynylphenyl)ethene [TPE-(TMS)4], with smaller bulky groups at the periphery of TPE, synthesized for comparative studies, was also observed to exhibit MFC. MFC is observed under visible and UV light excitation. The color change is reversed upon annealing or under solvent fumigation conditions. The luminophores show high quantum yields in the solid state ranging from 60 to 74%. Very interestingly, TPE-(TMS)4 exhibited quite an unusual crystal structure, where no intermolecular interactions attributed to mechanofluorochromism are observed. The solid state optical absorption and CP-MAS 13C NMR measurements strongly suggested that the mechanism of MFC could have originated from partial planarization of the molecule upon grinding/shearing, facilitated by the bulky peripheral/terminal groups. These high solid state emitting luminophores with MFC properties could find applications in the areas of solid state lighting and sensors. The synthetic design, in principle, should enable MFC as a function of pressure (through variation in steric handle) and temperature (through electronic and conformational handles). The novel and rational synthetic design, in principle, should enable MFC in a family of organic molecules as a function of pressure and temperature. - PublicationBiocompatible Porous Scaffolds of Chitosan/Poly(EG- ran-PG) Blends with Tailored Pore Size and Nontoxic to Mesenchymal Stem Cells: Preparation by Controlled Evaporation from Aqueous Acetic Acid Solution(31-08-2018)
;Sadhasivam, Balaji ;Ravishankar, Kartik ;Desingh, Rajpreeth ;Subramaniyam, RajalakshmiThe preparation of porous films (average size variation from 1 to 32 μm) of a 1:1 blend of chitosan with poly(EG-ran-PG) by the controlled evaporation of water from a 2 wt % aqueous acetic acid solution is reported. Interestingly, the blend exhibited porosity that could be tailored from 1 to 32 μm with the temperature of preparation of the blend film. The powder X-ray diffraction, Fourier transform infrared, and differential scanning calorimetry analyses of the films suggested the formation of partially miscible blends. Temperature-induced phase separation of the blend appears to be the mechanism of pore formation. The tensile strength, cytotoxicity, and biocompatibility of the blend films for the growth of mesenchymal stem cells were assessed vis-a-vis chitosan. The 1:1 blend film was observed to lack cytotoxicity and was also viable for the growth of mesenchymal stem cells. The tensile properties of the 1:1 blend were superior to those of the chitosan film. The simple preparation of porous, nontoxic, and biocompatible films could find use as a scaffold in the growth of tissue, and especially bone tissue, in wound dressing, and in filtration if a better control over pore size is achieved. - PublicationFacile synthesis of triphenylamine and phenothiazine-based Schiff bases for aggregation-induced enhanced emission, white light generation, and highly selective and sensitive copper(ii) sensing(01-01-2018)
;Anand, Vivek ;Sadhasivam, BalajiTwo new Schiff bases, one triphenylamine-based (TPA-SB) and another phenothiazine-based (PTz-SB), were synthesized via facile reactions. Both molecules showed aggregation-induced enhanced emission (AIEE) properties. In fact, an 8-fold increase in the fluorescence intensity was observed for a 20 : 80 THF : water mixture of TPA-SB as compared to that in pure THF. The AIEE nature was further confirmed by dynamic light scattering (DLS) experiment and transmission electron microscopy (TEM) studies. These two moieties were mixed with rhodamine B (Rh-B) dye to obtain efficient white light emission (WLE) in solution and gelatin gel phase. Excellent Commission Internationale d'Eclairage (CIE) coordinates (0.32, 0.34) and (0.31, 0.34) were obtained in the solution and gelatin gel phase, respectively. The correlated color temperatures (CCT) obtained in the two phases (6115 K in solution and 6500 K in gelatin gel) suggest that the system emitted cool white light. The mechanism of WLE as verified through fluorescence titration, lifetime and spectral overlap studies, was found to arise due to Förster resonance energy transfer (FRET) among the three fluorophores. The optical band gaps obtained from UV-visible spectroscopy were 2.82 and 2.59 eV for TPA-SB and PTz-SB, respectively. The SEM and TEM studies revealed that in the aggregated state, TPA-SB exhibited a spherical morphology while PTz-SB showed nanopyramidal morphology. The new molecules were thermally robust as reflected by their TGA and DSC studies. Interestingly, TPA-SB showed remarkable fluorescence quenching response towards copper(ii) cations with a limit of detection (LOD) value of 1.8 ppb, while PTz-SB showed a LOD value of 4.8 ppb. The Schiff bases were particularly selective towards Cu(ii) ions without interference from ten other common cations. Hence, these easily synthesizable Schiff bases have multiple applicability, viz., in AIEE, WLE and Cu2+ sensing.