ORCID Profile
0000-0003-2426-2235
Current Organisation
Singapore Institute of Food and Biotechnology Innovation (SIFBI)
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Publisher: Elsevier BV
Date: 02-2007
DOI: 10.1016/J.JCIS.2006.09.051
Abstract: Ultrathin films containing dendrimers are fabricated on amine- and anhydride-derivatized silicon dioxide surface through alternate layer-by-layer (LbL) assembly of pyromellitic dianhydride (PMDA) and poly(amidoamine) (PAMAM) dendrimer in supercritical carbon dioxide (SCCO2) with interlayer linkage established by covalent bonds. X-ray photoelectron and UV-visible absorption spectroscopies, atomic force microscopy (AFM), and ellipsometry were employed to study the interfacial chemistry, growth, morphology, and thickness of the assembled film. XPS analysis suggests that the PMDA/PAMAM interlayer covalent bond is established to completion, and functional surfaces for immobilization of the next layer are available after deposition of each layer. UV-visible absorption and ellipsometry revealed layer-by-layer growth of the film. The functional property film as a porous matrix was manifested in the reduction of the refractive index upon introduction of the dendrimer.
Publisher: American Chemical Society (ACS)
Date: 09-12-2006
DOI: 10.1021/IE060822Q
Publisher: Wiley
Date: 21-03-2016
Abstract: An ambipolar poly(diketopyrrolopyrrole-terthiophene)-based field-effect transistor (FET) sensitively detects xylene isomers at low ppm levels with multiple sensing features. Combined with pattern-recognition algorithms, a sole ambipolar FET sensor, rather than arrays of sensors, can discriminate highly similar xylene structural isomers from one another.
Publisher: Elsevier BV
Date: 07-2006
Publisher: American Chemical Society (ACS)
Date: 15-08-2023
Publisher: Elsevier BV
Date: 05-2009
DOI: 10.1016/J.JCIS.2008.10.084
Abstract: We report the formation of Pd, Pt and Pd/Pt nanoparticles in dendrimer-laden assemblies immobilized within a silica gel matrix and constructed by covalent layer-by-layer (LbL) assembly using supercritical carbon dioxide (SCCO(2)) as the processing medium. We show that the dendrimer plays a critical role in retaining the nanoparticle precursor within the silica gel. Smaller particle size, higher yield, a denser distribution of nanoparticles and greater stability were observed when the structures were assembled in SCCO(2).
Publisher: American Chemical Society (ACS)
Date: 07-2007
DOI: 10.1021/LA0635707
Abstract: The tribological properties of ultrathin films containing nanoparticles encapsulated in immobilized dendrimers are investigated. The films were formed by covalent molecular assembly in supercritical carbon dioxide, and the Au nanoparticles were formed in aqueous solution. End-capping of the terminal amine groups of the dendrimer by fluorinated species resulted in a reduction in the size of the nanoparticles formed. The resulting film structure displayed a lower coefficient of friction when the nanoparticles were formed after fluorination. The observed improvement in the tribological properties is attributed to the reduction in agglomeration of the nanoparticles due to the presence of the fluorine moieties.
Publisher: Elsevier BV
Date: 04-2009
DOI: 10.1016/J.JCIS.2009.01.011
Abstract: In this work we describe a general method for formation of Pt nanoparticles within an ultrathin film matrix and its application for non-volatile memory (NVM). Our approach involves the formation of Pt nanoparticles within ultrathin film matrix formed by covalent layer-by-layer (LbL) assembly of pyromellitic dianhydride (PMDA) and second generation of polyamidoamine (PAMAM) dendrimer in supercritical carbon dioxide (SCCO(2)). The hyperbranched component in the film structure serves to confine nanoparticle size and improve distribution. The memory effect and retention capability is demonstrated by means of a metal-insulator semiconductor (MIS) device fabricated using the nanoparticle-laden thin film as the insulating layer.
Publisher: Elsevier BV
Date: 04-2008
DOI: 10.1016/J.JCIS.2007.11.034
Abstract: We report the formation of Pd-Pt nanoparticles within a dendrimer-laden ultrathin film matrix immobilized on a solid support and constructed by covalent layer-by-layer (LbL) assembly using supercritical carbon dioxide (SCCO2) as the processing medium. Particle size distribution and composition were controlled by precursor composition. The precursor compositions are optimized for Pd-Pt nanoparticles and later extended to the formation of Fe-Ni nanoparticles. As an ex le of the application of nanoparticles in tribology, Fe-Ni nanoparticle-laden films were observed to exhibit better tribological properties than those containing the monometallic species, thereby suggesting that combination of nanoparticles can be used to derive greater benefits.
Publisher: Elsevier BV
Date: 06-2015
DOI: 10.1016/J.JCIS.2015.01.070
Abstract: Poly(sulfobetaine methacrylate) (PSBMA) films known for their resistance to nonspecific protein adsorption, cell/bacterial adhesion and biofilm formation were produced by surface initiated polymerization on a silicon surface via a batch reaction system in CO2 expanded liquid (CO2-EL) medium. Atom transfer radical polymerization (ATRP) was carried out using 2,2'-bipyridyl as ligand and CuBr as a catalyst in water/methanol mixture with trichloro[4-(chloromethyl)phenyl]silane (CMPS) used as the initiating species. The films were grown in the CO2-EL environment at a range of conditions and thickness up to 10nm. In contrast to films produced by conventional solvent systems at atmospheric pressure, the polymer films grown by the CO2-EL process showed uniform thickness and pin-hole free topography. Most importantly, the CO2-EL processed PSBMA films showed no trace of copper (used as the catalyst), thus obviating the need for post-deposition processing and avoiding adverse effects of the metal leaching during service. Finally, PSBMA films from both the conventional and CO2-EL processes were exposed to Human mesenchymal stem cells (hMSCs) and the results showed that, while in both the cases the cell proliferation rate was inhibited by the charged polymeric brush surface, the CO2-EL-processed brush exhibited inhibition to a larger extent due to the reduced occurrence of pinholes. The process can be easily exploited effectively when carrying out surface initiated polymerization on non-flat topographies, such as in trenches and nanostructured features with high aspect ratios.
Publisher: American Chemical Society (ACS)
Date: 19-07-2005
DOI: 10.1021/LA0509302
Abstract: An ultrathin film of oligoimide has been fabricated on amine-modified substrates of silicon and quartz through alternate layer-by-layer (LBL) assembly of pyromellitic dianhydride (PMDA) and diaminodiphenyl ether (DDE), with interlayer links established by covalent bonds. The assembly was formed in supercritical carbon dioxide (SCCO2) and in solution (dimethyl acetamide, DMAc), and the imidization reaction was performed by thermal and chemical methods, in benzene and in the supercritical medium. X-ray photoelectron and UV-visible absorption spectroscopies, atomic force microscopy (AFM), and ellipsometry were employed to study the interfacial chemistry, growth, morphology, and thickness of the assembled film. XPS analysis confirmed the sequential deposition of PMDA and DDE through formation of amic acids. At each deposition step, surface functionalities for the assembly of the next layer were generated. The interfacial chemical reaction was almost complete in the SCF (supercritical fluid) medium, as compared to the conversions observed in conventional assembly. Both the PMDA and DDE molecules were assembled in an organized manner, resulting in uniform surface morphology. Uniform film growth was revealed from the increase of UV absorption intensity and film thickness. The overall growth and quality of the films in SCF medium were greater than that for films formed in DMAc. The results of this novel study show that an environmentally friendly solvent can be used to obtain mechanically robust and thermally stable ultrathin films with little loss of material during the imidization step. In contrast to conventional deposition of the molecular layers that utilizes liquid solvents, use of SCCO(2) avoids solvent effects and posttreatment for solvent removal, while ensuring facile transport during contact.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3PY01142A
Publisher: American Chemical Society (ACS)
Date: 23-03-2006
DOI: 10.1021/LA052505E
Abstract: Layer-by-layer covalent assembly of an oligoimide on an anhydride- derivatized silicon dioxide surface is investigated using supercritical carbon dioxide (SCCO2) as the depositing medium. The deposited films were characterized by X-ray photoelectron spectroscopy (XPS), ellipsometry (VASE), UV-visible spectroscopy, electrochemical impedance spectroscopy, nano indentation, and atomic force microscopy (AFM) and the properties of the films compared with those of an oligoimide deposited on amine-derivatized surfaces. Films formed on the anhydride surface are more uniform and stable possibly because the silane precursor for the anhydride is anchored to the surface through two (-Si-O-Si-) tripods. XPS results indicate that the interfacial reaction resulting in amide formation is almost complete in the case of the anhydride, but not in the case of the amine. We infer that the twin tripods linking the anhydride group to the surface may have improved the accessibility of the functional groups for immobilization of the next layer, thereby contributing to the better quality.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2JM34394K
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3TC00562C
Publisher: American Chemical Society (ACS)
Date: 05-11-2013
DOI: 10.1021/AM4044085
Abstract: In this study, the nanomorphology of fluorenyl hexa-peri-hexabenzocoronene:[6,6]-phenyl C61-butyric acid methyl ester (FHBC:PC61BM) absorber layers of organic solar cells was investigated. Different electron microscopical techniques, atomic force microscopy, and grazing incidence wide-angle X-ray scattering were applied for a comprehensive nanomorphology analysis. The development of the nanomorphology upon s le annealing and the associated change of the device performance were investigated. It was shown that the annealing process enhances the phase separation and therefore the bulk heterojunction structure. Due to π-π stacking, the FHBC molecules assemble into columnar stacks, which are already present before annealing. While the nonannealed s le consists of a mixture of homogeneously distributed PC61BM molecules and FHBC stacks with a preferential in-plane stack orientation, crystalline FHBC precipitates occur in the annealed s les. These crystals, which consist of hexagonal arranged FHBC stacks, grow with increased annealing time. They are distributed homogeneously over the whole volume of the absorber layer as revealed by electron tomography. The FHBC stacks, whether in the two phase mixture or in the pure crystalline precipitates, exhibit an edge-on orientation, according to results from grazing incidence wide-angle X-ray scattering (GIWAXS), dark-field transmission electron microscopy (DF TEM) imaging and selective area electron diffraction (SAED). The best solar cell efficiencies were obtained after 20 or 40 s s le annealing. These annealing times induce an optimized degree of phase separation between donor and acceptor material.
Location: Singapore
No related grants have been discovered for SREENIVASA REDDY PUNIREDD.