Dr. Niranjan Patra | Imperial College London (original) (raw)

Papers by Dr. Niranjan Patra

Atomic force microscopy in vitro study of surface roughness and fractal character of a dental res... more Atomic force microscopy in vitro study of surface roughness and fractal character of a dental restoration composite after air-polishing

ACS Applied Nano Materials, 2018

Nano-sized powder composites of hafnium carbide/silicon carbide (HfC-SiC) were successfully prepa... more Nano-sized powder composites of hafnium carbide/silicon carbide (HfC-SiC) were successfully prepared by crosslinking and carbothermic reduction of a precursor. A novel high yield liquid precursor was synthesized by reacting acetylacetone (acac) modified hafnium tetrachloride (HfCl 4) with tetraethyl orthosilicate (TEOS) and hydroquinone (HQ). The synthesized materials were investigated by XRD, FT-IR, carbon analyzer, Raman, TG/DTA, SEM, TEM and EDS analysis. The resulting precursor pyrolysed at 1500 o C for 3 h in argon converted into nanostructured ultrahigh temperature composite powder (containing both HfC and SiC) with a trace of free carbon. The polymer-to-ceramic transformation was investigated by TG/DTA revealing that carbothermic reduction of HfC and SiC started at 1225 and 1450 o C respectively with a total yield of 64 % at 1500 o C. XRD revealed the powder composite was composed of HfC and β-SiC with a negligible amount of oxide impurities. SEM and TEM images reveals the Hf, Si and C were homogeneously distributed in the sample at submicron scale with an average grain size of less than 50 nm for both HfC and SiC. The result obtained by this synthesis approach is believed to be a promising candidate for hypersonic applications.

Journal of the European Ceramic Society, 2018

Ultra-high temperature ceramic infiltrated carbon-fibre composites were prepared by precursor inf... more Ultra-high temperature ceramic infiltrated carbon-fibre composites were prepared by precursor infiltration and pyrolysis (PIP) using a laboratory synthesized precursor. Microstructures and thermal properties including thermal expansion, thermal diffusivity, specific heat capacity and oxidative stability are correlated. XRD reveals the presence of C f-HfC and C f-HfC-SiC phases without formation of oxides. The CTE observed at 1200°C is slightly higher for C f-HfC (3.36 × 10 −6 K −1) compared to C f-HfC-SiC (2.95 × 10 −6 K −1) composites. Lower thermal diffusivity of the C f-HfC-SiC compared to C f-HfC composites is attributed to a thermal barrier effect and cracks in the composites which formed due to the CTE mismatch between carbon fibre and the matrix as well as CO generated during graphitization. The thermal conductivity of C f-HfC (4.18 ± 0.14 Wm −1 K −1) is higher than that of C f-HfC-SiC composite (3.33 ± 0.42 Wm −1 K −1). Composites microstructures were coarse with some protruding particles (5 μm) with a homogeneous dense (∼70%) matrix (HfC and HfC-SiC) for both composites.

Electrospun Nanofibers, 2017

Abstract A composite based on pectin and polyvinyl alcohol (PVA) was successfully electrospun int... more Abstract A composite based on pectin and polyvinyl alcohol (PVA) was successfully electrospun into nanofibers. This chapter demonstrates that pectin plays a major role in the structure–properties relationship of the composite nanofibers, even at a very small amount of 2 wt% pectin to PVA. Pectin caused an apparent increase in crystallinity, which can be further improved by post-spinning treatments of the nanofibers. Scanning electron microscope confirmed that the composite nanofibers are uniform and free of microbeads, and have a smaller diameter, which is probably due to the increase in crystallinity and the stretching caused by the higher charge density. These results suggest that the crystallinity of the PVA nanofibers can be modified by adding a small amount of pectin. PVA that is able to form nucleation and crystallization with pectin could serve to develop biodegradable and biocompatible, low-cost composite nanofibers for applications in biomedicine and material science.

Journal of the European Ceramic Society, 2016

Oxidation of silicon melt infiltrated SiC/SiC ceramic matrix composites (CMC) was studied in air ... more Oxidation of silicon melt infiltrated SiC/SiC ceramic matrix composites (CMC) was studied in air at 1200-1400 • C for 1, 5, 24 and 48 h. Weight gain and oxide layer thickness measurements revealed the oxidation follows parabolic reaction kinetics with increase in temperature and time. XRD showed the extent of oxide layer (SiO 2) formation was greatest after 48 h at 1400 • C: an observation confirmed by X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM) analyses. Oxide layer thickness varied from 1 m after 48 h at 1200 • C to 8 m after 48 h at 1400 • C. Oxidation of SiC/SiC composites is both temperature and time dependent with an activation energy of 619 kJ mol −1. BN coatings around SiC fibres showed good resistance to oxidation even after 48 h at 1400 • C.

Ceramics International, 2016

Nano-sized hafnium carbide was synthesized from organicinorganic hybrid polymer based on polycond... more Nano-sized hafnium carbide was synthesized from organicinorganic hybrid polymer based on polycondensation and carbothermal reduction reaction from pectin and hafnium tetrachloride followed by thermal treatment. Orthorhombic and monoclinic hafnia formed on pyrolysis which above 1300 oC transformed to hafnium carbide. Conversion of amorphous to crystalline hafnia was initiated at ~800 oC while the endothermic carbothermal reduction reaction started at ~1275 oC. Total yield of hafnium carbide was ~62%. The resulting carbide powders are equiaxed with narrow size distribution of crystallite size ~50 nm. SEM and EDX mapping confirm the uniform distribution of Hf and C. The high ceramic yield, uniform size particles, and simplicity of the process make it a promising route for polymer infiltration pyrolysis of carbon fibre/ultra high temperature composites.

Progress in Organic Coatings, 2015

The purpose of this study was to evaluate the 3-D surface micromorphology of polymer-oxide thin f... more The purpose of this study was to evaluate the 3-D surface micromorphology of polymer-oxide thin films spin-coated from a composite of poly-methyl-methacrylate as the matrix and elongated titania nanorods as the filler particles. The surfaces of these composite films were investigated by atomic force microscopy and characterized by fractal geometry analysis. The effect of increasing loading of the fillers between 0 and 30% by weigth relative to the matrix was assessed. An increasing roughness was observed, with typical emergence of protruding ripples progressively extending into larger stripes. The amplitude parameters of the surfaces were determined by analysis of the height distributions. The fractal analysis of roughness revealed that the films have fractal geometry. Triangulation method based on the linear interpolation type was applied to determine the fractal dimension. A connection was observed between the surface morphology and the physical properties of the coatings as assessed in previous works.

Science of Advanced Materials, 2012

Abstract: We have investigated the effect of polishing with two different systems, namely Venus S... more Abstract: We have investigated the effect of polishing with two different systems, namely Venus Supra and Enhance, on the properties of a resin composite currently in use for dental restorations, namely Venus Diamond. On both the non-polished and polished specimens, first the material surfaces have been imaged by scanning electron microscopy and atomic force microscopy, and quantitative information on the surface roughness has been extracted. Then the elastic properties of the composite have been measured in compression by ...

Journal of Thermal Analysis and Calorimetry, 2014

ABSTRACT Present research deals with the conversion of waste commodity plastics to valuable comme... more ABSTRACT Present research deals with the conversion of waste commodity plastics to valuable commercial product in the form of wax by pyrolysis. Optimization of both processes yield and produced wax quality was performed by means of a statistical tool originally proposed by G. Taguchi, using temperature, catalyst, carrier gas, and dwell time as the parameters. The obtained wax was characterized by Raman spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Yield of wax was found to be maximum when the parameters were 600�C, Fe catalyst, nitrogen gas atmosphere, and 15 min time. However, stability of the wax was found to be optimum at 700�C. Calorific value of the wax thus obtained was*43 MJ kg -1 , which supports its suitability as fuels like other petroleum products.

Journal of Colloid and Interface Science, 2013

IEEE Transactions on NanoBioscience, 2013

The purpose of this work was to investigate the porous polyetherimide scaffold (P-PEIs) as an alt... more The purpose of this work was to investigate the porous polyetherimide scaffold (P-PEIs) as an alternative biopolymer for bone tissue engineering. The P-PEIs was fabricated via solvent casting and particulate leaching technique. The morphology, phase composition, roughness, hydrophilicity, and biocompatibility of P-PEIs were evaluated and compared with polyetherimide (PEI) and Ti6Al4V disks. P-PEIs showed a biomimetic porous structure with a modulus of 78.95 ± 2.30 MPa. The water contact angle of P-PEIs was 75.4 ± 3.39 ∘ , which suggested that P-PEIs had a wettability surface. Moreover, P-PEIs provides a feasible environment for cell adhesion and proliferation. The relative cell adhesion capability and the cell morphology on P-PEIs were better than PEI and Ti6Al4V samples. Furthermore, the MC3T3-E1 cells on P-PEIs showed faster proliferation rate than other groups. It was revealed that the P-PEIs could be a potential material for the application of bone regeneration.

Dental Materials Journal, 2012

A photo-polymerizable Bisphenol-A diglycidylether methacrylate resin was characterized by Fourier... more A photo-polymerizable Bisphenol-A diglycidylether methacrylate resin was characterized by Fourier transform infrared spectroscopy after its irradiation under different conditions to identify the best curing. Bonding-agent free composites with particles of ball-milled glass, silica and titania at loading of 10 and 50%wt were prepared, and their viscoelastic properties investigated by dynamic mechanical analysis, in experimental conditions close to the working environment in the mouth. All composites showed good stability at the considered conditions. The stiffest composite was the silica one, which was based on the smallest primary particles. The storage moduli close to room temperature (25°C) and mastication frequency (1 Hz) were extracted as reference bending moduli for the materials, and compared to static compressive moduli measured by nanoindentation performed by atomic force microscopy. Nanoindentation showed qualitative results in agreement with dynamic mechanical analysis as to the ranking of different materials, while resulting in approximately twofold elastic modulus.

Analytical Chemistry, 2003

The development of surface-enhanced Raman scattering (SERS)-active substrates for cancer gene det... more The development of surface-enhanced Raman scattering (SERS)-active substrates for cancer gene detection is described. The detection method uses Raman active dye-labeled DNA gene probes, self-assembled monolayers, and nanostructured metallic substrates as SERS-active platforms. The mercaptohexane-labeled single-stranded DNA (SH-(CH(2))(6)-ssDNA)/6-mercapto-1-hexanol system formed on a silver surface is characterized by atomic force microscopy. The surface-enhanced Raman gene (SERGen) probes developed in this study can be used to detect DNA targets via hybridization to complementary DNA probes. The probes do not require the use of radioactive labels and have a great potential to provide both sensitivity and selectivity. The effectiveness of this approach and its application in cancer gene diagnostics (BRCA1 breast cancer gene) are investigated.

Journal of Nanomaterials, 2016

Journal of Thermal Analysis and Calorimetry, 2015

A quantitative measurement of degree of deacetylation of Sterculia urens gum and its effect on th... more A quantitative measurement of degree of deacetylation of Sterculia urens gum and its effect on the thermal properties changes is presented in this study. Sterculia urens gum was deacetylated at varying deacetylation reaction temperature and time. The acetyl group is replaced by hydroxyl which leads to better solubility of the sterculia gum in water. Thermal properties were characterized using differential scanning calorimetry and thermogravimetric analysis. DSC analysis reveals that after the deacetylation, the glass transition temperature appears at around 60°C of the S. urens gum. After deacetylation, the TG degradation clearly shows three different peaks. Deacetylation reaction temperature plays the major role in the thermal stability and structure of the S. urens gum. Keywords Sterculia urens Á Deacetylation Á Thermal properties Á TG Á DSC Experimental Sterculia urens (gum karaya) obtained from Sigma-Aldrich company was used in the experiment. Double-distilled water was used for dissolving S. urens gum. Ammonia

Polymer Degradation and Stability, 2013

We demonstrate here the structural, thermal, and wettability characteristics of low density polye... more We demonstrate here the structural, thermal, and wettability characteristics of low density polyethylene powder before and after plasma treatments. The plasma treatment was carried out using different working gas i.e. air, oxygen and a mixture of hydrogen and oxygen at an atmospheric pressure of 100 Pa. The plasma treatment time was kept constant at 2 min for all the specimens. Fourier transform infrared (FTIR), dynamic capillary rising using Washburn method, differential scanning calorimetry (DSC), and thermogravimetric analysis has been carried out for both pristine and plasma treated polyethylene specimens. Our study shows that there is 88% increase in the wettability after plasma treatments. Plasma treatment in air atmosphere gives the maximum wettability. Thermogravimetric analysis (TGA) investigation shows plasma treatment in the H 2 þ O 2 mixture atmosphere gives maximum thermal stability whereas the DSC results reveal the lowest crystallinity for plasma treatment in air atmosphere. The lowest latent heat of fusion (154 J/g) calculated from the melting curve of DSC is observed for LDPE treated in air atmosphere. The FTIR spectroscopy of the plasma-treated LDPE powder reveals that plasma treatment introduces polar group on the LDPE surface leading to the increased surface free energy and surface active sites. The CH 2 concentration increases after plasma treatments.

Journal of Thermal Analysis and Calorimetry, 2014

ABSTRACT In this work, we presented plasma modification of low-density polyethylene (PE) powder u... more ABSTRACT In this work, we presented plasma modification of low-density polyethylene (PE) powder using unconventional chemicals. This work focused on the thermal behavior of modified PE. Plasma modification of PE was carried out using unconventional chemical vapor i.e., acetone, toluene, ethanol, methanol, isopropanol, and chloroform, respectively. For all the process, the modification time was kept constant for 2 min. Chamber pressure of 100 Pa was used for the study. The thermal behavior of the plasma-modified and unmodified PE was carried out by differential scanning calorimetry and thermogravimetric analysis. We have found that there is a maximum improvement of crystallinity and thermal stability of PE when ethanol is used for plasma modification. Results obtained from DSC showed that plasma modification of PE in ethanol vapors increases the crystallinity of the PE without damaging the surface properties. Thermal stability of PE plasma modified in ethanol gives maximum thermal improvement to almost 25 °C at 5 mass% mass loss compared to unmodified PE.

Microscopy Research and Technique, 2010

This article discusses calibration issues for shallow depth nanoindentation experiments with Berk... more This article discusses calibration issues for shallow depth nanoindentation experiments with Berkovich tips with respect to the accurate measurement of the diamond area function (DAF). For this purpose, two different calibration procedures are compared: (i) the direct measurement of the DAF through atomic force microscopy (AFM) imaging of the Berkovich tip at shallow depth and (ii) a novel indirect calibration method based on an iterative robust and converging scheme in which both reduced modulus and indentation hardness are simultaneously used. These results are obtained by indentation measurements on a standard specimen of fused silica, performed in the 0.5-200 mN load range with a Berkovich indenter. Direct tip shape measurements were carried out through different AFM methods. Comparisons with the standard indirect calibration procedure are also reported. For both the indirect calibration procedures a sensitivity and convergence study is presented.

Atomic force microscopy in vitro study of surface roughness and fractal character of a dental res... more Atomic force microscopy in vitro study of surface roughness and fractal character of a dental restoration composite after air-polishing

ACS Applied Nano Materials, 2018

Nano-sized powder composites of hafnium carbide/silicon carbide (HfC-SiC) were successfully prepa... more Nano-sized powder composites of hafnium carbide/silicon carbide (HfC-SiC) were successfully prepared by crosslinking and carbothermic reduction of a precursor. A novel high yield liquid precursor was synthesized by reacting acetylacetone (acac) modified hafnium tetrachloride (HfCl 4) with tetraethyl orthosilicate (TEOS) and hydroquinone (HQ). The synthesized materials were investigated by XRD, FT-IR, carbon analyzer, Raman, TG/DTA, SEM, TEM and EDS analysis. The resulting precursor pyrolysed at 1500 o C for 3 h in argon converted into nanostructured ultrahigh temperature composite powder (containing both HfC and SiC) with a trace of free carbon. The polymer-to-ceramic transformation was investigated by TG/DTA revealing that carbothermic reduction of HfC and SiC started at 1225 and 1450 o C respectively with a total yield of 64 % at 1500 o C. XRD revealed the powder composite was composed of HfC and β-SiC with a negligible amount of oxide impurities. SEM and TEM images reveals the Hf, Si and C were homogeneously distributed in the sample at submicron scale with an average grain size of less than 50 nm for both HfC and SiC. The result obtained by this synthesis approach is believed to be a promising candidate for hypersonic applications.

Journal of the European Ceramic Society, 2018

Ultra-high temperature ceramic infiltrated carbon-fibre composites were prepared by precursor inf... more Ultra-high temperature ceramic infiltrated carbon-fibre composites were prepared by precursor infiltration and pyrolysis (PIP) using a laboratory synthesized precursor. Microstructures and thermal properties including thermal expansion, thermal diffusivity, specific heat capacity and oxidative stability are correlated. XRD reveals the presence of C f-HfC and C f-HfC-SiC phases without formation of oxides. The CTE observed at 1200°C is slightly higher for C f-HfC (3.36 × 10 −6 K −1) compared to C f-HfC-SiC (2.95 × 10 −6 K −1) composites. Lower thermal diffusivity of the C f-HfC-SiC compared to C f-HfC composites is attributed to a thermal barrier effect and cracks in the composites which formed due to the CTE mismatch between carbon fibre and the matrix as well as CO generated during graphitization. The thermal conductivity of C f-HfC (4.18 ± 0.14 Wm −1 K −1) is higher than that of C f-HfC-SiC composite (3.33 ± 0.42 Wm −1 K −1). Composites microstructures were coarse with some protruding particles (5 μm) with a homogeneous dense (∼70%) matrix (HfC and HfC-SiC) for both composites.

Electrospun Nanofibers, 2017

Abstract A composite based on pectin and polyvinyl alcohol (PVA) was successfully electrospun int... more Abstract A composite based on pectin and polyvinyl alcohol (PVA) was successfully electrospun into nanofibers. This chapter demonstrates that pectin plays a major role in the structure–properties relationship of the composite nanofibers, even at a very small amount of 2 wt% pectin to PVA. Pectin caused an apparent increase in crystallinity, which can be further improved by post-spinning treatments of the nanofibers. Scanning electron microscope confirmed that the composite nanofibers are uniform and free of microbeads, and have a smaller diameter, which is probably due to the increase in crystallinity and the stretching caused by the higher charge density. These results suggest that the crystallinity of the PVA nanofibers can be modified by adding a small amount of pectin. PVA that is able to form nucleation and crystallization with pectin could serve to develop biodegradable and biocompatible, low-cost composite nanofibers for applications in biomedicine and material science.

Journal of the European Ceramic Society, 2016

Oxidation of silicon melt infiltrated SiC/SiC ceramic matrix composites (CMC) was studied in air ... more Oxidation of silicon melt infiltrated SiC/SiC ceramic matrix composites (CMC) was studied in air at 1200-1400 • C for 1, 5, 24 and 48 h. Weight gain and oxide layer thickness measurements revealed the oxidation follows parabolic reaction kinetics with increase in temperature and time. XRD showed the extent of oxide layer (SiO 2) formation was greatest after 48 h at 1400 • C: an observation confirmed by X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM) analyses. Oxide layer thickness varied from 1 m after 48 h at 1200 • C to 8 m after 48 h at 1400 • C. Oxidation of SiC/SiC composites is both temperature and time dependent with an activation energy of 619 kJ mol −1. BN coatings around SiC fibres showed good resistance to oxidation even after 48 h at 1400 • C.

Ceramics International, 2016

Nano-sized hafnium carbide was synthesized from organicinorganic hybrid polymer based on polycond... more Nano-sized hafnium carbide was synthesized from organicinorganic hybrid polymer based on polycondensation and carbothermal reduction reaction from pectin and hafnium tetrachloride followed by thermal treatment. Orthorhombic and monoclinic hafnia formed on pyrolysis which above 1300 oC transformed to hafnium carbide. Conversion of amorphous to crystalline hafnia was initiated at ~800 oC while the endothermic carbothermal reduction reaction started at ~1275 oC. Total yield of hafnium carbide was ~62%. The resulting carbide powders are equiaxed with narrow size distribution of crystallite size ~50 nm. SEM and EDX mapping confirm the uniform distribution of Hf and C. The high ceramic yield, uniform size particles, and simplicity of the process make it a promising route for polymer infiltration pyrolysis of carbon fibre/ultra high temperature composites.

Progress in Organic Coatings, 2015

The purpose of this study was to evaluate the 3-D surface micromorphology of polymer-oxide thin f... more The purpose of this study was to evaluate the 3-D surface micromorphology of polymer-oxide thin films spin-coated from a composite of poly-methyl-methacrylate as the matrix and elongated titania nanorods as the filler particles. The surfaces of these composite films were investigated by atomic force microscopy and characterized by fractal geometry analysis. The effect of increasing loading of the fillers between 0 and 30% by weigth relative to the matrix was assessed. An increasing roughness was observed, with typical emergence of protruding ripples progressively extending into larger stripes. The amplitude parameters of the surfaces were determined by analysis of the height distributions. The fractal analysis of roughness revealed that the films have fractal geometry. Triangulation method based on the linear interpolation type was applied to determine the fractal dimension. A connection was observed between the surface morphology and the physical properties of the coatings as assessed in previous works.

Science of Advanced Materials, 2012

Abstract: We have investigated the effect of polishing with two different systems, namely Venus S... more Abstract: We have investigated the effect of polishing with two different systems, namely Venus Supra and Enhance, on the properties of a resin composite currently in use for dental restorations, namely Venus Diamond. On both the non-polished and polished specimens, first the material surfaces have been imaged by scanning electron microscopy and atomic force microscopy, and quantitative information on the surface roughness has been extracted. Then the elastic properties of the composite have been measured in compression by ...

Journal of Thermal Analysis and Calorimetry, 2014

ABSTRACT Present research deals with the conversion of waste commodity plastics to valuable comme... more ABSTRACT Present research deals with the conversion of waste commodity plastics to valuable commercial product in the form of wax by pyrolysis. Optimization of both processes yield and produced wax quality was performed by means of a statistical tool originally proposed by G. Taguchi, using temperature, catalyst, carrier gas, and dwell time as the parameters. The obtained wax was characterized by Raman spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Yield of wax was found to be maximum when the parameters were 600�C, Fe catalyst, nitrogen gas atmosphere, and 15 min time. However, stability of the wax was found to be optimum at 700�C. Calorific value of the wax thus obtained was*43 MJ kg -1 , which supports its suitability as fuels like other petroleum products.

Journal of Colloid and Interface Science, 2013

IEEE Transactions on NanoBioscience, 2013

The purpose of this work was to investigate the porous polyetherimide scaffold (P-PEIs) as an alt... more The purpose of this work was to investigate the porous polyetherimide scaffold (P-PEIs) as an alternative biopolymer for bone tissue engineering. The P-PEIs was fabricated via solvent casting and particulate leaching technique. The morphology, phase composition, roughness, hydrophilicity, and biocompatibility of P-PEIs were evaluated and compared with polyetherimide (PEI) and Ti6Al4V disks. P-PEIs showed a biomimetic porous structure with a modulus of 78.95 ± 2.30 MPa. The water contact angle of P-PEIs was 75.4 ± 3.39 ∘ , which suggested that P-PEIs had a wettability surface. Moreover, P-PEIs provides a feasible environment for cell adhesion and proliferation. The relative cell adhesion capability and the cell morphology on P-PEIs were better than PEI and Ti6Al4V samples. Furthermore, the MC3T3-E1 cells on P-PEIs showed faster proliferation rate than other groups. It was revealed that the P-PEIs could be a potential material for the application of bone regeneration.

Dental Materials Journal, 2012

A photo-polymerizable Bisphenol-A diglycidylether methacrylate resin was characterized by Fourier... more A photo-polymerizable Bisphenol-A diglycidylether methacrylate resin was characterized by Fourier transform infrared spectroscopy after its irradiation under different conditions to identify the best curing. Bonding-agent free composites with particles of ball-milled glass, silica and titania at loading of 10 and 50%wt were prepared, and their viscoelastic properties investigated by dynamic mechanical analysis, in experimental conditions close to the working environment in the mouth. All composites showed good stability at the considered conditions. The stiffest composite was the silica one, which was based on the smallest primary particles. The storage moduli close to room temperature (25°C) and mastication frequency (1 Hz) were extracted as reference bending moduli for the materials, and compared to static compressive moduli measured by nanoindentation performed by atomic force microscopy. Nanoindentation showed qualitative results in agreement with dynamic mechanical analysis as to the ranking of different materials, while resulting in approximately twofold elastic modulus.

Analytical Chemistry, 2003

The development of surface-enhanced Raman scattering (SERS)-active substrates for cancer gene det... more The development of surface-enhanced Raman scattering (SERS)-active substrates for cancer gene detection is described. The detection method uses Raman active dye-labeled DNA gene probes, self-assembled monolayers, and nanostructured metallic substrates as SERS-active platforms. The mercaptohexane-labeled single-stranded DNA (SH-(CH(2))(6)-ssDNA)/6-mercapto-1-hexanol system formed on a silver surface is characterized by atomic force microscopy. The surface-enhanced Raman gene (SERGen) probes developed in this study can be used to detect DNA targets via hybridization to complementary DNA probes. The probes do not require the use of radioactive labels and have a great potential to provide both sensitivity and selectivity. The effectiveness of this approach and its application in cancer gene diagnostics (BRCA1 breast cancer gene) are investigated.

Journal of Nanomaterials, 2016

Journal of Thermal Analysis and Calorimetry, 2015

A quantitative measurement of degree of deacetylation of Sterculia urens gum and its effect on th... more A quantitative measurement of degree of deacetylation of Sterculia urens gum and its effect on the thermal properties changes is presented in this study. Sterculia urens gum was deacetylated at varying deacetylation reaction temperature and time. The acetyl group is replaced by hydroxyl which leads to better solubility of the sterculia gum in water. Thermal properties were characterized using differential scanning calorimetry and thermogravimetric analysis. DSC analysis reveals that after the deacetylation, the glass transition temperature appears at around 60°C of the S. urens gum. After deacetylation, the TG degradation clearly shows three different peaks. Deacetylation reaction temperature plays the major role in the thermal stability and structure of the S. urens gum. Keywords Sterculia urens Á Deacetylation Á Thermal properties Á TG Á DSC Experimental Sterculia urens (gum karaya) obtained from Sigma-Aldrich company was used in the experiment. Double-distilled water was used for dissolving S. urens gum. Ammonia

Polymer Degradation and Stability, 2013

We demonstrate here the structural, thermal, and wettability characteristics of low density polye... more We demonstrate here the structural, thermal, and wettability characteristics of low density polyethylene powder before and after plasma treatments. The plasma treatment was carried out using different working gas i.e. air, oxygen and a mixture of hydrogen and oxygen at an atmospheric pressure of 100 Pa. The plasma treatment time was kept constant at 2 min for all the specimens. Fourier transform infrared (FTIR), dynamic capillary rising using Washburn method, differential scanning calorimetry (DSC), and thermogravimetric analysis has been carried out for both pristine and plasma treated polyethylene specimens. Our study shows that there is 88% increase in the wettability after plasma treatments. Plasma treatment in air atmosphere gives the maximum wettability. Thermogravimetric analysis (TGA) investigation shows plasma treatment in the H 2 þ O 2 mixture atmosphere gives maximum thermal stability whereas the DSC results reveal the lowest crystallinity for plasma treatment in air atmosphere. The lowest latent heat of fusion (154 J/g) calculated from the melting curve of DSC is observed for LDPE treated in air atmosphere. The FTIR spectroscopy of the plasma-treated LDPE powder reveals that plasma treatment introduces polar group on the LDPE surface leading to the increased surface free energy and surface active sites. The CH 2 concentration increases after plasma treatments.

Journal of Thermal Analysis and Calorimetry, 2014

ABSTRACT In this work, we presented plasma modification of low-density polyethylene (PE) powder u... more ABSTRACT In this work, we presented plasma modification of low-density polyethylene (PE) powder using unconventional chemicals. This work focused on the thermal behavior of modified PE. Plasma modification of PE was carried out using unconventional chemical vapor i.e., acetone, toluene, ethanol, methanol, isopropanol, and chloroform, respectively. For all the process, the modification time was kept constant for 2 min. Chamber pressure of 100 Pa was used for the study. The thermal behavior of the plasma-modified and unmodified PE was carried out by differential scanning calorimetry and thermogravimetric analysis. We have found that there is a maximum improvement of crystallinity and thermal stability of PE when ethanol is used for plasma modification. Results obtained from DSC showed that plasma modification of PE in ethanol vapors increases the crystallinity of the PE without damaging the surface properties. Thermal stability of PE plasma modified in ethanol gives maximum thermal improvement to almost 25 °C at 5 mass% mass loss compared to unmodified PE.

Microscopy Research and Technique, 2010

This article discusses calibration issues for shallow depth nanoindentation experiments with Berk... more This article discusses calibration issues for shallow depth nanoindentation experiments with Berkovich tips with respect to the accurate measurement of the diamond area function (DAF). For this purpose, two different calibration procedures are compared: (i) the direct measurement of the DAF through atomic force microscopy (AFM) imaging of the Berkovich tip at shallow depth and (ii) a novel indirect calibration method based on an iterative robust and converging scheme in which both reduced modulus and indentation hardness are simultaneously used. These results are obtained by indentation measurements on a standard specimen of fused silica, performed in the 0.5-200 mN load range with a Berkovich indenter. Direct tip shape measurements were carried out through different AFM methods. Comparisons with the standard indirect calibration procedure are also reported. For both the indirect calibration procedures a sensitivity and convergence study is presented.