The Experts below are selected from a list of 9282 Experts worldwide ranked by ideXlab platform
Michael Grunze - One of the best experts on this subject based on the ideXlab platform.
-
swelling behavior of self assembled monolayers of alkanethiol Terminated Poly ethylene glycol a neutron reflectometry study
Langmuir, 2004Co-Authors: J Fick, S Tokumitsu, Michael Himmelhaus, Roland Steitz, V Leiner, Michael GrunzeAbstract:The swelling behavior of alkanethiol-Terminated Poly(ethylene glycol) with an average molecular weight of 2180 Da (i.e., approximately 45 ethylene glycol, EG, units) in contact with water was investigated by neutron reflectometry as a function of the morphology of the PEG-SH layer. Amorphous films at a low grafting density show significant swelling with an increase of the film thickness from approximately 25 A in the dry state to approximately 70 A in contact with D2O, which corresponds to a total water uptake of approximately 38 mass %. In contrast, quasi-crystalline monolayers exhibit only a small amount of water penetrating into the film (approximately 8 mass %) with a corresponding change of the layer thickness from approximately 110 to approximately 125 A. The water uptake per EG unit corresponds to the literature value of 1.5 for the amorphous layer and to only 0.25 in the case of the quasi-crystalline film.
-
grafting of alkanethiol Terminated Poly ethylene glycol on gold
Langmuir, 2002Co-Authors: S Tokumitsu, A Liebich, Sascha Herrwerth, Wolfgang Eck, Michael Himmelhaus, Michael GrunzeAbstract:The grafting of alkanethiol-Terminated Poly(ethylene glycol) [HS(CH2)11(OCH2CH2)n−OCH3; n = 34−56, MW ≈ 2224 Da] onto Polycrystalline gold from dilute solutions was investigated by ellipsometry, X-ray photoelectron spectroscopy, infrared reflection−absorption spectroscopy, and in situ second harmonic generation. After immersion of a gold-coated Si wafer into a 50 μM dimethylformamide solution, the thickness of the grafted layer increases in a first rapid step up to ∼20 A. After about 10 min, the thickness rises notably again and reaches saturation after ∼2 h at ∼120 A. The kinetics of film formation clearly deviate from Langmuir kinetics, which is normally observed for the self-assembly of nonfunctionalized alkanethiols. Our observation can be explained by a conformational transition of the grafted Poly(ethylene glycol) chains from amorphous coils to a brush morphology, predominantly consisting of helices with an orientation perpendicular to the surface. The second harmonic generation experiments show tha...
Sabu Thomas - One of the best experts on this subject based on the ideXlab platform.
-
effect of hexamethyldisilazane modified nano fumed silica on the properties of epoxy carboxyl Terminated Poly butadiene co acrylonitrile blend a new hybrid approach
Industrial & Engineering Chemistry Research, 2020Co-Authors: Nisa V Salim, Aneesa Padinjakkara, Sabu ThomasAbstract:In this study, we have developed a hybrid system from epoxy/carboxyl-Terminated Poly(butadiene-co-acrylonitrile) (CTBN) and hexamethyldisilazane-modified nano fumed silica (HMDS NS). We aim to disclose the knowledge on how modified nano fumed silica influences the morphology and impacts properties of epoxy and epoxy-CTBN blend systems without significantly compromising the other desirable mechanical and thermal properties. High surface area and increased hydrophobicity of HMDS NS cause homogeneous dispersion in the hydrophobic Polymer matrix. The results confirmed that the improvement in impact and tensile properties of epoxy thermoset depends mainly on the optimum concentration of CTBN and HMDS NS. The thermomechanical analysis showed that HMDS NS acts as a plasticizer and it increased the mobility of CTBN chain and created flexible regions in system. The current research on the hybrid system from the epoxy/CTBN/HMDS NS approach has the potential for the development of improved structural adhesives, automotive structural part, and electronic encapsulate.
-
the role of clay modifier on cure characteristics and properties of epoxy clay carboxyl Terminated Poly butadiene co acrylonitrile ctbn hybrid
Materials Technology, 2017Co-Authors: Poornima Vijayan P, Debora Puglia, Pournami Vijayan P, J M Kenny, Sabu ThomasAbstract:AbstractEpoxy/clay/carboxyl-Terminated Poly(butadiene-co-acrylonitrile) (CTBN) hybrids were prepared with two different organically modified clays. Octadecyl amine and trimethyl stearyl ammonium-modified nanoclays (Nanomer I.30E and I.28E, respectively) were used. The dispersion of the nanoclay in binary epoxy/clay and epoxy/clay/CTBN hybrid nanocomposites was investigated using scanning electron microscopy and optical microscopy, and the observed morphological details were explained by the prediction of solubility parameter for each component in the nanocomposites. The effect of clay modifier on cure characteristics of binary epoxy/clay and epoxy/clay/CTBN hybrid nanocomposites was studied using rheological analysis. Glass transition temperatures (Tg) and thermal stability of binary and hybrid nanocomposites were also measured. The reduced cross-link density via epoxy homoPolymerization, the plasticizing effect of clay modifier/dissolved liquid rubber and the interfacial adhesion between the Polymer and ...
-
volume shrinkage and cure kinetics in carboxyl Terminated Poly butadiene co acrylonitrile ctbn modified epoxy clay nanocomposites
Journal of Macromolecular Science Part A, 2015Co-Authors: Poornima P Vijayan, Jurgen Pionteck, Sabu ThomasAbstract:The role of carboxyl-Terminated Poly(butadiene-co-acrylonitrile) (CTBN) liquid rubber and reactive surfactant modified nanoclay on the volume shrinkage during cure reaction and cure kinetics of epoxy/anhydride system in the presence of a catalyst was studied using Pressure-Volume-Temperature (PVT) measurements and real time FTIR spectroscopic analysis, respectively. The dilution effect of CTBN and catalytic effect of clay modifier on the epoxy/anhydride reaction reflected in the volume shrinkage behavior of CTBN modified epoxy/clay nanocomposites (epoxy/clay/CTBN hybrid) during cure. The kinetics of cure was studied based on the conversions derived from PVT data assuming a linear relation between network formation and volume shrinkage. The consumption of epoxy band (913 cm−1) during cure obtained from the real time FTIR spectroscopic analysis was employed to compare the effect of both CTBN and nanoclay on the cure kinetics. In epoxy/clay/CTBN hybrid, during the initial stage of cure the catalytic activity...
-
cure kinetics morphological and dynamic mechanical analysis of diglycidyl ether of bisphenol a epoxy resin modified with hydroxyl Terminated Poly ether ether ketone containing pendent tertiary butyl groups
Polymer, 2006Co-Authors: Bejoy Francis, R Ramaswamy, Lakshmana V Rao, Geert Vanden Poel, Fabrice Posada, Gabriel Groeninckx, Sabu ThomasAbstract:Abstract Hydroxyl Terminated Poly(ether ether ketone) based on tert -butyl hydroquinone (PEEKTOH) was used to modify a diglycidyl ether of bisphenol-A epoxy resin. A diamine, 4,4′-diaminodiphenylsulfone was used as the curing agent. Isothermal differential scanning calorimetric measurements of the blends were carried out at 180, 165 and 150 °C. The extent of reaction was found to decrease with the addition of PEEKTOH. The phenomenological model developed by Kamal was used for kinetic analysis of curing reaction. The curing reaction followed autocatalytic mechanism regardless of the presence and amount of oligomer present in the epoxy resin. The experimental and theoretical reaction rates were in good agreement during the initial stages of the reaction. The experimental values were lower than theoretical rate during the final stages of reaction due to increase in the viscosity of the system. A semiemperical model was used to explain diffusion control during final stages of reaction. The cured blends exhibited two phase morphology at all the curing temperatures. A uniform particle size distribution was observed at all compositions. The domain size decreased slightly with increase in oligomer content and with decrease in curing temperature. Finally, the viscoelastic properties were analysed using dynamic mechanical thermal analysis. Two T g s corresponding to epoxy rich and thermoplastic rich phases were evident from the dynamic mechanical spectrum.
-
synthesis of hydroxyl Terminated Poly ether ether ketone with pendent tert butyl groups and its use as a toughener for epoxy resins
Journal of Polymer Science Part B, 2006Co-Authors: Bejoy Francis, Sabu Thomas, R Ramaswamy, Viswanathan G Asari, Seno Jose, Lakshmana V RaoAbstract:Hydroxyl-Terminated Poly(ether ether ketone) with pendent tert-butyl groups (PEEKTOH) was synthesized by the nucleophilic substitution reaction of 4,4'-difluorobenzophenone with tert-butyl hydroquinone with potassium carbonate as a catalyst and N-methyl-2-pyrrolidone as a solvent. Diglycidyl ether of bisphenol A epoxy resin was toughened with PEEKTOHs having different molecular weights. The melt-mixed binary blends were homogeneous and showed a single composition-dependent glass-transition temperature (T g ). Kelley-Bueche and Gordon-Taylor equations gave good correlation with the experimental Tg. Scanning electron microscopy studies of the cured blends revealed a two-phase morphology. A sea-island morphology in which the thermoplastic was dispersed in a continuous matrix of epoxy resin was observed. Phase separation occurred by a nucleation and growth mechanism. The dynamic mechanical spectrum of the blends gave two peaks corresponding to epoxy-rich and thermoplastic-rich phases. The Tg of the epoxy-rich phase was lower than that of the unmodified epoxy resin, indicating the presence of dissolved PEEKTOH in the epoxy matrix. There was an increase in the tensile strength with the addition of PEEKTOH. The fracture toughness increased by 135% with the addition of high-molecular-weight PEEKTOH. The improvement in the fracture toughness was dependent on the molecular weight and concentration of the oligomers present in the blend. Fracture mechanisms such as crack path deflection, ductile tearing of the thermoplastic, and local plastic deformation of the matrix occurred in the blends. The thermal stability of the blends was not affected by blending with PEEKTOH.
Yukio Nagasaki - One of the best experts on this subject based on the ideXlab platform.
-
facile construction of sulfanyl Terminated Poly ethylene glycol brushed layer on a gold surface for protein immobilization by the combined use of sulfanyl ended telechelic and semitelechelic Poly ethylene glycol s
Langmuir, 2008Co-Authors: Keitaro Yoshimoto, Seiko Nemoto, Tamao Hatta, Takumi Hirase, Yukio NagasakiAbstract:A sulfanyl-Terminated Poly(ethylene glycol) (PEG)-brushed layer was constructed on a gold sensor platform by consecutive treatment with a sulfanyl-ended semitelechelic PEG (2 kDa, hereafter “MeO-PEG-SH (2k)”) and a sulfanyl-ended telechelic PEG (5 kDa, hereafter “SH-PEG-SH (5k)”). Our strategy of constructing the sulfanyl-Terminated PEG-brushed gold surface is based on mixed-PEG-brush formation from the longer SH-PEG-SH (5k) and the shorter MeO-PEG-SH (2k), where the preimmobilized shorter MeO-PEG-SH (2k) prevents loop formation in the longer SH-PEG-SH (5k) on the surface and the free sulfanyl group at one end of the longer SH-PEG-SH is exposed to the mixed-PEG tethered-chain surface. From the experimental results obtained from surface plasmon resonance analysis, it became apparent that the immobilization density and the orientation of the longer SH-PEG-SH (5k) on the gold surface could be controlled by the amount of preimmobilized shorter MeO-PEG-SH (2k). Under the optimized conditions of MeO-PEG-SH (2k)...
-
facile construction of sulfanyl Terminated Poly ethylene glycol brushed layer on a gold surface for protein immobilization by the combined use of sulfanyl ended telechelic and semitelechelic Poly ethylene glycol s
Langmuir, 2008Co-Authors: Keitaro Yoshimoto, Seiko Nemoto, Tamao Hatta, Takumi Hirase, Yukio NagasakiAbstract:A sulfanyl-Terminated Poly(ethylene glycol) (PEG)-brushed layer was constructed on a gold sensor platform by consecutive treatment with a sulfanyl-ended semitelechelic PEG (2 kDa, hereafter "MeO-PEG-SH (2k)") and a sulfanyl-ended telechelic PEG (5 kDa, hereafter "SH-PEG-SH (5k)"). Our strategy of constructing the sulfanyl-Terminated PEG-brushed gold surface is based on mixed-PEG-brush formation from the longer SH-PEG-SH (5k) and the shorter MeO-PEG-SH (2k), where the preimmobilized shorter MeO-PEG-SH (2k) prevents loop formation in the longer SH-PEG-SH (5k) on the surface and the free sulfanyl group at one end of the longer SH-PEG-SH is exposed to the mixed-PEG tethered-chain surface. From the experimental results obtained from surface plasmon resonance analysis, it became apparent that the immobilization density and the orientation of the longer SH-PEG-SH (5k) on the gold surface could be controlled by the amount of preimmobilized shorter MeO-PEG-SH (2k). Under the optimized conditions of MeO-PEG-SH (2k) premodification, the constructed MeO-PEG-SH (2k)/SH-PEG-SH (5k) mixed layer conjugated efficiently with the maleimide-installed proteins and the antibody Fab' fragments, accompanied by an appreciable nonfouling characteristic against bovine serum albumin as strong as that of the MeO-PEG-SH (5k)/MeO-PEG-SH (2k) mixed surface, which was reported in our previous work; it also showed a superior nonfouling characteristic compared to the commercially available carboxymethylated dextran surface (Uchida, K.; et al. Biointerphase 2007, 2 (4), 126-130). Furthermore, from the experimental results of the X-ray photoelectron spectrometry analysis, the presence of both Au-bound and Au-unbound sulfur species was confirmed on the SH-PEG-SH (5k)/MeO-PEG-SH (2k)-modified gold surface. These results clearly indicate that the preimmobilized shorter MeO-PEG-SH (2k) not only increased the nonfouling characteristic of the PEG tethered-chain surface but also prevented loop formation in the longer SH-PEG-SH (5k) on the gold surface. Since the protein-installed SH-PEG-SH (5k)/MeO-PEG-SH (2k)-modified surface showed a strongly nonfouling characteristic and recognized the target molecules selectively, this new mixed-brush-formation technique using longer sulfanyl-ended telechelic PEGs and shorter semitelechelic PEGs is a simple yet effective method of constructing a strongly nonfouling terminal-functionalized gold surface for protein immobilization.
E W Meijer - One of the best experts on this subject based on the ideXlab platform.
-
evaluation of gd iii dtpa Terminated Poly propylene imine dendrimers as contrast agents for mr imaging
NMR in Biomedicine, 2006Co-Authors: Sander Langereis, Quido G De Lussanet, Marcel H P Van Genderen, E W Meijer, Regina G H Beetstan, Arjan W Griffioen, Jos M A Van Engelshoven, Walter H BackesAbstract:Different generations of Gd(III)DTPA-Terminated Poly(propylene imine) dendrimers {G1 (n ¼ 4 Gd(III) ions per molecule), G3 (n ¼ 16) and G5 (n ¼ 64)} and reference Gd(III)DTPA complex (G0 (n ¼ 1)) were characterized in terms of (i) longitudinal (r1) and transverse (r2) relaxivities in mouse blood plasma, (ii) concentration detection limits in vitro and (iii) in vivo contrast-enhanced MR imaging (CE-MRI) in mice at 1.5 T. Serial and dynamic CE-MRI were performed to monitor the distribution of MRI contrast agent in the heart, arteries, renal system, liver, spleen, bladder and tumor periphery. The relaxivities increased non-linearly with molecular weight (for G0 ionic r1 ¼ 8.1 mM � 1 s � 1 and ionic r2 ¼ 8.6 mM � 1 s � 1 to G5 19.3 and 25.0, respectively). The minimal detectable dendrimer concentration was more than two orders of magnitude lower for G5 (8.1 � 10 � 8 M) than for G0 (3.1 � 10 � 5 M). Sub-millimeter-sized blood vessels were well visualized with serial CE-MRI with each contrast agent. Dynamic CE-MRI showed timely renal clearance for all contrast agents, but a stronger and a prolonged blood signal enhancement for the higher generations of the dendritic contrast agent. Moreover, G0 and G1 showed a rapid tumor wash-in and wash-out, whereas G3 and G5 displayed a more gradual and prolonged tumor wash-in. In conclusion, both G0 and dendritic contrast agents G1, G3 and G5 are well suited for non-tissue-specific MRI of sub- millimeter-sized blood vessels and evaluating tumor microcirculatory characteristics in mice. Higher generations of dendritic contrast agents display lower concentration detection limits, which suggests their future use for molecular imaging. Copyright # 2006 John Wiley & Sons, Ltd.
-
multivalent contrast agents based on gadolinium diethylenetriaminepentaacetic acid Terminated Poly propylene imine dendrimers for magnetic resonance imaging
Macromolecules, 2004Co-Authors: Sander Langereis, Quido G De Lussanet, Marcel H P Van Genderen, Walter H Backes, E W MeijerAbstract:A convenient methodology has been developed for the synthesis of gadolinium−diethylenetriaminepentaacetic acid (Gd−DTPA)-Terminated Poly(propylene imine) dendrimers as contrast agents for magnetic resonance imaging (MRI). In our strategy, isocyanate-activated, tert-butyl-protected DTPA analogues were coupled to different generations of Poly(propylene imine) dendrimers. Deprotection of the tert-butyl esters with trifluoroacetic acid in dichloromethane and extensive dialysis afforded gadolinium-chelating Poly(propylene imine) dendrimers. The corresponding Gd−DTPA-based dendritic contrast agents were prepared from GdCl3 in either water or citrate buffer. Atomic force microscopy and cryogenic transmission electron microscopy experiments of the fifth-generation Gd−DTPA based dendritic contrast agent in citrate buffer demonstrated the presence of well-defined spherical particles with nanoscopic dimensions (5−6 nm), and no self-aggregation of dendrimers was observed. The efficiencies of these dendritic contrast ...
-
multivalent contrast agents based on gd dtpa Terminated Poly propylene imine dendrimers for magnetic resonance imaging
Macromolecules, 2004Co-Authors: Sander Langereis, Walter H Backes, De Q G Lussanet, Van M H P Genderen, E W MeijerAbstract:A convenient methodol. has been developed for the synthesis of gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA)-Terminated Poly(propylene imine) dendrimers as contrast agents for magnetic resonance imaging (MRI). In our strategy, isocyanate-activated, tert-butyl-protected DTPA analogs were coupled to different generations of Poly(propylene imine) dendrimers. Deprotection of the tert-Bu esters with trifluoroacetic acid in dichloromethane and extensive dialysis afforded gadolinium-chelating Poly(propylene imine) dendrimers. The corresponding Gd-DTPA-based dendritic contrast agents were prepd. from GdCl3 in either water or citrate buffer. At. force microscopy and cryogenic transmission electron microscopy expts. of the fifth-generation Gd-DTPA based dendritic contrast agent in citrate buffer demonstrated the presence of well-defined spherical particles with nanoscopic dimensions (5-6 nm), and no self-aggregation of dendrimers was obsd. The efficiencies of these dendritic contrast agents in MRI, expressed in terms of longitudinal (r1) and transverse (r2) relaxivities, were detd. at 1.5 T at 20 °C. The r1 and r2 values increase considerably with increasing generation of Gd-DTPA-Terminated dendrimer. The fifth-generation dendritic contrast agent displays the highest ionic relaxivities (per gadolinium), r1 = 19.7 mM-1 s-1 and r2 = 27.8 mM-1 s-1, which are substantially higher than the ionic relaxivities of parent Gd-DTPA. Moreover, a series of combined gadolinium and yttrium complexes of the fifth-generation dendrimer are prepd., resulting in well-defined dendritic contrast agents with tunable mol. relaxivities
Richard M Crooks - One of the best experts on this subject based on the ideXlab platform.
-
effect of particle size on the kinetics of the electrocatalytic oxygen reduction reaction catalyzed by pt dendrimer encapsulated nanoparticles
Langmuir, 2007Co-Authors: John A Crooks, Richard M CrooksAbstract:Platinum dendrimer-encapsulated nanoparticles (DENs) containing an average of 55, 100, 147, 200, and 240 atoms were prepared within sixth-generation, hydroxyl-Terminated, Poly(amidoamine) dendrimers. These DENs were immobilized on glassy carbon electrodes, and the effect of particle size on the kinetics of the oxygen reduction reaction (ORR) was quantitatively evaluated using rotating disk voltammetry. The total areas of the Pt DENs were determined by electrochemical CO stripping and hydrogen desorption, and the results were found to be in reasonable agreement with calculated values. The largest particles exhibited the highest specific activities for the ORR.
-
electrocatalytic o2 reduction at glassy carbon electrodes modified with dendrimer encapsulated pt nanoparticles
Journal of the American Chemical Society, 2005Co-Authors: Richard M CrooksAbstract:Platinum dendrimer-encapsulated nanoparticles (DENs) were prepared within fourth-generation, hydroxyl-Terminated, Poly(amidoamine) dendrimers and immobilized on glassy carbon electrodes using an electrochemical coupling strategy. X-ray photoelectron spectroscopy, electron microscopy, and electrochemical experiments confirmed that the Pt DENs were about 1.4 nm in diameter and that they remained within the dendrimer following surface immobilization. The resulting Pt DEN films were electrocatalytically active for the oxygen reduction reaction. The films were also robust, surviving up to 50 consecutive cyclic voltammograms and sonication.
-
synthesis characterization and surface immobilization of platinum and palladium nanoparticles encapsulated within amine Terminated Poly amidoamine dendrimers
Langmuir, 2004Co-Authors: Robert W J Scott, Richard M CrooksAbstract:Platinum and palladium dendrimer-encapsulated nanoparticles (DENs) were prepared within commercially available, fourth-generation, amine-Terminated, Poly(amidoamine) dendrimers (G4-NH2). The synthesis is carried out by selectively encapsulating metal complexes within the dendrimer and then reducing the resulting composite. Intradendrimer complexation requires control over the solution pH to prevent attachment of the metal complexes to primary amine groups on the dendrimer periphery. That is, the surface primary amines of the dendrimer must be selectively protonated in the presence of the interior tertiary amines. The metal-ion encapsulation and reduction processes were characterized by UV−vis spectroscopy. Forty-atom Pt and Pd DENs were examined by high-resolution transmission electron microscopy, which showed that the mean particle sizes were 1.4 and 1.5 nm, respectively, and that both were nearly monodisperse (standard deviation = 0.3 nm). The free amine groups on the dendrimer surface were used to link...
