Ravinder Elupula

Efficient Synthesis of High Purity Homo-arm and Mikto-arm Poly(ethylene glycol) Stars Using Epoxide and Azide–Alkyne Coupling Chemistry

High purity homo-arm and mikto-arm poly(ethylene glycol) (PEG) stars are successfully prepared by the combination of epoxide ring-openings and azide-alkyne click reactions. First, monohydroxy-PEG was modified via epoxide chemistry to bear one hydroxyl and one azide functionality at the same end. An alkyne-functionalized PEG chain was then coupled to the azide. Subsequently, the remaining hydroxyl could be reactivated to an azide again and again to enable stepwise addition of alkyne-functionalized polymer arms. The use of efficient reactions for this iterative route provides star polymers with an exact number of arms, and a tailorable degree of polymerization for each arm. Detailed characterization confirms the high purity of multi-arm polyethylene glycol products.

Click-In Ferroelectric Nanoparticles for Dielectric Energy Storage

Polymer-ceramic nanocomposites have been thoroughly investigated previously for high energy storage devices. However, the increase in performance of these nanocomposites has proven to be significantly lower than predicted values. Through surface functionalization of high dielectric constant nanoparticles (NP), the flaws that reduce composite performance can be eliminated to form high energy density composite materials. Functionalization methods utilize high throughput printing and curing techniques (i.e., inkjet printing and xenon flash lamp curing) that are crucial for rapid adoption into industrial production. (Ba,Ca) (Zr,Ti)O3 NPs (50 nm) are synthesized through the solvothermal method and functionalized with alkene terminated methoxysilanes. A thiol-ene monomer ink system, PTD3 [pentaerythritol tetrakis (3-mercaptopropionate) (PEMP, P), 1,3-Diisopropenylbenzene (DPB, D), 2,4,6-Triallyloxy-1,3,5-triazine (TOTZ, T)], is used as a high breakdown polymer matrix. Neat polymer, alkene terminated NP-polymer composites, and hydrophilic, TBAOH functionalized NP-polymer composites were spin coated onto both copper laminated glass slides and printed onto copper substrates in 1 cm(2) patterns for testing. Alkene functionalized NPs increased the breakdown strength by ∼38% compared to the nonfunctionalized NPs. Functionalized NPs increased both the breakdown strength and dielectric constant compared to the neat polymer, increasing the energy density nearly 3-fold from 13.3 to 36.1 J·cm(-3).

Determination of polyethylene glycol end group functionalities by combination of selective reactions and characterization by matrix assisted laser desorption/ionization time-of-flight mass spectrometry

End groups play a critical role in macromolecular coupling reactions for building complex polymer architectures, yet their identity and purity can be difficult to ascertain using traditional analytical technique. Recent advances in mass spectrometry techniques have made matrix-assisted laser desorption/ionization time-of-fight (MALDI-TOF) mass spectrometry a rapid and powerful tool for providing detailed information about the identity and purity of homopolymer end groups. In this work, MALDI-TOF mass spectrometry was used to study end groups of linear polyethylene glycols. In particular, the identifications of alcohol, amine and thiol end groups are investigated because these nucleophilic moieties are among the most common within biological and synthetic macromolecules. Through comparative characterization of alcohol, amine, and thiol end groups, the exact identification of these end groups could be confirmed by selective and quantitative modification. The precision of this technique enables the unambiguous differentiation of primary amino groups relative to hydroxyl groups, which differ by only 1 mass unit. In addition, the quantitative conversion of various polyethylene glycol end groups using highly efficient coupling reactions such as the thiol-ene and azide-alkyne click reactions can be confirmed using MALDI-TOF mass spectrometry.

Surface modified BaTiO 3 -polystyrene nanocomposites for energy storage

Major research efforts have been focused towards developing high dielectric constant ( e ), low loss (tan δ ) and high electrical breakdown dielectrics for energy storage capacitors. Combining the low cost, ease of processing and high breakdown field strength (BDS) of polymers with the high e ceramic fillers will result in high-energy storage capacitors. Herein, we show progress in developing low cost, low weight and high electrical energy storage capacitors by mixing polystyrene (PS, mw = 177,000 g/mol) and hydroxyl-BaTiO 3 nanoparticles ( h -BT, ~50 nm) in a highly polar solvent (DMF) on weight percent basis. Surface modification of crude-BT( c -BT) by H 2 O 2 resulted in h -BT, which renders h -BT highly dispersed due to the surface hydroxyl functional groups. Ceramic-polymer nanocomposites (80PS-20 h BT and 20PS-80 h BT) exhibited relatively high BDS (~475 kV/cm and 247 kV/cm) and a large e (~13 and 40). Room temperature (300 K) energy density values for PS, 80PS-20 h BT, 20PS-80 h BT and h -BT are 4.33, 0.12, 0.10 and 0.36 J/cm 3 , respectively.

Photonic curing of aromatic thiol–ene click dielectric capacitors via inkjet printing

Dielectric capacitive energy storage has a wide range of applications such as microelectronic devices, grid scale load leveling, military applications, and personal power supplies. The high charge and discharge rate, along with the high retention and fatigue properties, make dielectric capacitors an attractive means of energy storage. Device manufacturing in industry requires high throughput and high pattern registry printing processes, such as inkjet, that are able to deposit a wide variety of materials. Thiol–alkene systems, [pentaerythritol tetrakis(3-meracproprinate) (PEMP, P), 1,3-diisopropenylbenzene (DPB, D), 2,4,6-triallyoxy-1,3,5-triazine (TOTZ, T)] of various compositions were printed via inkjet printing and cured with a xenon flash lamp system. For simplicity, inks were designated PTD0–4, correlating to the amount of DPB in the ink. PTD1–4 demonstrated fluid properties amenable to inkjet printing (with Z factors between 2–11) and were cured to produce mechanically and chemically stable dielectric films. PTD3 showed the best printability and was used for characterization of energy storage. It was found that the dielectric constant varied with curing intensity and energy/voltage. The breakdown strength had no correlation to the curing parameters tested. Weibull analysis of breakdown failure along with dielectric characterization resulted in a volumetric energy density distribution with a peak characteristic energy storage (63% chance of failure) of 32 J cm−3.

Low temperature sintered giant dielectric permittivity CaCu3Ti4O12 sol-gel synthesized nanoparticle capacitors

This paper reports on synthesis of polycrystalline complex perovskite CaCu3Ti4O12 (as CCTO) ceramic powders prepared by a sol–gel auto combustion method at different sintering temperatures and sintering times, respectively. The effect of sintering time on the structure, morphology, dielectric and electrical properties of CCTO ceramics is investigated. Tuning the electrical properties via different sintering times is demonstrated for ceramic samples. X-ray diffraction (XRD) studies confirm perovskite-like structure at room temperature. Abnormal grain growth is observed for ceramic samples. Giant dielectric permittivity was realized for CCTO ceramics. High dielectric permittivity was attributed to the internal barrier layer capacitance (IBLC) model associated with the Maxwell–Wagner (MW) polarization mechanism.

Synthesis and structural properties of Ba(1-x)LaxTiO3 perovskite nanoparticles fabricated by solvothermal synthesis route

We report the successful synthesis and structural characterization of barium lanthanum titanate Ba(1-x)LaxTiO3 (x=0.003,0.006,0.010) nanoparticles. The colloidal nanoparticles were prepared with high yield by a solvothermal method at temperatures as low as 150°C for 24h. The as-prepared nanopowders were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy. The XRD studies revealed pseudo-cubic crystalline structure, with no impurity phases at room temperature. However ferroelectric tetragonal modes were clearly observed using Raman spectroscopy measurements. From TEM measurements, uniformly sized BLT nanoparticles were observed. Selected area diffraction TEM images revealed polycrystalline perovskite ring patterns, identified as corresponding to the tetragonal phase.