A5034985589- Block Copolymer Self-Assembly
- Advanced Polymer Synthesis and Characterization
- Material Dynamics and Properties
- Theoretical and Computational Physics
- Machine Learning in Materials Science
- Multiferroics and related materials
- Polymer Surface Interaction Studies
- Spectroscopy and Quantum Chemical Studies
- Electrostatics and Colloid Interactions
- Magnetic and transport properties of perovskites and related materials
- Surfactants and Colloidal Systems
- Rheology and Fluid Dynamics Studies
- Advanced Chemical Physics Studies
- Phase Equilibria and Thermodynamics
- Advanced Condensed Matter Physics
- Polymer crystallization and properties
- Advanced Thermodynamics and Statistical Mechanics
- Ferroelectric and Piezoelectric Materials
- Fluid Dynamics and Thin Films
- Cold Atom Physics and Bose-Einstein Condensates
- Protein Structure and Dynamics
- GaN-based semiconductor devices and materials
- Polymer Nanocomposites and Properties
- Anodic Oxide Films and Nanostructures
- Model Reduction and Neural Networks
University of California, Santa Barbara
2015-2024
Division of Materials Research
2015
K Lab (United States)
2015
California Institute of Technology
2013
Oregon State University
2009-2010
University of Illinois Urbana-Champaign
2006-2007
University of York
2004
Advances in synthetic polymer chemistry have unleashed seemingly unlimited strategies for producing block polymers with arbitrary numbers (n) and types (k) of unique sequences repeating units. Increasing (k,n) leads to a geometric expansion possible molecular architectures, beyond conventional ABA-type triblock copolymers (k = 2, n 3), offering alluring opportunities generate exquisitely tailored materials unparalleled control over nanoscale-domain geometry, packing symmetry, chemical...
InGaN-based light-emitting diodes (LEDs) exhibit a significant efficiency loss (droop) when operating at high injected carrier densities, the origin of which remains an open issue. Using atomistic first-principles calculations, we show that this droop is caused by indirect Auger recombination, mediated electron-phonon coupling and alloy scattering. By identifying droop, our results provide guide to addressing issues in nitride LEDs development efficient solid-state lighting.
We report Auger recombination rates for wurtzite InGaN calculated from first principles density-functional and many-body-perturbation theory. Two different mechanisms are examined -- inter- intra-band that affect parts of the emission spectrum. In blue to green spectral region at room temperature coefficient can be as large 2x10^-30cm^6s^-1; in infrared even larger. Since scales with cubic power free-carrier concentration it becomes an important non-radiative loss mechanism high current...
QMCPACK is an open source quantum Monte Carlo package for ab initio electronic structure calculations. It supports calculations of metallic and insulating solids, molecules, atoms, some model Hamiltonians. Implemented real space algorithms include variational, diffusion, reptation Carlo. uses Slater–Jastrow type trial wavefunctions in conjunction with a sophisticated optimizer capable optimizing tens thousands parameters. The orbital auxiliary-field method also implemented, enabling cross...
Control of interfacial interactions leads to a dramatic change in shape and morphology for particles based on poly(styrene-b-2-vinylpyridine) diblock copolymers. Key these changes is the addition Au-based surfactant nanoparticles (SNPs) which are adsorbed at interface between block copolymer-containing emulsion droplets surrounding amphiphilic afford asymmetric, ellipsoid particles. The mechanism formation novel nanostructures was investigated by systematically varying volume fraction SNPs,...
Self-consistent field theory (SCFT) is a powerful tool for the design and interpretation of experiments on block polymer materials. In this Perspective, we lower barrier to entry use SCFT by experimental groups two means. First, present pedagogical introduction an improved version open-source Polymer Self-Consistent Field (PSCF) software package underlying theory. Second, discuss methods generating robust initial guesses fields that are computed in SCFT. To demonstrate our approach, case...
The self-assembly of block polymers into well-ordered nanostructures underpins their utility across fundamental and applied polymer science, yet only a handful equilibrium morphologies are known with the simplest AB-type materials. Here, we report discovery A15 sphere phase in single-component diblock copolymer melts comprising poly(dodecyl acrylate)-block-poly(lactide). A systematic exploration space revealed that forms substantial range minority lactide volume fractions (fL = 0.25 - 0.33)...
Abstract Complex coacervation driven liquid-liquid phase separation (LLPS) of biopolymers has been attracting attention as a novel in living cells. Studies LLPS this context are typically proteins harboring chemical and structural complexity, leaving unclear which properties fundamental to complex versus protein-specific. This study focuses on the role polyethylene glycol (PEG)—a widely used molecular crowder—in LLPS. Significantly, entropy-driven is recapitulated with charged polymers...
ZnSnN(2), a new earth-abundant semiconductor, is synthesized and characterized for use as photovoltaic absorber material. Results confirm the predicted orthorhombic Pna2(1) crystal structure in RF sputtered thin films. Additionally, optical measurements reveal direct bandgap of about 2 eV, which larger than our calculated 1.42 eV due to Burstein-Moss effect.
We show that the improper ferroelectric phase transition in multiferroic hexagonal manganites displays same symmetry-breaking characteristics as those proposed early-universe theories. present an analysis of Kibble-Zurek theory topological defect formation applied to manganites, discuss conditions determining range cooling rates which behavior is expected, and recent literature data are consistent with our predictions. explore experimentally for first time knowledge cross-over out regime...
We show that trivalent manganese, Mn(3+), imparts an intense blue color to oxides when it is introduced at dilution in trigonal bipyramidal coordination. Our optical measurements and first-principles density functional theory calculations indicate the results from absorption red/green region. This due turn a symmetry-allowed transition between valence-band maximum, composed of Mn 3d(x(2)-y(2),xy) states strongly hybridized with O 2p(x,y) states, narrow 3d(z(2))-based conduction-band minimum....
The complexation of mixtures cationic and anionic polymers to produce complex-coacervate phases is a subject fundamental importance colloid polymer science as well applications including drug delivery, sensing technologies, bio-inspired adhesives. Unfortunately the theoretical underpinnings complex coacervation are widely misunderstood conceptual mistakes have propagated in literature. Here, simple symmetric polyelectrolyte mixture model absence salt used discuss salient features phase...
The mechanism that leads to liquid-liquid phase separation (LLPS) of the tau protein, whose pathological aggregation is implicated in neurodegenerative disorders, not well understood. Establishing a diagram delineates boundaries co-existence key understanding whether LLPS an equilibrium or intermediate state. We demonstrate and RNA reversibly form complex coacervates. While can be fit analytical theory, more advanced model investigated through field theoretic simulations (FTS) provided...
We use self-consistent field theory (SCFT) to study the directed self-assembly of laterally confined diblock copolymers. In this study, we focus on systems in which self-assembled lamellae are oriented parallel selective sidewalls a channel. While well-ordered, perfect observed narrow channels both experimentally and numerically, undesirable defective structures also emerge. therefore investigate energetics two categories isolated defects (dislocations disclinations) for various segregation...
Brush block copolymers (BBCPs) enable the rapid fabrication of self-assembled one-dimensional photonic crystals with band gaps that are tunable in UV-vis-IR, where peak wavelength reflection scales molecular weight BBCPs. Due to difficulty synthesizing very large BBCPs, fidelity assembled lamellar nanostructures drastically erodes as domains become enough reflect IR light, severely limiting their performance optical filters. To overcome this challenge, short linear homopolymers used swell...
Significance By combining field-theoretic simulations and molecular-dynamics simulations, we show how the charge sequence of block polyampholytes affects their solution-phase behavior accessible chain conformations. We find a striking effect like length connectivity on self-coacervation or liquid–liquid phase separation. Charge patterning smaller lengthscales allows for more expanded configurations increased stability in dilute solution. These findings may provide insight into condensation...
We review the latest developments in computational methods for direct simulation of fully fluctuating field theories polymeric assemblies. In this context, we describe a newly developed theoretical and framework accurately computing fluctuation-corrected phase diagrams mesostructured polymer systems report first such complete diagram diblock copolymer melt. The method is based on complex Langevin sampling UV regularized field-theoretic model, with Helmholtz free energies computed using...
We report the phase behavior of a series poly(styrene)-b-poly(isoprene)-b-poly(styrene)′-b-poly(ethylene oxide) (SIS′O) tetrablock terpolymers. This study was motivated by self-consistent field theory (SCFT) calculations that anticipate rich array sphere-forming morphologies with variations in molecular symmetry parameter τ = NS/(NS + NS′), where N is block degree polymerization and volume fraction O less than about 0.22. Eight SIS′O samples, ranging from 0.21 to 0.73, were synthesized...
The effect of dispersity on block polymer self-assembly was studied in the monodisperse limit using a combination synthetic chemistry, matrix-assisted laser desorption ionization spectroscopy, and small-angle X-ray scattering. Oligo(methyl methacrylate) (oligoMMA) oligo(dimethylsiloxane) (oligoDMS) homopolymers were synthesized by conventional polymerization techniques purified to generate an array discrete, semidiscrete, disperse building blocks. Coupling reactions afforded oligo(DMS-MMA)...
We report the first simulations of nonsolvent-induced phase separation (NIPS) that predict membrane microstructures with graded asymmetric pore size distribution. In NIPS, a polymer solution film is immersed in nonsolvent bath, enriching nonsolvent, and leading to forms solid polymer-rich matrix polymer-poor pores. demonstrate how mass-transfer-induced spinodal decomposition, thermal fluctuations, glass-transition dynamics-implemented mobility contrast between phases-are essential formation...
The usual understanding in polymer electrolyte design is that an increase the dielectric constant results reduced ion aggregation and therefore increased ionic conductivity. We demonstrate here a class of polymers with extensive metal-ligand coordination tunable properties, extent delinked from systems considered comprise ether, butadiene, siloxane backbones grafted imidazole side-chains, dissolved Li+, Cu2+, or Zn2+ salts. nature probed using combination X-ray scattering, electron...
The grafting-through copolymerization of two distinct macromonomers via ring-opening metathesis polymerization is typically used to form statistical or diblock bottlebrush polymers with large total backbone degrees (NBB) relative that the side-chains (NSC). Here, we demonstrate Grubbs-type chemistry in opposite limit, namely NBB ≪ NSC, produces well-defined materials excellent control over ensemble-averaged properties, including molar mass, dispersity, composition, and number branch points....