Scalable Formation of Concentrated Monodisperse Lignin Nanoparticles by Recirculation-Enhanced Flash Nanoprecipitation

A highly controllable and scalable process for fabrication of large amounts of concentrated lignin nanoparticles (LNPs) is reported. These lignin core nanoparticles are formed through flash nanoprecipitation, however, scaling up of the fabrication process requires fundamental understanding of their operational formation mechanism and surface properties. It is shown how a semicontinuous synthesis system with a recirculation loop makes it possible to produce flash precipitated lignin nanoparticles in large amounts for practical applications. The roles of the process parameters, including flow rates and lignin concentration, are investigated and analyzed. The results indicate that the LNPs are formed by a process of continuous burst nucleation at the point of mixing without diffusive growth, which yields nanoparticles of highly uniform size following a modified LaMer nucleation and growth mechanism. This mechanism makes possible facile process control and scale-up. Effective control of the resulting nanoparticle size is achieved through the initial concentration of lignin in the injected solution. The impressive capability to produce suspensions of any predesigned multimodal distribution is demonstrated. The resulting nanofabrication technique can produce large volumes of concentrated LNP suspensions of high stability and tightly controlled size distributions for biological or agricultural applications.     

Negative spin polarization and large tunneling magnetoresistance in epitaxial Co/SrTiO(3)/Co magnetic tunnel junctions

We perform an ab initio study of spin-polarized tunneling in epitaxial Co/SrTiO(3)/Co magnetic tunnel junctions with bcc Co(001) electrodes. We predict a large tunneling magnetoresistance in these junctions, originating from a mismatch in the majority- and minority-spin bands both in bulk bcc Co and at the Co/SrTiO(3)/Co interface. The intricate complex band structure of SrTiO(3) enables efficient tunneling of the minority d electrons which causes the spin polarization of the Co/SrTiO(3)/Co interface to be negative in agreement with experimental data. Our results indicate that epitaxial Co/SrTiO(3)/Co magnetic tunnel junctions with bcc Co(001) electrodes are a viable alternative for device applications.     

Measurement of the decay amplitudes of B0 --> J/psiK*0 and B(s)(0) --> J/psistraight phi decays

An angular analysis of B0-->J/psiK(*0) and B(0)(s)-->J/psistraight phi has been used to determine the decay amplitudes with parity-even longitudinal ( A0) and transverse ( A( parallel)) polarization and parity-odd transverse ( A( perpendicular)) polarization. The measurements are based on 190 B0 and 40 B(0)(s) candidates obtained from 89 pb(-1) of &pmacr;p collisions at the Fermilab Tevatron. The longitudinal decay amplitude dominates with |A0|(2) = 0.59+/-0. 06+/-0.01 for B0 and |A0|(2) = 0.61+/-0.14+/-0.02 for B(0)(s) decays. The parity-odd amplitude is found to be small with |A( perpendicular)|(2) = 0.13(+0.12)(-0.09)+/-0.06 for B0 and |A( perpendicular)|(2) = 0.23+/-0.19+/-0.04 for B(0)(s) decays.     

Measurement of b-quark fragmentation fractions in p&pmacr; collisions at sqrt

We have studied the production of B hadrons in 1.8-TeV pp[over ˉ] collisions. We present measurements of the fragmentation fractions, f_{u}, f_{d}, f_{s}, and f_{baryon}, of produced b quarks that yield B^{+}, B^{0}, B_{s}^{0}, and Λ[over ˉ]_{b}^{0} hadrons. Reconstruction of five electron-charm final states yields f_{s}/( f_{u}+f_{d})=0.213±0.068 and f_{baryon}/( f_{u}+f_{d})=0.118±0.042, assuming f_{u}=f_{d}. If all B hadrons produced in pp[over ˉ] collisions cascade to one of these four hadrons, we determine f_{u}=f_{d}=0.375±0.023, f_{s}=0.160±0.044, and f_{baryon}=0.090±0.029. If we do not assume f_{u}=f_{d}, we find f_{d}/f_{u}=0.84±0.16.     

Search for new particles decaying to t&tmacr; in p&pmacr; collisions at radicals = 1.8 TeV

We use 106 pb (-1) of data collected with the Collider Detector at Fermilab to search for narrow-width, vector particles decaying to a top and an antitop quark. Model independent upper limits on the cross section for narrow, vector resonances decaying to t&tmacr; are presented. At the 95% confidence level, we exclude the existence of a leptophobic Z' boson in a model of top-color-assisted technicolor with mass M(Z')<480 GeV/c(2) for natural width gamma = 0.012M(Z'), and M(Z')<780 GeV/c(2) for gamma = 0.04M(Z').     

Search for second and third generation leptoquarks including production via technicolor interactions in p&pmacr; collisions at radicals = 1.8 TeV

We report the results of a search for second and third generation leptoquarks using 88 pb(-1) of data recorded by the Collider Detector at Fermilab. Color triplet technipions, which play the role of scalar leptoquarks, are investigated due to their potential production in decays of strongly coupled color octet technirhos. Events with a signature of two heavy flavor jets and missing energy may indicate the decay of a second (third) generation leptoquark to a charm (bottom) quark and a neutrino. As the data are found to be consistent with standard model expectations, mass limits are determined.     

Controlled, rapid deposition of structured coatings from micro- and nanoparticle suspensions

The objective of the study was to develop the operational basis for rapid and controlled deposition of crystal coatings from particles of a wide size range. We deposited such structured coatings by dragging with constant velocity a small volume of liquid confined in a meniscus between two plates. Two types of structured coatings were characterized: latex colloidal crystals and thin layers from metallic nanoparticles. The crystal deposition was sped up by use of preconcentrated suspensions. Crystal coatings larger than a few square centimeters were deposited in minutes from aqueous suspension volumes of approximately 10 microL. The governing mechanism of crystal deposition is convective assembly at high volume fractions. The two major process parameters that allow control over the coating thickness and structure were the deposition speed and particle volume fraction. The evaporation rate was not found to affect the process to a large extent. A volumetric flux balance was used to relate the deposition parameters to coating structure and properties. Operational "phase" diagrams were constructed, relating the crystal layer thickness and packing symmetry to the process parameters. These diagrams could be instrumental in transforming the convective colloidal deposition into a robust scaleable technology.     

Control and modeling of the dielectrophoretic assembly of on-chip nanoparticle wires

Suspensions of metallic nanoparticles in water were assembled via the action of an alternating electric field (dielectrophoresis) into wires of micrometer thickness. Two modes of microwire assembly, one through the bulk of the suspension and one as half-cylinders on the glass surface between the electrodes, were identified. The operating conditions responsible for the two assembly modes were recognized. The control of the process parameters allows making, for example, straight single connectors or massively parallel arrays of microwires on the surface of the chip, which can be extracted in dry form. The microwire assembly process was modeled using finite element electrostatic calculations. The direction of growth can be guided by introducing conductive islands or particles in the suspension. The experiments, supported by electrostatic calculations, show that the wires grow in the direction of highest field intensity, "automatically" making electrical connections to the objects between the electrodes. The results point the way to controlled dielectrophoretic assembly of nanoparticles into on-chip electrical connectors, switches, and networks.     

Magnetically responsive pickering foams

We introduce a new class of Pickering foams which can be manipulated using a magnetic field. These foams are stabilized by a mixture of magnetic and nonmagnetic particles. They exhibit excellent stability in the absence of a magnetic field, but can be rapidly destroyed on demand with the application of a threshold field. We characterize their stability in the absence of a magnetic field by measuring the rate of water drainage from the foam as a function of time. We also correlate their collapse behavior under a magnetic field to the foam liquid fraction, as well as the concentration of magnetic particles in the foam. This novel system can be used to study the properties of Pickering foams, and has potential applications in noncontact defoaming processes.     

Effect of ferroelectricity on electron transport in Pt/BaTiO3/Pt tunnel junctions

Based on first-principles calculations, we demonstrate the impact of the electric polarization on electron transport in ferroelectric tunnel junctions (FTJs). Using a Pt/BaTiO3/Pt FTJ as a model system, we show that the polarization of the BaTiO3 barrier leads to a substantial drop in the tunneling conductance due to changes in the electronic structure driven by ferroelectric displacements. We find a sizable change in the transmission probability across the Pt/BaTiO3 interface with polarization reversal, a signature of the electroresistance effect. These results reveal exciting prospects that FTJs offer as resistive switches in nanoscale electronic devices.