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Visit Vao-soongnern - One of the best experts on this subject based on the ideXlab platform.
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Molecular simulation and experimental studies of the miscibility of PLA/PLA_x-PEG_y-PLA_x blends
Journal of Polymer Research, 2017Co-Authors: Adisak Takhulee, Yoshiaki Takahashi, Visit Vao-soongnernAbstract:To design a more efficient plasticizer for PLA based on PEG derivative, the miscibility enhancement of PLA/PLA_x-PEG_y-PLA_x blends were investigated by both atomistic and mesoscale simulations. Flory-Huggins interaction parameters ( χ _ ij ) of PLA_x-PEG_y-PLA_x blends, with PLA block fractions = 0.1–0.5, were calculated using molecular Dynamic (MD) simulation to determine the miscibility of PLA/PLA_x-PEG_y-PLA_x blends and compared with PLA/PEG blends (Takhulee et al. J Polym Res 24:8, 2017 ). Based on the calculated χ _ ij and radial distribution functions, PLA/PLA_x-PEG_y-PLA_x showed better miscibility compared to PLA/PEG. The values of χ _ ij for PLA/PLA_x-PEG_y-PLA_x blends are always lower than those for PLA/PEG blends at the same PEG composition. For PLA/PLA_x-PEG_y-PLA_x blends, χ _ ij increased as a function of PLA block fractions. Mesoscale properties of PLA/ PLA_x-PEG_y-PLA_x blends were then determined using dissipative Particle Dynamic (DPD) simulation. Smaller PEG domain in PLA/PLA_x-PEG_y-PLA_x blends was observed, compared to that in PLA/PEG blend. Miscibility behavior of PLA/PLA_x-PEG_y-PLA_x blends was investigated by experiments at selected conditions based on the simulation results. By differential scanning calorimetry measurements, acceleration of the crystallization of PLA matrix by blending PLA_x-PEG_y-PLA_x was observed. Although PLA/PEG 70/30 (wt/wt) blend was phase separated when slowly cooled from the melt, due to the crystallization of PEG component, this phenomenon was not observed in PLA/PLA_x-PEG_y-PLA_x blends. The melting temperature ( T _ m ) depression of PLA/PLA_x-PEG_y-PLA_x blends was also more pronounced. From Dynamic mechanical analysis, the storage (G′) and loss moduli (G′′) curves in terminal region were determined. The slope of G′ curves for PLA/PEG 75/25 and 70/30 (wt/wt) was less than 2 while this deviation was found only at 70/30 (wt/wt) for PLA/PLA_x-PEG_y-PLA_x. These results indicate that PLA_x-PEG_y-PLA_x is better miscible with PLA.
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Mesoscale simulation and experimental studies of self-assembly behavior of a PLA-PEG-PLA triblock copolymer micelle for sustained drug delivery
Journal of Polymer Research, 2014Co-Authors: Mantana Chansuna, Nuttaporn Pimpha, Visit Vao-soongnernAbstract:Dissipative Particle Dynamic simulation (DPD) was employed to investigate PLA-PEG-PLA copolymer micelles to gain more understanding at the molecular level in addition to experimental studies. Critical micelle concentration ( cmc ), micelle size and small molecule encapsulation of these triblock copolymer micelles with different hydrophobic/hydrophilic (LA/EG) block ratios (2.56, 4.88 and 7.25 with fixed PEG length = 23 monomer units) were determined. Only the appropriated LA/EG block ratio (4.88 and 7.25) can induce the formation of spherical micelle in a dilute solution. The cmc and micelle size were decreased and increased, respectively, as a function of the LA/EG block ratio. Upon adding small solubilizate molecules, a larger micelle size was formed. Then, PLA-PEG-PLA with the same LA/EG block ratios as DPD simulation were synthesized and the micelle solution was prepared. Pyrene was used as the molecular probe to find the cmc by fluorescence spectroscopy. Light scattering was applied to determine the hydroDynamic radius ( R _ H ) of these micelles. The cmc and R_H were decreased and increased, respectively, with LA/EG ratio, qualitatively similar to the trends as simulation results. The behavior of these copolymer micelles to encapsulate the small solubilizate molecules was also studied by fluorescence technique. The partition coefficients of pyrene between the water phase and the micelle core were increased with a higher LA/EG block ratio similar to results from the simulation.
Carlos A Zuritz - One of the best experts on this subject based on the ideXlab platform.
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mathematical modeling of solid liquid two phase tube flow an application to aseptic processing
Journal of Food Process Engineering, 1995Co-Authors: Yansheng Liu, Carlos A ZuritzAbstract:The sizing of holding tubes for continuous sterilization of foods containing large Particles is affected by the flow behavior of the suspensions. Velocities of carrier fluid and model food Particles in holding tube flow were numerically simulated through an iterative solution of the Navier-Stokes equations and Particle Dynamic equations in three dimensions. the Lagrangian approach was used to predict the individual Particle trajectories under multiParticle tube flow. the physical domain included two straight tubes connected with a 180° bend. the system had an upward inclination of 1.194° (0.25 in./ft of straight run). the assumptions considered included Newtonian carrier, spherical and neutrally buoyant Particles, and 10% v/v Particle loading. the results indicate that the Particles have a significant back-influence on the fluid flow field. the 180° bend strongly affected both fluid and Particle flow fields, which further reinforced the interaction of the two phases. the fastest Particle velocities were less than the fluid streamline velocities passing through the Particles' center. the radial positions of the Particles on the cross section of the holding tube changed very little in the first straight section, but experienced a significant shifting in the bend and second straight-tube sections due to secondary flow. the residence times of Particles under secondary-flow effect are therefore different from those obtained under straight tube-only flow.
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MATHEMATICAL MODELING of SOLID‐LIQUID TWO PHASE TUBE FLOW: an APPLICATION to ASEPTIC PROCESSING
Journal of Food Process Engineering, 1995Co-Authors: Yansheng Liu, Carlos A ZuritzAbstract:The sizing of holding tubes for continuous sterilization of foods containing large Particles is affected by the flow behavior of the suspensions. Velocities of carrier fluid and model food Particles in holding tube flow were numerically simulated through an iterative solution of the Navier-Stokes equations and Particle Dynamic equations in three dimensions. the Lagrangian approach was used to predict the individual Particle trajectories under multiParticle tube flow. the physical domain included two straight tubes connected with a 180° bend. the system had an upward inclination of 1.194° (0.25 in./ft of straight run). the assumptions considered included Newtonian carrier, spherical and neutrally buoyant Particles, and 10% v/v Particle loading. the results indicate that the Particles have a significant back-influence on the fluid flow field. the 180° bend strongly affected both fluid and Particle flow fields, which further reinforced the interaction of the two phases. the fastest Particle velocities were less than the fluid streamline velocities passing through the Particles' center. the radial positions of the Particles on the cross section of the holding tube changed very little in the first straight section, but experienced a significant shifting in the bend and second straight-tube sections due to secondary flow. the residence times of Particles under secondary-flow effect are therefore different from those obtained under straight tube-only flow.
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MATHEMATICAL MODELING of PARTICULATE TWO-PHASE FLOW IN A HELICAL PIPE
Journal of Food Process Engineering, 1995Co-Authors: Yansheng Liu, Carlos A ZuritzAbstract:The design of helical tubes for continuous sterilization of low-acid foods (pH > 4.6) containing large discrete Particles depends on the knowledge of the flow behavior of the suspended Particles. The flow behavior of a carrier fluid with suspended solid spherical Particles in a helical tube was numerically simulated through an iterative solution of the Navier-Stokes equations and the Particle Dynamic equations in three dimensions. The Lagrangian approach was used to predict the individual Particle velocities and trajectories under solid-liquid two-phase flow situation. The results indicate that the residence time distribution of the Particles in helical tube flow was narrower than in a conventional holding tube (consisting of two straight tubes connected with a 180° bend). Also, the average velocity of the Particles was closer to the average velocity of the carrier fluid in the helical tubes. The secondary flow induced by the tube curvature greatly reduced the axial dispersion of the Particles. There was a substantial Particle influence on the fluid flow field, The pressure drop in helical tube was 18% higher for single-phase flow and 51% higher for two-phase flow than in conventional holding tube of equal length.
Yaxin Su - One of the best experts on this subject based on the ideXlab platform.
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experimental study on the gas solid suspension flow in a square cyclone separator
Chemical Engineering Journal, 2006Co-Authors: Yaxin SuAbstract:Abstract A three-dimensional Particle Dynamic analyzer (3D-PDA) was employed to measure the gas–solid two-phase flow in a lab-scale square cyclone separator with downward gas-exit. Several cases of different inlet velocity and Particle concentration were studied. The Particle used in the test was glass bead of mean diameter 30–40 μm. Discussion was given on the distribution of flow vector, mean velocity, turbulent intensity and kinetic energy of both gas and Particles of different diameter at different position in the separator. It was found that the center of the flow field deviated from the geometric center of the cyclone. The flow fields had the feature of Rankine eddy, i.e., strongly swirling region in the central part and pseudo-free eddy region of weak swirling intensity near the cyclone wall. Local vortex existed at the corners where the flow changed its direction sharply. When the cyclone wall was heated and the suspension temperature was elevated, the flow field became more uniform than that under room-temperature condition. The local vortexes at the corners were weakened and the swirling intensity became poorer which led to decreased total mean separation efficiency from about 81% to 76.5%. The right-side wall facing the suspension inlet gave the major contribution to the separation efficiency, where the largest downward velocity was measured. Back-flow (upward velocity) was found around the center of the separator above the gas-exit. The quasi-laminar motion of Particles enhanced the turbulent motion at the corners due to Particle–Particle or Particle-wall collision, which led to the local peak value of the turbulent kinetic energy and turbulent intensity. The corner was one of the major regions to cause pressure drop and was found to be beneficial to Particle separation mainly because the strong fluctuating flow consumed much of the kinetic energy of both the Particle and gas.
Haw Yang - One of the best experts on this subject based on the ideXlab platform.
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Determining the Spheroid Geometry of Individual Metallic NanoParticles by Two-Dimensional Single-Particle Dynamic Light Scattering
The Journal of Physical Chemistry C, 2019Co-Authors: Luis F. Guerra, Tom W. Muir, Haw YangAbstract:Single-Particle Dynamic light scattering (SP-DLS) is a recently developed technique that uses dark-field illumination, active real-time three-dimensional single-Particle tracking, and measurements of scattered photon polarizations to nonperturbatively evaluate the shapes of single, freely diffusing Particles under the assumption of the Particle having either prolate or oblate spheroid geometry. As originally developed, however, SP-DLS is incapable of unambiguously assigning either of these geometries to a single Particle. In this contribution, we resolve this ambiguity by introducing a second experimental observable—the scattering spectrum—so that both the scattering polarization and spectrum are simultaneously recorded and analyzed. We used numerical simulations of SP-DLS to characterize the performance of this new approach as well as the effects of key experimental parameters. We anticipate that the analyses presented here will not only form a straightforward guide for researchers seeking to optimize th...
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Single-Particle Dynamic Light Scattering: Shapes of Individual NanoParticles.
Nano Letters, 2019Co-Authors: Luis F. Guerra, Tom W. Muir, Haw YangAbstract:Metallic nanoParticles (MNPs) are prevalent in modern nanotechnologies due to their unique optical properties, chemical and photostability, and ease of manipulation. In particular, many recent adva...
Zhibao Dong - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of the concentration profile of a blowing sand cloud
Geomorphology, 2004Co-Authors: Zhibao DongAbstract:Abstract Detailed wind tunnel tests were carried out to establish the mean downwind velocity and transport rate of different-sized loose dry sand at different free-stream wind velocities and heights, as well as to investigate the vertical variation in the concentration of blowing sand in a cloud. Particle Dynamic analyzer (PDA) technology was used to measure the vertical variation in mean downwind velocity of a sand cloud in a wind tunnel. The results reveal that within the near-surface layer, the decay of blown sand flux with height can be expressed using an exponential function. In general, the mean downwind velocity increases with height and free-stream wind velocity, but decreases with grain size. The vertical variation in mean downwind velocity can be expressed by a power function. The concentration profile of sand within the saltation layer, calculated according to its flux profile and mean downwind profile, can be expressed using the exponential function: cz=ae−bz, where cz is the blown sand concentration at height z, and a and bare parameters changing regularly with wind velocity and sand size. The concentration profiles are converted to rays of straight lines by plotting logarithmic concentration values against height. The slope of the straight lines, representing the relative decay rate of concentration with height, decreases with an increase in free-stream wind velocity and grain size, implying that more blown sand is transported to greater heights as grain size and wind speed increase.