scholarly journals Calculations of the Average Number of Radicals per Particle in Emulsion Polymerization

2021 ◽  
Vol 9 (VI) ◽  
pp. 1056-1059
Author(s):  
Aishwarya Tiwari
Keyword(s):  
Free Radicals ◽  
Emulsion Polymerization ◽  
Aqueous Phase ◽  
Recursion Relation ◽  
Time Dependent ◽  
Small Particles ◽  
Emulsion Polymerisation ◽  
Large Particles ◽  
Polymerization System ◽  
Number Of Particles

In emulsion polymerization, the free radicals enter the particles intermittently from the aqueous phase. The number of radicals per particleis given by the Smith-Ewart recursion relation which balances the rate of radical entry into, the rate of radical exit from and the rate of radical termination inside the particle. Models for emulsion polymerisation are based on the 0-1 kinetics or the pseudo-bulk kinetics. Small particles, low initiator concentrations and large number of particles favour the 0–1 kinetics, whereas the large particles, high initiator concentrations and small number of particles will favour pseudo-bulk kinetics. A given polymerization system may exhibit both these kinetic behaviours, initially following the 0-1 kinetics and during the later stages of polymerization following the pseudo-bulk kinetics. The aim of this work is to calculate the time dependent values of the average number of radicals per particle in emulsion polymerization for the pseudo-bulk kinetics.

Stereo Electron Microscopy Applied to High Resolution Freeze-Etch Replicas

1970 ◽  
Vol 28 ◽  
pp. 306-307
Author(s):  
L. Andrew Staehelin
Keyword(s):  
Electron Microscopy ◽  
Plastic Deformation ◽  
High Resolution ◽  
Smooth Surfaces ◽  
Small Particles ◽  
Membrane Surfaces ◽  
Wide Acceptance ◽  
New Information ◽  
Number Of Particles ◽  
Small Holes

Freeze-etched membranes usually appear as relatively smooth surfaces covered with numerous small particles and a few small holes (Fig. 1). In 1966 Branton (1“) suggested that these surfaces represent split inner mem¬brane faces and not true external membrane surfaces. His theory has now gained wide acceptance partly due to new information obtained from double replicas of freeze-cleaved specimens (2,3) and from freeze-etch experi¬ments with surface labeled membranes (4). While theses studies have fur¬ther substantiated the basic idea of membrane splitting and have shown clearly which membrane faces are complementary to each other, they have left the question open, why the replicated membrane faces usually exhibit con¬siderably fewer holes than particles. According to Branton's theory the number of holes should on the average equal the number of particles. The absence of these holes can be explained in either of two ways: a) it is possible that no holes are formed during the cleaving process e.g. due to plastic deformation (5); b) holes may arise during the cleaving process but remain undetected because of inadequate replication and microscope techniques.

Entry of free radicals into latex particles in emulsion polymerization

1991 ◽  
Vol 24 (7) ◽  
pp. 1629-1640 ◽  
Author(s):  
Ian A. Maxwell ◽  
Bradley R. Morrison ◽  
Donald H. Napper ◽  
Robert G. Gilbert
Keyword(s):  
Free Radicals ◽  
Emulsion Polymerization ◽  
Latex Particles

Structure of Microphase-Separated Silica/Siloxane Molecular Composites

1989 ◽  
Vol 171 ◽  
Author(s):  
Dale W. Schaefer ◽  
James E. Mark ◽  
David Mccarthy ◽  
Li Jian ◽  
C. -C. Sun ◽  
...  
Keyword(s):  
Phase Separation ◽  
Kinetic Studies ◽  
Organic Content ◽  
Small Particles ◽  
X Ray ◽  
Filled Elastomers ◽  
Polymeric Networks ◽  
Large Particles ◽  
Molecular Composites

ABSTRACTThe structure of several classes of silica/siloxane molecular composites is investigated using small-angle x-ray and neutron scattering. These filled elastomers can be prepared through different synthethic protocols leading to a range of fillers including particulates with both rough and smooth surfaces, particulates with dispersed interfaces, and polymeric networks. We also find examples of bicontinuous filler phases that we attribute to phase separation via spinodal decomposition. In-situ kinetic studies of particulate fillers show that the precipitate does not develop by conventional nucleation-and-growth. We see no evidence of growth by ripening whereby large particles grow by consumption of small particles. Rather, there appears to be a limiting size set by the elastomer network itself. Phase separation develops by continuous nucleation of particles and subsequent growth to the limiting size. We also briefly report studies of polymer-toughened glasses. In this case, we find no obvious correlation between organic content and structure.

Analysis of the Particles’ Movement Over the Flat and Profiled Rotating Discs surface in the Velocity Layer of the Viscous Gas

2021 ◽  
Vol 6 (2) ◽  
pp. 17-23
Author(s):  
Valeriy I. Pinakov ◽  
Konstantin V. Kulik ◽  
Boris E. Grinberg
Keyword(s):  
Qualitative Difference ◽  
Surface Region ◽  
Vertex Angle ◽  
Oscillation Regime ◽  
Small Particles ◽  
Magnus Force ◽  
Near Surface ◽  
Rotating Discs ◽  
Large Particles ◽  
Velocity Layer

Experiments on the rotating in the air cones with vertex angle β = 120º and flat disc shown that on frequencies Ω ≥ 2.5 hertz exists a qualitative difference in movement for the particles with diameters d ≈ 1 mm and d ≈ 0.1 mm. The particles with d ≈ 0.1 mm move in the near-surface region, the particles with d ≈ 1 mm jump up to 3 cm. Comparison of the spherical and aspheric (ellipsoid with axles d, d and 4 /3 d) particles' kinematics moving shown the inevitability of the large particles jump occurrence. Large particles come to self-oscillation regime by reason of periodically appearance of the Magnus force. Small particles are localized in the velocity layer

Unusual Phase Inversion Behavior in an Emulsion Polymerization System Caused by Ammonia

2010 ◽  
Vol 39 (3) ◽  
pp. 274-275 ◽  
Author(s):  
Mingxian Liu ◽  
Lihua Gan ◽  
Zijie Xu ◽  
Longwu Chen ◽  
Jun Hu ◽  
...  
Keyword(s):  
Emulsion Polymerization ◽  
Phase Inversion ◽  
Polymerization System

scholarly journals The design, instrumentation, and validation of a multiphase shock tube facility

2017 ◽  
Author(s):  
◽  
Constantine Gregory Avgoustopoulos
Keyword(s):  
Shock Tube ◽  
Quantitative Data ◽  
Velocity Difference ◽  
Gas Cylinder ◽  
First Case ◽  
Experimental Apparatus ◽  
Large Particles ◽  
Particle Imaging ◽  
Atwood Number ◽  
Number Of Particles

This paper investigates the experimental work in Shock Driven Multiphase Instabilities (SDMI). SDMIs occur when an interface consisting of a particle seeded gas is instantaneously accelerated and begins mixing. SDMIs have similar flow morphologies to the Richtmyer-Meshkov Instability (RMI), however, the driving force inducing this flow is very different. SDMIs occur when there is a relative velocity difference between surrounding gas and the moving particles. This results to a shear at the edges and ultimately leads to rollups that are similar to a RMI. To investigate this phenomena, a shock tube facility was designed, calibrated, and tested to perform experiments. The experimental data was qualitatively compared to simulations performed, as well as to literature of similar experiments. Quantitative data was analyzed using Particle Imaging Velocimetry (PIV) to understand the flow of the instability. The flow morphologies observed in experiments have similar behavior to those performed in simulations. Additionally, the qualitative observations of experiments performed in this lab are also in agreement with experimental literature. Two different effective Atwood numbers are investigated in this study. The first case looks at a gas cylinder interface with an effective Atwood number of -0.01 and a gas Atwood number of -0.02, shocked with a Mach 1.66 shock wave. The observations show a dominating instability resulting in the gas Atwood number. What ends up happening is the smaller particles are pulled into the vortex and the large particles separate and trail behind. The second case looks at the same gas cylinder perturbation but with an effective Atwood number of 0.03 and a gas Atwood number of 0, shocked at Mach 1.66. The higher Atwood number was achieved by modifying the experimental apparatus slightly to deliver a greater number of particles to the shock tube. The experiments observed show that there is agreement with literature and simulations. Certain unusual filaments begin forming at late times, 4.0ms after shock. This was thought to only appear in a pure RMI. In the case of a SDMI, these filaments are a result of colliding particles.

scholarly journals Gravitational differentiation in the regimes from stokes settling to Rayleigh–Raylor flows

2019 ◽  
pp. 15-30
Author(s):  
V. P. Trubitsyn
Keyword(s):  
Viscous Fluid ◽  
Interacting Particles ◽  
Small Particles ◽  
Continuous Transition ◽  
New Approach ◽  
Earth's Core ◽  
The Core ◽  
The Earth ◽  
Large Particles ◽  
Two Component

The Earth’s core was formed under gravitational differentiation in the course of the separation of iron and silicates. Most of the iron has gone into the core as early as when the Earth was growing. However, iron continued to precipitate even during the subsequent partial solidification which developed from the bottom upwards. At the different stages and in the different layers of the mantle, iron was deposited in different regimes. In this paper, the mechanisms of the deposition of a cloud of heavy interacting particles (or drops) in a viscous fluid are considered. A new approach suitable for analytical and numerical tracing the changes in the structure of the flows in a two-component suspension under continuous transition from the Stokessettling (for the case of a cloud of large particles) to the Rayleigh–Taylor flows and heavy diapirs (for the case of a cloud of small particles) is suggested. It is numerically and analytically shown that the both regimes are the different limiting cases of the sedimentation convection in suspensions.

scholarly journals Flow and fouling in a pleated membrane filter

2016 ◽  
Vol 795 ◽  
pp. 36-59 ◽  
Author(s):  
P. Sanaei ◽  
G. W. Richardson ◽  
T. Witelski ◽  
L. J. Cummings
Keyword(s):  
Membrane Fouling ◽  
Membrane Filter ◽  
Small Particles ◽  
Porous Support ◽  
Equal Area ◽  
Membrane Filters ◽  
Membrane Pores ◽  
Dead End ◽  
Large Particles ◽  
Membrane Geometry

Pleated membrane filters are widely used in many applications, and offer significantly better surface area to volume ratios than equal-area unpleated membrane filters. However, their filtration characteristics are markedly inferior to those of equivalent unpleated membrane filters in dead-end filtration. While several hypotheses have been advanced for this, one possibility is that the flow field induced by the pleating leads to spatially non-uniform fouling of the filter, which in turn degrades performance. In this paper we investigate this hypothesis by developing a simplified model for the flow and fouling within a pleated membrane filter. Our model accounts for the pleated membrane geometry (which affects the flow), for porous support layers surrounding the membrane, and for two membrane fouling mechanisms: (i) adsorption of very small particles within membrane pores; and (ii) blocking of entire pores by large particles. We use asymptotic techniques based on the small pleat aspect ratio to solve the model, and we compare solutions to those for the closest-equivalent unpleated filter.

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