Scattering of Light in Crystalline Polymers. I. Formation and Melting of the Crystalline Phase in Neoprene

1959 ◽  
Vol 32 (2) ◽  
pp. 463-470
Author(s):  
O. N. Trapeznikova ◽  
G. E. Smirnova
Keyword(s):  
Particle Size ◽  
Angular Distribution ◽  
Polarized Light ◽  
Melting Process ◽  
Spherical Particles ◽  
Scattering Method ◽  
Melting Range ◽  
Crystalline Polymers ◽  
Further Development

Abstract The process of formation and melting of neoprene crystallites was investigated by the polarized light scattering method. Conclusions about the nonreversibility of the crystallization and melting processes were drawn on the basis of angular distribution measurements of depolarized and polarized components of light scattered from polymer films. The appearance of a relatively small number of large crystallites is characteristic for the initiation of crystallization; further development of crystallization is accompanied by a decrease in the size of the crystallites. All crystallites disappear simultaneously during the melting process. The size of the crystallites determined by microphotography corresponds approximately to the particle size determined by the formula for isotropic, spherical particles. A method for the determination of the melting range of crystalline polymers is proposed.

Unusual liquid-solid transition effects in a methoxypentamethylflavan

1958 ◽  
Vol 243 (1235) ◽  
pp. 518-533 ◽  
Keyword(s):  
Solid Phase ◽  
Polarized Light ◽  
Melting Process ◽  
X Rays ◽  
Melting Range ◽  
Crystalline Materials ◽  
External Conditions ◽  
Transition Effects ◽  
Solid Liquid ◽  
Crystal Boundaries

The solid phase of the compound 2'-methoxy-2 : 4 : 4 : 7 : 4'- pentamethylflavan differs in many respects from normally crystalline materials, yet is not amorphous. It tends to form spherical masses which exhibit no regular crystal boundaries, even when seen under the microscope. The solid melts over a range of up to 3° C and the actual temperatures at which melting begins and ends vary according to the thermal treatment previously received by the specimen. The temperature at which the melt starts to solidify on cooling is always several degrees below the melting range; this is not due to normal supercooling. Solidification from the melt presents several other interesting features, including some rhythmic effects. Variations in the external conditions during solidification can give rise to three superficially different forms of the solid phase. The solid-liquid and liquid-solid transitions have been followed by measurements of density, rigidity and dielectric constant, all of which give further indications of the diffuse nature of the melting process and the existence of hysteresis between melting and solidifica­tion. These effects recall the behaviour of some crystalline high polymers and examination of solid methoxypentamethylflavan by polarized light, X-rays and electron microscopy has revealed further analogies with such materials. It is tentatively concluded that the solid is composed of submicroscopic crystalline regions which are organized into larger spherulitic aggregates, but no definite explanations of the failure of the compound to form macroscopic crystals or of the similarities between it and polymers seem possible at present.

Determination of Particle Size of a Dispersed Phase by Small-Angle X-ray Scattering

1989 ◽  
Vol 171 ◽  
Author(s):  
Frank C. Wilson
Keyword(s):  
Particle Size ◽  
High Resolution ◽  
Spherical Particles ◽  
Dispersed Phase ◽  
X Ray ◽  
X Ray Scattering ◽  
Resultant Data ◽  
Log Normal ◽  
Log Normal Distribution

ABSTRACTA method for determining particle diameters up to ca 500 rnm is described. X-ray data are obtained with an ultra-high resolution Bonse-Hart diffractometer and subsequently desmeared. The resultant data, viewed as the invariant argument h l(h), are interpreted as arising from a log-normal distribution of independent spherical particles. The distribution is characterized by its median value and breadth.

Determination of Particle-Size Distribution and Concentration of Cigarette Smoke by a Light-Scattering Method

1977 ◽  
Vol 9 (3) ◽  
Author(s):  
T. Okada ◽  
Y. Ishizu ◽  
K. Matsunuma
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Cigarette Smoke ◽  
Scattered Light ◽  
Geometric Mean ◽  
Number Concentration ◽  
Scattering Method ◽  
Working Standard

AbstractA new method for determining particle-size distribution of cigarette smoke particles was developed by simultaneous measurement of scattered light at three angles for a fixed wavelength. A theoretical chart useful for this purpose, which was made of the relative intensities of scattered light at the angles 45° and 135° to that at the angle 90°, was calculated on the basis of the Mie theory. The number concentration was determined from the Rayleigh ratio using the working standard method. The measurements were rapidly performed, without change of particle size during measuring time, with a device for dilution. The geometric mean diameter, the logarithmic standard deviation and the number concentration of mainstream smoke were found to be about 0.18 um, 0.4 and 3 X 10

scholarly journals Determination of properties of non-spherical VT20 alloy powders for modelling packing density

2020 ◽  
Vol 96 (4) ◽  
pp. 56-63
Author(s):  
Z.A. Duriagina ◽  
◽  
I.A. Lemishka ◽  
V.V. Kulyk ◽  
H.A. Hrydova ◽  
...  
Keyword(s):  
Particle Size ◽  
Titanium Alloy ◽  
Packing Density ◽  
Alloy Powder ◽  
Fractional Composition ◽  
Spherical Particles ◽  
Vt20 Alloy ◽  
Powder Particles ◽  
Vt20 Titanium Alloy

The study of unfavorable titanium alloy powders of VT20 grades was carried out and the methods of computer analysis were applied to determine the parameters of their optimal packaging. Metallographic studies were performed on a scanning electron microscope EVO-40XVP, and elemental analysis was performed using an energy dispersion spectrometer OXFORD INCA Energy 350. Determination of particle size distribution of powders was performed using image analysis software ImageJ. The surface morphology of non-spherical particles of VT20 alloy powder was studied for three different fractions: 100 ... 160 μm, 160 ... 200 μm and 200 ... 250 μm. It is shown that the powder particles are characterized by a nonspherical shape and a small difference in size. There is a tendency according to which when the particle size of the powder of the investigated alloy decreases, their shape approaches spherical. According to the results of particle size analysis, it was found that the usual sieve analysis does not allow to fully assess the distribution of powder by fractions. It was found that for the fraction 200 ... 250 μm the dominant particles are with an average diameter of 226 μm, for the fraction 160 ... 200 μm - 177 μm and for the fraction 100 ... 160 μm - 114 μm, respectively. Thus, for the fraction of titanium powder of the BT20 brand 200 ... 250 the polydispersity is 6.4%, for the fraction 160 ... 200 - 8.3%, and for the fraction 100 ... 160 - 9.1%. It is established that the fluidity of titanium alloy powders of the BT20 brand is: for the fraction 200 ... 250 μm - 62.35 s, for the fraction 160 ... 200 μm - 65.44 s, and for the fraction 100 ... 160 - 68, 73 s. That is, the highest value of fluidity is characterized by the powder with the largest particle size. Simulation of the pre-defined volume filling was performed using the "Spheres test" program. The average radii of particles of VT20 titanium alloy powder particles and the probability of the sizes of each of fractions of powder which is necessary at filling of the set volume was calculatedthe possibility of their precipitation have been established. Based on the obtained results, the packing density of VT20 titanium alloy powders was calculated depending on their fractional composition. It is confirmed that as the particle size of the powder decreases, their packing density increases. The surface morphology of non-spherical particles of VT20 alloy powder of different fractional composition and their particle size characteristics were studied. It is shown that with decreasing fractional composition of powder fractions, their homogeneity and bulk density increase. It was found that finer fractions are characterized by poorer fluidity. The simulation results determine the optimal fractional composition of the powder to fill the pre-specified volume. It is shown that as the size of the test particles decreases, their packing density increases. Keywords: additive production, titanium, microstructure, particle size distribution, bulk density, fluidity, packing density modelingmodelling.

scholarly journals Determination of particle size by using the angular distribution of backscattered light as measured with low-coherence interferometry

2002 ◽  
Vol 19 (4) ◽  
pp. 737 ◽  
Author(s):  
Adam Wax ◽  
Changhuei Yang ◽  
Vadim Backman ◽  
Maxim Kalashnikov ◽  
Ramachandra R. Dasari ◽  
...  
Keyword(s):  
Particle Size ◽  
Angular Distribution ◽  
Low Coherence ◽  
Low Coherence Interferometry
Sign in / Sign up

Export Citation Format

Share Document