Non-equilibrium particle morphology in dispersion-polymerized polystyrene particles

1995 ◽  
Vol 73 (11) ◽  
pp. 1747-1756 ◽  
Author(s):  
Anthony J. Paine ◽  
Richard R. Shivers
Keyword(s):  
Freeze Fracture ◽  
Particle Morphology ◽  
Particle Growth ◽  
Equilibrium Structure ◽  
Polymer Chains ◽  
Small Particles ◽  
Transmission Electron ◽  
Large Particles ◽  
Equilibrium Morphology ◽  
Non Equilibrium

The interior particle morphology of dispersion-polymerized polystyrene particles was investigated by freeze fracture TEM (FFTEM) in order to compare the morphology of particles formed under two extreme mechanistic conditions: (a) particle growth by scavenging of dead polymer chains formed in solution (which gives rise to large particles of 5–10 μm) and (b) particle growth by oligomeric radical capture and polymerization inside the particle (giving rise to small particles of 1 μm or less). Although not generally recognized in the literature, ascribing mechanistic significance to an observed morphology requires a demonstration that the morphology is of the non-equilibrium type, i.e., the morphology depends upon how the particle was formed. An equilibrium morphology, by definition, must be independent of the particle formation route, and therefore carries no mechanistic information. In this case, large PS particles of 6.5 μm were found to have a nodular morphology that was unchanged on heating well above Tg, indicating an equilibrium structure (the nodularity of amorphous polymers is briefly rationalized by comparison with literature results over the past 20 years). On the other hand, small PS particles of 1.3 μm had a pronounced radial structure that could be converted into the nodular morphology by the same heat treatment, or by dissolving and precipitating from a suitable solvent combination. This means that the small particles have a non-equilibrium morphology, from which we may attempt to draw mechanistic inferences consistent with the suspected growth mechanism. Keywords: dispersion-polymerized polystyrene, non-equilibrium polystyrene particle morphology, freeze fracture transmission electron microscopy.

Cryomicroscopy of multiphase latices

1991 ◽  
Vol 49 ◽  
pp. 1060-1061
Author(s):  
O. L. Shaffer ◽  
M.S. El-Aasser ◽  
C. L. Zhao ◽  
M. A. Winnik ◽  
R. R. Shivers
Keyword(s):  
Electron Microscopy ◽  
Radiation Damage ◽  
Freeze Fracture ◽  
Particle Morphology ◽  
Second Stage ◽  
Transmission Electron ◽  
Important Approach ◽  
Carbon Coated ◽  
Preparation Techniques

Transmission electron microscopy is an important approach to the characterization of the morphology of multiphase latices. Various sample preparation techniques have been applied to multiphase latices such as OsO4, RuO4 and CsOH stains to distinguish the polymer phases or domains. Radiation damage by an electron beam of latices imbedded in ice has also been used as a technique to study particle morphology. Further studies have been developed in the use of freeze-fracture and the effect of differential radiation damage at liquid nitrogen temperatures of the latex particles embedded in ice and not embedded.Two different series of two-stage latices were prepared with (1) a poly(methyl methacrylate) (PMMA) seed and poly(styrene) (PS) second stage; (2) a PS seed and PMMA second stage. Both series have varying amounts of second-stage monomer which was added to the seed latex semicontinuously. A drop of diluted latex was placed on a 200-mesh Formvar-carbon coated copper grid.

Planar Defects in Small Particles

1985 ◽  
Vol 43 ◽  
pp. 392-393
Author(s):  
R. Pérez ◽  
M. Avalos-Borja
Keyword(s):  
Stacking Faults ◽  
Particle Growth ◽  
Small Particles ◽  
Planar Defects ◽  
Metallic Particles ◽  
Weak Beam ◽  
Transmission Electron ◽  
Imaging Conditions

Transmission electron microscope techniques have been extensively used in the determination of the morphology of fine metallic particles. These techniques have been of particular importance in obtaining topographical information during particle growth and sintering. Thus, for example, it has been found that some of the most elementary forms consist of half cubo-octahedral units with (111) faces and (100) basis. Furthermore, full cubo-octahedral units have also been found, some of them showing stacking faults (SF) through the particles.It is important to point out that the characterization of this type of planar defects in small metallic particles has commonly been based on geometrical con. siderations. Additionally, the imaging conditions which have been used are the so-called weak beam (WB) diffraction conditions. Recent investigations have shown, on the other hand, that SF images under WB conditions present serious inconveniences, for example, contrast asymmetries in SF images which are not totally explained. Another difficulty with these WB fault images arises from twin boundaries which display image contrast similar to SF when a common reflection is strongly excited.

Characteristics of fine pores in some halloysites

Clay Minerals ◽  
1995 ◽  
Vol 30 (2) ◽  
pp. 89-98 ◽  
Author(s):  
G. J. Churchman ◽  
T. J. Davy ◽  
L. A. G. Aylmore ◽  
R. J. Gilkes ◽  
P. G. Self
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
New Zealand ◽  
Nitrogen Adsorption ◽  
Size Distributions ◽  
Small Particles ◽  
Transmission Electron ◽  
Cylindrical Pores ◽  
Large Particles ◽  
Nm Range

AbstractIsotherms were obtained for nitrogen adsorption and desorption on seven halloysite-rich samples from New Zealand and Western Australia. Calculations from these isotherms indicate that halloysites with mainly small particles (<c. 0.08 μm in width) had abundant cylindrical pores with narrow size distributions in the 5-15 nm range. They also indicate that halloysites with mainly large particles (>c. 0.1 μm in width) had few if any pores in the mesopore range (2–50 nm). Transmission electron microscopy (TEM) shows that cylindrical pores originate from the central holes in tubular particles. The TEM also suggests that slit-shaped pores can originate from the shrinkage of blocks of layers upon dehydration of halloysite.

scholarly journals Freeze-fracture studies of frog neuromuscular junctions during intense release of neurotransmitter. III. A morphometric analysis of the number and diameter of intramembrane particles.

1980 ◽  
Vol 85 (2) ◽  
pp. 337-345 ◽  
Author(s):  
R Fesce ◽  
F Grohovaz ◽  
W P Hurlbut ◽  
B Ceccarelli
Keyword(s):  
Synaptic Vesicles ◽  
Neuromuscular Junctions ◽  
Freeze Fracture ◽  
Presynaptic Membrane ◽  
Small Particles ◽  
Vesicle Membrane ◽  
Intramembrane Particles ◽  
Large Particles ◽  
Black Widow Spider Venom ◽  
Indirect Stimulation

The intramembrane particles on the presynaptic membrane and on the membrane of synaptic vesicles were studied at freeze-fractured neuromuscular junctions of the frog. The particles on the P face of the presynaptic membrane belong to two major classes: small particles with diameters less than 9 nm and large particles with diameters between 9 and 13 nm. In addition, there were a few extralarge particles with diameters greater than 13 nm. Indirect stimulation of the muscle, or the application of black widow spider venom, decreased the concentration of small particles on the presynaptic membrane but did not change the concentration of large particles. Three similar classes of particles were found on the P face of the membrane of the synaptic vesicles. The concentrations of large and extralarge particles on the vesicle membrane were comparable to the concentrations of these particles on the presynaptic membrane, whereas the concentration of small particles on the vesicle membrane was less than than the concentration of small particles on the presynaptic membrane. These results are compatible with the idea that synaptic vesicles fuse with the presynaptic membrane when quanta of transmitter are released. However, neither the large nor the extralarge particles on the P face of the presynaptic membrane can be used to trace the movement of vesicle membrane that has been incorporated into the axolemma.

scholarly journals Abstract P-42: Structure of Hydrogels of an Anionic Polysaccharide Studied by Freeze-Fracture Transmission Electron Microscopy

2021 ◽  
Vol 11 (Suppl_1) ◽  
pp. S30-S31
Author(s):  
Andrey Shibaev ◽  
Maria Smirnova ◽  
Olga Philippova ◽  
Vladimir Matveev ◽  
Anatoly Chalykh
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Liquid Nitrogen ◽  
Freeze Fracture ◽  
Mesh Size ◽  
Polymer Chains ◽  
Self Healing ◽  
Polymer Backbone ◽  
Transmission Electron ◽  
Cross Linker

Background: Polysaccharide hydrogels draw attention due to the ability to form mechanically tough gels at low concentrations (typically 1 wt% or lower), combined with biocompatibility and biodegradability. Biopolymer hydrogels can be used as a matrix for cell growth, in order to obtain materials for the replacement of damaged tissues. “Physical” gels with macromolecules cross-linked by dynamic reversible cross-links are of great interest due to their self-healing ability. However, investigation of the native un-perturbed structure of such hydrogels presents a challenge, since they collapse upon drying, and present a difficulty for preparing a thin specimen for cryo-TEM experiments due to very high viscosity. The aim of this work is to study the native structure of hydrogels of an anionic polysaccharide – carboxymethyl hydroxypropyl guar (CMHPG) – cross-linked by borax. Methods: Freeze-fracture transmission electron microscopy (FF-TEM) was conducted on a Phillips EM-301 microscope. A small volume of the sample (100 μl) was put into the copper cell and cooled down by liquid nitrogen, put under vacuum (10−5 torr) at continuous cooling with liquid nitrogen, and fractured. The surface was etched for 10–20 min at 10−5 torr and then replicated by spraying platinum and carbon. Results: The gels have a microphase-separated microstructure – a rather thick (several nm) polymer backbone is seen, which is presumably formed by multiple aggregated macromolecules, and meshes between the backbone do not contain polymer and are filled with solvent. Mesh size determined from the micrographs qualitatively coincides with the value determined from the elastic modulus of the gels. Upon increasing the concentrations of cross-linker, the network becomes denser: the mesh size becomes lower, and the thickness of the backbone increases. Thus, the addition of cross-linker favors the aggregation of polymer chains forming the backbone. Conclusion: It was shown by FF-TEM that cross-linked CMHPG gels have a microphase-separated structure with a dense backbone formed by polymer chains and rather large meshes between them.

Characterization of Large Particles in Fumed Silica Based CMP Slurry

2010 ◽  
Vol 1249 ◽  
Author(s):  
W. Scott Rader ◽  
Timothy Holt ◽  
Kazusei Tamai
Keyword(s):  
Fumed Silica ◽  
Large Particle ◽  
Particle Morphology ◽  
Sedimentation Rates ◽  
Transmission Electron ◽  
Primary Particles ◽  
Large Particles ◽  
Small Primary ◽  
Morphological Differences

AbstractLarge particles in fumed silica dispersions were characterized by sedimentation, light scattering techniques, Transmission Electron Microscopy (TEM), and lacunarity. Applying centrifugation to fumed silica dispersions generated differences in sedimentation rates of large particles. The sedimentation rates of the large particles were affected by morphological differences and the particles remaining in the supernatant displayed buoyant behavior. The large particle morphology varied from branch like aggregates containing large primary particles to particles comprised of highly coalesced, tightly packed small primary particles. The results indicate the presence of different types of large particles in fumed silica dispersions to which conventional large particle characterization is unable to distinguish.

Precipitation of Uniform Particles: The Role of Aggregation

1990 ◽  
Vol 180 ◽  
Author(s):  
C.F. Zukoski ◽  
M. K. Chow ◽  
G.H. Bogush ◽  
J-L. Look
Keyword(s):  
Growth Mechanism ◽  
Critical Concentration ◽  
Particle Growth ◽  
Nucleation Time ◽  
Small Particles ◽  
Relevant Model ◽  
Uniform Particles ◽  
Large Particles ◽  
Soluble Species

The conventional mechanism developed by LaMer (1) is often considered as the most relevant model for describing the precipitation of uniform particles. In this model, the concentration of a species is slowly increased above its equilibrium value until a critical concentration is reached and nucleation occurs. The resulting particles consume soluble species and the supersaturation level is reduced until there is a balance between particle growth and the generation of reactive species. At this point nucleation stops. Particle growth then continues by molecular addition of soluble species to the growing particles. Uniformity is achieved through a short nucleation time and a particle growth mechanism where the small particles grow more rapidly than the large particles.

Techniques for cryoultramicrotomy of propane jet frozen biological samples

1986 ◽  
Vol 44 ◽  
pp. 260-261
Author(s):  
B. Craig ◽  
L. Hawkey ◽  
A. LeFurgey
Keyword(s):  
Freeze Fracture ◽  
Freeze Substitution ◽  
Heart Cells ◽  
Crystal Formation ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Chick Heart ◽  
Embryonic Chick Heart ◽  
A New Technique

Ultra-rapid freezing followed by cryoultramicrotomy is essential for the preservation of diffusible elements in situ within cells prior to scanning transmission electron microscopy and quantitative energy dispersive x-ray microanalysis. For cells or tissue fragments in suspension and for monolayer cell cultures, propane jet freezing provides cooling rates greater than 30,000°C/sec with regions up to 40μm in thickness free of significant ice crystal formation. While this method of freezing has frequently been applied prior to freeze fracture or freeze substitution, it has not been widely utilized prior to cryoultramicrotomy and subsequent x-ray microanalytical studies. This report describes methods devised in our laboratory for cryosectioning of propane jet frozen kidney proximal tubule suspensions and cultured embryonic chick heart cells, in particular a new technique for mounting frozen suspension specimens for sectioning. The techniques utilize the same specimen supports and sample holders as those used for freeze fracture and freeze substitution and should be generally applicable to any cell suspension or culture preparation.

Three-Dimensional Immunoelectron Microscopy of Yeast Cells by a New High-Resolution Replica Method

1985 ◽  
Vol 43 ◽  
pp. 562-563
Author(s):  
Hirano T. ◽  
M. Yamaguchi ◽  
M. Hayashi ◽  
Y. Sekiguchi ◽  
A. Tanaka
Keyword(s):  
High Resolution ◽  
Plasma Polymerization ◽  
Three Dimensional ◽  
Freeze Fracture ◽  
Replica Method ◽  
Yeast Cells ◽  
Dynamic Aspect ◽  
Replica Technique ◽  
Gaseous Hydrocarbon ◽  
Transmission Electron

A plasma polymerization film replica method is a new high resolution replica technique devised by Tanaka et al. in 1978. It has been developed for investigation of the three dimensional ultrastructure in biological or nonbiological specimens with the transmission electron microscope. This method is based on direct observation of the single-stage replica film, which was obtained by directly coating on the specimen surface. A plasma polymerization film was deposited by gaseous hydrocarbon monomer in a glow discharge.The present study further developed the freeze fracture method by means of a plasma polymerization film produces a three dimensional replica of chemically untreated cells and provides a clear evidence of fine structure of the yeast plasma membrane, especially the dynamic aspect of the structure of invagination (Figure 1).

Effect of synthesis and activation methods on the character of CoMo/ultrastable Y-zeolite catalysts

2021 ◽  
Vol 19 (1) ◽  
pp. 745-754
Author(s):  
Khoirina Dwi Nugrahaningtyas ◽  
Eddy Heraldy ◽  
Rachmadani ◽  
Yuniawan Hidayat ◽  
Indriana Kartini
Keyword(s):  
Electron Microscopy ◽  
Reduction Process ◽  
Particle Morphology ◽  
Zeolite Catalysts ◽  
X Ray Diffraction ◽  
Y Zeolite ◽  
X Ray ◽  
Irregular Particle ◽  
Transmission Electron ◽  
Pure Metals

Abstract The properties of three types of CoMo/USY catalysts with different synthesized methods have been studied. The sequential and co-impregnation methods followed by activation using calcination and reduction process have been conducted. The properties of the catalysts were examined using Fourier-transform-infrared (FTIR) spectroscopy, X-ray diffraction (XRD) with refinement, and surface area analyzer (SAA). The FTIR spectrum study revealed the enhanced intensity of its Bronsted acid site, and the XRD diffractogram pattern verified the composition of pure metals, oxides, and alloys in the catalyst. The SAA demonstrated the mesoporous features of the catalyst. Scanning electron microscopy showed an irregular particle morphology. Additional analysis using the transmission electron microscopy indicated that the metal has successfully impregnated without damaging the USY structure.

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