Staining osmium tetroxide

ABA type poly(hydroxyethyl methacrylate) (HEMA) and PDMS copolymers were synthesized by the coupling reactions of preformed a,co-isocyanate terminated PDMS oligomers and amine-terminated HEMA macromonomers312). Polymerization reactions were conducted in DMF solution at 0 °C. Products were purified by precipitation in diethyl ether to remove unreacted PDMS oligomers. After dissolving in DMF/toluene mixture, copolymers were reprecipitated in methanol/water mixture to remove unreacted HEMA oligomers. Microphase separated structures were observed under transmission electron microscope, using osmium tetroxide stained thin copolymer films. 

Figure 8-4 Bimolecular lipid layers and membranes. (Top) A molecule of phosphatidylcholine. (Center) Lipid bilayer structure. (Bottom) Bilayer structure as seen by the electron microscope with osmium tetroxide staining.

Fig, 3. Transmission electron micrograph of osmium-tetroxide stained section of a typical rubber-modified epoxy thermosetting polymer... 

Figure 7. Thin section, osmium tetroxide stained. I mm = 800 A,...

Figure 7. Enhancing SEM contrast in blends by osmium tetroxide staining bromobutyl/neoprene blend.

The morphology of ruber modified epoxy photopolymers was found to depend on the cure conditions as well as the nature and concentration of rubber. The commercially available acrylonitrile-butadiene copolymer rubber modifiers with varying percentages of acrylonitrile content were used. They were polymerized using a photocationic initiator involving a UV exposure followed by a thermal cure. Transmission electron micrographs of osmium tetroxide stained specimens, coupled with dynamic mechanical measurements indicated that phase separation and particle size distribution depended not only on rubber concentration and compatibility, but also on the cure conditions. 

Osmium tetroxide staining can be accomplished by exposing a sample to osmium tetroxide vapor for a week, or by soaking overnight in a 1 %... 

The simplest method of polyblending involves equipment such as rolls or extruders, which can effect the mechanical blending of the two polymeric components in the molten state (Matsuo, 1968). High-impact polystyrene (HiPS) is an important example of a polyblend made by this technique. Such materials commonly contain 5-20 % of rubber, usually polybutadiene, dispersed in a polystyrene matrix. As shown in Figure 3.1, electron microscopy studies on specimens stained with osmium tetroxide reveal well-defined, irregular rubber particles (1-10 fim in diameter) dispersed in the polystyrene matrix. The elastomer domains appear dark because the osmium tetroxide stains the elastomer preferentially (see Section 2.4). 

Upon comparing Figure 3.3 with Figure 3.2, the advantages of osmium tetroxide staining, coupled with transmission electron microscopy, become clear. It is easier to distinguish phases and to determine morphological... 

Figure 3.32. Electron micrograph of ultrathin section of irradiated ABS plastic (osmium tetroxide staining). Note cracking, which occurred after 400 h exposure to Fade-o-Meter irradiation. (Hirai, 1970.)...

Electron Microscopy The sample preparation was based on Kato s (10) osmium tetroxide staining technique and a two-step sectioning method. The specimens were exposed to O5O4 vapor and cut with a LKB ultratome III to get a 0.1 y slice. The electron micrographs were taken with an AEI 6B and a Phillips 300 transmitting electron microscope with a magnification of 95,000. 

Osmium tetroxide stained electron micrographs of polystyrene-Z>/ucA -polybutadiene-Z /ocA -polystyrene block copolymer produced by extrusion. (a) Micrograph demonstrating the orientation of the styrene cylinders in the direction of the extrusion (direction A in the schematic) and (b) shows a close-packed structure transverse to the extrusion direction (direction B in the schematic). Scale bar = 1 pm. 

Osmium tetroxide stain/contrast agent Poss/no OSO4... 

Figure 6.2. Electron micrographs of IPN s of (a) 75/25 poly(ethyl acrylate)/poly(methyl methacrylate), and (b) 50/50 poly (ethyl acrylate)/polystyrene. A small amount of butadiene was copolymerized with the poly(ethyl acrylate) to aid in osmium tetroxide staining.

Figure 6.13. Morphology of castor oil-urethane/polystyrene IPNs. Transmission electron microscopy, osmium tetroxide staining of the castor oil component.(a) NCO/OH = 0.95 (b) NCO/OH = 0.85 (c) NCO/OH = 0.75. The scale indicator at the bottom of each photograph is 0.1 /am.

Fig. 19. Electron micrograph of an osmium tetroxide stained ultrathin section of HIPS. This micrograph shows the typical morphology of the dispersed rubber particles. The thin lines connecting the particles are crazes formed after the material has undergone deformation.

Andrews [107], who stained unsaturated synthetic rubbers, and then further developed by Kato [108-110], to show the morphology of rubber modified plastics and unsaturated latex particles. The polybutadiene in ABS pol)m[ ers is not apparent in unstained cross sections in the TEM, but staining results in contrast enhancement due to increased density of the unsaturated phase. Latex particles flatten and aggregate upon drying and early attempts at hardening, such as by bromination, were not considered successful. Thirty years after its first application, the method of osmium tetroxide staining is still widely and successfully applied to unsaturated rubbers and latexes. 

The second reactive inclusion method was developed [129] for microporous membranes. Stretched polypropylene, Celgard 2500 (trademark, Hoechst Celanese Corp.), shows little fine structure after ultrathin sectioning and examination in the TEM (Fig. 4.13A), although SEM study clearly reveals a surface pore structure. In order to enhance contrast, the membrane was treated with an unsaturated surfactant followed by osmium tetroxide staining and ultrathin sectioning. A 1-2% solution of polyoxyethylene allyl ether, Brij 97 (available from ICI Americas Inc.), in 50/50 methanol/water solution was used to... 

Widmaier and Meyer [256] studied the structure of an ABA polystyrene-isoprene block copolymer as a function of temperature by osmium tetroxide staining thin cast films. Hsiue and Yang [257] studied the morphology and properties of a-methylst3n ene-butadiene diblock copolymer films cast from several solvents. Films at a 0.1% concentration were cast on water and stained with 2% osmium tetroxide solution for 1 h. The microstructure was shown to differ for films cast from different solvents as there is a pol)nner-... 

Fig. 5.54 A transmission electron micrograph of an osmium tetroxide stained thin section of a poly(st)TCne-butadiene) diblock copolymer (16.1 wt% polybutadiene shows the (100)) projection of a body centred cubic lattice. (From Kinning et al. [265] reproduced with jjermission.)...

Stress-strain relationships are determined by DMA and temperature scans reveal glass transitions, crystallization and melting information. Blends of polypropylene and rubber have been studied by where the intensity of one of the two crystallization exotherms was used as a measure of the polypropylene domains and compared to the size determined by TEM cryomicrotomy and osmium tetroxide staining methods [25]. Isothermal annealing of PET above the crystallization temperature was shown to influence the morphology and increase thermal stability by combined SAXS and DSC analysis [26]. An excellent text edited by Turi [21] described the instrumentation and theory of thermal analysis and its application to thermoplastics, copolymers, thermosets, elastomers, additives and fibers. 

Figure 13.12 (21) shows that the osmium tetroxide-stained polybutadiene has occluded SAN inside the core latex portion, with SAN also forming the shell. On film formation, the SAN shell component makes up the continuous phase. A straight SAN latex may be added to increase the separation of the polybutadiene rubber domains. The rubber portion must be cross-linked to minimize morphological damage to the core during processing. 

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