Stir opalescence

A hot-stage-equipped polarizing microscope was used for measurement of these parameters. The anisotropic melting temperature (Tn) was determined as the onset temperature of stir-opalescence observed on the hot-stage. The liquid crystalline-isotropic transition temperature (71) was also determined by the use of the hot-stage-equipped microscope. 

For polymer concentrations < 3 % the mixtures remain isotropic during polymerisation and become a rubbery mass that is too viscous to stir in the later stages of heating. In contrast polymer concentrations of 5-10% form yellow green stir-opalescent solutions within 30 minutes of the dissolution of the terephthalic acid. Such solutions remain stirrable throughout the polymerisation despite the higher concentrations — an indication of the liquid-crystalline nature of the medium. 

A large length/width ratio was also important for the achievement of liquid crystallinity in the poly(ethers). All five of the R=H and all five of the R=Me materials were LC, exhibiting robust birefringence and stir opalescence. For R=MeO only three of five were LC, and for R=EtO, only the two mixed-spacer length polymers were LC. 

The mesophase exhibiting a homeotropic texture can still shew stir opalescence, which is a method of identification particularly suited for thermotropic polymers. This somewhat crude method of characterizing a liquid crystalline material is performed by shearing a thin film of the mesophase and looking for momentary appearances of turbidity in the otherwise transparent melt. No microscope is need to observe stir opalescence, but simple shearing of the homeotropic melt between crossed-polars can also reveal the mesophase. 

S. L. Kwolek, a woman scientist of DuPont, invented the liquid crystal aromatic polyamides which eventually paved the way to the first commercial liquid crystalline polymer product—poly-p-phenyleneterephthalamide under the trade name Kevlar. She recently recalled, When I dissolved the PBA (poly-p-aminobenzamide) polymer at 10% concentration in tetram-ethylurea with 6.5% LiCl, the solution was unusually fluid, turbid, stir-opalescent, and butter-milk-like in appearance. The fiber that was spun turned out to be extremely strong with a modulus of 430 gpd This discovery in 1964 remains a milestone of this field. In recognition of her contribution, the American Society of Chemistry Industry awarded Kwolek the 1997 Perkin Medal. 

The samples containing racemic spacers with less than approximately ten were found unambiguously to have mesomorphic properties by means of their optical behaviour and stir-opalescence. No melting transition could be identified by DSC, according to a mainly glassy nature, while the flow temperature was detected by optical analysis. No visual clearing was oserved and these polymers showed no isotropization endotherm below decomposition ... 

The obtained photocros-slinkable polymers show birefringence and stirred opalescence properties... 

Compound 3 is an example of a star polymer with benzoxazole arms. The three dimensional rigid-rod polymer was obtained from the polycondensation of 4-[5-amino-6-hydroxybenzoxazol-2-yl]benzoic acid (ABA) with l,3,5,7-tetrakis(4-carboxylatophenyl)adamantane (TCBA) in polyphosphoric acid (PPA). Polymer structures were confirmed by FTIR and elemental analysis, although the extent of attachment of PBO arms to the adamantane core was not confirmed. In addition, stir opalescence was observed indicating lyotropic-like behavior. However, the more compact star structure resulted in intrinsic viscosities that were significantly less than linear PBO s obtained under identical conditions. The onset for weight loss under TGA in air occurred at 500 C for both linear and star polymers and no transitions were observed by DSC. 

For ethyl alcohol, two volumes of dicycZohexyl are mixed with one volume of the alcohol, a thermometer is introduced, and the mixture heated until it becomes clear. The solution is then slowly cooled, with constant stirring, and the temperature is determined at which the opalescent solution suddenly becomes turbid so that the immersed portion of the mercury thread of the thermometer is no longer clearly visible. This is the C.S.T. The water content may then be evaluated by reference to the following table. 

The preparation of high molecular weight PPT in HMPA/NMP shows a strong dependence of inherent viscosity on reactant concentrations. In 2 1 (by volume) HMPA/NMP, the highest inherent viscosity polymer is obtained when each reactant is present in concentrations of ca 0.25 M higher and lower concentrations result in the formation of polymer of lower inherent viscosities. A typical procedure is as foUows 1,4-phenylenediamine, HMPA, and NMP are added to an oven-dried resin ketde equipped with a stirrer and stirred for ca 15 min with cooling to — 15°C, foUowed by the addition of powdered terephthaloyl chloride to the rapidly stirred solution. The reaction mixture changes to a thick, opalescent, paste-like gel in ca 5 min. 

Standard Opalescence Place 1.0 ml of a 0.05845% w/v solution of NaCI in 10 ml of dilute HN03 in a Nessler cylinder. Dilute to 50 ml with DW and add 1 ml of AgN03 solution. Stir immediately with a glass rod and allow to stand for 5 minutes. 

If one follows the solution viscosity in concentrated sulfuric acid with increasing polymer concentration, then one observes first a rise, afterwards, however, an abrupt decrease (about 5 to 15%, depending on the type of polymers and the experimental conditions). This transition is identical with the transformation of an optical isotropic to an optical anisotropic liquid crystalline solution with nematic behavior. Such solutions in the state of rest are weakly clouded and become opalescent when they are stirred they show birefringence, i.e., they depolarize linear polarized light. The two phases, formed at the critical concentration, can be separated by centrifugation to an isotropic and an anisotropic phase. A high amount of anisotropic phase is desirable for the fiber properties. This can be obtained by variation of the molecular weight, the solvent, the temperature, and the polymer concentration. 

Stir vigorously and slowly add the hot solution of items 3 to 5. Clear or slightly opalescent, colorless liquid. 

Add this slowly to the well-stirred mixture of items 1 to 5. Yellow clear or slightly opalescent liquid is obtained. 

Adsorbents. The macroreticular resins XAD-2 and XAD-4 were separately suspended in distilled water, and the suspensions were stirred to leave the fine particulates floating. These fines were removed by decantation of the supernatant layer. This operation was repeated until no opalescence was noticeable in the supernatant layer. After filtration through Whatman no. 1 filter paper and washing with methanol, the resins were dried at 70 °C in a convection oven prior to further purification. The average weight per milliliter of the resin was found to be 0.40 0.02 g. 

A. Transfer a 2-g sample into a 400-mL beaker, moisten it thoroughly with about 4 mL of isopropyl alcohol, add, with vigorous stirring, 200 mL of cold water, and continue to stir until the gum is completely and uniformly dispersed. An opalescent, viscous dispersion forms. 

B. Add 1 g of sample to 100 mL of boiling water, and stir the mixture. A slurry forms that when cooled to 20°, dissolves to form a clear or opalescent, mucilaginous solution. 

It is essential that the solution be just neutral to litmus or, at most, barely alkaline the latter will be indicated by a very slight brown opalescence (due to Ag20) obtained upon stirring or shaking. If much silver oxide separates, it will redissolve only with difficulty. 

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