Microdrop test

For a given fiber/matrix combination, a relatively large scatter in the test data is obtained from the microdrop test. Such wide distribution of shear strengths have been attributed mainly to testing parameters such as position of the nficro-drop in the loading fixture, droplet gripping, faulty measurement of fiber diameters, etc. 

To evaluate the effect of MFC content on the interfacial shear strength, the microdrop test was conducted at a test speed of 1 mm min with the specimen shown in Figure 9.6. The interfacial strength was calculated by Eq. (9.1) ... 

Figure 9.13 also shows interfacial shear strength between fiber and resin, measured by microdrop tests. In this case, the content ratio of the MFC to matrix was 10 50 in weight. High interfacial strengths were observed if a small amount of the MFC was added to the resin drop. It was found that enhanced MFC prevents interfacial failure between the BF and resin in the PLA/BF/MFC composite. 

In another extensive series of studies, Clarke and coworkers developed sensitive microchemical tests for the determination of alkaloids [32-34], anesthetics [35], antihistamines [36], antimalarials [37], and analgesics [38]. One of the useful techniques introduced by Clarke was that of the hanging-microdrop [32], which permitted identification tests to be made on submicrogram quantities of analyte. Results obtained on the cinchona alkaloids are shown in Table 5 to illustrate the methodology. 

E.G.C Clark s Isolation and Identification of Drugs (The Pharmaceutical Press, London) specifies a method for making "microtests of a "pedant drop or "microdrop. The sulfuric acid-formaldehyde testing of DMT, to illustrate, yields dull orange with a sensitivity of 1.0 meg. sensitivity, while the ammonium molybdate test yields blue going to green and then yellow with a sensitivity of 0.1 meg. 

Stock solution. Measure 1 ml. of phenylhydrazine by pipet into a 10-ml. volumetric flask, add 3 ml. of acetic acid and swirl under the tap to cool to room temperature, and dilute with water to 10 ml. The solution contains 1 mmole of phenylhydrazine acetate per milliliter. If a substance to be tested for the presence of a carbonyl function is soluble in water to the extent of 8-10 microdrops in 1 ml. of water, dissolve 1 mmole of sample in 1 ml. of water and add 1 ml. of the stock solution. Separation of an oil or solid indicates the presence of a carbonyl function. If the sample is soluble to the extent of only about 4 microdrops in 1 ml. of water (diethyl ketone), treat 1 mmole of material with 1 ml. of water and add a few drops of methanol until solution is complete then add 1 mole of stock solution. A sample insoluble in water can be dissolved in methanol, ethanol, or dioxaiie and treated with 1 ml. of stock solution. 

The use of a new microdrop apparatus (Fig. 39) is suggested for placing a large number of drops of the same or different reagents along the sides of a trace in order to perform local qualitative tests on the various drops. Thus, it is possible to place at least fifteen 0.0001 ml drops on a 30 mm long ichnos. 

Procedure, b) A spot plate or a micro crucible is used, a drop of the test solution is mixed with a microdrop of 1 % alcoholic fluorescein solution and a microdrop of a 10 1 mixture of glacial acetic acid and 30 % hydrogen peroxide, and evaporated to dryness. A pink to red color appears. A blank test on a drop of water is advisable when small amounts of bromine are suspected. 

Procedure. The test is made in a micro test tube. A drop of the test solution is warmed with a drop of oxine solution, a drop of hydrogen peroxide solution, and a microdrop of nitric acid for about 4 minutes. A drop of 1 % AgNOj solution is then added. If chloride is present, a colorless precipitate or turbidity will appear, the intensity of the response depending on the quantity of chloride involved. 

Procedure. A spot plate or micro crucible is used. A drop of the neutral or acid test solution is treated with a drop of the reagent and then made alkaline with 1 N sodium hydroxide. If the color changes from red-violet to cornflower-blue, copper is present. When very small quantities of copper are involved, a mixed color appears. In this case, it is best to use not more than a microdrop of the reagent and to compare the color with that obtained from a solution known to contain no copper. 

Procedure. A drop of the neutral or acid test solution is placed on a spot plate along with a microdrop of 1 iV potassium hydroxide or saturated lime water followed by a microdrop of iodine solution the mixture is stirred with a glass rod. The solution should be definitely brown if necessary more iodine should be added. After a minute, the alkali content is increased until the solution becomes lemon yellow. In the presence of magnesium, the brown adsorption compound is clearly visible. A blank is necessary only when very small amounts of magnesium are suspected. 

A microdrop (0.01 ml) of the test solution and one drop of an acetic acid solution of benzidine are brought successively on filter paper. The diazotization and coupling give a yellow or brown dye. (Idn, Limit 0.7 y NaNOa). ... 

Procedure. One drop of the test solution, which may be neutral or 0.1 AT with respect to hydrochloric acid, and which must be free from interfering substances, is mixed on a spot plate with a microdrop of 1 % titanous chloride solution and a microdrop of a 0.005% water solution of malachite green. Depending on the concentration of tungsten, the solution becomes colorless (very pale violet) more or less rapidly. With small quantities of tungsten, it is well to make a blank test. 

The microdrops for this resin are allowed to cure at room temperature for 24 h, and are then post-cured for 2 h at 75°C (165°F) and for 2 h at 125°C (255°F). (This procedure would be adjusted depending on the matrix chemistry.) After curing, the fiber is affixed to an aluminum plate and kept in a desiccator to wait testing. 

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