Miscibility testing

Studies on 180 binary systems of 120 substances by Sackmann and coworkers have led to the empirical rule of selective miscibility (Sackmann and Demus, 1965) All liquid crystalline states which exhibit an uninterrupted series of mixed crystals in binary systems without contradiction can be marked with the same symbol. On the other hand, the liquid crystalline states having the same symbol exhibit in no case an uninterrupted series of mixed crystals with the liquid crystalline states of another symbol. Therefore, the nature of a mesophase can be determined by establishing its isomorphy with a known mesophase of a reference compound. The applicability of this empirical rule has been repeatedly justified in low mass systems. For instance, Sackmann and Demus (1973) have observed in only one case a heterogeneous region between two modifications of the same type. In contrast, in over 100 cases these researchers have observed heterogeneous regions between modifications of different types. 

This empirical rule has been applied to mixtures composed of well-known model liquid crystals with polymeric liquid crystals in order to identify the type of mesophase of the polymers (Nyitrai et al., 1977 Millaud et al., 1978  

Nevertheless, the rule of selective miscibility must be applied with caution. The highly viscous nature of polymeric mesophases could possibly prevent the mixing of the mesophase of polymers and certain model compounds. Therefore, while the miscibility of model compounds with a polymer may be used to identify the type of mesophase, the lack of compatibility does not necessarily suggest that the mesophases are not the same. Some model compounds and polymers with the same mesophase may even be inherently incompatible. As a result, some judgment is required in order to make both the proper choice of the model compound and the correct assignment of the mesophase when using this technique. 

---

For Part A, you should work as part of a team. Five teams will be needed. Each team should rotate through four stations in the lab, one for the water miscibility test, one for density measurement, one for viscosity measurement, and one for refractive index measurement. Each team should be assigned 2 of the 10 liquids to test at each station. As the results are obtained at each station, each team should record the results on the grid similar to the example given in the SOP. Perhaps you could put the same grid on a blackboard accessible and visible to each team. At the end of Part A, each worker can then fill in the entire grid in his/her notebook and have a complete set of data for the 10 compounds. This data will then be used in Part B to identify unknowns that are issued to each worker. In Part B, each worker should test several unknowns and identify each based on how well their properties match up with those measured in Part A. The property of odor may be used in Part B for confirmation if desired, comparing unknowns with knowns. In Part B, it may not be necessary to measure all five properties if you can identify your unknowns with just a few tests. 

Some liquid substances are able to mix completely with water while others will mix only partially or not at all. If a substance mixes freely with water, only one liquid layer will be seen in the container. If a substance does not mix freely with water, two separate liquid layers will be observed in the container. With the water miscibility test, we observe this ability or lack of ability to mix. If an unknown mixes freely with water, we can conclude with certainty that it is not the same liquid as any liquid studied in Part A that does not mix with water. While at the same time we can conclude that it may be one of those that does mix with water. Thus, this test helps to narrow down the possibilities of what an unknown s identity might be. 

Perform the water miscibility test first to narrow down the possibilities for your unknown. Then select and perform whatever test(s) will identify the unknowns. Be sure to keep good records in your notebook. When you think you have identified your assigned unknowns, compare the odors of the unknowns with odors of the pure liquids. This will serve as a final confirmation of your results. 

Results of Water Miscibility Test (miscible or immiscible) ... 

The X-ray diffraction of polymeric liquid crystal systems and their low mass counterparts are the same in principle, but the diffraction results for the polymers are often less ideal and more difficult to interpret. In practice the oriented specimens are often preferred over the unoriented samples for an unambiguous determination. X-ray diffraction is nearly always used together with texture observations using a polarizing optical microscope. Miscibility tests are also used in some cases for confirmation. For smectic phases with higher translational and orientational orders, X-ray diffraction is the most useful (if not the only) technique for unmistakable characterization. A few examples are cited below. The details of each characterization of the various polymeric smectic phases were described by individual authors. 

Removal of hydrocarbons from methanol cannot be done easily by fractionation because of the existence of many azeotropes, but the partition of methanol between water and hydrocarbons is very strongly in favour of the former, although methanol separated by this route will seldom have a good water miscibility test. Because of its small molecular diameter methanol should not be dried by molecular sieves, but silica gel, calcium oxide and anhydrous potassium carbonate are effective. 

The bundles of fibrils for helical polyacetylenes synthesized in the (fi-2)- and (S-2)-chiral nematic LCs are screwed counterclockwise and clockwise, respectively The screw directions of helical polyacetylene are opposite to those of the corresponding (fi-2)- and (S-2)-chiral nematic LCs whose directions are confirmed to be clockwise and counterclockwise, respectively, through the miscibility test with choles-teryl oleyl carbonate. This is the same situation as that of the (fi-1)- and (S-l)-chiral nematic LCs including (fi)- and (S)-PCH506-Binol. 

FIGURE 3.2 Miscibility test between the chiral nematic LC induced by (J )- or (S)-PCH506-Binol and the standard LC, cholesteryl oleyl carbonate of counterclockwise (left-handed) screw direction. 

Sub-problem 2 The miscibility test foimd five ternary mixtures with a multiphase region. They were excluded, and 32,200... 

It is recommended to carry out miscibility tests to check that no separation (flotation, sedimentation, coagulation) will occur due to the preservation treatment. This is very important for coating slurries preservation where any rheological change in these complex formulations can destabilise the coating. These tests can include enduction ( draw down test ), brightness test, printability tests. 

Figure 32. Miscibility test for 10 with n = 1 (see Figure 31) with a reference AFLC.

Liquid crystallinity of the PCHn03A monomer was examined with a miscibility test. Figure 9-2 shows a phase diagram of the mixture of PCH803A monomer and l-hexyloxy-4-(rran5-4-propylcyclohexyl)benzene, PCH306. The latter is known to have a nematic liquid crystalline phase and therefore is used as a reference. 

In this chapter an attempt is made to integrate the information available from the thermal data, textural phenomena, miscibility tests and x-ray diffraction patterns in a discussion of the specific features of the nematic, cholesteric and smectic phases exhibited by liquid crystalline main-chain and side-chain polymers. Results obtained by these methods on liquid... 

As mentioned earlier, texture observation cannot always be counted on to produce an unambiguous determination of the type of mesophase present. It can happen that similar textures are observed with two LC states separated by a phase transition. It is advisable, therefore, to use this method in conjunction with other types of characterization such as miscibility tests. Sackman and his school at Halle have produced a classification scheme for LMMLCs based on the criterion of complete miscibility of identical phases. " Isomorphous LCs are considered as equivalent and characterized by the same symbol. Therefore, the mesophases of a new compound can be positively identified by isomorphy with known mesophases of reference compounds. Assuming that the method is applicable to LCPs, the type of mesophase can be determined by establishing the isobaric temperature-composition phase diagram of a binary system composed of the polymer and a reference compound. Such diagrams can be generated from thermal data or, because of the various optical features characteristic of each mesophase... 

---