HW9-solutions.pdf - 121 pts EMA 3066 Fall 2019 Name Homework#9-Canvas Thermal Transitions 1 Solutions Gower Question 1(4 pts Name the 4 types of

HW9-solutions.pdf - 121 pts EMA 3066 Fall 2019 Name...

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EMA 3066- Fall 2019 Name: Gower Homework #9-Canvas- Thermal Transitions 1- Solutions Question 1 ( 4 pts) Name the 4 types of mesophase ordering: (be sure to use the correct spelling) nematic smectic cholesteric dicotic Question 2 ( 5 pts) Fill in the blanks with the correct choice. Be careful with using the exact spelling of phrases for Canvas to recognize: The polarized light micrograph shows the texture of a liquid crystalline (LC) sample. This LC texture, which was obtained by increasing the concentration of the molecules within the solvent to the point of ‘molecular crowding’, is referred to as a ( thermotropic / lyotropic / metallotropic ) lyotropic transition. The molecules, or rigid regions of the molecules, are referred to as (amphiphiles / threads / mesogens ) mesogens . A common type of defect in LC materials is called a (dislocation / disclination / screw ) disclination . The wide bluried dark lines on the micrograph (which sort of look like a Maltese cross, and are parallet to the directions of the crossed polars, are non-birefringent because the LCs are (isotropic in that region/aligned along their optic axis/ rotated into their extinct position ) rotated into the . The narrow sharp lines that seem to spiral from the center are dark because the LCs are (isotropic in that region/ aligned along their optic axis /rotated into their extinct position) aligned along t . (Added comment box: Hint- Consider the pattern similar to a banded spherulites) 121 pts
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Question 3 ( 2 pts) In the LC display illustrated in the schematic below, the transmitting state has molecules that are oriented as a twisted nematic, which resembles the ( smectic / cholesteric / discotic ) cholesteric type of LC, but does not naturally twist; it is created by grooves that align the nematic molecules in opposing orientations at the two surfaces. In the non-transmitting state, the reason there is no transmission of light through the second polarizer is because of one of the following (fill in the blank with choice of A – D): C A) the LC molecules are aligned in their extinct position, parallel to one of the crossed polars. B) the LC molecules are no longer aligned, which is needed for them to be birefringent. C) the LC molecules are aligned with their isotropic (optic) axis parallel to the axis of light D) the LC are no longer liquid crystalline, and amorphous materials are not birefringent. Question 4 ( 5 pts) Engineering plastics often use liquid crystalline polymers to obtain a high degree of alignment of the chains, which leads to a ( increase /decrease) increase in modulus and strength of the fibers, as well as high thermal stability. The melting point of these polymers is usually very high, particularly if they contain aromatic rings in their backbone, which yields a ( small /large) small entropy change during the transition. Sometimes a small amount of co-monomer units are added to (increase/ decrease ) decrease the melting point, making it easier to process and/or avoid chemical degradation. The best type of copolymer for this purpose would be a (block/graft/ random ) random copolymer.
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