Liquid Crystal and Crystal Solutions

Before the activity, discuss what is the “nanoscale” using this concept, during our senses unit, discuss the idea of how we smell different products and can tell them apart. And what this means to our brain, as well as our ability to discern different smells from another. Reference: Smell: Sensing on the Nanoscale 

Spray a perfume. Have students to a modeled drawing of what is happening in the air to get the smell from the “puff moment” to their nose. Discuss how a material travels in air. Have students conclude that our nose is acting as a sensor to interpret what we smell. Consider the importance of knowing the importance of the smell of smoke in your bedroom versus cookies baking in the oven. Why do we need to smell? Students should conclude that our nose is acting as a sensor to protect us. It is able to interpret a small particle as delicious or dangerous.

Watch the video from MRSEC “What is nanotechnology?” (7:47 minutes long) http://www.youtube.com/watch?feature=player_embedded&v=ow6CnWeWU2U

Once students are thinking on a nano level, have students discuss phases of matter and determining the differences between them. Draw how they believe the molecules align in each of the stages. Introduce liquid crystals. First break down the name. Based on what they currently know, what is a liquid and what is a crystal, what does that tell us about its state of matter. This is a great strategy for ESL and special education students.

When students are thinking about the chemical make-up of liquid crystal, begin a guided discussion about liquid crystals with PowerPoint note slides for the students.

1. Have materials set on a common lab area for students to grab. Otherwise create containers for students to easily have materials to take back to their lab stations.
2. Create four molar sodium iodide and four molar sodium chloride. Each group will need 5 ml of each in a glass container for ease at stations. Be sure to label each container with the solution.
3. Tape a polarizer so that when they are stacked, you see only black. Tape one to the bottom of the stand and the other to the 4x lens. This will create your polarizing microscope.
4. In each crate for a lab group students will need: NaCl and NaI, glass syringe, 10 ml syringe, 1 ml syringe, 2 glass bottom dishes, 10 ml of distilled water.

With a pen or pencil, have students move to determine the:
1. Straight up and down (Perpendicular to the surface)= homeotropic (black) The long direction is always up and down, the short is side to side – – ALWAYS
2. Roll in fingers when perpendicular – – rotating in vertical access=doesn’t change
3. Flat (parallel to surface)= planer (gold or colorful)
4. Flat rotate on surface (helicopter) = planer but you can see that it is different with orientation creating different colors. You can see there is a long direction and a short direction and that effects where the black brush directions are located.
5. Then tilting the pen away from the hand at an angle creates another type of rotation affecting the color.

The color is affected by the tilt and thickness of the LC. Home tropic/perpendicular alignment with water interface and they are the light is only seeing one aspect of the material and how the light is seeing it is.

To begin, have the student get their group materials. At their table, they should begin by placing both glass bottom dishes on their table.

1. Using the 10 ml plastic syringe, extract 7 ml of distilled water from the provided container.
2. Once the water in the dish has settled, place it under the microscope. Use the glass syringe to place 6µl of 5CB liquid crystal onto the surface of the distilled water.
3. Have students make an observation. Draw, including color, what they observe in their science notebooks. Using what they know about alignment of LC molecules, draw what they predict the orientation of the molecules is currently in their dish.
4. Next added 3ml of 4M NaI to the dish. At this point the dish should go black. Again, have students record what happened to their sample. Write a description and draw what happened. If their solution has changed, draw how they now interpret the molecules to be aligned.
5. Place the dish with NaI and liquid crystal to the side.
6. Repeat steps 1-3 in a second dish.
7. Tell the student they are next going to add NaCl to their second dish. Make a prediction of what will happen to the liquid crystals this time when a different solution is added.
8. Next added 3ml of 4M NaCl to the dish. At this point the dish should have slight changes in the liquid crystals, but the students should still see the colorful patterns.
9. Again, have students record what happened to their sample. Write a description and draw what happened. If their solution has changed, draw how they now interpret the molecules to be aligned.
10. When complete with both samples, students need to write a brief conclusion of what they believe occurred with each solution as it interacted with the LC.
11. Answer the follow-up question in lab notebooks.

When complete clean up materials by rinsing the glass trays with a water, ethanol, water process.

Return all materials to the back counter to be refilled for the next class period.

1. Have students begin to dilute the NaI solution. By removing half of the liquid and replacing it with distilled water, students should make observations if there are any changes that are occurring within the dish.

a. After the first dilution, were there any changes?

b. After how many dilutions did you see change?

c. If there was change, what did you observe? Draw your observations and write a hypothesis of what occurred.

d. Based on what you now about liquid crystals, what conclusions can you draw about the order or structures of the liquid crystals before and after you changed the make-up of the dish.

1. Repeat the hands-on pen activity. Check for understanding of the movement and alignment of liquid crystals.
2. Show an image and ask students to determine who the liquid crystal molecule would be situated.

a. Example images:

i. Gold, white and black

ii. Colorful

iii. Black

iv. Colorful with black brush strokes

With a pen or pencil, have students move to determine the:

1. Straight up and down (Perpendicular to the surface)= homeotropic (black) The long direction is always up and down, the short is side to side – – ALWAYS
2. Roll in fingers when perpendicular – – rotating in vertical access=doesn’t change
3. Flat (parallel to surface)= planer (gold or colorful)
4. Flat rotate on surface (helicopter) = planer but you can see that it is different with orientation creating different colors. You can see there is a long direction and a short direction and that effects where the black brush directions are located.
5. Then tilting the pen away from the hand at an angle creates another type of rotation affecting the color.