Liquid Crystal and Crystal Solutions

 

Audience

Age Group: Middle School
This activity would work best in groups of 2-4 students depending on materials.

 

Time Frame

Three days- Day 1: Background Day 2: Lab Day 3: Drawing conclusions

Day 2: Lab
Set-up: 15 minutes Activity: 20 Clean-up: 15

 

Objective(s)

 

After completing the activity, participants will be able to:

1. Students will be able to define the purpose of nanotechnologies.
2. Students will be able to evaluate the importance of sensors and their effects on daily life.
3. Students will be able to identify benefits of liquid crystals
4. Students will be able to interpret the orientation of liquid crystals, with the use of polarized light and the effects of solutions on their alignment.

Standards Addressed

 

Madison School District Standards:

  • investigate the properties of lenses, including how they can refract light. C.8.6, C.12.5, D.8.8, D.8.9
  • the senses of touch, hearing, taste and smell have specialized neurons that carry messages to the brain. F.8.1, F.8.3, F.12.12
  • messages travel through neurons as electricity and from neuron to neuron via neurotransmitter chemicals. F.8.1, F.8.3, F.12.12
Next Generation Science Standards

MS-PS1-1. Develop models to describe the atomic composition of simple molecules and extended structures. MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.

MS-PS1-4. Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.

Engineering principles
Students who demonstrate understanding can:

MS-ETS1-3. Analyze data from tests to determine similarities and differences among several design solutions to identify the best characteristics of each that can be combined into a new solution to better meet the criteria for success.

Activity Materials

Day 1:
Student writing materials
Small plastic container
Toothpicks
Aerosol Perfume

Day 2
For each group:
2 10mL Glass Bottom Dishes
1 10 µL Glass Syringe
5CB Liquid Crystal
1 20 mL Glass Vial with distilled water __________Polarizers
Microscope
5 ml 4 M NaI in a 20ml glass vial
5 ml4M NaCl in a 20ml glass vial
10 ml plastic syringe
1 ml plastic syringe
Scotch tape
For the Class:
Ethanol
Kim Wipes
___________NaI
___________ NaCl
Scale to the _____________ place value
Scale papers
MQ water
Metal Spatula

 

Activity Instructions

Set-up

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.

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.

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.

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.

Introduction (50 min)

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 http://education.mrsec.wisc.edu/34.htm

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.

Hand-On Activity: 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

The Next Part of the Activity (35 min)

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.

TAG Extension:

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.

The Third Part of the Activity (10 min)

  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

Hand-On Activity:

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.

Conclusion (X min)

Give instructors some ideas on how to conclude and wrap up the activity.

Assessment

How will you assess your activity?

1. List at least four questions that participants could be asked, either verbally or in writing, to evaluate the quality of your activity and if the objectives (listed earlier) were met.

Background

Liquid crystals were first discovered over 100 years ago in studies of cholesterol and related molecules. Liquid crystals are a fourth state of matter; they have greater ordering than more normal liquids but less ordering than crystalline solids. All phase changes have a characteristic phase transition temperature for a given set of conditions. Liquid crystals have separate transition temperatures where they change into "normal" liquids (melt) and into "normal" solids (solidify).

Liquid crystals have become very common in the last 20 years as displays for electronic devices. This is the result of the unusual optical and electrical properties of liquid crystals. The long thin liquid crystal molecules cause light to travel at different speeds along the molecular axis and perpendicular to that axis. This leads to their ability to rotate the plane of polarized light (see below).

• How they work

These long thin molecules also have a tendency to align parallel to an applied electrical field. This response and the optical properties of liquid crystals lead to their application in various electronic deviceshow they work ranging from watches and calculators to computers and televisions.

• Polarizing Filters and Polarized Light

As shown in Figure 1, polarizing filters are materials that allow only the passage of light waves whose electric fields are oscillating in a particular plane.

Figure 1. Initially unpolarized light passing through a polarizing filter becomes polarized. The polarized light will not be transmitted by a second polarizing filter turned at 90o to the axis of the first filter.

Unpolarized light passing through a polarizing filter becomes polarized. Polarized light directed onto a second polarizer, oriented 90o to the first polarizer, will not be transmitted. Many natural substances, including liquid crystal materials, have the ability to rotate the plane of the polarized light.

For more information access the Wisconsin MRSEC website: http://education.mrsec.wisc.edu/147.htm

Supplemental Materials

How Smell Travels Model #1 Worksheet

• Are there any supplemental materials, like overheads or worksheets?

• If so, list the document names here and make sure to email the files to Ben at  bltaylor2@wisc.edu.

References

Please cite all references.

Additional References

Any supplemental and age-appropriate material that an instructor might use to increase participants’ knowledge and interest on the topics addressed in your teaching activity.

Authors

Ashley Adams, Rebecca Carlton, Nicolas Abbott,………………………. MRSEC IEG Leadership Team: Ben Taylor, [any other faculty members, grad students, undergrads, post docs, etc., from the lab you were in], and Anne Lynn Gillian-Daniel.