Drexel-SDP GK-12 ACTIVITY Activity: Liquid Crystal Thermometer Subject Area(s) Metrology, Physics, Chemistry and Engineering Associated Unit: Meterology, Engineering Concepts Associated Lesson: Weather around us Activity Title: Liquid Crystal Thermometer Grade Level (_6_-_8) Time Required: 1 hour Group Size individual students Expendable Cost per Group: $5 dollars Summary: Students will build a liquid crystal thermometer using cholesteric liquid crystals and transparency film. Engineering Connection Engineers frequently design tools to measure physical quantities by taking advantage of physical properties. Keywords Liquid crystals, thermometer, pitch Educational Standards Science: 3.1.7 Math: 2.3.5, 2.2.8 Pre-Requisite Knowledge Students should be familiar with change in states of matter and know that materials are made of atoms and molecules. Learning Objectives After this lesson, students should be able to: Build a liquid crystal thermometer Describe pitch Calculate pitch Convert temperature scales Describe phase changes in liquid crystals Model phase changes in liquid crystals with popsicle sticks Describe light as a wave Materials List Each student needs: 1 self laminating ID Badge Transparency with thermometer scale printed on it 20 popsicle sticks pipe cleaner ruler To share with the entire class: 5 formulations of cholesteric liquid crystals (one for each temperature range) wood sticks ( wooden cotton swabs work fine…remove the cotton from the end) Table1. Inventory sheet, part numbers and vendors. Cholesterols can be stored for future uses) Cholesteryl benzoate 98% Cholesteryl Pelargonate 97% Cholesteryl oleyl carbonate Aldrich C75802 $112 100g Aldrich Aldrich C78801 151157 $91.40 $49.40 100g 25g Clear vials Swabs Kimpads Fisher Fisher Fisher 03-339-25C 23-400-107 S47299 Lamenation Strips Transparency Sheets Office Depot Office Depot 920531 753611 Introduction / Motivation What is the difference between heat and temperature? Heat is the average kinetic energy of the atoms in a system, whereas temperature the measurement of heat. Typically temperature is measured with a thermometer and reported as a value a temperature scale. Scientists and engineers use the Celsius Scale, in the USA weather temperatures are reported in the Fahrenheit Scale. To make a thermometer you need a substance that has a measureable linear change in physical properties over the range of heats you are interested. You can build a thermometer based on the expansion of a metal or alcohol (mercury and alcohol thermometers), change in resistance, or in our case color. 2 Procedure Background Liquid crystals (LC) have two melting temperatures, one representing a phase change from the solid to liquid crystal and then a phase change from liquid crystal to liquid. The phase change from solid to liquid crystal is accompanied by a change in optical properties. The LCs used in this activity were cloudy in the solid and became a translucent pearly color in the LC temperature range. This change in appearance over a range of temperature close to room temperature (and body temperature) makes LCs a convenient fun thermometer. Before the Activity 2 weeks before Activity: 1. Review attached presentation: Liquid Crystal Presentation ( in pdf format) 2. Purchase materials 2 days before Activity 3. Prepare the LCs, follow the synthesis protocol in the Mchale reference below. 4. Print out thermometer templates on transparency film 5. Cut up the transparency film so that the thermometer scales fit in the self laminating pockets 1 hour before Activity 6. Heat up the LC by heating a water bath and putting the sealed vials in the bath. Direct heating on a hot plate will burn the LCs. 7. Put together the materials for the students (I gave each student one self laminating pocket, one thermometer scale transparency) I kept the sticks at each temperature station to prevent contamination) I put 2 or three vials of the same LC temperature range at each station so that the students could move from station to station and complete their thermometers. ( ie Station 1. had LC in the 20-25 C range, Station 2. LC in the 26.5-30.5 C range, Station 3. LC in the 30-33 range, Station 4. LC in the 33-36 C range, and Station 5. LC in the 37-40 C range) With the Students: Go through the information and activities in the power point presentation Attachments Liquid Crystal Presentation LCThermometer template Safety Issues Students should not eat the LC. Recommend using gloves and eye protection because LCs could be an irritant Recommend the LC vials be removed from the heat bath and put on tables away from the hot plate to prevent burns. Troubleshooting Tips 3 If the LC overheats the thermometer will not work. Have the student remove the tape barrier on the sticky side of the self-laminating pocket and affix the transparency temperature scale to the sticky side before applying the LC. Important: the transparency scale must be slightly smaller than the self laminating pocket or the two sides will not stick together when you are done. Investigating Questions 1. Why do different LCs have different colors in the LC phase? 2. Can you think of other applications for LCs? References McHale, M. Nanotechnology: Ferrofluids and Liquid Crystals, Connexions Web site. http://cnx.org/content/m15532/1.10/, Nov 6, 2008. Follow the synthesis directions for the liquid crystals http://dept.kent.edu/spie/liquidcrystals/ Owner Drexel University GK-12 Program Contributors Anna Fox Jennifer Atchison Dorothea Holmes -Stanley Copyright Copyright 2008 Drexel University GK-12 Program. Reproduction permission is granted for nonprofit educational use. 4