The Interdisciplinary Laboratory
Pre-Lab Assignment
#2 for Experiment #7:
Synthesis and Characterization
of Liquid Crystals
Pre-Lab Assignment
#2 for Experiment #7:
Synthesis and Characterization
of Liquid Crystals
1. The following data were obtained for cholesteryl nonanoate/cholesteryl
chloride mixtures with x = 0.42 mole fraction of cholesteryl chloride.
Develop an equation for the line that represents the average refractive
index as a function of temperature in the range 35 to 65 °C.
(Note this exercise is exactly what you did for PreLab #1, without the
need to average three values of n parallel and three values of n perpendicular.)
| T/°C | n parallel | n perpendicular |
| 35.0 ± 0.2 | 1.5179 ± 0.0002 | 1.4943 ± 0.0002 |
| 45.0 ± 0.2 | 1.5141 ± 0.0001 | 1.4914 ± 0.0001 |
| 55.0 ± 0.2 | 1.5100 ± 0.0001 | 1.4887 ± 0.0002 |
| 65.0 ± 0.2 | 1.5055 ± 0.0002 | 1.4865 ± 0.0002 |
| Refractometer Calibration = -0.0026 ± 0.0001 | ||
2. The following data are available for the selective reflection as
a function of temperature of a mixture of cholesteryl chloride and cholesteryl
nonanoate with x = 0.42 (mole fraction) of cholesteryl chloride.
| T/°C | l/nm | %T |
| 30.1 ± 0.1 | 627 ± 1 | 63.5 ± 0.1 |
| 40.0 ± 0.1 | 642 ± 1 | 65.5 ± 0.1 |
| 50.0 ± 0.1 | 658 ± 1 | 67.8 ± 0.1 |
| 60.0 ± 0.1 | 679 ± 1 | 70.0 ± 0.1 |
| 70.0 ± 0.1 | 702 ± 1 | 72.3 ± 0.1 |
Using the line found in #1 and the data above, calculate the pitch of the cholesteric phase as a function of temperature in the range of 30 to 70 °C. Note: Pitch is not a linear function of temperature (nor is the peak transmission a linear function of temperature). A second-order polynomial should fit the data well. Read below for hints on the calculational method. BE SURE TO DESCRIBE YOUR CALCULATION PROCEDURE.
Hints on calculation procedure: Follow the instructions on p. 24 (Analysis) - do not worry about using/needing any isotropic refractive index data. (1) Calculate average refractive index values using equation 2. (2) Fit average refractive index as a linear function of temperature. (3) Fit the wavelength data above as a second-order polynomial in temperature. (By the way, %T is %Transmission. You do not need these data for the pre-lab assignment.) (4) Now find average n and wavelength at 5-10 set values of temperature (e.g., 30.0, 35.0, 40.0 degrees Celsius, etc.). (5) Calculate pitch at these 5-10 temperatures using equation 8. (6) Now fit the pitch values to a second-order polynomial in temperature.
Do you have any remaining questions about the background and/or protocol from the first week of the experiment?
Submit via e-mail the solutions to this pre-lab assignment to Professor
Karukstis (Kerry_Karukstis@hmc.edu)
by 8 p.m. on Monday, March 19 or 8 p.m. on Monday, April 9 (i.e., prior
to your second laboratory day).