May 26 - June 1

Week 9
After creating the final prototype last week, the focus of this week was drafting the report and final powerpoint presentation. For the paper, tables and figures had to be collected from previous weeks along with pictures of the project's progress. Also, the final prototype was tested this week using an AC power source. The test plate was also connected to a voltmeter and tested in increasing increments of 5 volts. It was not until 25 volts were applied that the prototype became fully transparent. 


Due to time constraints, not all aspects of the design were explored. If this project was to be developed in the future, the final working prototype would be connected to a dimmer switch and variable resistor. This way, the user would have full control over the transparency of the windowpane. An ambient light sensor would be incorporated into the circuit as well. This would allow the opacity to be self-adjusting based on the sensor's reading on the intensity of incoming light. 


In preparation for the final report, additional research was conducted on the polarization of the liquid crystals and its electro-optic properties. The variety of uses for PDLC films was also researched over the course of this week. The uses for electrically switchable thin films is growing, as this technology can be applied to automotive moonroofs and displays, architectural facades and windows, and aircraft information display panels. PDLC films and electrochromic and suspended particle devices are examples of common glazing technologies that operate on an electric switch [6]. PDLC films are widely accepted for use in automotive and architectural applications because they have excellent optical properties, are simple to produce, and are durable and long lasting.

[7].

May 19 - May 25

Week 8
During this week's lab, the final prototype was created using the 70% liquid crystal to polymer ratio determined in Week 7. This model was constructed on conductive glass plates as opposed to the plastic substrates because glass creates a better seal with fewer air bubbles within the thin film. In addition to forming a more effective seal, the glass also allowed the wires to be soldered directly onto the plates. The final prototype can be connected directly to the voltage supply through these wires, which serve to set up a potential difference across the thin film. Below is the ratio of polymer to liquid crystal within the PDLC thin film of the final prototype. 

Polymer	Mass Added	Experimental Ratio
0.15 g	0.3571 g	0.702
Liquid Crystal	Mass Added	Experimental Ratio
0.35 g	0.1517 g	0.298

After measuring the correct ratio, spacers were added to the mixture in order to distribute the thin film at a uniform thickness of 8 microns. The balloon press was again used to flatten the film between the plates uniformly. A latex balloon inflates over the glass and thin film, applying a great deal of pressure that distributes the film evenly between the plates. The seal is created by the immense pressure and then the plates are cured for approximately five minutes. This serves to harden the film so that the liquid crystal can set and a voltage can be applied across the plates. 
Once the prototype had been cured, the wires were soldered onto opposite sides of the conductive plates using an equally conductive metal pellet. 

May 12 - May 18

Week 7 
Returning to the Nanoparticles lab on Tuesday, larger ratios of liquid crystal to polymer were tested. Each test mixture was approximately 0.50 g, with the ratio of liquid crystal varied from 55 to 70%. Four different mixtures were again measured using the same procedure. The substrates containing 55%, 60%, and 65% liquid crystal were placed in the vacuum press, which served to both uniformly distribute the polymer dispersed liquid crystal and harden the film. The mixture containing 70% liquid crystal was placed between glass and the PDLC distributed evenly under a balloon press. Spacers were also added to each PDLC mixture in order to regulate the droplet size of the liquid crystal. The table below shows the measurements and experimental ratios for each of the four tests. 

Polymer	Mass Added	Experimental Ratio
0.45	0.2399 g	0.4272
0.40	0.2065 g	0.4066
0.35	0.1762 g	0.3524
0.30	0.1504 g	0.2926
Liquid Crystal	Mass Added	Experimental Ratio
0.55	0.2864 g	0.5728
0.60	0.2967 g	0.5934
0.65	0.3238 g	0.6476
0.70	0.3537 g	0.7074

The results of this experiment showed that greater ratios of liquid crystal have greater transparency changes under an applied voltage. As a result, the prototype will use a mixture containing approximately 70% liquid crystal to maximize the shift in opacity. Each of the experimental substrates below were tested with an applied voltage of around 28 volts. This changed the orientation of the liquid crystal and the polarization allowing light to pass through.   In the image below, the four test plates are shown with varying ratios of liquid crystal. The tests with PDLC film between conductive substrates contain multiple air bubbles, while the glass showed uniform opacity. 

May 5 - May 11

Week 6
This past Tuesday, the ratios of polymer to liquid crystal were tested in the Nanoparticles Lab. Each test mixture was around 0.50 g, with the ratio of liquid crystal to polymer varied each time. Four different mixtures were measured, with the amount of liquid crystal added ranging from 25% to 40%. The table below shows the measurements and experimental ratios for each of the four tests. 

Polymer	Mass Added	Experimental Ratio
0.75	0.3823 g	0.7561
0.70	0.3613 g	0.7033
0.65	0.3359 g	0.6531
0.60	0.3013 g	0.6009
Liquid Crystal	Mass Added	Experimental Ratio
0.25	0.1233 g	0.2439
0.30	0.1524 g	0.2967
0.35	0.1784 g	0.3469
0.40	0.2001 g	0.3391

The polymer dispersed liquid crystal mixture was then placed between two thin sheets of conductive substrate in order to create a thin film. A balloon press was used to distribute the PDLC evenly across the substrate. The four test plates had to be cured in order for the polymer dispersed liquid crystal film to harden. Each was then tested with an applied voltage of 2.0 V to find the polymer to liquid crystal ratio which maximized the privacy glass effect. 

However, the results of this experiment showed that an even greater ratio of liquid crystal to polymer would be more effective. The substrate with the PDLC mixture containing 40% liquid crystal had only a faint difference in transparency under the applied voltage. 

The hardened polymer dispersed liquid crystal thin film should appear as a translucent white material or milky, in order to become transparent under the applied voltage. The only test plate that shows this characteristic is the one with the least amount of polymer. 

Each of the 4 substrates tested with varied ratios of polymer to liquid crystal. 

April 28 - May 4

Week 5
This week further research on liquid crystals and the components used to build the privacy glass was conducted. Additionally, a prototype of the dimmer switch was built using a variable resistor, wire, a bread board, and batteries. During construction of the prototype, the dimmer switch was tested with an LED in lieu of the privacy glass, as the polymer dispersed liquid crystal film has not yet been constructed.

Prototype dimmer switch with 6volt battery and LED to test the switch.

During class this week, the procedure was written out for the construction and testing of the PDLC film. The original plan to use panes of glass as a surface on which the liquid crystals will be fixed were modified. This was decided due to the ability of plastic to resist breaking, unlike the inert fragility of glass.

The following procedure will be used for creating the PDLC film and testing the different types of liquid crystal and polymer combinations. The procedure also outlines the process of finding the ratio of liquid crystals to polymer. This ratio is important in forming the proper size bubbles that will block or let in light within the privacy glass. Once the correct ratio has been found, different polymer types will be tested to find the one that works best as a solution to the problem. 

In the upcoming class this week, the above procedure is expected to be successful, but as any experiment goes, there will most likely be unaccounted problems that will cause changes to be made in this procedure.