How to make Smart Glass Film ?
The smart glass film is PDLC Technology product.
Its main material is PET film+ITO +Polymer Dispersed Crystal+Ito+PET film, it is sandwich layer structure.
PET full name is Polyethylene Glycol Terephthalate.
ITO Full name is Indium tin oxide（ITO),In2O3 • SnO2.
The smart glas film is made by dispersing liquid crystal in the form of micron-sized droplets in the polymer matrix between two transparent film materials, and is made by a special process. Since the optical axis of the small droplet composed of liquid crystal molecules is in a disordered state of freely oriented liquid crystal material, its refractive index does not match that of the matrix. When the light passes through the matrix, the back droplet is strongly scattered and presents an opaque opalescent state. or translucent state. Applying an electric field can adjust the orientation of the optical axis of the liquid crystal droplet, and turn the disordered liquid crystal material into an ordered state. When the refractive index of the two matches, it is transparent. When the electric field is removed, the liquid crystal microdroplets return to the original state of astigmatism, thereby displaying.
In the smart glass film system, the nematic liquid crystal is uniformly dispersed in the solid organic polymer matrix as micron-sized droplets. Without voltage, the optical axis of each small droplet is in a preferred orientation, while all particles The optical axis is in a disordered orientation state. Since liquid crystal is a material with strong optical and dielectric anisotropy, its effective refractive index does not match the refractive index of the matrix (the difference is large), and the incident light can be strongly scattered to appear opaque or translucent opalescent state. When an external electric field is applied, the direction of the optical axis of the nematic liquid crystal molecules is uniform along the direction of the electric field, and the ordinary refractive index of the liquid crystal particles matches that of the matrix to a certain extent, and the light can pass through the matrix and become transparent or translucent. When the external electric field is removed, the liquid crystal particles return to the original scattering state under the action of the elastic energy of the matrix, so the polymer dispersed liquid crystal film has the characteristic of electrically controlled optical switching under the action of the electric field.
1. The relationship between transmittance and voltage
The relationship between transmittance and voltage is affected by temperature. When the temperature is low, the voltage value and threshold voltage value required to obtain a large transmittance increase. This is the characteristic of all PDLC films since the temperature. In addition, when the temperature is low, the hysteresis effect of the T-V curve becomes more obvious.
2. The relationship between transmittance and slope length
When λ>700nm, the transmittance begins to increase significantly in the off state. In the vicinity of near-infrared and visible red light, the transmittance in the off state can be reduced by increasing the particle diameter, increasing the thickness of the film and adding dyes, but increasing the cell thickness will reduce the transmittance in the on state , increasing the particle size reduces the valve voltage and increases the total scattering area, that is, increases the percentage of scattered light.
3. Response time
For films with a film thickness of less than 20 microns, the typical turn-off time can vary from 50ms at room temperature to 600ms at minus 10oC; the turn-off time is not strongly dependent on the starting voltage, except at very low temperatures, because when the temperature When it is low, it is difficult to completely arrange the LC in the particle, and this arrangement is related to the transmittance, and the off time at this time increases with the increase of the voltage.
For a reasonable start-up voltage of 60-100V, the turn-on time of PDLC is a few ms at room temperature, and about 250ms at minus 10oC. Like conventional TN elements, the turn-on time is inversely proportional to the square of the start-up voltage. At any temperature, increasing the film thickness increases the turn-on voltage and decreases the turn-off time, because the arrangement of molecules in the film depends on the electric field, and the electric field is correspondingly smaller when the film is thicker.
4. Operating temperature range
The effect of high polymer matrix on the operating temperature range of LC can be understood by the measurement of DSC phase transition temperature. Studies have shown that LC should be dissolved in polymers as a plasticizer. When LC is a mixture, one of them dissolved in polymers will affect the phase transition of LC. Similarly, polymer prepolymers should be dissolved in LC. It can act as an impurity to lower the phase transition temperature of LC.
5. Contrast (contrast)
Contrast is the most widely accepted indicator to measure the characteristics of PDLC film optoelectronic materials. There are two different methods to measure the contrast ratio of PDLC film.
The first method is based on measuring the normalized luminance in the on and off states using a diffuse light source. This method depends largely on the nature of the light source used for illumination, so the nature of the light source must be specified when measuring.
The second method is based on the spectral transmittance of the on state and off state of the PDLC film. The values measured by the transmittance method can be compared between laboratories, as long as there is no difference between the acceptance angles of the measuring instruments. big difference.
In order to improve the contrast, dichroic dyes can be mixed into the liquid crystal, because PDLC does not have controllable absorption and reflection. Generally, in the film made of microcapsules, the liquid crystal and the dye can be mixed first and then dispersed in the polymer. , so that the amount of dye dissolved in the polymer is small, and the contrast of PDLC is high. In the PDLC film prepared by the phase separation method, some dyes should be dissolved in the polymer to affect the light transmission of the on state, making the contrast smaller. In order to understand the optical properties of PDLC after adding dyes, it is necessary to clearly understand the orientation of liquid crystals in the film and the order parameters of the mixture of liquid crystals and dyes. These are the two most important factors when PDLC films work according to the guest-host effect.