RU2707424C1 - Electrically controlled light polarizer based on light scattering anisotropy - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: electrically controlled light polarizer based on light scattering anisotropy, having high light transmission and polarizing capacity, relates to optoelectronic equipment, in particular, to devices and elements based on liquid crystals and intended to control polarization and intensity of transmitted light using an electric field. Polarizer consists of two parallel transparent plates, at least on one of which electrodes are formed, which set direction of electric field along the plate, and arranged between plates and electrodes of polymer film with encapsulated therein drops of nematic liquid crystal, wherein components for composition "polymer – nematic liquid crystal" are selected so that n_⊥=n_p. Used composition provides a conical cohesion of the nematic liquid crystal with the polymer, as a result of which the director is oriented at angle of 40° to normal at polymer-liquid crystal interface, and in drops of nematic liquid crystal axial-bipolar ordering of director is formed.

EFFECT: technical result of invention is creation of electrically controlled light polarizer based on composite polymer-liquid crystal film with conical surface adhesion, having high light transmission value T_⊥ for directly passing polarized light component and high value of ratio T_⊥:T_|| when exposed to an electric field.

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Description

The invention relates to optoelectronic technology, in particular to devices and elements based on liquid crystals (LC) and designed to control the polarization and intensity of transmitted light using an electric field.

Known film polarizer based on the anisotropy of light scattering [Zyryanov V.Ya. et al. Elongated films of polymer dispersed liquid crystals as scattering polarizers. Molecular Engineering. 1992, v. 1, p. 305-310.], Which is a polymer-oriented polymer film with droplets of a nematic liquid crystal encapsulated in it, having an elongated ellipsoidal shape with a long axis parallel to the direction of extension of this composite film. The polymer used determines the tangential adhesion, in which the director of the LC (the preferred direction of orientation of rod-shaped molecules of the LC) is oriented parallel to the surface of the polymer. The composition of the composite film is selected so that the perpendicular component of the nematic's refractive index n _⊥ (the value of the refractive index for light polarized perpendicular to the director of the LC) is equal to the refractive index n _{p of the} polymer matrix (n _⊥ = n _p ), and the birefringence of the LCD (Δn = n _|| -n _⊥ ) was maximum. Here the || and ⊥ the polarization of light is noted parallel or perpendicular to the director of the LCD, respectively. In this case, light polarized parallel to the direction of stretching of the film is intensively scattered due to the large gradient of the refractive index (n _|| -n _p ) at the polymer-LC interface. The perpendicularly polarized light component passes without experiencing strong scattering if the relation n _⊥ = n _p is satisfied. Such a light polarizer based on the anisotropy of light scattering can have a sufficiently large value of the ratio of the polarized components of the light transmission (contrast) T _⊥ : T _|| and a large transmittance T _{⊥ of} directly transmitted radiation. For example, when a composite film is stretched 1.5 times, T _⊥ : T _|| = 420: 1 at T _⊥ = 0.5. Here T _⊥ and T _|| denote the light transmission components of light normally incident on the film polarizer, polarized, respectively, perpendicularly or parallel to the direction of extension of the composite film. In this case, the transmittance T _{⊥, ||} is determined by the ratio of intensity I _{CR, ⊥, ||} light transmitted through the film to intensities I _{⊥, ||} incident light polarized, respectively, perpendicularly or parallel to the direction of extension of the composite film T _{⊥, ||} = I _{pr, ⊥, ||} / I _{⊥, ||} . Film polarizers based on light scattering anisotropy, which are a polymer film with droplets of liquid crystal encapsulated in it, are characterized by mechanical strength, flexibility, and a simple and inexpensive manufacturing technology.

The closest analogous combination of essential features is a device for electrically controlled polarization of light [V. Presnyakov, S. Smorgon, V. Zyryanov, V. Shabanov. Volt-contrast curve anisotropy in planar-oriented PDChLC films // Mol. Cryst. Liq. Cryst. 1998. V. 321. P. 259 [703] -270 [714];], containing two parallel glass substrates with transparent electrodes on the inner sides, between which there is a uniaxially stretched polymer film with droplets of chiral nematic (cholesteric ) of a liquid crystal having an elongated ellipsoidal shape with a long axis parallel to the direction of extension of this composite film. The polymer used determines the tangential adhesion for the selected liquid crystal, in the drops of which a twisted ordering of the director is formed with the spiral axis of the perpendicular surface of the drop. The composition of the composite film was selected so that the perpendicular component of the refractive index of the liquid crystal n _⊥ was close to the refractive index n _{p of the} polymer matrix (n _⊥ = n _p ). In the initial state, the composite film intensively scatters normally incident light of any polarization, and under the action of an electric field directed perpendicular to the film of about 70 V at a film thickness of 45 μm (i.e., at a field strength of about E = 1.5 V / μm) goes into a partially transparent state with light transmission T _⊥ = 0.37 for light polarized perpendicular to the direction of film stretching. In this case, the value T _⊥ is achieved: T _|| = 74: 1 ratio of the perpendicular component of the light transmission to the parallel component.

The disadvantages of the known device are the low transmittance T _⊥ for the directly transmitted polarized light component and the small ratio T _⊥ : T _|| achieved by exposure to an electric field.

The technical result of the invention is to provide a light polarizer electrically controlled on the basis of a composite polymer-liquid crystal film with a conical clutch surface having a high value of light transmittance T _⊥ for directly passing light polarized components and a large value of the ratio T _⊥: T _|| when exposed to an electric field.

The indicated technical result is achieved in that in an electrically controlled light polarizer based on light scattering anisotropy, consisting of two parallel arranged transparent plates, at least one of which has electrodes formed that specify the direction of the electric field along the plate, and located between the plates and electrodes of the polymer film with droplets of a nematic liquid crystal encapsulated in it, the components for the composition “polymer - nematic liquid crystal” being selected t Since n _⊥ = n _p , it is new that the components selected for the specified composition provide conical adhesion of the nematic liquid crystal to the polymer, as a result of which the director is oriented at an angle of 40 ° normal to the polymer-LC interface, and in drops Nematic liquid crystal forms an axial-bipolar ordering of the director.

The differences of the claimed electrically controlled light polarizer from the prototype are that for the polymer-liquid crystal composition, components are selected that provide conical adhesion of the nematic liquid crystal to the polymer, as a result of which the director is oriented at an angle of 40 ° to the normal at the polymer-LCD interface , and in the droplets of a nematic liquid crystal an axially bipolar director ordering is formed.

These signs allow us to conclude that the proposed technical solution meets the criterion of "novelty."

When studying other well-known technical solutions in this technical field, the features that distinguish the claimed invention from the prototype are not identified and therefore they provide the claimed technical solution with the criterion of "inventive step".

The invention is illustrated in the drawing, which schematically shows a cross section of the inventive electrically controlled light polarizer (Fig. 1).

The inventive electrically controlled light polarizer contains a polymer film 1 with droplets of nematic liquid crystal 2 encapsulated in it, having the form of an ellipsoid flattened in the plane of the film, in which the axial-bipolar configuration of the director is realized. Polyisobutyl methacrylate (PiBMA) (www.sigmaaldrich.com) was used as a polymer. The nematic mixture LN-396 [MN Krakhalev, O.O. Prishchepa, VS Sutormin, V.Ya. Zyryanov. Director configurations in nematic droplets with tilted surface anchoring // Liq. Cryst. 2017. V. 44. P. 355-363], for which a conical coupling is realized on the border with PiBMA, as a result of which the director is oriented at an angle of 40 ° to the normal at the polymer-ZhK interface. In this case, the perpendicular component of the refractive index of the nematic mixture LN-396 n _{⊥ is} approximately equal to the refractive index n _{p of the} polymer matrix (n _⊥ = n _p ). The composite film is located between two transparent plates 3, which can be used glass substrates or flexible polymer films made, for example, of polyethylene terephthalate. The thickness of the composite film is set by the spacers 4. Two electrodes 5 are applied on one of the plates (in FIG. 1, lower) in the form of parallel strips, the cross section of which is shown in FIG. one.

The inventive electrically controlled polarizer of light functions as follows. In the absence of an external electric field (Fig. 1a), the composite film scatters normally incident light of any polarization due to the random orientation of the bipolar axes 6 in LC droplets 2 with an axial-bipolar director configuration. When applying an electric signal to the electrodes 5, the bipolar axes of 6 drops of nematic 2 are oriented along the electric field E directed along the plates (Fig. 1b). In this case, normally incident light 7 polarized along the applied electric field is intensively scattered, and light 8 polarized perpendicular to the electric field passes through the composite film without experiencing strong scattering due to the proximity of the perpendicular component of the refractive index of the LC n _⊥ and the refractive index of the polymer matrix n _p . As a result, when unpolarized radiation is incident on the device at the exit from it, the light becomes polarized perpendicular to the direction of the applied electric field.

Examples:

As a first example, an electrically controlled light polarizer was manufactured based on the anisotropy of light scattering using the following operations:

1. On a glass plate coated with two transparent ITO electrodes separated by a distance of 650 μm from each other, there was a composite film made by phase separation by evaporation of the solvent based on PiBMA polymer and nematic mixture LN-396. The weight ratio of PiBMA and LN-396 was 40:60, respectively.

2. Teflon spacers with a thickness of 20 μm were placed on a part of the plate with an uncoated composite film.

3. The composite film and Teflon spacers were covered with a glass plate, and the resulting cell was placed under a press.

4. The press with the cell described above was heated to 70 ° C and held at this temperature for 30 minutes, and then cooled to room temperature. As a result, an electrically controlled light polarizer was formed based on the light scattering anisotropy shown in FIG. one.

For such a polarizer, when an electric field of about 0.34 V / μm is applied, unpolarized light after passing through the composite film becomes linearly polarized in the direction perpendicular to the applied electric field. The value of the ratio of the polarized light transmission components T _⊥ : T _|| is 81: 1, and the transmittance of directly transmitted radiation is T _⊥ = 0.7.

As a second example, an electrically controlled light polarizer was manufactured based on the anisotropy of light scattering using the following operations:

1. On one glass plate coated with two transparent ITO electrodes, separated by a distance of 650 μm from each other, was a composite film made by phase separation by evaporation of the solvent based on PiBMA polymer and nematic mixture LN-396. The weight ratio of PiBMA and LN-396 was 40:60, respectively.

2. Teflon spacers 15 μm thick were located on a part of the plate with an uncoated composite film.

3. The composite film and Teflon spacers were covered with a second glass plate with two transparent ITO electrodes separated by a distance of 650 μm from each other and located opposite the electrodes of the first plate (Fig. 2), after which the resulting cell was placed under the press.

4. The press with the cell described above was heated to 70 ° C and held at this temperature for 30 minutes, and then cooled to room temperature. As a result, an electrically controlled light polarizer was formed based on the light scattering anisotropy shown in FIG. 2., where structural elements have the same designations as in FIG. one.

For such a polarizer, when an electric field of about 0.34 V / μm is applied, unpolarized light after passing through the composite film becomes linearly polarized in the direction perpendicular to the applied electric field. The value of the ratio of the polarized light transmission components T _⊥ : T _|| is 590: 1, and the transmittance of directly transmitted radiation is T _⊥ = 0.89.

As a third example, an electrically controlled light polarizer was manufactured based on the anisotropy of light scattering using the following operations:

1. On one glass plate coated with two transparent ITO electrodes, separated by a distance of 650 μm from each other, was a composite film made by phase separation by evaporation of the solvent based on PiBMA polymer and nematic mixture LN-396. The weight ratio of PiBMA and LN-396 was 40:60, respectively.

2. Teflon spacers 25 μm thick were located on a part of the plate with an uncoated composite film.

3. The composite film and Teflon spacers were covered with a second glass plate with two transparent ITO electrodes separated by a distance of 650 μm from each other and located opposite the electrodes of the first plate, after which the resulting cell was placed under the press.

4. The press with the cell described above was heated to 70 ° C and held at this temperature for 30 minutes, and then cooled to room temperature. As a result, an electrically controlled light polarizer was formed on the basis of light scattering anisotropy, the design of which corresponds to FIG. 2.

For such a polarizer, when an electric field of about 0.34 V / μm is applied, unpolarized light after passing through the composite film becomes linearly polarized in the direction perpendicular to the applied electric field. The value of the ratio of the polarized light transmission components T _⊥ : T _|| is 2580: 1, and the transmittance of directly transmitted radiation is T _⊥ = 0.62.

Studies of the obtained experimental samples showed that the claimed electrically controlled light polarizer in terms of physical and technical characteristics is not inferior to the prototype. At the same time, simultaneously achieved higher values of light transmission T _⊥ for the directly transmitted polarized light component and the ratio T _⊥ : T _|| when exposed to an electric field. So, for the device described in the 2nd example, under the influence of an electric field, an increase in the ratio of the polarized transmittance components T _⊥ : T _|| 8 times, and the value of the light transmission component T _⊥ increased by 2.4 times in comparison with the prototype.

The proposed electrically controlled light polarizer based on light scattering anisotropy can be used in such optoelectronic devices and devices where it is necessary to have a compact, cheap, easy to manufacture and reliable in operation element for controlling the polarization of transmitted high-intensity optical radiation. Such light polarizers are promising for use in projection devices, lighting, and laser systems.

Claims (1)

An electrically controlled light polarizer based on light scattering anisotropy, consisting of two parallel transparent plates, at least one of which is formed of electrodes that specify the direction of the electric field along the plate, and located between the plates and electrodes of the polymer film with nematic liquid crystal droplets encapsulated in it moreover, the components for the composition "polymer - nematic liquid crystal" are selected so that n _⊥ = n _p , characterized in that for the specified composition The components were selected to ensure conical adhesion of the nematic liquid crystal to the polymer, as a result of which the director is oriented at an angle of 40 ° to the normal at the polymer-LC interface, and axial-bipolar director ordering is formed in the nematic liquid crystal droplets.

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