1 / 67

670 likes | 905 Vues

LC Applications. Behzad Pourabbas Polymer Eng. Department Sahand University of Technology Tabriz-Iran pourabas@sut.ac.ir. Overview:. Order Parameter Anisotropic Properties Light, polarization and materials . Order parameter “s”. The Order Parameter. n. q. n. perfect crystal

Télécharger la présentation
## LC Applications

**An Image/Link below is provided (as is) to download presentation**
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.
Content is provided to you AS IS for your information and personal use only.
Download presentation by click this link.
While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

**LC Applications**Behzad Pourabbas Polymer Eng. Department Sahand University of Technology Tabriz-Iran pourabas@sut.ac.ir**Overview:**• Order Parameter • Anisotropic Properties • Light, polarization and materials**The Order Parameter**n q n perfect crystal isotropic fluid**n**n Maier-Saupe Theory - Mean Field Approach 1.0 Isotropic Fluid Nematic Liquid Crystal Order Parameter, S 0.0 -0.6 Temperature**The Order Parameter:**How does it affects display performance ? The order parameter, S, is proportional to a number of important parameters which dictate display performance. proportional to Parameter Nomenclature Elastic ConstantKiiS2 BirefringenceDnS Dielectric Anisotropy De S Magnetic Anisotropy Dc S Viscosity Anisotropy Dh S Example: Does the threshold switching voltage for a TN increase or decrease as the operating temperature increases. Scales as the square root of S therefore lowers with increasing temperature**External Electric Field and Dielectric Properties of LC**molecules**Anisotropy: Dielectric Constant**E ++ e + ++ positive - - - - - e De = e - e > 0 E E + + + + - - - - negative all angles in the plane to E are possible for the -De materials De = e - e < 0**Anisotropy: Duel Frequency**high frequency, De<0 low frequency, De>0 MLC-2048 (EM Industries), Duel Frequency Material Frequency (kHz) 0.1 1.0 10 50 100 Dielectric Anisotropy (De) 3.28 3.22 0.72 -3.0 -3.4**Dielectric Constant**Dielectric Constant ke0L = C = q/V**E**Dielectric Material? • Dielectric materials consist of polar molecules which • are normally randomly oriented in the solid. • They are not conductors. • When a dielectric material is placed in an external • electric field, the polar molecules rotate so they align with • the field. This creates an excess of positive charges on • one face of the dielectric and a corresponding excess • of negative charges on the other face.**Dielectric Material**is smaller in many materials than it would be in a vacuum for the same arrangement of charges. Eg. Parallel plates: Dielectric material Eo Ei + + + + Net field: E=Eo-Ei This makes the potential difference smaller (V=Ed) between the parallel plates of the capacitor for the same charges on the plates and thus capacitance is larger, since Q=C/V.**Dielectric Constant**(“kappa”) = “dielectric constant” = (a pure number ≥ 1) So, (for parallel plates) Or Where C0 is the capacitance without the dielectric. Hence, the capacitance of a filled capacitor is greaterthan an empty one by a factor**Materials Dielectric Constant**Vacuum 1.0000 Air 1.0005 Polystyrene 2.56 Polyethylene 2.30 Nylon 3.5 Water 78.54 Dielectric Constants (@20oC, 1kHz) *Mixture Application Deee BL038 PDLCs 16.7 21.7 5.3 MLC-6292 TN AMLCDs 7.4 11.1 3.7 ZLI-4792 TN AMLCDs 5.2 8.3 3.1 TL205 AM PDLCs 5 9.1 4.1 18523 Fiber-Optics 2.7 7 4.3 95-465 -De material -4.2 3.6 7.8 *EM Materials PD: Polymer Dispersed AM: Active Matrix TN: Twisted Nematic**Flow of ions in the presence of electric field**Internal Field StrengthE = E0 – E’**Alignment of LC molecules in Electric Field**S = 0 1 > S > 0**m**m Dielectric Anisotropy and Permanent Dipole Moment**Dielectric Constants:**Temperature Dependence 4’-pentyl-4-cyanobiphenyl Temperature Dependence Average Dielectric Anistropy**Magnetic Anisotropy: Diamagnetism**Diamagnetism: induction of a magnetic moment in opposition to an applied magnetic field. LCs are diamagnetic due to the dispersed electron distribution associated with the electron structure. Delocalized charge makes the major contribution to diamagnetism. Ring currents associated with aromatic units give a large negative component to c for directions to aromatic ring plane. Dc is usually positive since:**Magnetic Anisotropy: Diamagnetism**Compound**light is a transverse wave: perpendicular to**Optical polarization • for any wavevector, there are two field components • any wave may be written as a superposition of the two polarizations**Light as Electromagnetic Wave**Plane Polarized light can be resolved into Ex and Ey**Ordinary light travels in the crystal with the same speed v**in all direction. The refractive index n0=c/v in all direction are identical. Extraordinarylighttravels in the crystal with a speed v that varies with direction. The refractive index n0=c/v also varies with different direction**Optical Anisotropy: Birefringence**ordinary ray (no, ordinary index of refraction) extraordinary ray (ne, extraordinary index of refraction)**Optical Anisotropy: Birefringence**ordinary wave extraordinary wave optic axis q For propagation along the optic axis, both modes are no**Birefringence (20oC @ 589 nm)**EM Industry Dn ne no Application Mixture BL038 0.2720 1.7990 1.5270 PDLC TL213 0.2390 1.7660 1.5270 PDLC TL205 0.2175 1.7455 1.5270 AM PDLC ZLI 5400 0.1063 1.5918 1.4855 STN ZLI 3771 0.1045 1.5965 1.4920 TN ZLI 4792 0.0969 1.5763 1.4794 AM TN LCDs MLC-6292 0.0903 1.5608 1.4705 AM TN LCDs ZLI 6009 0.0859 1.5555 1.4696 AN TN LCDs MLC-6608 0.0830 1.5578 1.4748 ECB 95-465 0.0827 1.5584 1.4752 -De devices MLC-6614 0.0770 --------- --------- IPS MLC-6601 0.0763 --------- --------- IPS 18523 0.0490 1.5089 1.4599 Fiber Optics ZLI 2806 0.0437 1.5183 1.4746 -De device**Birefringence: Temperature Dependence**Average Index Temperature Dependence**coefficients differ only by factor**• linear (plane) polarization • coefficients differ only by real factor Categories of optical polarization • circular polarization • elliptical polarization • all other cases**e.g. linear polarization at angle**• wavevector insufficient to define electromagnetic wave • we must additionally define the polarization vector Characterizing the optical polarization

More Related