Liquid Crystal Testing
Polymer liquid crystal is a special state of polymer liquid, and its rheological behavior in the molding process is different from that of polymer solution and melt. After the liquid crystal is condensed into a solid state, its molecular orientation factors have a great influence on the mechanical and photoelectric properties of the solid polymer. Therefore, the characterization of liquid crystal state is an important means to obtain the necessary data to study the properties and processing conditions of liquid crystalline polymer materials. At present, polymer liquid crystals have been widely used in the fields of high performance engineering materials, graphic displays, information storage media and chromatographic separation materials. As a professional reliability third-party testing organization, T,C&A Lab can provide Liquid Crystal Testing service according to ISO, ASTM standards and industry requirements. Welcome to contact our experts for consultation.
Types of liquid crystal materials
According to the conditions of liquid crystal formation, it can be divided into lyotropic liquid crystal and thermotropic liquid crystal.
- Lyotropic liquid crystals are liquid crystals formed by putting certain organics in a certain solvent and the solvent destroys the crystalline lattice, which is called lyotropic liquid crystals. For example: simple fatty acid salts, ionic and non-ionic surfactants, etc.
- Thermotropic liquid crystals are liquid crystal phases that appear due to temperature changes. It has a crystalline structure at low temperature, and becomes liquid at high temperature. The temperature here is indicated by the melting point (TM) and the clearing point (TC). The materials used for display are basically thermotropic liquid crystals. In thermotropic liquid crystals, it is divided into three categories according to the arrangement of liquid crystal molecules: smectic phase, nematic phase and cholesteric phase.
Key testing items for polymer liquid crystal materials
- Is there a liquid crystal state
- What kind of phase change
- Phase transition temperature
Performance testing services of liquid crystal materials
- Melting point
- Clearing point
- Optical anisotropy
- Dielectric anisotropy
- Elastic constant
- Threshold voltage
- Saturation voltage
Our testing methods
- Hot Stage Polarizing Optical Microscope (POM)
- Differential Scanning Calorimeter Method (DSC)
- X-ray Diffraction Method (XRD)
- Nuclear Magnetic Resonance Spectroscopy (NMR)
- Dielectric Relaxation Spectroscopy
- Birefringence Method
- Electron Microscope
- Infrared Spectrum
It is the most commonly used, easiest and preferred method to detect new liquid crystal substances. If a substance is observed to have fluidity, optical anisotropy and various color optical patterns, it can be confirmed that there is a liquid crystal state and liquid crystallinity. In addition, the POM method can also study the molecular orientation of the thermotropic liquid crystal, the defects of the orientation state, and other phase morphology information, the optical positive and negative of the liquid crystal, the number of light, and the generation and phase separation process of the lyotropic liquid crystal.
Observation results through a polarizing microscope
|Liquid Crystal||Appearance||Optical properties|
|Cholesteric phase||Fluids that are similar to both smectic and nematic phases||Negative uniaxial crystal, extremely strong optical rotation, reflecting circular polarization of a specific wavelength.|
|Nematic phase||A flowing turbid liquid that forms a meniscus in a capillary||Positive uniaxial crystal shows a filamentous texture texture image under a polarized light microscope.|
|Smectic phase||Greasy, viscous turbid liquid||Positive uniaxial crystal shows a pyramidal texture texture image under a polarized light microscope.|
DSC is mainly used to study the phase behavior of liquid crystals. One of the uses of the DSC method is to provide phase transition temperature data for liquid crystal polymer materials. The second use is to judge the type of liquid crystal according to the hot melt value of each transition point on the graph. The smectic phase has the highest order, so the hot melt value is the highest, about 6.3-21 KJ/mol. The enthalpy value of nematic liquid crystal is relatively low, about 1.3-3.5 KJ/mol. The internal structure of the cholesteric liquid crystal is similar to the nematic phase, so its enthalpy value is also similar to that of the phasic liquid crystal.
X-ray diffraction method is one of the most powerful means to identify three-dimensional ordered structures. It is also very effective to judge the type of liquid crystal phase. Its function cannot be replaced by POM and DSC methods.
NMR technology is an analytical technique to determine the structure of a specific electron spin magnetic moment in a molecule that is affected by the surrounding chemical environment. The research and development of polymer liquid crystals have shown that NMR technology is a very effective analysis tool for hot melt forming of liquid crystals. NMR spectroscopy can provide useful information for molecular orientation, molecular dynamics and solid-state structure research.
Polymer liquid crystals are aggregates in which molecules are arranged according to a specific law, which can be reacted by the shape of dielectric relaxation spectra.
Birefringence method is one of the more effective and simple methods to determine the degree of molecular orientation. Most polymer liquid crystals have obvious birefringence, so the birefringence measurement of polymers is an important detection method.
For different crystalline polymer liquid crystals, due to the different microstructure, the micro-morphology displayed under the microscope is different. According to the micro-morphology observed under the electron microscope, it can provide a lot of direct evidence for the study of the phase state of the polymer liquid crystal. Based on this, the crystal phase structure of liquid crystal can be judged.
Infrared spectroscopy is often used as a tool for chemical structure analysis of polymer liquid crystals.
Note: this service is for Research Use Only and Not intended for clinical use.
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