Solutions for Research & Development of Liquid Crystal (LC) Materials and Process Control
LCDs today are ubiquitous in daily life and the workplace, from TVs, mobile phones and computer displays to industrial instrument panels, avionics displays, and outdoor signage. However, the quality control, product life cycle, and safety of the LCD remain dependent on the purity of the liquid crystal materials used and the impurity control level during the manufacturing process. Nevertheless, several methods of analysis can be employed to address these issues and improve the overall process control.
1. Liquid crystal display (LCD) mechanisms
Liquid crystal (LC) is an organic material in a liquid state, but with properties of a solid crystal. LC maintains liquidity in a state of phase transition between a liquid and crystal state, and at the same time has a crystalline organization (molecular orientation and position).
The LC materials used in LCDs exhibit an elongated, rod-like molecular structure and show anisotropic characteristics, such as optical anisotropy (birefringence) and dielectric constant anisotropy. When LC is sandwiched between two finely grooved alignment layers, the LC molecules are oriented along the grooves of the alignment layer. If the two alignment layers are positioned, the grooves of each layer will be orthogonally oriented, and thus the LC molecules will be aligned in a distorted direction.
In a LCD panel, the LC layer sandwiched between the alignment layers is further sandwiched between two PVA polarization films that have a different oscillation direction than the transmitted light. A backlight is oscillated omnidirectionally, but the polarization film orients the incoming light in one direction.
In the state in which LC molecules are orthogonally oriented, incoming light is also distorted along the orientation of the LC molecules, and so the light can pass through the second polarization film. In contrast, when AC voltage is applied to the LC molecules, the direction of molecules is changed and oriented along the electric field. Incoming light then goes straight and passes through, and is then blocked by the second polarization film. The orientation of the LC materials can be controlled by turning the AC voltage ON/OFF, while the screen display can be controlled by turning the backlight ON/OFF.
2. Examples of LC materials
The basic structure of LC material exhibits a rod- or disk-like form molecule, and the long axis of the molecule is oriented in a single direction. LCD materials contain some solid component sat room temperature, and subsequently, the mixture is liquefied at a freezing point. The combination and mixing ratio of the materials are determined by the expertise of each supplier. Manufacturers are constantly looking to improve the performance of LC displays and some are working on enhancements through changing the mixing method for different types of LC materials with the base material, such as ester-based LC, biphenyl-based LC, and phenylcyclohexane-based LC. Target improvements for such R&D projects include:
- Voltage: Reduce electric consumption by decreasing the driving voltage.
- Temperature: Expand the stable-working temperature, ranging from low to high temperature.
- Viscosity: Improve the response speed applicable to video.
- Refractive index: Control colors and obtain bright white.
- Elasticity: Improve the orientation features of LC molecules when an AC voltage is applied to yield higher contrast.
Examples of LC material structure
3. Quality assessment of LC materials
When developing or manufacturing LCDs, identification and control of impurities in the materials, and of the degradation factors generated in the accelerated degradation test, are extremely important, from the perspective of quality control, extending product life, and the safety of the LC materials. HPLC and GC are commonly used for quality control and analysis of LC materials, and the proper method is selected depending on the intended purpose and of the materials. Although the column is a key component for separation, limited types of columns are available in GC due to the boiling point of materials and other limiting factors. GC also has limitations, especially for isomer separation. In HPLC, on the other hand, the separating capability is inferior to GC, and the possible overlooking of micro-components is a concern.
The combination of technology with high separation capability, a UPLC, and a high-resolution mass spectrometer (Xevo G2-XS QTof MS) allows for the high-quality separation analysis of LC materials. UPLC technology allows for the separation of several major LC materials in a short time, with micro-components as well. Additionally, in tandem with a time-of-flight mass spectrometer (Tof-MS) —characterized by comprehensive and high-sensitivity detection — the factors that vary minutely between pre- and post-accelerated degradation tests can easily and visually be identified, and the information related to the composition of these factors is able to be acquired. In MS/MS spectra, the components of fragment structure (product ions) can be analyzed, the structure can be predicted, and the predicted structure can be verified using MassFragment software.
- Accelerated degradation test using UV irradiation
- Accelerated degradation test by heating
- Test related to electrical resistance
Approach to quality assessment using instrumental analysis
Differential analysis between pre- and post-accelerated degradation test
→ UPLC H-Class/Xevo G2 Qtof MS
- High-speed, high-performance separation and analysis
- Scan speed
- Separation capability
- Long-term stability of accurate mass
- ESCi probe
- Ultra-high speed, high-performance separation and analysis
- Separation of low-polarity compounds
- Separation of isomers
- Separation of isomers
- Preparation and purification of targeted compounds at an industrial scale
- Large-scale preparation of a small amount of impurity
- Increase in the efficiency of the evaporation process
4. Examples of analysis of LC materials using UPLC/Xevo G2-XS Qtof MS
Examples of the separation/analysis of LC materials
With UPLC technology, LC materials with a similar structure can be clearly separated and analyzed in a short period of time. High-throughput analysis is available for more complex samples, such as generated impurities and deterioration products.
Examples of results from the component analysis of LC materials
This figure shows the results of component computing using MS/MS spectra with a component analysis function, which is a technology unique to Waters. Candidate components are reliably provided from the detected spectra using i-Fit (a unique Waters’ algorithm), that employs the extremely high accuracy of accurate mass and the spectra information of a stable isotope.
Examples of the MS/MS spectra of LC materials
MS/MS, using a Xevo G2-XS QTof system, enables the ability to analyze the product ions from the molecular structure with high accuracy and sensitivity. Regarding the product ion spectra as well, reliable component information can be obtained from the spectra information of accurate mass and a stable isotope.
Examples of the component analysis of product ions in MS/MS spectra
MS/MS, using a Xevo G2-XS QTof system enables the ability to analyze the product ions from the molecular structure with high accuracy and sensitivity. The simultaneous component computing of the product ions is available in MS/MS spectra. This is effective in structural analysis because it allows for the visual confirmation of the type of ion detachment reaction that occurs between major product ions.
Examples of the MassFragment fragmentation prediction software
The predicted structure in an MS/MS spectra can be verified using the MassFragment software. If there are contradictions in the fragment structural assignment from the predicted structure, the position of functional groups or other structural groups as well as the frame are reviewed and corrected, and verification using MassFragment is conducted again.
Waters’ solutions for research & development of LC materials and process control
- Auto-calibration by IntelliStart
- Long-term, highly precise accurate mass measurement by LockSpray
- Precise elemental composition analysis by i-Fit