Newswise — In the present era of digital information, an immense volume of data is exchanged and stored on a daily basis. Back in the 1980s, IBM introduced the first hard drive, which was as large as a refrigerator, capable of storing 1 GB of data. However, the progress made since then has been staggering, as we now possess memory devices with a thousand-fold greater data-storage capacity, compact enough to fit in the palm of our hand. With the exponential growth of digital information, the need for newer data recording systems becomes evident, emphasizing the importance of lighter, environmentally friendly options, and above all, higher data storage density.
In this context, a promising candidate for future high-density memory storage materials has emerged: axially polar-ferroelectric columnar liquid crystals (AP-FCLCs). These materials consist of liquid crystals arranged in parallel columns through molecular self-assembly, and they exhibit polarization along the column axis. The columns can switch their polar directions when subjected to an external electric field. If these AP-FCLCs can retain their polarization even after the electric field is removed, they present a host of advantages, such as flexibility, absence of metals in their composition, power-saving capabilities, and minimal environmental impact. All of these factors make AP-FCLCs highly suitable for ultra-high-density memory devices. However, there is a challenge to overcome - the fluid nature of liquid crystals makes the induced polarity vulnerable to external stimuli, resulting in potential data loss.
A team of researchers from Chiba University, led by Professor Keiki Kishikawa from the Graduate School of Engineering, alongside Doctoral Course student Hikaru Takahashi from the Graduate School of Science and Engineering and Associate Professor Michinari Kohri from the Graduate School of Engineering, has proposed an innovative solution to the aforementioned problem. Their groundbreaking study, which was made available online on June 12, 2023, and subsequently published in Volume 6, Issue 12 of ACS Applied Nano Materials on June 23, 2023, introduces a polarization fixation mechanism for a urea-based AP-FCLC system. With this mechanism, the materials can smoothly transition from the AP-FCLC phase to a crystal (Cr) phase without compromising the induced polar structure.
The researchers set out to create a compound that exhibits three distinct states: a writable and rewritable state, an erasure state, and a save state. They focused on minimizing any changes in the molecular packing structures during the FCLC−Cr phase transition process, which is crucial for the stability and reliability of the system. According to Professor Kishikawa, the main goal was to achieve a seamless and controlled phase transition, preserving the polarization and ensuring the integrity of data storage.
To create a polarization-fixable AP-FCLC system, the team synthesized 1,3-bis(3’,4’-di(2-butyloctyloxy)[1,1’-biphenyl]-4-yl)urea—an organic molecule consisting of urea at its molecular center for generating a hydrogen bonding network that can facilitate the formation of columnar aggregate in a liquid crystal (LC) state, two biphenyl groups as substituents for generating strong intermolecular interactions in the column structure, and four bulky alkyl groups as terminal chains to prevent tight molecular packing and enable lower-temperature FCLC−Cr phase transition.
The prepared FCLC system exhibited preservation of polarization in the Cr phase, with thermally stable polarization information storage and resistance to the external electrical field at room temperature. Furthermore, we found that the molecules self-sorted into nanosized helical columns, which then formed small domains and became ferroelectric in nature.
This study introduces an innovative approach to advancing AP-FCLC systems, enabling them to retain polarization information over extended periods. The proposed framework holds the promise of developing robust memory materials with remarkable resistance to external influences and minimal environmental impact. Professor Kishikawa emphasizes that AP-FCLCs possess the potential to achieve recording densities over 10,000 times larger than Blu-ray Discs. However, their practical application has been hindered by stability concerns. By addressing this instability issue, the research opens up opportunities for enhancing reliability, thus paving the way for the creation of lightweight, flexible electronic devices, and secure confidential information-recording systems that can be safely incinerated.
With these exciting advancements in liquid crystal technology, the future of memory storage appears to be on solid ground!
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