Physicists at the University of Colorado Boulder have become the first to observe a new phase of matter in liquid crystals. The “ferroelectric nematic” phase, which was first predicted to exist over 100 years ago, could find applications in many different areas, from new types of display screens to reimagined computer memory, says study leader Noel Clark.
美國科羅拉多大學博爾德分校的物理學家們，已經成為觀察液晶中，一種新物質相的第一人。該項研究領導人Noel Clark表示，1百多年前，首度被預測存在的“鐵電向列”相，在諸多不同領域中可能找到，從新型顯示幕到重新構想之電腦記憶體的若干應用。
“There are 40 000 research papers on nematics, and in almost any one of them you see interesting new possibilities if the nematic had been ferroelectric,” Clark explains. “Our discovery of one such liquid crystal could open up a wealth of technological innovations.”
Clark解釋：「針對向列(液晶的特徵，其分子的長軸排列，成平行線而不是層)有4萬篇研究論文，且幾乎在其中任一篇論文中，倘若已經是鐵電體，皆能發現有趣的新可能性。我們有關一種此類液晶的發現，可能開啟大量的技術創新。」
Nematic liquid crystals display an odd mix of fluid- and solid-like behaviours, and get their name from the Greek word nema, meaning “thread” – a reference to the characteristic thread-like topological defects they contain. These defects are known as disclination lines, and they can be made of elongated molecules or colloidal particles.
向列型液晶展現了，混合類似液體與固體的奇特變化，並從希臘語nema得其名，意味著“線”，意指它們具有特徵性的線狀拓撲缺陷。這些缺陷，被通稱為錯位線。它們會由細長的分子或膠質粒子造成。
These molecules are polar, with one end carrying a positive charge and the other a negative one. In a traditional nematic crystal, half of these molecules will on average point in one direction (right, for example) and the other half in the other (say, left).
此些分子是極性的，一端具有正電荷，另一端具有負電荷。在傳統向列晶體中，此些分子平均，一半會指向一個方向(譬如右)，而另一半指向另一方向(亦即左)。
A ferroelectric nematic liquid crystal is more organized. Within specific patches or “domains”, all of its molecules point in the same direction. This phenomenon is known as polar ordering, and its appearance in nematic liquid crystals was first hypothesized in the 1910s by the Nobel laureates Peter Debye and Max Born.
鐵電向列液晶是更為有序的。在特定小區域(也就是疇)內，其所有分子皆指向相同方向。此現象，被通稱為極性的有序化。諾貝爾獎得主，Peter Debye及Max Born，於1910年代，首度臆測這種現象，出現於向列液晶中。
They predicted that if a liquid crystal were designed correctly, its molecules could spontaneously fall into a polar ordered state. Shortly afterwards, researchers discovered solid crystals in which molecules did indeed point in uniform directions.
他們預測，倘若正確設計液晶，其分子會自發地進入一種極性的有序狀態。其後不久，研究人員們發現，於固態晶體中，實際上分子確實指向，一致的方向。
The direction of these molecules could be reversed, from right to left or vice versa, when an electric field was applied – a property that inspired the name “ferroelectrics” because of similarities to ferromagnets. Despite much searching, however, a liquid crystal phase that behaves in the same way proved elusive – until now.
當施加電場時，此些分子的方向，能從右被反轉到左，反之亦然。這是使人給予鐵電體名稱之靈感的一種屬性，因為與鐵磁體的相似性。儘管進行了大量探查，不過迄今為止，以同樣方式表現的液晶相，經證實是難以捉摸。
Clark and colleagues observed their ferroelectric nematic liquid crystal phase in an organic molecule known as RM743. This molecule was created by another team a few years ago, in a study that showed that it exhibits a conventional nematic crystal phase at high temperatures. When cooled, however, another unusual phase appeared, and it is this phase that the Colorado researchers analysed using polarized light microscopy.
在一種被通稱為RM743的有機分子中，Clark及同僚們觀察到，他們的鐵電向列液晶相。這種分子是幾年前，於一項顯示其在高溫下，展現一種傳統向列晶體相的研究中，由另一個團隊創造的。不過，當被冷卻時，出現了另一種不尋常的相，這是科羅拉多大學博爾德分校研究人員們，使用偏光顯微鏡技術分析出的相。
During their measurements, the researchers observed that when they applied a weak electric field to the material, a striking palette of colours developed towards the edges of the cell containing the liquid crystal. Overall, the team found that in this phase, RM734 is 100 to 1000 times more responsive to electric fields than traditional nematic liquid crystals. According to their calculations, this means that the molecules making up the crystals show strong polar order.
在進行測定期間，當他們向材料施加弱電場時，此些研究人員觀察到，一道色調顯眼的色彩，向具有此種液晶之小腔的邊緣展開。總體上，該團隊發現，在此相中，RM734比傳統向列液晶，對電場更敏感1百到1千倍。根據他們的計算，這意味著組成此晶體的分子，展現強烈的極性順序。
圖1. 隨著研究人員施加小電場，這種新發現之液晶相中的顏色發生變化。 (圖援用自原文)
The researchers also discovered that distinct domains form spontaneously in the liquid crystal when it is cooled from higher temperatures. This suggests that there are patches within the materials in which the molecules seem to be aligned – a hallmark of a ferroelectric nematic fluid, Clark says. Surprisingly, the alignment was more uniform than expected for a fluid, in which entropy reigns and there should be a lot of disorder.
此些研究人員也發現，當從較高溫度被冷卻時，在此液晶中，自然形成諸多不同的疇。Clark表示，這暗示，在分子似乎對齊(鐵電向列液體的一種特徵)的此材料內，有諸多小區域。令人訝異的是，就一種熵(對物理系統之無秩序或亂度的量)占優勢且應該有很多無秩序的液體而言，這種對齊比預期更為均勻。
When the team analysed how well aligned the molecules were inside a single domain, they were “stunned” by the result. The molecules were nearly all pointing in the same direction, with only a few pointing in a completely different direction.
當該團隊分析，在單一疇內，分子排列有多整齊時，他們被結果“驚呆了”。此些分子幾乎全指向同一方向，僅少數指向完全不同的方向。
The researchers, who report their work in PNAS, say they are now busy trying to understand the mechanisms behind this alignment. “Our work suggests that there are other ferroelectric fluids hiding in plain sight,” says Clark. “It is important for us now to broaden the pool of molecules beyond the few (roughly five) now known to show this phase,” he tells Physics World.
這些在《美國國家科學院院刊》(PNAS：Proceedings of the National Academy of Sciences)記述其研究結果的研究人員們表示，目前他們正忙著試圖瞭解，這種排列背後的機理。Clark宣稱：「我們的研究暗示，隱藏在眼前的有其他鐵電液體。」他告訴Physics World：「目前對我們而言，擴大除了少數(大約五種)已知展現這種相之外的分子庫，這是重要的。」
The materials unearthed so far show the ferroelectric phase at elevated temperatures, so one goal of future research is to find room temperature materials, he adds. “We’re moving towards using artificial intelligence (AI) to screen potential new molecules without having to actually synthesise them. Indeed, 200 000 new molecular designs were made in the development and evolution of conventional nematic crystals LCDs, so we could avoid going through this.”
迄今為止，被發現的此些材料，在提升的溫度下，展現了鐵電相。他附言，因此未來研究的一個目標，是找尋室溫材料。「我們正邁向，使用人工智能(AI)來篩選潛在的新分子，而無需實際合成它們。實際上，在傳統向列晶體LCDs(Liquid Crystal Display：液晶顯示器)的開發及發展中，進行了20萬種新的分子設計。因此，我們能避免經歷這一切。」
原文網址：https://physicsworld.com/a/ferroelectric-nematic-appears-in-a-liquid-crystal/
翻譯：許東榮
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