Friday, January 21, 2011

The bigram “ionic liquid” and related terms in the Ngram Viewer

The Google Books Ngram Viewer provides interesting options to analyze the frequency of use of words and phrases (n-grams) over time—relative, as a percentage of all other n-grams occurring in a corpus of books published in a selected language. By simultaneously generating time-percentage graphs for a set of different terms, one can easily compare their “importance” relative to each other and establish their culturomics.

Let's see how it works for chemistry. I choose the term “ionic liquid” to check if the graph reflects the recent growth in the design and application of ionic liquids. The graph clearly indicates a rise from almost zero up to 0.00001% between 1998 and 2008. This growth trend parallels the one found in an analysis of journal publications [1]. Interestingly, the synonymous term “liquid salt,” although used before the appearance of the term “ionic liquid”, continues on after 1998 at the same low percentage as before 1998. The 4-grams “room temperature ionic liquid” and “task specific ionic liquid” are too specific and do not produce a graph. However, their acronyms “RTIL” and “TSIL” do, following the trend of the parent term “ionic liquid”, while the unigram “RTIL” has a much higher frequency than “TSIL”.

For a final “ionoculturomics” diagram, I entered the unigrams “cation”, “anion” and “zwitterion”. As expected, the percentage for the term “zwitterion” stays near zero over the whole time range from 1900 to 2008. The shapes of the “cation” and “anion” graph are very similar, showing a maximum around 1980 and declining thereafter. Consistently over time, the term “cation” is used almost twice as often as the term “anion”. I don't have an explanation for that.

Figure 1: “The rise in publications concerning ionic liquids as a function of time, as determined using SciFinder” in the Preface of the book entitled “ Ionic Liquids in Synthesis,” edited by P. Wasserscheid and T. Welton. Wiley-VCH Verlag, Weinheim, Germany, 2003.

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