Paulo Teixeira is an Assistant Professor at ISEL and a researcher at Universidade de Lisboa. Teixeira has been on the JPCM Liquids, soft matter and biological physics board since 2013 and studies the structure and phase behavior of liquids, liquid crystals at surfaces and interfaces and, the geometry and topology of liquid foams. The topical review he chose to highlight is “Hard-body models of bulk liquid crystals” by Luis Mederos et al 2014 J. Phys.: Condens. Matter 26 463101 and is right at the heart of Teixeria’s research.
This Topical Review is on a popular set of models for understanding the basics of liquid crystalline (LC) behaviour. The authors have a long track record of work in this area and are thus ideally qualified to undertake this review.
The focus is, of course, on theory. The main theoretical approaches, many of them developed, or at least employed, by the authors themselves, are briefly but clearly explained. This is, in my view, the review’s most commendable aspect, as it brings together information scattered over a vast number of sources, thus providing a quick overview of the state-of-the art of LC theories. As such, this review is complementary to ref. 15 on simulations of hard-body fluids, and to the (uncited) review by C. M Care and D. J Cleaver, 2005 Rep. Prog. Phys. 68 2665 covering a wider variety of models and methods. There is, however, ample comparison with simulations, and experimental studies are not overlooked either. Here the authors are careful to discuss the limitations of their models when applied to real-world systems.
At more than 60 pages this review is comprehensive, well-written (there are few typos and rare instances of awkward syntax) and, most usefully, contains a collection of more than 300 references, with titles. A short table of contents, as appears, e.g., in Rev. Mod. Phys. or Rep. Prog. Phys. articles, would have been helpful, such is the breadth of coverage.
I particularly enjoyed reading about polydispersity in LC systems, a subject that I know little about but find fascinating; here, perhaps some basic concepts, such as cloud point and shadow curve could have been defined a little more carefully, as they are unobvious to the uninitiated. Also the sections on LC biaxiality, with which I have been concerned for a number of years, are a pertinent reminder of a vexing problem that will not go away.
I take exception to just a few details. The analogy between entropy-driven orientational order and the stacking of matches in a box is eloquent but, strictly speaking, only applies to confined systems. Moreover, in section 3.1, I feel it would have been illuminating to relate the virial expansion of the free energy to its expansion in terms of direct correlation functions, as is done in density-functional theory.
Of course, a review of this nature is out of date the moment it is published – nay, the moment you finish proof-reading it. Some omissions I noticed are: exact or approximate results for the excluded volumes of less-standard hard bodies, such as by Mulder 2006 Molec. Phys. 103 1411 or by Virga et al 2013 Phys. Rev. E 88 064501 smectic phases beyond smectic-A; and the recent revival of interest in hard-body models of cholesterics (see Belli et al., 2014 Phys. Rev. E 90 020503(R)). But these do not at all detract from the general usefulness of the review.
You can read the original topical review by Luis Mederos et al 2014 J. Phys.: Condens. Matter 26 463101, here. Look out for more JPCM board member highlights through the year.
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Thumbnail used on homepage adapted from Luis Mederos et al 2014 J. Phys.: Condens. Matter 26 463101. Copyright 2015 IOP Publishing.
Categories: Journal of Physics: Condensed Matter