Two experimental tests of a fluctuation-induced first-order phase transition: intensity fluctuation microscopy at the nematic-smectic-A transition.
TL;DR: It is shown that the NA transition in 4'-n-octyl-4-cyanobiphenyl (8CB) is clearly first order, contrary to calorimetric studies but in agreement with conclusions drawn from front-velocity measurements.
Abstract: We have developed a new, extremely sensitive real-space technique (intensity fluctuation microscopy) to probe the order of the nematic-smectic-A (NA) transition Using this technique, we show that the NA transition in 4'-n-octyl-4-cyanobiphenyl (8CB) is clearly first order, contrary to calorimetric studies but in agreement with conclusions drawn from front-velocity measurements We characterize the strength of the discontinuity at the first-order transition by the dimensionless quantity t(0)=(T(NA)-T*)/T(*) By precisely measuring t(0), we have made the first detailed tests of predictions based on the Halperin-Lubensky-Ma (HLM) theory of fluctuation-induced, first-order phase transitions First, we explore the effect of an external magnetic field on the NA transition Although modest fields (of order 10 T) are predicted to drive the weakly first-order transition in pure 8CB second order, we observe no such effect; we establish instead that the lower bound on this critical field is approximately 30 T Likewise, we observe no effect in mixtures of 8CB with its longer chemical homolog 4'-n-decyl-4-cyanobiphenyl (10CB) Second, we examine the dependence of t(0) as a function of 8CB-10CB mixture concentration and find that the data in mixtures with small nematic temperature range are well-fit by the parameters derived by Anisimov et al based on calorimetric measurements As we increase the nematic range (by using concentrations closer to pure 8CB), the measured t(0) deviates more and more from the HLM predictions Smectic fluctuations, which are neglected in the HLM calculation, are an obvious candidate to explain such a discrepancy, but one's naive expectation is that they would reduce t(0) below the HLM levels, whereas the observed values are too large However, a recent renormalization-group calculation concludes that smectic fluctuations, surprisingly, should indeed increase t(0), explaining the observations presented here
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TL;DR: The Oonk's method is extended in order to account for second-order phase transitions and allows performing calculations of the tricritical temperature.
Abstract: A complete thermodynamic analysis on four two-component phase diagrams between liquid crystals belonging to the nCB and nOCB series of compounds, the so-called cyanobiphenyls, has been performed through the Oonk's equal Gibbs energy method. The binary systems dealt with in this paper show as a common feature the existence of a tricritical point at the SmA-to-N phase transition, all of which reported elsewhere. As a singular finding of the work proposed in this paper, the Oonk's method is extended in order to account for second-order phase transitions. Likewise, this extension allows performing calculations of the tricritical temperature.
3 citations
TL;DR: In this article, the influence of an external magnetic field in the fluctuation-induced surface-surface interaction of free-standing smectic liquid crystals was investigated within a quadratic functional integral approach, and it was shown that the typical 1/l decay of the Casimir-like contribution to the free-energy of a film with thickness l in the absence of external fields is replaced by a faster 1/ l 2 decay for finite fields.
Abstract: Within a quadratic functional integral approach, we investigate the influence of an external magnetic field in the fluctuation-induced surface–surface interaction of free-standing smectic liquid crystals. We find that the typical 1/ l decay of the Casimir-like contribution to the free-energy of a film with thickness l in the absence of external fields is replaced by a faster 1/ l 2 decay for finite fields. We show the existence of a characteristic thickness delimiting the crossover between these distinct regimes which continuously decreases as stronger fields are considered.
1 citations
TL;DR: In this paper, the effects of assembly misalignment and fluctuation on light leakage transmittance were studied for three misoriented cases: misaligned homogeneous case, misaligned analyzer case, and mistwisted nematic case.
Abstract: By introducing geometrical optics approximation (GOA) solutions to a nearly extinct homogeneous nematic director, the effects of assembly misalignment and director fluctuation on light leakage transmittance are studied. Transmittance expressions including fluctuation swing are obtained for three misoriented cases: misaligned homogeneous case, misaligned analyzer case, and mistwisted nematic case. Except for the misaligned homogeneous case with second-order fluctuation, all the other expressions have a linear contribution caused by their own misorientation. From these results, the transmittance variance from fluctuation at a misaligned situation is more enhanced than that in the extinction situation. After introducing thermal average statistics, expressions for the average and variance of transmittance with fluctuation are given. A numerical estimation for these expressions shows that in the misaligned homogeneous case by 1°, the standard deviation of transmittance is 20% of its average.
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Book•
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01 Jan 1980
TL;DR: In this article, a modern pedagogic introduction to the ideas and techniques of quantum field theory is presented, with a brief overview of particle physics and a survey of relativistic wave equations and Lagrangian methods.
Abstract: This book is a modern pedagogic introduction to the ideas and techniques of quantum field theory. After a brief overview of particle physics and a survey of relativistic wave equations and Lagrangian methods, the quantum theory of scalar and spinor fields, and then of gauge fields, is developed. The emphasis throughout is on functional methods, which have played a large part in modern field theory. The book concludes with a brief survey of 'topological' objects in field theory and, new to this edition, a chapter devoted to supersymmetry.
8,581 citations
Book•
01 Jan 1977
232 citations