A wide variety of two- and three-dimensional physical-chemical systems display domain patterns in equilibrium. The phenomenology of these patterns, and of the shapes of their constituent domains, is reviewed here from a point of view that interprets these patterns as a manifestation of modulated phases. These phases are stabilized by competing interactions and are characterized by periodic spatial variations of the pertinent order parameter, the corresponding modulation period generally displaying a dependence on temperature and other external fields. This simple picture provides a unifying framework to account for striking and substantial similarities revealed in the prevalent "stripe" and "bubble" morphologies as well as in commonly observed, characteristic domain-shape instabilities. Several areas of particular current interest are discussed.

Suspensions of colloidal particles form a variety of ordered planar structures at an interface in response to an a.c. or d.c. electric field applied normal to the interface 1-3 . This field-induced pattern formation can be useful, for example, in the processing of materials. Here we explore the origin of the ordering phenomenon. We present evidence suggesting that the long-ranged attraction between particles which causes aggregation is mediated by electric-field-induced fluid flow. We have imaged an axially symmetric flow field around individual particles on a uniform electrode surface. The flow is induced by distortions in the applied electric field owing to inhomogeneities in the 'double layer' of ions and counterions at the electrode surface. The beads themselves can create these inhomogeneities, or alternatively, we can modify the electrode surfaces by lithographic patterning so as to introduce specified patterns into the aggregated structures.Our experiments were performed in planar, rectangular wells, fabricated by sandwiching ~50-μm polymer (Kapton) spacers between a bottom electrode of oxide-capped silicon, SiO x , and a top electrode of indium tin oxide, ITO (SiO x /ITO); a pair of indium tin oxide electrodes (ITO/ITO) was also used in some cases. In this simple two-electrode arrangement, currents were monitored (in constant-voltage mode) by a potentiostat. Carboxylated (anionic) and aminated (cationic) polystyrene beads of 1 μm or 2 μm diameter, and with a titrated (total) surface charge density of ~50μC/cm −2 , were obtained from Molecular Probes (Eugene, OR). Polystyrene beads in the range 2-20 μm were obtained from Polysciences (Warrington, PA). Beads were suspended in aqueous sodium azide solution and observed in epifluorescence or reflection differential interference contrast.The photographs in Fig. 1 depict planar aggregates of beads adjacent to a uniform SiO x electrode in configurations of increasing internal order: gaseous (Fig. 1a), liquid (Fig. 1b) and crystalline (Fig. 1d) states, as well as a possible hexatic state (Fig. 1c), resembling thatCorrespondence and requests for materials should be addressed to M.S. moire@worldnet.att.net. † Previous address: AT&T Bell Laboratories, Murray Hill, New Jersey 07974, USA. Remarkably, aggregates on uniform surfaces spontaneously form large-scale structures in two distinct morphologies. Under the same conditions as those producing the crystalline state ( Fig. 1d), a network of finite elongated patches or interconnected bands is simultaneously observed on large scales (Fig. 2a) 1 . In response to increasingly higher fields (≥0.04 V μm −1 , at typically several kilo-hertz), the crystalline state gives way to a configuration composed of mutually repelling particle clusters. Both morphologies display a characteristic scale, Λ, which exceeds the particle diameter, D, by an order of magnitude and does not vary significantly when the electrode spacing ('gap'), L, is varied in the range 5D ≤ L ≤ 40D. For the pattern of bands ( Fig. 2a), Λ corresponds t...

DNA analysis with BeadChip format, combined with computerized data entry and analysis, permits the prediction of minor blood group antigens.

It has been shown that microarray technology can be used to type DNA and detect new alleles in donor cohorts.

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Domain-shape instabilites are investigated in a two-dimensional binary mixture of near-critical composition, a monomolecular film confined to an air-water interface and composed of a phospholipid and cholesterol. We apply the methodology of spectral analysis to the quantitative description of domainwall configurations. This permits us to identify an elliptic instability and a branching instability leading into a "melted" stripe phase in the vicinity of the consolute point. In between, a regime exists in which domain-wall fluctuations exhibit a capillary-wave spectrum. PACS numbers: 68.10.-m, 61.30.Cz, 64.60.-i, 77.80.DjCompeting interactions give rise to a variety of complex phases in condensed matter. x A realization of this principle is afforded by systems whose constituents simultaneously experience mutual magnetostatic or electrostatic repulsion and an attractive interaction of short range. This scenario has been invoked to account for the formation of domains in uniaxial ferromagnets, 2 " 5 in ferrofluids, 6 and in ferroelectrics 7 by predicting periodic modulations of the magnetization and polarization, respectively. The competition of demagnetizing and domain-wall contributions to the free energy also leads to instabilities of individual domain and droplet shapes and governs the dynamics of their fluctuations. 4,8 Recently, the formation of domains has been discovered during phase coexistence in monomolecular films of phospholipids confined to an air-water interface. 9 Theoretical analyses 10,11 assume the complete equivalence, at the level of mean-field theory, of this phenomenon in two-dimensional amphiphilic films to domain formation in the aforementioned magnetic systems. Specifically, they invoke the van der Waals attraction between aliphatic chains as the source of a domainwall energy which is balanced by a depolarizing term arising from repulsive electrostatic interactions between the polar moieties of these compounds. Consequently, the predicted phase diagram contains a coexistence region marked by the appearance of periodic intralayer density or composition modulations. 10 In contrast to the rich diversity of domain morphologies and patterns documented to date in amphiphilic monolayers, 912 one notes the relative scarcity of quantitative analysis. In this Letter we introduce the methodology of spectral analysis, based on digital imageprocessing techniques, to the quantitative description of domain-wall configurations and their excitations. Its application to the study of binary mixed monomolecular films containing cholesterol and dimyristoylphosphatidylcholine (DMPC) (Ref. 13) permits us to identify several distinct regimes of domain-shape stability which are encountered as a film of near-critical composition ap-proaches the upper consolute point terminating a fluidfluid coexistence region. 14 In particular, we document the existence of an elliptic and of a branching instability of the domain walls. The latter manifests itself in the immediate vicinity of the critical point and represents the pr...

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Reçu le 17 novembre 1989, révisé le 7 février 1990, accepté le 2 avril) Résumé.-Nous avons mesuré les isothermes pression-surface de monocouches mixtes composées de dimyristoyl lécithine et de cholestérol à 23,5 °C, et nous les avons analysées afin d'établir le diagramme de phase pression-composition de ces mélanges bidimensionnels. Ces mesures sont confirmées par l'observation directe de la séparation de phase. Nous identifions un intervalle de non-miscibilité des états fluides qui se termine par un point critique, accessible à la température ambiante. Nous proposons que, dans les phases mixtes coexistantes, la lécithine se trouve dans des états distincts.