Yuri Martínez-Ratón

Bio: Yuri Martínez-Ratón is an academic researcher from Charles III University of Madrid. The author has contributed to research in topics: Liquid crystal & Phase (matter). The author has an hindex of 23, co-authored 93 publications receiving 1553 citations. Previous affiliations of Yuri Martínez-Ratón include Complutense University of Madrid & Spanish National Research Council.

Density Functional Theories of Hard Particle Systems

Abstract: This chapter deals with the applications of the density functional (DF) formalism to the study of inhomogeneous systems with hard core interactions It includes a brief tutorial on the fundamentals of the method, and the exact free energy DF for one-dimensional hard rods obtained by Percus The development of DF approximations for the free energy of hard spheres (HS) is presented through its milestones in the weighted density approximation (WDA) and the fundamental measure theory (FMT) The extensions of these approaches to HS mixtures include the FMT treatment of polydisperse systems and the approximations for mixtures with non-additive core radii The DF treatment of non-spherical hard core systems is presented within the generic context of the study of liquid crystals phases The chapter is directed to the potential users of these theoretical techniques, with clear explanations of the practical implementation details of the most successful approximations

Dimensional Crossover of the Fundamental-Measure Functional for Parallel Hard Cubes

Abstract: We present a regularization of the recently proposed fundamental-measure functional for a mixture of parallel hard cubes. The regularized functional is shown to have correct dimensional crossovers to any smaller dimension, thus allowing its use to study highly inhomogeneous phases (such as the solid phase). Furthermore, it is shown how the functional of the slightly more-general model of parallel hard parallelepipeds can be obtained using the zero-dimensional functional as a generating functional. Extensions to the multicomponent system, a restricted-orientation model, and mixtures or prallel hard cylinders are also given. [S0031-9007(97)03105-0]

Fundamental measure theory for mixtures of parallel hard cubes. I. General formalism

Abstract: This article, the first of a series of two, describes the formulation of Rosenfeld’s fundamental measure theory for a mixture of parallel hard cubes, a model recently introduced to study the demixing transition for additive hard core potentials. Special emphasis is put on the good performance of the functional when reducing the dimensionality of the system, a necessary feature to give reasonable results in highly inhomogeneous situations. This property allows for an extremely simple formulation of the theory in arbitrary dimensions. In a subsequent article we will describe the properties of the mixture as they are predicted by the theory, in particular the demixing in presence of the freezing transition.

Stable smectic phase in suspensions of polydisperse colloidal platelets with identical thickness

Abstract: We report the nematic and smectic ordering in an aqueous suspension of monolayer $\ensuremath{\alpha}$-Zirconium phosphate platelets possessing a high polydispersity in diameter but uniform thickness. We observe an isotropic-nematic transition as the platelet volume fraction increases, followed by the formation of a smectic, an elusive phase that has been rarely seen in discotic liquid crystals. The smectic phase is characterized by x-ray diffraction high-resolution transmission electron microscopy, and optical microscopy. The phase equilibria in this highly polydisperse suspension are rationalized in terms of a theoretical approach based on density-functional theory.

Hard-body models of bulk liquid crystals

Abstract: Hard models for particle interactions have played a crucial role in the understanding of the structure of condensed matter. In particular, they help to explain the formation of oriented phases in liquids made of anisotropic molecules or colloidal particles and continue to be of great interest in the formulation of theories for liquids in bulk, near interfaces and in biophysical environments. Hard models of anisotropic particles give rise to complex phase diagrams, including uniaxial and biaxial nematic phases, discotic phases and spatially ordered phases such as smectic, columnar or crystal. Also, their mixtures exhibit additional interesting behaviours where demixing competes with orientational order. Here we review the different models of hard particles used in the theory of bulk anisotropic liquids, leaving aside interfacial properties and discuss the associated theoretical approaches and computer simulations, focusing on applications in equilibrium situations. The latter include one-component bulk fluids, mixtures and polydisperse fluids, both in two and three dimensions, and emphasis is put on liquid-crystal phase transitions and complex phase behaviour in general.

Effective interactions in soft condensed matter physics

Abstract: In this work, we present a review of recently achieved progress in the field of soft condensed matter physics, and in particular on the study of the static properties of solutions or suspensions of colloidal particles. The latter are macromolecular entities with typical sizes ranging from 1 nm to 1 μm and their suspension typically contain, in addition to the solvent, smaller components such as salt ions or free polymer chains. The theoretical tool introduced is the effective Hamiltonian which formally results by a canonical trace over the smaller degrees of freedom for a fixed, “frozen” configuration of the large ones. After presenting the formal definitions of this effective Hamiltonian, we proceed with the applications to some common soft matter systems having a variable softness and ranging from free polymer chains to hard colloidal particles. We begin from the extreme case of nondiverging effective interactions between ultrasoft polymer chains and derive an exact criterion to determine the topology of the phase diagrams of such systems. We use star polymers with a variable arm number f as a hybrid system in order to interpolate between these two extremes. By deriving an effective interaction between stars we can monitor the change in the phase behavior of a system as the steepness of the repulsion between its constituent particles increases. We also review recent results on the nature and the effects of short-range attractions on the phase diagrams of spherical, nonoverlapping colloidal particles.

Graphene chiral liquid crystals and macroscopic assembled fibres

Abstract: Chirality and liquid crystals are both widely expressed in nature and biology Helical assembly of mesophasic molecules and colloids may produce intriguing chiral liquid crystals To date, chiral liquid crystals of 2D colloids have not been explored As a typical 2D colloid, graphene is now receiving unprecedented attention However, making macroscopic graphene fibres is hindered by the poor dispersibility of graphene and by the lack of an assembly method Here we report that soluble, chemically oxidized graphene or graphene oxide sheets can form chiral liquid crystals in a twist-grain-boundary phase-like model with simultaneous lamellar ordering and long-range helical frustrations Aqueous graphene oxide liquid crystals were continuously spun into metres of macroscopic graphene oxide fibres; subsequent chemical reduction gave the first macroscopic neat graphene fibres with high conductivity and good mechanical performance The flexible, strong graphene fibres were knitted into designed patterns and into directionally conductive textiles

Theory Of Simple Liquids

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