Entropy driven phase transitions:

Esto va, esto va que explotaaaa !!!!


    - What are liquid crystals?

    - Viruses as a model of liquid crystal.

    - Fd Cholesteric phase and pictures.

    - Fd Smectic phase and pictures.

    - Mixtures of viruses and spheres.


    One of the systems studied in the Fraden lab is rod shaped colloidal viruses in aqueous suspension or colloidal suspensions of viruses. These suspensions exhibit entropy driven liquid crystalline phases. Current research focuses on describing the phase behavior of suspensions of rods, mixtures of rods and spheres, rods and polymers or rods of different sizes. We use the bacteriophage fd as our model rod. It exhibits cholesteric and smectic phases.

    Click on any of the links above to expand the concept.

    Past projects studying colloidal liquid crystals with fd virus rods include:

    • Phase behavior of thin and thick rod mixture.
    • Movies of Isotropic-Smectic coexistence induced by adding attraction inducing polymers.

    Recent projects studying colloidal liquid crystals with fd virus rods include:

    • Phase diagram determination using microfluidic technology.

    What are liquid crystals?

    A liquid crystal is a phase of matter that lies between the disorder of liquids and the neatly arranged lattices of crystals.

    Unlike regular liquids, liquid crystals must have at least one degree of macroscopic order, even if it is only the angular alignment of a nematic. Liquid crystals lack the full three dimensional position and orientation order of ordinary crystals.

    In the isotropic phase, the particles are at random positions and orientations. In the nematic phase, the particles have an overall direction of orientation, but the positions of the individual particles are still random. The direction of alignment is called the director. The nematic order is not perfect and there can be considerable fluctuation about the director. A cholesteric is similar to a nematic, but in a certain direction the director twists about in a helix of a given pitch. In smectics, the particles form a set of parallel planes of regular spacing. Within a given plane of a smectic liquid crystal, the order is liquid-like. Several types of smectics have been found. In the columnar phase, the particles have liquid order within a regular two-dimensional lattice of columns; usually the lattice is hexagonal.

    Although many liquid crystals are composed of only one kind of molecule, they need not be. The main property needed is one dimension much different from another. The particles can be long rod-like objects or flat disks.

    While some liquid crystals consist of just one chemical, a great number are mixtures. When the multicomponent property is crucial to a liquid crystal's existence, then this system is referred to as lyotropic.

    The most common applications for liquid crystals are in liquid crystal displays (LCD). LCDs are found in wrist-watches, calculators, portable computes and various other devices where a low-power display is needed. The optical properties can be used to make electronic shutters and other optical switches. An experimetal microware adaptive array antenna uses the variable birefrigence properties of liquid crystals.

    The liquid crystals phases can affect the texture of soaps; indeed, the term smectic comes from the Greek word for soap. Polymer liquid crystals have been extensively studied; liquid crystal phases are important in the formation of super-strength polymers, such as Kevlar. Liquid crystals whose phases depend on temperature have been exploited for such thermographic applications as Mood Rings.

    Liquid crystals also seem to be intimately involved in the functions of biological structures, such as living tissue.