We successfully prepared monodisperse, hard rodlike colloidal particles with a wide range of length-to-width ratios (L/W). In their suspensions liquid crystals, or nematic (N) and smectic (Sm) phases, spontaneously appeared. The size of the particles made it possible to directly observe their arrangement and dynamics with an optical microscope. The phase behavior observed exhibited an I (isotropic)-Sm transition for L/W=3.5-8.0 and I-N-Sm transitions for L/W=10-35. In pre-Sm transition regions, lateral clustering of the particles and subsequent layering of the clusters were observed exactly.

Smectic, or multilayer, structures in dry sol sediments of β-FeOOH (ferric oxyhydroxide) have been investigated using an atomic force microscope (AFM). The AFM technique has provided three-dimensional information of the smectic structures in a nondestructive manner. The shading in the AFM images of the dry sol surfaces evidently shows that in the iridescent (red, orange, yellow-green, green, and blue) regions, the β-FeOOH crystals are standing upright at a tilt (with respect to the plane of the smectic layer) and form approximately a square lattice. In contrast, in the noniridescent (gray and brown) regions, the crystals lie parallel or randomly oriented to each other. By determining the tilt angle of the crystals in the layer and the refractive index of the layer, we have found the thickness of the layer to be close to the wavelength of visible light in the layer. This supports an earlier periodic-spacing model that attempts to explain the origin of the iridescent colors. The AFM images also show that the individual crystal surface is homogeneous crystallographically, thus disputing an earlier bundle-structure model of individual β-FeOOH crystals. Furthermore, the AFM images show that the crystals have stepped surfaces, tapered ends, and either convex or concave ends, thus indicating nonuniform crystal growth. The dry sol surfaces of β-FeOOH have been further investigated with a scanning electron microscope (SEM) on a larger scale than is used with AFM. In the SEM images, we have found the following:  (1) The in-layer structure of the smectics is, at least locally, square. Although defects destroy the two-dimensional crystalline order, a longer-ranged bond-orientational order still exists. (2) The smectic structures exhibit bending of the directors (which is usually observed in nematics) and overall layer undulation. We have also observed the coexistence of several smectic domains, each of which has a distinct orientation, and mono- and several-folded layers confined in the sols. The smectic structures of dry β-FeOOH sols have been found to be obtained not only from suspensions with attractive-force interparticle interactions but also from those with repulsive-force interactions.

The propensity for various diluents to cause antiplasticization of poly(phenylene oxide) was examined and compared with similar responses for polysufone. Of the diluents used, none resulted in significant stiffening of poly(phenylene oxide) at 35°C relative to what was observed for polysulfone in an earlier paper. However, these diluents did cause substantial reduction in gas sorption levels and permeability coefficients. The latter is consequently a more sensitive indicator of changes in molecular motions of glassy polymers caused by diluents. The permeability response of adding low molecular weight diluents is compared with that of adding a high molecular weight polymer, polystyrene, to poly(phenylene oxide). The data were analyzed and interpreted along lines used in the companion paper for polysulfone.

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Peptide nucleic acid (PNA) has outstanding affinity over DNA for complementary nucleic acid sequences by forming a PNA-DNA heterodimer upon hybridization via Watson-Crick base-pairing. To verify whether PNA probes on an electrode surface enhance sensitivity for potentiometric DNA detection or not, we conducted a comparative study on the hybridization of PNA and DNA probes on the surface of a 10-channel gold electrodes microarray. Changes in the charge density as a result of hybridization at the solution/electrode interface on the self-assembled monolayer (SAM)-formed microelectrodes were directly transformed into potentiometric signals using a high input impedance electrometer. The charge readout allows label-free, reagent-less, and multi-parallel detection of target oligonucleotides without any optical assistance. The differences in the probe lengths between 15- to 22-mer dramatically influenced on the sensitivity of the PNA and DNA sensors. Molecular type of the capturing probe did not affect the degree of potential shift. Theoretical model for charged rod-like duplex using the Gouy-Chapman equation indicates the dominant effect of electrostatic attractive forces between anionic DNA and underlying electrode at the electrolyte/electrode interface in the potentiometry.