Detailed characterization of (3X3) iodine adlayer on Pt(111) by unequal-sphere packing model

in JOURNAL OF CHEMICAL PHYSICS (2005), 122(9),

A simple unequal-sphere packing model is applied to study the iodine (3x3) adlayer on the Pt(111) surface. By using a newly introduced parameter, defined as the average adsorbate height, three ... [more ▼]

A simple unequal-sphere packing model is applied to study the iodine (3x3) adlayer on the Pt(111) surface. By using a newly introduced parameter, defined as the average adsorbate height, three characteristic adlattices, (3x3)-sym, (3x3)-asym, and (3x3)-lin, have been selected and characterized in great detail, including the exact adatom registry. The (3x3)-sym iodine adlattice, observed in many experimental studies appears to be, on average, the closest one to the substrate surface. A special contour plot of average adsorbate height vs X and Y positions of the (3x3) iodine unit cell indicates the existence of two local minima which are related to preferential formation of (3x3)-sym and (3x3)-asym iodine adlattices. Our model gives good agreement with experimental findings, and explains the mechanism of preferential appearance of (3x3)-sym and (3x3)-asym structures. (C) 2005 American Institute of Physics. [less ▲]

Generation of frustrated liquid crystal phases by mixing an achiral n–smc mesogen with an antiferroelectric chiral smectic liquid crystal

in Journal of Chemical Physics (2005), 122(14), 144906

By mixing the achiral liquid crystal HOAB, exhibiting a nematic (N)-smectic-C (SmC) mesophase sequence, with the chiral antiferroelectric liquid crystal (AFLC) (S,S)-M7BBM7, forming the antiferroelectric ... [more ▼]

By mixing the achiral liquid crystal HOAB, exhibiting a nematic (N)-smectic-C (SmC) mesophase sequence, with the chiral antiferroelectric liquid crystal (AFLC) (S,S)-M7BBM7, forming the antiferroelectric SmCa phase, at least seven different mesophases have been induced which neither component forms on its own: a twist-grain-boundary (TGB) phase, two or three blue phases, the untilted SmA phase, as well as all three chiral smectic-C-type ``subphases,'' SmCalpha, SmCbeta, and SmCgamma. The nature of the induced phases and the transitions between them were determined by means of optical and electro-optical investigations, dielectric spectroscopy, and differential scanning calorimetry. The induced phases can to a large extent be understood as a result of frustration, TGB at the border between nematic and smectic, the subphases between syn and anticlinic tilted smectic organization. X ray scattering experiments reveal that the smectic layer spacing as well as the degree of smectic order is relatively constant in the whole mixture composition range in which AFLC behavior prevails, whereas both these parameters rapidly decrease as the amount of HOAB is increased to such an extent that no other smectic-C-type phase than SmC/SmC exists. By tailoring the composition we are able to produce liquid crystal mixtures exhibiting unusual phase sequences, e.g., with a direct isotropic-SmCa transition or a temperature range of the SmCbeta subphase of about 50 K. (C) 2005 American Institute of Physics. [less ▲]

Wetting in ternary mixtures - with and without amphiphiles

in Journal of Chemical Physics (2002), 117(15), 7284-7294

The interfacial wetting behavior of ternary fluid mixtures is investigated, both for systems where all components have isotropic interaction potentials, as well as for systems where one component is an ... [more ▼]

The interfacial wetting behavior of ternary fluid mixtures is investigated, both for systems where all components have isotropic interaction potentials, as well as for systems where one component is an amphiphile. The BEG model and the corresponding two-order-parameter Ginzburg–Landau model are employed for systems without amphiphiles. We calculate the global wetting phase diagram for nonamphiphilic mixtures. In the investigated range of interaction parameters, the wetting transitions are always continuous at three-phase coexistence. The critical behavior is found to be universal in some, nonuniversal in other parts of the phase diagram. For systems with amphiphiles, two additional interaction terms are taken into account. The first models the aggregation of amphiphilic molecules at the air–water interface, the second the formation of amphiphilic bilayers in water. We find that the first term leads to a reduction of the tension of the air–water interface, and favors wetting by the water-rich phase, while the second—bilayer—term leads to a reduction of the tension of the interface between the water-rich and amphiphile-rich phases. [less ▲]