Andrzej Żywociński

Determination of the excess molar volumes of (cyclohexane + benzene) between 293.15 and 308.15 K by use of a continuous-dilution dilatometer

Abstract Excess molar volumes of (cyclohexane + benzene) have been measured by a means of a continuous-dilution dilatometer at 293.15, 298.15, 303.15, and 308.15 K. The results are compared with other recent measurements.

Aggregation and Layering Transitions in Thin Films of X-, T-, and Anchor-Shaped Bolaamphiphiles at the Air–Water Interface

Aggregation in Langmuir films is usually understood as being a disorderly grouping of molecules turning into chaotic three-dimensional aggregates and is considered an unwanted phenomenon causing irreversible changes. In this work we present the studies of 11 compounds from the group of specific surfactants, known as bolaamphiphiles, that exhibit reversible aggregation and, in many cases, transition to well-defined multilayers, which can be considered as a layering transition. These bolaamphiphiles incorporate rigid π-conjugated aromatics as hydrophobic cores, glycerol-based polar groups and hydrophobic lateral chains. Molecules of different shapes (X-, T-, and anchor) were studied and compared. The key property of these compounds is the partial fluorination of the lateral chains linked to the rigid cores of the molecules. The most interesting feature of the compounds is that, depending on their shape and degree of fluorination, they are able to resist aggregation and preserve a monolayer structure up to relatively high surface pressures (T-shaped and some X-shaped molecules), or create well-defined trilayers (X- and anchor-shaped molecules). Experimental studies were performed using Langmuir balance, surface potential and X-ray reflectivity measurements.

Stable, ordered multilayers of partially fluorinated bolaamphiphiles at the air–water interface

The article presents systematic research on Langmuir films of partially fluorinated bolaamphiphiles of different shapes. Such films exhibit a layering transition from a monolayer to a trilayer during compression on the air–water interface. Further compression gives different results depending on the shape and degree of fluorination of the molecules. Partially fluorinated compounds form well defined multilayers in a reversible process. The balance between rigidity and flexibility of the molecules, adjusted by the fluorination and shape of the molecules, seems to be the key factor in avoiding irreversible aggregation of the molecules and creating ordered multilayer structures. Anchor-shaped bolaamphiphiles form a trilayer and, subsequently, a 9-layer film due to a double roll-over mechanism. In contrast, when trilayer films of X-shaped bolaamphiphiles are compressed, 5- and 7-layer films are created according to a different mechanism. Films of thickness of up to nine layers were transferred from the water surface to solid substrates in a single step procedure without any distortion in the structure of the layers. X-ray reflectometry (XRR) was used to measure the thickness of the layers. Perfect fits of the XRR data to theoretical equations allowed for a conclusion that the multilayers are well-ordered lamellar structures. These investigations lead to an improvement in the general understanding of trilayer and multilayer formation and indicate that only in exceptional cases it happens due to a roll-over process.

Dynamic charge separation in a liquid crystalline meniscus

Oscillating electric fields can sustain a macroscopic and steady separation of electrostatic charges. The control over the dynamic charge separation (dyCHASE) is presented for the example of circular menisci of thin, free standing smectic films. These films are subject to an in-plane, alternating radial electric field. The boundaries of the menisci become charged and unstable in the electric field and deform into pulsating, flower-like shapes. This instability ensues only at frequencies of the electric field that are lower than a critical one. The critical frequency is a linear function of the strength of the electric field. Since the speed of electrophoretic drift of ions is also linearly related to the strength of the field, the linear relation between critical frequency and the amplitude of the field sets a characteristic length scale in the system. We postulate that dyCHASE is due to (i) electrophoretic motion of ions in the liquid crystalline (LC) film, (ii) microscopic separation of charges over distances similar in magnitude to the Debye screening length, and (iii) further, macroscopic separation of charges through an electro-hydrodynamic instability. Interestingly, the electrophoretic motion of ions couples with the macroscopic motion of the LC material that can be observed with the use of simple optical microscopy.