L. G. Yanusova

Order and frustration in liquid-crystalline dendrimers

Abstract.X-ray diffraction has been used to elucidate the structure and phase behavior of several liquid-crystalline dendrimers with a different surface topology of the terminal chains. This includes second-generation liquid-crystalline block and statistical dendrimers with mixed aliphatic and mesogenic terminal groups as well as homo-dendrimers of several generations containing only mesogenic end groups. The homo-dendrimers of generation one to four display a monolayer smectic phase, while the fifth generation shows a more ordered columnar phase. The block-dendrimer of the second generation has a bilayer smectic phase. The precise structure of the lamellar ordering has been determined by X-ray reflectivity from thin films on a substrate. The second-generation statistical dendrimer does not show any mesogenic phase. The observed phase behavior is discussed in terms of the frustration due to competition between the stiff geometry of the dendritic matrix and the close-packing conditions of the terminal chains.Graphical abstract

Estimation of the characteristic parameters of the multilayered film model using the patterson differential function

The possibility of estimating the layered film structural parameters by constructing the autocorrelation function PF(z) (referred to as the Patterson differential function) for the derivative dρ/dz of electron density along the normal to the sample surface has been considered. An analytical expression PF(z) is presented for a multilayered film within the box model of the electron density profile. The possibilities of selecting structural information about layered films by analyzing the features of this function are demonstrated by model and real examples, in particular, by applying the method of shifted systems of peaks for the function PF(z).

Formation of Langmuir-Blodgett films in solutions of comblike polymers

The structures have been analyzed of the monolayers of comblike precursor polymers of polyimides and mixed cellulose esters formed at the water/air interface and of the Langmuir-Blodgett films obtained by transfer of these condensed monolayers onto solid substrates. The important factors that ensure the structure control and supramolecular organization of these monolayers and films are established.

Model of packing of cellulose acetomyristinate in Langmuir-Blodgett films

The variation of the structural characteristics in the transition from a block polymer to a Langmuir-Blodgett film has been investigated for cellulose acetomyristinate by the methods of X-ray diffraction analysis. The effect of length and number of acid residues on the diffraction pattern of block cellulose acetomyristinate is studied. The role of acyl substituent in the formation of an ordered structure of multilayer Langmuir-Blodgett films is established. A model of packing of cellulose acetomyristinate molecules in the Y-type films is suggested. The model is based on a two-domain structure in which close-packed myristic-acid residues are located either normally or at a certain angle to the plane of glucoside rings on one side of the polymer chain.

Basic analysis of reflectometry data software package for the analysis of multilayered structures according to reflectometry data

The main principles of developing the Basic Analysis of Reflectometry Data (BARD) software package, which is aimed at obtaining a unified (standardized) tool for analyzing the structure of thin multilayer films and nanostructures of different nature based on reflectometry data, are considered. This software package contains both traditionally used procedures for processing reflectometry data and the authors’ original developments on the basis of new methods for carrying out and analyzing reflectometry experiments. The structure of the package, its functional possibilities, examples of application, and prospects of development are reviewed.

X-ray characterization of cellulose LB films

Abstract Polymer molecules of cellulose acetomyristat (CAM) with different degrees of substitution (γ) on acyl groups of myristic and acetic acids were synthesized and their crystals were investigated by X-ray diffraction methods to choose a proper γ for fabrication of well-packed LB films. It was shown that there is a possibility of fabricating CAM LB films in which one-third of the long side chains is changed into different functional groups: drugs (for medical purposes), light sensitive compounds (for micro electronics) or others.

Application of time–frequency wavelet analysis in the reflectometry of thin films

The application of time–frequency wavelet analysis for solving the reflectometry inverse problem is considered. It is shown that a simultaneous transform of specular intensity curve, depending on the grazing angle and spatial frequency, allows one to determine not only the thickness but also the alteration order of individual regions (layers) with characteristic behavior of electron density. This information makes it possible to reconstruct the electron density profile in the film cross section as a whole (i.e., to solve the inverse reflectometry problem). The application of the time–frequency transform is illustrated by examples of reconstructing (based on X-ray reflectivity data) the layer alternation order in models of two-layer films with inverted arrangement of layers and a four-layer film on a solid substrate.

Langmuir-Blodgett Films of Hydroxamic Acid of the Quinoxalinone Series

Amphiphilic hydroxamic acid 2-(4-decyloxyphenyl)-4-hydroxy-3-oxo-3,4-dihydroquinoxalin-1-oxide was synthesized. The conditions of the formation of hydroxamic acid and its lead, europium, cadmium, and copper salt monomolecular layers were studied. Multimolecular systems were prepared by the Langmuir-Blodgett method from various solvents, including chloroform, carbon tetrachloride, and toluene. The films were characterized by small angle X-ray scattering, UV and IR spectroscopy, ellipsometry, and atomic-force microscopy. The UV data and monolayer compression isotherms showed changes in the state of hydroxamic acid in various solvents in the presence of light and in the dark. The suggestion was made that changes in solutions were related to aggregation phenomenon.

Difference method for solution of the inverse problem of reflectometry of multilayer films

A schematic of a reflectometric experiment whose results make it possible to reconstruct the structure of multilayer films on substrates is proposed. A mathematical apparatus is developed that allows for determining the numerical values of the main parameters (electron density, thickness, and roughness) for each layer of the model film. Until now, there have been no methods for determining the structure of multilayer films from experimental data, and the problem has been solved by the trial-and-error method. Some model examples of reconstruction of the film structure are reported.

Investigation into the Structure of Langmuir-Blodgett Films Prepared from Salts of Acetylenic Acids

Langmuir-Blodgett films are prepared from lead, cadmium, and copper salts of carboxylic acids, namely, 23-tetracosynoic acid HC≡C(CH2)21COOH (with the terminal triple bond) and 2-docosynoic acid CH3(CH2)18C≡CCOOH (with the internal triple bond). The structural transformations in the films during polymerization under exposure to UV radiation are investigated using X-ray reflectomertry. It is found that the X-ray reflectograms of the initial films prepared from salts of both acids exhibit no less than four or five pronounced intense Bragg reflections. This suggests that the initial films have good layer ordering. The bilayer periods for all the films are determined, and the influence of the salt type on the bilayer period is analyzed. It is established that, under exposure to UV radiation, the structural transformations in the films prepared from the salts of 23-tetracosynoic acid occur without substantial disturbances and defects, as can be judged from the absence of significant changes in the location and intensity of the Bragg reflections. An increase in the time of irradiation of the films prepared from the salts of 2-docosynoic acid leads to an increase in the bilayer period. This effect is especially pronounced for the lead and copper salts. However, upon long-term exposure to UV radiation, the salts undergo photolysis, the bilayer period decreases, and the structure of the film begins to break down.