Application of Brewster angle microscopy and fractal analysis in investigations of compressibility of Langmuir monolayers

The aim of this study was to investigate the connection between the lipid/amphiphile monolayer structure at the interface and its macroscopic/rheological properties, in particular, to establish the link between the fractality of the monolayer structure and its compressibility modulus. To that purpose we have used fractal analysis of images obtained by Brewster angle microscopy to infer the fractal dimension of the monolayer structure and relate its change to the corresponding changes in compressibility derived from a simultaneously measured π-A isotherm. The results of the study confirmed the starting assumption based on theoretical considerations that the fractal dimension of an amphiphilic monolayer and its compressibility should be correlated. We have shown that there exists a strong correlation between the fractal dimension and the corresponding compressibility modulus of different amphiphilic materials. Thus, confirming the link between the short ordered structure on the molecular level and the macroscopic property-compressibility of the monolayer. The established correlation between the fractal dynamics and compressibility modulus of the monolayer enabled identification of onset of percolation-a second-order phase transition that is otherwise not easy and unambiguously detectable. We have found that the signature of percolation in a monolayer, regardless of its composition, is the occurrence of a sharp increase (a jump) of compressibility modulus (at macroscopic level) at the characteristic value of the corresponding fractal dimension D = 1.89. This is the result of the abrupt establishment of a connected structure on the molecular level, consequently involving a change in the elastic properties of the monolayer on a macroscopic scale. The results of this investigation provide means for unambiguous identification of the onset of percolation in the Langmuir layer and should facilitate a more efficient application of the percolation theory in further study of processes and structures at the interface during the monolayer compression.     

Estimation of surfactant activity of polluted seawater by kalousek commutator technique

The polarographic method of discontinuously changing potential, known as the Kalousek commutator technique, was applied to the estimation of surfactant activity of seawater samples from polluted area of a harbour. Adsorption isotherms of different detergents, lecithin and lauric acid at the HMDE have been used as calibration curves. The method is recommended for direct and rapid determination of the degree of seawater pollution by organic surface active substances.     

Application of hydrocolloids as baking improvers

Hydrocolloids (or gums) belong to a group of biopolymers widely used in food technology. In the bakery industry, these compounds help to improve food texture and moisture retention, to retard starch retrogradation, and, finally, to enlarge the overall quality of the products during storage. Since recently, some hydrocolloids are being used due to their polymeric structure as fat replacers to obtain low calorie products and to substitute gluten in the formulation of gluten-free breads. This study describes the applications of some hydrocolloids in the bakery industry. Technological effects of these substances for different types of bakery products are also discussed.     

Use of electrochemical impedance spectroscopy to characterise the physical properties of ex situ reconstructed sea surface microlayer

The objective of this work was to develop electrochemical impedance spectroscopy (EIS) to characterise the physical properties of the sea surface microlayer ( ssm ). Samples from Lake Rogoznica in Croatia were extracted by n-hexane and dichloromethane (dcm) respectively and transferred to mercury electrodes. The EIS results were compared with those of a model phospholipid, dioleoyl phosphatidylcholine (DOPC) which forms near defect-free monolayers on a mercury surface. The ssm extracts formed inhomogeneous monolayers on the mercury surface and the dcm ssm extract monolayer showed greater surface roughness than the hexane ssm extract. The hexane ssm extract introduced defects and a greater surface roughness into mixed DOPC- ssm extract monolayers than the dcm ssm extract due to the lower compatibility of the non-polar hexane extract with the DOPC than that of the polar ssm extract. In addition, the dcm ssm component in the mixed DOPC- ssm monolayer showed an association with pyrene added to the solution.     

Interaction of nitrophenols with lipids at the air/water interface

The uptake of ortho and para nitrophenol to charged and neutral lipid monolayers spread at the air/solution interface was studied by reflection spectroscopy. The adsorption characteristics of the two nitrophenols have been studied by measuring the surface pressure and surface potential as a function of molecular area of the different lipid monolayers in the presence of nitrophenols in the subphase. The results have been interpreted in terms of the electrostatic interaction between the negatively charged dissociated phenolate ions and the positively charged head group of dioctadecyldimethylammonium bromide monolayers.     

Effect of lentil and bean flours on rheological and baking properties of wheat dough

The potential of legume flours (lentil and bean) in bakery applications was investigated. The study indicated that legume flours were characterised by high protein (27.30–27.35 mass %) and total dietary fibre (14.91–21.52 mass %), relatively high water holding capacity (4.71–5.42 g g^?1), and good emulsifying properties (emulsifying capacity: 32.73–46.96 cm³ per 100 cm³ and emulsion stability: 60.52–90.90 cm³ per 100 cm³). Fine wheat flour was partially substituted with 10 mass %, 20 mass %, and 30 mass % levels of lentil and bean flours in order to study their farinographic characteristics and baking behaviour. The addition of legume flours increased water absorption capacity (from 58.50 mass % to 74.90 mass %) and dough development time (from 3.50 min to 5.50 min), whereas dough stability was reduced (from 6.67 min to 2.30 min). The presence of legume flours in dough negatively affected the physical parameters of baked rolls and resulted in the reduction in volume, specific volume, and cambering. Sensory evaluation showed that the most acceptable baked rolls were obtained when the wheat-legume blend flour containing 10 mass % of legume flour was applied. Higher levels of legume flours in the products adversely affected the shape, crust colour, crumb elasticity, and hardness of the final products.     

The structure of percolating lipid monolayers

The lattice structure and in plane molecular organization of Langmuir monolayer of amphiphilic material is usually determined from grazing incidence X-ray diffraction (GIXD) or neutron reflectivity. Here we present results of a different approach for determination of monolayer lattice structure based on application of fractal analysis and percolation theory in combination with Brewster angle microscopy. The considerations of compressibility modulus and fractal dimension dynamics provide information on percolation threshold and consequently by application of percolation theory on the lattice structure of a monolayer. We have applied this approach to determine the monolayer lattice structures of single chain and double chain lipids. The compressibility moduli were determined from measured π-A isotherms and fractal dimensions from corresponding BAM images. The monolayer lattice structures of stearic acid, 1-hexadecanol, DPPC and DPPA, obtained in this way conform to the corresponding lattice structures determined previously by other authors using GIXD.     

Inhibition of the electrode reaction in the presence of surfactants studied by differential pulse polarography: Cadmium(II) in seawater in the presence of the Triton-X-100

The inhibition of the electrode reaction of Cd(II) in seawater as supporting electrolyte in the presence of the non-ionic surfactant T-X-100 was studied by differential pulse polarography in a wide concentration range of surfactant (10^?7?5×10^?4 mol dm^?3). The kinetic parameters, the rate constant k_s and the transfer coefficient α of the electrode reaction were estimated from the shape and the height of the corresponding differential pulse polarograms, using theoretical curves obtained by digital simulation.