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Comparative Studies of Film-Forming Properties of partially Fluorinated Tetracosanes

Broniatowski M., Miňones J., Sandez Macho I, Dynarowicz-Łątka P.

Polish Journal of Chemistry

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2005

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Vol. 79 / nr 6

1047-1061

EN

Contrary to simple n-alkanes of moderate molecular weight, which are not capable of Langmuir monolayer formation, partially fluorinated hydrocarbons of the general formula: F(CF2)m(CH2)nH (abbreviated as FmHn) were found to form monomolecular layers at the air/water interface. The aim of this study was to characterize several semifluorinated alkanes (SFA) containing 24 carbon atoms in total (tetracosanes) differing in the m/n ratio, as Langmuir monolayers at the free water surface. The following compounds have been investigated: F4H20, F6H18, F8H16, F10H14 and F12H12. Surface pressure (pi) and electric surface potential deltaV) isotherms were recorded in addition to quantitative Brewster angle microscopy results. The negative sign of deltaV evidenced for the orientation of all the semifluorinated tetracosanes investigated here, regardless the length of the hydrogenated segment, with their perfluorinated parts directed towards the air. As inferred from apparent dipole moment values and relative reflectivity results, tetracosanes with shorter perfluorinated fragment (F4H20 and F6H18) were found to take vertical orientation at the air/water interface, while those with longer perfluorinated moiety (F8H16, F10H14 and F12H12) remain tilted even in the vicinity of the film collapse. The observed differences may result from a different conformation of the perfluorinated chain, i.e. more fluorinated tetracosanes (F10H14 and F12H12) have their perfluorinated parts sufficiently long to form a helix, while less fluorinated derivatives (F4H20 and F6H18) may possibly exist in all-trans configuration. In particular, the perfluorinated fragment in F8H16 is considered to have an intermediate character between these two structures.

2

A Study of the Properties of Tri-n-octylphosphine Oxide (TOPO) Monolayers at the Air/Water Interface

Hąc-Wydro K., Wydro P., Dynarowicz-Łątka P.

Polish Journal of Chemistry

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2005

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Vol. 79 / nr 4

773-781

EN

Tri-n-octylphosphine oxide (TOPO) was found to be capable of Langmuir monolayer formation at the air/water interface. Surface pressure-area ( -A) isotherms obtained at different experimental conditions (barrier speed, number of deposited molecules, temperature and presence of metal ions in the aqueous subphase), compression modulus (Cs 1) values andBAMimages have been analyzed. The stability of TOPO monolayers has also been thoroughly examined. The obtained results indicate a liquid state of TOPO monolayers independently of subphase temperature or ionic strength. Such experimental conditions as the barrier speed or the number of deposited molecules were found to have no influence on the shape and position of the isotherms. Moreover, the performed experiments proved a high stability of monolayers from TOPO at the air/water interface.

3

Microstructured cobalt catalyst for VOC combustion. Preparation of active Catalytic Surface

Łojewska J., Kołodziej A., Dynarowicz-Łątka P., Wesełucha-Birczyńska A.

Polish Journal of Chemical Technology

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2005

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Vol. 7, nr 2

31-39

EN

VOC combustion is a demanding process for both reactor and catalyst design. The microstructural reactor based on the wire gauze was regarded as an alternative to ceramic monoliths comparing their heat and mass transfer coefficients. Chromium-aluminum (CrAl) and chromium-nickel steel were surveyed in terms of their applicability for carrier manufacturing and catalyst depositing. The alumina washcoat and cobalt catalyst were deposited as organic precursors using the Langmuir-Blodgett method (LB) which allows to control the amount of the deposited metal. The carriers were characterized at various stages of the preparation by SEM/EDX, XPS, RM methods and tested in n-hexane combustion. Oxidation of the Al washcoat precursor led to the gamma-Al2O3 formation improving the properties of the Al2O3 layer developed on the precalcined CrAl carrier. Oxidation of cobalt stearate deposited on the CrAl gave cobalt oxide, which was assigned to the dispersed spinel Co3O4. The activation energy for the obtained cobalt catalyst (47 kJ/mol) was twice as low as for a standard Pt/Al2O3 catalyst.

4

Semifluorowane alkany (SFA) - właściwości w ciele stałym, roztworach i na granicach międzyfazowych

Broniatowski M., Dynarowicz-Łątka P.

Wiadomości Chemiczne

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2004

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[Z] 58, 7-8

535-569

EN

Semifluorinated n-alkanes (SFA), of the general formula F(CF2)m-(CH2)nH (abbreviated as FmHn) consist of a linear hydrocarbon segment linked to a fluorocarbon chain. These two units are highly incompatible, what arises from a very different physical and mechanical properties of hydrogenated and perfluorinated hydrocarbons. The presence of two opposing segments within one molecule makes semifluorinated alkanes a very interesting class of compounds, which show a particular behavior in bulk and at interfaces. Their highly asymmetric structure, arising from the incompatibility of the both constituent parts, results in surface activity of these molecules (so-called primitive surfactants) when dissolved in organic solvents, and allows for the Langmuir monolayer formation if spread at the air/water interface, despite of the absence of polar group. Since 1984, semifluorinated alkanes have been subject to many studies concerning their structure and physicochemical properties in bulk phase (solid and liquid) and at interfaces (oil/water; air/water). The present article reviews the results obtained so far.

5

Properties of Langmuir Monolayers from Perfluorohexyl-n-alkanes

Broniatowski M., Dynarowicz-Łątka P.

Polish Journal of Chemistry

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2004

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Vol.78 /nr 11-12

2149-2162

EN

A series of semifluorinated n-alkanes (SFAs), of the general formula: F(CF2)m(CH2)nH, (in short FmHn), where m = 6 and n = 16-20, have been synthesized and employed for Langmuir monolayer characterization. Surface pressure and electric surface potential measurements were obtained under a variety of experimental conditions. The Langmuir monolayer experiments have been complemented with Brewster angle microscopy results, which enabled both a direct visualization of the monolayers structure and the estimation of their thicknesses at different stages of compression. Our results show, that these "non-classical" film-forming materials, which are completely hydrophobic in nature and do not possess any polar group in their structure, are capable of monolayer formation at the air/water interface. The negative sign of the measured surface potential, DeltaV, proves that SFA molecules are oriented at the air/water interface with their perfluorinated parts directed towards the air, independently on the length of hydrogenated moiety. The change of electric surface potential achieves the minimum value of ca. -0.75 V for all the investigated SFA. The minimum effective dipole moment is achieved for a molecule oriented at the angle of about 35 graduate to the surface normal. The relative intensity measurements allow one to conclude, that film molecules are oriented vertically in respect to the surface normal at the vicinity of collapse.

6

Perfluoroalkyl-n-eicosanes at the Air-Water Interface-A Monolayer Study

Broniatowski M., Dynarowicz-Łątka P.

Polish Journal of Chemistry

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2004

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Vol. 78 / nr 7

973-985

EN

Perfluoroalkyl-n-eicosanes of the general formula F(CF2)m(CH2)20H, where m = 4,6, 8,10,12 were spread at the air/water as Langmuir monolayers and studied at different experimental conditions, such as spreading volume, subphase temperature and compression speed. The Langmuir monolayer experiments (-A isotherms) have been complemented with quantitative Brewster angle microscopy results, which enabled estimation of the film thickness at different stages of compression. Although the investigated molecules do not possess any polar group and are purely hydrophobic, they form stable monomolecular layers at the free water surface. The negative sign of the measured surface potential, Delta V, evidences for the orientation of the molecules with their perfluorinated parts exposed towards the air, independently of the length of the perfluorinated moiety. The relative intensity measurements allow one to conclude that the molecules with shorter perfluorinated part (F4H20, F6H20 and F8H20) are oriented almost vertically (in respect to the interface) in the vicinity of film collapse, while F10H20 and F12H20 are tilted to the water surface.

7

Interaction in mixed amphotericin B / sterols monolayers spread at the air / water interface

Dynarowicz-Łątka P., Seoane J. R., Trillo J. M., Mouzo O. C., Parada M. C.

Bulletin of the Polish Academy of Sciences. Chemistry

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1999

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Vol. 47, No.2

153-166

EN

Different methods for studying molecular interaction between film-forming components in Langmuir monolayers were applied and compared for the mixed systems of amphotericin B with four different sterols: cholesterol, ergosterol, stigmasterol and B-sitosterol. Among the sterols studied, ergosterol exhibits the strongest interaction with amphotericin B and B-sitosterol the weakest. Cholesterol and stigmasterol show interme-diate behaviour. As a consequence of the interactions, deviations from ideality are ob-served; negative at low and positive at high surface pressures. 1'he interactions are most pronounced for monolayers with the mole fraction of amphotericin Xa == 0.5 and 0.7 which lea.ds to the formation of an amphotericin B-sterol complexes of 2:1 stoichiometry. The obtained results support pharmacological assumption that amphotericin B has a greater affinity to ergosterol than to other sterols. Also the presence of amphotericin B-sterol com-plexes of 2: 1 stoichiometry, responsible for the formation of channels in cell membranes, has been confirmed.

8

Molecular interaction in Langmuir monolayers - statistical thermodynamics approach

Dynarowicz-Łątka P., Jawień W., Minones Trillo J., Vila Romeu N., Conde Mouzo O.

Bulletin of the Polish Academy of Sciences. Chemistry

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1998

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Vol. 46, No. 2

195-206

EN

A regular solution theory for a two-dimensional system with three components of different molecular sizes, adapted from statistical thermodynamics, is used to derive equations describing parameters related to the molecular interactions in mixed Langmuir monolayers. The theory has been applied by examining interactions at the interface for the mixed system of 1-hexadecanol and 1,16-hexadecanediol spread at the water/air interface, basing on experimental data of surface pressure/area (/area (p/A) isotherms. The obtained results show that the attractive forces between film-forming molecules are much stronger than those between particular amphiphiles and water.