Pentadecanoic Acid Monolayers Research Articles

Competition for space between a protein and lipid monolayers

Competitive adsorption is a general problem both in polymer and in biological systems. The equilibrium composition at a surface in contact either with polymer solutions or biological fluids depends on the competition between all the surface active material present in the medium. Such competition is particularly important in cell membranes where membrane proteins generated on ribosomes have to incorporate in the cell. Here we use fluovideo microscopy to study the competition for adsorption at the air/water interface between the enzyme glucose oxidase (GOx) and fluid monolayers of pentadecanoic acid (PDA). Although water soluble, GOx has a strong affinity for the air/water interface. We show that under certain conditions it inserts in the monolayer and causes a contraction of the Langmuir film and the formation of condensed domains. When exposed to a heterogeneous surface it is inserted in the less dense regions. Its crystallization leads to the deformation of the condensed domains followed by the destruction of their initial shape. By compressing the layer the protein is not removed from the interface where it eventually forms three-dimensional structures.

Observation of Continuous and Quantized Domain Size and Shape Evolution in Monolayers at Air–Water Interface

Langmuir monolayers of pentadecanoic acid (C15) and dipalmitoyl phosphatidylcholine (DPPC) are investigated in liquid expanded–liquid condensed (LE–LC) phase co-existence region in order to study evolution of circular and undulating LC domains. The Brewster angle microscopy is analyzed to evaluate LC domain size and shape for various average molecular areas. For C15 monolayer circular domain shape and continuous increase of domain size are observed. In contrast, for DPPC monolayer undulating domain shapes are observed, where the mode of oscillations m is quantized depending on the average molecular area. Surprisingly, also the average domain size is quantized and depends on m. These observations are discussed in accordance with the phase rule modified for the monolayer phase co-existence region and observed levels of domain sizes are compared with theories of m-fold distortion.

Observation of Continuous and Quantized Domain Size and Shape Evolution in Monolayers at Air–Water Interface

Langmuir monolayers of pentadecanoic acid (C15) and dipalmitoyl phosphatidylcholine (DPPC) are investigated in liquid expanded–liquid condensed (LE–LC) phase co-existence region in order to study evolution of circular and undulating LC domains. The Brewster angle microscopy is analyzed to evaluate LC domain size and shape for various average molecular areas. For C15 monolayer circular domain shape and continuous increase of domain size are observed. In contrast, for DPPC monolayer undulating domain shapes are observed, where the mode of oscillations m is quantized depending on the average molecular area. Surprisingly, also the average domain size is quantized and depends on m. These observations are discussed in accordance with the phase rule modified for the monolayer phase co-existence region and observed levels of domain sizes are compared with theories of m-fold distortion.

Dynamics in Ultrathin Films: Particle Tracking Microrheology of Langmuir Monolayers

Particle tracking has been shown to be a powerful technique for measuring bulk and interfacial rheology of flu- ids. The Brownian motion of microparticles trapped at interfaces is very sensitive to the viscosity of the subphase, and to the contact angle of the particles. The Stokes-Einstein relation is fulfilled if the friction factor is properly taken into ac- count. The diffusion coefficient of the latex microparticles spread on surfactant monolayers allows one to calculate the shear viscosity of the monolayer using Danov's theory. Good agreement was found with previous results for monolayers of pentadecanoic acid. The method has also been used to study monolayers of n-dodecanol. Moreover, the shear viscosity of a polymer monolayer has been calculated by particle tracking, and the results show good agreement with data obtained by canal viscosimetry. The temperature dependence of the shear viscosity shows the existence of a glass transition for monolayers of poly(4-hydroxystyrene).

Alignment of Inverse Boojums in a Langmuir Monolayer

Insoluble monomolecular films at the air–water interface (Langmuir monolayers) exhibit a variety of textures in tilted condensed domains in both one phase and two coexisting phase regions. They include mosaics, stripes, stars, and boojums. The appearance of these striking textures are a manifestation of a long ranged orientational order of the constituent amphiphilc molecules in mm length scales. It is well known that the textures in monolayers can be understood in terms of a Landau–de Gennes theory of tilted hexatic phases. Besides the above mentioned textures, there are inverse boojum, i.e., liquid droplets (in the L1 phase) or gas bubbles (in the G phase) surrounded by an anisotropic tilted condensed (L2) phase. They have been observed in polarized fluorescence microscopy and atomic force microscopy. Inverse boojums are virtual topological defects the texture of tilt director, since they are created and located inside the isotropic substance if we extend the cdirector (the projecton of the molecular axis on the water surface) pattern in the monolayer into the isotropic gas or liquid domain. The liquid condensed domains with no internal textures in a liquid expanded (or gas) phase form a hexagonal superstructure and the formation was explained by the line tension between the two coexisting phases and long range electrostatic repulsion between domains. There has been, however, less studied on the interactions between isotropic inclusions surrounded by a tilted liquid condensed phase. In ref. 4, Fang et al. observed an interesting alignment of inverse boojums in Langmuir monolayers of pentadecanoic acid. While this ovservation seems to be closely associated with the problem that is posed by colloidal particles suspended in an anisotropic fluid, it has not been examined theoretically before. In this note we present a simplified model for the alignment of inverse boojums. It is shown that an inverse boojum constitutes a topological dipole (a pair of point disclinations with opposite topological charges (winding numbers)) and that the dipole– dipole interaction arising from the topological charges leads to the alignment of the inverse boojums. First, we follow the the approach of Fang et al. for the minimization of the total energy for a two-dimensional gas cavity of an isotropic phase surrounded by an orientationally ordered liquid condensed phase (Fig. 1):

Dipolar Foams in Langmuir Monolayers Dry at Low Bubble Fraction

We study the crossover from a hexagonal lattice of circular bubbles to a monodisperse hexagonal foam in two dimensions (2D). A long range 1/r3 repulsive interaction (e.g., dipole interaction) is taken into account, and the bubble shape is calculated by numerical solution of the 2D Young−Laplace equation. Unlike short range interaction foams, these foams do not coarsen persistently but reach a local thermodynamic stability at a well-defined bubble size. We find that in (local) thermodynamic equilibrium the bubble shapes depend only on the area fraction of the two phases and not on any material constants; i.e., the bubble shapes of these foams are universal. Experiments with polydisperse dipolar foams in Langmuir monolayers of pentadecanoic acid and myristic acid showed that deformations of the bubbles with respect to the circular shape occur at bubble fractions of ≈70%in good agreement with the calculated monodisperse foams. This area fraction is much smaller than in short range interaction foams.

Reflection–absorption FT-IR spectroscopy of pentadecanoic acid at the air/water interface

Reflection–absorption Fourier transform infrared (RA FT-IR) spectra of spread monolayers of pentadecanoic acid have been obtained for a range of surface pressures at 292 and 297 K. Unpolarised and s- and p-polarised radiation at 30° angle of incidence have been used. Results in the C–H stretching region reveal disorder in the arrangement of the acyl chains with numerous gauche bonds when the monolayer is in the liquid expanded (LE) phase and highly ordered chains with mostly trans bonds in the condensed phases (LC and S). The transition from one form to the other occurs at nearly constant surface pressure in the LE↔LC coexistence region.

Desorption of Fatty Acids from Monolayers at the Air/Water Interface to β-Cyclodextrin in the Subphase

In this study the cyclodextrin (CD)-induced desorption of fatty acids from monolayers at the air/water interface was examined. Desorption rates were determined while maintaining the monolayer at constant surface pressure. Of the three fatty acids examined (tetra-, penta-, and hexadecanoic acids), tetra- and pentadecanoic acids displayed a liquid-expanded (LE) to liquid-condensed (LC) phase transition at ambient temperature. We examined the effect of the phase transition on desorption rates with pentadecanoic acid monolayers. The cyclodextrin-induced desorption of pentadecanoic acid was a linear function of time (zero-order kinetics) when the monolayer surface pressure was kept constant during the course of the experiments. With different fatty acid monolayers, the desorption rates (with the monolayers in the LC state) were observed to decrease as the fatty acid chain length increased (from 14 to 16 carbons). The desorption rates with pentadecanoic acid monolayers increased curvilinearly with increasing te...

Domain morphology in a two-dimensional anisotropic mesophase: Cusps and boojum textures in a Langmuir monolayer

Brewster angle microscopy (BAM) and polarized fluorescence microscopy (PFM) were used to observe domains of a tilted condensed phase in coexistence with an isotropic liquid phase in Langmuir monolayers of pentadecanoic acid. The orientation of the molecular tilt direction inside the domains can be described as a ‘‘virtual boojum’’ texture and a cusp appears in the domain boundary at the vertex of the boojum. The angle subtended by the cusp increases with the domain size for domains greater than 25 μm in diameter. All of these observations are at least qualitatively consistent with the recent predictions of a generalized Wulff construction for deformable materials [J. Rudnick and R. Bruinsma, Phys. Rev. Lett. (submitted)].

Critical Consideration on the Phase Diagrams of Monolayers Drawn from the π–A Isotherms

Abstract The shape of π–A isotherms of insoluble monolayers on a water surface was determined by balancing the relaxation times of the molecular processes which occur during the compression of monolayers and the time of observation (tob). Here, tob is defined in terms of the reciprocal of the strain rate of compression; to keep tob constant during compression, monolayers should be compressed under a constant strain rate rather than a constant speed. π–A isotherms of high-purity pentadecanoic acid monolayers were measured under two different tob (300 and 3000 s). Phase diagrams of the pentadecanoic acid in monolayers drawn from the π–A isotherms differ considerably upon changing tob by ten times. Therefore, if one wishes to draw a phase diagram from the results of the temperature dependence of the π–A isotherm, tob of the measurements should be annexed to compare these results with those of other investigators. The so-called solid film region of the monolayers at low temperatures disappeared for isotherms measured at longer tob than 3000 s, in contrast to the general sense of relaxation phenomena. This was explained by the large deviation from πesp of the pentadecanoic acid at the lower end of the solid film region (21 mN m−1) at lower temperatures.

Morphology of pentadecanoic acid monolayers at the air/water interface studied by BAM

Brewster angle microscopy (BAM) provides the opportunity to visualize birefringence and long‐range orientational order in floating monolayers with the advantage over fluorescence microscopy that no probe molecules are required. The Figure shows the hexagonal domains formed during the compression of pentadecanoic acid monolayers. The method and its potential are discussed. magnified image

Evolution of foam structures in Langmuir monolayers of pentadecanoic acid.

Measurements are reported of the evolution of foam structures in monolayers of pentadecanoic acid at the air-water interface. The foams are observed by fluorescence microscopy. Various statistical properties of this random two-dimensional cellular structure have been determined: the second moment of the cell-side distribution is constant with time, the characteristic size grows according to a power law with an exponent \ensuremath{\approxeq}0.4, Aboav's law is obeyed, and the average cell perimeter is proportional to the number of sides. Comparisons are made with experiments on soap foams, metal grains, and simulations.

Phase diagram of Langmuir monolayers of pentadecanoic acid: quantitative comparison of surface pressure and fluorescence microscopy results

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhase diagram of Langmuir monolayers of pentadecanoic acid: quantitative comparison of surface pressure and fluorescence microscopy resultsBrian G. Moore, Charles M. Knobler, Silvere. Akamatsu, and Francis. RondelezCite this: J. Phys. Chem. 1990, 94, 11, 4588–4595Publication Date (Print):May 1, 1990Publication History Published online1 May 2002Published inissue 1 May 1990https://doi.org/10.1021/j100374a042RIGHTS & PERMISSIONSArticle Views588Altmetric-Citations101LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts

Viscoelasticity of pentadecanoic acid monolayers

Pentadecanoic acid monolayers have been studied by light scattering from thermally excited capillary waves. This approach is sensitive to the surface tension and dilational modulus as well as the associated viscosities. The elastic properties have been compared with the classically determined moduli. Significant differences between the high frequency (light scattering) and equilibrium moduli are attributed to molecular or collective relaxation processes within the monolayer; the monolayer viscosities are compatible with this suggestion. In particular the dilational elasticity and viscosity can be interpreted in terms of an exponential relaxation of stress within the system. Over the liquid expanded region of the isotherm, where the analysis is straightforward, the time constant of this process remains roughly constant, about 45 ωs.

Static and dynamic properties of pentadecanoic acid monolayers at the air-water interface

Static and dynamic properties of pentadecanoic acid monolayers at the air-water interface

Absolute surface manometry: thermodynamic fixed points for air-water monolayers of pentadecanoic acid at 25°C

An extensive series of experiments on pentadecanoic acid monolayers has been made at 25°C with several independent methods of surface manometry. The purpose of the study was to establish a set of surface pressures for the three monolayer phase transitions to act as surface manometric standards. It was coincidentally demonstrated in high purity systems that the so-called liquid-expanded-liquid-condensed transition is simply first order. The experimental requirements for reproducible surface manometry are described. Less extensive data on hexadecanoic acid are also given to invite further critical experiments.

Rigid rod adsorption including long-range dispersion interactions

The Caillé-Ågren analysis of rigid rod adsorption is extended by applying the van Kampen theory of condensation to include long-range dispersion interactions between the adsorbed rods. We discuss in greater detail the characteristics of the phase transition predicted by Caillé and Ågren between states having an isotropic and anisotropic distribution of rods adsorbed parallel to the surface. The maximum density range over which the anisotropic adsorbed phase is stable is determined as a function of the length-to-breadth ratio x of the rigid rods and the strength of the anisotropic dispersion energy. Critical surface adhesion and anisotropic dispersion energies necessary for anisotropic adsorption are also obtained as a function of x. In agreement with Caillé and Ågren the isotropic-anisotropic transition for rigid rod adsorption with attractive forces present is found to be second order. We also discuss the spreading pressure-density or area per molecule isotherms obtained for adsorbed rods having various values of x and surface adhesion and dispersion energies. Whenever feasible we compare our results with the spreading pressure isotherms obtained for monolayers of lyotropic molecules on either aqueous or mercury subphases and obtain qualitative agreement. In particular, the critical density and pressure associated with the two dimensional adsorbed gas-liquid condensation for rigid rods with x = 10 gives reasonable agreement with the critical constants observed by Hawkins and Benedek and Kim and Cannell for the corresponding condensation of pentadecanoic acid monolayers on neutral and acidified aqueous subphases. This agreement suggests that considerable dimerization of the pentadecanoic acid molecules may occur on aqueous surfaces.