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2002 | Book

Molecular Organisation on Interfaces

Editor: G. Lagaly

Publisher: Springer Berlin Heidelberg

Book Series : Progress in Colloid and Polymer Science

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About this book

This volume contains studies on the molecular organisation on interfaces and nanoparticles. The contributions were presented during the 40. General Meeting (Hauptversammlung) of the Kolloid-Gesellschaft in Potsdam in September 2001 and are related to the subject "Colloids and Life Science". Therefore, a diversity of papers were collected covering a large field: synthesis of polymer colloids, biominerals and nanoparticles, investigations on monolayers, lyotropic mesophases, polymeric surfactants, micellar transitions, supramolecular compounds for modifying polymers, solid particles for emulsion stabilisers, and adsorbents for odour control.

Table of Contents

Frontmatter
Preparation strategies for phosphate-based mineral biomaterials
Abstract
Minerals with different particle size and morphology were prepared, and the effects of different preparation methods were analyzed. The minerals, fluoroapatites, were synthesized from CaCl2, Na2HPO4 and KF by precipitation in aqueous solution, precipitation in microemulsions and by a biomimetic synthesis in a gelatine matrix. Several characterization methods were used. The effects of varying the synthesis conditions on the size and the morphology of the powder were analyzed with scanning and transmission electron microscopy. The crystallinity and phase purity were determined by X-ray diffraction and Fourier transform IR spectroscopy. The particle sizes were measured by transmission electron microscopy and dynamic light scattering. Precipitation from aqueous solution yielded particles with rodshaped and amorphous morphology, whereas precipitation from a microemulsion resulted in rod-shaped crystals and after tempering in amorphous shapes. Spherical particles were obtained by biomimetical synthesis. The smallest size of the primary particles was about 15 nm and the largest was about 200 μm.
S. F. Willigeroth, K. Beneke, M. Hannig, R. Zimehl
Effects of surfactants on the crystallization and polymorphism of lipid nanoparticles
Abstract
Colloidal dispersions of solid triglycerides as potential drug carriers are preferably prepared by high-pressure homogenization of molten triglycerides in an aqueous phase with adequate stabilizers and subsequent crystallization of the emulsified lipid particles. The influence of several commercial ionic and nonionic stabilizers and their blends with phosholipid on the crystallization and subsequent polymorphic transitions of tripalmitin nanoparticles was investigated. The stabilizers differed, for example, in the hydrophilic head group and the length and degree of saturation of the hydrophobic chains. Besides macroscopic effects in some of the systems, the stabilizers had pronounced effects on crystallization and polymorphic transitions. There was a clear lower limit for the critical crystallization temperature in agreement with the theory of homogenous nucleation. For some of the dispersions, the appearance of X-ray reflections and thermal events suggested that interactions with the stabilizer layer induced crystallization of the triglyceride at higher temperatures. The transformation of the nanoparticles from the metastable α polymorph to the stable β polymorph proceeded at different rates for the different types of stabilizers and was in most cases not quantitative within the time scale of the X-ray experiments. A complex X-ray diffraction pattern for some of the dispersions complicated the direct comparison of the transition processes. The presence of ionic surfactants often led to a slower transformation than stabilization with nonionic surfactants and their blends with phospholipids.
Heike Bunjes, Michel H. J. Koch, Kirsten Westesen
Solid particles as emulsion stabilisers
Abstract
It has long been known that solid particles can act as very effective stabilisers of emulsions in the absence of surfactant. The particles are usually small in relation to the emulsion drop size (say, particle radius 0.1 times the drop radius or less). There are apparent similarities in the ways in which particles and low-molar-mass surfactants act as emulsion stabilisers. For systems with roughly equal volumes of oil and water, hydrophobic particles tend to stabilise water-in-oil emulsions whereas hydrophilic particles favour the formation of oil-in-water emulsions. Particle wettability therefore appears to parallel the hydrophile/lipophile balance of surfactants, with, for example, high hydrophile/lipophile surfactants corresponding to hydrophilic particles. In the cases of both surfactants and particles, it is probable that for significant emulsion stability, close-packed layers coating the droplets are required. Here, we give a preliminary account of work directed towards understanding more clearly the origins of the stability of solid-stabilised emulsions. Surfactant-stabilised emulsions are kinetically rather than thermodynamically stable, and we ask if the same is also true for solid-stabilised emulsions. Aspects of the stability of surfactant-stabilised emulsions can be understood in terms of the curvature properties of surfactant monolayers, and we probe the possibility that close-packed monolayers of spherical particles have curvature properties similar to those of surfactant monolayers.
Robert Aveyard, John H. Clint, Tommy S. Horozov
Hot moulding of zirconia micro parts
Abstract
Zirconia micro parts were fabricated by a sequence of process steps. A master model (a positive to the final ceramic part) was copied into a silicone rubber mould insert and the rubber mould insert was used for producing ZrO2 prototypes by hot moulding. Hot moulding was carried out with suspensions of ZrO2 in a mixture of paraffin and a dispersant. The rheological properties of different commercial ZrO2 powders were tested with respect to their hot moulding application. A different sequence of process steps was developed to be able to start with a negative and to fabricate the ceramic micro parts as positives. This sequence included as a final step that the hot-moulding feedstock was filled into a mould insert which consisted of an organic material. Debinding was carried out without prior separation of the green body and the mould insert (lost mould technique).
Gunter Bartelt, Werner Bauer, Juergen Hausselt
Characterization of adsorbents for odour reduction
Abstract
The application of adsorbents in odour control can be traced back for centuries, but with low efficiency. Owing to the variety of odours and the sensitivity of the population, powerful techniques for odour control have to be developed. Specific sorption processes are promising. Surface modification of silica gel is a possible way to increase the specificity of the adsorbents. A simple method is introduced to characterize the adsorption behaviour of these materials.
Peter H. Thiesen, Ingo T. Mahlke, Bernd Niemeyer
Structure and dynamics of spherical polymer brushes in a homopolymer matrix
Abstract
This article discusses the dynamical properties of homogeneous colloid—polymer blends consisting of hairy nanospheres and linear polymer chains, respectively. Two different model systems of hairy particles have been prepared: a system with comparatively short hairs off molecular weight below the entanglement regime, polyorganosiloxane microgels grafted with polystyrene hairs of molecular weight 13,000 gmol−1, embedded in polystyrene chains with molecular weight varying from 600 to 4,000 gmol−1; a system with comparatively long hairs of molecular weight above the entanglement regime, kinetically frozen copolymer micelles with a polystyrene core and polyisoprene corona chains of molecular weight 50,000 gmol−1, embedded in homopolyisoprene chains with molecular weight from 4,000 to 50,000 gmol−1. The effect of the particle topology, i.e. the molecular weight of the polymer brush hairs with respect to the homopolymer chains, on interparticle interactions has been investigated by dynamic mechanical measurements. The effective volume swelling ratio and particle softness as estimated from the dependence of the zero-shear viscosity of the blends with respect to the hard-sphere reference system are discussed for both systems.
Yongming Chen, Kerstin Gohr, Wolfgang Schaertl, Manfred Schmidt, Lee Yezek
The osmotic coefficient of spherical polyelectrolyte brushes in aqueous salt-free solution
Abstract
A study on the osmotic coefficient of polyelectrolyte brushes in aqueous solution is reported. The systems studied here consist of a solid polystyrene core with chemically grafted linear poly(sodium styrenesulfonate) chains. The osmotic pressure of the counterions of these spherical polyelectrolyte brushes in aqueous solution without added salt has been investigated in the dilute regime (0.05-0.50 gl-1). The osmotic coefficient, φ, as a function of particle concentration was deduced from the measured osmotic pressure. The range of φ is a few percent, which demonstrates that nearly all the counterions are confined within the charged corona of the spherical polyelectrolyte brushes. It is also observed that the greater the contour length of the grafted polyelectrolyte chains, the lower is the number of osmotically active counterions in these spherical polyelectrolyte brushes. A comparison with φ measured for free polyelectrolyte chains demonstrates that φ is much lower in the case of the polyelectrolyte brushes. This demonstrates directly the trapping of counterions in an osmotic brush predicted by theory.
B. Das, X. Guo, M. Ballauff
Surface modification of polymers using supramolecular compounds
Abstract
Cyclodextrins and cucurbit[6]uril are macrocyclic host molecules with rigid cavities. They are able to form complexes with a large number of organic molecules in solution. The fixation of cyclodextrins on polymer surfaces offers new applications for the use of textiles if the ability to form complexes is maintained. The cyclodextrins can act as depots for cosmetics, pharmaceutics, fragrances and perfumes. The complexed substances are only released in contact with the human skin owing to the presence of humidity. The complexes of cyclodextrins and cucurbit[6]uril can also be used as starting material for the synthesis of rotaxanes. Comparable synthetic strategies applied on polymer foils result in the formation of surface rotaxanes.
E. Schollmeyer, H. -J. Buschmann, K. Jansen, A. Wego
Field-flow fractionation on poly(vinyl formamide), other polymers and colloids
Abstract
(Flow-)field-flow fractionation was used for the characterization of colloidal particles. The separation according to the hydrodynamic diameter is used in the range 20–400 nm, and differences in diameter exceeding 20–30% are well recognized. The method is rather tolerant of the type and the architecture of the sample. Coupling with a light scattering and a refractive index detector gives the molar-mass distribution and the molecular radius as a function of the absolute molar mass. Dextrane and polystyrene sulfonate sodium were analyzed as a control: they are examples of branched and linear molecules. Poly(vinyl formamide) is available on a large industrial scale for paper manufacturing. Samples from that synthesis are shown to be represented by a chain architecture. In earlier examples only branched architectures were found. As examples for more complex colloidal particles, β-carotene hydrosols were analyzed using a UV—vis detector. The size distribution of the particles differs depending on the preparation process, and free protecting colloid was obtained.
Horst Schuch, Stefan Frenzel, Frank Runge
Nanostructuring of liquids at solid—liquid interfaces
Abstract
The behavior of liquid molecules, confined in nanometerscale spaces or at solid—liquid interfaces, is quite different from that in the bulk, which is attributed to the surface-induced structuring of liquids. The structuring of liquids at solid—liquid interfaces was investigated by employing new approaches based on surface force measurement. The combination of surface force measurement and Fourier transform IR spectroscopy in attenuated total reflection (ATR) mode revealed a novel hydrogen-bonded molecular architecture, macroclusters of alcohol (e.g., ethanol) and carboxylic acid (e.g., propionic acid), on silica in cyclohexane. The ATR spectra showed that alcohol (or carboxylic acid) adsorbed on the surface formed macroclusters even in a low alcohol concentration such as 0.1 mol%. The spectra indicated that the cluster formation of alcohol involved hydrogen-bonding interactions between surface silanol groups and alcohol hydroxyl groups and those between alcohol hydroxyl groups. The force measurement demonstrated long-range attraction extending to 30–40 nm, which could be explained by the contact of opposed adsorption layers of alcohol on the surfaces. Similar results were obtained in the cases of carboxylic acids. This phenomenon was used for preparing polymer nanofilms on solid substrates. A shear-force resonance method was developed in order to examine in detail the ordering behavior of liquid (liquid-crystal) molecules confined between two mica surfaces. The frequency and the amplitude of the resonance peak are highly sensitive to the long-range order within the confined sample, affording information about the liquid structuring from the surface to the bulk at the nanometer level. This measurement was used to study 4-cyano-4′-hexyl biphenyl confined between mica surfaces.
Kazue Kurihara
A supramolecular construction kit based on surface-layer proteins
Abstract
Crystalline monomolecular cell surface layers (S layers) represent one of the most commonly observed cell envelope components of prokaryotic organisms (bacteria and archaea). Owing to their high degree of structural regularity, S layers represent interesting model systems for studies on structure, genetics, functions and dynamic aspects of assembly of supramolecular structures. One of the key features of isolated S-layer subunits is their capability to assemble into monomolecular arrays either in suspension, at liquid-air interfaces, on lipid films, on liposomes and on solid supports (e.g. polymers, metals, silicon wafers). S layers have already found a broad spectrum of applications, such as patterning elements in molecular nanotechnology, nanobio-technology and biomimetics.
Uwe B. Sleytr, Dietmar Pum, Erika Györvary, Bernhard Schuster, Seta Küpcü, Margit Sára
Molecular recognition at the air—water interface and Langmuir—Blodgett films
Abstract
The novel amphiphile 9-octadecyladenine (AdC18), which has an adenine headgroup and a long hydrocarbon chain, was synthesized. Its monolayer behavior and its interactions with three guest molecules were investigated at the air—water interface by means of surface pressure—area isotherms. The structures of multilayer Langmuir—Blodgett (LB) films of AdC18 were characterized by Fourier transform IR spectroscopy. When the monolayer was transferred from a uridine aqueous solution to a solid substrate, the IR spectra varied significantly from the spectrum of the film transferred from the pure water subphase. Shifts of band positions and particularly the appearance of a broadened band demonstrated that guest molecules were transferred to the solid substrate along with the AdC18 monolayer and that hydrogen bonds were formed between complementary nucleobases within the LB films.
Ximing Ding, Yoshiaki Kawaida, Ken-Ichi Iimura, Teiji Kato
Temperature-dependent domain growth in 9-hydroxypalmitic acid monolayers
Abstract
The surface pressure—molecular area isotherms and the texture features of 9-hydroxyhexa-decanoic acid monolayers are studied using the film-balance technique and Brewster-angle microscopy. In the two-phase coexistence region, homogeneously reflecting condensed-phase domains of a regular shape are formed. The 9-hydroxy-hexadecanoic acid monolayers show an unusual low, but linear, increase in the transition pressure with temperature and striking shape changes of the condensed-phase domains at different temperatures. The features of the monolayer are drastically changed by alkyl chain substitution by an OH group at the 9-position. The morphological features indicate molecular packing of nontilted alkyl chains in an orthorhombic and hexagonal lattice, respectively. OH substitution at different positions of the alkyl chain affects strongly and in a different way both the phase behaviour and the domain texture of the nonsubstituted palmitic acid monolayers.
S. Siegel, D. Vollhardt
Thermodynamics of two-dimensional cluster formation at the water/air interface. A quantum chemical approach
Abstract
In the framework of the parametric method 3 quantum chemical approximation reasonable values are obtained for the thermo-dynamic characteristics of the cluster formation for the fatty alcohol series CnH2n+1OH (n = 8–16) with various structures at the air/water interface. The calculated values of the enthalpy, the entropy and the Gibbs energy for the formation of a definite cluster structure can be satisfactorily represented by a linear dependence on the number of CH2 groups in the alcohol molecule. The data obtained from the surface pressure—area isotherms are in qualitative, and for the Gibbs energy also in quantitative, agreement with the results of the quantum chemical calculations.
Y. B. Vysotsky, V. S. Bryantsev, V. B. Fainerman, D. Vollhardt, R. Miller
The role of buoyancy in the development of surface tension auto-oscillations
Abstract
The role of the buoyancy force for the development of the auto-oscillations of the surface tension is considered by comparison of the oscillation characteristics for the corresponding pairs of fatty acids and aliphatic alcohols. The effect of buoyancy on the oscillation characteristics is negligibly small for systems with low solubility surfactants, such as octanol, octanoic acid or diethyl phthalate; however, the role of buoyancy increases with increasing solubility of the surfactant and should be taken into account for hexanol.
N. M. Kovalchuk, D. Vollhardt
Dynamics in polymer layers investigated by NMR techniques
Abstract
A large number of different NMR methods are of great usefulness in the investigation of molecular mobility in organic bulk systems, while studies at interfaces are rare owing to the low intrinsic sensitivity of NMR methods. This article presents two examples of the application of spin resonance in investigations of polymers at interfaces, employing polymer-coated colloids: Applying 1H liquid-state NMR to monitor segmental mobility, the phase transition of the ther-moreversible polymer poly(N-isopropylacrylamide) is investigated in the restricted geometry of an adsorption layer, and furthermore under the influence of charges in a statistical copolymer. The phase transition is substantially broader than in solution and for the charged copolymer, mobile segments remain even above the transition temperature. This is attributed to a comparatively mobile arrangement of the copolymer layer. Owing to the electrostatic repulsion from the surface, the copolymer layer is confined to a configuration with charged loops extending further from the interface. The second example concerns polyelectrolyte multilayers formed by self-assembly of polyanions and polycations onto colloidal particles. The hydration of the layer system is studied using 1H spin-relaxation rates, R2, of water, which are a measure for the immobilisation of water molecules in the multilayers. A linear increase in R 2 with the number of layers is found for [poly(sodium 4-styrenesulfate)/ poly(diallyl dimethyl ammonium chloride)]N, reflecting a constant increase in the amount of hydration water with the adsorption of each layer. For [poly(sodium 4-styrene-sulfate)/poly(allylamine hydrochlo-ride)]N, involving a weak polyelectrolyte, the data show reversible swelling behaviour with respect to the electric potential of the outer layer: A positive surface charge leads to a swelling of the multilayers, while owing to a negative surface charge deswelling occurs.
Monika Schönhoff, Bernd Schwarz, Anders Larsson, Dirk Kuckling
A novel way for the alignment of lyotropic hexagonal and Lα phases in magnetic fields
Abstract
An ionically charged Lα phase can be prepared without shear by mixing a small amount of meth-ylformiate to an L3 phase from alkyldimethylaminoxide, hexanol and water. If the structural transformation induced by the hydrolysis reaction of the ester is carried out in the presence of a high magnetic field, a macroscopically aligned lamellar phase is obtained. The alignment process was studied by 2H NMR measurements. The NMR measurements allow the determination of the rate constant of the alignment process and at the same time they can be used to control the degree of macroscopic orientation of the system. In addition, we studied the formation and the alignment process of a hexagonal lyotropic mesophase. The hexagonal phase can be prepared without shear by protonating a highly concentrated alkyldimethylaminoxide solution. The reaction that is used for the protonation is the hydrolysis reaction of methylformiate to formic acid and methanol.
Annette Fischer, HeinzS Hoffmann, Peter Medick, Ernst Rössler
Shear flow of lamellar polymer surfactants
Abstract
Two new polymer surfactants consisting of a polysiloxane backbone with amphiphilic side chains of the nonionic oligo (ethylene oxide) type have been synthesized. The phase behavior of aqueous solutions of the low-molecular-weight surfactants, from which the side chains are formed, and of the polymer surfactants was characterized by polarizing microscopy and 2H NMR spectroscopy. Both polymers form a lamellar Lα phase over a broad range of concentrations, whereas no liquid-crystalline phases were found for the low-molecular-weight surfactants. The orientation of lamellar solutions of the polymers in steady shear flow was investigated in situ by 2H NMR spectroscopy in cone-and-plate geometry. The NMR results indicate an orientation of the layer normals parallel to the velocity gradient at low shear rates and the formation of multilamellar vesicles (onions) at intermediate shear rates for both polymers. The range of shear rates where NMR spectra characteristic of vesicles are found as well as the state of orientation at high shear rates are different for the two systems.
Claudia Schmidt, Daniel Burgemeister
Solvatochromism in organized assemblies: effects of the sphere-to-rod micellar transition
Abstract
The solvatochromic behavior of 2,6-dichloro-4-(2,4,6-tri-phenyl-1-pyridinium-1-yl) phenolate (WB), 1-methyl-8-oxyquinolinium betaine (QB), and sodium 1-methyl-8-oxyquinolinium betaine-5-sulfo-nate (QBS) has been studied in the presence of spherical, and rod-shaped micelles of 1-hexadecyltrim-ethylammonium bromide (CTABr) and 1-hexadecylpyridinium bromide. Rod-shaped aggregates were obtained either by increasing the surfactant concentration or by adding NaBr, or a mixture of NaBr plus 1-decanol to the surfactant solution. The microscopic polarity of water at the solubilization site of the micelle-bound probe, E T mic , has been calculated from the position of its intramolecular charge-transfer band in the UV—vis region. The calculated polarities depend on the structure and charge of the probe, the additive present, but not on the surfactant headgroup (trimethylammonium, and pyridinium ion, respectively). Hydrophobic WB is solubilized in a relatively nonpolar microenvironment; its E T mic is only slightly dependent on the additive present. Anionic QBS behaves as a surfactant counterion, so it essentially reports the polarity changes that occur at the outer layer of the interfacial region. QB is sensitive to the presence of additives because they displace it to the outer part of the interfacial region. Our conclusions have been confirmed by measuring 1H NMR chemical shifts of the discrete hydrogen atoms of CTABr and QB. The “effective” water concentration at the probe solubilization site has been calculated from E T mic and solvatochromic data in bulk aqueous solvents, 1-propanol and 1,4-dioxane. Both solvent mixtures gave consistent concentrations of the effective water concentration at the probe solubilization site, except where preferential solvation of the probe (by one component of the binary mixture) is sizeable. The relevance of our data to micelle-mediated reactions is discussed.
Erika B. Tada, Omar A. El Seoud
Backmatter
Metadata
Title
Molecular Organisation on Interfaces
Editor
G. Lagaly
Copyright Year
2002
Publisher
Springer Berlin Heidelberg
Electronic ISBN
978-3-540-47822-5
Print ISBN
978-3-540-43637-9
DOI
https://doi.org/10.1007/3-540-47822-1