Structure of salted-out, solubilized micelles and microemulsions on the perfluorinated anionic surfactant tetraethylammonium perfluorooctyl sulfonate studied by cryogenic transmission electron microscopy

 Tetraethylammonium perfluorooctyl sulfonate (TEAFOS; critical micelle concentration, 1 mM), which forms a threadlike micelle in its pure solution, was adopted to study the structure of salted-out, solubilized micelles and microemulsions by cryogenic transmission electron microscopy. The concentration of the surfactant was kept constant at 60 mM. The micelle solution salted out with LiNO₃ provided a surfactant phase in the presence of a clear interface. The surfactant phase was studded, being formed of homogeneously dispersed spherical micelles, and had no obvious threadlike forms. The micelles, which solubilized the maximum amount of perfluorinated oil, were spherical and had the same size as isolated spherical micelles in pure TEAFOS solution. The microemulsions were formed in the presence of perfluorinated alcohol as cosurfactant and the particles were rotund even when the concentration of the perfluorinated oil was equivalent to that for solubilization and the sizes increased with increasing oil content. The difference in size between the solubilized micelles and microemulsions with the same amount of oil suggested that the oil molecules had been solubilized between palisades of perfluorinated alkyl chains in the micelles and had dissolved in the cores of the microemulsions. Received: 10 September 1999/Accepted: 2 December 1999     

Metallo‐supramolecular micelles: Studies by analytical ultracentrifugation and electron microscopy

In aqueous solutions, amphiphilic block copolymers in which a polystyrene (PS) segment is connected to a poly(ethylene oxide) (PEO) block via a bis(2,2′:6′,2″‐ terpyridine ruthenium) complex can form micelles. Such micelles of the protomer type PS₂₀‐[Ru]‐PEO₇₀, according to the preparation procedure representing frozen micelles, were studied by sedimentation velocity and sedimentation equilibrium analysis in an analytical ultracentrifuge and by transmission electron microscopy, with different techniques applied for the sample preparation. The particles obtained were surprisingly multifarious in size. In ultracentrifugation experiments performed at relatively low salt concentrations, the distributions of the sedimentation coefficient s_20,w showed a pronounced peak at 9.6 S and a broad, only partly separated second peak around 14 S. The molar mass of the particles at the peak was around 430,000 g/mol, corresponding to an aggregation number of approximately 85. The average hydrodynamic diameter of the particles in the peak fraction was approximately 13 nm. In electron micrographs of negatively stained samples, spheres of diameters between 10 and 25 nm were the most abundant particles, but larger ones with a wide size range were also visible. The latter particles apparently were composed of smaller ones. The data from both sedimentation analysis and electron microscopy showed that (1) the studied compound formed primary micelles of diameters around 20 nm and (2) the primary micelles had a tendency toward aggregation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3159–3168, 2003     

Thermal transitions in associating aqueous block copolymers: light scattering,rheology and spectroscopy

Solutions containing a polyoxy-ethylene/polyoxy-propylene/polyoxy-ethylene (PEO–PPO–PEO) block copolymer, indicated as F68, in water were investigated as a function of composition and temperature. Hydrogen nuclear magnetic resonance (¹H NMR) line width, chemical shift, self-diffusion, spin-lattice relaxation times, laser light scattering and rheological methods were used. The monomer–micelle equilibrium and the micelle–liquid crystalline phase transitions depend on the F68 content in the mixture and temperature. Significant changes in light scattering intensity and apparent hydrodynamic radius are associated to micelle formation above the critical micellar temperature (CMT). According to a Contin analysis, this behaviour is reflected in the presence of two populations in the intensity–intensity autocorrelation functions. The contributions due to molecules and micelles can be evaluated separately. No such effects are observed below the CMT. Micelle onset is also associated to variations in ¹H NMR spectra, affecting the chemical shift, line width and spin-lattice relaxation time of the PPO methyl protons and self-diffusion, as well. Spin-lattice relaxation times of PEO chains, conversely, change significantly at temperatures close to the micelle–liquid crystalline thermal transition. Similar results were obtained from the line width of ²H NMR spectra as a function of T. Significant changes in both viscous and elastic modulus were also observed and ascribed to PPO dehydration, at the CMT, as well as to squeezing and dehydration of PEO units in liquid crystal formation, respectively.     

Atomic force microscopy and transmission electron microscopy of cellulose from Micrasterias denticulata; evidence for a chiral helical microfibril twist

Atomic force microscopy (AFM), tapping mode atomic force microscopy (TM-AFM) and transmission electron microscopy (TEM) have been used to image the cell wall, ultrathin sections of whole cells and cellulose microfibrils prepared from the green alga Micrasterias denticulata. Measurements of the microfibril dimensions are in agreement with earlier observations carried out by electron microscopy. Images at the molecular level of the surface of the microfibrils were obtained with AFM and show regular periodicities along the microfibril axis that correspond to the fibre and glucose repeat distances of cellulose. Twisted regions visible at intervals along the microfibrils dried down onto substrates were noted to be right-handed in over 100 observations by TEM, AFM and TM-AFM. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dynamic light scattering from micelle complexes of cetyltrimethylammonium bromide-sodium salicylate in aqueous solutions

The diffusion coefficient of cetyltrimethylammonium bromide-sodium salicylate in aqueous solutions has been determined, using the dynamic light-scattering technique, as a function of sodium salicylate concentration, as well as of temperature. Using a gel model the results are discussed in terms of intermicellar pseudo-linkages, entanglements of threadlike micelles, and formation of pseudo-network.     

Application of analytical transmission electron microscopy to the characterization of interlayers in fibre-reinforced composites with ceramic and glass matrices

The microchemistry of interfaces and corresponding interlayers in different fibre-reinforced ceramic and glass composite systems has been investigated by using a dedicated scanning transmission electron microscope demonstrating the potential applicabilities of such an instrument to this large field of materials science. Energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy were used to determine the materials composition on a nanometre scale. Besides analyses performed in the spot mode of the electron probe the distributions of the elements present in the interface region were measured as line profiles across the relevant interface structure by X-ray spectroscopy with a lateral resolution of about 5 nm, even for the detection of a light element as carbon. Moreover, in the composite systems under investigation the two-dimensional element distribution was also attained by energy-filtered imaging. In addition, first results of energy loss near edge structure analyses are presented indicating variations of the chemical bonding of silicon at the interface in a Nicalon fibre/Duran glass composite.     

Freeze-fracture transmission electron microscopy studies on the self-assemblies of amphiphilic solutions

Self-assemblies of amphiphiles in solutions were investigated by using freeze-fracture transmission electron microscopy (FF-TEM). Especially, vesicles were characterized by FF-TEM and the transition of self-assemblies was determined. The stacked lamellar La-phase was prepared without shear forces by a chemical reaction. The stacked lamellar La-phase can be transformed into multilamellar vesicles by the shearing forces that occur when the stacked lamellar La-phase sample is turned upside down a few times. The multilamellar vesicles can also be transformed into unilamellar vesicles by high shearing forces. These transitions were demonstrated by FF-TEM measurements. 2n2+-induced vesicle formation in the single-chain surfactant solutions was first achieved.     

Structure of polydispersed colloids characterised by light scattering and electron microscopy

The dynamics of growth and aggregation of colloidal silver iodide particles was followed by the static light scattering method. The particles were treated as spheres and they were stable in size in the defined time interval. This approach enabled the use of the Zimm plots in order to determine the radii of gyration and the radii of spherical particles. Stable AgI colloids, either positively or negatively charged, showed the usual Zimm diagrams, while the diagrams were untypical when the stability of the colloids decreased. The untypical Zimm diagrams showed 'curves' with envelopes and 'curves' with minima in the unstable domain and in the domain where the most rapid nucleation occurs, respectively. Satisfactory agreement of particle sizes within the limits of accuracy, determined using static--and dynamic light scattering data and of the values obtained from the electron microscopic images was shown. Fitting the theoretical and experimental data, P(theta) functions showed that the particle shapes approach the theoretical model for spheres and thin discs. The colloid stability of polydispersed aggregates was also explained using the second virial coefficient, its negative sign implying interaction of particles in the solution, its positive value indicating formation of new particles from the supernatant solution. In addition, the colloid stability can be characterised by the mass fractal dimension. For positive stable colloids, Dm = 2.70 +/- 0.26, it can be related to the reaction controlled processes, whereas for negative stable colloids, Dm = 1.97 +/- 0.19, it was attributed to the diffusion controlled processes.     

Influence of surfactant and lipid chain length on the solubilisation of phosphatidylcholine vesicles by micelles comprised of polyoxyethylene sorbitan monoesters

Photon correlation spectroscopy and freeze-fracture electron microscopy have been used to determine the ability of a range of micelle-forming, polyoxyethylene (20) sorbitan monoesters (Tweens) to solubilise vesicles prepared from phosphatidylcholines of different acyl chain lengths and degrees of saturation with a view to rationalising (in terms of their membrane toxicity) which of the micelle-forming surfactants to use as drug delivery vehicles. The phosphatidylcholines used were dimyristoyl-, dipalmitoyl-, distearoyl- and dioleoylphosphatidylcholine (DMPC, DPPC, DSPC and DOPC, respectively) while the nonionic polyoxyethylene sorbitan monoesters studied were polyoxyethylene (20) sorbitan monolaurate (Tween 20), a 9:1 weight ratio mixture of polyoxyethylene (20) sorbitan monopalmitate and monostearate (Tween 40), a 1:1 weight ratio mixture of polyoxyethylene (20) sorbitan monopalmitate and monostearate (Tween 60), and polyoxyethylene (20) sorbitan monooleate (Tween 80). The ability of the Tween micelles to solubilise phospholipid vesicles was found to depend both upon the length of the surfactant acyl chain and the length of the acyl chains of the phospholipid comprising the vesicle. Vesicles composed of long saturated diacyl chain phospholipids, namely DSPC and DPPC, were the most resistant to solubilisation, while those prepared from the shorter acyl chained DMPC were more readily solubilised. In terms of their solubilisation behaviour, vesicles made from phospholipids containing long, unsaturated acyl chains, namely DOPC behaved more akin to those vesicles prepared from DMPC. None of the Tween surfactants were effective at solubilising vesicles prepared from DPPC or DSPC. In contrast, there were clear differences in the ability of the various surfactants to solubilise vesicles prepared from DMPC and DOPC, in that micelles formed from Tween 20 were the most effective solubilising agent while those formed by Tween 60 were the least effective. As a consequence of these observations it was considered that Tween 60 was the surfactant least likely to cause membrane damage in vivo and, therefore, is the most suitable surfactant for use as a micellar drug delivery vehicle.     

Dynamic light scattering of CTAB:NaSal threadlike micelles in the semidilute regime. II. effect of surfactant concentration

Dynamic light scattering measurements are made on networks formed by elongated threadlike micelles of cetyltrimethylammonium bromide (CTAB) in aqueous sodium salicylate (NaSal) solutions at 25°C. The surfactant concentrationC _D of the samples is varied from 0.006 to 0.3 M and the ratio of the salt concentrationC _s toC _D is fixed at unity. The time correlation functionA _q (t) of light intensity scattered from the solutions exhibits transition from the unimodal to the bimodal distribution of the decay rate at aroundC _D=0.05 M. The dependence of the first cumulant _e on the scattering vectorq for the samples withC _D0.03 M is described by the dynamic scaling law. The cooperative diffusion coefficientD _c is obtained from extrapolation of _e/q² for the samples withC _D0.03 M and of _f/q² forC _D0.05 M where _f is the first cumulant from the fast mode. TheD _c is found in proportion toC _D ^0.45, being in agreement with the theoretical prediction for a rigid rod in the semidilute regime by the scaling law. The decay rate _s characteristic of the slow mode is independent ofq, and _s ^–1 roughly agrees with the mechanical relaxation time estimated from a fit of the dynamic viscoelastic data of the same samples by a Maxwell type of model with the single relaxation time .     

Dynamic light scattering and rheology studies of aqueous solutions of amphiphilic sodium maleate containing copolymers

Light scattering techniques, video particle‐tracking microrheology, and bulk rheology were employed to examine the structure and dynamics of a series of alternating sodium maleate copolymers with moderately hydrophobic comonomers (diisobutylene, styrene, and isobutylene) in aqueous solutions. The scaling dependence of the specific viscosity (η_sp) on the polyelectrolyte concentration (c) was studied with and without added salt; similar trends were found in both conventional rheology and particle‐tracking microrheology measurements, showing good performance of the technique with flexible polyelectrolytes. Furthermore, with dynamic light scattering performed in high added salt conditions, we examined the behavior of the amplitude of the fast mode, which is in agreement with scaling predictions. In contrast, the slow modes are not understood and display three separate behaviors for the wavevector q dependence of the decay rate (Γ), depending on the comonomer; superdiffusive (Γ ～ q^2.7, isobutylene) possibly because of sticky aggregates, wavevector independent (Γ ～ q⁰, styrene) most likely because of coupled polyion‐ion diffusion and diffusive (Γ ～ q^2.0, diisobutylene) presumably because these aggregates are not sticky. The hydrophobicity of the comonomer appears to switch the aggregation process between “open,” “closed,” and “non” association for isobutylene, diisobutylene, and styrene respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 774–785, 2007     

Temperature-induced association and gelation of aqueous solutions of pectin. A dynamic light scattering study

Dynamic light scattering (DLS) measurements were carried out on aqueous solutions of low-methoxyl pectin at different temperatures and polymer concentration. Low temperature and increased polymer concentration promote the formation of multichain aggregates. The time correlation data obtained from the DLS experiments revealed, for all polymer solutions, the existence of two relaxation modes, one single exponential at short times followed by a stretched exponential at longer times. In the semidilute regime, a temperature reduction induced enhanced chain associations in the solutions with high values of the slow relaxation time and a strong wave vector dependence of the slow mode. These features could be rationalized in the framework of the coupling model of Ngai. At low temperatures (10 °C), gelation occurs in the semidilute regime and a transparent gel is formed. In this state, the profile of the correlation function changes and nonergodic signs are observed. The conjecture is that the association complexes and the gel network are stabilized through intermolecular hydrogen bonds, which are broken-up at higher temperatures. The hydrogen-bonded structures are formed in a process where the polymer chains have been “zipped” together in a cooperative manner.     

ZnS nanoparticle decorated ZnO nanowall network: investigation through electron microscopy and secondary ion mass spectrometry

We report on the fabrication of ZnO nanowall networks decorated with ZnS nanostructures on aluminum substrates using simple chemical route. The structural features and elemental constituents of the ZnS/ZnO heterostructure systems have been extensively studied using electron microscopy and energy dispersive X‐ray spectroscopy. The light emission characteristics of the bare and heterostructured systems have been analyzed using room temperature photoluminescence spectroscopy. The decoration of ZnS nanostructures over ZnO nanowalls has been evidenced through secondary ion mass spectrometry (SIMS). The ‘matrix effect’ has been found to be prominent during SIMS analysis of the bare and heterostructured nanowalls indicating the presence of ZnS phase over ZnO surface. ‘MCs⁺‐SIMS’ has been employed to suppress the matrix effect and is found to be potentially effective in making a semi‐quantitative estimation of Zn and O surface–atom concentrations in both systems. The luminescence responses of the ZnS/ZnO heterostructures have been found to be strongly dependent on the extent of ZnS phase over ZnO. The higher luminescence responses in ZnS/ZnO heterostructures fabricated with smaller ZnS nanoparticles have been explained in terms of a mechanism of charge‐carrier transfer from ZnS to ZnO. Copyright © 2014 John Wiley & Sons, Ltd.     

Ultrafine grain formation and coating mechanism arising from a blast coating process: A transmission electron microscopy analysis

This article examines the substrate/coating interface of a coating deposited onto mild steel and stainless steel substrates using an ambient temperature blast coating technique known as CoBlast. The process uses a coincident stream of an abrasive blast medium and coating medium particles to modify the substrate surface. The hypothesis for the high bond strength is that the abrasive medium roughens the surface while simultaneously disrupting the passivating oxide layer of the substrate, thereby exposing the reactive metal that then reacts with the coating medium. The aim of this study is to provide greater insight into the coating/substrate bonding mechanism by analysing the interface between a hydroxyapatite coating on both mild and stainless steel substrates. The coating adhesion was measured via a tensile test, and bond strengths of approximately 45 MPa were measured. The substrate/coating interface was examined using transmission electron microscopy and selected area diffraction. The analysis of the substrate/coating interface revealed the presence of ultrafine grains in both the coating and substrate at interface associated with deformation at the interface caused by particle impaction during deposition. The chemical reactivity resulting from the creation of these ultrafine grains is proposed to explain the high adhesive strength of CoBlast coatings.     

Structure of composite films comprising Nafion, polyaniline, and palladium particles: A transmission electron microscopy study

Effect of conditions, under which a Nafion-polyaniline-palladium composite is formed, on the size and distribution of Pd particles in the composite is studied by transmission electron microscopy. It is shown that the size of most of the particles is a few nanometers. The number of the particles remains practically invariant following the composite degradation.     

Crystallite morphology in thermotropic random copolymers: Application of transmission electron microscopy

The morphology of nonperiodic layer (NPL) crystallites appearing in three thermotropic random copolyesters composed of 30/70, 58/42, and 75/25 monomer ratios of p-oxybenzoate (B) and 2,6-oxynaphthoate (N) is investigated with transmission electron microscopy. Copolymer films, produced by shearing the materials above their melting points and subsequently annealing them above their glass transition temperature, exhibit ordered entities averaging no more than 20 nm thick and 40–60 nm long, as observed with dark-field imaging. Selected-area electron diffractograms exhibit sharp equatorial reflections, indicating ordered packing of random intramolecular sequences of the molecules. Microdensitometry of these diffraction patterns reveal that both the equatorial and first meridional reflections are radiation sensitive, decaying exponentially with dose. Saturation doses (v) for the crystallites depend on the copolymer composition and degree of polymerization (DP) and are estimated to be approximately 130–150C/m² for the high-molecular-weight copolymers (DP ≈ 150), with the N-rich copolymer possessing greater radiation resistance, and about 430 C/m² for a low-molecular-weight copolymer (DP ≈ 25).     

Microstructural characterization of oxide layers formed on Ni–20Cr–8Al alloy foam using transmission electron microscopy

Microstructural characterization was carried out during the pre‐oxidation of Ni–20Cr–8Al alloy foam using transmission electron microscopy (TEM). During the pre‐oxidation at 1000 °C for 1, 30, and 60 min in air, the sequential formations of NiO, NiCr₂O₄, Cr₂O₃, and α‐Al₂O₃ 1‐μm‐thick oxide layers were, respectively, characterized. Initially, during pre‐oxidization, the layers formed abnormally in an island growth mode, but they grew to be morphologically uniform after 30 min. Pores were found after only 1 min in the middle region of the oxide layers, near the Cr₂O₃ layer, and then these developed into critical micro‐cracks after 60 min. Copyright © 2017 John Wiley & Sons, Ltd.     

Synthesis of block copolymers based on poly(2,3-epithiopropylmethacrylate) via RAFT polymerization and preliminary investigations on thin film formation

New block copolymers with narrow molecular weight distribution based on (2,3-epithiopropylmethacrylate) (ETMA), methylmethacrylate (MMA) and n-butylmethacrylate (nBMA) have been successfully synthesized via reversible addition-fragmentation transfer (RAFT) polymerization. First, RAFT homopolymerization of ETMA and MMA was carried out using 2-(2-cyanopropyl) dithiobenzoate (CPDB) as the chain transfer agent (CTA) and 2,2-azobisisobutyronitrile (AIBN) as the initiator. PETMA-b-P(nBMA) copolymers were synthesized using PETMA homopolymers as the macro-chain transfer agent (MCTA), while PMMA-b-PETMA diblock copolymers were synthesized using PMMA as the MCTA. The evolution of the molecular weight and molecular weight distribution of the homo- and co-polymers were compatible with the RAFT polymerization features. Thin films from the block copolymers were prepared by spin coating a 1 wt% polymer solution from toluene, chloroform or THF. After the preparation, the films were annealed under 80% vapor pressure of chloroform for 1, 2 and 4 h and investigated with scanning electron microscopy (SEM). The most interesting results were found in the films prepared using PETMA-b-P(nBMA) copolymers (). The observed images suggested the formation of hybrid lamellar structures, ascribed to the combination of its higher molecular weight and solvents viscosity.     

Characterization of poly(methyl methacrylate) nanoparticles prepared by nanoprecipitation using analytical ultracentrifugation,dynamic light scattering,and scanning electron microscopy

Nanoprecipitation represents an effective method for the production of polymeric nanoparticles. This technique was used to prepare nanoparticles from solutions of poly(methyl methacrylate) and its copolymers. Since the regulation of main parameters like particle size, particle size distribution, and molar particle mass is very important for future applications, the stable nanoparticle dispersions were examined by scanning electron microscopy, velocity sedimentation, and dynamic light scattering, whereby advantages and disadvantages of each characterization techniques are discussed. Polydispersities of particle size distributions are determined by the ratio of d_w/d_n, where d_w and d_n are weight‐ and number‐average diameters, respectively. The particle characteristics strongly depend on the chemical structure of the polymers and the way of preparation and, therefore, vary in the studied cases in the range of 6 < d_w < 680 nm, whereas the polydispersity index d_w/d_n changes in the range of 1.02 to 1.40. It is shown that nanoparticles in a desirable size range can be prepared by solvent–nonsolvent methods (dialysis technique or dropping technique). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3924–3931, 2010