Freeze-fracture Transmission Electron Microscopy Research Articles

Self-assembling properties of a series of homologous ester-diamides – from ribbons to nanotubes

We have studied the aggregation properties of a series of compounds BHPB-n bearing two amide groups and an ester alkyl chain. The number (n) of carbon atoms in this alkyl chain has been varied from 5 to 16. These compounds form gels at low concentration in alkanes. The gel concentrations and the heats of formation of the gels, measured by DSC, are divided into three different regimes: n ≤ 7, 8 ≤ n ≤ 12 and n ≥ 13. Freeze fracture TEM shows that all the compounds self-assemble into high aspect ratio objects, i.e. flat ribbons for n ≤ 7 and irregular helical ribbons for n ≥ 13. For 8 ≤ n ≤ 12, the compounds form tubes (except BHPB-11) and were studied by SANS. The outer and inner diameter distributions of the tubes were determined from the scattered intensities with a model of paired tubes. The diameters are controlled by the length of the ester chain (n) and vary from 21 for BHPB-8 to 32 nm for BHPB-12 (outer diameters). The SANS measurements also provide an estimate of the ratio of paired tubes and the proportion of non-tubular objects that eventually co-exist with these tubes. Variable temperature FTIR and DSC proved that H-bonds between the amide groups are involved in all types of self-assemblies. In addition, FTIR spectra of helical tapes and nanotubes exhibit a double ester νCO band whereas flat tapes display a single band, which confirms the involvement of the ester in the self-assemblies.

Effect of Water on Interfacial Chemical Properties of Nonionic Surfactants in Hydrophobic Ionic Liquid bmimPF6

We studied the effect of water addition on interfacial properties and aggregate behavior of nonionic surfactants (polyoxyethylene alkyl ether; CnEm) in an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate; bmimPF₆). When a small amount of water was added to mixtures of CnEm and bmimPF₆, two breaking points (cac1, cac2) were observed in the surface tension/CnEm concentration plots, suggesting the formation of two kinds of aggregates. This two-step aggregate formation was also confirmed by the fluorescence probe method using pyrene. The particle size of the aggregates measured by dynamic light scattering (DLS) was around 200 nm at cac1, and decreased to 4 nm above cac2. These results, together with freeze-fracture TEM observations, showed that the aggregate formed at cac1 was water in bmimPF₆ emulsions, which then transformed to micelles solubilizing water in the palisade layer above cac2. This concentration-dependent aggregate formation was supported thermodynamically by studying the dependence of cacs on temperature and alkyl and POE chain lengths of the surfactant.

Unique Aggregation Behavior of a Carboxylate Gemini Surfactant with a Long Rigid Spacer in Aqueous Solution

A new gemini surfactant with a long and rigid spacer, O,O'-bis(sodium 2-dodecylcarboxylate)-p-dibenzenediol (referred to as C(12)φ(2)C(12)), has been synthesized. Its aggregation in aqueous solution has been studied using static and dynamic light scattering measurements. The homologue O,O'-bis(sodium 2-dodecylcarboxylate)-p-benzenediol (C(12)φC(12)) whose spacer only contains a single phenyl group was also examined for comparison. Dynamic light scattering (DLS) revealed the unexpected existence of large aggregates in the solution of C(12)φ(2)C(12). However, C(12)φC(12) showed rather normal aggregation behavior. Both the results of intrinsic viscosity and light scattering demonstrated a loose structure for the large aggregates of C(12)φ(2)C(12). This behavior was attributed to an extending configuration of C(12)φ(2)C(12) with the two alkyl tails stretching toward the solution due to the rigidity of the long spacer. The large network-like aggregate formation was an inevitable outcome of spontaneously reducing the energy of the system. Freeze-fracture transmission electron microscopy (FF-TEM) images and (1)H NMR measurements supported this speculation. Due to the columnar-like molecular geometry, the large network-like aggregates were directly transformed into rodlike micelles with increasing surfactant concentration. Depending on further micellar growth, the wormlike micelles were finally formed as confirmed by rheological measurements.

Microstructure transition of hydrophilic modified ibuprofen and Pluronic copolymer F127 complexes

The effect of the aggregation state of Pluronic copolymer (PEO100–PPO65–PEO100, F127) and the concentration of hydrophilic modified ibuprofen (Ibuprofen–PEG800, IP800) on the interaction between F127 and IP800 was systematically investigated by nuclear magnetic resonance, dynamic light scatter (DLS), surface tension, and freeze-fractured transmission electron microscopy. In the solution of F127 unimers (5 °C), F127 unimers tended to wrap around IP800 micelles, and the binding model of F127 unimers to IP800 micelles transferred from wrapping around to partly threading through with increasing IP800 concentration. The latter binding model was straightly confirmed by nuclear Overhauser enhancement spectroscopy. As the aggregation state of F127 is in the beginning of the micellization (20 °C), the addition of IP800 significantly promoted the micellization of F127 to form the F127/IP800 complex with F127 micelles as the skeleton called the F127–micelle complex. The sudden decrease of the size obtained from DLS stemmed from the disruption of the F127–micelle complex and accompanying rehydration of PPO which is weaker compared with refs. The amount of IP800 to disintegrate the F127–micelle complex increased in the F127–micelle-dominated solution (40 °C) compared to that at 20 °C.

Unusual viscoelastic behavior of aqueous solutions of fluorocarbon–hydrocarbon hybrid surfactant and its morphological transformations

The mechanisms of the viscoelastic behavior and morphological transformations of aggregates of aqueous solutions of a sulfate-type hybrid surfactant (F8EH3OS), whose molecules have a hydrocarbon chain (propyl group) and a fluorocarbon chain (perfluorooctyl group), have been investigated. A 160mM aqueous solution of F8EH3OS is a transparent gel and exhibits high viscoelasticity. The zero-shear viscosity of aqueous F8EH3OS solutions is maximum at a concentration of 160mM. The frequency dependence of the dynamic viscoelasticity and freeze-fracture transmission electron microscopy observations of the 160mM F8EH3OS solution indicate the formation of wormlike micelles. The high viscoelasticity of the 160mM solution is attributed to the formation of wormlike micelles and these solutions are called micelle gels in this paper. F8EH3OS forms aggregates of various morphologies, such as spherical or spheroidal micelles, rod-like and wormlike micelles, vesicles, and lamellar phases, in aqueous solutions. A hydrocarbon surfactant (H8EH3OS), in which the fluorocarbon chain in F8EH3OS is replaced by a hydrocarbon chain, does not exhibit high viscoelasticity at any concentration. This unusual viscoelastic behavior is caused by the formation and disruption of micelle gels, and the fluorocarbon chain in F8EH3OS is essential for the formation of micelle gels. 1H NMR experiments suggest that the conformation of the hydrocarbon chain in F8EH3OS changed with surfactant concentration. This conformational change leads to transformation of the aggregates formed from F8EH3OS by changing the critical packing parameter. The hybrid nature of the hydrophobic part of F8EH3OS causes the unusual viscoelastic behavior and the formation of various morphologies.

Thermotropic and structural effects of poly(malic acid) on fully hydrated multilamellar DPPC–water systems

The thermotropic and structural effects of low molecular weight poly(malic acid) (PMLA) on fully hydrated multilamellar dipalmitoylphosphatidylcholine (DPPC)–water systems were investigated using differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and freeze-fracture transmission electron microscopy (FFTEM). Systems of 20wt% DPPC concentration and 1 and 5wt% PMLA to lipid ratios were studied. The PMLA derivatives changed the thermal behavior of DPPC significantly and caused a drastic loss in correlation between lamellae in the three characteristic thermotropic states (i.e., in the gel, rippled gel and liquid crystalline phases). In the presence of PBS or NaCl, the perturbation was more moderate. The structural behavior on the atomic level was revealed by FTIR spectroscopy. The molecular interactions between DPPC and PMLA were simulated via modeling its measured infrared spectra, and their peculiar spectral features were interpreted. Through this interpretation, the poly(malic acid) is inferred to attach to the headgroups of the phospholipids through hydrogen bonds between the free hydroxil groups of PMLA and the phosphodiester groups of DPPC.

Study on the Morphology Feature of 1-Butyl-3-methylimidazolium Tetrafluoroborate Based Ionic Liquid Reverse Microemulsions

The micromorphology of 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4)-in-cyclohexane and bmimBF4-in-triethylamine ionic liquid microemulsions was investigated by two-dimensional NMR and freeze-fracture transmission electron microscopy. The reverse micelles of Triton X-100/cyclohexane were destroyed by adding bmimBF4 and reverse microemulsions were induced to form by successively adding bmimBF4. However, no micelles appeared in triethylamine. But if adding bmimBF4 to a certain extent, a reverse microemulsion was also formed. The driving force of such aggregations could be attributed to the presence of different types of interactions between Triton X-100 and bmimBF4. A staggered arrangement of surfactant led to the irregular droplet structure and large aggregate size.

Influence of Counterions on Micellization of Tetramethylammonium Perfluorononanoic Carboxylate in 1-Butyl-3-methylimidazolium Ionic Liquid

The influence of counterions on micellization of perfluorononanoic carboxylate ammonium salts in water and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF(4)) solutions was investigated by surface tension and (19)F NMR measurements and freeze-fracture transmission electron microscopy (FF-TEM) observations. Changes in the counterions of the fluorocarbon surfactants have different effects on the two solvents. With the increase of counterion volume, the critical micelle concentration (cmc) value of relevant fluorinated surfactant decreases in aqueous solutions. This is because the counterions with larger size, such as (+)N(CH(3))(4), can be little hydrated, which can screen the electrostatic repulsion of the headgroups of the fluorocarbon surfactant and thus facilitate micelle formation. However, the fluorocarbon surfactants can dissolve and form micelles in [bmim]BF(4) only when they provide with largest counterion such as (+)N(CH(3))(4). This is because the counterion, (+)N(CH(3))(4), disperses the charge of the cations, which could weaken the electrostatic interaction between the ion pair of the surfactant, leading to a higher degree of counterion binding. The thermodynamic parameters estimated from the temperature dependence of the cmc values tell us that the micelle formation for tetramethylammonium perfluorononanoic carboxylate (C(8)F(17)COON(CH(3))(4), PFNT) in ionic liquids (ILs) is an entropy-driven process at low temperature but an enthalpy-driven process at high temperature. The driving force of the micellization for fluorocarbon surfactants in [bmim]BF(4) is the solvophobic effect, due to the hydrophobic and oleophobic properties of fluorocarbon chains.

Reformulation of etoposide with solubility-enhancing rubusoside

Etoposide (ETO), a widely used anti-cancer drug, is constrained by its low aqueous solubility and by side effects from both the drug and its solubilizing excipients. In this study, a recently discovered natural solubilizer rubusoside (RUB) was used to achieve the solubilization of ETO. Dynamic light scattering and freeze-fracture transmission electron microscopy studies showed that ETO and RUB formed ETO–RUB nanoparticles (∼6nm in diameter). The powder of ETO–RUB nanoparticles was completely reconstitutable in water and remained stable in this solution at 25 and 37°C for at least 24h. Under other physiologic conditions, ETO solution was clear and free of precipitation at 25°C, but underwent various structural transformations. In PBS and simulated intestinal fluid, RUB-solubilized ETO underwent epimerization and equilibrated to cis-ETO. In simulated gastric fluid, RUB-solubilized ETO degraded to 4′-demethylepipodophyllotoxin-beta-d-glucoside and 4′-demethylepipodophyllotoxin. Higher temperatures favored epimerization or degradation. Furthermore, a side-by-side comparison with DMSO-solubilized ETO confirmed that the RUB-solubilized ETO showed no significant differences in cytotoxicity in colon, breast and prostate cancer cell lines. RUB effectively solubilized and stabilized etoposide, which sets the stage for further toxicology, bioavailability, and efficacy investigations.

Retinyl palmitate polymeric nanocapsules as carriers of bioactives

Nanocapsules containing poly(d,l-lactide) shell and retinyl palmitate core have been prepared by the pre-formed polymer interfacial deposition method. Dynamic light scattering measurements yielded an average hydrodynamic diameter of ∼220nm and a polydispersity index of ∼0.12. Small-angle neutron scattering experiments revealed the presence of two populations of nanocapsules of core diameters ∼192 and 65nm. Freeze fracture transmission electron microscopy showed a polydisperse population of nanocapsules (NC), with a poly(d,l-lactide) shell thickness between 11 and 3nm. For comparison purposes, nanoemulsions (NE, no polymer) and nanospheres (NS, polymer matrix) were also prepared. Each type of nanoparticles exhibited a different morphology (when examined by electron microscopy), in particular NC showed deformability by capillary adhesion. All three types of nanoparticles successfully encapsulated the poorly water-soluble molecules baicalein and benzophenone-3. The thermal behavior of the various nanoparticles was different to a physical mixture of its individual components. Cytotoxicity and phototoxicity assays, performed in human keratinocytes (HaCaT) and murine fibroblasts (BALB/c 3T3), showed that the NC were only cytotoxic at high concentrations. In vitro release studies of benzophenone-3, by the dialysis bag method using NC and NS, showed a sustained release; however, permeation studies using plastic surgery human abdominal skin in Franz diffusion cells showed that a higher amount of benzophenone-3 from NC penetrated into the skin, most probably due to the deformable nature of these nanoparticles.

Ionic Structures of Nanobased FeCl3/[C4mim]Cl Ionic Liquids

We synthesized a series of FeCl(3)/[C(4)mim]Cl (iron(III) chloride with 1-butyl-3-methylimidazolium chloride) ionic liquids. The temperature dependence of the Raman spectra of the FeCl(3)/[C(4)mim]Cl ionic liquids was measured for the first time to analyze their ionic species. In addition, the infrared spectra, thermodynamic properties, and freeze-fracture transmission electron microscopy were combined together with the Raman spectra to reveal the microscopic information of the FeCl(3)/[C(4)mim]Cl ionic liquids. When the mole ratio of FeCl(3)/[C(4)mim]Cl is less than 1, the Raman scattering identifies the presence of [FeCl(4)](-) in the ionic liquid. When FeCl(3) is in excess, [Fe(2)Cl(7)](-) begins to appear. Besides, we found that the relative intensity of the two symmetry vibrations of [Fe(2)Cl(7)](-) is changing as the temperature is varied. The strength of the interionic interactions in FeCl(3)/[C(4)mim]Cl ionic liquids follows the order 1/1.5 > 1.5/1 > 1/1 due to the formation of [FeCl(4)](-) and [Fe(2)Cl(7)](-). The nanostructures in FeCl(3)/[C(4)mim]Cl ionic liquids were observed for the first time by using biological imaging. The sizes of the local domains are found to be tens of nanometers.

Bilayer swelling of nonionic surfactant and sodium dodecylsulfate mixed system by refractive-index matching

Bilayer swelling behavior of nonionic and anionic surfactant mixed aqueous solution induced by adding glycerin was studied. The phenomenon were performed on a system, polyethylene glycol ether of tridecyl alcohol with the average number of ethylene oxide of 5 (CH3(CH2)12(OCH2CH2)5OH; abbreviation IT5) and SDS mixed aqueous solution, with white cream of the upper phase and micelles (L1) of the lower phase. White cream containing densely packed multilamellar vesicles was revealed by freeze-fracture transmission electron microscopy and polarized microscope observations. Phase transition from white cream/L1, two-phase, to clear unique vesicle phase can be induced by adding glycerin to replace water. The addition of glycerin lowers the turbidity of the dispersion and swells the interlamellar distance between bilayers, which could be explained by refractive-index matching between solvent and bilayers.

Surface adsorption and vesicle formation of dilauroylphosphatidylcholine in room temperature ionic liquids

Surface chemical properties of a phospholipid, dilauroylphosphatidylcholine (DLPC), in two ionic liquids (ILs), 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) and hexafluorophosphate (bmimPF6), were investigated by means of surface tension, dynamic light-scattering, and freeze-fracture transmission electron microscopy. It was found that DLPC shows finite solubility in the ILs and spontaneously forms vesicles with size distribution around 400nm in diameter above the critical vesicular concentration (CVC) of 0.040wt.% (in bmimBF4) and approx. 0.08wt.% (in bmimPF6). Other than the CVC value, anion specificity of the ILs was also seen in the temperature effect on the vesicular aggregation; that is, a temperature-induced reversible aggregation was observed in bmimPF6, but not in bmimBF4. The differences in the vesicular stability against the temperature-induced aggregation could be attributed to differences in the interaction between anion species of the ILs and zwitterionic phosphatidylcholine head groups. The apparent molecular area occupied by DLPC at the air/solution interface was estimated to be 0.37nm2 in bmimBF4 and 0.20nm2 in bmimPF6 by applying the Gibbs adsorption equation. These values are much smaller than the molecular area of 0.69nm2 reported for the hydrated DLPC bilayer of lamellar liquid-crystalline phase. This result is not consistent with the traditional Gibbs adsorption model, but can be interpreted in terms of a picture for the surface adsorption of soluble amphiphiles proposed by Moroi et al. Differential scanning calorimetric study is also reported regarding the phase transition behavior of DLPC bilayer solvated by the ILs.

Freeze-Fracture Electron Microscopy on Nano- and Microcarrier for Theranostics and Antibiotics

Nano- and microparticles are frequently used as carrier systems for delivering therapeutics as well as diagnostics (theranostics) at cellular level. We studied the morphology of a wide variety of such particles suitable as theranostic-carrier by freeze-fracture transmission electron microscopy (ff-TEM). As a cryofixation, replica, and transmission EM method it is a powerful tool to monitor self-assembling of lipid-, polymer-, as well as protein/peptide-based carriers encapsulating drug-, gene-, vaccine, antimicrobial- and imaging molecules [1]. At the resolution limit of 2nm we are able to characterize nano particles such as quantum dots (coupled to drug-loaded immunoliposomes), gold nano-particles, superparamagnetic iron oxide nano-particles loaded in polymeric immunomicelles, micelles (spherical-, disc-, and worm-type micelles), single-wall carbon nano-tubes embedded in hydrated gels, and small unilamellar liposome (targeted and non-targeted) on nano-scale resolution. Furthermore, ff-TEM allows the production of beam-damage-resistant replica from much larger, micrometer-size objects such as multilamellar liposome, niosomes, cationic liposome/DNA complexes, integrin-targeted lipopolyplexes, polymer-, lipid- or surfactant-stabilized gas bubbles, cochleate cylinder [2], depofoam particles, and drug crystals. This way we are able to study nano-scale events in micro-scale biological as well as artificial assemblies. Ff-TEM enables us not only to characterize nano- and microcarriers suitable for theranostics, but is the method of choice as well to study their fate related to their pay load, application milieu, and during cell interaction. Furthermore, we investigated structural modifications within bilayers such as domain-formation [1] but also transformations to non-bilayer structures such as hexagonal and cubic phases. Currently we are focused on cochleate cylinder as macrocarrier for antibiotics combating bacterial multidrug resistance [2].

Secondary Structure Formation by Bilayer-Active Peptides Studied by Freeze-Fracture Electron Microscopy: From Disc Micelles to Cochleate Cylinder

Melittin, a 26 amino acid, amphipatic peptide, is known for its hemolytic activity but some short-chain, cationic peptides show antimicrobial properties. Employing freeze-fracture transmission electron microscopy (ff-TEM) we investigated structural modifications within bilayers caused by these two membrane-active peptide groups. Ff-TEM as a cryofixation replica technique is a powerful tool to explore bilayer alterations in a probe-free mode down to a resolution limit of 2nm. Moreover, the fact that the fracture plane follows the area of weakest forces allows insides into the hydrophobic center of lipid bilayer [1]. Here we report the formation of disc micelles as a result of the reversible bilayer to micelle transformation caused by melittin in synthetic lipid bilayer [2]. Furthermore, we explored lipid domain formation in lipid films mimicking the lipid pattern of cytoplasmic membranes of Gram negative bacteria by arginine-rich antimicrobial peptides [3]. Additionally to lipid domains we observed secondary structure formation such as doughnut-type structures caused by arginine-rich peptides and cochleate cylinder (CCC) triggered by lysine-rich peptides. The new type of CCC has been proven to encapsulate and transport traditional, ineffective antibiotics such as erythromycin to resistant bacteria cells. The double-function of these antimicrobial peptides in forming CCC and promoting encapsulation and effective delivery of traditional antibiotics in/by these assemblies provides an interesting approach combating bacterial multidrug resistance [4].

Lyotropic liquid crystal phases of lithium perfluorinated fatty acid salts in aqueous solutions and molecular dynamics study of the lamellar phase

Anisotropic lyotropic liquid crystal (LLC) of lithium perfluorinated fatty acid salts with long fluorocarbon chains (PFL-Li and PFM-Li, denotes lithium perfluorolaurate and perfluoromyristate, respectively) were prepared in aqueous solutions, and characterized by a variety of techniques in detail. Results of small-angle X-ray scattering (SAXS) study indicate that PFL/M-Li molecules are arranged to form lamellar liquid crystal in water, which were determined by freeze-fracture transmission electron microscopy (FF-TEM) images. Differential scanning calorimetry (DSC) measurements showed that, with the increase of the concentration of lithium perfluorolauric (PFL-Li), the temperature-dependent transition of LLC phases to micelle phases increases. However, LLC phases of lithium perfluoromyristate (PFM-Li), which is not temperature-sensitive, can not be transferred to micelle solution below 100°C. Based on the SAXS measurements, constant volume and temperature (NVT) molecular dynamics (MD) simulation have been carried out to investigate the mechanism for the formation of lamellar LLC phases and their properties.

Rheological behavior and microstructure of an anionic surfactant micelle solution with pyroelectric nanoparticle

The rheological behavior and microstructure of anionic fatty acid methyl ester sulfonate sodium (MES) surfactant micelle solution with pyroelectric nanoparticle were investigated by dynamic light scattering (DLS), freeze-fracture transmission electron microscopy (FF-TEM) and rheological measurement. The formation of wormlike micelle due to salt addition was observed and the nanoparticle can accelerate the micelle growth and entanglement with each other. The effect of concentration of surfactant, added salt and pyroelectric barium titanate (BaTiO 3) nanoparticle were investigated, respectively. The viscosity of MES micelle solution increases with the temperature rise within a certain range because of the pyroelectric effect of nanoparticles. At low temperature (∼25 °C), the sample with 0.6 wt.% nanoparticle behaves like an elastic gel with an infinite relaxation time and viscosity. The change of microstructure and rheological properties for MES viscoelastic micelle solutions may be attributed to the electrostatic interaction and pseudo-crosslinking between micelles and nanoparticles. MES viscoelastic micelle solution can retain high viscosity at elevated temperature due to nanoparticle addition and has very attractive for reservoir stimulation and enhanced-oil-recovery in higher temperature reservoirs.

Characterization of the Self-Assembly of meso-Tetra(4-sulfonatophenyl)porphyrin (H2TPPS4–) in Aqueous Solutions

The aggregation of meso-tetra(4-sulfonatophenyl)porphyrin (H(2)TPPS(4-)) in phosphate solutions was investigated as a function of pH, concentration, time, ionic strength, and solution preparation (either from dilution of a freshly prepared 2 mM stock or by direct preparation of μM solution concentrations) using a combination of complementary analytical techniques. UV-vis and fluorescence spectroscopy indicated the formation of staggered, side-by-side (J-type) assemblies. Their size and self-associative behavior were determined using analytical ultracentrifugation and small-angle X-ray scattering. Our results indicate that in neutral and basic solutions of H(2)TPPS(4-), porphyrin dimers and trimers are formed at micromolar concentrations and in the absence of NaCl to screen any ionic interactions. At these low concentrations and pH 4, the protonated H(4)TPPS(2-) species self-assembles, leading to the formation of particularly stable aggregates bearing 25 ± 3 macrocycles. At higher concentrations, these structures further organize or reorganize into tubular, rod-like shapes of various lengths, which were imaged by cryogenic and freeze-fracture transmission electron microscopy. Micron-scale fibrillar aggregates were obtained even at micromolar concentrations at pH 4 when prepared from dilution of a 2 mM stock solution, upon addition of NaCl, or both.

Structure of the B4 Liquid Crystal Phase near a Glass Surface

The B4 liquid crystal phase of bent-core molecules, a smectic phase of helical nanofilaments, is one of the most complex hierarchical self-assemblies in soft materials. We describe the layer topology of the B4 phase of mesogens in the P-n-OPIMB homologous series near the liquid crystal/glass interface. Freeze-fracture transmission electron microscopy reveals that the twisted layer structure of the bulk is suppressed, the layers instead forming a structure with periodic layer undulations, with the topography depending on the distance from the glass. The surface layer structure is modeled as parabolic focal conic arrays generated by equidistant parabolas whose foci are defect lines along the glass surface. Nucleation and growth of toric focal conics near the glass substrate is also observed. Although the growth of twisted nanofilaments, the usual manifestation of structural chirality in the B4 phase, is suppressed near the surface, the smectic layers are intrinsically chiral, and the helical filaments that form on top of them grow with specific handedness.

Aggregation Behavior of Long-Chain N-Aryl Imidazolium Bromide in a Room Temperature Ionic Liquid

The aggregation behavior of long-chain N-aryl imidazolium ionic liquids (ILs), 1-(2,4,6-trimethylphenyl)-3-alkylimidazolium bromide [Cnpim]Br (n = 10, 12, 14), was investigated in a room temperature IL, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) by surface tension measurements. Freeze-fracture transmission electron microscopy (FF-TEM) and dynamic light scattering (DLS) measurements further verified that micelles are formed. A relatively lower critical micelle concentration (CMC) and smaller micelle size were observed compared with that of N-alkylimidazolium ILs [Cnmim]Br. The main reason for this phenomenon is that the electrostatic repulsion between the head groups of [Cnpim]Br is weakened due to the incorporation of the 2,4,6-trimethylphenyl group. The thermodynamic parameters of micelle formation of [Cnpim]Br in [bmim][BF4] were estimated from the CMC values and their temperature dependence. The micelle formation process is enthalpy-driven in the investigated temperature range, similar...