Freeze-fracture Transmission Electron Microscopy Research Articles

How Many Glucan Chains Form Plant Cellulose Microfibrils? A Mini Review.

Assessing the number of glucan chains in cellulose microfibrils (CMFs) is crucial for understanding their structure-property relationships and interactions within plant cell walls. This Review examines the conclusions and limitations of the major experimental techniques that have provided insights into this question. Small-angle X-ray and neutron scattering data predominantly support an 18-chain model, although analysis is complicated by factors such as fibril coalescence and matrix polysaccharide associations. Solid-state nuclear magnetic resonance (NMR) spectroscopy allows the estimation of the CMF width from the ratio of interior to surface glucose residues. However, there is uncertainty in the assignment of NMR spectral peaks to surface or interior chains. Freeze-fracture transmission electron microscopy images show cellulose synthase complexes to be "rosettes" of six lobes each consistent with a trimer of cellulose synthase enzymes, consistent with the synthesis of 18 parallel glucan chains in the CMF. Nevertheless, the number of chains in CMFs remains to be conclusively demonstrated.

Hierarchical Emulsion Structure and Functionality Regulated by Coexisting Bicontinuous Microemulsion and Liquid Crystal Domains.

Since microemulsions are usually low viscosity fluids, enhanced rheological properties while maintaining their structure-derived functionality have long been desired from an industrial application point of view. However, for instance, it is practically difficult to thicken bicontinuous microemulsions (BCMEs) without perturbing their alternating domain structure or to emulsify oils using BCME having ultralow interfacial tension as an external phase. In this study, a methodology called a BCLC emulsification technique has been constructed to obtain oil-in-water emulsions stabilized by coexisting BCME and liquid crystal (LC) phases. The produced emulsions based on polyglyceryl-10 diisostearate, polyglyceryl-6 dicaprate, cetyl ethylhexanoate, and water are structurally scrutinized by means of small- and wide-angle X-ray scattering (SWAXS), freeze fracture transmission electron microscopy (FF-TEM), and scanning electron assisted dielectric microscopy (SE-ADM). The data provide experimental evidence that this methodology enables one to control the bending elasticity of the interfacial membranes and consequent long-range order of the BCME domains. Moreover, closely correlated with the interfacial membrane properties, submicrometer-sized fine oil droplets are supported by the LC networks and agglomerated into spongy or network-like phase-separation patterns. The resulting nonfluidic, jelly emulsions are particularly useful in cosmetics because of combined BCME-derived high cleansing performance and excellent usability owing to the enhanced viscosity. The thickening mechanisms are essentially different from those of common lamellar-gel-stabilized oil-in-water emulsions, which utilize crystalline lamellar gel networks as oil droplet stabilizers.

Multiscale organisation of lead carboxylates in artistic oil binders.

The supramolecular and mesoscopic architectures of lead-saponified linseed oil, used by painters since the Renaissance, have been characterised and linked to their rheological properties. The multi-scale organization of saponified oils has been demonstrated by SAXS (Small Angle X-ray Scattering), FF-TEM (Freeze-Fracture Transmission Electron Microscopy) and DIC (Differential Interference Contrast): some of the lead soaps (formed when the oil is heated in the presence of PbO) are organized into microscopic lamellar domains, distributed in a continuous matrix made up of unorganized species (partially saponified triglycerides, glycerol, remaining soaps, etc.). The concentration of lead soaps in the oil controls the average size and interaction between the lamellar domains. Linseed oil + PbO 17 mol% is viscous and consists of aggregates of lamellar domains isolated within the continuous unorganized matrix. In contrast, in linseed oil + PbO 50 mol%, the domains are homogeneously dispersed and form what can be described as a three-dimensional network, giving the system viscoelastic properties.

Self-Assembled Structure of α-Isostearyl Glyceryl Ether Affects Skin Permeability-a Lamellar with 70-nm Spaces and L3 Phase Enhanced the Transdermal Delivery of a Hydrophilic Model Drug.

Self-assembled surfactant structures, such as liquid crystals, have the potential to enhance transdermal drug delivery. In the present study, the pseudo-ternary system of GET (composed of α-Isostearyl glyceryl ether (GEIS) and polysorbate 60)/1,3 butanediol (BG)/water) was shown to exhibit a complex phase diagram. Small- and wide-angle X-ray scattering (SWAXS) and freeze-fracture transmission electron microscopy (FF-TEM) revealed that GET6BG60 (6%GET/60%BG/34%Water) formed a lamellar phase with a repeated distance of approximately 72nm. Such a long-repeated distance of the lamellar phase was unique in the surfactant system. Moreover, the various structures, such as multilamellar vesicles and branched-like layers, were observed, which suggested that they might be deformable. On the other hand, only core-shell particles were observed in GET6BG20, the core of which was an L3 phase. GET6BG20 and GET6BG60 significantly enhanced the skin permeation of the hydrophilic model drug, antipyrine (ANP) (log Ko/w, - 1.51). However, their permeation profiles were distinct. Liquid chromatography-tandem mass spectrometry revealed that epidermal accumulation of GEIS was significantly higher with GET6BG60 than GET6BG20 after 1.5h of permeation, which might be attributed to differences in their deformable properties. Furthermore, GEIS was reported to affect intercellular lipids. Accumulated GEIS in the epidermis may have interacted with intercellular lipids and enhanced the transdermal delivery of ANP. The difference in the permeation profiles of ANP may be attributed to the penetration process of GEIS in the epidermis. This study suggests that GET6BG20 and GET6BG60 are unique carriers to enhance the permeation of hydrophilic drugs, such as ANP.

Stabilization of all-aqueous droplets by interfacial self-assembly of fatty acids bilayers

All-aqueous microdroplets produced by liquid–liquid phase separation have emerged as promising models of artificial cells, and offer new approaches for the solvent-free encapsulation of fragile solutes. Yet, the lack of a membrane on such droplets makes them intrinsically unstable against coarsening, and precludes a fine control over chemical localization, as solutes can freely diffuse through the interface. Herein, we report the construction of stable and impermeable water-in-water emulsions via the interfacial self-assembly of mixed sodium oleate/1-decanol bilayers on dextran-rich droplets produced by segregative liquid–liquid phase separation with poly(ethylene glycol). Lipids spontaneously self-assemble as multilamellar structures at the surface of the droplets as revealed by freeze-fracture transmission electron microscopy and small-angle X-ray scattering. We further demonstrate that the lipid-based membrane is impermeable to oligonucleotides and proteins, but also to a low molecular weight dye, so that a strict chemical encapsulation can be achieved by spontaneous partitioning within the droplets before membrane self-assembly. Taken together, our results highlight the ease of production of fatty acid-stabilized all-aqueous emulsions droplets able to encapsulate a range of solutes without the need of oil or organic solvents, paving the way to the construction of robust membrane-bounded, polymer-rich artificial cells.

Elastic and electro-optical properties of flexible fluorinated dimers with negative dielectric anisotropy

ABSTRACT We report the synthesis and the temperature dependencies of optical, dielectric, and elastic properties of four homologous dimeric mesogens in the uniaxial nematic (N) phase. The studied dimers are derived from 2ʹ,3ʹ-difluoroterphenyl units connected via flexible alkyl chains. The compounds differ in the length of either the flexible alkyl chain or the terminal groups. These achiral bimesogens exhibit the twist-bend nematic (NTB) phase with a nanoscale pitch of the modulated nematic director, as established by the freeze-fracture transmission electron microscopy. All four homologs have negative dielectric anisotropy owing to the permanent dipole oriented normal to the long molecular axes. A longer flexible bridge length yields an expanded temperature range of the N phase, stronger dielectric anisotropy, larger birefringence and bend elastic constant . Longer alkyl terminal chains increase birefringence but decrease the absolute value of dielectric anisotropy and . All four bimesogens show a dramatic decrease of down to ~0.5 pN on approaching the N-NTB transition. A longer bridge yields a longer period of twist-bend modulation in the NTB phase.

Potential of quercetin in combination with antioxidants of different polarity incorporated in oil-in-water nanoemulsions to control enzymatic browning of apples

Quercetin in combination with other antioxidants from natural sources and different polarity, including quercetin-3-rhamnoside, ascorbic acid, and α-tocopherol, were incorporated into oil-in-water (O/W) nanoemulsions to evaluate their effects on the activity of polyphenol oxidase (PPO) and browning of Granny Smith apple fruits. Additionally, molecular modeling methods were used to determine the ability and possible mechanisms of action of quercetin and quercetin-3-rhamnoside to inhibit PPO and to reduce the o-quinones derived from (–)-epicatechin, chlorogenic acid, catechol and methylcatechol (PPO substrates). Nanoemulsions were prepared using a low-energy emulsification method. In all nanoemulsions, Dynamic Light Scattering (DLS) analysis showed a size distribution of droplets between 100 and 500 nm diameter, whereas microscopical observation by freeze-fracture transmission electron microscopy (FF-TEM) corroborated the presence of the droplets and their size. Also, occasional arrangements consisting of stacked layers, with vesicle-like structures between them, were seen. The nanoemulsion 1, that contained the four antioxidants was the one that showed the best effect on PPO, inhibiting it by 41%, and inhibiting the browning of the apple flesh between 81 and 74% in a period of 6 h. Calculations with molecular modeling methods suggest that quercetin may be a more effective reducing agent than ascorbic acid and quercetin-3-rhamnoside, and could also act as a non-competitive inhibitor of PPO. While quercetin-3-rhamnoside represents a selective and competitive inhibitor of PPO. The most important function of α-tocopherol in the nanoemulsions could be the regeneration of quercetin to prolong its antioxidant activity.

Rhodopsins build up the birefringent bodies of the dinoflagellate Oxyrrhis marina

The ultrastructure of the birefringent bodies of the dinoflagellate Oxyrrhis marina was investigated by transmission electron microscopy. Ultrathin sectioning revealed that the bodies consist of highly ordered and densely packed lamellae, which show a regular striation along their longitudinal axis. A lattice distance of 6.1 nm was measured for the densely packed lamellae by FFT (Fast Fourier Transformation) analysis. In addition, a rather faint and oblique running striation was registered. Lamellae sectioned rather oblique or almost close to the surface show a honeycombed structure with a periodicity of 7.2–7.8 nm. Freeze-fracture transmission electron microscopy revealed that the lamellae are composed of highly ordered, crystalline arrays of particles. Here, FFT analysis resulted in lattice distances of 7.0–7.6 nm. Freeze-fracture transmission electron microscopy further revealed that the bodies remained intact after cell rupture followed by ascending flotation of the membrane fractions on discontinuous sucrose gradients. The birefringent bodies most likely are formed by evaginations of membranes, which separate the cytoplasm from the food vacuoles. Distinct, slightly reddish-colored areas, which resembled the birefringent bodies with respect to size and morphology, were registered by bright field light microscopy within Oxyrrhis marina cells. An absorbance maximum at 540 nm was registered for these areas, indicating that they are composed of rhodopsins. This was finally proven by immuno-transmission electron microscopy, as antisera directed against the C-terminal amino acid sequences of the rhodopsins AEA49880 and ADY17806 intensely immunolabeled the birefringent bodies of Oxyrrhis marina.

Abstract P-42: Structure of Hydrogels of an Anionic Polysaccharide Studied by Freeze-Fracture Transmission Electron Microscopy

Background: Polysaccharide hydrogels draw attention due to the ability to form mechanically tough gels at low concentrations (typically 1 wt% or lower), combined with biocompatibility and biodegradability. Biopolymer hydrogels can be used as a matrix for cell growth, in order to obtain materials for the replacement of damaged tissues. “Physical” gels with macromolecules cross-linked by dynamic reversible cross-links are of great interest due to their self-healing ability. However, investigation of the native un-perturbed structure of such hydrogels presents a challenge, since they collapse upon drying, and present a difficulty for preparing a thin specimen for cryo-TEM experiments due to very high viscosity. The aim of this work is to study the native structure of hydrogels of an anionic polysaccharide – carboxymethyl hydroxypropyl guar (CMHPG) – cross-linked by borax. Methods: Freeze-fracture transmission electron microscopy (FF-TEM) was conducted on a Phillips EM-301 microscope. A small volume of the sample (100 μl) was put into the copper cell and cooled down by liquid nitrogen, put under vacuum (10−5 torr) at continuous cooling with liquid nitrogen, and fractured. The surface was etched for 10–20 min at 10−5 torr and then replicated by spraying platinum and carbon. Results: The gels have a microphase-separated microstructure – a rather thick (several nm) polymer backbone is seen, which is presumably formed by multiple aggregated macromolecules, and meshes between the backbone do not contain polymer and are filled with solvent. Mesh size determined from the micrographs qualitatively coincides with the value determined from the elastic modulus of the gels. Upon increasing the concentrations of cross-linker, the network becomes denser: the mesh size becomes lower, and the thickness of the backbone increases. Thus, the addition of cross-linker favors the aggregation of polymer chains forming the backbone. Conclusion: It was shown by FF-TEM that cross-linked CMHPG gels have a microphase-separated structure with a dense backbone formed by polymer chains and rather large meshes between them.

Recovery of Fuels Using the Supramolecular Gelation Ability of a Hydroxybenzoic Acid Bisamide Derivative

In order to remedy the environmental pollution caused by oil spills, new materials with gelation capacity of organic solvents and fuels have been synthetized during the recent years. Among them, some of the most promising materials contain amide groups, which are often incorporated into the chemical structure of organogelators due to their effectiveness in gelling organic solvents through hydrogen bonds. A bisamide derivative of hydroxybenzoic acid (Bis-HUB1) was designed and synthesized in two steps and is able to congeal organic solvents. Gelation tests, critical gelation concentrations, and gel-sol transition temperatures were discussed in terms of its supramolecular interactions. Intermolecular hydrogen bonds and π-π stacking were studied through variable-temperature FTIR and UV-visible spectroscopy, while the structural characterization was performed via freeze-fracture TEM. Interestingly, Bis-HUB1 showed the ability to gel gasoline and diesel from monophasic and biphasic systems, which implies its potential use as a remediation agent in fuel spills. The results encourage further research.

A hydrogel-based in vitro assay for the fast prediction of antibiotic accumulation in Gram-negative bacteria.

The pipeline of antibiotics has been for decades on an alarmingly low level. Considering the steadily emerging antibiotic resistance, novel tools are needed for early and easy identification of effective anti-infective compounds. In Gram-negative bacteria, the uptake of anti-infectives is especially limited. We here present a surprisingly simple in vitro model of the Gram-negative bacterial envelope, based on 20% (w/v) potato starch gel, printed on polycarbonate 96-well filter membranes. Rapid permeability measurements across this polysaccharide hydrogel allowed to correctly predict either high or low accumulation for all 16 tested anti-infectives in living Escherichia coli. Freeze-fracture TEM supports that the macromolecular network structure of the starch hydrogel may represent a useful surrogate of the Gram-negative bacterial envelope. A random forest analysis of in vitro data revealed molecular mass, minimum projection area, and rigidity as the most critical physicochemical parameters for hydrogel permeability, in agreement with reported structural features needed for uptake into Gram-negative bacteria. Correlating our dataset of 27 antibiotics from different structural classes to reported MIC values of nine clinically relevant pathogens allowed to distinguish active from nonactive compounds based on their low in vitro permeability specifically for Gram-negatives. The model may help to identify poorly permeable antimicrobial candidates before testing them on living bacteria.

Supramolecular assembly of ionic liquid induced by UO2 2+: a strategy for selective extraction-precipitation

Abstract In this work, a novel task specific ionic liquid (TSIL) [tributyl(hexyl)phosphonium]2[diglycolic acetate] ([P6,4,4,4]2[DGA]) was prepared and used to construct a vesicle system. The addition of UO2 2+, La3+ or Th4+ exhibited different effects on the system. It was found that small amount of UO2 2+ could induce large-sized aggregation of vesicles and make the precipitation happen, while La3+ and Th4+ did not have such capacity. The whole process was characterized by dynamic light scattering and freeze-fracture transmission electron microscopy. An extraction-precipitation strategy was then developed for the selective recovery of UO2 2+. Different factors were further studied to optimize the separation efficiency of the extraction-precipitation process.

Microfluidisation trends in the development of nanodelivery systems: characterisation and release study of resveratrol‐loaded nanostructured lipid carrier prepared with high‐pressure microfluidisation

The release behaviour and kinetic evaluation of resveratrol (Res) from nanostructured lipid carrier (NLC) have been conducted after characterisation for Res-NLC in this study. High-pressure microfluidisation technique was successfully applied to manufacturing Res-NLC, and the morphology of nanoparticle was observed via freeze-fracture transmission electron microscopy. Photon correlation spectroscopy was used to characterise the NLC system for particle size (PS) and polydispersity index (PDI). The in vitro release research was implemented by the dialysis method with active ingredient determined by high-performance liquid chromatography. Fitting of release data to different kinetic models was carried out. The optimised Res-NLC was physically stable with the PS below 200 nm, PDI below 0.3 and zeta potential (ZP) above 50 mV. The encapsulation efficiency was above 80%. Moreover, an in vitro release analysis demonstrated the sustained release profile of contents from NLC formulation over 12 h, with about 90% of the active ingredient released. Res-NLC presented the best fit with the Weibull model accompanied by better correlation value. In conclusion, all the obtained results demonstrated that the release study of Res-loaded NLC exhibited the promising application of the NLC formulation system in active ingredient sustained release carrier.

In silico structure prediction of full-length cotton cellulose synthase protein (GhCESA1) and its hierarchical complexes

Cellulose synthase (CESA) polymerizes glucose into β-1,4-glucan chains that assemble to form cellulose microfibrils. Cellulose is the most abundant natural polymer in the world and a major structural component of the plant cell wall. An understanding of cellulose synthesis in plants is crucial for advancement in biofuels research and requires high-resolution 3D CESA structures. However, the determination of 3D structures of plant CESAs and their specific hierarchical arrangement into cellulose synthesis complexes (CSCs) has been a challenge. The prediction of CESA structures using computational methods presents a challenge due to poor sequence homology with resolved structures, long sequence, and structural complexity due to a mixture of globular, transmembrane, and intrinsically disordered regions. Herein, we present a 3D atomic-resolution model of a full-length (974-aa) cotton CESA (GhCESA1) structure using a variety of computational techniques with a reasonable ProSA-web z-score of − 8.32 (PDB available in SI). The overall fold of the CESA model indicates that there are similarities to BcsA bacterial cellulose synthase, such as the transmembrane topology and the internalization of conserved catalytic motifs. The plant-specific regions (CSR, P-CR, and N-term) fold into distinct subdomains, indicating the importance of these regions in CESA assembly into plant CSCs. We further examined possible assemblies of CESA monomers forming trimers and 18-mer CSCs, and we compared our results to those obtained by freeze fracture transmission electron microscopy. We observed that there are numerous competing ways in which CESAs may be arranged into homotrimers and CSCs. Our predicted structure can be used to probe CESA structure–activity relationships, select and subsequently test possible mutants, and investigate CESA aggregation into CSCs and microfibril formation to optimize biomass properties.

PH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions.

Cross-linking of polysaccharides by metal ions provides polymer gels highly required by industrial applications. In this article, we study the rheological properties and microstructure of solutions of a stiff anionic polysaccharide xanthan cross-linked by chromium (III) ions, and we demonstrate that their properties are highly sensitive to the preparation pH. Stable gels are obtained in a wide range of pH from 2.4 to 7.8. The maximum elastic modulus is observed for the gels made at pH 6.3, and by freeze-fracture transmission electron microscopy it is shown that they are characterized by the most dense network structure. However, out of this pH interval, no gelation is observed. At low pH (< 2.4) it is due to high protonation of carboxylic groups of xanthan preventing their interaction with chromium ions, and to the disappearance of oligomeric ions, which are effective in cross-linking. At high pH (> 7.8) the absence of gelation is caused by the transformation of reactive chromium ions into insoluble chromium hydroxide. At the same time, for the gels initially formed at pH 6.3, subsequent change of pH to strongly acidic (1.4) or basic (8.9) medium does not affect appreciably their properties, meaning that chromium cross-links are stable once they are formed. These observations open a reliable route to produce polysaccharide gels with required mechanical properties in a wide pH range where they initially cannot be prepared. It is also shown that the increase of pH to 6.3 of the initially ungelled solution prepared at pH 1.5 results in gelation. This effect offers a facile way for delayed gelation of polysaccharides, which is especially required by oil industry.

Frustration between two- and three-dimensional smectic ordering leads to a biaxial nematic phase.

The bola-amphiphilic, T-shaped mesogen CT2 has an aromatic, biphenyl core terminated on both ends by hydrophilic groups and a semi-perfluorinated, aliphatic side chain. Upon cooling from the isotropic phase, the fluorinated tails and the polar, rod-like cores nanophase-segregate to form a fluid lamellar phase. At high temperatures, the biphenyl cores are orientationally disordered in two dimensions (2D) in the lamellar planes but on further cooling the cores order orientationally, giving a biaxial lamellar phase with 2D nematic in-plane ordering. At lower temperature, the aromatic and hydrophilic parts of the cores nanosegregate within the lamellae and 2D smectic correlations of the head groups develop. X-ray diffraction shows that this 2D smectic ordering is incompatible with the initial lamellar structure, with both structures becoming short-ranged, resulting in a 3D biaxial nematic phase with macroscopic orthorhombic symmetry featuring strong smectic correlations in two orthogonal spatial dimensions. Freeze-fracture transmission electron microscopy enables direct visualization of the resulting short-ranged periodic structures.

Hydrogels Consisting of Vesicles Constructed via the Self-Assembly of a Supermolecular Complex Formed from α-Cyclodextrin and Perfluorononanoic Acid.

The self-assembly of α-cyclodextrin (α-CD) mixed with a fluorocarbon surfactant, perfluorononanoic acid (PFNA), in aqueous solution was studied. Interestingly, the 1:1 inclusion complex, PFNA@α-CD, was verified to form by 1H nuclear magnetic resonance measurement. Also as the building block, the PFNA@α-CD complex was further self-assembled into worm-like micelles under lower concentrations while hydrogels were self-assembled under higher concentrations. The hydrogels were composed of unilamellar vesicles with polydisperse size, which were clearly detected by freeze-fracture transmission electron microscopy measurements. Besides, the vesicle hydrogels showed high viscoelasticities and a substantial elastic characteristic. Also as revealed by the results of Fourier transform infrared measurements, the driving force for the vesicle and worm-like micelle formation was the hydrogen bonding between α-CD molecules. Then, these vesicles were densely packed to form hydrogels. As far as we know, the self-assembly of CDs and fluorocarbon surfactants based on host-guest inclusion in aqueous solution has been limitedly reported. Our work successfully constructed hydrogels consisting of vesicles through the self-assembly of the α-CD/PFNA complex for the first time and will also provide a better understanding and enrich the fundamental research of the self-assembly behavior of the CD/fluorosurfactant complex.

Micellization of trisiloxane surfactants appended with phenyl groups and polyether in aqueous solution

Polyether based trisiloxane surfactants with phenylsiloxyl hydrophobic groups (Ph-Si3-PG and Ph2-Si3-PG) were successfully synthesized and confirmed by 1H NMR, 13C NMR, 29Si NMR, and FT-IR. The effect of phenyl groups on the micellization and adsorption behavior in aqueous solution were investigated by surface tension, dynamic light scattering (DLS), freeze-fracture transmission electron microscopy (FF-TEM), transmission electron microscopy (TEM), and steady-state fluorescence spectroscopy. The γCMC values of Ph-Si3-PG and Ph2-Si3-PG obviously increase resulting from the phenylsiloxyl groups grafting onto the trisiloxane hydrophobic groups. The γCMC values follow the order, Ph-Si3-PG (35.5 mN·m−1) < Ph2-Si3-PG (39.7 mN·m−1), and the CMC values follow the order, Ph-Si3-PG > Ph2-Si3-PG. The results of steady-state fluorescence spectroscopy show that Ph2-Si3-PG has smaller I1/I3 value attributed to the more hydrophobic solubilizing site for the pyrene probe. Ph-Si3-PG and Ph2-Si3-PG can form non-uniform size of spheroidal aggregates in aqueous solution and confirmed by FF-TEM and TEM.

Aggregation properties of siloxane surfactants with phenyldimethylsiloxyl groups in aqueous solution

Two siloxane surfactants (Ph-Si3-EO16 and Ph-Si4-EO16) with two or three phenyldimethylsiloxyl groups were successfully synthesized by Piers-Rubinsztajn and thiol-ene reaction. The aggregation behavior in aqueous solution was investigated by surface tension, dynamic light scattering (DLS), transmission electron microscopy (TEM), and freeze-fracture transmission electron microscopy (FF-TEM). Owing to the steric hindrance and hydrophobicity of phenyldimethylsiloxyl groups, Ph-Si3-EO16 (40.4 mN·m−1) and Ph-Si4-EO16 (35.4 mN·m−1) have higher γCMC values. In comparison with Ph-Si3-EO16, Ph-Si4-EO16 has smaller CMC, γCMC, and Amin values attributed to the three phenyldimethylsiloxyl groups and intermolecular interaction. In the aqueous solution of Ph-Si4-EO16, the coexistence of spherical and rodlike aggregates resulting from intermolecular interaction (π-π interactions) was confirmed by TEM and FF-TEM. The results show that phenyldimethylsiloxyl groups play a vital role in the aggregation behavior of siloxane surfactants.

A Thermally Stable Polyamine/Unsaturated Fatty Acid System: Gelation Behaviors and Application

AbstractThe gelation behavior of diethylenetriamine (DETA) and oleic acid (OLA) with different molar ratios in water was investigated. The gels, which were composed of lamellar phase and vesicles, were characterized using small‐angle X‐ray scattering (SAXS) and freeze‐fracture transmission electron microscopy (FF‐TEM). The responsive rheological properties were also investigated. Our results show that lamellar gels and rodlike micelles were formed successively with the increase of the DETA/OLA molar ratio. The lamellar gels exhibiting high thermal stability can be obtained in a wide range of polyamine/unsaturated fatty acid molar ratios. The mechanism of lamellar gel formation was explained by the packing parameter and the noncovalent interactions between the building blocks. Moreover, gel–sol transition can be triggered by tuning pH and ionic strength. This system has a good emulsification property, and no obvious nanoemulsion droplet coarsening is observed upon dilution after 30 days.