Microstructural investigation of monoglyceride–water coagel systems by NMR and CryoSEM

Effects of Domain Size on Viscosity of α-Gel (α-Form Hydrated Crystal) Prepared from Eco-friendly Cationic Surfactant

We determine the effects of the α-gel (α-form hydrated crystal) domain size on the viscosity of water-diluted α-gels consisting of the N-[3-(dimethylamino)propyl]docosanamide (APA-22) L-lactic acid salt, 1-octadecanol (C₁₈OH), and water. A decrease in the C₁₈OH mole content results in increased domain size and viscosity of the water-diluted α-gel system. Additionally, when a sample is prepared by slow cooling and/or at low stirring speed, the domain size and viscosity of the water-diluted α-gel system increase. A similar increase in the domain size and viscosity of the α-gel system is observed for annealed samples. The observed change in the α-gel domain size is explained by the crystal growth theory.

α-Gel (α-Form Hydrated Crystal) Prepared by Eco-Friendly Cationic Surfactant

We studied the structures and properties of gel samples prepared by mixtures of N-[3-(dimethylamino)propyl]docosanamide (APA-22) acid salt (APA-22 L-lactic acid), 1-octadecanol (C₁₈OH), and water. The gel samples prepared at the mole ratios [APA-22 L-lactic acid]:C₁₈OH = 1:3, 1:4, and 1:5 yielded two phases; one being the α-gel (α-form hydrated crystal) phase, incorporating a significant quantity of water between lamellar bilayers, and the other being the excess water phase. The lamellar d-spacing remained practically unaltered at these mole ratios, thus maintaining the quantity of water incorporated between the lamellar bilayers relatively constant. Starting at 30°C, the gel samples transformed into a lamellar liquid crystal phase at high temperatures (85°C) and a β-gel phase at low temperatures (5°C). Interestingly, following dilution by pure water, the viscosity of the gel samples decreased with increasing C₁₈OH content. We expect that the viscosity change affects the performance of the gel samples as hair conditioners.

Sediment Microstructure and the Establishment of Gas Migration Pathways during Bubble Growth

Soft sediments exhibit complex and varied deformation behavior during in situ bubble growth; however, the sediment microstructure is often neglected when predicting bubble networking or fracture propagation dynamics. This study considers three chemically similar Mg(OH)₂-rich sediments, which differ slightly in their particle size distributions and morphologies but exhibit significant differences in their porosity, stiffness, and pore throat dimensions at equivalent yield strengths. At low yield strengths, microstructure greatly influenced the size distribution and connectivity of spherical bubble populations, with narrow sedimentary pore throats promoting coarser bubbles with diminished connectivity. Increased connectivity of the bubble population appeared highly significant in limiting bed expansion, either by establishing pathways for gas release or by dissipating excess internal bubble pressure, thereby diminishing further growth. During in situ gas generation, each sediment demonstrated a critical fracture strength, which demarcated the populations with high void fractions (0.27 < ν < 0.4) of near-spherical bubbles from a fracturing regime supporting reduced void fractions (ν ≈ 0.15) of high aspect ratio cracks. However, critical fracture strengths varied significantly (in the 60-1000 Pa range) between sediments, with coarser-grained and higher porosity sediments promoting fracture at lower strengths. Fracture propagation greatly enhanced the connectivity and diminished the tortuosity of the void networks, thereby augmenting the continuous gas release flux.

Internal and external factors affecting the stability of glycerol monostearate structured emulsions

High SSL concentration, xanthan gum, and slow cooling rates without shear could stabilize the α-gel phase of MG-structured emulsion.

Effect of intrinsic and extrinsic factors on the stability of the α-gel phase of a glyceryl monostearate–water system

The α-gel phase of glycerlyl monostearate was stabilized by using specific co-surfactants, by setting slowly from the Lα phase and by avoiding shear.

Long-timescale motions in glycerol-monopalmitate lipid bilayers investigated using molecular dynamics simulation

The occurrence of long-timescale motions in glycerol-1-monopalmitate (GMP) lipid bilayers is investigated based on previously reported 600 ns molecular dynamics simulations of a 2×8×8 GMP bilayer patch in the temperature range 302-338 K, performed at three different hydration levels, or in the presence of the cosolutes methanol or trehalose at three different concentrations. The types of long-timescale motions considered are: (i) the possible phase transitions; (ii) the precession of the relative collective tilt-angle of the two leaflets in the gel phase; (iii) the trans-gauche isomerization of the dihedral angles within the lipid aliphatic tails; and (iv) the flipping of single lipids across the two leaflets. The results provide a picture of GMP bilayers involving a rich spectrum of events occurring on a wide range of timescales, from the 100-ps range isomerization of single dihedral angles, via the 100-ns range of tilt precession motions, to the multi-μs range of phase transitions and lipid-flipping events.

Comparing the crystallization and rheological behavior of organogels developed by pure and commercial monoglycerides in vegetable oil

We investigated the crystallization and rheological behavior of organogels developed with commercial (MSG_C) and pure (MSG_P) monoglycerides in safflower oil solutions (0.5% to 8% wt/wt). The MSG_C was composed of 1-mono-stearoyl-glycerol (1-MSG, 37.7%) and 1-mono-palmitoyl-glycerol (1-MPG, 54.0%), and the MSG_P essentially by 1-MSG (93.51%). The elastic (G') and loss (G″) moduli of the MSG_C and MSG_P-oil solutions were measured from 80°C until achieving 5°C, and then during isothermal conditions. The d(G')/d(time) rheograms, where d(G')/d(time) is the difference in G' between subsequent time-temperature conditions during cooling, followed closely the phase transition observed by the monoglycerides (MG). The d(G')/d(time) profile showed that the formation of the inverse lamellar α mesophase provided a limited structure to the vegetable oil. In contrast, the crystallization of the sub-α phase in the MSG_C-oil system, and of the sub-α₁ and sub-α₂ phases in the MSG_P-oil system structured the vegetable oil through the uptake and retention of oil within their microstructure. Additionally, smaller crystals formed the three-dimensional crystal structure in the MSG_C organogels. This is in comparison with the larger crystal size observed in MSG_P organogels. Nevertheless, for a similar MG concentration the MSG_C organogels showed higher G' and solid fat content (SFC) than the MSG_P organogels, and the differences were greater as the MG concentration increased. We consider that the mixed sub-α structure developed by 1-MSG and 1-MPG in the MSG_C-oil systems favored the incorporation and retention of higher amounts of oil, in comparison with the sub-α₁ and sub-α₂ structures developed just by 1-MSG in the MSG_P-oil systems.

α-Gel formation by amino acid-based gemini surfactants

Ternary mixtures being composed of surfactant, long-chain alcohol, and water sometimes form a highly viscous lamellar gel with a hexagonal packing arrangement of their crystalline hydrocarbon chains. This molecular assembly is called "α-crystalline phase" or "α-gel". In this study, we have characterized α-gels formed by the ternary mixtures of amino acid-based gemini surfactants, 1-hexadecanol (C16OH), and water. The surfactants used in this study were synthesized by reacting dodecanoylglutamic acid anhydride with alkyl diamines and abbreviated as 12-GsG-12 (s: the spacer chain length of 2, 5, and 8 methylene units). An amino acid-based monomeric surfactant, dodecanoylglutamic acid (12-Glu), was also used for comparison. At a fixed water concentration the melting point of the α-gel increased with increasing C16OH concentration, and then attained a saturation level at the critical mole ratio of 12-GsG-12/C16OH = 1/2 under the normalization by the number of hydrocarbon chains of the surfactants. This indicates that, to obtain the saturated α-gel, a lesser amount of C16OH is required for the gemini surfactants than for the monomeric one (the critical mole ratio of 12-Glu/C16OH = 1/3). Small- and wide-angle X-ray scattering measurements demonstrated an increase in the long-range d-spacing of the saturated α-gels in the order 12-Glu <12-G8G-12 < 12-G5G-12 < 12-G2G-12. In the three gemini surfactant systems, the decreased spacer chain length resulted in the increased maximum viscosity and elastic modulus of the saturated α-gels at a given water concentration. This is caused by the decreased amount of excess water being present outside the α-gel structure (or the increased amount of water incorporated between the surfactant-alcohol bilayers). To the best of our knowledge, this is the first report focusing on the formation of α-gel in gemini surfactant systems.

Stability conditions and mechanism of cream soaps: role of glycerol

Fatty acids, fatty acid potassium soaps, glycerol and water are essential ingredients in the production of stable cream soaps. In this study, the behavior of these components in solution was investigated to elucidate the stability conditions and mechanism of cream soaps. It was determined that the cream soaps were a dispersion of 1:1 acid soap (1:1 molar ratio of potassium soap/fatty acid) crystals in the lamellar gel phase, which has confirmed from the phase behavior diagrams and small angle X-ray scattering data. Glycerol was crucial ingredient in the formation of the lamellar gel phase. The cleansing process of the cream soaps was also evaluated using the same diagrams. The structure of the continuous phase in cream soaps changed from lamellar gel to a micellar aqueous solution upon the addition of water. This structural change during the washing process is important in producing the foaming activity of acid soaps to wash away dirt or excess fats from the skin surface.

Nature and dynamics of monostearin phase transitions in water: stability and the sub-α-gel phase

GMS–water system transformed to the sub-α-gel phase below 13 °C. The α-gel is stable at 5 °C but fractionation takes place.

Effects of water on aggregation and stability of monoglycerides in hydrophobic solutions

We apply a set of different techniques to analyze the physical properties and phase transitions of monoglyceride (MG)-oil-water ternary systems. The effect of MGs on water absorption in food-grade hazelnut oil and in pure hydrocarbon oil (decane) is reported. Comparison between decane and hazelnut oil backgrounds indicates that the effect of water absorption is significant and universal in different MG ternary systems. Adding small amounts of cosurfactant (stearic acid) is necessary to stabilize the MGs in oil-water combinations by enhancing the swelling capacity of lamellar layers; as a result, the structures become sensitive to the pH of the aqueous phase used. The dramatic changes on increasing the aqueous content are recorded by the calorimetry. In samples with small quantities of water, the phase behavior is almost independent of the pH. Once the proportion of water increases, the effect of pH is prominent. At low pH, the solubility of MG in water is limited, and the ternary system retains key features of the oil-dominated environment, such as the sequence of two transitions on cooling, with the low-temperature sub-alpha crystalline phase. At high pH and a sufficient amount of water, the MG layers remain properly swollen, and the crystalline phase disappears from the phase diagram. We spend considerable effort identifying the inverse lamellar phase of MGs in an oil-dominated environment with the so-called alpha-gel phase that is well-established in water-dominated systems, and distinguishing "demixing" from water and from oil. The rheology is examined in different fluid and gel phases; the storage modulus generally decreased on increasing the water proportion, but a gel-like response is found in the high-temperature lamellar phase over a wide range of water dilution. We then focus on aging phenomena in the inverse lamellar (or alpha-gel) phase and show that the rearranging of hydrogen bonds is slowed down and disrupted by the presence of water, giving the lamellar gel longer life times.

A technique for improved focused ion beam milling of cryo-prepared life science specimens

The combination of focused ion beam and scanning electron microscopy with a cryo-preparation/transfer system allows specimens to be milled at low temperatures. However, for biological specimens in particular, the quality of results is strongly dependent on correct preparation of the specimen surface. We demonstrate a method for deposition of a protective, planarizing surface layer onto a cryo-sample, enabling high-quality cross-sectioning using the ion beam and investigation of structures at the nanoscale.

Ultrasonic velocity measurements as a method for investigating phase transitions of monoglyceride emulsifier systems in pearlescent cosmetic creams

The phase transitions of monoglyceride emulsifier systems and pearlescent effects in cosmetic creams are investigated using ultrasonic velocity measurements. The transitions between the different phases of monoglyceride emulsifier systems--the coagel, liquid-crystalline lamellar phase, and gel phase--are detected in creams by changes in the ultrasonic velocity with variation of the temperature. The phase transition temperatures correspond to DSC results. Furthermore, the slope of the ultrasound velocity curve correlates with the amount of bound water in the different phases. These insights into the ultrasonic velocity properties of the monoglyceride emulsifier system of creams make it possible to more closely study the pearlescent effect of the coagel. The temperature domain of the short time reversibility of the pearlescence as well as the back-formation time of the coagel can be determined with this method, which enable the optimization of the formulation of pearlescent creams.