Α-gel Phase Research Articles

Aggregation behaviors of alkyl α-keto acids in water

Single-tailed α-keto acids are a kind of fatty acid derivatives and weakly acidic amphiphiles. Only the aggregation behavior of α-ketooctanoic acid (KC8) in water was investigated so far, and thus the current understanding of their aggregation behavior, such as the effect of alkyl chain length, is still limited. It is essential to investigate the aggregation behavior of alkyl α-keto acids such as α-ketodecanoic acid (KC10) and α-ketododecanoic acid (KC12), to fully understand the features of α-keto acids. The aggregation behavior of KC10 and KC12 in water was investigated by changing their concentrations (C), using equilibrium surface tension, cryogenic transmission electron microscopy, dynamic light scattering, small-angle X-ray scattering, and deuterium nuclear magnetic resonance, and compared with that of KC8. A C-dependent stepwise aggregation was observed for the KC10 and KC12 systems. With increasing C, vesicles, precipitates, micelles, and lamellar phase (or α-gel phase) form successively in the systems, where precipitates and micelles both coexist with vesicles, similar to the case of KC8. With an increase in chain length, the pKa of α-keto acids increases while their critical concentrations of stepwise aggregations decrease, arising from the enhancement of the interactions between alkyl chains. The aggregation behavior observed can be explained by the existence of multispecies (including the “acid-soap” dimers) and the interaction between alkyl chains.

The leaf of Agapanthus africanus (L.) Hoffm.: A physical-chemical perspective of terrestrialization in the cuticle

Although Agapanthus africanus (L.) Hoffm. is one of the most popular ornamental species in both hemispheres, it has an extremely restricted wild occurrence (Cape province, South Africa). This contradiction between generalized ornamental application and natural distribution was the basis for the analytical approach adopted in the present work. We hypothesized that characteristic features of the cuticular waxes were adopted by this species to help it cope with severe dehydration associated with marine salinity on account of the short distance of the wild populations to the sea. A comprehensive morpho-anatomical, histological and physical-chemical analysis was performed on the epicuticular and intracuticular layers of the adaxial and abaxial surfaces of leaves of specimens of A. africanus. The adaxial epicuticular surface is hydrophilic and the abaxial epicuticular surface exhibits globally hydrophobic behavior. The main chemical compounds detected in the wax layers of both surfaces of the leaf are the short-chain monocaprylin monoglyceride (C8), and very long-chain 1-hexacosanol (C26) and 1-octacosanol (C28) alcohols. While monocaprylin is particularly abundant in the intracuticular layers, the epicuticular adaxial surface revealed the highest concentration of both alcohols. We demonstrate that the smart combination of these two classes of molecules with opposite water affinity endows the A. africanus leaf cuticle with a unique water management system combining the efficient entrapment of water in the disordered α-gel phase formed by monocaprylin and the high resistance to water transport provided by ordered domains composed of tightly packed, all-trans alkyl chains of the above pair of alcohols. The remarkable structural similarity existing between the monocaprylin α-gel and the mucilage of algae is an evidence of the terrestrialization process.

Structural Change of an α-Gel (α-Form Hydrated Crystal) Induced by Temperature and Shear Flow in an Oleic Acid Based Gemini Surfactant System.

We studied the effects of temperature and shear flow on the structures of α-gel bilayers and domains. The α-gel samples were prepared by a carboxylate-type gemini surfactant synthesized from oleic acid and a long-chain alcohol (1-tetradecanol) with water. The structural change as a function of temperature was investigated using small- and wide-angle X-ray scattering (SWAXS) measurements, spin-spin relaxation time (T2) measurements, and optical microscopy observations. SWAXS measurements suggested that the decreased temperature yielded the α-gel phase from a lamellar liquid-crystal phase. We also found that the lamellar d-spacing drastically decreased at the phase transition temperature. The T2 measurements suggested that two kinds of protons with different mobilities coexisted in amphiphiles consisting of lamellar bilayers. The abundance of the protons with low mobility increased with decreasing temperature. Optical microscopy results indicated that the size of the α-gel domains increased with decreasing temperature. We assumed that the increased abundance of the low-mobility protons, indicating low flexibility of lamellar bilayers, led to a decreased lamellar d-spacing and increased size of the α-gel domains. Shear-induced structural changes in the α-gel were also studied using simultaneous small-angle neutron scattering and rheological measurements. The α-gel can maintain bilayer structures even at high shear rates. We also found that the lamellar d-spacing was independent of the shear rate.

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.

The alkyl polyglucoside/fatty alcohol ratio effect on the formation of liquid crystal phases in binary systems

The present research focuses on the alkyl polyglucoside, a non-ionic surfactant, in combination with a fatty alcohol of the same chain length used as a co-surfactant. A series of solutions were prepared, with varying both APG/FA ratio and its concentration in water. Different structures were then obtained, depending on these two parameters: aqueous micellar solutions, normal hexagonal liquid crystalline phase, α-gel phase, as well as the mixture of normal hexagonal/α-gel phases. A specific term “auto-emulsion” was introduced to describe the pseudo emulsions formed by the APG≤FA containing solutions because of the fatty alcohol, which dispersion in water was similar to an emulsion representation. The presence of the liquid crystals was revealed by optical microscopy under the polarized light, as different anisotropic conformations corresponding to the lamellar phase, the hexagonal phase and the coexistence of the lamellar and hexagonal phases, mainly for the most concentrated samples, were observed. These structures were characterized at the molecular level through the wide-angle X-ray diffraction technique and their macroscopic behaviour was investigated by rheology tests. Two main observations were then made: the variation of the surfactant concentration in solution promotes the transition between micellar region towards the liquid crystalline formation zone, while the APG/FA ratio impacts the formation of hexagonal phases (APG>FA) or of lamellar ones (APG<FA).

Gel phase nano formulation: The effect of triglycerides

Gel phase formation is commonplace for surfactants, lipids and oils. The most frequently encountered states are the α-gel phase for non-polar lipids such as triglycerides and the Lβ phase for surfactants and polar lipids. It is well known that both the Lβ phase and the α-gel phase consist of surfactant layers where the alkyl chains are mostly in an all-trans conformation with no translational mobility. These are packed in a two dimensional hexagonal lattice with rotational disorder (high angle X-ray peak at 4.2Å). However, in the case of the α-gel phase for unsaturated monglycerides, the alkyl chains cannot be in the all-trans state. The high angle X-ray pattern shows a broad peak at 4.1Å plus at ca. 4.5Å. Clearly, this cannot pack in the same hexagonal structure as the α-gel phase of the saturated lipids, but the cis double bond can be accommodated. Limited information is available regarding the effect of saturated and unsaturated triglyceride on stability of the gel phase in aqueous systemWe have examined the phase behaviour of mixed saturated and unsaturated monoglycerides [glycerol monostearate (GMS) and glycerol monooleate (GMO) (1:1)] in palm oila and olive oil with water. Optical microscopy was used to study the mesomorphic behaviour as function of temperature. We also employed differential scanning calorimetry (DSC) to determine the transition enthalpies between mesophases. In parallel we use small angle X-ray diffraction to characterize the different mesomorphic phases at different temperatures.The finding of this work cast light on the phase behaviour of saturated and unsaturated monoglycerides in oil with water system, Our results suggest that saturated triglycerides promotes the stability of gel phase while unsaturated triglycerides promotes the forming of the cubic phase at room temperatureFrom an industrial point of view, both the cubic phase and gel phase could be attractive systems for making stable products with low fat content.

Effect of the addition of palm stearin and storage temperatures on the thermal properties of glycerol monostearate-structured emulsions

Monoglyceride (MG) structured oil-in-water emulsions have been developed as low fat shortening alternatives. In this work, the effect of the addition of palm stearin (PS) and storage at different temperatures on the thermal properties of glycerol monostearate (GMS)-structured emulsions were characterized. The melting profile and the dropping point of GMS-structured emulsions were investigated during five weeks of storage at 8°C and 22°C. Results showed that the addition of PS changed the melting profiles of GMS-structured emulsions that were stored under refrigeration temperatures, possibly by reducing phase separation between GMS and co-emulsifiers. Storage at refrigeration temperatures increased the stability of the α-gel phase while storing at room temperatures accelerated emulsion destabilization. Even though samples stored at refrigeration temperatures had lower dropping points, they were in the α-gel phase, making refrigeration temperatures the desirable storage condition to achieve maximal stability of MG-structured emulsions.

Microstructural basis for water release from glycerol monostearate structured emulsions upon transformation from the α-gel to the coagel phase

Abstract This work characterized changes in surface morphology of a glyceryl monostearate structured emulsion (MG-structured emulsion) during the polymorphic transformation from the α-gel phase to the coagel phase. The effects of using various concentrations of co-emulsifier and adding xanthan gum on emulsion structure and stability were also investigated. Microscopy methods, including light microscopy, cryogenic-scanning electron microscopy, and X-ray diffraction were employed in the examination of the emulsion microstructure. Results showed that the MG-structured emulsion has a smooth droplet surface in the α-gel phase and a porous surface in the coagel phase. The formation of a porous surface during the polymorphic transformation leads to water release upon emulsion destabilization. Formulating with higher content of co-emulsifier or adding xanthan gum enhanced the multi-lamellar structure and stability of this structured emulsion.

The phase behaviour of mixed saturated and unsaturated monoglycerides in hydrophobic system

Lyotropic liquid crystals are formed on the dissolution of most surfactants in water as represented by regions on the phase diagram, and are more common than micellar solutions. Monoglycerides with saturated or unsaturated fatty acids are one of the most commonly used food surfactants. While there is considerable interest in the behaviour of monoglycerides mixed with oils (particularly triglycerides), limited information is available regarding the phase behaviour of such systems. We have examined the phase behaviour of mixed saturated and unsaturated monoglycerides1:1 (by weight) together with different oils systems. The main technique employed was X-ray diffraction, supplemented by optical microscopy, proton nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC). Our results suggest that six phases (L2, α-gel phase, sub α- phase, β1 and oil crystallisation phase (β` for palm oil or β2 for miglyol oil or olive oil) were observed for G50/oil mixture. Furthermore, this paper proves that miglyol and palm oil incorporate into α-gel phase of G50. In contrast, olive oil dose not incorporate into α-gel phase of G50.

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.

PH and stability of the α-gel phase in glycerol monostearate–water systems using sodium stearoyl lactylate and sodium stearate as the co-emulsifier

Changing the environmental pH altered the melting profiles of monostearate–water systems and affects the stability of the α-gel phase using sodium stearoyl lactylate (SSL) and sodium stearate (NaS) as co-emulsifiers.

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.

The phase behaviour of mixed saturated and unsaturated monoglycerides in water system

Abstract Lyotropic liquid crystalline phases are formed over a limited range of surfactant concentrations and temperatures as represented by regions on the phase diagram. Acknowledgement of the surfactant phase diagram is a major step in developing any industrial application. In this work; we have examined the phase behaviour of mixed saturated and unsaturated monoglycerides 1:1 (by weight) together with water. The main technique employed was X-ray diffraction, supplemented by optical microscopy and differential scanning calorimetry (DSC). The phase diagram which is a novel finding shows six phases for GMS/GMO mixture without water: α-gel (Lβ) phase, new α-gel (Lβ1) structure, β1 crystal phase, sub-α phase, β2-crystal, as well as an isotropic, L2, phase. In the presence of water five additional phases are formed, fluid lamellar phase, three bicontinous cubic phases, Ia3d, Pn3m and Im3m with increasing the water content, and on further heating all bicontinous cubic phase convert to a hexagonal phase. Our results show that the maximum swelling capacity of the mixture of monoglycerides in water is obtained at 50% (w/w) water content, and there are important differences in the phase behaviour between mixed saturated and unsaturated monoglycerides with and without water.

Gel phase (Lβ) formation by mixed saturated and unsaturated monoglycerides

It is commonly thought that the α-gel phase (Lβ) consists of surfactant layers where the alkyl chains are mostly in the all-trans conformation and packed in a two dimensional hexagonal lattice with rotational disorder, but no translational mobility. We have examined the phase behaviour of mixed saturated and unsaturated monoglycerides [glycerol monostearate (GMS) and glycerol monooleate (GMO)] to investigate whether gel phases will be formed from unsaturated monoglycerides. In addition, this study examined the effect of aging on the phase behaviour of the mixture. An array of techniques was employed to investigate the phase behaviour as function of temperature: optical microscopy to observe optical textures, differential scanning calorimetry (DSC) to determine the transition enthalpies between phases, and nuclear magnetic resonance (NMR) to study surfactant mobility in the various phases. Additionally, we used small angle X-ray scattering (SAXS) to characterise the different mesomorphic phases at different temperatures. Finally, Fourier transform infrared spectroscopy (FTIR) was used to study the states of hydrogen bonding in the systems. Our results suggest that various phases for GMS/GMO mixture were observed α-gel (Lβ) phase, new α-gel (Lβ1) structure, β1 crystal phase, sub-α phase, β2-crystal, as well as an isotropic, L2, phase. Additionally there is some unsaturated monoglyceride incorporated into the α-gel phase of the saturated monoglyceride, which generated the new type of α-gel structure (Lβ1) characterised by a more disordered structural arrangement. GMO cannot pack in the same hexagonal structure as the α-gel phase of saturated lipids (Lβ). During storage, all monoglyceride structures transform to a highly ordered packing β crystal structure.

Microstructure and viscoelastic properties of low-fat yoghurt structured by monoglyceride gels

Abstract Three monoglyceride gels (MG gels) made up by 5 g of monopalmitin/monostearin blends in ratios of 0.10:0.87, 0.30:0.65 and 0.43:0.50, and 0.05 g of an anionic co-surfactant per 100 mL of water were prepared. Differential Scanning Calorimetry (DSC) results indicated that when cooled below the Krafft temperature ( T krafft ) the three MG gels were predominantly in the α-gel phase, and were used under this condition to prepare three low-fat yoghurt variations (Y 0.1MP,0.87MS , Y 0.3MP,0.65MS , and Y 0.43MP,0.50MS ). Scanning electron micrographs showed that Y 0.1MP,0.87MS and Y 0.3MP,0.65MS structure was characterized by aggregated fused casein micelles, which had attached to their surface MG gels, with comparatively smaller interspaced voids than those showed by the control full-fat yoghurt (Y 100 ). Y 0.1MP,0.87MS and Y 0.3MP,0.65MS exhibited higher viscoelastic parameters over the whole frequency experimental sweep than Y 100 , Y 0.43MP,0.50MS , and low-fat control yoghurt (Y 50 ).