Formation Of Lamellar Phase Research Articles

Formation of lamellar phase with 18R-type LPSO structure in an as-cast Mg96Gd3Zn1(at%) alloy

A lamellar Mg10GdZn phase was observed near the secondary eutectic β-phase ((Mg,Zn)3Gd) in an as-cast Mg–Gd–Zn alloy. It shows that the Mg10GdZn phase exhibits a 18R-type long period stacking ordered (LPSO) structure, while the lamellae within the α-Mg matrix exhibits a 14H-type LPSO structure. Moreover, it reveals that the hardness and elastic modulus of Mg10GdZn phase are much higher than those of the α-Mg by nano-mechanical measurements.

Rheological Investigation of Self-emulsification Process: Effect of Co-surfactant

The aim of study is to investigate role of co-surfactant in self-emulsification through rheological analysis of intermediate liquid crystalline (LC) phase formed during self-emulsification. To mixture of Captex 200P (C200) and tween 80 (T80) (SES Plain), either medium hydrocarbon chain co-surfactant (Capmul MCM (CMCM): SES C) or long hydrocarbon chain co-surfactant (Peceol (P): SES P) was added separately at different concentration levels. Self-emulsification was monitored by visual observations, turbidimetric and droplet size measurement. Mesophases were obtained by 30% v/v aqueous hydration of SES and characterized by polarizing microscopy, differential scanning calorimetry (DSC) and rheological studies. SES Plain exhibited 'bad' emulsification owing to instantaneous gel formation in aqueous media. Almost all SES C have shown 'good' emulsification with transparent appearance, very low turbidity value and nano size droplets. All SES P presented 'moderate' emulsification with milky appearance, high turbidity value and coarse droplets. Polarizing microscopy revealed formation of lamellar phase in SES Plain and in all SES P while almost all SES C exhibited formation of micellar cubic phase. In DSC studies, higher extent of LC phase formation was observed in SES C as compared to SES P. Rheological study clearly demonstrated presence of elastic and partially recoverable mesophase in SES Plain, which was transformed into a viscous and non-recovering mesophase with addition of CMCM while there was no change in rheological status of SES Plain after addition of P. The weak and viscous LC phase in SES C must have not presented any resistance to strain induced deformation. Therefore, it might have ruptured easily and quickly, releasing jet of nanosize droplets whereas elastic mesophase in SES P might have ruptured with little resistance resulting in coarse droplets. The ability of co-surfactant to promote self-emulsification was attributed to their influence on viscoelastic properties of intermediate LC phase.

Effect of HLB of additives on the properties and drug release from the glyceryl monooleate matrices

Glyceryl monooleate (GMO) is an amphiphilic surfactant, which as such can solubilize hydrophilic, lipophilic and amphiphilic drug molecules in its different polarity regions. Addition of additives with different polarities in GMO leads to change in phase behavior and related properties of GMO. Effect of the additives with different hydrophilic lipophilic balance (HLB; 1.5, 3, 4, 5, 7, 10 and 11) in GMO matrices on its phase transformation, rheological properties, mechanical properties, wetting and release behavior was investigated. Polarizing light microscopy showed that the GMO matrices incorporated with lower HLB additive (1.5, 3, 4 and 5) form cubic phase at higher rate while lamellar phase was prominent for matrices with additive of HLB 7, 10 and 11. The diametrical crushing strength and viscosity was decreased with increased HLB of additive. Lower HLB additives enhanced contact angle as compared to plain matrices and high HLB additives induced change in solid–liquid interface from hydrophobic to hydrophilic leading to decline in contact angle. Percent swelling of matrices was increased linearly with increase in HLB of additives. Tensiometric method was used for determination of bioadhesive strength of hydrated matrices and it was observed that matrices with additives of HLB 10 presented highest bioadhesion due to higher rate of hydration and formation of lamellar phase. As the HLB of additives in matrix increased, release was shifted from anomalous (non-Fickian) diffusion and/or partially erosion-controlled release to Fickian diffusion. Initial lag was observed for drug released from matrices with additive of HLB 1.5, 3, 4 and 5. Thus incorporation of the additives of different HLB changed molecular packing, which significantly affected drug release pattern.

1-Butanol and 3,3-dimethyl-1-butanol as cosurfactants of the laurylsulfobetaine/water system

Phase and rheological behaviors for laurylsulfobetaine with 1-butanol and with 3,3-dimethyl-1-butanol at 30.0±0.1°C are presented. Both systems show three liquid crystal phases: lamellar, hexagonal and cubic. Only one micellar phase appears with 1-butanol while two different micellar phases (L 1 and L 2) appear with the branched alcohol. For the system with 1-butanol, the transition from normal to reverse micelles goes through bicontinuous structures without phase separation. The shape of the mixed laurylsulfobetaine/1-butanol micelles in water change from spherical to large cylindrical micelles with the surfactant content. For the system with 3,3-dimethyl-1-butanol, the normal micelles in water solution are small and spherical and they exist in a narrow range of alcohol content. The reverse micelles in 1-butanol are larger than in 3,3-dimethyl-1-butanol. The extension of the cubic phase is the same for both systems. This phase is the most viscous phase with elastic properties which fits to the Maxwell model at low frequencies. On the contrary, the extension of lamellar and hexagonal phases is different depending of the alcohol structure. The formation of lamellar phase is favoring for the branched alcohol while the hexagonal region is larger for the system with the linear alcohol. Both phases show also viscoelastic properties but they do no fit to Maxwell model.

Structure of Cationic Starch (CS)/Anionic Surfactant Complexes Studied by Small-Angle X-ray Scattering (SAXS)

The structure of lyotropic liquid crystalline or gellike phases formed in cationic starch (CS)/anionic surfactant/water systems in the temperature range 25−80 °C has been investigated by small-angle X-ray scattering. The surfactants were sodium dodecyl sulfate (SDS), sodium decanoate (NaDe), sodium dodecanoate (NaDod), sodium palmitate (NaPal), sodium oleate (NaOl), and sodium erucate (NaEr). The phases were in equilibrium with aqueous solutions at 60 °C and contained 15−25 wt % of CS and 10−30 wt % of surfactant, depending on the charge density of the CS and the chain length of the surfactant. The phases consist of CS/surfactant aggregates arranged in long-range structures similar to lyotropic mesophases formed by the pure surfactants alone, but they separate from aqueous solutions at much lower surfactant concentrations. When the charge density of the CS is low or the surfactant hydrocarbon chain is short, cubic or hexagonal phases are formed. As expected, the formation of lamellar phase is promoted by ...