Mohammad Mydul Alam

Hexagonal phase based gel-emulsion (O/H1 gel-emulsion): formation and rheology.

The formation, stability, and rheological behavior of a hexagonal phase based gel-emulsion (O/H1 gel-emulsion) have been studied in water/C12EO8/hydrocarbon oil systems. A partial phase behavior study indicates that the oil nature has no effect on the phase sequences in the ternary phase diagram of water/C12EO8/oil systems but the domain size of the phases or the oil solubilization capacity considerably changes with oil nature. Excess oil is in equilibrium with the hexagonal phase (H1) in the ternary phase diagram in the H1+O region. The O/H1 gel-emulsion was prepared (formation) and kept at 25 degrees C to check stability. It has been found that the formation and stability of the O/H1 gel-emulsion depends on the oil nature. After 2 min observation (formation), the results show that short chain linear hydrocarbon oils (heptane, octane) are more apt to form a O/H1 gel-emulsion compared to long chain linear hydrocarbon oils (tetradecane, hexadecane), though the stability is not good enough in either system, that is, oil separates within 24 h. Nevertheless, the formation and stability of the O/H1 gel-emulsion is appreciably increased in squalane and liquid paraffin. It is surmised that the high transition temperature of the H1+O phase and the presence of a bicontinuous cubic phase (V1) might hamper the formation of a gel-emulsion. It has been pointed out that the solubilization of oil in the H1 phase could be related to emulsion stability. On the other hand, the oil nature has little or no effect on the formation and stability of a cubic phase based gel-emulsion (O/I1 gel-emulsion). From rheological measurements, it has found that the rheogram of the O/H1 gel-emulsion indicates gel-type structure and shows shear thinning behavior similar to the case of the O/I1 gel-emulsion. Rheological data infer that the O/I1 gel-emulsion is more viscous than the O/H1 gel-emulsion at room temperature but the O/H1 gel-emulsion shows consistency at elevated temperature.

New biocompatible thermo-reversible hydrogels from PNiPAM-decorated amyloid fibrils

New biocompatible temperature-responsive hydrogels have been obtained by using unprecedented low concentration of amyloid fibril-PNiPAM hybrids. The viscoelasticity of the hydrogels can be finely controlled by tuning the PNiPAM layers without changing the structure or concentration of the amyloid fibrils.

Effect of molecular weight of triglycerides on the formation and rheological behavior of cubic and hexagonal phase based gel emulsions

The effect of triglyceride molecular weight on the formation and rheology of cubic (O/I(1)) and hexagonal (O/H(1)) phase based gel emulsions has been studied in water/C(12)EO(8) systems. It was found that the addition of TDG (1,2,3-tridecanoyl glycerol) in the micellar solution leads to the formation of the I(1) phase, which can solubilize some added oil. From SAXS data, it is revealed that the interlayer spacing (d) and the length of hydrophobic part (r(I)) increase with increasing TDG concentration in the I(1) phase, whereas the effective cross-sectional area (a(s)) decreases. After the oil solubilization limit, the d value remains nearly constant, indicating the I(1)+O phase appears. The high viscosity of the I(1) phase facilitates the formation of the O/I(1) gel emulsion. It has been observed that the formation and stability of the O/I(1) and O/H(1) gel emulsion is highly dependent on the molecular weight of triglycerides, namely, the high molecular weight triglycerides show better performance (formation and stability) compared to the low molecular weight triglycerides. The rheological behavior of the I(1) phase was found to change from viscoelastic to elastic nature with TDG content. The values of the complex viscosity, mid absolute value(eta*) show different trends at different fixed frequencies within the I(1) phase, whereas it decrease monotonically in the O/I(1) gel emulsions. The increasing values of the absolute value(eta*) (at lower frequency) could be due to the neighboring micellar interaction and decreasing values of the absolute value(eta*) in the O/I(1) gel emulsion could relate to the volume fraction of the I(1) phase in the system. It is also figured out that the rheological parameters (elastic modulus, viscous modulus, and absolute value(eta*)) of the O/I(1) the gel emulsion do not depend on the oil nature, whereas the O/H(1) gel emulsion shows oil nature dependency.

Solubilization of triglycerides in liquid crystals of nonionic surfactant

The solubilization of triglycerides [1,2,3-tributanoylglycerol (TBG) and 1,2,3-trihexanoylglycerol (THG)] in water/octa(oxyethylene) dodecyl ether (C(12)EO(8)) systems has been investigated. Oil-induced changes in the structure of liquid crystals in water/C(12)EO(8) system have been studied by optical observation and small-angle X-ray scattering (SAXS) measurements. In the water/C(12)EO(8)/oil systems, solubilization of THG and TBG induces a transition between H(1) (hexagonal) and L(alpha) (lamellar) liquid crystals at high C(12)EO(8) concentrations, whereas at low surfactant concentrations a H(1)-I(1) (discontinuous micellar cubic phase) transition occurs. This anomalous behavior is attributed to the partitioning of solubilized oil in the micelles. At low surfactant concentrations THG is mainly solubilized into the hydrophobic cores of the surfactant micelles, indicating high swelling or low penetration tendency, resulting in a steep increase in the radius of the aggregates (r(H)), thereby inducing a rod-sphere transition. At high surfactant concentrations, THG is not mainly solubilized into the core but distributed between the palisade layer and the core of the aggregates. The TBG is considerably solubilized into the surfactant palisade layer, indicating a high penetration tendency, resulting in an increase in the effective cross-sectional area per surfactant molecule, a(s). The thermal stability of the I(1) phase increases with the solubilization of THG into the aggregate cores. The percentage deviation of the experimental interlayer spacings (P(d)) from complete swelling was also evaluated for different triglycerides in the H(1) and L(alpha) phases or different surfactant concentrations. It is found that the penetration tendency of triglycerides could be used as a tuning parameter for I(1) phase formation depending on the surfactant concentration and the molecular weight of the oil.

Template free synthesis of dendritic silver nanostructures and their application in surface-enhanced Raman scattering

A facile method has been proposed to synthesize dendritic silver nanostructures without any template. UV-vis and TEM images revealed that the dendritic silver nanostructures with pronounced trunks and branches have been synthesized. Surface-enhanced Raman scattering (SERS) experiments showed that the synthesized dendritic silver gives an intense signal when p-aminobenzenethiol at very low concentration is used as a probe molecule.

The effect of ethanol on the phase behaviour and micro-rheology of liquid crystals

The effect of ethanol on the phase behaviour and micro-rheology of lyotropic liquid crystals (LC) has been studied using a binary mixture of monoglyceride (MG) and aqueous ethanol. The phase behaviour study reveals the structural modulation of surfactant aggregates with increasing ethanol concentration, namely a bicontinuous cubic phase (Ia3d) transitions to the lamellar phase (Lα), at a fixed MG concentration. This behaviour is explained by considering the critical packing parameter (CPP) of the surfactant molecule. Because ethanol dehydrates the surfactant head group (a s), the CPP values increase (decreasing a s) and thus the formation of larger CPP aggregates is favoured (i.e., the Ia3d–Lα transition occurs). Cross-polarised images and X-ray scattering data support this conclusion. The structural modulation of the LC has further been investigated using a diffusing wave spectroscopy technique. The correlation and relaxation times, determined from the intersection point at short and long time scales of the mean square displacement (MSD), decrease with increasing concentrations of ethanol, indicating structural modulation of the LC. The micro-viscoelastic moduli (G′ and G′′) derived from the Laplace transformation of the MSD decrease with increasing ethanol concentrations, due to the LC modulation. The thermal effects on the micro-rheology of the LC have also been studied.

Lyotropic Behavior of Nonionic Sugar Surfactant and Rheology of the Liquid Crystal

Lyotropic behavior of sugar surfactant is investigated by analyzing the phase behavior and rheology of the liquid crystal (LC) and related LC-based emulsions in a ternary water/sugar surfactant (C12SE)/hexadecane system in presence and absence of a Polyol(1,2-propanediol). A micellar cubic phase (I1) is formed when hexadecane is added into the hexagonal (H1) phase, which exists up to 45 wt% 1,2-propanediol without structural modification. Increasing the complex viscosity on the addition of oil in the I1 phase is possibly associated with the neighboring micellar (due to swelling) interaction or steric interaction (due to shape transformation).

Schizophrenic micelle of a water-soluble diblock polymer and its application to a thermo-optical device

An investigation has been carried out to understand the schizophrenic behavior of a water-soluble diblock polymer poly-(methacrylic acid-block-N-isopropyl acrylamide) (PMAA18-b-PNIPAM86) and to fabricate a thermo-optical device. At room temperature, the polymer is molecularly dissolved in an aqueous solution which is indicated by weak scattering signal. The scattering intensity increased abruptly with increasing temperature, an indication of the formation of PNIPAM-core/PMAA-corona micelles. On the other hand, in the presence of calcium ion (Ca2+), PMAA-core/PNIPAM-corona micelles are formed at room temperature. Interestingly, the PMAA-core and PNIPAM-core are reversibly interchangeable to each other by removing/adding the outer stimuli (i.e., Ca2+ and heat). The UV-vis spectra reveal that the optical properties of the gold-polymer conjugate changes with heating and cooling. This suggests that the schizophrenic micelle can be used to fabricate a thermo-optical device.