Misni Misran

Thermodynamic and kinetic stability. Properties of micelles and vesicles formed by the decanoic acid/decanoate system

The dialysis of micellar and vesicular systems, through a cellulose acetate membrane permeable only to monomer surfactant, has been investigated for the system sodium decanoate/decanoic acid as a function of pH, in pH regions where micelles (pH 9) or vesicles (pH 7.5) are present. The results provide data that are helpful in establishing the thermodynamic state of the systems and the interplay of the relevant equilibrium and kinetic considerations. Additionally, the kinetics of spontaneous formation and destruction of vesicles when subjected to a pH-jump perturbation have been studied. Changes are rapid, taking place over a time scale of a few seconds.

Investigation on the use of graphene oxide as novel surfactant to stabilize weakly charged graphene nanoplatelets

This paper presents a unique synergistic behavior between a graphene oxide (GO) and graphene nanoplatelet (GnP) composite in an aqueous medium. The results showed that GO stabilized GnP colloid near its isoelectric point and prevented rapid agglomeration and sedimentation. It was considered that a rarely encountered charge-dependent electrostatic interaction between the highly charged GO and weakly charged GnP particles kept GnP suspended at its rapid coagulation and phase separation pH. Sedimentation and transmission electron microscope (TEM) micrograph images revealed the evidence of highly stable colloidal mixtures while zeta potential measurement provided semi-quantitative explanation on the mechanism of stabilization. GnP suspension was confirmed via UV-vis spectral data while contact angle measurement elucidated the close resemblance to an aqueous solution indicating the ability of GO to mediate the flocculation prone GnP colloids. About a tenfold increase in viscosity was recorded at a low shear rate in comparison to an individual GO solution due to a strong interaction manifested between participating colloids. An optimum level of mixing ratio between the two constituents was also obtained. These new findings related to an interaction between charge-based graphitic carbon materials would open new avenues for further exploration on the enhancement of both GO and GnP functionalities particularly in mechanical and electrical domains.

The kinetics and mechanism of micelle-vesicle transitions in aqueous solution

Bi-chained surfactants, e.g. sodium dialkylbenzenesulphonates, can spontaneously form vesicles when salts (e.g. NaCl) are added to water. Critical vesicle concentrations can be readily determined. The kinetics and mechanism for the breakdown and formation of vesicles will be discussed. A mechanism for assembly/disassembly is proposed. Organic dyes can be encapsulated inside the vesicles and their release rates can be monitored using flow experiments. It is found that the vesicle bilayer provides a rather low energy barrier to the transport of the dye from the vesicle core to the external aqueous medium.

Optimization of processing parameters for the preparation of phytosterol microemulsions by the solvent displacement method.

The purpose of this study was to optimize the parameters involved in the production of water-soluble phytosterol microemulsions for use in the food industry. In this study, response surface methodology (RSM) was employed to model and optimize four of the processing parameters, namely, the number of cycles of high-pressure homogenization (1-9 cycles), the pressure used for high-pressure homogenization (100-500 bar), the evaporation temperature (30-70 degrees C), and the concentration ratio of microemulsions (1-5). All responses-particle size (PS), polydispersity index (PDI), and percent ethanol residual (%ER)-were well fit by a reduced cubic model obtained by multiple regression after manual elimination. The coefficient of determination (R(2)) and absolute average deviation (AAD) value for PS, PDI, and %ER were 0.9628 and 0.5398%, 0.9953 and 0.7077%, and 0.9989 and 1.0457%, respectively. The optimized processing parameters were 4.88 (approximately 5) homogenization cycles, homogenization pressure of 400 bar, evaporation temperature of 44.5 degrees C, and concentration ratio of microemulsions of 2.34 cycles (approximately 2 cycles) of high-pressure homogenization. The corresponding responses for the optimized preparation condition were a minimal particle size of 328 nm, minimal polydispersity index of 0.159, and <0.1% of ethanol residual. The chi-square test verified the model, whereby the experimental values of PS, PDI, and %ER agreed with the predicted values at a 0.05 level of significance.

Experimental investigation on the use of highly charged nanoparticles to improve the stability of weakly charged colloidal system

The present work highlighted on the implementation of a unique concept for stabilizing colloids at their incipiently low charge potential. A highly charged nanoparticle was introduced within a coagulated prone colloidal system, serving as stabilizer to resist otherwise rapid flocculation and sedimentation process. A low size asymmetry of nanoparticle/colloid serves as the new topic of investigation in addition to the well-established large size ratio nanoparticle/microparticle study. Highly charged Al2O3 nanoparticles were used within the present research context to stabilize TiO2 and Fe3O4 based colloids via the formation of composite structures. It was believed, based on the experimental evidence, that Al2O3 nanoparticle interact with the weakly charged TiO2 and Fe3O4 colloids within the binary system via absorption and/or haloing modes to increase the overall charge potential of the respective colloids, thus preventing further surface contact via van der Waals attraction. Series of experimental results strongly suggest the presence of weakly charged colloids in the studied bimodal system where, in the absence of highly charged nanoparticle, experience rapid instability. Absorbance measurement indicated that the colloidal stability drops in accordance to the highly charged nanoparticle sedimentation rate, suggesting the dominant influence of nanoparticles to attain a well-dispersed binary system. Further, it was found that the level of colloidal stability was enhanced with increasing nanoparticle fraction within the mixture. Rheological observation revealed that each hybrid complexes demonstrated behavior reminiscence to water with negligible increase in viscosity which serves as highly favorable condition particularly in thermal transport applications.

Characterization of fatty acid liposome coated with low-molecular-weight chitosan.

Preparation of chitosan-coated fatty acid liposomes is often restricted by the solubility of chitosan under basic conditions. In this experiment, the preparation of chitosan-coated oleic acid (OA) liposomes using low molecular weight (LMW) chitosan (10 and 25 kDA) was demonstrated. These selected LMW chitosans are water soluble. The coating of the chitosan layer on OA liposomes was confirmed by its microscope images and physicochemical properties, such as zeta potential and the size of the liposomes. The “peeling off” effect on the surface of chitosan-coated OA liposomes was observed in the atomic force microscope images and showed the occurrence of the chitosan layer on the surface of OA liposomes. The size of the chitosan-coated liposomes was at least 20 nm smaller than the OA liposomes, and the increase of zeta potential with the increasing amount of LMW chitosan further confirmed the presence of the surface modification of OA liposomes.

Development of a Controlled Release of Salicylic Acid Loaded Stearic Acid-Oleic Acid Nanoparticles in Cream for Topical Delivery

Lipid nanoparticles are colloidal carrier systems that have extensively been investigated for controlled drug delivery, cosmetic and pharmaceutical applications. In this work, a cost effective stearic acid-oleic acid nanoparticles (SONs) with high loading of salicylic acid, was prepared by melt emulsification method combined with ultrasonication technique. The physicochemical properties, thermal analysis and encapsulation efficiency of SONs were studied. TEM micrographs revealed that incorporation of oleic acid induces the formation of elongated spherical particles. This observation is in agreement with particle size analysis which also showed that the mean particle size of SONs varied with the amount of OA in the mixture but with no effect on their zeta potential values. Differential scanning calorimetry analysis showed that the SONs prepared in this method have lower crystallinity as compared to pure stearic acid. Different amount of oleic acid incorporated gave different degree of perturbation to the crystalline matrix of SONs and hence resulted in lower degrees of crystallinity, thereby improving their encapsulation efficiencies. The optimized SON was further incorporated in cream and its in vitro release study showed a gradual release for 24 hours, denoting the incorporation of salicylic acid in solid matrix of SON and prolonging the in vitro release.

Formulation and in vitro and in vivo evaluation of a new osteoprotegerin-chitosan gel for bone tissue regeneration

The osteoprotegerin (OPG) system plays a critical role in bone remodelling by regulating osteoclast formation and activity. The study aimed to determine the physicochemical properties and biocompatibility of a newly formulated OPG-chitosan gel. The OPG-chitosan gel was formulated using human OPG protein and water-soluble chitosan. The physicochemical properties were determined using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Gel morphology was determined using scanning electron microscopy (SEM) and then it was subjected to a protein release assay and biodegradability test. An in vitro cytotoxicity test on normal human periodontal ligament (NHPL) fibroblasts and normal human (NH) osteoblasts was carried out using the AlamarBlue assay. In vivo evaluation in a rabbit model involved creating critical-sized defects in calvarial bone, filling with the OPG-chitosan gel and sacrificing at 12 weeks. In vitro results demonstrated that the 25 kDa OPG-chitosan gel had the highest rate of protein release and achieved 90% degradation in 28 days. At 12 weeks, the defects filled with 25 kDa OPG-chitosan gel showed significant (p < 0.05) new bone formation and the highest expression of osteocalcin and osteopontin compared to controls. Thus, the 25 kDa OPG-chitosan gel could be a promising new biomaterial for tissue engineering.

Albumin-fatty acid interactions at monolayer interface

The fluid mosaic model of Singer and Nicolson in 1972 shows how proteins are embedded in membranes. To elucidate the interactions between proteins and the surrounding lipids, stearic acid (SA) and bovine serum albumin (BSA) were used as lipid-protein components to mimic the normal membrane bilayer environment using the Langmuir-Blodgett technique. Surface pressure (π)-molecular area (A) isotherms were recorded for the SA monolayer in the presence of BSA on water. The mixed monolayer was successfully transferred onto an oxidized silicon wafer and imaged by tapping mode atomic force microscopy (AFM). Miscibility, compressibility and thermodynamic stability of the mixed system were examined. A large negative deviation of Aex, together with the minimum value of ΔGex, was observed when the mole fraction of BSA (XBSA) was 0.8, indicating this to be the most stable mixture. In a compressibility analysis, XBSA was observed at below 50 mN m-1, denoting a liquid-expanded phase and showing the occurrence of a strong interaction of SA with BSA molecules in this phase. AFM observations supported the quantitative data indicating that BSA was strongly attracted onto the membrane surface as predicted.

Single step fabrication of CuO–MnO–2TiO2 composite thin films with improved photoelectrochemical response

Novel trimetallic composite oxide CuO–MnO–2TiO2 thin films have been deposited on glass substrates, which were coated with fluorine-doped tin oxide (FTO), by aerosol-assisted chemical vapor deposition (AACVD) using a 1 : 1 : 2 non aqueous mixture of copper(II) acetate monohydrate (Cu(CH3COO)2·H2O), anhydrous manganese(II) acetate (Mn(CH3COO)2) and titanium(IV) butoxide (Ti(O(CH2)3CH3)4) in the presence of trifluoroacetic acid (TFA). Thin films were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS), suggesting the formation of a crystalline mixture of CuO–MnO–2TiO2 composite with well defined and evenly distributed particles. The direct band gap energy of 1.95 eV was estimated by UV-Vis spectroscopy. From its current–voltage characterization, it is evident that the nanostructured CuO–MnO–2TiO2 photoelectrode deposited at 550 °C for 45 minutes displayed enhanced photocatalytic activity in photoelectrochemical (PEC) water splitting and yielded a photocurrent of 2.21 mA cm−2 at +0.7 V vs. Ag/AgCl/3 M KCl using a 0.5 M Na2SO4 electrolyte under AM 1.5 G illumination (100 mW cm−2). The charge transfer dynamics of the thin film were also explored using an electrochemical impedance spectroscopy (EIS) technique.