Understanding the adsorption behavior of surface active molecules on ZnO nanostructures by experimental and first-principles calculations.

Zinc oxide (ZnO) nanostructures with different morphologies are prepared in the presence of surface active molecules such as sodium dodecyl sulphate (SDS), Tween 80 and Triton X-100 by a chemical method. The experimental and first principles methods are employed to understand the microscopic origin of the asymmetric growth mechanism of ZnO in the presence of various surface active molecules. Effect of increase in the amount of surface active molecules and temperature is studied on the growth morphology of ZnO. An innovative method is developed to synthesize ZnO nanowires (NWs) in the presence of SDS. Spherical nanoparticles (NPs) to spherical clusters are obtained in the presence of Triton X-100 and Tween 80. These results are then supported by first principles calculations. The adsorption of the -OH functional group on both polar and nonpolar surfaces of ZnO is modelled by using density functional theory (DFT). The calculated binding energy (BE) is almost equivalent on both the surfaces with no preference on any particular surface. The calculated value of BE shows that the -OH group is physio-adsorbed on both the surfaces. This results in the spherical morphology of nanoparticles prepared in the presence of Tween 80. Bader charge analysis shows that the charge transfer mainly takes place on top two layers of the ZnO(101[combining macron]0) surface. The absence of high values of electron localization function (ELF) reflects the lack of covalent bonding between the -OH group and the ZnO(101[combining macron]0) surface.

pH and thermo-responsive tetronic micelles for the synthesis of gold nanoparticles: effect of physiochemical aspects of tetronics.

Micelles of the star shaped block polymers "tetronics" were employed for the synthesis of gold (Au) nanoparticles (NPs) under the effect of pH and temperature variation. The presence of the diamine core in the tetronic macromolecule made its micelles highly pH responsive, thereby dramatically altering the physiochemical properties. Likewise, a high degree of hydration made the micelles temperature sensitive. UV-visible studies, transmission electron microscopy (TEM), gel electrophoresis, and structure optimization by energy minimization were applied to understand the physiochemical aspects of tetronic micelles and their further role in the synthesis of Au NPs. Synthesis of Au NPs was triggered by the surface cavities of the micelles and hence the NPs simultaneously adsorbed on the micelle surface. Low pH induced high hydration and temperature responsive well defined vesicular morphologies bearing Au NPs, while high pH produced mainly large and compact compound micelles carrying NPs. Both pH and temperature responsive behaviors of different tetronics significantly influenced the synthesis of Au NPs and thus demonstrated their ability to act as nanoreactors for the materials synthesis under different experimental conditions.

Bovine serum albumin driven interfacial growth of selenium-gold/silver hybrid nanomaterials.

Selenium (Se) nanorods (NRs) capped with BSA were used as precursor to synthesize Se-Au/Ag hybrid nanocrystals (NCs). Aqueous Au/Ag ions in the presence of fixed amount of purified dried Se NRs were reduced by ascorbic acid at 80 degrees C to generate respective nucleating centres which subsequently grew on the capped BSA hot spots. The hybrid NCs thus obtained were characterized by SEM, TEM, and EDS analysis while their synthesis was monitored simultaneously by UV-visible absorbance due to the surface plasmon resonance of Au and Ag nanoparticles (NPs). In both cases, a gradual decrease in the absorbance of Au/Ag NPs with respect to reaction time was observed which indicated a diminishing number density of such particles in colloidal aqueous phase. SEM and TEM analyses then explained the presence of Au NPs in self assembled ball shaped aggregates and their selective adsorption on Se NRs, whereas no self aggregated balls of Ag NPs were observed and they always grew on the Se NRs. The results were discussed on the basis of different routes followed by the Au and Ag nucleating centres to produced hybrid nanomaterials.

Effect of sodium dodecylsulfate and dodecyltrimethyl ammonium bromide on the morphologies of gold nanoparticles in the presence of poly(amidoamine) dendrimers.

The synthesis of gold nanoparticles has been carried out in aqueous phase in the presence of both ionic surfactants (i.e., sodium dodecylsulfate (SDS) and dodecyltrimethylammonium bromide (DTAB)) and poly(amidoamine) dendrimers (PAMAM). It has been observed that the fluoroderivative of 2G PAMAM (2D) acts as reducing agent in reducing Au(lll) to Au(0) leading to the formation of fine gold nanoparticles. This process has been further evaluated in the presence of fixed amounts of both SDS and DTAB in their respective pre and post micellar concentration regions. The presence of SDS leads to the appearance of clear ordered morphologies such as triangular, hexagonal, spherical, and rod shaped, while the presence of DTAB does not show this effect. The formation of nanoparticles in triangular morphologies is more significant in the premicellar concentration range of SDS whereas hexagonal morphologies in the post micellar concentration range. On the contrary, increase in the DTAB concentration from pre to post micellar range only reduces the size of gold nanoparticles without the appearance of any ordered morphology. The formation of ordered gold nanoparticles in the presence of SDS has been further attributed to the significant SDS-dendrimer interactions and an appropriate mechanism has been proposed to justify the results.

Synthesis of colloidal gold nanoparticles of different morphologies in the presence of triblock polymer micelles.

The Au nanoparticles have been synthesized in the presence of micellar solutions of fixed concentration (i.e. 1.4 x 10(-3) mol dm(-3)) of each poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), triblock polymers (TBP), such as P103, P84, P123, and F127. The nanoparticles have also been synthesized in the presence of mixed micellar solutions of binary TBP mixtures such as P103+ P84 and P103+P123. In the previous case, "raspberry type" Au nanoparticle-TBP aggregates have been observed in which nanoparticles of 2-3 nm have been uniformly distributed throughout the TBP micelle. On the other hand, in the latter case, apart from such aggregates, prominent ordered morphologies of nanoparticles such as rod, sphere, triangle, and hexagonal have also been observed with much larger dimensions. This has been attributed to the nucleation process occurring in the mixed micelles rather than in the micelles of single TBP components.

Effect of temperature on the unfavorable mixing between tetraethylene glycol dodecyl ether and Pluronic P103.

The fluorescence measurements of tetraethylene glycol dodecyl ether (C12E4) and triblock polymer (Pluronic P103), poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), (EO)17(PO)60(EO)17, binary mixtures have been performed over the whole mixing range in the temperature range of 20-40 degrees C. The results have been evaluated by computing various micellar parameters and excimer formation. It has been concluded that mixed micelle formation takes place due to unfavorable mixing at lower temperature range, and the magnitude of which decreases with the increase in temperature up to 40 degrees C. The reduction in the unfavorable mixing has been attributed to the dehydration of P103 micelles with the increase in temperature.

Fluorescence studies of interactions of ionic surfactants with poly(amidoamine) dendrimers.

The pyrene fluorescence measurements have been carried out for the micelle formation of sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and dimethylene bis(dodecyldimethylammonium bromide) (12-2-12) in the presence of fixed different amounts of various generations of poly(amidoamine) (PAMAM). The critical micelle concentration (cmc) of SDS decreases with an increase in the fixed amount of PAMAM, suggesting the facilitation of micellization due to the participation of SDS-PAMAM complex in the micelle formation. This behavior has not been observed for DTAB/12-2-12 in the presence of various generations of PAMAM. The results indicate that SDS always has stronger interactions with all the generations of PAMAM in comparison to those of DTAB and 12-2-12.

Sodium dodecyl sulfate-poly(amidoamine) interactions studied by AFM imaging, conductivity, and Krafft temperature measurements.

The conductivity, kappa, and Krafft temperature, TK, of sodium dodecyl sulfate (SDS) with poly(amidoamine) dendrimers (PAMAM) of 0.0, 0.5, and 1.0 generations (G) have been determined at different surfactant as well as PAMAM concentrations. The critical micelle concentration of SDS increases with the increase in the amount of each generation and the additive effect of 0.5G is maximum. TK of SDS shows a systematic decrease with maximum reduction in the presence of 0.5G. Atomic force microscopy (AFM) captures a layered pattern of 1.0G in the form of nanorods and no AFM images are detected for 1.0G in the presence of SDS. All results demonstrate that SDS has favorable interactions with ester-terminated 0.5G PAMAM rather than amine-terminated 0.0G and 1.0G.