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Amino acid-based anionic gemini surfactants (2C(n)diCys, where n represents an alkyl chain with a length of 10, 12, or 14 carbons and "di" and "Cys" indicate adipoyl and cysteine, respectively) were synthesized using the amino acid cysteine. Biodegradability, equilibrium surface tension, and dynamic light scattering were used to characterize the properties of gemini surfactants. Additionally, the effects of alkyl chain length, number of chains, and structure on these properties were evaluated by comparing previously reported gemini surfactants derived from cystine (2C(n)Cys) and monomeric surfactants (C(n)Cys). 2C(n)diCys shows relatively higher biodegradability than does C(n)Cys and previously reported sugar-based gemini surfactants. Both critical micelle concentration (CMC) and surface tension decrease when alkyl chain length is increased from 10 to 12, while a further increase in chain length to 14 results in increased CMC and surface tension. This indicates that long-chain gemini surfactants have a decreased aggregation tendency due to the steric hindrance of the bulky spacer as well as premicelle formation at concentrations below the CMC and are poorly packed at the air/water interface. Formation of micelles (measuring 2 to 5 nm in solution) from 2C(n)diCys shows no dependence on alkyl chain length. Further, shaking the mixtures of aqueous 2C(n)diCys surfactant solutions and squalane results in the formation of oil-in-water type emulsions. The highly stable emulsions are formed using 2C₁₂diCys or 2C₁₄diCys solution and squalane in a 1:1 or 2:1 volume ratio.

Amphiphilic telomers with multiple sugar chains and a terminal undecyl or heptadecyl chain (i.e., C(n)Am-mGEMA, where n and m represent alkyl chain lengths of 11 or 17 with a degree of polymerization of 2.0 or 3.0 for glucosyloxyethyl methacrylate (GEMA) units, respectively) were synthesized via monomeric radical telomerization in the presence of 2-aminoethanethiol hydrochloride. Surface tension, pyrene fluorescence, and dynamic light scattering were measured to characterize the solution properties of the synthesized telomers. In addition, the effects of alkyl chain length and degree of polymerization of hydrophilic GEMA units on the measured properties were evaluated by comparison with those of conventional polyoxyethylene dodecyl ether nonionic surfactants. C(n)Am-mGEMA telomers exhibited higher critical micelle concentration (CMC) values than polyoxyethylene dodecyl ether surfactants with similar number of hydrophilic groups did. The synthesized telomers are highly efficient in reducing the surface tension of water, despite the relatively large hydrophilic structures within the sugar units (GEMA). A unique behavior was observed in that adsorption at the air-water interface and solution aggregation occurred simultaneously at a concentration below CMC (as determined by the surface tension method). This suggests that aggregate formation occurs readily in solution along with the adsorption at the interface because of strong attractive interactions between multiple sugar GEMA chains. Further, aggregates formed by C(n)Am-mGEMA telomers differ depending on the number of sugar chains, i.e., an increase in the degree of polymerization of the telomers increases the size of the aggregates. This indicates that it is easier for telomers with more sugar GEMA chains to form large aggregates due to the interactions between their hydroxyl groups.

The aqueous solution properties of oppositely charged gemini–gemini surfactant mixtures have been studied with a combination of static surface tension, dynamic light scattering (DLS) and cryogenic transmission electron microscope (cryo-TEM) measurements. Two gemini surfactants were employed in this study: one is a partially fluorinated cationic gemini surfactant, 1,2-bis[dimethyl-(3-perfluorohexyl-2-hydroxypropyl)ammonium]ethane dibromide, and the other is a novel anionic gemini surfactant having hydrocarbon tail groups ( N , N ′-didodecyl- N , N ′-dipropanesulfonylethylenediamine). Synergistic surfactant mixtures are frequently exploited to lower the mixed critical micelle concentration (cmc), however, such a decrease in the cmc is not observed in the current study. This suggests that limited mutual miscibility between the fluorocarbon and hydrocarbon tail groups plays a key role for the formation of the adsorbed layer, rather than attractive interactions such as electrostatic forces. On the other hand, spontaneous formation of vesicle-like molecular aggregates is suggested to occur as a result of their synergistic interaction in bulk solution.

The adsorption behavior of sugar-based surfactants at the silica/aqueous solution interface has been characterized on the basis of the adsorption isotherm, ζ potential and in situ atomic force microscopy (AFM) data. The surfactants used in the current work are monomeric Glu(n) (N-alkyl-N-methylgluconamide) and gemini Glu(n)-2-Glu(n) (N,N′-dialkyl-N,N′-digluconamide ethylenediamine), where n is the hydrocarbon chain length of 10 and 12. The adsorption isotherm reveals that, for all the surfactants, the adsorbed amount increases even above the critical micelle concentration (cmc) and an adsorption plateau region appears at the equilibrium concentration well above the cmc. The driving force for this adsorption is deemed to be a combination of the hydrogen bonding between the sugar moieties and the surface silanol groups and the intermolecular hydrophobic interaction of free monomers to the surfactants pre-adsorbed on silica. In the adsorption plateau region, the occupied area per molecule adsorbed on silica is calculated to be generally larger for the gemini surfactants than for the monomeric ones. This reflects the bulky structure of the headgroups of the sugar-based gemini surfactants and/or the relatively less favorable interaction of the headgroups with the silica surface. The combination of the soft-contact AFM and force curve data suggests that a structural transformation of the adsorbed layer occurs with an increase in the surfactant concentration, depending on the packing parameter of each surfactant. At the concentration above the cmc, the monomeric surfactants form either worm-like surface micelles or a patchy bilayer whereas the gemini surfactants only form a patchy bilayer.

Poly(amidoamine) (PAMAM) dendron surfactants bearing a focal quaternary alkyldimethylammonium group and terminal sugar groups (C m qb-G n Lac; m = 12, 18, 22; n = 0, 1) have been synthesized. Solution properties of these dendron surfactants were investigated by means of static surface tension, electric conductivity, fluorescence probing with pyrene, dynamic light scattering (DLS) and static light scattering (SLS). In the surface tension profiles all C m qb-G n Lac systems indicate a clear break point corresponding to the critical micelle concentration (cmc). The cmc decreases with increasing length of alkyl chain, from 8.2 × 10 −3 (C 12 ) to 4.5 × 10 −6 mol dm −3 (C 22 ) for G0Lac, from 1.0 × 10 −2 (C 12 ) to 3.7 × 10 −5 mol dm −3 (C 22 ) for G1Lac systems. Unlike conventional cationic surfactants, the surface tension at cmc (γ cmc ) significantly increases with increasing alkyl chain length, associated with a slight increase in the molecular occupied area. Degree of counter ion (Br − ) binding to the micelles is found to be very low due to an effective charge shielding by bulky non-ionic headgroups. In all C m qb-G n Lac systems the micellar size decreases above a certain concentration. In the higher concentration regime, formation of micelles with a very small number of (at most a few) molecules is suggested from DLS data.

Direct measurement of interaction forces between bovine serum albumin (BSA) adsorbed layers on amino-thiolated gold surfaces has been carried out using colloidal probe atomic force microscopy (AFM). The substrate was prepared via self-assembly of 2-aminoethanethiol on gold in aqueous media. In the absence of BSA, an electric double layer interaction was observed, resulting from protonation of the primary amine groups on the gold surface. Similar electric double layer repulsions were seen in the presence of BSA over a whole range of BSA concentration investigated. These repulsive interactions were found to be dependent on the BSA concentration, that is, the magnitude of the repulsion increases with the BSA concentration. This phenomenon is attributed to the difference in the adsorbed amount of BSA on the amino-thiolated gold surface, which was confirmed using a 27 MHz quartz crystal microbalance (QCM).

Adsolubilization of 2-naphthol into an adsorbed layer of triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO, Pluronics) copolymers on hydrophobically modified silica particles has been investigated. Four kinds of Pluronics (P103, P105, P123, and F108) were employed in order to understand the effect of the hydrophobicity of the surfactants on the adsolubilization. The amount of the Pluronics adsorbed of the maximum/saturation adsorption level was increased with a decrease in the HLB value, suggesting that the more hydrophobic Pluronics (P103 and P123) adsorb preferentially onto the hydrophobic silica surface over the more hydrophilic Pluronics (P105 and F108). The greater adsorbed amount of the more hydrophobic surfactants resulted in a greater amount of 2-naphthol adsolubilized into the adsorbed Pluronics layers. In the case of simultaneous addition of the Pluronics and 2-naphthol, the amount adsolubilized into the adsorbed P123 and P103 layers increased in their low-surfactant-concentration regime, reached a maximum, and then decreased with a further increase in the Pluronics concentration. On the other hand, for both the P105 and F108 copolymers, a decrease in the adsolubilized amount was not observed over the whole range of copolymer concentration investigated. This difference is attributed to a difference in the hydrophobicity of the micellar aggregates in solution and of the adsorbed layers on the hydrophobic surface. When 2-naphthol was added after replacement of the Pluronics supernatant by a surfactant-free solution, the final decrease in the adsolubilization was insignificant for all the Pluronics. Indeed, the maximum amount of adsolubilization was comparable to the corresponding amount obtained in the case of simultaneous addition.

A novel gemini surfactant with two hydrocarbon chains and two different hydrophilic parts containing a quaternary ammonium salt and a sulfobetaine moiety, N,N-dimethyl-N-{2-[N'-methyl-N'-(3-sulfopropyl)-alkylammonium]ethyl}-1-alkylammonium bromides (2C(n)AmSb, where n represents hydrocarbon chain lengths of 8, 10, 12, and 14), was synthesized by reacting N,N,N'-trimethylethylenediamine with n-alkyl bromide, followed by reacting with 1,3-propane sultone. The adsorption and aggregation properties of 2C(n)AmSb in the absence and presence of NaCl were characterized by the measurement of surface tension, steady-state fluorescence, and dynamic light scattering. The critical micelle concentration (cmc) and surface tension at the cmc of 2C(n)AmSb were compared with those for the corresponding monomeric surfactants, their mixtures, and gemini surfactants. The poor solubility in water shown by 2C(n)AmSb was improved by the addition of NaCl. The cmc of 2C(n)AmSb in the presence of NaCl is lower than that in the absence of NaCl, and the surface tension is almost identical for both systems. The radius of the aggregates formed by 2C(n)AmSb in a solution containing NaCl is found to be 0.70+/-0.3, 2.5+/-0.7, 5.6+/-1.4, and 10.7+/-2.4 nm for n=8, 10, 12, and 14, respectively. The particle size increases with an increase in hydrocarbon chain length; in particular, relatively large aggregates are formed for n=12 and 14.

The steady state fluorescence measurements have been performed for the binary mixtures of N -hexadecyl- N ′-lactobionylethylenediamine (C 16 peLac) with a variety of surfactants such as 3-( N , N -dimethylhexadecylammonio) propane sulphonate (HPS), dodecylhexadecyldimethyl ammonium bromide (12-0-16), trimethylene-1,3-bis(dodecyldimethylammonium bromide) (12-3-12), and hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (12-6-12) over the whole mixing range in the temperature range of 15–45 °C. From the variation of I 1 / I 3 intensity ratio of pyrene fluorescence, the critical micelle concentration (cmc) of single and mixed surfactants has been determined. The nature of the mixed micelles has been evaluated with the help of regular solution theory. The micellar parameters such as micelle mole fraction ( X 1 ), and regular solution interaction parameter ( β ), have been determined for all the binary mixtures. It has been observed that the mixed micelles of C 16 peLac + 12-0-16/HPS are formed due to synergistic interactions while unfavorable interactions have been found during the mixed micellization of C 16 peLac + 12-3-16/12-6-12 mixtures. The former behavior came from the reduction in the polar head group repulsions of 12-0-16 and HPS upon the intercalation of C 16 peLac. On the other hand, large spacer groups in bulky dimeric head groups as in case of 12-3-12 and 12-6-12 results in unfavorable interactions with C 16 peLac.

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.

The equilibrium and dynamic surface tension properties of a partially fluorinated quaternary ammonium salt gemini surfactant 1,2-bis[dimethyl-(3-perfluoroalkyl-2-hydroxypropyl)ammonium]ethane bromide (C(n)(F)C3-2-C3C(n)F, where n represents fluorocarbon chain lengths of 4, 6, and 8) were investigated, and the effects of the fluorocarbon chain length and the number of chains on them were discussed. The plot of the logarithm of the critical micelle concentration (cmc) against the fluorocarbon chain length for C(n)(F)C3-2-C3C(n)F showed a linear decrease with an increase in chain length. On the basis of the slope of this plot, it was found that the variation in cmc with respect to the chain length is large for fluorinated gemini surfactants. The surface tension at the cmc decreased significantly; this surface tension value is lower than that of conventional fluorinated monomeric surfactants. In particular, the lowest value was 13.7 mN m(-1) for n = 8. Furthermore, it was confirmed that the kinetics of adsorption at the interface decrease with an increase in the fluorocarbon chain length and the concentration.

The mixed micelle study of C 10 E 8 , C 12 E 4 , and C 14 E 8 nonionic surfactants with 12-0-8, 12-0-10, 12-0-12, and 12-0-16 twin tail alkylammonium bromides has been carried out with the help of pyrene fluorescence, dynamic light scatterings (DLS), and electron spin resonance (ESR) measurements. The pyrene fluorescence allowed us to determine the mixed cmc and aggregation number ( N agg ), while the size of the mixed aggregates, and rotation correlation time ( τ c ) of the spin probe have been evaluated from DLS and ESR, respectively. Application of the regular solution theory showed that the mixed micelle formation in the mixtures of C 10 E 8 /C 12 E 4 + cationic surfactants occurred due to the synergistic interactions, and the regular solution theory interaction parameter, β , became more negative with an increase in the hydrophobicity of the cationic component. A variation in the micelle mole fraction suggested that the mixed micelles are mainly rich in the nonionic component. An increase in the hydrophobicity of the nonionic surfactant from C 10 E 8 to C 14 E 8 induced antagonistic mixing in the mixtures of C 14 E 8 with cationic surfactants of longer hydrophobic tail. This was attributed to the mutual incompatibility among the longer hydrophobic tails of the unlike components. The DLS and ESR measurements fully supported the above results, where the size of the aggregates increases with the increase in hydrophobicity.

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(III) 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.

Sulfobetaine-type zwitterionic gemini surfactants of 1,2-bis[ N -methyl- N -(3-sulfopropyl)-alkylammonium]ethane (2C n Sb, where n represents hydrocarbon chain lengths of 6, 8 and 10) were synthesized by the reaction of N , N ′-dimethylethylenediamine with alkyl (hexyl, octyl or decyl) bromide, followed by the reaction with 1,3-propane sultone. The physicochemical properties of 2C n Sb were characterized by equilibrium and dynamic surface tension, dynamic light-scattering (DLS) and pyrene fluorescence spectroscopy techniques. 2C n Sb showed poor solubility in water at 25 °C. The values of critical micelle concentration (cmc) and surface tension at the cmc for 2C n Sb became small with increasing hydrocarbon chain length. The dynamic surface tension measurements indicated that the longer the hydrocarbon chain length of 2C n Sb becomes, the slower the adsorption rate to the air/water interface is. The fluorescence intensity ratio and the scattering intensity by DLS changed sharply at the concentrations around the cmc. The apparent hydrodynamic diameter obtained from DLS for 2C 8 Sb and 2C 10 Sb micelles was determined to be 1.2 ± 0.7 and 2.2 ± 1.0 nm, respectively, suggesting the formation of very small micelles.

Interaction between cationic gold nanoparticles ligated with 3-mercaptopropyltrimethylammonium chloride (MPTAC) and anionic poly(amidoamine) (PAMAM) dendrimers with carboxylate terminals (Generation 3.5 and 5.5-COONa) has been investigated in aqueous solution and on carbon film by UV–vis, TEM, DLS and zeta potential measurements. In the absence of PAMAM dendrimers, the MPTAC–Au nanoparticles in water exhibited a surface plasmon resonance (SPR) band at 520 nm. The gold particles of 4.2 nm in mean diameter were homogeneously dispersed on the carbon grids. Addition of PAMAM brought about an increase in the absorbance and redshift of the SPR band, which was attributed to aggregation of the gold nanoparticles by adsorption of the dendrimer to the MPTAC ligand layers owing to electrostatic attraction. In particular, chainlike aggregates were formed at low concentrations of the dendrimer (r = [PAMAM]/[MPTAC] ≤ 1). While a further increase in the dendrimer concentration (r = 2) led to a remarkable decrease in the size of aggregates, and λmax of the SPR band returned to approximately the same wavelength as that for r = 0.5.

Catalytic activity of Au-Pt, Au-Pd, and Pt-Pd dendrimer nanocomposites for reduction of p-nitrophenol was investigated in water. The bimetallic dendrimer nanocomposites were prepared by simultaneous reduction with sodium borohydride in the presence of poly(amidoamine) (PAMAM) dendrimers with amine and carboxyl terminal groups. Average diameters of the obtained particles were 2-4 nm by transmission electron microscopy. From UV-vis spectroscopy, it was found that the particles were not mixtures of monometallic particles but binary ones. X-ray photoelectron spectroscopy showed that formation of binary composite particles prevents palladium atoms from oxidation. The Au-Pd and Pt-Pd binary particles exhibited higher catalytic activity than monometallic ones. On the other hand, catalytic activity of Au-Pt binary particle was comparable to that of platinum nanoparticles.

The sugar-based gemini surfactant with peptide bonds, N,N'-bisalkyl-N,N'-bis[2-(lactobionylamide)ethyl]hexanediamide (2C(n)peLac, in which n represents hydrocarbon chain lengths of 12 and 16), was synthesized by reacting adipoyl chloride with the corresponding monomeric surfactant N-alkyl-N'-lactobionylethylenediamine (C(n)peLac), which was obtained by reacting ethylenediamine with alkyl bromide and lactobionic acid. The adsorption and micellization properties of C(n)peLac and 2C(n)peLac were characterized by the measurement of their equilibrium and dynamic surface tension, steady-state fluorescence using pyrene as a probe, dynamic light scattering (DLS), and time-resolved fluorescence quenching (TRFQ), and their biodegradability was also investigated. The critical micelle concentration (cmc) decreases with an increase in the hydrocarbon chains from monomeric to gemini surfactants, whereas it increases with an increase in the chain length from 12 to 16 for both systems. The increases in both the hydrocarbon chain and the chain length of sugar-based surfactants reduce surface activities such as the ability to lower the surface tension, the occupied area per molecule, and the adsorption rate at the air/water interface. The sugar-based surfactants C(n)peLac and 2C(n)peLac exhibit unique aggregation behavior in aqueous solution. The DLS results indicate that the apparent hydrodynamic diameter of C(n)peLac micelles decreases sharply with increasing concentration, whereas that of 2C(n)peLac micelles decreases gradually. From the TRFQ measurement, it was observed that, as concentration increases, the aggregation numbers are almost constant for C(n)peLac, whereas they increase for 2C(n)peLac. These results imply that loosely packed micelles formed by sugar-based surfactants become tightly packed micelles as the concentration increases. Furthermore, it was found that 2C(n)peLac shows lower biodegradability than does C(n)peLac because it contains tertiary amines in the molecule.

The atomic force microscopy (AFM) and transmission electron microscopy (TEM) have been performed on the poly(amidoamine) dendrimers of second generation (2G) and its fluoroderivative (2D) at room temperature. Both studies have demonstrated that 2G and 2D exist in large aggregates on solid surface. The presence of ionic surfactants facilitates their solubilization in micellar phase resulting in the aggregates of much smaller dimensions. The aqueous bulk properties of 2G and 2D both in the absence as well as in the presence of ionic surfactants (i.e. dodecyltrimethylammonium bromide (DTAB), dimethylene bis (dodecyldimethylammonium bromide) (12-2-12), and sodium dodecyl sulfate (SDS)) have been carried out with the help of pyrene fluorescence and turbidity ( τ ) measurements. From the variation of I 1 / I 3 pyrene intensity and the τ of these aqueous solutions, it has been found that both DTAB and 12-2-12 interact with the surface groups of 2G and 2D favorably in basic medium, while SDS has been found to interact with that in acidic medium. Apart from this, interactions of cationic surfactants have been found to be stronger with 2D in comparison to 2G, while reverse has been observed in the case of SDS.

Au/TiO2 nanocomposites have been prepared by UV photolysis or chemical reduction of a Au(III) complex formed on a spherical or a rodlike TiO2 support, and their catalytic activity for 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging reaction was investigated. The chemical reduction with dimethylamine borane (DMAB) provided smaller gold nanoparticles than those synthesized by UV photolysis. Type of the TiO2 also affected the size of gold particles; smaller gold particles were deposited on the spherical TiO2 support than on rodlike one. For the radical scavenging reaction, the Au/TiO2 nanocomposites prepared by chemical reduction exhibited a higher catalytic activity than those photochemically prepared, and rodlike TiO2 provided a higher activity than spherical one. The effects of preparation methods and type of TiO2 supports on the catalytic activity are discussed.

The aggregates of aliphatic (AL-PE) and aromatic polyester (AR-PE) hyperbranched dendrimers were imaged by tapping mode atomic force microscopy (AFM). The second and third generations of AL-PE dendrimers were adsorbed on mica in large aggregates of 150- and 166-nm diameters with little heights (ca. 1–2 nm). The origin of such flattened aggregates is attributed to their favorable adsorption on mica in view of the presence of –OH surface groups. AR-PE did not show such flattened aggregates instead small aggregates of 63 nm were observed in an organized manner beaving a cavity in the center of each aggregate. The organized aggregates of AR-PE with smaller dimension than AL-PE are ascribed to less favorable adsorption of the latter on mica in view of its stronger hydrophobicity.

Gold–silver binary nanoparticles, which feed atomic ratios of gold to silver were 3:1, 1:1, and 1:3, were prepared. These particles were stabilized by amine-terminated (generation ( G ) 3.0 and 5.0) and carboxyl-terminated ( G 3.5 and 5.5) poly(amidoamine) (PAMAM) dendrimers in water. UV–vis spectra indicate that the particles are not mere physical mixtures of monometallic particles or core/shell type but alloy. According to transmission electron microscope (TEM) observation, the mean diameters of the particles were 7–10 nm for silver particles and 3–4 nm for both gold and alloy particles, respectively. Catalytic activities for reduction of p -nitrophenol were investigated by monitoring the absorbance at 400 nm during the reaction. They were proportional to the feed ratio of gold in the particles and showed a maximum at the ratio of Au:Ag = 3:1.

Zwitterionic heterogemini surfactants with two hydrocarbon chains and two different hydrophilic groups, N,N-dimethyl-N-[2-(N'-alkyl-N'-beta-carboxypropanoylamino)ethyl]-1-alkylammonium bromides (2C(n)AmCa, where n represents the hydrocarbon chain lengths of 8, 10, 12, and 14), were synthesized by N,N-dimethylethylenediamine with alkyl bromide, followed by reaction with succinic anhydride. One of the hydrophilic groups is a carboxylate anion, and the other is an ammonium cation. Their physicochemical properties were characterized by measuring equilibrium and dynamic surface tension, fluorescence intensity of pyrene, and light-scattering intensity. A relationship between a logarithm of critical micelle concentration (cmc) and hydrocarbon chain length showed a linear decrease upon increasing chain length and then a departure from linearity at n = 14. This is due to the existence of premicellar aggregations at concentrations below the cmc for n = 14. The surface tension of 2C(n)AmCa reached 27-30 mN m(-1) at each cmc, indicating efficiencies typical of hydrocarbon chain surfactants. The adsorbing rate at the air/water interface became slow with an increase of the chain length. From the fluorescence intensity ratios of 373 and 384 nm using pyrene as a probe, for n = 8, 10, and 14, the pyrene was solubilized in surfactant micelles at around the cmc, whereas for n = 12 the pyrene was solubilized from a concentration of 10-fold the cmc. The scattering intensities by dynamic light scattering also increased from around these concentrations for each chain length, showing the formation of aggregates in solution.

Three different platinum-biopolymer nanocomposites have been prepared independently in the presence of hexachloroplatinic acid and biopolymers like fucoidan, alginic acid and sodium hyaluronate (NaHA) via sodium borohydride reduction. The average particle diameter of platinum nanoparticles using fucoidan becomes slightly smaller, with a decrease of the concentration of fucoidan, ranging from 3.1 to 2.6nm. On the other hand, the average particle diameter of platinum nanoparticles using NaHA becomes slightly larger, with a decrease of the concentration of NaHA, ranging from 3.4nm to 3.8nm. The average particle diameter of platinum nanoparticles using alginic acid is 3.2-3.4nm which is independent of the biopolymer concentrations. The antioxidant activities of the platinum-biopolymer nanoconiposites upon elimination of hydroxyl radicals formed in an H 2 O 2 /FeSO 4 system have been studied using a spin-trapping method; All the nanocomposites exhibit high catalytic activities that are affected by the concentration and the kind of the biopolymer. In addition, the activities of the platinum-biopolymer nanocomposites are higher than those of the gold biopolymer nanocomposites. The highest antioxidant activity for the platinum-alginic acid nanocomposites was 110 times higher than that of ascorbic acid.

Calcium carbonate particles were prepared using solutions of CaCl 2 , urea, and poly(amidoamine)PAMAM dendrimers (G 1.5, G 3.5, and G5.5) with terminal carboxylates at 90°C. In the absence of dendrimers, uniform needle -like aragonite particles were formed, whereas when the concentration of dendrimers increased particles transformed to spherical vaterite. We used another method to obtain calcium carbonate particles from solutions containing CaCl 2 , urea, urease, and dendrimer at 25°C. Transmittance in the samples and X-ray diffraction measurements indicate that in the presence of dendrimer, at first vaterite particles are formed which then transform to calcite with the elapsed time, while in the absence of dendrimer only calcite particles are formed.

A quaternized dendrimer-type surfactant with 16 octyl chains and 16 ammonium groups (refer to C8qbG1) has been synthesized by the reaction of poly(amidoamine) dendrimer of generation 1 with glycidyldimethyloctylammonium bromide, and its physicochemical properties have been characterized by measuring surface tension, fluorescence spectroscopy of pyrene, specific conductivity, dynamic light-scattering (DLS) and electrophoretic light-scattering (ELS). The surface tension of C8qbG1 decreases gradually with increasing concentration, and reaches two break points, probably indicating that the quaternized dendrimers adsorb and saturate at the air/water interface, and then interact strongly with them being at the interface. The concentrations at two break points coincide with those obtained by the electrical conductivity method. The fluorescence intensity ratio of the first to the third band in the emission spectrum of pyrene for C8qbG1 continues to decrease slowly from 3-fold-concentration of first break point obtained by the surface tension method. In addition, the results of DLS and ELS show that C8qbG1 forms large aggregates with positive ζ-potentials in the solution, and these sizes become large with the concentration. One of the reasons for such a bulk behavior may be caused by the attractive interaction between multiple hydrocarbon chains of C8qbG1.

The association behavior of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymers in aqueous solution with hexadecyltrimethylammonium bromide (HTAB), tetradecyltrimethylammonium bromide (TTAB), and dimethylene bis(decyldimethylammonium bromide) (10–2–10), was studied by fluorescence, viscosity, and Krafft temperature measurements. It has been observed that (EO) 18 (PO) 31 (EO) 18 interacts more strongly than (EO) 2 (PO) 15.5 (EO) 2 and (EO) 2.5 (PO) 31 (EO) 2.5 with HTAB/TTAB due to synergistic interactions. A stronger capability of (EO) 18 (PO) 31 (EO) 18 to interact with cationic surfactants arises from the greater number of electronegative EO units (total 36 EO units) than of (EO) 2 (PO) 15.5 (EO) 2 (total 4 EO units) and (EO) 2.5 (PO) 31 (EO) 2.5 (total 5 EO units). The antagonistic mixing behavior of present triblock polymers has been observed with 10–2–10. A difference in the mixing behavior of the latter from that of HTAB/TTAB has been attributed to its dimeric nature, which may create steric hindrances with triblock polymer components at the head group region in the mixed state.

Cetylpyridinium chloride(CPC)-stabilized gold organosol in toluene has been prepared by using a two-phase (water−toluene) extraction of AuCl4- followed by its reduction with sodium borohydride in the presence of the surfactant, CPC. The surfactant-stabilized gold nanoparticles were exploited to examine their optical properties when exposed to various solvent systems and ligands by measuring the changes in the localized surface plasmon resonance (LSPR) spectrum. It was seen that the position of the surface plasmon band of metal nanoparticles is greatly influenced by the solvents and the ligands under consideration. The surface plasmon absorption maxima modulates/varies between 520 and 550 nm for gold nanoparticles, depending on the refractive index of the solvent. The significant discovery presented here is that λmax of the LSPR shifts to the blue by 3 nm for the increase of one carbon atom in the alcohol chain. Cationic and anionic surfactants of different chain lengths induce changes in the optical prope...

Novel anionic gemini surfactants, 1,2-bis(N-beta-carboxypropanoyl-N-alkylamino)ethane (2CnenAm; n is hydrocarbon chain length of 6, 8, 10, 12, or 14), with two hydrocarbon chains, two carboxylate groups, and two amide groups, were synthesized by three-step reactions. Their solution properties were characterized by equilibrium and dynamic surface tension, steady-state fluorescence spectroscopy of pyrene, and dynamic light-scattering techniques. The surface tension measurements of 2CnenAm give low critical micelle concentrations (cmc), great efficiency in lowering the surface tension, and strong adsorption at air/water interface. Gemini surfactants behave normally with the logarithm of cmc decrease linearly with the chain length. In addition, adsorption and micellization behavior of 2CnenAm was estimated by parameter of pC20, cmc/C20, and standard free energy (DeltaG(0)mic and DeltaG(0)ads); they are significantly influenced by hydrocarbon chain length, and the adsorption is promoted more than the micellization as chain length becomes longer. The results of dynamic light-scattering and fluorescence quenching indicate that small micelles of 2CnenAm are observed at the concentrations above the cmc, and further large particles are also seen. Further, from the dynamic surface tension measurements, it is found that the shorter hydrocarbon chain length of 2CnenAm, the faster the rate of decrease of surface tension.

The interactions of cationic gemini surfactants, 1,2-bis(alkyldimethylammonio)ethane dibromide (m-2-m: m is hydrocarbon chain length, m = 10 and 12), and an anionic polymer, sodium poly(styrene sulfonate) (PSS), have been characterized by several techniques such as tensiometry, fluorescence spectroscopy, and dynamic light scattering. The surface tension of gemini surfactant/PSS mixed systems decreases with surfactant concentration, reaching break points, which are taken as critical aggregation concentrations (cac). The surface tension at the cac of mixtures is higher than that of single surfactants, and it is found that at concentrations above the cac, the surfactant molecules are associated with the polymer in the bulk. The 12-2-12/PSS mixed system shows higher surface activity than both 10-2-10/PSS and the monomeric surfactant of dodecyltrimethylammonium bromide/PSS systems. Fluorescence measurements of these mixed systems suggest the formation of a complex with a highly hydrophobic environment in the bulk of the solution. Additionally, dynamic light scattering measurements show that the hydrodynamic diameter of the 12-2-12/PSS mixed system is smaller than that of PSS only at low concentration, indicating interactions between surfactant and polymer. These result from the electrostatic attraction between ammonium and sulfate headgroups as well as the hydrophobic interaction between their hydrocarbon chains.

Interaction forces between glass surfaces with adsorption of quaternary trimeric ammonium surfactants have been studied using colloidal probe atomic force microscopy. The trimeric surfactants used are referred to as m -2-m-2-m (m is the hydrocarbon chain length of each surfactant : 8, 10, and 12). Dimeric (or gemini) 12-2-12 and monomeric dodecyltrimethylammonium bromide (DTAB) surfactants are also used for comparison. In the absence of the surfactants, the electric double layer repulsion was detected between the two glass surfaces. On the other hand, the force curve was dramatically changed by the addition of the surfactants : with increasing surfactant concentrations a repulsive-attractive repulsive sequence of the surface forces was observed for 8-2-8 2 -8 and 10-2-10-2-10, while the attractive concentration region was not seen for 12 2-12-2-12 adsorption. This difference is induced by the intermolecular strong affinity of 12 2 12 2 12 at the glass/solution inerface. In addition, for a given alkyl chain length 12 2 12 -2-12 shows a strong intermolecular association at the interface, comparing with 12-2-12 or DTAB. The obtained force results were well correlated with dispersion stability of corresponding silica suspensions.

Gold-dendrimer nanocomposites were prepared in the presence of poly(amidoamine) (PAMAM) dendrimer (generation 3, 3.5, 5, and 5.5) or poly(propyleneimine) (PPI) dendrimer (generation 3 and 4) via reduction of HAuCl 4 with sodium borohydride. The average particle sizes of the gold nanoparticles were independent of the dendrimer concentration as well as the dendrimer generation, ranging between 3.0 and 4.3nm in diameter for PAMAM dendrimers and between 2.1 and 2.3nm in diameter for PPI dendrimers. The catalytic activities of the gold-dendrimer nanocomposites upon elimination of hydroxyl radicals formed in an H 2 O 2 /FeSO 4 system was examined using a spin-trapping method. The catalytic activity of gold-PPI dendrimer nanocomposites was slightly lower than that of gold-PAMAM dendrimer nanocomposites. In addition, the gold-dendrimer nanocomposites exhibited high catalytic activities which were hardly affected by the concentration as well as the generation of the dendrimer except PAMAM dendrimer 3.5. The highest activity for the gold-PAMAM dendrimer G3.5 nanocomposites was 85 times that of ascorbic acid.

The binary adsolubilization behaviors of 2-naphthol+biphenyl and 2-naphthol+1,3-dichlorobenzene in a cationic fluorocarbon surfactant adsorbed layer formed on TiO 2 have been investigated as a function of pH. In the binary adsolubilization of 2-naphthol+biphenyl, the adsolubilized amount of 2-naphthol increases gradually until pH 7 and then sharply with a further increase of pH, whereas the adsolubilization of biphenyl is not observed in the wide pH region. In the binary adsolubilization of 2-naphthol +1,3-dichlorobenzene, the adsolubilization behavior of 2-naphthol shows a similar trend as that of 2-naphthol+biphenyl system, while the adsolubilized amount of 1,3-dichlorobenzene increases gradually with pH from 3 to 10. The enhancement in the adsolubilization of 2-naphthol at high pH is attributed to the interaction between deprotonated 2-naphthol and the cationic surfactant as well as the increase of interaction between negatively charged TiO 2 and the surfactant. The adsolubilized sites for binary adsolubilization of 2-naphthol+1,3-dichlorobenzene are also discussed from the admicellar partitioning coefficients.

The adsorption of poly(amidoamine) (PAMAM) and poly(propylene imine) (PPI) dendrimers having different generations from their aqueous solutions on gold electrode has been investigated using a 27 MHz quartz crystal microbalance. The adsorption of PAMAM dendrimers (generation G =3, 4, and 5) depends on the generation, whereas that of PPI dendrimers ( G =2, 3, and 4) is almost independent on the generation. The occupied area by the dendrimers adsorbed suggests a formation of multilayer of the dendrimers where the number of the layer for PAMAM dendrimers is larger than that for PPI dendrimers. The mechanism for the formation of multilayer is also discussed.

Adsolubilization of 2-naphthol by cationic multi-chained surfactants such as gemini (m-2-m, m=alkyl chain length ; 10-2-10, 12-2-12) and trimeric surfactants (m-2-m-2-m ; 10-2-10-2-10, 12-2-12-2-12) on silica has been investigated. For comparison, a similar experiment has been performed using a cationic single-chained surfactant, dodecyltrimethylammonium bromide (DTAB). Adsorption of the surfactants increases with an increase of the concentration and reaches a saturation, while adsolubilization of 2-naphthol increases and shows a maximum and then decreases with the surfactant concentration for all the surfactant systems. The ratio of maximum amount of 2 -naphthol adsolubilized to the adsorbed amount of surfactant on silica is decreased as in the order, 10-2-10-2-10> 12-2-12-2-12>12-2-12=DTAB>10-2-10. In addition, the order of the ratio per one-hydrocarbon chain is 10-2-10-2-10 =12-2-12>12-2-12-2-12 =10-2-10, where the ratio of DTAB is considerably large compared to those of the multi -chained surfactants. These results can be interpreted by the compactness of surfactant adsorbed layer. The effect of the surfactant structure on the adsolubilization is also discussed using admicellar partitioning coefficients of 2-naphthol.

Electrochemical activity of dendrimer-stabilized gold nanoparticles on a glassy carbon electrode (GCE) was studied by means of cyclic voltammetry of sodium hypochlorite. Dendrimer-stabilized gold nanoparticles were deposited onto a glassy carbon surface by electrophoresis and the deposition was observed by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Both anodic and cathodic peak currents were found to increase after the deposition of dendrimer-stabilized gold nanoparticles. In the case of dendrimers deposited onto the GCE surface, the magnitude of the current was smaller than for dendrimer-stabilized-gold-nanoparticle-modified GCE. This indicates the enhancement in the rate of electrolysis due to gold nanoparticles.

Trimeric-type anionic surfactants (3CntaAm, where n is a hydrocarbon chain length of 8, 10, or 12) with three hydrocarbon chains and three carboxylate headgroups were synthesized from tris(2-aminoethyl)amine, and their properties were investigated by surface tension, electrical conductivity, dynamic and static light-scattering, fluorescence of pyrene, and emulsification power techniques. The critical micelle concentrations (CMC) of 3CntaAm were 0.00092–0.00834 mmol dm−3, and the surface tensions at the CMC were 33.3–39.9 mN m−1. The areas per molecule occupied by 3C10taAm and 3C12taAm were extremely small, showing they were highly compact at the air/water interface. In addition, adsorption or micellization behavior of 3CntaAm was estimated by parameters such as pC 20 (the efficiency of surface adsorption), CMC/C 20 (the ease of adsorption relative to the ease of micellization), and ΔG M o (Gibbs energy of micellization). Dynamic and static light-scattering mesurements of 3CntaAm showed a hydrodynamic radius of 45–61 nm above the CMC and aggregation numbers of 10–82 at the CMC, respectively. The fluorescence intensity ratio of the first to the third band in the emission spectra of pyrene started to lower from far above the CMC for 3C8taAm and 3C10taAm, and below the CMC for 3C12taAm. This suggests that loose micelles or premicellar aggregates are formed in solutions. Mixtures of aqueous solutions of 3CntaAm and toluene formed oil-in-water-type emulsions, and the stabilizing abilities were in the order of 3C8taAm>3C10taAm>3C12taAm. The degree of emulsification of 3C8taAm remained at 69% after 24 h of standing. Thus, 3CntaAm exhibited unique properties superior to monomeric or dimeric surfactants that were significantly influenced by their hydrocarbon chain lengths.

Direct measurement of interaction forces between α-alumina surfaces with coadsorbed anionic sodium dodecyl sulfate (SDS) and nonionic hexaoxyethylenedodecyl ether (C 1 2 E 6 ) at pH 3.5 is carried out by colloidal probe atomic force microscopy. The strength of interaction forces is found to be dependent on the initial SDS concentrations, whereas the addition of C 1 2 E 6 alone causes negligible effects on the interaction. This is due to the absence of attractive interactions between C 1 2 E 6 molecules and α-alumina. On the other hand, the interaction forces are remarkably different for the simultaneous addition of the two surfactants. At lower C 1 2 E 6 concentrations the observed repulsion induced by the electric double layer is larger than that in the corresponding single SDS solution, suggesting the stronger SDS adsorption as a consequence of the reduction of the electrostatic repulsion between the ionic headgroups of SDS admicelles. By the further addition of C 1 2 E 6 a steric stabilizing force is detected from the separation of approximately 5 nm. This is attributed to the formation of a closely packed adlayer comparing with the case of the single SDS admicelles. The effects of sequential addition of C 1 2 E 6 to the α-alumina preadsorbed hydrophobically with SDS are also investigated to understand the complex phenomena that occur at the interface.

Gold nanoparticles were prepared in the presence of chitosan via reduction of HAuCl 4 with sodium borohydride. The average particle size of gold nanoparticles was significantly affected with the concentration of chitosan added and was ranged between 6 and 16 nm. The gold–chitosan nanocomposites are formed by adsorbing chitosan molecules on the gold nanoparticles. The catalytic activity of gold–chitosan nanocomposites upon elimination of hydroxyl radicals formed in an H 2 O 2 /FeSO 4 system was examined using a spin-trapping method. The catalytic activity increased with the concentration of chitosan added and showed a maximum and then decreased with a further concentration of chitosan added, although a strict correlation between the average diameter of gold and the catalytic activity was not found. In addition, the activity of gold–chitosan was 80 times higher than that of ascorbic acid, which is well known as an antioxidant.

Gold nanoparticles were prepared in the presence of poly(amidoamine) (PAMAM) dendrimers (generations 3.0 and 5.0) or poly(propyleneimine) (PPI) dendrimers (generations 3.0 and 4.0) with surface amino groups by laser irradiation. UV−visible absorption, dynamic light scattering, and transmission electron microscopy have been used to study the formation and structure of the nanocomposites. The reduction of Au3+ ions proceeded with an increase of the irradiation time, and the average diameters of the gold nanoparticles obtained tended to decrease with an increase of the dendrimer concentration. It is suggested that the dendrimers are adsorbed on the nanoparticles as a monolayer. Studies of the reduction reaction of 4-nitrophenol by the gold nanoparticles with NaBH4 reveal that the rate constants for PPI dendrimers are higher than those for PAMAM dendrimers, whereas the size of the PPI dendrimer of the same generation is considerably smaller than that of the PAMAM dendrimer.

The interactions of bovine serum albumin (BSA) with sugar-persubstituted poly(amidoamine)dendrimers (SB, generation 3 and 5) have been studied using several techniques including interfacial rheometer. The sample solutions are prepared by mixing SB5 or SB3 to BSA under a fixed concentration of BSA. In BSA–SB5 system, mixed solutions become turbid due to the formation of aggregates between BSA and SB5 by adding a small amount of SB5, but a further addition of SB5 renders the aggregates redispersed. These results are reflected in the changes of surface tension, interfacial rheology, and circular dichroism (CD) spectra for BSA–SB5 system. On the other hand, BSA–SB3 system does not show significant physicochemical properties due to a weak interaction between BSA and SB3.

Silver, palladium, and silver–palladium nanoparticles have been prepared by reduction of silver acetylacetonate and palladium acetate with dimethylamine–borane in the presence of a fluorinated surfactant (FOMBLIN HC/P2-1000) in supercritical carbon dioxide. The sizes of silver and palladium nanoparticles increases with increasing concentrations of both the soluble precursors and FOMBLIN. The size of silver nanoparticles obtained is 3–12 nm, while that of palladium nanoparticles is 3–6 nm. For preparation of silver–palladium nanoparticles, the particle size is ranged between 4 and 5 nm and dependent on the feed molar ratio of palladium acetate. It is found that silver–palladium nanoparticles consist of a core-shell structure with enriched palladium in the surface.

The physicochemical properties of mixed systems of fluorocarbon-modified poly(acrylic acid) (FA) with a cationic fluorocarbon surfactant, bis(2-hydroxyethyl)(2-hydroxy-3-perfluoro-octylpropyl)methylammonium chloride (DEFUMAC), have been investigated by surface tension, fluorescence, solubility, and 19F NMR spin–lattice relaxation measurements. The result obtained from the surface tension measurement indicates that surface DEFUMAC–FA complexes are formed by strong electrostatic attraction at pH 10, while they are formed by hydrogen bond at pH 4. However, hydrophobic interaction is hardly observed at both pHs. In the bulk properties estimated from fluorescence and solubility measurements, DEFUMAC–FA complexes exhibit large solubility capacity for fluorocarbon compounds when the content of fluorocarbon in FA increases. Moreover, the result obtained from the spin–lattice relaxation time measurement suggests that the mobility of hydrophobic end group of DEFUMAC for DEFUMAC–FA complex at pH 10 is more restricted than that at pH 4.

Direct measurements of interaction forces between α-alumina surfaces with coadsorbed anionic surfactant sodium dodecyl sulfate (SDS) and anionic polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS) at pH 3.5 are carried out by colloidal probe atomic force microscopy. It is found that in aqueous PSS solutions the interaction forces are dependent on the initial PSS concentration. At low PSS concentration the electrostatic repulsion initially present is neutralized, resulting in a weak attraction between the surfaces, while as the concentration is increased further, repulsive forces reappear due to the additional adsorption of PSS on the surface. The adsorbed PSS adopts a relatively flat conformation at all PSS concentrations investigated. On the other hand, the interaction forces are dramatically different for the simultaneous addition of SDS and PSS: the force profile for the coaddition comes progressively close to that for the addition of SDS alone with increasing SDS concentration. This is attributed to the fact that SDS plays a key role for the coadsorption of SDS and PSS over a high SDS concentration region. The dispersion stability and ζ potential of α-alumina suspensions are evaluated for comparison with the resultant forces, and a good correlation is obtained between them. The effects of sequential addition of SDS and PSS are also investigated.