Laterally nanostructured adsorbed layers of surfactant/surfmer mixtures before and after polymerisation

The adsorbed layer structure of mixed films of the polymerisable cationic surfactant dodecyldimethyl(ethylmethacrylate)ammonium bromide (MEDDAB) with the cationic and non-ionic surfactants dodecyltrimethylammonium bromide (DTAB) and polyoxyethylene-23-lauryl ether (C12E23) has been investigated by AFM soft-contact imaging before and after solution polymerisation of MEDDAB. MEDDAB alone adsorbs on mica as a planar bilayer, but the adsorbed layer structure can be modified by mixing with DTAB or C12E23 to yield an adsorbed mesh or cylinders. The equilibrium adsorbed film structure after solution polymerisation of the methacrylate group on MEDDAB was found to depend on the solubilising ability of the non-polymerisable surfactant. C12E23 effectively prevented precipitation of polymerised MEDDAB, retaining the unpolymerised adsorbed layer structure, whereas DTAB mixtures became cloudy above 23 mol% MEDDAB. The resultant structure remained similar to the adsorbed rods formed prior to polymerisation, but had a diameter several times larger.     

Adsorbed layer structure of cationic gemini and corresponding monomeric surfactants on mica

We report a comprehensive study of the adsorbed layer morphologies of cationic gemini surfactants of the type dodecanediyl-alpha,omega-bis(dimethylalkylammonium bromide) and their corresponding monomers, dimethyldodecylalkylammonium bromide, on mica using atomic force microscopy soft-contact imaging. As in the bulk, aggregate curvature of the adsorbed geminis is found to increase with increasing spacer length, but the adsorbed aggregate curvature also increases in the presence of CsCl and CsBr. The monomeric surfactants exhibit an unexpected transition from globular adsorbed aggregates to a bilayer when the alkyl side chain reaches butyl, and this transition is also sensitive to added electrolyte.     

Effect of adsorbed layer surface roughness on the QCM-D response: focus on trapped water

The effect of surface roughness on the quartz crystal microbalance with dissipation monitoring (QCM-D) response was investigated with emphasis on determining the amount of trapped water. Surfaces with different nanoroughnesses were prepared on silica by self-assembly of cationic surfactants with different packing parameters. We used surfactants with quaternary ammonium bromide headgroups: the double-chained didodecyltrimethylammonium bromide (C12)2DAB (DDAB), the single-chained hexadecyltrimethylammonium bromide C16TAB (CTAB), and dodecyltrimethyl-ammonium bromide C12TAB (DTAB). The amount of trapped water was obtained from the difference between the mass sensed by QCM-D and the adsorbed amount detected by optical reflectometry. The amount of water, which is sensed by QCM-D, was found to increase with the nanoroughness of the adsorbed layer. The water sensed by QCM-D cannot be assigned primarily to hydration water, because it differs substantially for adsorbed surfactant layers with similar headgroups but with different nanoscale topographies.     

Size-dependent interaction of silica nanoparticles with different surfactants in aqueous solution

The size-dependent interaction of anionic silica nanoparticles with ionic (anionic and cationic) and nonionic surfactants has been studied using small-angle neutron scattering (SANS). The surfactants used are anionic sodium dodecyl sulfate (SDS), cationic dodecyltrimethyl ammonium bromide (DTAB), and nonionic decaoxyethylene n-dodecylether (C(12)E(10)). The measurements have been carried out for three different sizes of silica nanoparticles (8, 16, and 26 nm) at fixed concentrations (1 wt % each) of nanoparticles and surfactants. It is found that irrespective of the size of the nanoparticles there is no significant interaction evolved between like-charged nanoparticles and the SDS micelles leading to any structural changes. However, the strong attraction of oppositely charged DTAB micelles with silica nanoparticles results in the aggregation of nanoparticles. The number of micelles mediating the nanoparticle aggregation increases with the size of the nanoparticle. The aggregates are characterized by fractal structure where the fractal dimension is found to be constant (D ≈ 2.3) independent of the size of the nanoparticles and consistent with diffusion-limited-aggregation-type fractal morphology in these systems. In the case of nonionic surfactant C(12)E(10), micelles interact with the individual silica nanoparticles. The number of adsorbed micelles per nanoparticle increases drastically whereas the percentage of adsorbed micelles on nanoparticles decreases with the increase in the size of the nanoparticles.     

Effect of surfactant type on surfactant-maltodextrin interactions: isothermal titration calorimetry, surface tensiometry, and ultrasonic velocimetry study

Isothermal titration calorimetry (ITC), surface tensiometry, and ultrasonic velocimetry were used to characterize surfactant-maltodextrin interactions in buffer solutions (pH 7.0, 10 mM NaCl, 20 mM Trizma base, 30.0 degrees C). Experiments were carried out using three surfactants with similar nonpolar tail groups (C12) but different charged headgroups: anionic (sodium dodecyl sulfate, SDS), cationic (dodecyl trimethylammonium bromide, DTAB), and nonionic (polyoxyethylene 23 lauryl ether, Brij35). All three surfactants bound to maltodextrin, with the binding characteristics depending on whether the surfactant headgroup was ionic or nonionic. The amounts of surfactant bound to 0.5% w/v maltodextrin (DE 5) at saturation were < 0.3 mM Brij35, approximately 1-1.6 mM SDS, and approximately 1.5 mM DTAB. ITC measurements indicated that surfactant binding to maltodextrin was exothermic. Surface tension measurements indicated that the DTAB-maltodextrin complex was more surface active than DTAB alone but that SDS- and Brij35- maltodextrin complexes were less surface active than the surfactants alone.     

Study of mixtures of n-dodecyl-beta-D-maltoside with anionic, cationic, and nonionic surfactant in aqueous solutions using surface tension and fluorescence techniques

Surfactants of practical interest are invariably mixtures of different types. In this study, mixtures of sugar-based n-dodecyl-beta-D-maltoside with cationic dodecyltrimethylammonium bromide, anionic sodium dodecylsulfate, and nonionic pentaethyleneglycol monododecyl ether in solution, with and without supporting electrolyte, have been studied using surface tension and fluorescence spectroscopic techniques. Interaction parameters and mole fraction of components in mixed micelles were calculated using regular solution theory. The magnitude of interactions between n-dodecyl-beta-D-maltoside and other surfactants followed the order anionic/nonionic > cationic/nonionic > nonionic/nonionic mixtures. Since all surfactants have the same hydrophobic groups, strengths of interactions are attributed to the structures of hydrophilic headgroups. Electrolyte reduced synergism between n-dodecyl-beta-D-maltoside and ionic surfactant due to charge neutralization. Industrial sugar-based surfactant, dodecyl polyglucoside, yielded results similar to that with dodecyl maltoside, implying that tested commercial alkyl polyglucosides are similar to the pure laboratory samples in synergistic interactions with other surfactants. Fluorescence study not only supported the cmc results using tensiometry, but showed that interfaces of all the above mixed micelle/solution interfaces are mildly hydrophobic. Based on these results, an attempt is made to discover the nature of interactions to be a combination of intermolecular potential energies and free energy due to packing of surfactant molecules in micelles.     

Adsorption of mixtures of nonionic sugar-based surfactants with other surfactants at solid/liquid interfaces II. Adsorption of n-dodecyl-beta-D-maltoside with a cationic surfactant and a nonionic ethoxylated surfactant on solids

Synergy and antagonism between sugar-based surfactants, a group of environmentally benign surfactants, and cationic surfactants and nonionic ethoxylated surfactants have been investigated in this study with solids which adsorbs only one or other when presented alone. Sugar-based n-dodecyl-beta-D-maltoside (DM) does not adsorb on silica by itself. However, in mixtures with cationic dodecyltrimethylammonium bromide (DTAB) and nonionic nonylphenol ethoxylated decyl ether (NP-10), DM adsorbs on silica through hydrophobic interactions. In contrast, although DM does adsorb on alumina, the presence of NP-10 reduces the adsorption of DM as well as that of the total surfactant adsorption. Such synergistic/antagonistic effects of sugar-based n-dodecyl-beta-D-maltoside (DM) in mixtures with other surfactants at solid/liquid interfaces were systematically investigated and some general rules on synergy/antagonism in mixed surfactant systems are identified. These results have implications for designing surfactant combinations for controlled adsorption or prevention of adsorption.     

Adsorption characteristics of monomeric/gemini surfactant mixtures at the silica/aqueous solution interface

The adsorption of the monomeric/gemini surfactant mixtures at the silica/aqueous solution interface has been characterized on the basis of quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM) data. The gemini surfactant employed in this study was cationic 1,2-bis(dodecyldimethylammonio)ethane dibromide (12-2-12). This surfactant was mixed with monomeric surfactants (dodecyltrimethylammonium bromide (DTAB), hexadecyltrimethylammonium bromide (HTAB), and octaoxyethylenedodecyl ether (C(12)EO(8))) in the presence of an added electrolyte (NaBr). The key finding in our current study is that the addition of the gemini surfactant (12-2-12) makes significant impact on the adsorption properties even when the mole fraction of 12-2-12 is quite low in the surfactant mixtures. This is suggested by the experimental results that (i) the QCM-D adsorption isotherms measured for the monomeric/gemini surfactant mixtures shift to the region of lower surfactant concentrations compared with the monomeric single systems; (ii) the adsorbed layer morphology largely depends on the mole fraction of 12-2-12 in the surfactant mixtures, and the increased 12-2-12 mole fraction results in the less curved surface aggregates; and (iii) the addition of 12-2-12 yields a relatively rigid adsorbed layer when compared with the layer formed by the monomeric single systems. These adsorption properties result from the fact that the more favorable interaction of 12-2-12 with the silica surface sites drives the overall surfactant adsorption in these mixtures, which is particularly obvious in the region of low surfactant concentrations and at the 12-2-12 low mole fractions. We believe that this knowledge should be important when considering the formulation of gemini surfactants into various chemical products.     

Properties of binary surfactant systems of nonionic surfactants C12E10, C12E23, and C12E42 with a cationic gemini surfactant in aqueous solutions

Properties of binary surfactant systems of nonionic surfactants poly(ethylene oxide) (PEO) lauryl ethers (C(12)E(10), C(12)E(23), C(12)E(42)) with a cationic gemini surfactant, butanediyl-α,ω-bis(tetradecyldimethylammonium bromide) (14-4-14), have been investigated by Steady-state Fluorescence (FL), zeta potential, Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), Cryogenic Transmission Electron Microscopy (CryoTEM), and X-ray Diffraction (XRD). Through FL measurements, critical micelle concentration (CMC) of the three binary systems for different mixing mole fractions is determined and the values fall between those of pure constituent surfactants. Ideal CMC (CMC(ideal)), mole fraction in aggregates (X), interaction parameter (β), activity coefficients (f(1) and f(2)), and excess free energy of mixing (ΔG(ex)) have been calculated. All these parameters indicate nonideal behavior and synergistic interactions between the constituent surfactants, which is explained in terms of electrostatic attraction between headgroups of constituent surfactants and reduction of electrostatic repulsion between headgroups of 14-4-14 due to the presence of nonionic surfactants. DLS, TEM and CryoTEM results show that nonionic surfactants facilitate the formation of larger aggregates. Micelles and vesicles in larger size compared with those of 14-4-14 coexist in the mixed solutions. Both surfactant composition and PEO chain length are found to play a strong effect on the properties of the binary systems.     

Micellar Interactions in Nonionic/Ionic Mixed Surfactant Systems

To study the influence of the chemical nature of headgroups and the type of counterion on the process of micellization in mixed surfactant systems, the cmc's of several binary mixtures of surfactants with the same length of hydrocarbon tail but with different headgroups have been determined as a function of the monomer composition using surface tension measurements. Based on these results, the interaction parameter between the surfactant species in mixed micelles has been determined using the pseudophase separation model. Experiments were carried out with (a) the nonionic/anionic C(12)E(6)/SDS ((hexa(ethyleneglycol) mono-n-dodecyl ether)/(sodium dodecyl sulfate)), (b) amphoteric/anionic DDAO/SDS ((dodecyldimethylamine oxide)/(sodium dodecyl sulfate)), and (c) amphoteric/nonionic C(12)E(6)/DDAO mixed surfactant systems. In the case of the mixed surfactant systems containing DDAO, experiments were carried out at pH 2 and pH 8 where the surfactant was in the cationic and nonionic form, respectively. It was shown that the mixtures of the nonionic surfactants with different kinds of headgroups exhibit almost ideal behavior, whereas for the nonionic/ionic surfactant mixtures, significant deviations from ideal behavior (attractive interactions) have been found, suggesting binding between the head groups. Molecular orbital calculations confirmed the existence of the strong specific interaction between (1) SDS and nonionic and cationic forms of DDAO and between (2) C(12)E(6) and the cationic form of DDAO. In the case for the C(12)E(6)/SDS system, an alternative mechanism for the stabilization of mixed micelles was suggested, which involved the lowering in the free energy of the hydration layer. Copyright 2000 Academic Press.     

Effect of preferential adsorption on the synergism of a homologous cationic surfactant mixture

To evaluate the effect of preferential surface adsorption of bromide ions on the synergism of homologous cationic surfactant mixtures reported previously, the surface tension of the aqueous solutions of the hexadecyltrimethylammonium chloride (HTAC)-dodecyltrimethylammonium bromide (DTAB) system was measured as a function of the total molality of surfactants and the relative proportion of DTAB at 298.15 +/- 0.05 K under atmospheric pressure. The excess Gibbs energies calculated from them were -2.6 kJ mol(-)(1) in the mixed adsorbed film and -2.0 kJ mol(-)(1) in the mixed micelle, respectively. A useful analytical procedure to evaluate the composition of individual ions (hexadecyltrimethylammonium, dodecyltrimethylammonium, chloride, and bromide ions) in the adsorbed film and micelle was developed and applied.     

The Adsorption of Dodecyltrimethylammonium Bromide on Mica in Aqueous Solution Studied by X-Ray Diffraction and Atomic Force Microscopy

The adsorption of dodecyltrimethylammonium bromide (DTAB) onto natural muscovite mica and a synthetic expandable mica (EM) in aqueous solution has been investigated using both microscopic and macroscopic surface characterization techniques. The electrokinetic properties of the surfaces were monitored as a function of the concentration of DTAB using atomic force microscopy and microelectrophoresis. The adsorption isotherm of DTAB on EM was measured up to a solution concentration just below the critical micelle concentration of the surfactant. The thickness of the adsorbed layer on EM was determined using X-ray diffraction. Results indicate that the adsorbed layer consists of molecules lying quite flat on the mica surface at low concentrations and adsorbed in interleaved aggregate structures at concentrations approaching the critical micelle concentration of the surfactant in solution. Copyright 2001 Academic Press.     

阳离子与非离子混合表面活性剂模板合成介孔SiO2

利用各种两亲分子有序组合体构成超分子模板,合成从介观到宏观尺度不同形态的无机材料成为材料科学新崛起的研究方向[1].介孔SiO2在催化、吸附、分离介质及化学传感器等方面有广阔的应用前景.     

Adsorption and adsolubilization of surfactants on titanium dioxides with functional groups

Adsorption of ionic surfactants on titanium dioxide with dodecyl chain groups or quaternary ammonium groups (XNm, where m is the carbon number of the alkyl chain, 4–16) was investigated. The adsorbed amount of cationic surfactants (dodecyltrimethylammonium bromide, DTAB; 1,2-bis(dodecyldimethylammonio)ethane dibromide, 2RenQ) on titanium dioxide with dodecyl chain groups increased with increasing concentration of the dodecyl chain due to hydrophobic interaction, where the adsorbed amounts of DTAB at saturation was considerably greater than those of 2RenQ. Adsorption of an anionic surfactant (sodium dodecyl sulfate, SDS) on XNm occurred mainly due to both electrostatic attraction force and hydrophobic interaction, depending on the alkyl chain length on XNm. On the other hand, adsorption of cationic surfactants, DTAC and 2RenQCl (their counter ions are chloride ions), on XNm was quite smaller compared with that of SDS due to electrostatic repulsion force. Adsolubilization of 2-naphthol in the surfactant-adsorbed layer on the titanium dioxides with the functional groups was also studied. The adsolubilized amounts of 2-naphthol on titanium dioxide with dodecyl chain groups were enhanced by adsorption of DTAB, but no distinct increase in the adsolubilization was observed by adsorption of 2RenQ. In the case of XNm, the amount of 2-naphthol adsorbed in the absence of surfactants increased with increasing alkyl chain length on XNm. Further, an appreciable increase in the adsolubilization of 2-naphthol on XNm with adsorption of 2RenQCl was observed. It was found from the admicellar partitioning coefficients that the adsolubilization of 2-naphthol preferably occurs on XNm by adsorption of SDS or 2RenQCl compared with that by DTAC. These differences in the adsolubilization were discussed by microproperties of the surfactant-adsorbed layers estimated using a spin probe.     

Aggregate formation in aqueous solutions of carboxymethylcellulose and cationic surfactants

The addition of cationic surfactants to an aqueous solution of an anionic polymer, carboxymethylcellulose (carboxyMC), causes the spontaneous formation of aggregates in a certain range of concentrations. Here we studied two surfactants, dodecyl and hexadecyl trimethylammonium bromide (DTAB and CTAB, respectively). Using different techniques (light scattering, potentiometry, viscosimetry, and zetametry), we found that a simple lengthening of the surfactant tail length by four CH2 groups drastically changes the aggregate morphology, size, and charge. We explored in detail how the surfactant and polymer concentrations act on these systems.     

1H NMR relaxation of water: a probe for surfactant adsorption on kaolin

In this study, (1)H NMR is used to investigate properties of sodium dodecyl sulfate (SDS), tetradecyl trimethyl ammonium bromide (TTAB), and dodecyl trimethyl ammonium bromide (DTAB) adsorbed on kaolin by NMR T(1) and T(2) measurements of the water proton resonance. The results show that adsorbed surfactants form a barrier between sample water and the paramagnetic species present on the clay surface, thus significantly increasing the proton T(1) values of water. This effect is attributed to the amount of adsorbed surfactants and the arrangement of the surfactant aggregates. The total surface area covered by the cationic (DTAB and TTAB) and anionic (SDS) surfactants could be estimated from the water T(1) data and found to correspond to the fractions of negatively and positively charged surface area, respectively. For selected samples, the amount of paramagnetic species on the clay surface was reduced by treatment with hydrofluoric (HF) acid. For these samples, T(1) and T(2) measurements were taken in the temperature range 278-338 K, revealing detailed information on molecular mobility and nuclear exchange for the sample water that is related to surfactant behavior both on the surface and in the aqueous phase.     

Self-assembly of hydrophobin and hydrophobin/surfactant mixtures in aqueous solution

The self-assembly of the protein hydrophobin, HFBII, and its self-assembly with cationic, anionic, and nonionic surfactants hexadecylterimethyl ammonium bromide, CTAB, sodium dodecyl sulfate, SDS, and hexaethylene monododecyl ether, C(12)E(6), in aqueous solution have been studied by small-angle neutron scattering, SANS. HFBII self-assembles in solution as small globular aggregates, consistent with the formation of trimers or tetramers. Its self-assembly is not substantially affected by the pH or electrolytes. In the presence of CTAB, SDS, or C(12)E(6), HFBII/surfactant complexes are formed. The structure of the HFBII/surfactant complexes has been identified using contrast variation and is in the form of HFBII molecules bound to the outer surface of globular surfactant micelles. The binding of HFBII decreases the surfactant micelle aggregation number for increasing HFBII concentration in solution, and the number of hydrophobin molecules bound/micelle increases.     

Hydrophobic terminal group of surfactant initiating micellization as revealed by 1H NMR spectroscopy

The critical aggregation concentration (CAC) of four with three kinds of conventional surfactants, namely, two cationic surfactants [hexadecyltrimethyl ammonium bromide (CTAB) and tetradecyltrimethyl ammonium bromide (TTAB)], one anionic surfactant [sodium dodecyl sulfate (SDS)], and a nonionic surfactant [Triton X-100 (TX-100)], were determined by variation of ¹H chemical shifts with surfactant concentrations. Results show that the CAC values of protons at different positions of the same molecule are different, and those of the terminal methyl protons are the lowest, respectively, which suggests that the terminal groups of the alkyl chains aggregates first during micellization. Measurement of the transverse relaxation time (T₂) of different protons in SDS also show that the terminal methyl protons start to decrease with the increase in concentration first, which supports the above mentioned tendency.     

Interaction between the water soluble poly{1,4-phenylene-[9,9-bis(4-phenoxy butylsulfonate)]fluorene-2,7-diyl} copolymer and ionic surfactants followed by spectroscopic and conductivity measurements

The interaction has been studied in aqueous solutions between a negatively charged conjugated polyelectrolyte poly{1,4-phenylene-[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer (PBS-PFP) and several cationic tetraalkylammonium surfactants with different structures (alkyl chain length, counterion, or double alkyl chain), with tetramethylammonium cations and with the anionic surfactant sodium dodecyl sulfate (SDS) by electronic absorption and emission spectroscopy and by conductivity measurements. The results are compared with those previously obtained on the interaction of the same polymer with the nonionic surfactant C12E5. The nature of the electrostatic or hydrophobic polymer-surfactant interactions leads to very different behavior. The polymer induces the aggregation with the cationic surfactants at concentrations well below the critical micelle concentration, while this is inhibited with the anionic SDS, as demonstrated from conductivity measurements. The interaction with cationic surfactants only shows a small dependence on alkyl chain length or counterion and is suggested to be dominated by electrostatic interactions. In contrast to previous studies with the nonionic C12E5, both the cationic and the anionic surfactants quench the PBS-PFP emission intensity, leading also to a decrease in the polymer emission lifetime. However, the interaction with these cationic surfactants leads to the appearance of a new emission band (approximately 525 nm), which may be due to energy hopping to defect sites due to the increase of PBS-PFP interchain interaction favored by charge neutralization of the anionic polymer by cationic surfactant and by hydrophobic interactions involving the surfactant alkyl chains, since the same green band is not observed by adding either tetramethylammonium hydroxide or chloride. This effect suggests that the cationic surfactants are changing the nature of PBS-PFP aggregates. The nature of the polymer and surfactant interactions can, thus, be used to control the spectroscopic and conductivity properties of the polymer, which may have implications in its applications.     

Controllable synthesis of conducting polypyrrole nanostructures

Wire-, ribbon-, and sphere-like nanostructures of polypyrrole have been synthesized by solution chemistry methods in the presence of various surfactants (anionic, cationic, or nonionic surfactant) with various oxidizing agents [ammonium persulfate (APS) or ferric chloride (FeCl3), respectively]. The surfactants and oxidizing agents used in this study have played a key role in tailoring the nanostructures of polypyrrole during the polymerization. It is inferred that the lamellar structures of a mesophase are formed by self-assembly between the cations of a long chain cationic surfactant [cetyltrimethylammonium bromide (CTAB) or dodeyltrimethylammonium bromide (DTAB)] and anions of oxidizing agent APS. These layered mesostructures are presumed to act as templates for the formation of wire- and ribbon-like polypyrrole nanostructures. In contrast, if a short chain cationic surfactant octyltrimethylammonium bromide (OTAB) or nonionic surfactant poly(ethylene glycol) mono-p-nonylphenyl ether (Opi-10) is used, sphere-like polypyrrole nanostructures are obtained, whichever of the oxidizing agents mentioned above is used. In this case, micelles resulting from self-assembly among surfactant molecules are envisaged to serve as the templates while the polymerization happens. It is also noted that, if anionic surfactant sodium dodeyl surfate (SDS) is used, no characteristic nanostructures of polypyrrole were observed. This may be attributed to the doping effect of anionic surfactants into the resulting polypyrrole chains, and as a result, micelles self-assembled among surfactant molecules are broken down during the polymerization. The effects of monomer concentration, surfactant concentration, and surfactant chain length on the morphologies of the resulting polypyrrole have been investigated in detail. The molecular structures, composition, and electrical properties of the nanostructured polypyrrole have also been investigated in this study.