Number Of Small Aggregates Research Articles

Self-aggregation of cationic gemini surfactants with amide groups in the spacer and variable alkyl chain length

AbstractSynthesis, aggregation parameters and antimicrobial activity of novel cationic gemini surfactants with two amide groups in gemini spacer structure and a variable number of carbon atoms in alkyl tails ranging from 12 to 15 are reported. The critical micelle concentration of gemini surfactants was determined using surface tension and electrical conductivity methods. The cmc values were found in the range 0.83 to 0.06 mM. The interfacial area, micelle ionisation degree and the Gibbs free energy per molecule and alkyl chain were calculated from the surface tension and conductivity curves. Particle size analysis using the dynamic light scattering method confirmed the formation of small spherical micelles 6–7 nm large in size for gemini surfactants with 12 and 13 carbon atoms in the alkyl chain. A large size above 50 nm was found for the aggregates composed of long-chain gemini molecules with 14 and 15 carbon atoms. The zeta potential of gemini surfactants shows a continuous increase with the increasing alkyl chain length. Micelle aggregation number of gemini surfactants correlates well with the hydrodynamic size data. Small aggregation number values were found for short-chain gemini molecules with 12 and 13 carbon atoms in the alkyl chain. Long-chain gemini molecules with 14 and 15 carbon atoms exhibit aggregate growth represented by an increase in the aggregation number values while maintaining the spherical or spheroidal shape of micelles. The investigations of antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria and yeast indicate the increasing antimicrobial efficiency towards the short-chain surfactant with 12 carbon atoms in the alkyl chain. A possible cut-off effect presence is proposed to explain the dependence of antimicrobial activity on the surfactant alkyl tail length.

Model of inverse “dry” micelles with coexisting spherical, globular and cylindrical aggregates

A new statistical thermodynamic model of inverse nonionic aggregates of surfactant molecules in nonpolar solvents is considered. This model admits the fluctuation coexistence of inverse spherical, globular, and spherocylindrical aggregates without activation barriers between them. The model is based on the assumption of a uniform bulk density of the number of molecular groups inside the core of an aggregate that can continuously transform into a sphere, a globule, and a spherocylinder. In this model, for any aggregation numbers, the work of aggregation depends not only on the aggregation numbers and the concentration of surfactant monomers, but also on two independent geometric parameters characterizing, at the same aggregation numbers, the deviation from the spherical form of the aggregate towards globular and spherocylindrical forms. Even in the range of small aggregation numbers, this fact leads to a significant difference between the equilibrium distribution function of aggregates, which depends on the aggregation number and two form parameters, and the one-dimensional distribution function in terms of aggregation numbers. It is shown that the optimal values of the form parameters, which minimize the work of aggregation, are in good agreement for spherocylindrical aggregates with the predictions of a purely geometric model of such aggregates under the additional assumption of a uniform surface density of molecular groups at the micelle core. The predictions of a new molecular thermodynamic model for the degrees of surfactant micellization in inverse aggregates of various forms at different surfactant concentrations are considered.

Self-assembly of Quillaja saponin mixtures with different conventional synthetic surfactants

Saponins are surface active glycosides which can be extracted from a range of different plant species. This class of biosurfactants is of much current interest because of their biocompatibility and biosustainability, and a range of other interesting properties. The Quillaja saponin, the focus of this paper, is extensively used in foods, beverages and cosmetics due to their accessibility and agency approval. Aspects of their wider application rests with their use in combination with different synthetic surfactants, to optimise and tailor performance and functionality. Characterising and understanding the self-assembly of such mixtures is an essential requirement for that wider exploitation. The surface activity of a range of different saponins has been extensively reported, but the self-assembly properties of the Quillaja saponin, and its mixture with different synthetic surfactants has not been reported in any detail. Of particular interest is how the bidesmodic structure of the Quillaja saponin and the mixing with the different cosurfactants affects the evolution in the micelle structure, and this is the focus of this study. Small angle neutron scattering, SANS, has been used to characterise the micelle formation of the Quillaja saponin and of its mixtures with the anionic surfactant sodium dodecyl sulfate, SDS, and the nonionic surfactants, dodecaethylene glycol monododecyl ether, C12E12, and pentaethylene glycol monododecyl ether, C12E5. The Quillaja saponins form relatively small globular micelles with a relatively small aggregation number. In mixtures with SDS and the nonionic surfactants the micelles retain their globular structure. In the mixtures the micelle aggregation number evolves towards the value for the pure synthetic surfactant component, as the packing constraints change with the decreasing mole fraction of saponin in the micelle. The evolution in the micelle structure and size reflects the change in the structure and geometry of the associated surfactant components, and is largely dominated by the Quillaja structure. The results provide an interesting insight into the factors controlling the self-assembly in saponin – surfactant mixtures, and how the saponin structure affects the self-assembly.

Gold nanoparticles obtained by ns-pulsed laser ablation in liquids (ns-PLAL) are arranged in the form of fractal clusters

Gold nanoparticles (AuNPs), synthesized by ns-pulsed laser ablation in liquid (ns-PLAL) in the absence of any capping agents, are potential model systems to study the interactions with biological structures unencumbered by interference from the presence of stabilizers and capping agents. However, several aspects of the physics behind these AuNPs solutions deserve a detailed investigation. The structure in solution of ns-PLAL-synthesized AuNPs was investigated in solution by means of small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS). Furthermore, the (dried) NPs have been examined using TEM. The analysis of the SAXS curve shows the presence of a large number of small aggregates with a fractal structure stabilized by strong long-range repulsive interactions. Fitting of the SAXS curve to a suitable “fractal model” allows the estimation of the features of the fractal including the fractal dimension d = 1.9. The latter allows to estimate the fraction of light scattered by fractals of different sizes and thus permits a fair comparison between the DLS and TEM data. Here, a stable abundant population of fractal clusters is reported reflecting a mechanism where primary AuNPs (size 7.6 nm) are forced to aggregate forming clusters during the collapse of the cavitation bubble. When these clusters are released in the aqueous phase, their large negative charge builds up repulsive interactions that prevent cluster-cluster aggregation imparting colloidal stability.

Breakdown of the Stokes-Einstein Equation for Solutions of Water in Oil Reverse Micelles.

An experimental study is presented for the reverse micellar system of 15% by mass polydisperse hexaethylene glycol monodecylether (C10E6) in cyclohexane with varying amounts of added water up to 4% by mass. Measurements of viscosity and self-diffusion coefficients were taken as a function of temperature between 10 and 45 °C at varying sample water loads but fixed C10E6/cyclohexane composition. The results were used to inspect the validity of the Stokes-Einstein equation for this system. Unreasonably small reverse average micelle radii and aggregation numbers were obtained with the Stokes-Einstein equation, but reasonable values for these quantities were obtained using the ratio of surfactant-to-cyclohexane self-diffusion coefficients. While bulk viscosity increased with increasing water load, a concurrent expected decrease of self-diffusion coefficient was only observed for the surfactant and water but not for cyclohexane, which showed independence of water load. Moreover, a spread of self-diffusion coefficients was observed for the protons associated with the ethylene oxide repeat unit in samples with polydisperse C10E6 but not in a sample with monodisperse C10E6. These findings were interpreted by the presence of reverse micelle to reverse micelle hopping motions that with higher water load become increasingly selective toward C10E6 molecules with short ethylene oxide repeat units, while those with long ethylene oxide repeat units remain trapped within the reverse micelle because of the increased hydrogen bonding interactions with the water inside the growing core of the reverse micelle. Despite the observed breakdown of the Stokes-Einstein equation, the temperature dependence of the viscosities and self-diffusion coefficients was found to follow Arrhenius behavior over the investigated range of temperatures.

Synthesis and Characterization of a Novel Short Fluorocarbon Chain Cationic Surfactant

AbstractA novel short fluorocarbon chain cationic surfactant has been synthesized to reduce the bioaccumulation of traditional fluorocarbon surfactants and maintain excellent surface properties simultaneously. The structure, surface activity, and micelle formation of surfactants have been investigated by surface tension, conductivity, dynamic light scattering, steady‐state fluorescence, Fourier transform infrared spectroscopy, and Nuclear magnetic resonance. The novel surfactant (yield more than 81%) exhibited good surface activity, the critical micelle concentration and surface tension were below 2.35 mmol L−1 and 20.54 mN m−1 in the range of temperature from 288 to 303 K, respectively. The surface tension decreased to 17.45 mN m−1 with an increase in temperature. The thermodynamic parameters (, and ) of micellization for surfactants were evaluated, which implying the micellization process was contributed primarily by the entropy driving. In addition, the aggregation behavior of surfactants was also studied in detail, which demonstrated a small micelle aggregation number of 9.40 and large size distribution of 164–342 nm.

Functional platelet activity in Dutch newborn calves

The hemostatic properties of platelets in cattle are physiologically very significant, as they affect the course of metabolic processes. This is especially significant in early ontogenesis and, apparently, strongly depends on the genetic characteristics of animals. The study was carried out on 37 Dutch calves, which were obtained from healthy cows after a normal pregnancy. All calves were examined and examined for 1-2 days, 3-4 days, 5-6 days, 7-8 days and 9-10 days of their ontogenesis. In the work were applied biochemical, hematological and statistical research methods. In the examined animals, during the neonatal phase, there was a tendency to inhibition of platelet aggregation in response to all inductors used. The number of platelet-discocytes in the blood of the examined Dutch calves in the first 10 days of their life experienced an upward trend. The amount of active platelet species they had decreased by 11.1%. The number of small and large platelet aggregates in the blood also decreased in them during the observation period. This was provided in the observed calves with a tendency to weaken the severity of synthesis in thromboxane platelets, a decrease in the level of adenosine phosphates in them and a weakening of their secretion. The level of platelet actin and myosin on the 1-2nd day in the examined calves was small and tended to decrease during the observation. Additional self-assembly of actin and myosin during platelet aggregation of the observed animals experienced some decrease during the observation period. It is clear that newborn calves of the Dutch breed are characterized by a high degree of functional sufficiency of platelets, creating physiologically favorable conditions for microcirculation processes. At the basis of these changes they have a small activity of the mechanisms that implement the hemostatic properties of platelets. Low intravascular activity of platelets in newborn calves of the Dutch breed is able to provide them with optimum perfusion and metabolic processes in all animal tissues that are necessary for the normal development of animals.

Evolution of structural dimensions in mesoporous template precursor from hexagonal lyotropic liquid crystals

Producing nanopores from hexagonal lyotropic liquid crystals (LLCs) templates requires not only retaining phase morphology of the templates but also precisely controlling structural dimensions of unit cells. In this study, SAXS and 2H NMR are used to investigate dimensional evolutions of ternary systems consisting of polymerizable species, (ethylene glycol) diacrylate (PEGDA) and/or 2-hydroxyethyl methacrylate (HEMA), in a LLCs template of hexagonally packed cylinders formed from dodecyl trimethylammonium bromide (DTAB) and water. With the addition of those polymerizable species, the system rearranges into a new hexagonal system with a smaller aggregation number, smaller pores and a thicker pore wall thickness. The hexagonal system will coexist with an aqueous-rich phase containing isotropically distributed DTAB if sufficient PEGDA is applied but the single hexagonal system could be restored by partially replacing the PEGDA with HEMA. The mobility of DTAB molecules within the aggregates varies depending on monomer compositions. The changes in structural dimensions of the unit cells and phase behaviors after adding polymerizable monomers allow dimensional control of mesochannels and potentially enable the control of selectivity and robustness of polymerized nanomaterials via molecular design.

Chitosan-graft-poly(methyl methacrylate) amphiphilic nanoparticles: Self-association and physicochemical characterization

In this work, we synthesized and characterized the self-assembly behavior of a chitosan-poly(methyl methacrylate) graft copolymer and the properties of the formed nanoparticles by static and dynamic light scattering, small-angle neutron scattering, and transmission electron microscopy. Overall, our results indicate that the hydrophobization of the chitosan side-chain with PMMA leads to a complex array of small unimolecular and/or small-aggregation number “building blocks” that further self-assemble into larger amphiphilic nanoparticles.

Structural analysis of a calix[4]arene-based Platonic Micelle

We have recently introduced the concept of “Platonic micelles”, the preference of spherical micelles to specific aggregation numbers mostly coinciding with the number of faces of platonic solids. This effect was observed on bulky, mostly calix[4]arene-based surfactant systems with small aggregation numbers. The preferred aggregation numbers result in better sphere coverage, highliting the packing and the “protection” of hydrophobic cores from the aqueous solvent as the most important factor for this preference. In the present study we further explore the interactions that drive the packing of the highly charged PACaL3 surfactant into highly symmetrical hexameric micelles. We performed a series of molecular dynamics simulations that yielded a large set of structures and an ensemble in good agreement with the experimental Small Angle X-ray Scattering data was selected. The geometry and the rigidity of the calix[4]arene group with proper tail length and headgroup volume are the driving forces for the high symmetry and monodispersity of the micelle. The charge of the headgroups is mainly responsible for inhibiting the formation of higher order structures. Sodium, shown to be important for the stability of the micelle, is not directly interacting with the micelle implying that the calix[4]arene ring is a C2ν symmetry conformation.

Combination of pharmacological and non-pharmacological approaches in patients with hypertensive encephalopathy and hemorheological disorders

objective. To study the impact of complex treatment (acetylsalicylic acid, hirudotherapy, phytotherapy) on the functional activity of thrombocytes in patients with hypertensive encephalopathy. design and methods. An open prospective study included 25 patients with hypertensive encephalopathy and dysfunction of thrombocytes activity. All patients took acetylsalicylic acid. A simultaneous course of hirudotherapy (10 sessions, 2,5 months; own patent of the Russian Federation № 2327494) and a course of phytotherapy (polycomponent infusion, for 2,5 months; own patent of the Russian Federation № 2542423) were conducted. Functional activity of thrombocytes was studied by the phase contrast microscope at baseline and after the treatment was completed. Results. Initially, 25 patients with hypertensive encephalopathy showed abnormal platelet functional activity in the presence of acetylsalicylic acid: a decrease in the number of intact platelets — discocytes in 9 patients; increased number of activated cells with discoquinocyte sprouts on the surface — in 18 people; active forms in 17 patients; platelet aggregates — in 15 patients; increased number of small aggregates per 100 free thrombocytes — 13 patients; large aggregates — in 2 patients. After hirudotherapy and herbal medicine were applied in addition to acetylsalicylic acid, complete normalization of platelet functional activity was achieved in 11 of 25 patients, and partial normalization — in 12 subjects. conclusions. The complex approach, including both drug treatment (acetylsalicylic acid) and the course of hirudotherapy and phytotherapy showed a positive impact on the intravascular platelet activity in patients with hypertensive encephalopathy and initial disturbances of the platelet functional activity. As a result, the number of intact forms of platelets increased, the number of early and late active forms (discoquinocytes, spheroechinocytes and bipolar cells) decreased. Also the number of platelet aggregates and small aggregates reduced. Such a multimodal approach can be implemented in aspirin resistance, a high risk of primary and recurrent vascular events. The method is safe and well tolerated by patients.

On the Localization of CMC and Maximum Concentration of Surface-Active Ions According to the Theory of Micellar Solutions

The micellization theory that I previously developed on the basis of the definition of critical micelle concentration (CMC) using the constant of the law of mass action as applied to ionic surfactants (Colloid. J., 2016, vol. 78, p. 669) has been supplemented and refined. The problem concerning the relative positions of the maximum in the surface-active ion concentration and CMC as functions of aggregation number has been solved in the general form. It has been shown that the curves of these functions may intersect. On the side of smaller aggregation numbers relative to the intersection point, the maximum lies above the CMC, while, at larger aggregation numbers, it is, on the contrary, located below the CMC in the concentration axis. The influence of the type of an electrolyte on this effect has been studied by the example of an ionic surfactant. If the charge of a counterion is higher than the charge of a surface-active ion, the maximum is located above the CMC; otherwise, it is below the CMC. At the same time, the question of the formulation of the law of mass action for ionic surfactants with multivalent ions has been answered. It has been shown that the definition of CMC via the constant of the law of mass action must, in this case, comprise stoichiometric coefficients. The theory has been formulated under the condition of a constant aggregation number in the vicinity of CMC. In addition, an ideal behavior of a mixture of monomers and micelles is assumed, which is inherent in ionic surfactants with rather low CMCs.

Phase behaviour, micellar structure and linear rheology of tetrablock copolymer Tetronic 908

Tetronics are X-shaped block-copolymers of polyethylene oxide and polypropylene oxide, which self-assemble into micelles and can undergo a sol-gel transition; these transitions are dependent on temperature, concentration but also pH, due to the central diamine group of the tetrablock. We report the nanoscale morphologies underlying these different phases and the rheology of the systems for a very large, highly hydrophilic block copolymer, Tetronic 908, through the combined use of oscillatory rheology, steadyblock-state and time-resolved fluorescence, small-angle neutron scattering (SANS), dynamic light scattering (DLS) and Fourier transform infrared attenuated total reflectance (FTIR-ATR). At low concentrations, SANS reveal core-shell micelles of ca. 10 nm radius, presenting a dehydrated core and a highly hydrated shell, with relatively small aggregation numbers (Nagg ≈ 13). The micelles are notably affected by the pH, due to the protonation of the central amine spacer at low pH (pH ≈ 2), which shifts micellization to higher temperature, with smaller micelles than at natural pH. In the intermediate concentration regime (10–15%), micelles become smaller (Nagg ≈ 5), and present a higher hydration of the core. In the high concentration regime, Tetronic 908 undergoes a sol-gel transition above a threshold temperature, which is fully inhibited at acidic pH. SANS data from the gel phase reveal a BCC order of tightly packed spheres. Temperature sweeps in oscillatory rheology show a shift of the onset of gelation towards lower temperatures as concentration increases, an increase in the elastic modulus G′ and an expansion of gel region over a larger range of temperatures. SANS and rheology reveal that at pH below the natural pH (ca. 8), gelation is shifted to higher temperatures, but the morphology of the gels is similar, while under highly acidic conditions the gelation is fully suppresed.

Solubilization ability of N,N-dimethyl-N-alkyladamantylammonium bromide

Adamantane is difficult to dissolve in water owing to its bulky steric hydrocarbon structure. We designed a novel amphiphilic molecule by introducing an alkyl chain and a cation group into an adamantyl group. N,N-dimethyl-N-alkyladamantylammonium bromide (CnAdAB; n is the alkyl chain length, where n=10, 12, and 14) dissolves easily in water by forming micelles above the critical micelle concentration. Aggregates of this surfactant series form small nonspherical micelles several nanometers in size with relative small aggregation number; 53 (n=10), 59 (n=12), and 63 (n=14) at the typical concentration. Small-angle X-ray scattering measurement showed that the micellar structure of C12AdAB was changed slightly by solubilization of naphthalene and stearic acid. Moreover, the solubilization ability of the aggregates was studied using naphthalene and long-alkyl-chain fatty acids (myristic, palmitic, and stearic acids). The same solubilization experiments were performed using typical cationic surfactants (dodecyltrimethylammonium bromide and a gemini surfactant) for comparison. The molar solubilization ratios indicate that the CnAdAB series can solubilize the aromatic compound naphthalene as well as the other surfactants, whereas they can barely solubilize the long-alkyl-chain fatty acids. The solubilization stability can be analyzed by estimating the Gibbs free energy change (ΔG0) for the transfer of solubilizate molecules to the aggregate phase. The gemini surfactant system showed the largest negative value of ΔG0 for both naphthalene and the fatty acids. On the other hand, solubilization of fatty acids into CnAdAB micelles was not advantageous energetically. These results indicate that the solubilization ability of CnAdAB surfactants is not generally suitable for solubilization of long-alkyl-chain fatty acids owing to the smallness of the micelles.

Thrombocytic activity in patients with arterial hypertension associated with metabolic syndrome

This work was aimed to elucidate the level of in vitro and in vivo aggregation activity of platelets and the functional significance of individual mechanisms of its regulation in patients with grade III arterial hypertension and metabolic syndrome. The study included 29 adult patients (15 men and 14 women) and 25 clinically healthy subjects of similar age. Biochemical, hematological and statistical methods were used. Marked dyslipidemia was associated with active lipid peroxidation. Plasma thromboxane B2 level was increased by 84,8% while 6-ketoprostaglandin F1α level was decreased by 17,9% and the total amount of NO metabolites by 28,7%. The degree of platelet aggregation and their aggregation with collagen 25,0 and 27,5% lower than the respective control values while the respective indices of their aggregation with ristomycin were 25,7 and 46,4% higher. The degree of platelet aggregation and their aggregation with ADP inducer were 25,7 and 58,4% higher than in control while the platelet-discocyte levels were reduced to 48,6 ± 0,4%. The sum of active platelet forms reached 51,4 ± 0,12% vs 17,9 ± 0,09% in control was, the number of small and large aggregates 18,6 ± 0,08 and 5,4 ± 0,04 per 1000 free platelets respectively vs 2,9 ± 0,06 и 0,2 ± 0,06 in control. Excess platelet activity in the patients was due to their enhanced adhesive and aggregative potential and reduced ability to disaggregate. The most important causs of thrombocytopathy was AH, negative changes in plasma lipid composition, and enhanced lipid peroxidation.

The dynamics of early-state transcriptional changes and aggregate formation in a Huntington\u2019s disease cell model

BackgroundHuntington’s disease (HD) is a fatal neurodegenerative disorder caused by a CAG expansion in the Huntingtin (HTT) gene. Proteolytic cleavage of mutant huntingtin (Htt) protein with an expanded polyglutamine (polyQ) stretch results in production of Htt fragments that aggregate and induce impaired ubiquitin proteasome, mitochondrial functioning and transcriptional dysregulation. To understand the time-resolved relationship between aggregate formation and transcriptional changes at early disease stages, we performed temporal transcriptome profiling and quantification of aggregate formation in living cells in an inducible HD cell model.ResultsRat pheochromocytoma (PC12) cells containing a stably integrated, doxycycline-inducible, eGFP-tagged N-terminal human Htt fragment with an expanded polyQ domain were used to analyse gene expression changes at different stages of mutant Htt aggregation. At earliest time points after doxycycline induction no detectable aggregates and few changes in gene expression were observed. Aggregates started to appear at intermediate time points. Aggregate formation and subsequent enlargement of aggregates coincided with a rapid increase in the number of differentially expressed (DE) genes. The increase in number of large aggregates coincided with a decrease in the number of smaller aggregates whereas the transcription profile reverted towards the profile observed before mutant Htt induction. Cluster-based analysis of the 2,176 differentially expressed genes revealed fourteen distinct clusters responding differently over time. Functional enrichment analysis of the two major gene clusters revealed that genes in the up-regulated cluster were mainly involved in metabolic (antioxidant activity and cellular ketone metabolic processes) and genes in the down-regulated cluster in developmental processes, respectively. Promoter-based analysis of the identified gene clusters resulted in identification of a transcription factor network of which several previously have been linked to HD.ConclusionsWe demonstrate a time-resolved relationship between Htt aggregation and changes in the transcriptional profile. We identified two major gene clusters showing involvement of (i) mitochondrial dysfunction and (ii) developmental processes implying cellular homeostasis defects. We identified novel and known HD-linked transcription factors and show their interaction with known and predicted regulatory proteins. Our data provide a novel resource for hypothesis building on the role of transcriptional key regulators in early stages of HD and possibly other polyQ-dependent diseases.

Molecular interactions involving aqueous Triton X-100 micelles and anionic surfactants: Investigations on surface activity and morphological transitions

The micellar solutions of nonionic surfactant Triton X-100 (TX-100) were investigated in the presence of several anionic surfactants, namely sodium 1-butanesulfonate, sodium 1-decanesulfonate, sodium octanoate, sodium perfluorooctanoate, sodium decanoate and sodium alkyl sulphates. The resultant structures formed have been analysed using cloud point (CP), wettability and scattering techniques (DLS and SANS). CP and DLS show marked morphological changes for existing TX-100 micellar solutions in presence of an anionic surfactant depending on its respective hydrophilicity or hydrophobicity. Hydrophobic anionic surfactants induced strong demicellization effect and shifted clouding temperature to higher values. SANS study shows typical transition in ellipsoidal shaped micelles of TX-100 based on the specific interactions. The analysis of SANS data revealed that ellipsoidal shaped TX-100 micelles transform to smaller ellipsoidal mixed micelles with lower axial ratio and smaller aggregation number. Wettability of TX-100 aqueous solution on PTFE surface changes significantly on addition of small amount of anionic surfactant. The water penetration through porous channels of packed PTFE powder in a metal cylinder depicts reduction in wettability due to formation of stable micelles in presence of fluorinated surfactants. The specific changes in CP and morphology of TX-100 micelles are explained in terms of critical molecular interactions as influenced by the hydrophobic chain length and polar head group of surfactants.

Micellization and Adsorption of Heterogemini Surfactants Containing a Hydroxyl Headgroup in Aqueous Solution

The micellization of a homologous series of heterogemini surfactants, CmOhpNCn (m, n = 10, 8; 12, 8; 14, 8; 16, 8; and 10, 14), in aqueous solution and their adsorption at the air/water interface have been investigated by surface tension, conductivity, and fluorescence techniques. The surface tension curves of C16OhpNC8 and C10OhpNC14 showed two break points, corresponding to the critical concentration of the premicellar aggregation and the general micellization, respectively. The results of conductivity and fluorescence spectra using pyrene as probe confirmed the premicellization behavior in the two cases. This indicated that these surfactants have strong aggregation ability in the solution. The micelle formed nearby the cmc displayed only a small aggregation number but a large ionization degree. The C20 that characters the efficiency in surface tension reduction was quite small in comparison with those of conventional surfactant and even smaller than those of symmetric gemini surfactants such as 12-s-12...

Structure and Rheology of Poloxamine T1107 and Its Nanocomposite Hydrogels with Cyclodextrin-Modified Barium Titanate Nanoparticles.

We report the preparation of a nanocomposite hydrogel based on a poloxamine gel matrix (Tetronic T1107) and cyclodextrin (CD)-modified barium titanate (BT) nanoparticles. The micellization and sol-gel behavior of pH-responsive block copolymer T1107 were fully characterized by small-angle neutron scattering (SANS), dynamic light scattering (DLS), and Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy as a function of concentration, pH and temperature. SANS results reveal that spherical micelles in the low concentration regime present a dehydrated core and highly hydrated shell, with a small aggregation number and size, highly dependent on the degree of protonation of the central amine spacer. At high concentration, T1107 undergoes a sol-gel transition, which is inhibited at acidic pH. Nanocomposites were prepared by incorporating CD-modified BT of two different sizes (50 and 200 nm) in concentrated polymer solutions. Rheological measurements show a broadening of the gel region, as well as an improvement of the mechanical properties, as assessed by the shear elastic modulus, G' (up to 200% increase). Initial cytocompatibility studies of the nanocomposites show that the materials are nontoxic with viabilities over 70% for NIH3T3 fibroblast cell lines. Overall, the combination of Tetronics and modified BaTiO3 provides easily customizable systems with promising applications as soft piezoelectric materials.

Quantifying the micellar structure formed from hydrocarbon-fluorocarbon surfactants

Many technological formulations contain mixtures of surfactants, each contributing some distinct property. Characteristics of each surfactant are often modulated in the mixture, based on the interactions between the various components present. Here, the mixing of the hydrocarbon surfactant cetyltrimethyl ammonium bromide (C16TAB) and the fluorocarbon surfactant, Zonyl-FSN-100 with average chemical structure of C8F17C2H4 (OC2H4)9OH, is quantified, in particular, the size and shape of the micelles and their critical micelle concentration (CMC). The CMC data suggest there are specific interactions between the two components which are strongly antagonistic. Small-angle neutron scattering (SANS) has been used to quantify the size and shape of the micelle, and these data indicate that the single component FSN-100 forms disc-like micelles with a small aggregation number (∼65) and the C16TAB forms globular, charged micelles with a larger aggregation number (135). The aggregation number of the mixed micelle is substantially greater than either of the pure species. Overall, a detailed study of CTAB, FSN-100 and their mixture systems will be presented in this paper.