Synthesis,characterization and self-assembly of amphiphilic block copolymer poly(4-vinyl benzene chloride)-b-poly(N-vinylpyrrolidone) in aqueous solution

The synthesis, characterization and self-assembly of a novel amphiphilic block copolymer containing a poly(N-vinylpyrrolidone) as a segment of hydrophilic and poly(4-vinyl benzene chloride) (PVBC) arms are reported. The copolymer was characterized by FT-IR spectroscopy ¹H NMR. The composition and the molecular weights of the block copolymers were established using gel permeation chromatography and ¹H NMR. The water-soluble fraction of poly(N-vinyl-2-pyrrolidone) (PVP)/PVBC block copolymers formed micelles which were investigated at 25 °C in water at 5 mg/ml concentration using a tensiometer. The morphology of micelles in aqueous solution was determined by the AFM, SANS, and SAXS methods.     

Structure and spacing of cellulose microfibrils in woody cell walls of dicots

The structure of cellulose microfibrils in situ in wood from the dicotyledonous (hardwood) species cherry and birch, and the vascular tissue from sunflower stems, was examined by wide-angle X-ray and neutron scattering (WAXS and WANS) and small-angle neutron scattering (SANS). Deuteration of accessible cellulose chains followed by WANS showed that these chains were packed at similar spacings to crystalline cellulose, consistent with their inclusion in the microfibril dimensions and with a location at the surface of the microfibrils. Using the Scherrer equation and correcting for considerable lateral disorder, the microfibril dimensions of cherry, birch and sunflower microfibrils perpendicular to the [200] crystal plane were estimated as 3.0, 3.4 and 3.3 nm respectively. The lateral dimensions in other directions were more difficult to correct for disorder but appeared to be 3 nm or less. However for cherry and sunflower, the microfibril spacing estimated by SANS was about 4 nm and was insensitive to the presence of moisture. If the microfibril width was 3 nm as estimated by WAXS, the SANS spacing suggests that a non-cellulosic polymer segment might in places separate the aggregated cellulose microfibrils.     

Quantum mechanics and the structure of noble-gas clusters

The importance of quantum mechanics for the thermal behaviour of Argon clusters with special respect to phase transitions is investigated applying a Path-Integral Monte-Carlo (PIMC) method. Results for the small-angle neutron scattering function (SANS) for various cluster sizes and temperatures are presented.     

Small angle neutron scattering measurements on micellar solutions of perfluor detergents

Small angle neutron scattering experiments (SANS) were carried out with solutions of the Lithium salt of Perfluoroctanoic acid (LIPFO) in pure D₂O and mixtures of D₂O and H₂O and Diethylammoniumperfluorononanoate (DEAFN). For LIPFO the scattering intensity as a function of the scattering angles could be fitted with calculated scattering functions for spheres. The contrast variation method allowed us to extract accurate values for the radius, the concentrations of the micelles and the aggregation number. For DEAFN the observed scattering function could be fitted on the basis of spherical vesicles with an appreciable variance in diameter. For several solutions these parameters and the concentration of the vesicles could be evaluated.     

Shear induced deformation of polystyrene coils in dilute solution from small angle neutron scattering

The deformation of the overall conformation of polystyrene,M _w =280000 g/ mole in dilute solution in a constant shear gradient has been investigated by small angle neutron scattering (SANS). The experiments were performed with a new Couette-type apparatus, consisting of two concentric quartz cylinders in which the outer one rotates and the solution is confined in the gap between both cylinders. The observation of the elastic coherent small angle scatterring intensity at a shear gradient ofG=400 s^?1 has revealed a distinct anisotropy of the scattering pattern on the two dimensional detector, as estimated from equilibrium chain dynamics. After extrapolation to zero angle and zero concentration two different values for the overall size of the single macromolecule parallel and perpendicular to the flow-direction are deduced.     

Effect of head group polarity and spacer chain length on the aggregation properties of gemini surfactants in an aquatic environment

The aggregation behavior of cationic gemini surfactants with respect to variation in head group polarity and spacer length is studied through conductance, surface tension, viscosity, and small-angle neutron-scattering (SANS) measurements. The critical micellar concentration (cmc), average degree of micelle ionization (beta(ave)), minimum area per molecule of surfactant at the air-water interface (A(min)), surface excess concentration (gamma(max)), and Gibb's free energy of micellization (delta G(mic)) of the surfactants were determined from conductance and surface tension data. The aggregation numbers (N), dimensions of micelles (b/a), effective fractional charge per monomer (alpha), and hydration of micelles (h(E)) were determined from SANS and viscosity data, respectively. The increasing head group polarity of gemini surfactant with spacer chain length of 4 methylene units promotes micellar growth, leading to a decrease in cmc, beta(ave), and delta G(mic) and an increase in N and b/a. This is well supported by the observed increase in hydration (h(E)) of micelles with increase in aggregation number (N) and dimension (b/a) of micelle.     

Structural Behavior of Aggregate Assemblies of Cationic Surfactants and Their Mixtures with Triblock Polymers

Small angle neutron scattering (SANS) technique has been employed to study the structural aspects of micellar system of cationic surfactants viz. alkyltriphenylphosphonium bromide (C₁₂-, C₁₄-, C₁₆TPB) and hexadecylpyridinium chloride (C₁₆PyCl) with triblock polymers (L64, F68, and F127). SANS data analysis reveals the prolate ellipsoidal shape of mixed micelles and increase in the micellar size upon addition of triblock polymers (L64, F68, and F127). The influence of effective size of the head group segment on the growth of micelles of HTPB (larger head group) has also been compared with that of HPyCl (smaller head group). A proportionate micellar growth of cationic surfactants has been found with increase in the length of tail segment of cationic surfactants. The observed mixed micellar growth in mixed systems is also accounted on the basis of simultaneous increase in the hydrophobicity of both the components in the mixed system. Results from the present study enlightened the effect of variation in head group segment and hydrophobicity on the structural aspects of mixed micellar system.     

Role of added counterions in the micellar growth of bisquaternary ammonium halide surfactant (14-s-14): 1H NMR and viscometric studies

The change in the morphology of a series of dicationic gemini surfactants C(14)H(29)(CH(3))(2)N(+)-(CH(2))(s)-N(+)(CH(3))(2)C(14)H(29), 2Br(-) (14-s-14; s=4-6) on their interaction with inorganic (KBr, KNO(3), KSCN) and organic salts (NaBenz, NaSal) have been thoroughly investigated by means of (1)H NMR spectral analysis and the results are well supported by viscosity measurements. The presence of salt counterions results in structural transition (spherical to nonspherical) of gemini micelles in aqueous solution. With an increase in salt concentration all the three gemini surfactants showed changes in their aggregate morphology. This change is dependent on the nature and size of the added counterion. The effect of inorganic counterions on the micellar growth is observed to follow the Hofmeister series (Br(-) < NO(3)(-) < SCN(-)). The roles of organic counterions are discussed on the basis of probable solubilization sites of the substrate molecule in the gemini micelles, showing more growth in case of Sal(-) than Benz(-). The results are confirmed in terms of the obtained values of chemical shift (δ), line width at half height (lw), and relative viscosity (η(r)). Also, the growth of micelles was most pronounced for the gemini surfactant with the shortest spacer (s=4). This was attributed to the unique molecular structure of gemini surfactant micelles having flexible polymethylene spacer chain linking the twin polar headgroups.     

Significance of glass transition temperature to polymer latex stabilisation by nonionic surfactants

Equilibrium colloid stability measurements with nonionic surfactant (C₁₂E₈) stabilised polybutyl methacrylate (PBMA) latex dispersions indicate a sudden temperature induced destabilisation coinciding with the glass transition temperature,Tg, of the polymer. In control experiments with polystyrene latex particles of similar size, for whichTg was not approached, the flocculation temperature was significantly higher. The effect is interpreted in terms of a reduced adsorbed layer thickness aboveTg caused by mixing of part of the surfactant molecule with the polymer. This interpretation is supported by DSC, elastic modulus and mechanical damping measurements on films made from dispersions of the same latex containing commercial nonionic surfactants. These measurements indicate a shift inTg in the presence of surfactant consistent with partial penetration of the polymer surface by the surfactant. In addition, C₁₂E₈ adsorption measurements show increased adsorption (or absorption) onto PBMA aboveTg which is irreversible on both dilution and temperature reduction.     

Shape and Size of Highly Concentrated Micelles in CTAB/NaSal Solutions by Small Angle Neutron Scattering (SANS)

Highly concentrated micelles in CTAB/NaSal solutions with a fixed salt/surfactant ratio of 0.6 have been studied using Small Angle Neutron Scattering (SANS) as a function of temperature and concentration. A worm-like chain model analysis of the SANS data using a combination of a cylindrical form factors for the polydisperse micellar length, circular cross-sectional radius with Gaussian polydispersity, and the structure factor based on a random phase approximation (RPA) suggests that these micelle solutions have a worm-like micellar structure that is independent of the concentration and temperature. The size of the micelle decreases monotonically with increasing temperature and increases with concentration. These observations indicate that large micelles are formed at low temperature and begin to break up to form smaller micelles with increasing temperature.     

Effects of sodium salicylate on the microstructure of a novel zwitterionic gemini surfactant and its rheological responses

Solutions of a novel zwitterionic gemini surfactant, 1,2-bis[N-ethyl-N-(sodium 2-hydroxyl-3-sulfopropyl)-dodecyl-ammonium] ethane betaine (DBA_2-12), in presence of sodium salicylate (NaSal) can form wormlike micelles and thereby show a viscoelasticity. At low molar ratio of NaSal/DBA_2-12, R?≤?0.3, the systems behaved like a Newton fluid. However, as the R increased, the systems exhibited shear-thinning behavior. The zero-shear viscosity η ₀ increased dramatically with increasing R and peaked with R?=?0.8 at a value of 18.8 Pa s. This was attributed to the formation of long wormlike micelles (1.6?～?2.9 μm) and network structure confirmed by scanning electron microscopy. Further increase in R beyond 0.8 resulted in a slight decrease in η ₀, which may be caused by the branched micelles formed at high salt concentration. In addition, the tested systems showed a Maxwellian behavior at lower frequencies, but deviated from the Maxwellian mode at higher frequencies.     

Physicochemical properties of anionic triple-chain surfactants in alkaline solutions

A series of novel gemini cationic surfactants alkanediyl-alpha,omega-bis (hydroxyethylmethylhexadecylammonium bromide) with polymethylene spacer chain length of 4, 6, 8, and 10 carbon atoms was synthesized and characterized. Critical micellar concentrations of the gemini surfactants in aqueous solutions as determined by the surface tension and conductance measurements were observed to be in the range 1.39-3.63 microM. The critical micellar concentration was observed to increase initially with spacer length up to 6 methylene groups and to decrease thereafter with the increase in spacer length. The micellar microstructure in aqueous solutions examined through small angle neutron scattering (SANS) revealed that the extent of aggregation growth and variation in shapes of micelles strongly depend on head group polarity, spacer chain length, and temperature. The propensity to micellar growth with spacer chain length 4 was found to be much higher than with the longer spacer lengths. The fractional charge on the micelle increases with increased spacer chain length and temperature.     

A study of the interaction between polyvinylpyrrolidone and gemini surfactant G12-3-12 by NMR

The interaction between a water-soluble polymer polyvinylpyrrolidone (PVP) and a gemini surfactant N,N'-didodecyl-N,N,N',N'-tetramethyl-N,N'-propanediyl-diammonium dibromide (G12-3-12) was investigated by means of NMR in a D₂O solution at 298 K. The critical micelle concentration (СMC), critical aggregation concentration (СAC) and adsorption reached the saturated concentration (C2) were confirmed by chemical shift and self-diffusion coefficients, respectively. The results of the relaxation time ratio (T_R = T₂/T₁) of G12-3-12 show that the motion of the ionic head N⁺–CH₃^* proton (G6) is seriously restricted, and thus, it can be proved that the cationic head groups are situated in the hydrophilic layer of the micelle. The size of the mixed-aggregates in the G12-3-12/PVP solution is larger than pure G12-3-12 micelles according to self-diffusion coefficients, indicating that the G12-3-12 and PVP has formed mixed micelles, and ionic heads N⁺–CH₃^* become more tightly packed in the hydrophilic layer of the micelle shell. On the other hand, strong cross peaks, such as G1-P2, G1-P3, and G2-P3, appear in the 2D nuclear Overhauser enhancement spectroscopy (2D NOESY) spectra of the G12-3-12/PVP system, further indicating that the interaction sites are located between the hydrophobic tail of G12-3-12 and PVP ring.     

Degree of micelle ionization and micellar growth for gemini surfactants detected by 6-methoxy-N-(3-sulfopropyl)quinolinium fluorescence quenching

The degree of micelle ionization of gemini surfactants has been investigated by using halide-sensitive fluorescence probes (e.g., 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ)). The fluorescence is quenched by the free bromide ions dissociated from surfactants. The degree of micelle ionization increased with increasing spacer chain length, but it decreased with increasing surfactant concentration. The Stern-Volmer plot gave two inflection points (i.e., not only at the cmc but also far above the cmc). The second inflection point suggested spherocylindrical micellar growth with decreases in the degree of micelle ionization. The spherocylindrical micellar growth was depressed with increasing spacer chain length, whereas it was enhanced with increasing tail chain length. The degree of micelle ionization of spherocylindrical micelles depended on the concentration and chain length of gemini surfactants. The change in SPQ fluorescence spectra upon hydrogenation was utilized to evaluate the solubilization site in micelle solutions. The dissolved SPQ in water was instantly reduced by the addition of NaBH4, resulting in abrupt changes in fluorescence intensity and spectral shift. All of the SPQ in micelle solution was also instantly reduced by NaBH4, indicating the existence of SPQ in the water bulk phase, but its fluorescence intensity increased upon the solubilization of hydrogenated SPQ into micelles.     

Effect of dicationic gemini surfactants 16–s‐16 (s = 4, 5, 6) on the ninhydrin‐dipeptide (glycyl‐tyrosine) reaction

The effect of dicationic gemini surfactants H₃₃C₁₆(CH₃)₂N⁺‐(CH₂)_s‐N⁺(CH₃)₂ C₁₆H₃₃, 2Br^? (s= 4, 5, 6) on the reaction of a dipeptide glycyl–tyrosine (Gly–Tyr) with ninhydrin has been studied spectrophotometrically at 70°C and pH 5.0. The reaction follows first‐ and fractional‐order kinetics, respectively, in [Gly–Tyr] and [ninhydrin]. The gemini surfactant micellar media are comparatively more effective than their single chain–single head counterpart cetyltrimethylammonium bromide (CTAB) micelles. Whereas typical rate constant (k_Ψ) increase and leveling‐off regions, just like CTAB, are observed with geminis, the latter produces a third region of increasing k_Ψ at higher concentrations. This subsequent increase is ascribed to the change in the micellar morphology of the geminis. The pseudophase model of micelles was used to quantitatively analyze the k_Ψ ? [gemini] data, wherein the micellar‐binding constants K_S for [Gly–Tyr] and K_N for ninhydrin were evaluated. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 800–809, 2012     

A 1H NMR study of 1,4-bis(N-hexadecyl-N, N-dimethylammonium)butane dibromide/sodium anthranilate system: spherical to rod-shaped transition

The effect of addition of sodium anthranilate to 5 mM micellar solutions of gemini surfactant 1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide is investigated by ¹H NMR. The solubilization site of anthranilate anion near the micellar surface is inferred. In the micelles, the An⁻ ions intercalate among the surfactant headgroups producing morphological changes.     

Meander model of amorphous polymers

Assuming bundles (of shortrange ordered macromolecules, folding back and forth statistically), their equilibrium superstructure and diameter are described on the basis of cluster-entropy-hypothesis (CEH). As primary blocks in the bulk polymer and in thin films coupled meander cubes are most probable, which are linked via their cube diagonals serving as axis of statistical rotation and aggregate to coarse grains. Magnetic birefringence, SANS and elctronmicroscopy are used as further methods to determine the cube side length. Applying the same concept to myosin-, collagen-, and elastin-aggregates, these can be interpreted as equilibrium meander fibrils, additionally stabilized by specific interactions and by the length of the molecules.     

Effect of hydrotropic salt on the assembly transitions and rheological responses of cationic gemini surfactant solutions

Cationic gemini surfactant dimethylene-1,2-bis(dodecyldiethylammonium bromide), referred to as C12C2C12(Et), was synthesized. The effect of sodium salicylate (NaSal) on the assembly formation and transition of this cationic gemini surfactant solution was studied. Addition of NaSal induced rich aggregate morphologies in the C12C2C12(Et) system. The microstructures and rheological responses resulting from the addition of NaSal were studied systematically to explore the interaction between gemini surfactants and hydrotropic salts. The rich aggregation behavior can be attributed to the special molecular structure of the gemini surfactant and the appropriate interaction between the surfactant and NaSal. The study of gemini surfactant and hydrotropic salt interaction brings promise for applications in materials synthesis as soft templates.     

Mixed micelles of homologous perfluoropolyether anionic surfactants in water

The mixtures of sodium and ammonium salts of three homologous perfluoropolyether carboxylic acids having Cl-terminated perfluoroalkyl group (Cl-PFPE) and differing in the average molecular weight (MW) were examined. The surfactants, namely n2, n3 and n4, have two, three and four PFPE units, respectively. Each surfactant was studied alone and in mixture with the other surfactants with the same counterion. NMR chemical shifts were measured for each surfactant and for the mixtures in different concentrations. For a given mixture the micelle composition, X_i, can be determined from the observation of the chemical shifts of the micellar components. It was found that Cl-PFPE surfactant mixtures form in water mixed micelles which contain the surfactants in equilibrium with monomeric species. The analysis of NMR chemical shift variations allowed evaluating the partition of the various surfactants in the mixed aggregates as a function of the total concentration. Composition of mixed micelles resembles ideal mixing predictions particularly at high surfactant concentrations.     

Functional Detergents Containing an Imidazole Ring and Typical Fragments of α-Nucleophiles Underlying Micellar Systems for Cleavage of Esters of Prosphorus Acids

1-Cetyl-3-(2-oximinopropyl)imidazolium, 1-cetyl-3-(2-oxaminoethyl-2-one)imidazolium, and 1-cetyl-3-(2-amino-2-oximinoethyl)imidazolium halides were synthesized.These compounds form in water solutions functional zwitter-ionic micelles as surfactants. The cleavage kinetics of 4-nitrophenyl diethyl phosphate, 4-nitrophenyl ethyl ethylphosphonate, and 4-nitrophenyl tosylate in micelles of the functional detergents and combined micelles of the functional detergents with cetyltrimethylammonium chloride are adequately described in a framework of a simple pseudophase distribution model, and the micellar systems of the detergents are typical -nucleophilic reagents. An equation was suggested for quantitative estimation of the micellar effect of the surfactants that took into account the change in the nucleophilic and basic characteristics of the -nucleophilic center of the detergent and also the influence of the reagents concentrating on transition of the reaction from the water into micelle phase. The maximum acceleration of the S N 2-reaction in the micelles of the functional zwitter-ionic detergents for the cleavage of 4-nitrophenyl diethyl phosphate and 4-nitrophenyl tosylate reached 3500 and 75 000 (oximate surfactant), 3300 and 66 000 (amidoximate surfactant ), and 4800 and 12200 (hydroxamate surfactant) times respectively. New functional detergents underlie unique supernucleophilic micellar system affording extremely high cleavage rates of organophosphorus substrates-ecotoxicants.