Investigations of a series of nonionic surfactants of sugar-lipid hybrids by light scattering and electron microscopy

Sugar-lipid hybrids of the type C_nC_m were prepared by coupling an alkane chain (C_n) with a maltooligosaccharide (G_m) over an amide linkage. Coupling was performed with maltobionolactone (G₂) and n-alkylamine chains C_n withn=8,10,12,14,16, i.e. variation of the hydrophobic part of the molecule, and with hexadecylamine (C₁₆) and different maltooligosaccharides (G_m, m=2,3,4,6). The solution properties of the various products were studied by means of static and dynamic light scattering (LS) and by electron-microscopy (EM).The results may be summarized as follows: If the alkane chain is shorter thann=14, small spherical micelles with a radius of about 3 nm are observed. In time these micelles aggregate further to form increasingly larger spherical clusters which eventually precipitate. Long rod-like micelles form whenn 14. Contour length and chain stiffness were determined by applying theories of semiflexible chains. A qualitative confirmation of the light scattering results, i.e., micelle size and shape, was obtained from electron microscopy.     

The flexibility of rodlike micelles in aqueous solutions and the crossover concentrations among dilute,semidilute, and concentrated regimes

A flexibility parameter, the persistence length, has been evaluated from the radii of gyration and the contour lengths for rodlike micelles of heptaoxyethylene alkyl ethers (C _n E₇,n=12, 14, 16) and tetradecyldimethylammonium chloride (C₁₄DAC) and bromide (C₁₄DAB) at the observed crossover concentrations between dilute and semidilute regimes. The persistence length range is 43–73 nm, except for C₁₂E₇, for which it is 32 nm. The crossover concentrations between dilute and semidilute regimes for the semiflexible rodlike micelles calculated according to Ying and Chu as a function of the molecular weight, the contour length, and the persistence length are consistent with the observed values. The crossover concentration between semidilute and concentrated regimes was, on the other hand, calculated by using the same micelle parameters, including the value of thickness of cross-section of the rodlike micelles. The obtained values are at variance with the observed values. This means that rodlike micelles in semidilute and concentrated solutions might differ in size and/or flexibility from those in dilute solution.     

Stability of spherical and rod-like micelles of ionic surfactants,in relation to their counterion binding and modes of hydration

Aqueous salt solutions of ionic surfactants in both spherical and rod-like micelles have been treated on the basis of a statistical thermodynamic theory, and the double logarithmic relationship between micelle molecular weight and ionic strength is derived for each micelle. Counterion binding on both micelles are assumed to occur specifically, and their degrees of dissociation are related to the slopes of the linear double logarithmic relations. It is found from the relationship observed for typical surfactants that the effective charge of spherical micelles is 29±4. The degree of dissociation of rod-like micelles of these surfactants is primarily determined by the counterion species, yielding values 0.8 for Na⁺, 0.4–0.6 for Cl^– and 0.2–0.3 for Br^–. Hydrophilic hydration of both micelles can be evaluated from the intercepts of the linear relations. Hydrophilic hydration acts repulsively in spherical micelles, while it is attractive or much less repulsive in rod-like micelles.     

Small angle X-ray scattering study of an extremely elongated micelle system of CTAB-p-toluidine solution

Whenp-toluidine is added to an aqueous solution of CTAB, a remarkable increase of viscosity is accompanied by a spectacular elasticity. We detected the existence of extremely elongated rod-like micelles in electron micrographs. SAXS measurements indicate a closely packed array of cylindrical rod-like micelles, brought about when solutions flow through a thin capillary. A scattering maximum ofd=160 Å almost corresponds to the distance between the nearest neighbours of the cylindrical rod-like micelles. This value agrees with the diameter measured on electron micrographs. The second broad peak (d=75 Å) is assigned to a subsidiary maximum of the shape function of the cylinder with infinite length.     

Micelle hydration by1H-NMR

¹H-NMR studies were carried out for solution of amphiphilic betaine ester derivatives (of the general formula (CH₃)₃N⁺CH₂COOC _n H_2n+1Cl^– (V-n), wheren=10, 12, 14, and 16) andn-dodecyltrimethylammonium chloride (I-12). The spectra were taken at concentrations above and below critical micelle concentrations and chemical shifts were analyzed. It was stated that micelles are hydrated at the depth of the two CH₂ groups in the case ofV-n and the CH₂COO group in the case ofI-12. Therefore, the CH₂COO group during the micellization behaves as if it were CH₂CH₂ group.     

Interface stabilization and micelle formation in blends with a block copolymer

The phase separation behavior of ternary blends of two homopolymers, PMMA and PS, and a block copolymer of styrene and methylmethacrylate, P(S-b-MMA), was studied. The homopolymers were of equal chain length and were kept at equal amounts. Two copolymers were used with blocks of equal length, which exceeded or equaled that of the homopolymer chains. Varied was the copolymer contentf. Films were cast from toluene, which is a nonselective solvent. The morphologies of the cast films were compared with the structure of the critical fluctuations in solution, which were calculated in mean field approximation. The axis of blend compositionsf can be divided into parts of dominating macrophase and microphase separation. Above a transition concentrationf _o, all copolymer chains are found in phase interfaces. Belowf _o, part of them form micelles within the homopolymer phases.     

Rigid-rod polymers with flexible side chains

Modeling studies were performed for a rigid-rod polyester with hexadecyloxy side chains (n=16) in order to simulate x-ray scattering curves in the medium angle scattering region (s=4 sin / from 0.2 Å^–1 to 2.2 Å^=t–1). The experimental ones were taken from a material obtained by cooling to room temeperature from the smectic mesophase at 150°C. The wide-angle x-ray diffractograms were calculated for given conformations and molecular arrangements using Debye's equation. The theoretical result thus obtained for a great variety of possible packing models and structures was compared to the experimental result. The size of the effective scattering region is found to be 61×18×52=6×10⁴ ų and consists of approximately five layers, each of which is composed of two rigid rods and 20 side chains. The planes form by the rigid rods, together with the side chains, have a distance of 3.6 Å, the distance between the rods being 26 Å. As the main result, it was found that the side chains form regions with a denser ordering (clustering). The interchain distance for side chains decreases in the regions from 5.3 Å to 4.8 Å.     

Small-angle neutron scattering on shear-induced micellar structures

Small-angle neutron scattering (SANS) experiments on sheared aqueous surfactant solutions of tetradecyltrimethylammoniumsalicylate (TTMA-Sal) are reported. A5-mM-solution without shear shows a weak correlation peak at a momentum transfer of 0.09 nm^–1 which has its origin in the micellar interaction. For shear rates above a threshold value of =40 s^–1 the scattering pattern shows an irregular increase in anisotropy. The analysis of the anisotropic pattern reveals the existence of two types of micelles: Small rodlike micelles which are weakly aligned and very large rodlike aggregates which are strongly aligned and which are present above the threshold value of. The two micelles are in equilibrium with each other and the equilibrium shifts with increasing shear rate to the side of the large oriented micelles.     

Charge carrier photogeneration on some substituted polyacetylenes

The photogeneration of charge carriers was studied with the following polymers: poly-[N-(2-propinyl)-phenothiazine] (PPPT) and copolymers of N-(2-propinyl)-carbazole with N-(2-propinyl)-phenothiazine (PCz+PPT) and N-(2-propinyl)-carbazole with phenylacetylene (PCz+PA). In the case of PCz+PA, the experimentally found dependence of the photogeneration efficiency on the strength of an externally applied electric field could be well fitted with the curve calculated on the basis of Onsager's model of geminate recombination. In the cases of PPPT and PCz+PPT, on the other hand, the experimental values deviated strongly from the theoretical curve at field strengths between 10⁶ and 10⁷ V/m.Equal values for the separation distancer ₀ and the primary charge carrier yield ₀ were found for all polymers:r ₀=2.0 nm and ₀=0.20 at _inc=254 nm;r ₀=2.5 nm and ₀=0.15 at _inc=355 nm.With PPT and PCz+PPT a strong dependence of the electric resistance on the humidity content of surrounding air was observed.     

Structure of casein micelles II. α s1-casein

Following the earlier study of the- and-casein micelle structure, we will now report results from the _s1-casein. Static and dynamic light scattering measurements were performed in a concentration range from 0.5 to 6.0 mg/ml atT=35 °C. A constant apparent molecular weight of 3.4×10⁶ daltons was found over the whole range. The apparent radii of gyration and the diffusion coefficients also show no detectable concentration dependence. The ratio of the two radiiR _g /R _H =2.78+0.21 is characteristic of extended rigid structures.R _g is the radius of gyration andR _H the hydrodynamic radius defined via the Stokes-Einstein relationship from the translational diffusion coefficient. This is in agreement with the analysis of the pronounced angular dependence of the scattered light, which leads to the conclusion that _s1-casein forms very long worm-like micelles. The contour length of one cylinder was found to beL1600 nm and the chains appear to be composed of about 12 Kuhn segments. At higher concentrations, lateral aggregation proportional to the concentration is observed. Beyond the overlap concentrationc ^* the asymptotic scattering curve changes its shape, which is interpreted as the beginning of a reversible gelation.     

Pecularities of the thermomechanical behaviour of ultra-high molecular weight linear polyethylene and its blends with linear polyethylene of normal molecular weight

Ultra-high molecular weight polyethylene UHMWPE (M _w=4 · 10⁶,I _s=O g/ 10 min), high density polyethylene of normal molecular weight NMWPE (I _s= 4.8 g/10 min) and their blends have been investigated by means of thermomechanical loading in constant and impulse regime. It has been established that after melting, NMWPE passes to a viscous-liquid state. After melting at 138 °C UHMWPE passes to a high-elastic state. The transition of UHMWPE to a viscous-liquid state takes place at temperatures higher than 180 °C and is accompanied by a high-elastic reversible deformation. The blends of UHMWPE with 10 and 20 mass % of NMWPE show a plateau on the thermomechanical curves, corresponding to a high-elastic state, in a shorter temperature range where the deformation is greater. The blends containing the higher percent of NMWPE show thermomechanical curves lacking such a plateau. All blends are characterized by a singular thermomechanically defined temperature of melting, which increases with increase of UHMWPE content. The existence of the high-elastic state in the curves of UHMWPE and its blends containing NMWPE less than 30 mass % above their melting temperatures is explained by the high degree of physical crosslinking of UHMWPE.     

Mass,size and shape of micelles formed in aqueous solutions of ethoxylated nonyl-phenols

The study was extended to analysis of mass, size and conformation of micelles formed in aqueous solutions of ethoxylated nonyl phenols. The results obtained by ultracentrifugal technique between 293 and 323 K have proved that the slightly ethoxylated nonyl phenols form micelles with high molecular mass and larger size at constant temperature, while the increasing length of the ethylene oxide chain favours formation of micelles of smaller molecular mass and size. The transformation of conformation from oblate to spherical shapes ensues with increasing temperature at constant ethoxy number or with ethoxylation at constant temperature. The second virial coefficient decreases with increasing temperature and decreasing ethoxy number. In accordance with the earlier conclucions, the change of the second virial coefficient relates to enhanced variation of monomer solubility, stabilization of micelle structure and increased deviation from ideal behaviour of a given micellar system.Symbols a major axis of micelle, Å - a _m attractivity factor, cm³ erg molecule² - b minor axis of micelle, Å - c concentration, g dm^–3 - c _b equilibrium concentration at the bottom of the cell, g dm^–3 - c _m equilibrium concentration at the meniscus of the cell, g dm^–3 - c _o initial concentration in the cell, g dm^–3 - c _M critical micellization concentration, mol dm^–3 - e eccentricity - f _IS Isihara-constant - f/f _o frictional ratio of micelle - amount of water in micelle per ethoxy group, mol H₂O/mol EO - n aggregation number, monomer micelle^–1 - n _EO number of ethoxy groups - r distance of Schlieren peak from the axis, cm - r _b distance of cell bottom from the axis, cm - r _m distance of cell meniscus from the axis, cm - R _h equivalent hydrodynamic radius of micelle, Å - s _t sedimentation coefficient, s - reduced sedimentation coefficient, s - reduced limiting sedimentation coefficient, s - ¯v _t volume of micelle, cm³ micelle^–1 - partial specific volume of solute, cm³g^–1 - partial specific volume of solute reduced to 293 K, cm³ g^–1 - B _a, B_e constants, cm³ mol g^–2 - B ₂ second virial coefficient, cm³ mol g^–2 - M _m ^a mass average apparent molecular mass of micelle, g mol^–1 - M _m mass average molecular mass of micelle corrected withB ₂, g mol^–1 - M _m ^cM mass average molecular mass of micelle belonging toc _M, g mol^–1 - M ¹ mass average molecular mass of monomer, gmol^–1 - N _A the Avogadro's number, molecule mol^–1 - R universal gas constant, erg mol^–1 K^–1 - T temperature, K - _t ^o dynamic viscosity of solvent atT temperature, g cm^–1 s^–1 - dynamic viscosity of solvent at 293 K, g cm^–1 s^–1 - _t density of solution atT temperature, g cm^–3 - _t ^o density of solvent atT temperature, g cm^–3 - density of solvent at 293 K, g cm^–3 - angular velocity, rad s^–1 - time, s     

Polymer adsorption on fine particles; the effects of particle size and its stability

The effects of particle size on polyacrylamide (PAAm,M _w =59×10⁴, 500×10⁴) adsorption were investigated using a series of well-characterized hematite (-Fe₂O₃) dispersions. The -Fe₂O₃ particles with highly monodisperse and nearly spherical shape ranged in radius from 23 nm to 300 nm. the maximum amount of PAAm adsorption (M _m ) in each system, showed a steady increase with decreasing particle radius and was influenced strongly by particle concentrations in the medium. Furthermore, it was realized that the diameter of -Fe₂O₃ particles after treatment with PAAm under different particle concentrations decreased with increasing particle concentration. The relation between particle concentration in the medium and particle size after treatment was also influenced by the medium pH, i.e., at the medium pH close to the isoelectric point of -Fe₂O₃ particles (pH^o=9.2), the particle size after treatment increased with increasing particle concentration. All these results suggest that in the system of ultra-fine particles, the mixing process between particle-particle and polymerparticle will play an important role on the conformation of adsorbed polymer layer.     

Theory of ring formation in a reversible system: general solutions

The enumeration theory is extended in this work into a more general theory, taking back-reactions into consideration. The solutions may faithfully reproduce real processes from arbitrary starting points to a steady-state. Therefore, the presented theory includes the equilibrium theory by Jacobson-Stockmayer, the numerical solution by Gordon-Temple, and the irreversible theory by the present authors. The solutions are described first in general forms of transition probabilities {P}, and then explicitly with the aid of rate equations; simple proofs are given. The presented theory was applied to an experimental data: the distribution of cyclic species in poly(ethylene terephthalate). We shall show that agreement between theory and experiment is nearly perfect.AB model N ₀ Total number of units - V System volume - C ₀=N ₀/N _A ·V Initial concentration (N _A : Avogadro's number) - L _x AB type chain x-mer; (AB)_x - N _x Number of AB type x-mers - R _x Ring x-mer - N _Rx Number of ring x-mers - E Small molecule eliminated by bond-formation - N _E Number of small molecules eliminated by bond-formation - h _k Number of reacted functional units (f.u.) in statek - _k Number of reacted functional units (f.u.) in chains in statek - _k Total number of units in chains in statek - D=h _k /N ₀ Extent of reaction in statek - D ^*= _k / _k Extent of reaction in chains in statek - k _L Chain-propagation rate constant - k _Rx Cyclization rate constant of chain x-mers - k _B Bond breakage rate constant of chains - k _B,Rx Bond breakage rate constant of cyclic x-mers - <k _Rx > _k Mean cyclization rate constant in statek - g(x)=k _B,Rx /k _B Ring-opening factor of cyclic x-mers - P _Lx,k Probability that a chain x-mer will be formed in statek - {P} Set of transition probabilities per single jump in forward direction or reverse direction (see the text on individual transition probabilities) AB model M _A Total AA monomer unit number - M _B Total BB monomer unit number - M ₀=M _A +M _B Total particle number - _A,i =2M _A –h _i Unreacted A functional unit (f.u.) number in statei - _B,i =2M _B –h _i Unreacted B f.u. number in statei - _Ax Unreacted A f.u. number on x-mers - h _i Number of reacted A (or B) f.u. in statei - _i Number of reacted A (or B) f.u. in chains in statei - _A,i =2M _A –h _i + _i A f.u. number in chains in statei - _B,i =2M _B –h _i + _i B f.u. number in chains in statei - _i =2(M ₀–h _i + _i ) Total f.u. number in chains in statei - D=h _i /M ₀ Extent of reaction in statei - D _A ^* = _i / _A,i Extent of reaction of A f.u. in chains in statei - D _B ^* = _i / _B,i Extent of reaction of B f.u. in chains in statei - D ^*=2 _i / _i Extent of reaction in chains in statei - L _x (AA-BB)_x-1-AA type chain x-mer;x=1,2,3,... - L _x BB-(AA-BB)_x type chain x-mer;x=0,1,2,... - L _x (AA-BB)_x type chain x-mer;x=1,2,3,... - N _x Number of type x-mers - N _x Number of type x-mers - N _x Number of type x-mers     

Longitudinal volume viscosity of 1,4 cis polybutadiene

Volume flow of 1,4 cis polybutadiene (1,4 cis PB) of ¯M _n =311.900,T _g =156 K, andT _m =266 K, has been measured.Elastic modulus of the elastic wave, longitudinal volume viscosity, initial longitudinal volume viscosity, and retardation times are described at compression rates of ca. 1.0 to 200.0×10^–5 s^–1, and at temperatures of 293 K to 373 K, and pressures up to 150 MPa.Longitudinal volume viscosity decreases with increasing compression rate, and with decreasing volume deformation, the behavior being in all cases a typical non-equilibrium one. Longitudinal volume viscosity decreases with increasing temperature (except at 293 K), the volume flow activation energy being of about 18.2 KJ/mol.     

Structure formation of surfactants in concentrated sulphuric acid: a light scattering study

A common cationic surfactant,n-hexadecylammonium hydrogensulphate, dissolved in concentrated sulphuric acid, has been studied by static and dynamic light scattering. Micelle formation has been observed even in this unusual solvent. An apparent molar mass of 45 500±4.5% was found for the aggregates. A translational diffusion coefficientD ₀=5.5×10^–9 cm²/s was measured which gave a hydrodynamically effective radius ofR _h=17.7 nm. The geometric radius of gyration wasR _g=76.2 nm. The ratioR _g/R _h=4.33 is indicative for rodlike structures. Assuming a polydispersity ofL _w/L _n=2 this corresponds to a cylinder ofL _w=152 nm. An axial ratiop _w=(L _w/d)=60.4 nm was estimated which leads to a cylinder diameter of 2.53 nm. At surfactant concentrations higher than 5% (w/vol) the rod-like micelles aggregate to form more globular structures. The time correlation function, recorded by dynamic light scattering, exhibited a two-step decay which indicates a bimodal distribution of particle sizes. The fast motion coincides with that of the micelles at low concentrations while the other is slower than the fast one by three orders of magnitude and corresponds to the translational motion of large clusters.     

Free radical copolymerization of 1-vinyl naphthalene with styrene,methyl methacrylate,and acrylonitrile

Investigations on free radical copolymerization of 1-vinyl naphthalene (1-VNph, monomerM ₂) with styrene (St), methyl methacrylate (MMA) and acrylonitrile (AN) (monomersm ₁) in bulk at 60°C with AIBN as initiator are presented. Relative reactivity ratios were calculated by the Kelen-Tüdös method yielding:r _st=0.70 ±0.23 andr _1–VNph=2.02 ±0.40 for system St/1-VNph;r _MMA=0.32 ±0.10 andr _1–VNph=0.57 ±0.07 for system MMA/1-VNph andr _AN=0.11 ±0.03 andr _1–VNph=0.45 ±0.09 for system AN/1-VNph.Q, e values for 1-VNph according to Alfrey, Price scheme were calculated toQ _1–VNph=1.02,e ₁–VNph=–0.62.     

Spreading and compression of n-hexadecyl acrylate at liquid-air interface

Usingn-hexadecyl acrylate, surface pressure-area (F-A) curves and equilibrium spreading pressuresF ^e were measured at various temperatures (5.7°–46°C) by the Langmuir balance (F-A) and the Wilhelmy-plate method (F ^e). At low temperatures (T<13 °C) condensed films and the liquid-condensed/solid condensed transition can be observed. At high temperatures (T>30 °C) liquid-expanded films occur. In the intermediate range the compression curves have two transition points. The transition pressureF ₁ between liquid-expanded and condensed film has a marked temperature dependence. The transition enthalpiesH ₁ decrease with increasing temperature and become zero at 29.2 °C. The second transition is related to a transition between the condensed films (F ₂). The slight temperature dependence of this transition is accompanied by an increasing change of area as well as by increasing transition enthalpiesH ₂.TheF ^e-T curve has two distinct breaks, at the melting pointT _m and atT=30 °C. The break atT _m is due to the melting process and the break atT=30 °C is caused by a phase transition between a liquid-expanded film and a condensed film.The phase diagram was constructed from the transition pressures. It can be demonstrated that the highest pressures of the thermodynamic stable film occurs atT _m. At temperaturesT>T _m equilibrium spreading pressure and equilibrium collapse pressure are identical whereas atT _m supercompression of the monolayer occurs. The film in this state behaves like a supercooled liquid. Obviously, rupture and collapse of such a film lead to a thermodynamically metastable bulk phase.     

The behaviour of drag-reducing cationic surfactant solutions

The behaviour of two types of drag reducing surfactant solutions was studied in turbulent flows in pipes of different diameters. Our surfactant systems contained rod-like micelles; they consisted of equimolar mixtures ofn-tetradecyltrimethylammonium bromide,n-hexadecyltrimethylammonium bromide, and sodium salicylate. The structure of the turbulence was studied using a laser-Doppler anemometer in a 50 mm pipe. In the turbulent flow regime both surfactant solutions exhibited characteristic flow regimes. These flow regimes can be influenced by changing the amount of excess salt, the surfactant concentration, or the temperature. Shear viscosity measurements in laminar pipe and Couette flows show the occurrence of the so-called shear-induced state, where the viscosity increases and the surfactant solution becomes viscoelastic. The shape of the turbulent velocity profile depends on the flow regime. In the turbulent flow regime at low Reynolds numbers, velocity profiles similar to those observed for dilute polymer solutions are found, whereas at maximum drag reduction conditions more S-shaped profiles that show deviations from a logarithmic profile occur. An attempt is made to explain the drag reduction by rod-like micelles by combining the results of the rheological and the turbulence structure measurements.     

Characterization of water-soluble,cationic polyelectrolytes as exemplified by poly(acrylamide-co-trimethylammoniumethylethacryate chloride) and the establishment of structure-property relationships

The cationic copolymerization products of poly (acrylamide-co-trimethylammoniumethylmethacrylate chloride (PTMAC) having cationic monomer percentages of 8%, 25%, and 50% as well as the cationic homopolymer, were characterized with respect to their molecular dimensions. The light-scattering and viscometric measurements were carried out for molecular weights ranging from 200 000 to 12 800 000 g/mol in 1 M NaCl solution at 25°C. It was possible to establish a relationship between the molecular weight and the two parameters: intrinsic viscosity and radius of gyration, for all four polymers.Rheological investigations of the flow properties in 1 M NaCl solution were also carried out using the polymer with a cationic monomer of 50% (PTMAC 50). Structure-property relationships were formulated which made it possible to describe and predict the shear viscosity, both in the zero-shear region (Newtonian region) and in the shear-dependent region (non-Newtonian region) as a function of the polymer concentration, the molecular weight, and shear rate.Abbreviations a exponent of the []-M relationship - A ₂ 2^nd virial coefficient/mol·cm³·g^–2 - AAm acrylamide - b slope of the flow-curve in the shear-rate dependent region - c concentration/g·cm^–3 - dn/dc refractive index increment/cm³·g^–1 - f function - K constant of the []-M relationship/cm³·g^t-1 - m _c proportion of cationic monomers/mol % - M molecular weight/g·mol^–1 - M _w weight-average molecular weight/g·mol^–1 - M _n number-average molecular weight/g·mol^–1 - NaCL sodium chloride - PAAm polyacrylamide - PS polystyrene - PTMAC poly(acrylamide-co-trimethylammoniumethylme thacrylate chloride) - R_G ^20.5 radius of gyration/nm - TMAC trimethylammoniumethylmethacrylate chloride - shear rate/s^–1 - critical shear rate/s^–1 - viscosity/Pa·s - 0 zero-shear viscosity/Pa·s - _s solvent viscosity/Pa·s - _sp specific viscosity - [] intrinsic viscosity/cm³·g^–1 - relaxation time/s