Showing papers in "Colloid and Polymer Science in 1988"

Rheological properties of filled gels. Influence of filler matrix interaction

Abstract: The dynamic moduli of gels filled with particles have been studied as a function of the volume fraction of dispersed particlesϑ f (0–0.4) and of the way in which they interact with the gel matrix. Two gels of different nature were studied, viz. polyvinyl alcohol (PVA) — Congo red gels (a so-called rubber gel) and casein gels made by acidification of skimmed milk. Emulsion droplets stabilized by different macromolecules have been used as dispersed particles. If there was no interaction between the macromolecules adsorbed on the particles and the gel matrix, both the filled PVA and the filled casein gels showed a small decrease in the elastic moduli withϑ f , approaching the behaviour theoretically predicted for foams. In the case of interaction, the results for filled PVA gels roughly fitted the theoretical predictions, if the deformability of the emulsion droplets and the formation of an intermediate layer between the dispersed particles and the gel matrix was taken into account. The increase in the elastic moduli of the acid milk gels withϑ f was much greater than expected and was probably due to aggregation of the dispersed particles during gelation.

The behaviour of drag-reducing cationic surfactant solutions

Abstract: 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.

Some structural and mechanical properties of bacterially produced poly-β-hydroxybutyrate-co-β-hydroxyvalerate

Abstract: Some structural and mechanical properties of PHB homopolymer and copolymers containing 17 and 25–30% PHV have been investigated. X-ray scattering, optical microscopy, density measurements and differential scanning calorimetry were used to interpret the results of load-elongation curves and thermomechanical softening measurements.

Patch controlled attractive electrostatic interactions between similarly charged proteins and adsorbents

Abstract: A non-uniform distribution of ionic groups on the surface of a protein can lead to attractive electrostatic interactions between itself and an adsorbent, even when the net charge of the protein is of the same type as that of the adsorbent. Chromatographic retention mapping as a function of pH and ionic strength is employed to identify electrostatic repulsion or attraction. Thus, it can be determined whether the global characteristics or an oppositely charged patch controls the adsorptive behavior of a protein on a charged adsorbent.

Interaction between ethyl(hydroxyethyl)cellulose and sodium dodecyl sulphate in aqueous solution

Abstract: Using sodium activity, viscosity, and cloudpoint measurements, it has been shown that sodium dodecyl sulphate (SDS) binds to ethyl(hydroxyethyl)cellulose in a cooperative manner. In the absence of salt the binding leads to an increase in the clouding temperature, but when a small amount of salt (0.01 molal) is present first a drastic decrease and then an equally drastic increase in the cloud point temperature is observed. The binding of SDS also initially leads to an increase in viscosity followed by a decreased viscosity at higher SDS concentrations. A molecular mechanism explaining the observed behavior is given.

Mechanical selfsimilarity of polymers during chemical gelation

Abstract: Network polymers near their gel point exhibit selfsimilar mechanical behavior, as expressed by power law relaxations The range of selfsimilarity is defined by two limiting length scales The upper limit is the correlation length, defined by the linear size of the typical cluster, and a lower limit, roughly given by the size of one preformed linear chain, i e, the mean distance between crosslinks The correlation length increases with the approach to the gel point, and diverges at the critical extent of reaction, i e, the gel point where the infinite cluster is formed Above the gel point, it decreases again with further crosslinking Dynamic mechanical measurements of the complex modulus at the gel point show a power law in the frequency dependence over the entire frequency range, monitoring selfsimilarity Swelling effects reduce the fractal dimension of the percolation cluster form 25 to 2 It is shown how the power law G(ω) ∼ω 1/2, found by experiment, is connected to the structure of the polymeric cluster

Counterion binding behaviour of micelles of sodium dodecyl sulphate and bile salts in the pure state, in mutually mixed states and mixed with a nonionic surfactant

Abstract: The counterion binding behaviour of micelles of sodium dodecyl sulphate (SDS) and several bile salts in the pure state have been studied, as well as in mutually mixed states, and in a mixed state with polyoxyethylene sorbitan monolaurate (PSML) as a nonionic surfactant. Electrochemical measurements have shown no counterion binding by the pure bile salt micelles and their mixtures with PSML; they can bind counterions when mixed with SDS, whereas the surfactant anions of SDS micelles bind counterions in the pure state and/or in mixed states with PSML. In the SDS-PSML and SDS-bile salts combinations, the counterion association is decreased by the increased proportions of the second component. The extent of counterion binding by the different systems is presented.

The modification of the triple helical structure of gelatin in aqueous solution I. The influence of anionic surfactants, pH-value, and temperature

Abstract: The modification of the triple helical structure in aqueous gelatin solutions by changing pH and adding alkyl sulphates at 298 K and after rechilling the solution to 283 K was investigated by CD-measurement. At 298 K the triple helical content at the IEP of the gelatin has its maximum value. It is only weakly affected by adding sodium dodecyl sulphate (SDDS) at concentrations <10−4 M/dm3. The unfolding of the triple helix affected by pH and SDDS is reversible by rechilling the solution. The triple helical content of gelatin solutions decreases at SDDS concentrations higher than 10−4 M/dm3. In all cases the decrease of the amount of triple helical structure is connected with an increase of the cis-configuration in single chains and leads to chain reversals. At sufficiently high SDDS concentrationsβ-sheets are formed. These changes are thermally irreversible. Sodium decyl sulphate (SDS) has a more minor influence than SDDS except in the range of the c.m.c. of SDS. At sufficiently high SDS concentrations,β-turns appear.

Synergisms in binary surfactant mixtures

Abstract: Significant correlations become apparent between synergisms of micelle formation in surfactant mixtures and a series of physico-chemical properties and applications. Examples are emulsifying, dispersing, wetting, flotation, washing and cleaning ability. As a result, the effect of a co-surfactant with respect to problems of application can be predicted by a few surface tension measurements only.

Effect of random copolymerization on growth transition and morphology change in polypropylene

Abstract: The growth rate of an ethylene-propylene random copolymer with a 2.8% w/w ethylene content was studied in a similar manner to polypropylene. A growth regime transition associated with a birefringence change was observed at 130‡C, while the same phenomena appeared at 138‡C in isotactic polypropylene. In both polymers positive birefringence corresponds to Regime III, whereas negative birefringence of spherulites is associated with Regime II. The birefringence change is attributed to a change in the organization of crystalline lamellae: quadritic arrays of intercrossing lamellae at low temperature (Regime III) and preferentially radiating lamellae at higher temperature (Regime II). We confirm that such a morphological change can be interpreted using the concept of “non-adjacent re-entry” introduced in Hoffman's kinetic theory. Thus, quadritic morphology seems to have a partly kinetic origin. The shift of the transition temperature in the copolymer is due to the rejection of ethylene segments at the surface of crystalline lamellae of polypropylene.

Theory of shear-induced crystallization of polymer melts

Abstract: In the presented model elements of polymer melt rheology and polymer crystallization kinetics are combined. In particular, the proneness of the melt to the special type of crystallization which is characteristic for shear treatment is supposed to emerge only gradually during shear flow. Following Avrami's early ideas on crystal growth, an induction time is introduced. In principle, the model can be applied to any flow and temperature history. The special case of isothermal flow at constant shear rate is covered in greater detail: A favorable comparison is made with experimental results, as published by Lagasse and Maxwell [10].

Shear-induced deformation of polystyrene coils in dilute solution from small angle neutron scattering 2. Variation of shear gradient, molecular mass and solvent viscosity

Abstract: The technique of small angle neutron scattering (SANS) has been used to study the conformation of polystyrene chains in dilute solution under a constant shear gradient. The experiments reveal a distinct anisotropy of the molecular dimensions with regard to the directions parallel and perpendicular to the flow direction on the 2D-multidetector. The deformation ratio of the single polymer chain (〈R2〉/〈Riso2〉)−1 as a function of the reduced shear gradientβ=([η] · η · MwG)/RT shows a transition from the idealβ2-behaviour for dynamic infinitely flexible coils found at small gradients, to a behaviour with smaller increase at largerβ. These results are qualitatively consistent with the theory of Cerf for a polymer with finite internal viscosity in a shear gradient. At lowβ(β<1), a better agreement with the model of a free-draining coil (Rouse behaviour) than with the Zimm model is observed.

Comparison of galactomannan crosslinking with organotitanates and borates

Abstract: Water-soluble polymers crosslinked with metal ions form stable gels that are used in oil and gas production processes. We present an investigation of the chemistry of the binding between guar galactomannans and both borates and titanates using NMR and dynamic light scattering. The two monosaccharides comprising guar — methyl-β-D-galactopyranoside and methyl-α-D-mannopyranoside — have been studied as model compounds. High resolution13C NMR detected complexation of the sugars with borate but displayed no sign of complexation with either of the two titanates even at high titanate concentrations. Dynamic light scattering studies demonstrated the existence of colloidal titanium dioxide particles for both titanate crosslinkers. The loss of free titanium to the colloidal particles reduces the concentration of titanium crosslinking sites to below the detectable limits of NMR. The role of colloidal titanium dioxide colloids in these crosslinking reactions has not been reported previously. Data are presented following the growth of these particles with time as a function of pH and salt concentration. The observed particle growth kinetics explains the observed sensitivity of the guar gelation process to these variables.

Numerical analysis of complex dielectric mixture formulae

Abstract: As a continuation of our earlier work (Ref. [9]) the complex (frequency dependent) dielectric behaviour of some mixture formulae are studied numerically. These include matrix-inclusion type formulae (as the Wagner-Sillars or the Bruggeman-Boyle equations), mean-field statistical mixture formulae (as the Bottcher-Hsu equation) and symmetrical integral formulae (as the Looyenga equation). The frequency dependent dielectric properties are first calculated for a model system at various particle shapes, field orientations and volume fractions. After this, the validity of these equations is checked on typical sets of experimental data. For low loss powders, the Bottcher and Looyenga equations are suggested; for emulsions, suspensions and filled polymers, the matrix-inclusion type formulae give acceptable results in most cases, while for metal-insulator composites mean-field statistical mixture formulae have to be used, as they are capable of describing the percolation phenomenon.

Quantitative aspects of the growth of (charged) silica spheres

Abstract: It is shown that the growth of monodisperse, charged silica spheres in ethanolammonia upon addition of tetraethoxysilane can be adequately studied with static light scattering. The resulting growth curves (radius vs time) are analyzed in terms of a model for diffusion-controlled growth of (charged) spheres in a solution of reactive (charged) monomers, the bulk concentration of which decreases due to this growth. This decrease is sufficient to account for the essential shape of the curves. A coulombic sphere-monomer repulsion is theoretically shown to modify the growth rate only with a constant factor.

Thermoplastic elastomers by hydrogen bonding 4. Influence of hydrogen bonding on the temperature dependence of the viscoelastic properties

Abstract: The temperature dependence of the viscoelastic properties of thermoreversible polybutadiene networks based on hydrogen bond linkages is analyzed from the logarithmic shift factors loga T . For binary hydrogen bond complexes thermorheologically simple behavior is observed. The temperature dependence of loga T is described by the Williams-Landel-Ferry (WLF) equation. The thermoreversible linkages cause an increase in the apparent activation enthalpy of flow which is related to the number of complexing sites in the polymer. Thermorheologically complex behavior is observed in a system with more complex association.

Gelled emulsions with a high water content

Abstract: The structure of a gel containing 99% water, 0.5% of a nonionic surfactant and 0.5% of a hydrocarbon was investigated by analysis of its equilibrium phases and their state of dispersion by liquid helium freeze fracture electron microscopy.

SAXS experiments on gel-spun polyethylene fibers

Abstract: The tensile strength of gel-spun polyethylene fibers obtained after hot-drawing depends on spinning conditions such as spinning speed, spinning temperature, spinline stretching, polymer concentration, and molecular weight/molecular weight distribution. High deformation rates in the spinline result in shish-kebab structures which after hot-drawing lead to fibers with poor properties. This is in contrast to hot-drawn fibers obtained from gel-spun fibers with a lamellar structure. Lamellar or shish-kebab structures in the gel-spun fibers can be distinguished by means of DSC experiments on strained fibers. On the basis of these experiments a qualitative prediction of the final tensile properties can be made. DSC experiments on (un)strained hot-drawn fibers show that in the case of shish-kebab structures an incomplete transformation into a fibrillar structure takes place which partly explains the low tensile strength. Chain slippage which becomes possible after the orthorhombic-hexagonal phase transition is involved in the fracture mechanism. The shift of the orthorhombic-hexagonal phase transition to higher temperatures with increasing tensile strength indicates that the increase in strength corresponds to an increase in length of the crystal blocks. Consequently, creep failure also occurs at higher stresses. The melting behavior of cold-drawn and hot-drawn fibers is qualitatively similar, but the transformation into a fibrillar structure is more complete in the latter case.

DSC of γ-irradiated ultra-high molecular weight polyethylene and high density polyethylene of normal molecular weight

Abstract: The melting and the crystallization ofγ-irradiated (doses: 0–6Mrad) ultra-high molecular weight nascent polyethylene (UHMWPE) and high density nascent polyethylene with normal molecular weight (NMWPE) were investigated by DSC. The heat of melting of the nascent UHMWPE (DSC degree of crystallinity, respectively) increases up to a dose of 3 Mrad, after which it slightly decreases. The heat of the second melting of UHMWPE and of the first and second melting of NMWPE increases slightly up to a dose of 3 Mrad, after which it does not change. The X-ray degree of crystallinity of the nascent non-irradiated and irradiated polymers was 0.62±0.02. The calorimetric crystallinity was compared to the X-ray one. The results show that radiation does not affect the polymer crystallinity, but influences the thermodynamic heat of melting. The increase ofH m vs. dose in UHMWPE is explained in terms of processes of tie molecule scission within the amorphous regions and on the surface of the crystals, which predominate over crosslinking up to a dose of 3 Mrad. That leads to an increase in the conformational mobility of the molecules and to an increase in the enthalpy, according to Peterlin's formula. The scission of the chains at the points of entangling of the tie molecules leads to a decrease in the temperature and to an increase in the enthalpy of crystallization of UHMWPE vs. dose. In NMWPE these effects are considerably weaker.

Permeability of Newtonian black foam films to gas

Abstract: The gas permeability of Newtonian black foam films, formed on the top of a small bubble at the solution surface, was studied experimentally. The aqueous solutions contained sodium dodecylsulphate with concentrations in the range 1.5×10−4 to 3×10−3 mol/dm3 and sodium chloride (constant concentration of 0.5 mol/dm3). A dependence of the gas permeability coefficient on the surfactant concentration was obtained. The experimental results are discussed on the basis of a theory assuming the presence of clusters of molecule vacancies (holes) in the bilayer foam film, their number and size depending on the surfactant concentration. The experimental results are in agreement with this film structure and confirm the existence of flow through both the hole-free bilayer film and the holes. It was found that the holes of three molecule vacancies make the main contribution to gas permeability at low surfactant concentration. The diffusion coefficients through the hole-free film and through the three-vacancy holes are calculated.

Short range order of silica particles bound through adsorbed polymer layers

Abstract: Small angle neutron scattering was used to examine the organization of silica spheres which had been flocculated by various cationic copolymers. When the adsorbed polymers bound the spheres without compensating their surface charge, the resulting aggregates had a liquid-like short range order. When the polymers compensated for the surface charges, we found only tenuous aggregates with self-similar structures.

Reversible aggregation Part I. Reversible flocculation monitored by turbidity measurements

Abstract: The aggregation of four separate polystyrene latices, ranging in diameter from 210 nm to ca. 1 μm, using sodium chloride and magnesium sulphate as the electrolytes, has been examined turbidimetrically. The reversibility of the aggregation was examined using a dialysis technique. It was found that for large particle size latices, diameters 781 nm and 1 μm, aggregation was reversible in sodium chloride even at concentrations up to 0.5 mol dm−3. The aggregation of smaller particles was not reversible. The aggregation of large particles in magnesium sulphate solutions was not readily reversed by dialysis. The latter result does not appear to agree with theoretical predictions.

Prediction of the non-Newtonian viscosity and shear stability of polymer solutions

Abstract: The structure-property relationships derived here permit the prediction of both the zero-shear viscosityη0, as well as the shear rate dependent viscosity\(\eta (\dot y)\). Using this molecular modeling it is now possible to predictη over the whole concentration range, independently of the molecular weight, polymer concentration and imposed shear rate. However, the widely accepted concept: dilute — concentrated, is insufficient. Moreover it is necessary to take five distinct states of solution into account if the viscous behavior of polymeric liquids is to be described satisfactorily. For non-homogeneous, semi-dilute (moderately concentrated) solutions the slope in the linear region of the flow curve (η=\(f(\dot y))\) must be standardized against the overlap parameterc · [η]. As with theη0-Mω-c-relationship, aη-M ω -c-\(\dot y\) relationship can now be formulated for the complete range of concentration and molecular weight. Furthermore, it is possible to predict the onset of shear induced degradation of polymeric liquids subjected to a laminar velocity field on the basis of molecular modeling. These theoretically obtained results lead to the previously made ad hoc conclusion (Kulicke, Porter [32]) that, experimentally, it is not possible to detect the second Newtonian region.

The structure of water and methanol adsorbed on silica gel by FT-NIR spectroscopy

Abstract: The NIR adsorption spectra were analyzed quantitatively on the fundamental, combination and first overtone region of OH vibrations of silanol groups, water and methanol adsorbed on mesoporous silica gels. Adsorbed methanol constitutes first layer of about 3 molecules/um−2 and second layer, the structure of which is similar to that of bulk methanol liquid. Adsorbed water consists of a first layer of about 3 molecules/nm−2, the second layer of about 9 molecules/nm−2 and the third layer has a structure similar to the that of bulk water. The molecular configuration at the interface is discussed.

New aspects of yielding in semicrystalline polymers related to microstructure: branched polyethylene':')

Abstract: The application of thermodynamics of eutectoid copolymers and a generalized Tabor-relation to relationships between mechanical properties (microhardness, yield stress) and microstructure in semicrystalline polymers is considered. The approach is illustrated by results on melt-crystallized low density polyethylene, investigated near the yield point at different temperatures. The success of the approach emphasizes that semicrystalline polymers, despite being viscoelastic hetereogeneous systems, give rise to a yielding process entailing the irreversible deformation of a larger number of crystals within cooperative super-structure units. Microhardness provides, within this context, a unique measure of the crystal size average. Comparison of calculated and experimental data favors the view of deformed crystals containing basal defective surface boundaries (“meso-crystals”) which yield cooperatively.

Spectral and photophysical studies of thiazine dyes in triton X-100

Abstract: The absorption spectra of several thiazine dyes such as thionine, azure A, azure B, azure C and methylene blue in aqueous solution of Triton X-100 show that dyes as electron acceptors form 1∶1 charge-transfer (CT) or electron-donor-acceptor (EDA) complexes with Triton X-100, which acts as an electron donor. From the thermodynamic and spectrophotometric properties of these complexes, the abilities of dyes to accept an electron are in the order: azure C > thionine > azure A > azure B > methylene blue. The photogalvanic effect in the aqueous solution dye-surfactant has been studied. Generation of photovoltage supports a CT or EDA interaction between thiazine dyes and Triton X-100. There is a good correlation among the photophysical (photovoltage), spectral and thermodynamic properties of these complexes.

Lower critical solution temperature (LCST) and theta temperature of aqueous solutions of nonionic surface active agents of various polyoxyethylene chain lengths

Abstract: Cloud points of aqueous solutions of homogeneous poly(oxyethylene)dodecyl ether derivatives (C12(OE)n: n=2–8) and the apparent theta temperatureTθ ap were determined from the abrupt changes in optical transmittance and the temperature dependence of the second virial coefficient obtained by light scattering measurements. It was found that the lower critical solution temperature (LCST) shifts to a lower temperature and lower concentration as the number of oxyethylene units in a molecule decreases. Because of this behavior of LCST, the modified Flory-Schultz plot of phase separation was applied to the present nonionic surfactant-water system, and its theta temperature obtained. The dependence ofTθ ap on the number of oxyethylene units suggests that the polyoxyethylene chain has different effects on the solubility of C12(OE)n in water forn less than or equal to 3 from those forn greater than or equal to 4.

Effects of surfactants on wave-induced drainage of foam and emulsion films

Abstract: It is well established that the plane-parallel models of foam and emulsion films underestimate the velocity of film thinning by up to several orders of magnitude and show an incorrect dependence of thinning velocity on film radius. A new theory of film thinning has been previously formulated for tangentially immobile films [12, 13], and shows that the reason for this discrepancy is the neglect of experimentally observed finite amplitude surface waves. For thin films of relatively large radii (> 1o−2 cm), the pumping of the fluid generated by oscillations of the surface waves, provides the dominant contribution to film thinning velocity. The present hydrodynamic model includes the effects of surfactants (Marangoni-Gibbs-effect, surface viscosity and surface diffusion) and surface waves on thinning velocity. As in the case of a tangentially immobile film, it is concluded that the thinning velocity varies inversely with less than the first power of the film radius, and not with the square of the film radius, as predicted by the plane-parallel models of thin film. Also, the velocity of thinning is found to be up to several orders of magnitudes larger than that evaluated from the plane-parallel models. The influence of waves in enhancing the thinning velocity is found to be most significant for a tangentially immobile film and this effect decreases by a factor of up to 3, with a decrease in surface elasticity and surface viscosity.

Nucleation parameters for polymer crystallization from non-isothermal thermal analysis

Abstract: Differential scanning calorimetry (DSC) has been used to obtain kinetic and nucleation parameters for polymer crystallization under a non-isothermal mode of operation. The available isothermal nucleation growth-rate equation has been modified for non-isothermal kinetic analysis. The values of the nucleation constant (K g ) and surface free energies (sgr, sgr e ) have been obtained for i-polybutene-1, i-polypropylene, poly(L-lactic acid), and polyoxymethylene and are compared with those obtained from isothermal kinetic analysis; a good agreement in both is seen.

Scattering function and the dynamics of phase separation in polymer mixtures under shear flow

Abstract: The phenomenological mean-field theory describing concentration fluctuations and spinodal decomposition of binary mixtures of long flexible macromolecules is generalized to mixtures under steady shear flow. This shear flow leads to a partial orientation and stretching of the coils, as well as to an anisotropic deformation of concentration fluctuations. Generalizing the approach of Onuki and Kawasaki, we obtain the collective scattering function describing these concentration fluctuations in the mixture under shear flow. Both the steady-state situation in the one-phase region and the initial stages of spinodal decomposition for concentrations inside of the spinodal curve are considered.