Search

We investigated the hierarchical structure of complex coacervate core micelles formed by mixing a supramolecular coordination polymer and a diblock copolymer. Cryogenic transmission electron microscopy (cryo-TEM) on those systems was only possible for very dilute samples and suggested the existence of wormlike micelles or strings of spherical micelles (Y. Yan, N. A. M. Besseling, A. de Keizer, R. Fokkink, M. Drechsler and M. A. Cohen Stuart, J. Phys. Chem. B 2007, 111, 11662). Using small-angle X-ray scattering (SAXS) we investigated those mixtures with a concentration of up to 0.6 vol%. Depending on the charge ratio and the concentration the above mixtures was proven to build spherocylindrical objects of different sizes. In the case of charge neutrality spherical micelles are found. Thus, we confirmed by SAXS experiments that the structures seen by cryo-TEM indeed exist in solution.

We present a comprehensive study of the interaction of spherical polyelectrolyte brushes (SPBs) with cationically modified polyacrylamide (CPAM), calcium carbonate (CaCO3) particles, and cellulose fibers. A link to the use of this system as a model for retention aids in the papermaking process is elaborated. Anionically functionalized SPBs with a high cation exchange capacity (CEC) are used together with CPAM as a model system for fiber flocculation and deposition of CaCO3, which are integral steps in the papermaking process. The flocculation efficiency is tested by means of a dynamic drainage jar. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) are used to analyze the system, the structure of the agglomerated flocs, and the mechanism of floc formation. The data suggest that the flocculation efficiency can be attributed to the high CEC of SPB in combination with the flexibility of grafted polyelectrolyte chains. FESEM images and AFM support the model of anionic SPBs acting as a particle bridge between fibers and CaCO3. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:233–241, 2006

Recently performed small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) experiments (Macromolecules 30 (1997) 273) had provided experimental data for measurement of the static scattering formfactor which are in very good agreement with the theoretical results for the formfactor obtained with the help of the Dirac model of semiflexible polymer chains. This agreement had prompted us to make additional detailed comparisons between the observables which can be calculated with help of the Dirac and the Kratky–Porod (K-P) models of semiflexible chains. In this work we provide comparison between the closed form exact analytic results for the Dirac formfactor and various approximations of the static formfactor obtained with help of the K-P model. Remarkable agreement between the exact result and various approximations is thoroughly investigated through systematic classical and semiclassical analysis of the K-P model. We found conditions (approximations) under which the K-P model could be obtained from the Dirac model. This enabled us to calculate the observables related to measurements of optical anisotropy and magnetic birefringence and to reanalyze previously obtained exact analytic results for the force–extension relations based on the Dirac model.

A turbidimetric analysis of particle interaction in the presence of dissolved polymer is presented. The system consists of polystyrene latex particles of 75.5 nm diameter and hydroxyethyl cellulose (HEC; M w = 172.000 g/mol; radius of gyration = 41.5 nm). To avoid the adsorption of HEC on the surface of the particles, Triton X-405 has been added. The maximum latex concentration investigated was 100 g/L whereas the HEC concentration has been varied between 0 and 0.7 g/L. It can be shown that the scattering in this system is fully determined by the scattering of the latex particles. Turbidimetry, which is insensitive to multiple scattering, allows therefore the determination ofthe partial structure factor ofthe latex spheres in the region of long wavelengths. This analysis can be extended to high latex concentrations and yields the osmotic compressibility of the latex spheres. The depletion potential based on a volume-exclusion mechanism is found to provide a good description of the osmotic compressibility.

We reconsider the analysis of the structure of colloidal particles by small-angle scattering. Special emphasis is laid on the structural parameters derived from a small-angle experiment conducted at different contrast. The forward scattering of the particles, their radius of gyration and the invariant are reconsidered in terms of a model introduced by Harrison (1969). Here the finite resolution of the experiment as well as the small size of the constituents of typical polymeric colloids are taken into account by definition of a shape function φ ( r ) which varies continuously between 0 and 1. Model calculations show that careful measurements of the scattering intensity over a wide range of scattering angles and contrasts may be used for a detailed analysis of the shape function.

We report a turbidimetric study of the depletion forces between latex particles induced by a dissolved polyelectrolyte. The system consists of a polystyrene latex and potassium polystyrene sulfonate (PSS). Since turbidimetry is practically insensitive to multiple scattering the analysis of the mixtures of the colloid and the dissolved polymer could be extended up to latex concentrations of 50 g/l. The amount of dissolved PSS was varied between 0.025 and 0.2 wt.%. The scattering contribution of the polymer can be neglected in very good approximation and the change in scattering intensity upon addition of PSS can directly be related to the effective attraction of the latex spheres caused by the dissolved polymer. It is demonstrated that a potential based on the volume-exclusion mechanism can describe in good approximation the osmotic compressibility resulting from the turbidimetric analysis.

A small-angle X-ray scattering (SAXS) study of PMMA-latex particles swollen with methyl methacrylate (MMA) is presented. The electron density of the swollen particles can easily be matched by addition of sucrose to the latex. Also, there is an excellent contrast between the polymer and its monomer. SAXS measurements in conjunction with contrast variation near the match point are therefore well-suited for the detection of even minute changes of the radial concentration profile. Thus, this method is capable of detecting the depletion of the polymer chains near the particle surface due to the wall-repulsion effect. The results point to an outer shell of approximately 2 nm thickness in which the swelling agent is enriched. It is concluded that the present system exhibits a small but non-negligible wall-repulsion effect which is discussed in terms of recent theoretical approaches to the problem.

A precise analysis of turbidity spectra of a concentrated polystyrene latex (number-average diameter of particles : 68 nm) for a range of wavelength between 400 and 1100 nm is given. By suitable definition, the measured turbidity of the nonuniform system as function of λ (λ is the wavelength in the medium) is factored into a measured integrated form factor Q M (λ 2 ) and a measured integrated structure factor z M (λ 2 ,c) (c is the weight concentration). The normalized scattering cross sections Q M (λ 2 ) evaluated from the experimental specific turbidities extrapolated to vanishing concentration are in full agreement with the theoretical results provided by the Mie theory. The turbidities measured at finite concentrations (up to 8.2 wt %) yield the function z M (λ 2 ,c) which furnishes the structure factor S(q) [q = (4π/λ) sin(θ/2) ; θ : is the scattering angle] in the region of low scattering angles. In particular, it can be demonstrated that S(0) as well as α, the first coefficient of the expansion of S(q) in terms of even powers of q, can be obtained with good accuracy without the need of assuming a specific model of particle interaction.

An analysis of the conformation of a stiff-chain polyimide in solution is given. It is shown that these polyimides exhibit the rather low persistence length of 13 nm despite the fact that the repeating unit consists of stiff and fully linear building blocks. A comparison with recent experimental and theoretical findings on similar systems corroborates the present analysis and suggests the bending fluctuations of the bonds as the main reason for the rather high flexibility.

The synthesis of stiff-chain poly(1,4-phenylene terephthalamide)s substituted by two as well as by four flexible side chains per repeating unit is described. The solubility of the materials bearing only two side chains is still very low. Appending of four side chains leads to polyamides which dissolve in common organic solvents. All polyamides reported herein form layered structures in the solid state as well as in the mesophase. Polyamides with two side chains have a very weak tendency for crystallization and do not exhibit a transition to the isotropic state even for the longest side chains. Polyamides with four side chains show three reversible thermal transitions: a disordering transition of the side chains, a transition to a layered, smectic-like mesophase, and finally the transition to an isotropic melt. It is shown that the phase behavior of these materials is mainly governed by the strong segregation of main- and side-chains which can be compared best to the microphase separation in block copolymers. © 1993 John Wiley & Sons, Inc.

We present anomalous small-angle X-ray scattering (ASAXS) as a new tool for the study of rod-like polyelectrolyte. The polyelectrolyte consists of a stiff poly(p-phenylene) backbone with attached positive charged groups that are balanced by Bromine counterions. ASAXS uses the dependence of the scattering length of a given element if the energy of the incident X-ray beam is near the absorption edge of this element. The analysis of the ASAXS-data leads to three partial intensities. In particular, the scattering intensity that is solely due to the cloud of the counterions can be determined and compared to the prediction of the Poisson-Boltzmann cell model. Quantitative agreement is found. ASAXS is thus shown to be a new and highly effective tool for the analysis of polyelectrolytes.

This chapter describes the kinetics of the early stage of dispersion polymerization in supercritical CO 2 . The early stage of dispersion polymerization of MMA in SC-CO 2 has been studied by turbidimetry. The average number of particles, the turbidity-average diameter, and the mass of polymer as a function of time has been derived from these data for conversions lower than 0.1%. In the early stages investigated here, the polymerization solely takes place in the homogeneous phase. This can be concluded from the kinetic analysis of the reaction rates and from a comparison of the experimental rates with theoretical estimates. The dispersion polymerization proceeds through two stages. In stage I, the polymer forms new particles with a critical diameter of 150–170 nm. After this very short period of particle formation, all polymers precipitate on the particles. The rate of polymerization, however, remains constant in all stages. The experimental data derived from this analysis are in semiquantitative agreement with the model proposed by Paine.

Fabrication of microstructures by X-ray deep lithography (XRDL), galvanoforming, and plastic molding (German acronym LIGA) has made its way from Forschungszentrum Karlsruhe to many labs throughout the world. The acronym ANKA stems from Angstrom and Karlsruhe to indicate the main spectral range and the location. ANKA is designed to satisfy the needs of XRDL as well as of X-ray analysis, in particular, of microstructures. Industrial demand of service in both fields will play a major role for ANKA. The main design parameters of the storage ring are an electron energy of 2.5 GeV, magnetic field of 1.5 T, and an ensuing characteristic wavelength of 0.2 nm. The lattice has fourfold symmetry with four dispersion-free straight sections, each about 4 m long. The optics is a double DBA structure with four 22.50 bending magnets per cell resulting in a compact medium-emittance design with a circumference of 97.2 m and an emittance in the range of 40 to 80 nmrad. Four 500 MHz RF cavities are placed one in the middle of each cell. In this way, only one straight section is needed for injection leaving three for optional insertion devices. Electron current will be 200 mA in a first phase. Lifetime will exceed 17 h. Dynamic aperture is large enough to insert wigglers and wavelength shifters and to double the current when upgrading the RF system. 14 out of 32 available bending magnet radiation ports will be equipped with beamlines in the first phase.

Dendrimers are synthetic macromolecules with defined architecture which are synthesized by iterative controlled reaction steps [1–3]. Starting from a trifunctional monomer (generation 0) subsequent generations are connected to this initial core , resulting in a tree-like structure. Figure 1 displays a typical dendritic structure of thefourth generation: Emanating from a central or focal group a branched structure is formed which consists of three-functional entities. The fractal-like structure may be terminated by end groups. The spatial organization of these molecules can also be viewed upon as consisting of “dendrons” emanating from the focal unit. Hence, the dendrimer of fourth generation shown in figure 1 is built up from four dendrons hold together by a central ethylenediamine group.

Preface.- In memoriam Klaus Schatzel.- Reviewing my time of personal cooperation with Klaus Schatzel.- Reviewing almost two decades of digital correlator development.- Hard-sphere colloidal suspensions studied by two-colour dynamic light scattering.- Dark speckle imaging of colloidal suspensions in multiple light scattering media.- Depolarized forward light scattering from anisotropic particles.- Assessment of the depletion forces in mixtures of a latex and a non-adsorbing polymer by turbidimetry.- Hard spheres versus Yukawa particles: Differences and similarities.- Multi-speckle autocorrelation spectroscopy - a new strategy to monitor ultraslow dynamics in dense and nonergodic media.- Single-mode DLS: colloids in opaque porous media.- Quantitative real-space analysis of colloidal structures and dynamics with confocal scanning light microscopy.- Spinodal decomposition of colloids in the intermediate stage.- Very low-angle static light scattering from steady-state and time-dependent nonequilibrium fluctuations.- Freezing in confined suspensions.- Investigation of shear-induced structures in lyotropic mesophases by scattering experiments.- Comparison of Bragg and SALS studies of crystallization in suspensions of hard spheres.- Effective interaction potential obtained from experimental structure factors: The inverse problem.- The use of reflectometry for the study of swelling of latex particles at a silica surface.- Measurement of particle diffusion coefficients with high accuracy by dynamic light scattering.- Photon correlation spectroscopy for analysis of low concentration submicrometer samples.- Approaching the limits of multiple scattering decorrelation: 3D light-scattering apparatus utilising semiconductor lasers.- Suppression of multiple scattered light by photon cross-correlation in a 3D experiment.- Coherent backscattering of light in multiple scattering media.- Polyorganosiloxane-microgels as probes for forced Rayleigh scattering.- Collective and self diffusion of PS microgels in solution as observed by thermal diffusion forced Rayleigh scattering.- Properties of TiO2 hydrosols synthesized by hydrolysis of titanium tetraethoxide.- Experimental study of fractal aggregation by static and dynamic light scattering.- Single cluster light scattering and photon correlation spectroscopy: Two powerful techniques for monitoring cluster aggregation.- Experimental evidence regarding the influence of surface charge on the bridging flocculation mechanism.- Colloidal stability - investigations by single-particle scattering photometer.- The micelle-to-vesicle transition as observed by time-resolved scattering experiments.- Droplet microemulsions: Determination of the bending elastic constants by photon correlation spectroscopy.- A hard sphere microemulsion.- Unusual phase behaviour from peculiar pair potentials: A density-functional-perturbation study.- DWS behaviour in gelling systems: Preliminary comparison with rheological measurements over sol-gel transition in latex-doped gelatin.- Phase transitions in nonadditive hard disc systems: a Gibbs ensemble Monte Carlo Study.- Diffusion of colloids at short times.- Phase transitions in magnetic fluids.- Cell theory for the phase diagram of hard spherocylinders.- Structures of spherical particles dispersed in density matched media under oscillatory shear.- Is there scaling of the intermediate scattering function without hydrodynamic interactions? Brownian rods on a 1d-ring.- Static and dynamic light scattering from the nematic wetting layer in an Isotropic liquid crystal.- Film formation of latex dispersions observed with evanescent dynamic light scattering.- Direct observation of a buckling transition during the formation of thin colloidal crystals.- Microemulsions: Phase transitions and their dynamics.

A statistical mechanical treatment of phase equilibria in mixtures of thermotropic nematic liquid crystals with nonuniformly distributed polymers is given. Based on the Flory lattice model of nematic fluids it allows the explicit calculation of coexistence curves, cloud point curves and phase volume ratios without invoking adjustable parameters. It is shown that the strong fractionation taking place in nematic-isotropic phase equilibria has a profound influence on the phase behavior.

The Journal of Physical Chemistry

The influence of lateral substituents or side chains attached to thermotropic nematogens is considered on the basis of the Flory lattice model. The rigid core of the nematogen is characterized by its axial ratio x and the characteristic temperature T∗ which measures the strength of the anisotropic dispersion forces operative between the cores. For the side chain an additional parameter zm which is proportional to its hard core volume enters the partition function. Given these quantities and the free volume as obtained from the thermal expansion coefficient, the nematic-isotropic transition temperature TNI and the temperature dependence of the order parameter may be calculated. The results show that the lowering of T NI by lateral substituents is caused by (1) their interference with molecules packing and (2) the dilution of the anisotropic dispersion forces between the central nematogenic cores. As an additional consequence of this the order parameter is lowered considerably. A survey of recent e...

Syntheses of the trimer (n = 3), tetramer (n = 4) and the pentamer (n = 5) of the p-oxybenzoate series C6H5CO(–OC6H4CO)n-2-OC6H5 are reported. Densities and thermal expansion coefficients of the neat liquids were measured and phase transitions in the pure compounds and their binary mixtures were investigated by differential scanning calorimetry (DSC). The nematic-isotropic transition is directly accessible only in the case of the tetramer (melting point 181°C, nematic-isotropic transition temperature TNI = 254°); the trimer melts to an isotropic liquid at 136°C and the nematic-isotropic transition of the pentamer (melting point 224°C) lies above the range of thermal stability. DSC results for the binary mixtures show the coexistence range of the nematic and the isotropic phases to be very small; it is obscured by pre- and post-transition effects. In satisfactory approximation therefore, the binary mixtures can be treated as one-component systems, and TNI may be identified with the maximum of the DSC peak. Values of TNI thus obtained are linear with respect to composition and may be extrapolated to obtain TNI = 100°C for the pure trimer and 464°C for the pure pentamer. As shown by conformational analysis, all conformers of a given homolog have virtually the same axial ratio. These compounds therefore can be treated as rigid rods.

Application du modele elabore aux donnees de la litterature: diagramme de phase du systeme EBBA/polystyrene

The Flory lattice theory of neat nematic fluids is reviewed and compared to other current statistical-mechanical treatments of systems of ordered hard rods. It is shown that the model provides a sound description of the nematic state. At intermediate concentrations the free energy derived thereby reduces to the expression given by the decoupling approximation.1 At low concentrations the result of the Onsager Theory is obtained. The Flory theory is easily extended to include thermotropic systems by introducing the characteristic temperature of anisotropic interaction T*. This parameter is in semi-quantitative agreement with values estimated from optical and thermodynamic data.

The full experimental phase diagrams of mixtures of the nematic liquid crystal 4.4′-azoxyanisole, (PAA), and n-tetracosane and of PAA and n-octadecane are given. Equilibria of a nematic phase with an isotropic phase, of two isotropic phases, and a reentrant isotropic phase could be observed directly. The experimental phase diagram is in qualitative agreement with the result derived from the Flory lattice model adopted for thermotropic systems.

A series of poly(2-n-alkyl-l, 4-phenylene terephthalate)s with n =3 to 18 has been investigated by DSC, optical microscopy and wide-angle x-ray analysis. The degree of crystallinity as inferred from x-ray analysis is rather low but increases upon annealing. None of the materials under consideration here exhibits a glass transition. If n ≥ 12 the polyesters form nematic melts, appending of longer side chains lead to the observation of a layered mesophase.

Solution semiconcentree dans la trans-decaline, a des vitesses de cisaillement moderees 5.10 3 ≤6≤10 4 s −1 ). La vitesse de degradation augmentee avec la concentration

This paper analyzes the effect of gravity on polymer solutions near the consolute point. Calculations are carried out for monodisperse polystyrene in cyclohexane using the Flory-Huggins expression with a concentration-dependent interaction parameter for the free energy of mixing. Depending on molecular weight and distance to the demixing temperature, the influence of gravity leads to non-negligible gradients of the volume fraction in the one-phase region as well as in the two-phase region. In particular, the effect of gravity on the measurement of the coexistence curve in a finite sample is calculated explicitly.

Characteristic temperatures T* have been evaluated for the oligomeric p-oxybenzoates, C6H5CO(-OC6H4CO)n-2-OC6H5 from the transition temperatures TNI presented in the preceding paper. For n = 3, 4 and 5 they are, respectively, 343, 316 and 306 K. These parameters that measure the intensities of the orientation-dependent intermolecular interactions are correlated with the optical anisotropy Δα and the average intermolecular cohesive energy expressed by the characteristic pressure p*. The characteristic temperature T* decreases slightly with chain length. The lattice theory of nematic fluids is extended to include mixtures of rodlike molecules having different characteristic temperatures T* in order to treat binary and ternary mixtures of the p-oxybenzoate oligomers. The wide biphasic gaps predicted for the several binary systems and the concomitant pronounced partitioning of the components between the nematic and isotropic phases are not confirmed by experiments. Compositions of the coexisting phases in ternary systems were found to be identical within limits of experimental determinations. These marked departures from theory are explicable on the premise that facile rotational diffusion of the nematogens here considered, which are of comparatively low chain length, leads to rapid generation of ordered domains of large dimensions. Subsequent diffusional transport over the required distances consequently is very slow. The transition temperatures observed in binary systems are in excellent agreement with calculations carried out in the “single component” approximation using mean values of the axial ratio and of T* for the mixture, these being taken to be the same in the two phases at equal concentrations.

Measurements of the viscosity coefficient η of solutions of polystyrene (Mw = 6.0 × 105 and 1.77 × 106) in trans-decalin (TD, θ solvent) and toluene (TL, good solvent) as function of shear rate (11−104 s−1), concentration (4.24−11.21 wt %), and temperature (10–50°C) are reported. As a new theoretically grounded method for the determination of the zero-shear viscosity η0 it is proposed to plot η as a function of . The intercepts of the straight lines obtained by this procedure give η0 in good agreement with directly measured values.

A theory of the nematic isotropic phase equilibrium in mixtures of thermotropic nematogens and flexible coils is presented. The steric part of the partition function is evaluated along the lines given earlier by Flory for phase equilibria of rods and coils in lyotropic systems. The soft anisotropic forces between the molecules of the nematogenic component are treated by an additional factor in the partition function. From these premises the respective phase diagrams may be calculated using the characteristic parameters of the pure components (nematogen: axial ratio, characteristic temperature, thermal expansion coefficient; coiled solute: contour length, thermal expansion coefficient) without resort to adjustable parameters. The biphasic region where a nematic and an isotropic phase coexist is predicted to increase markedly with increasing chain length of the coiled component; in case of a polymeric solute there is a virtually complete exclusion of the coils from the nematic phase. Experimental p...

The viscosity data of moderately concentrated polystyrene solutions in trans-decalin (TD) (θ solvent, θ temperature 21°C) and toluene (TL) (good solvent) reported in Part I are discussed in terms of Graessley's entanglement theory. Under good solvent conditions, Graessley's master curve provides an excellent fit up to high shear rates, whereas in the vicinity of the θ conditions the data have to be modified by a parameter ηfric introduced by Ito and Shishido. The characteristic time of mechanical response to flow of chains approximately given by the shift factor τ0 is found in good solvents to be on the order of the Rouse relaxation time. In poor solvents, close to demixing, τ0 tends to much higher values, indicating a reduced chain mobility. The influence of temperature on the viscosity decreases with increasing shear. The resulting apparent energy of activation of flow shows very small or even negative values at high shear rates. This behavior can be explained by the modified Graessley theory, however, in a quite natural way.

A series of fully aromatic polyesters, polyamides, and polyimides bearing n-alkoxy side chains (n=2–18) have been investigated by optical microscopy, X-ray analysis and DSC. All members of these series have a rigid backbone and exhibit a decreasing melting range with increasing length of the side chains. The polyester with short side chains (n=2–6) form nematic melts. Longer side chains lead to the observation of a novel layered mesophase for all systems under consideration here. There is a linear relationship between the length of the side chains and the layer spacing observed in the mesophase. All findings can be explained by assuming a packing model with interdigitated side chains.

The shear degradation of polymers in semiconcentrated solutions is viewed as a function of solvent quality. It is shown that the deterioration of the thermodynamic quality of the solvent leads to a marked flow resistance due to an increasing number of contacts between the chains. This may be probed by viscosimetric measurements as well as by degradation experiments (“thermodynamically induced shear degradation”). For a detailed discussion of this phenomenon the experimental setup for the mechanochemical experiment is outlined first, followed by a survey of the kinetics of chain scission. Finally, experiments mostly obtained on polystyrene in the theta-solvent trans-decalin are discussed. The results of mechanochemical investigations together with those of viscosimetric investigations are shown to provide useful information on polymer dynamics at high shear rates in semiconcentrated solutions.