Depolarized light scattering from critical polymer blends

Depolarized light scattering of binary polymer blends in disordered state near the demixing critical point is considered both theoretically and experimentally. It is shown that the depolarized scattering in such systems is predominantly due to double scattering processes induced by composition fluctuations. For long enough polymer chains, this scattering is stronger than the contribution from intrinsic anisotropy fluctuations. The general equation for the static and dynamic double scattering function is obtained in terms of the system structure factor. The scattering functions are calculated both analytically and numerically (dynamic part) for polymer blends. We found that the depolarized intensity depends on the polymerization degree N and the relative distance from the critical point τ = 1 – χ*/χ (where χ is the Flory‐Huggins interaction parameter and χ* its critical value) as I_vh ∼︁ N²/τ², which is in good agreement with the experimental data. It is also shown that the dynamic scattering function is decaying non‐exponentially. We calculate the relaxation rate and the non‐exponentiality parameter as functions of the scattering angle and τ. These theoretical predictions are compared with experimental data for three chemically different blends.     

Effect of multiple scattering on SANS spectra from bicontinuous microemulsions

The adsorption kinetics of protein A, BSA, IgG, and fibronectin has been investigated using a homemade quartz crystal microbalance. Information about the energy losses appearing in the system is measured by the maximal oscillation amplitude and the dissipation factor. Only the maximal oscillation amplitude allows us to distinguish the different contributions of liquid and mass to the total frequency shift. The adsorption of proteins has been performed on Ti and Au surfaces at different concentrations. The amount of irreversible adsorbed protein A and IgG increases with increasing bulk concentrations. On Au more proteins adsorb, but their biological activity is reduced in comparison to Ti. Protein A forms a first monolayer in a few seconds, which shows practically no energy losses, and following this a second monolayer is formed. The adsorption rate for the second monolayer is much smaller and energy losses are present. Fibronectin is forming a very viscoelastic system, whose mechanical properties are affected by immersion in different buffer solutions.     

Hybrid polymer inorganic materials prepared from ternary microemulsions

The microemulsion system containing vinyl acetate (Vac), silane derivatives tetraethoxysilane (TEOS), methacryloxypropyltrimethoxysilane (MPTS), vinyltriethoxysilane (VTES), methyltriethoxysilane (MeTES), octyltriethoxysilane (OTES), nonylphenol etoxylated with 25 mol of ethylene oxyde (NPEO₂₅) and water was studied. It was established that the probability of microemulsion formation increases with surfactant concentration. The microenviroment of the solubilization of the VAc and of silane derivatives in the aggregates of NPEO₂₅ was affected by their polarity. Hybrid materials were obtained by sol-gel reaction of silane derivatives combined with free-radical polymerization of VAc. The change of the glass transition temperature and of thermal stability of the polymer chains in the presence of the inorganic one proved the formation of simultaneous polymer inorganic hybrids.     

Synthesis of sponge-like polymer dispersions via polymerization of bicontinuous microemulsions

Polymer gels with high water content are made by polymerization of hydrophilic/hydrophobic monomer mixtures in bicontinuous microemulsions. These structures can be described as a heterophasic, bicontinuous polymer colloid-in-water structure, the characteristic length of which is only indirectly influenced by the original microemulsion mixture.The structure formation and phase changes throughout the polymerization reaction are followed with rheology, polarization microscopy, and scanning and transmission electron microscopy. It is shown that already the very first formed polymer changes disturb the bicontinuous phase structure and nucleate a vesicular phase; with further consumption of the monomer mixture, at least three other phase transitions can be detected, ending with a simple globular surfactant structure.Although direct templating of the original mesomorphous structure does not occur, the existence of the diverse lyotropic phases influences the final structure. It is shown that simple dilution changes the characteristic length of the network elements from about 2 m down to 50 nm. This is explained by a combination of a nucleation-and-growth mechanism with the influence of a restricted colloidal stability in anisometric lyotropic phases.     

Dynamic light scattering method of polymer solutions

The main features of dynamic light scattering are briefly outlined. The capability of this method to characterizing molar mass distributions and to distinguishing different molecular architectures is demonstrated with some examples. Special attention is given to the question of internal mobility and the spectrum of relaxation times. Recent results on asymptotic behavior are presented and discussed. Scaling behavior of the first cumulant with respect of space and of the time correlation function with respect of time (shape function) is found. All examples studied so far demonstrate the dynamic scaling of Zimm-Rouse chains, but the prefactors strongly depend on branching and crosslinking.     

Neutron and light scattering studies of polymer blends and block copolymers

The structure of compatible polymer mixtures and its temperature dependence can be well described in many cases by the mean-field approximation. Deviations with regard to the temperature dependence of the correlation length of concentration fluctuations can be explained by taking into account the spatial structure of the interaction potential. Concentration fluctuations and the microphase separation in diblock copolymers are in good agreement with theories based on the random phase approximation. In the two-phase region the temperature dependence of the scattered X-ray or neutron intensity is governed by the difference in the thermal expansion coefficients of the two components of the diblock copolymer. Photon correlation spectroscopy (PCS) yields valuable information on the concentration dependence of the mutual diffusion coefficient D_AB.     

Neutron scattering from polymer blends under pressure

A procedure is used to analyze small-angle neutron-scattering (SANS) data from a pressurized polymer blend mixture (deuterated polystyrene/polyvinylmethylether). The Lattice-Fluid (LF) equation-of-state model is used along with a compressible random phase approximation (RPA) in order to obtain free volume fractions and intermonomer interaction potentials. Solving the two sets of equations (LF and RPA) self-consistently within the fitting procedure to the SANS data provides an improvement over the familiar incompressible RPA model. In this approach, the free volume fraction is the main varying parameter. Intermonomer interaction potentials were found to depend on pressure (weakly) and temperature (linearly). © 1995 John Wiley & Sons, Inc.     

Miscibility and phase separation in polymer blends studied by laser light scattering

In this paper major emphasis has been placed on the phase behavior of miscible polymer blends, especially on blends containing random copolymers. Blends containing random copolymers generally tend to phase separation at elevated temperatures (LCST behavior). Experimental determination of miscibility areas as a function of temperature and copolymer composition by laser light scattering provides the interaction parameters necessary for theoretical explanations and predictions of various phase separation phenomena. Just above the LCST polymer blends exhibit regular highly interconnected two-phase morphologies. The rate of decay of these structures is estimated. The phase separation kinetics can be pursued by laser light scattering and is discussed in terms of CAHN's linearized theory. It can be shown that the linear theory adequately describes the early stage of phase decomposition. The linear theory is also applicable to the reverse phenomenon, the phase dissolution below LCST. unlike the case of phase separation the diffusion-controlled regime is that in the late stage of phase dissolution.     

Phase equilibria in ternary polymer blends

The phase states and rheological properties of blends of three polymers??polystyrene, poly(methyl methacrylate), and the styrene-acrylonitrile copolymer??in the common solvent chloroform are studied. The phase diagrams are constructed and the positions of spinodals are determined via the method of turbidity points. The effect of the third polymer on the compatibility of the binary blend obeys Prigogine??s rule; that is, it is determined by the solubility of the added polymer in the first two components. The extremum composition dependence of rheological properties of ternary polymer systems in the vicinity of the separation point (the metastable region) is found. Through the method of convex-shell construction, the phase diagrams are calculated.     

A closed-loop behavior of ternary polymer blends composed of three miscible binaries

Poly (methyl methacrylate) (PMMA) was known to be miscible with poly (vinyl phenol) (PVPh). According to literature, poly (vinyl cinnamate) (PVCN) was also miscible with PVPh. The miscibility between PMMA and PVCN was corroborated on the basis of preliminary experiments. Is a ternary blend consisting of PMMA, PVPh and PVCN miscible in all the blend compositions? To answer this question, the miscibility of this ternary was examined in different blend compositions mainly based on calorimetry data in this investigation. The results using two different molecular weights of PVPh demonstrated an interestingly closed-loop behavior of immiscibility. The reason is likely because of the “Δχ effect”.     

Photoinitiated polymerization in bicontinuous microemulsions: Fluorescence monitoring

The photopolymerization of bicontinuous microemulsions was simultaneously monitored with differential scanning calorimetry and fluorescence. The kinetics and mechanism of the reaction were studied throughout the entire photopolymerization reaction. The role played by the surfactant in the kinetics and morphology was studied. The nature of the surfactant changed the autoacceleration process and final conversion. The behavior was explained as a result of the differences in the interfacial properties. Anionic cetyltrimethylammonium bromide (CTAB) gave rise to a more flexible interfacial film than anionic sodium dodecyl sulfate (SDS), resulting in competition between the intramolecular and intermolecular reactions in the former systems. As cyclization did not contribute to the increase in the degree of crosslinking, SDS photopolymerization gave solids with a more rigid microstructure. Fluorescence methodology was applied to monitor bicontinuous microemulsion polymerization and to reveal the microstructure and morphology development during photopolymerization. The microemulsion composition was designed to prepare nanoporous, crosslinked materials. Even though the nanostructure of the precursor microemulsions was not retained because of phase separation during polymerization, mesoporous solids were obtained. Their morphologies depended on the nature of the surfactant, and membranes with open cells were successfully prepared with CTAB, whereas more complex morphologies resulted with SDS. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5291–5303, 2006     

Diffusion behavior of pharmaceutical O/W microemulsions studied by dynamic light scattering

Dynamic light scattering experiments have been performed at various concentrations, of pharmaceutical oil-in-water microemulsions consisting of Eutanol G as oil, a blend of a high (Tagat O2) and a low (Poloxamer 331) hydrophilic–lipophilic balance surfactant, and a hydrophilic phase (propylene glycol/water). We probe the dynamics of these microemulsions by dynamic light scattering. In the measured concentration range, two modes of relaxation were observed. The faster decaying mode is ascribed classically to the collective diffusion D _c (total droplet number density fluctuation). We show that the slow mode is also diffusive and suggest that its possible origin is the relaxation of polydispersity fluctuations. The diffusion coefficient associated with this mode is then the self-diffusion D _s of the droplets. It was found that D _c and D _s had opposite volume fractions of oil plus surfactants (ϕ) dependence and a common limiting value D ₀ for ϕ=0. Average hydrodynamic radius (R _h=10.5 nm) of droplets was calculated from D ₀. R _h is supposed to compose the inner core, a surfactant film including possible solvent molecules, which migrate with the droplet. The concentration dependence of diffusion coefficients reflects the effect of hard sphere and the supplementary repulsive interactions which arises due to loss of entropy, when absorbed chains of surfactant intermingle on the close approach of the two droplets. This mechanism could also explain the observed stability of our systems. The estimated extent of polydispersity is 0.22 from the amplitude of slower decaying mode. The polydispersity in microemulsion systems is dynamic in origin. Results indicate that the time scale for local polydispersity fluctuations is at least three orders of magnitude longer than the estimated time between droplet collisions.     

Phase behavior and a modified Kwei equation for ternary polymer blends containing stereoregular PMMA

Previously, poly(methyl methacrylate) (PMMA) was found to be almost immiscible with poly(vinyl acetate) (PVAc) regardless of tacticity of PMMA and casting solvent. Poly(vinyl phenol) (PVPh) was found successful previously in making immiscible atactic PMMA/PVAc miscible. In this investigation, tacticity effect of PMMA on a ternary composed of PMMA, PVAc and PVPh was studied. Isotactic PMMA ternary was shown to be miscible in all the studied compositions on the basis of single T_g observation. However, syndiotactic PMMA ternary demonstrated immiscibility at ca. 25% PVPh and miscibility was observed at higher PVPh concentrations. A modified Kwei equation based on the binary interaction parameters was proposed to describe the experimental T_g of the miscible ternary almost quantitatively.     

Dynamic light scattering from spherical particles

The dynamic light scattering behavior of poly(butylmethacrylate) PBMA microgels and of kappa-casein micelles is compared with that from hard sphere latex particles. The latex particles and the kappa-casein micelles exhibited a single exponential decay of the time correlation function (TCF). For the microgels, progessively stronger deviations from a single exponential were observed as the scattering angle was made larger. These deviations are interpreted as being the result of internal modes of motion. From measurement of the first cumulant of the TCF, extrapolated towards zero angle, the translational diffusion coefficients D were determined, and the hydrodynamically effective radii were calculated via the Stokes-Einstein relationship. The ratio of the radius of gyration to the hydrodynamic radius was found to be?=0.775+0.012 for the latex particles, in good agreement with theory. The microgels, however, exhibit much lower?-parameters of 0.49 to 0.58, while the kappa-casein micelles showed the opposite behavior with values between 1.1 and 2.5. The results are interpreted on the basis of the DebyeBueche and Deutsch-Felderhof theory for porous spheres.     

Determination of microscopic interaction parameters of ternary polymer solutions with light scattering data

Using a renormalized form of the Random Phase Approximation (or Tree Graph Approximation) we analysed data on the zero angle scattering intensity and the apparent radius of gyration for the system polystyrene-poly(methyl methacrylate)-bromobenzene. Since the microscopic parameters of this system are known from the analysis of the zero-angle scattering data, the theory yields a parameterfree prediction of the apparent radius of gyration which fits the data very well. To show the influence of renormalization we also analyse the data by an unrenormalized version of RPA.     

Scattering intensity of bicontinuous microemulsions and sponge phases

Monte Carlo simulations of dynamically triangulated surfaces of variable topology are used to investigate the scattering intensities of bicontinuous microemulsions. The bulk scattering intensity is shown to follow the Teubner-Strey expression. The domain size and the correlation length are extracted from the scattering peaks as a function of the bending rigidity, saddle-splay modulus, and surfactant density. The results are compared to earlier theories based on Ginzburg-Landau and Gaussian random field models. The ratio of the two length scales is shown to be well described by a linear combination of logarithmically renormalized bending rigidity and saddle-splay modulus with universal prefactors. This is in contrast to earlier theoretical predictions in which the scattering intensity is independent of the saddle-splay modulus. The equation of state, and the asymptotics of the bulk and film scattering intensities for high and low wave vectors are determined from simulations and compared with theoretical results.