Morphology development in immiscible polymer blends

This chapter discusses the morphology development of immiscible binary polymer blends. It first describes morphology development in droplet-matrix structures, the dynamics of fibrillar structures and cocontinuous structures. The chapter then considers binary immiscible polymer blends, such systems consist of either dispersed domains in a continuous phase or of two cocontinuous phases. Polymer blends are generally solid at room temperature but they constitute a very viscous emulsion during their processing in the melt. This allows for morphology development during blending and further processing, while the blends are subjected to flow. The chapter also focuses on the morphology development in shear flow, which is the main flow component in many processing, mixing and other operations that involve rotating or moving parts. The polymer blending is industrially used for quite a long time to develop polymeric materials with properties that are a synergistic combination of those of the components

Complexation of lysozyme with sodium caseinate and micellar casein in aqueous buffered solutions

We present an extended structural and morphological study of the complexation of lysozyme (Lys) with sodium caseinate (SC) and micellar casein (MC) by means of turbidity measurements, phase analysis, dynamic, static and electrophoretic light scattering, bright-field and confocal laser scanning (CLSM) microscopy, fluorescence anisotropy and circular dichroism measurements. The solution behavior, structure, effective charge and morphology of the formed complexes as well as the protein structure within the complexes are dependent on the state of the casein molecules (SC versus MC), pH, ionic strength, and the [Cat+]/[An−] charge ratio (ChR). Absorption measurements indicate complexation of Lys with caseins at a pH as high as 11.29 (I = 0.01). At ChR>1, i.e. in excess of lysozyme, CLSM clearly showed formation of complex Lys/SC particles with a neutral core and an exterior part consisting exclusively of hydrophilic Lys macromolecules, whereas in the case of Lys/MC particles a uniform distribution of both proteins was observed. Binding of Lys with SC or MC leads to disruption of the secondary structure of Lys. Binding isotherms from fluorescence anisotropy are well described by an independent binding site model

The effect of geometrical confinement on coalescence efficiency of droplet pairs in shear flow

Droplet coalescence is determined by the combined effect of the collision frequency and the coalescence efficiency of colliding droplets. In the present work, the effect of geometrical confinement on coalescence efficiency in shear flow is experimentally investigated by means of a counter rotating parallel plate device, equipped with a microscope. The model system consisted of Newtonian droplets in a Newtonian matrix. The ratio of droplet diameter to plate spacing (2R/H) is varied between 0.06 and 0.42, thus covering bulk as well as confined conditions. Droplet interactions are investigated for the complete range of offsets between the droplet centers in the velocity gradient direction. It is observed that due to confinement, coalescence is possible up to higher initial offsets. On the other hand, confinement also induces a lower boundary for the initial offset, below which the droplets reverse during their interaction, thus rendering coalescence impossible. Numerical simulations in 2D show that the latter phenomenon is caused by recirculation flows at the front and rear of confined droplet pairs. The lower boundary is independent of Ca, but increases with increasing confinement ratio 2R/H and droplet size. The overall coalescence efficiency is significantly larger in confined conditions as compared to bulk conditions

Dielectric properties of phase separated blends containing a microcapacitor network of carbon nanotubes : compatibilization by a random or block copolymer

The mechanisms governing the dielectric blend properties at different length scales for phase separating blends with multiwall carbon nanotubes (MWNTs) are unravelled by tuning the microstructure. Thereto, compatibilization by interfacially segregated block copolymers (bcp) and random copolymers (rcp) of poly(styrene-random/block-methyl methacrylate) (PS-r/b-PMMA) was achieved in phase-separating blends of poly[(α-methylstyrene)-co-acrylonitrile] and poly(methyl methacrylate) (PαMSAN/PMMA) undergoing spinodal decomposition. In our recent work, we elucidated the effects of copolymer architecture and molecular weight on the percolating network of selectively localized MWNTs. Only short bcp and long rcp/bcp improved the connectivity and refinement of the PαMSAN phase laden with MWNTs and the resulting conductivity. In the present work, we study the effects of copolymer type, architecture, and concentration on the dielectric properties. We demonstrate a concurrent increase of the interfacial capacitance and decrease of the interfacial resistance of MWNTs with entrapped PαMSAN upon effective compatibilization. This is attributed to the increasing amount of connected parallel microcapacitor RC elements formed by the network of adjacent MWNTs enclosing a thin dielectric layer of PαMSAN. At high frequencies (above 1 MHz) the electrons hop between the neighboring MWNTs, whereas at intermediate frequencies, the electrons of the MWNTs tunnel through the barriers imposed by the entrapped PαMSAN. The physical characteristics of the microcapacitor network, namely the thickness of the microcapacitors and the volume fraction of entrapped PαMSAN contributing to the microcapacitor network, are estimated by describing the dielectric relaxation time and strength using the fluctuation induced tunneling model and the interlayer model, respectively. Combining the knowledge of the aforementioned parameters allows to describe the evolution of the total interfacial capacitance of the microcapacitor assembly as a function of copolymer type and concentration. Our robust and simple procedure to tune the MWNT microcapacitor network in polymer blends via the efficiency of the compatibilizer can be used to achieve a synergistic increase in the dielectric properties at different length scales

Specific effect of the linear charge density of the acid polysaccharide on thermal aggregation/ disaggregation processes in complex carrageenan/lysozyme systems

We study thermal aggregation and disaggregation processes in complex carrageenan/lysozyme systems with a different linear charge density of the sulphated polysaccharide. To this end, we determine the temperature dependency of the turbidity and the intensity size distribution functions in complex kappa-carrageenan/lysozyme (kCG/lys) and lambda-carrageenan/lysozyme (lCG/lys) systems. We demonstrate that increasing the temperature up to 80 °C in complex kCG/lys systems results in a monotonous decrease of the turbidity and the average sizes of the complex particles. On the contrary, for lCG/lys systems these values considerably increase with temperature. This suggests that disruption of the intermacromolecular hydrogen bonds at high temperature is mainly responsible for the temperature induced disaggregation in kCG/lys systems, whereas enhancement of the hydrophobic forces in lCG/lys systems at high temperature is responsible for the intensification of its aggregation. SEM images of these systems confirm the strong difference in microstructure. DSC data also show that the temperature induced disaggregation in kCG/lys systems is in disagreement with a decreased thermal stability of lys in the presence of kCG

Macromolecular complexes of lysozyme with kappa carrageenan

\u3cp\u3eWe present a structural study of the complexation and binding of lysozyme (Lys) with kappa carrageenan (kCG) by means of turbidity measurements, phase analysis, dynamic and electrophoretic light scattering, differential scanning microcalorimetry (DSMC), confocal laser scanning (CLSM) microscopy, fluorescence and circular dichroism measurements. Complexation is governed by both electrostatic interactions and secondary forces, and exhibits a maximum at the kCG to Lys ratio for which mutual compensation of charges occurs. The effect of the ionic strength (I) on complexation has a nonmonotonous character displaying a maximum in complex formation at I ≈ 0.03. The specific pH value at which complex formation is completely suppressed (pH\u3csub\u3eSet\u3c/sub\u3e), is only slightly dependent on the I value. Turbidity measurements indicate complexation of Lys with kCG at a pH as high as 11.5 (I = 0.01). Molecules of Lys are placed mainly on the periphery of the complex particles and the localization of kCG has an irregular character without formation of a single center of binding. Complexation in dilute solutions leads to a spectacular increase in the helix content, whereas in semidilute solutions complexation causes a decrease of the temperature of denaturation, suggesting that kCG has a higher affinity for the unfolded state than for the native state of Lys.\u3c/p\u3

An experimental and numerical investigation of the dynamics of microconfined droplets in systems with one viscoelastic phase

The dynamics of single droplets in a bounded shear flow is experimentally and numerically investigated for blends that contain one viscoelastic component. Results are presented for systems with a viscosity ratio of 1.5 and a Deborah number for the viscoelastic phase of 1. The numerical algorithm is a volume-of-fluid method for tracking the placement of the two liquids. First, we demonstrate the validation of the code with an existing boundary integral method and with experimental data for confined systems containing Newtonian components. This is followed by numerical simulations and experimental data for the combined effect of geometrical confinement and component viscoelasticity on the droplet dynamics after startup of shear flow at a moderate capillary number. The viscoelastic liquids are Boger fluids, which are modeled with the Oldroyd-B constitutive model and the Giesekus model. Confinement substantially increases the viscoelastic stresses and the elongation rates in and around the droplet. We show that the latter can be dramatic for the use of the Oldroyd-B model in confined systems with viscoelastic components. A sensitivity analysis for the choice of the model parameters in the Giesekus constitutive equation is presented