Erosion and breakup of polymer drops under simple shear in high viscosity ratio systems

The deformation and breakup of a single polycarbonate (PC) drop in a polyethylene (PE) matrix were studied at high temperatures under simple shear flow using a specially designed transparent Couette device. Two main breakup modes were observed: (a) erosion from the surface of the drop in the form of thin ribbons and streams of droplets and (b) drop elogation and drop breakup along the axis perpendicular to the velocity direction. This is the first time drop breakup mechanism (a), “erosion,” has been visualized in polymer systems. The breakup occurs even when the viscosity ratio (η_r) is greater than 3.5. although it has been reported that breakup is impossible at these high viscosity ratios in Newtonian systems. The breakup of a polymer drop in a polymer matrix cannot be described by Capillary number and viscosity ratio only; it is also controlled by shear rate, temperature, elasticity and other polymer blending parameters. A pseudo first order decay model was used to describe the erosion phenomenon and it fits the experimental data well.     

Effect of compatibilization on the deformation and breakup of drops in step-wise increasing shear flow

Drop deformation and breakup were investigated in the presence of a block copolymer in step-wise simple shear flow using a home-made Couette cell connected to an Anton Paar MCR500 rheometer. Polyisobutylene (PIB) was used as the matrix, while five different molecular weights of polydimethylsiloxane (PDMS) were selected to provide drops with a relatively wide range of viscosity ratio. A block copolymer made of PDMS-PIB was used for interfacial modification of the drop-matrix system. The copolymer concentration was 2 wt% based on the drop phase. The experiments consisted in analyzing the drop shape and measuring the variation of the length to diameter ratio, L/D, both in steady state and in transient regimes till breakup. This allowed revising of the classical Grace curve that reports the variation of the critical capillary number for breakup as a function of viscosity ratio and providing also a new one for blends compatibilized with an interfacial active agent with a given molecular weight.     

Influence of normal stress difference on polymer drop deformation

Polypropylene drops of varying viscosity and elasticity were sheared in a polystyrene matrix. Two transparent, counter-rotating parallel disks provided simple shear flow. By adjusting the speed of one disk the drop center was fixed in the laboratory frame and deformation followed via high magnification video camera. It was found that with high matrix elasticity drops of the minor phase stretched perpendicular (x₃) to the flow direction (x₁). This is the first report of widening of drops in shear flow. An analytical relation was established between the second normal stress differences of the phases and degree of widening. The formation of sheets and the phenomena of widening results in a larger than affine area generation.     

Development of polymer blend morphology during compounding in a twin-screw extruder. Part I: Droplet dispersion and coalescence—a review

The theoretical and experimental data on the breakup of droplets are reviewed. Several factors influence development of droplets: flow type and its intensity, viscosity ratio, elasticity of polymers, composition, thermodynamic interactions, time, etc. For Newtonian systems undergoing small, linear deformation, both the viscosity ratio and the capillary number control deformability of drops. On the other hand, the breakup process can be described by the dimensionless breakup time and the critical capillary number. Drops are more efficiently broken in elongational flow than in shear, especially when the viscosity ratio λ ? 3. The drop deformation and breakup seems to be more difficult in viscoelastic systems than in Newtonian ones. There is no theory able to describe the deformability of viscoelastic droplet suspended in a viscoelastic or even Newtonian medium. The effect of droplets coalescence on the final morphology ought to be considered, even at low concentration of the dispersed phase, ?_d ? 0.005. Several drop breakup and coalescence theories were briefly reviewed. However, they are of little direct use for quantitative prediction of the polymer blend morphology during compounding in a twin-screw extruder. Their value is limited to serving as general guides to the process modeling.     

Retarded relaxation and breakup of deformed PA6 droplets filled with nanosilica in PS matrix during annealing

The effect of hydrophilic silica nanoparticles (SiO₂) on the relaxation and breakup dynamics of selectively filled polyamide (PA6) droplets with different degrees of deformation in polystyrene (PS) matrix during quiescent annealing were in situ investigated. It was found that, with the increase of silica content, the relaxation process of PA6 droplets was slowed down gradually and the relaxation mode was changed correspondingly. The critical break aspect ratios (AR_cr) of PA6 droplets were also improved with the increase in SiO₂ nanoparticle contents. Comparisons of the experimental values of AR_cr, characteristic relaxation time (τ_d) and breakup time (t_b) of the SiO₂-filled PA6 droplets with corresponding theoretical values were made. The results of comparison were discussed in terms of viscoelasticity and interfacial tension. It was proposed that the alternation of the viscoelastic properties of PA6 droplets in stead of the interfacial tension change of the blends was responsible for the phenomena observed.     

Single and two-phase pressure drop in serpentine mini-channels

The pressure differential of single and two-phase flow in mini-channel serpentine geometries was investigated to determine the effects of flow patterns and radius of curvature of the serpentine on pressure drop. The friction factor for single phase flow through a straight channel was comparable to existing literature, while that in the serpentine geometry fell between conventional theory for straight channels and fully developed flow in helical coils. Extension of the single phase results to two-phase flow using a separated flow model led to the development of empirical correlations for two-phase pressure drop in the straight and serpentine configurations. Five operating regions were identified within the serpentine, each with distinct pressure drop characteristics dependent on the flow pattern and extent of bubble deformation. Two of the operating regions corresponded to bubbly and slug/unstable-annular flow, while the boundaries between the three remaining regions occurred at We_LGL_C = 2.7 and 15.5; corresponding to the onset of mild cap deformation and continuous bubble breakup, respectively.     

Clamping of ferroelectric PVDF to enhance the electromechanical performance of a 1–3 PMN-PT/PVDF piezoelectric composite

A group of 1–3 type piezoelectric Pb (Mg_1/3Nb_2/3)O₃-PbTiO₃/polyvinylidene fluoride (PMN-PT/PVDF) composite sheets are prepared using a complex two-step hot-pressing method. Then the molecular structure model of piezoelectric materials and an inverse piezoelectric simulation of the composites are performed to express the horizontal compression, indicating the clamping activity of ferroelectric PVDF on PMN-PT. As such, this composite sheet possesses a high dielectric permittivity (ε_r) of 560 at 100 Hz for its compacted connecting of two phases. After polarization, a very large piezoelectric coefficient (d₃₃) of 1125 pC/N and a considerable electromechanical coupling factor (k_t) of 0.43 is obtained in PMN-PT/PVDF sheet with a proper aspect ratio of 1.4 and a thickness of 2.1 mm, further indicating that promoting effect of PVDF matrix on the strain in Z-direction of PMN-PT. The result shows that ferroelectric PVDF serving as polymer matrix favors the electromechanical coupling effect, and may provide a prospect of the potential application of PMN-PT/PVDF composite in sensor or transistor for matrix ultrasonic probes.     

Drop Deformation and Breakup Mechanisms in Viscoelastic Model Fluid Systems and Polymer Blends

This paper reviews the dispersion mechanisms in viscoelastic systems under relatively high shear rate conditions. In particular, two non‐Newtonian deformation and breakup mechanisms were revealed by flow visualization in a transparent Couette shearing setup. The first one is the dispersed droplet elongation perpendicular to the flow direction. This was observed only for viscoelastic drops and had been associated to normal force buildup in the droplet. The second deformation/breakup mechanism was observed in very high viscosity ratio polymer systems. It consists in erosion at the drop surface. Clouds of very small ribbons and sheets were developed around the drop then stretched and finally broken into very small droplets, rapidly distributed in the matrix.     

Application of an interpenetrating network model to the necking in the microcrystalline region in four annealed isotactic polypropylene films subjected to uniaxial stretching at room temperature

The microscopic infrared dichroism, mesoscale deformation and macroscopic stress measurements are made on the microcrystalline region in four annealed isotactic polypropylene (iPP) thin films subjected to uniaxial stretching at room temperature. Results reveal that volume dilatation might occur during stretching and the necking causes the anisotropic shrinkage in the thickness and the width directions. The average orientation function f_av and the true stress as a function of local draw ratio in the samples showing volume dilatation can be respectively overlapped onto those of the sample undergoing constant volume deformation. The pseudo-affine deformation is applicable for molecular orientation at f_av<0.50 and the true stress-strain relationship on the mesoscale can be well described in the same region by the interpenetrating network model previously proposed for necking in the quenched iPP film. This model becomes invalid for deformations above f_av=0.50 due to that plastic deformations in the crystalline phase, depending on the annealing time, start to play a major role.     

Nanoindentation study on nanomechanical characteristics of a-CN film deposited by shielded arc ion plating

Mechanical properties of the a-CN films including elastic modulus (E_r), hardness (H), elastic recovery (R), contact stiffness (S) and deformation energies were measured by a nanoindentation system. We also evaluated wear resistant behavior of the layered a-CN films in nanometer scale by the same nanoindentation system. All the a-CN films, irrespective of V_b, showed better wear-resistance characteristics than sapphire and quartz. The a-CN (− 300 V)/Si sample showed the best wear-resistance, although its hardness was lower than the a-CN (− 300 V)/a-C (− 100 V)/Si. The wear resistant characteristic of the films can be understood by considering the other mechanical properties including that of R, hardness-to-elastic modulus ratio (H / E_r), and elastic deformation energy (W_e) obtained from the nanoindentation. These various nanomechanical properties certainly govern the wear-resistance of the film.     

Entropy of electrochemical formation of p-semiquinones—I. Effect of dipolar aprotic solvents

The entropy of formation, ΔS⁰_r, of anion radicals for 1,4-benzoquinone, 1,4-naphthoquinone, 9,10-anthraquinone and 5,12-tetracenequinone in a number of aprotic solvents has been determined in a nonisothermal cell from the temperature dependences of the reversible half wave potentials. Linear correlations between the ΔS⁰_r values and the acceptor numbers of solvents have been observed. The same approach to the literature ΔS⁰_r data for other organic molecules is discussed.     

Cold forming of plastics part I. Draw forming of thermoplastic sheets

An experimental procedure is outlined to examine the potential of thermoplastic sheets in draw forming. Experiments carried out on a variety of materials indicate that the following requirements must be fulfilled for a thermoplastic sheet to be cold formable: (1) The glass transition of polymer should be above ambient temperature and above the temperature of forming, (2) tensile elongation at break should equal or exceed 30%, (3) ratio of tensile to compressive yield stress should equal or exceed 1.6 and (4) sheet must not yield locally (neck) when strained in tension. An experimental method has been developed to determine the compressive, friction and bending forces which oppose the drawing force exerted by the punch. It is shown that the compressive force is, in most cases, largest. A stress analysis is carried out leading to an expression correlating the maximum depth of draw as a function of basic properties of sheets such as tensile strength (S_t*) and compressive yield stress (S_c). The effect of rolling on drawability is examined and interpreted in terms of the ratio S_t*/S_c. The cold formed items have a lower heat distortion temperature than their thermoformed counterparts.     

Experimental study on drop breakup time and breakup rate with drop swarms in a stirred tank

The direct experimental data for breakup parameters of drop breakup time, multiple breakage, and breakup rate are urgently required to understand drop breakup phenomena. In this regard, drop breakup experiments were carried out in a stirred tank using a high-speed online camera. The influences of the rotating speed, interfacial tension, and drop viscosity on the above breakup parameters were then quantitatively investigated. An mechanism correlation for the breakup time is proposed and is further verified by comparing with the results of Solsvik and Jakobsen (Chem Eng Sci, 2015;131:219-234). The percentage of multiple breakage comparing to binary breakup was statistically counted. The results indicated that the dimensionless drop diameter η = d/d_max can be adopted to characterize the proportion of binary breakup. Finally, the breakup rate was experimentally measured and the breakup probability was calculated using the inverse method.     

Thermometry of red nanoflaked SrAl12O19:Mn4+ synthesized with boric acid flux

This paper presents the luminescence properties and potential of red SrAl₁₂O₁₉:Mn⁴⁺ (SAO:Mn⁴⁺) phosphor for optical thermometry application. The SAO crystal consisted of a spinel block along with two mirror-like blocks. The Al³⁺/Sr²⁺ molar ratio of the precursor solution affected the crystalline-phases, morphology, and photoluminescence of the phosphor. The addition of flux H₃BO₃ promoted the growth of hexagonal-nanoflakes and enhanced the external quantum efficiency of phosphor 2.6-fold. The absolute sensitivity S_a and relative sensitivity S_r of SAO:Mn⁴⁺ showed a linear function of the temperature. The value of S_a was 4.17?×?10^?3 K^?1, and the maximum S_r was 2.70?×?10^?3 K^?1 at 393?K. A stable emission color was observed even with a change in temperature and a bright red light was seen in both daylight and a darkroom.     

Production of sugar fatty acid estrs by enzymatic esterification in a stirred-tank membrane reactor: Optimization of parameters by response surface methodology

6-O-β-D(+)-Glucose stearate serving as a model product of glucose fatty acid monoesters was synthesized using lipase B from Candiada antarctica (Chirazyme^® L-2) in a mainly solid-phase system in a stirred-tank membrane reactor. Esterification was performed in the presence of a small amount of ethyl methylketone (EMK), maintaining a catalytic liquid phase as well as forming an azeotrope with the reaction water. The azeotrope was evaporated and broken by membrane vapor permeation, then the dried EMK was returned to the reaction medium. The process was optimized by response surface methodology based on five major reaction parameters [time (T), substrate ratio (acyl donor to glucose, S _r, temperature (R _t), amount of solvent [solvent to substrates, [w/w], S _a), and enzyme load (E _l)] varied at three levels, resulting in higher yields. Thus, under optimized conditions [T _r=58 h; S _r=2.7; E _l=8.9% (w/w); R _t=78°C; S _a=1.9], up to 93% yields of glucose stearate were achieved.     

Poroplastic properties of calcium-leached cement-based materials

Asymptotic calcium leaching of cement-based materials produces a new material composed of C-S-H with low C/S ratio on the order of 1 and a high porosity generated by the dissolution of Portlandite (CH) crystals, which creates a new pore-size family in the micrometer range. This paper investigates the role of these two phenomena in the multiaxial inelastic and hardening deformation behavior, in compression, of calcium-leached cement pastes and mortars. From triaxial tests and SEM microscopy, it is shown that the low C/S C-S-H matrix is highly plastically deformable, which is consistent with the high degree of polymerization and the effect of the C/S ratio on the intrinsic cohesion of C-S-H. The validity of the effective stress concept is experimentally proven for calcium-leached cement paste and mortar and provides evidence that the low C/S C-S-H solid phase of the cement paste is a pure cohesive incompressible material. In turn, the large pores created by the CH dissolution provides expansion space for the incompressible solid during compressive loading. Once this porosity is filled, the volume deformability is exhausted, and the material dilates to failure. In a similar way, the early tendency of mortars to dilate is found to be a consequence of a competition between plastic material behavior of the matrix (plastic hardening) and porosity-controlled structural deformation (geometrical hardening) triggered by frictional dilation mechanisms in the Interfacial Transition Zone (ITZ).     

Adhesion improvement in glass fiber reinforced polyethylene composite via admicellar polymerization

Admicellar polymerization (polymerization of monomer solubilized in adsorbed surfactant bilayers) has been used to form a thin film of polyethylene onto the surface of milled glass fibers using sodium dodecyl sulfate as the surfactant. The decrease in ethylene pressure was used to follow the solubilization and adsolubilization processes as well as the reaction processes. An increase in initiator (Na₂S₂O₈) to surfactant ratio gave thicker and more uniform coatings of polymer onto the glass fiber surface according to SEM micrographs. Although a substantial amount of ethylene polymerized in solution according to the pressure drop, the decrease in pressure attributed to admicelle polymerization corresponded to the amount of polymer formed on the glass fiber, indicating little, if any, solution polymer deposited on the fibers. The admicellar‐treated glass fiber was used to make composites with high‐density polyethylene. The composites showed an increase in tensile and flexural strength over composites made from as‐received glass fiber, indicating an improvement in the fiber‐matrix adhesion of the admicellar‐treated glass fiber.     

Ultrasonic-vibration-assisted laser annealing of fluorine-doped tin oxide thin films for improving optical and electrical properties: Overlapping rate optimization

An ultrasonic-vibration-assisted laser annealing method was developed to enhance the performance of fluorine-doped tin oxide (FTO) thin films. The influences of ultrasonic vibration, laser scan line overlapping rate (L_OR) and laser spot overlapping rate (S_OR) on surface morphology, FTO layer thickness, RMS roughness, crystal structure and photoelectric properties of the FTO films were investigated. The results indicated that the presence of ultrasonic vibration during laser annealing could significantly enhance the film compactness, and using moderate L_OR and S_OR values resulted in significantly decreased FTO layer thicknesses and RMS roughnesses as well as slightly increased crystallite sizes, thus yielding significantly improved optical transmittance values and slightly enhanced electrical conductivity values. It was found that the optimal L_OR and S_OR values for ultrasonic-vibration-assisted laser annealing of the FTO films were 80% and 90%, respectively. The as-obtained film possessed the best overall photoelectric property with an average transmittance (400–800?nm) of 85.9%, a sheet resistance of 8.7?Ω/sq and a figure of merit of 2.51?×?10^–2 Ω^–1. This work may be of great significance in terms of performance optimization of transparent conducting oxide (TCO) thin films.     

Molecular dynamics simulation of AlN thin films under nanoindentation

A large-scale molecular dynamics (MD) simulation of nanoindentation was performed to study the structural deformation on wurtzite aluminum nitride (B4-AlN). The nanoindentation induced B4-B1 phase-transition, amorphization and dislocation glide in AlN (0001) thin films were found. It shows that the B4-B1 phase-transition path includes two processes: an anti-parallel vertical movement of N and Al atoms along the [0001] axis, followed by horizontal rearrangements of the two types of atoms. Indentation force-depth (P-h) curve shows minor and major pop-in events. Detailed analysis of the results shows that the first three minor load drops in the P-h curve are related to the nucleation of amorphous structure, whereas the subsequent major load drop is related to the dislocation nucleation and expansion. The dislocations in AlN thin film involve perfect dislocations and Shockley partial dislocations, the latter is associated with the formation of intrinsic stacking faults (SFs) type I₂ during the expansion of dislocation loops.