Flow Birefringence Research Articles

Macromolecules of poly-(12-acryloylaminododecanoic acid) in organic solvent: Synthesis and molecular characteristics

The samples of poly(12-acryloylaminododecanoic acid) were synthesized in micellar solutions of the monomer. The possibility of obtaining polymeric ionogenic surfactants of different molecular masses by varying concentration of monomeric surfactant was demonstrated. Detailed studies of the obtained polymer were performed using macromolecular hydrodynamic methods, dynamic light scattering, scanning probe microscopy and flow birefringence. The parameter of equilibrium rigidity of macromolecules (the Kuhn segment length A = 62 × 10−8 cm) and their effective hydrodynamic diameter were determined in mixed solvent (dioxane-cyclohexanol). Contributions made by optical microform and macroform effects to the observed dynamic birefringence were analyzed in detail. The intrinsic optical anisotropy of the monomer unit was estimated; it correlates well with the corresponding values for comb-shaped polymers of similar structure.

Dynamic Segment Size of the Cellulose Chain in an Ionic Liquid

Viscoelasticity and strain-induced birefringence under oscillatory shear flow of cellulose/1-buthyl-3-methylimidazolium chloride (BmimCl) solutions were measured at various temperatures covering a wide frequency zone from the terminal flow to the glassy zone for dilute (2 wt %) and semiconcentrated solution (10 wt %) to clarify the dynamical segment size of the cellulose chain. The estimated dynamical segment size, MS, obtained from viscoelasticity is much smaller than that from flow birefringence. MS estimated from dynamic birefringence was 2300 corresponding to 14 repeating glucose residues from 2–10 wt %, showing weak concentration dependence. This value is comparable to the reported value of Kuhn segment size, MK. This relationship, MS ≈ MK, holding even at dilute solution, is in contrast with the large difference (MS ≈ 5MK) for polystyrene in dilute solution, indicating that the chain rigidity affects the relationship between MS and MK.

Instabilities in stagnation point flows of polymer solutions

A recently developed microfluidic device, the optimized shape cross-slot extensional rheometer or OSCER [S. J. Haward, M. S. N. Oliveira, M. A. Alves, and G. H. McKinley, “Optimized cross-slot flow geometry for microfluidic extensional rheometry,” Phys. Rev. Lett. 109, 128301 (2012)10.1103/PhysRevLett.109.128301], is used to investigate the stability of viscoelastic polymer solutions in an idealized planar stagnation point flow. Aqueous polymer solutions, consisting of poly(ethylene oxide) and of hyaluronic acid with various molecular weights and concentrations, are formulated in order to provide fluids with a wide range of rheological properties. Semi-dilute solutions of high molecular weight polymers provide highly viscoelastic fluids with long relaxation times, which achieve a high Weissenberg number (Wi) at flow rates for which the Reynolds number (Re) remains low; hence the elasticity number El = Wi/Re is high. Lower concentration solutions of moderate molecular weight polymers provide only weakly viscoelastic fluids in which inertia remains important and El is relatively low. Flow birefringence observations are used to visualize the nature of flow instabilities in the fluids as the volumetric flow rate through the OSCER device is steadily incremented. At low Wi and Re, all of the fluids display a steady, symmetric, and uniform “birefringent strand” of highly oriented polymer molecules aligned along the outflowing symmetry axis of the test geometry, indicating the stability of the flow field under such conditions. In fluids of El > 1, we observe steady elastic flow asymmetries beyond a critical Weissenberg number,Wicrit, that are similar in character to those already reported in standard cross-slot geometries [e.g., P. E. Arratia, C. C. Thomas, J. Diorio, and J. P. Gollub, “Elastic instabilities of polymer solutions in cross-channel flow,” Phys. Rev. Lett. 96, 144502 (2006)10.1103/PhysRevLett.96.144502]. However, in fluids with El < 1 we observe a sequence of time-dependent inertio-elastic instabilities beyond a critical Reynolds number, ${\mathop{\rm Re}\nolimits} _{crit} $ Re crit, characterized by high frequency spatiotemporal oscillations of the birefringent strand. By plotting the critical limits of stability for the various fluids in the Wi-Re operating space, we are able to construct a stability diagram delineating the distinct steady symmetric, steady asymmetric and inertio-elastic flow regimes in this idealized planar elongational flow device.

Previous Experimental Polymer Rheology Versus Flow Induced Crystallization

Experimental results, which have mostly been obtained with the aid of flow birefringence, are quoted. For a series of polystyrenes insights are obtained into the adjustment times for steady flow. For shear rates of practical interest these times are extremely short compared with the times showing up in the relaxation time spectrum. The question arises, whether this spectrum can still be of influence. Measurements on polyethylenes are quoted, which are in agreement. But this means that, fortunately, in capillary rheometry mostly the steady state viscosity is measured. This statement also holds for duct flow, which has often been used for the investigation of shear induced crystallization, in particular on polypropylenes. The linear stress optical rule is recalled. It reflects the persistence of an internal equilibrium, which breaks down only at high enough shear rates. This equilibrium seems to hold for the random flight statistics of chain segments connecting entanglements. The mentioned adjustment times are already short, before the said break down occurs.

Molecular, conformational, and optical characteristics of poly(dodecylammonium-2-acrylamido-2-methylpropanesulfonate) in organic solvents

A number of samples of poly(dodecylammonium-2-acrylamido-2-methylpropanesulfonate)—a comb-like polymer with ionically bound side chains—are obtained by the polymerization of dodecylammonium-2-acrylamido-2-methylpropanesulfonate in an aqueous medium. The samples are obtained in a wide molecular-mass range. Molecular, hydrodynamic, and optical characteristics of the samples are determined by the methods of sedimentation-diffusion analysis, viscometry, and flow birefringence in dilute polymer solutions in chloroform and dimethyl sulfoxide containing small amounts of 0.1 M LiCl. It is shown that conformational and optical characteristics based on hydrodynamic and dynamo-optic investigations agree with the data available for acrylic and methacrylic polymers with the same lengths of side groups. In other words, the character of attachment (covalent or ionic) of long side chains to the backbone has no effect on the conformational and optical characteristics of macromolecules.

In-line optical techniques to characterize the polymer extrusion

In the past 15 years our research group has been creating new optical devices to characterize in real time the extrusion process. These detectors are made of a slit-die fitted at the extruder exit from where the molten polymer flows, with a pair of transparent windows that allows a light beam to pass orthogonally through the molten flow. Following the reduction of the transmitted light intensity one is able to quantify the turbidity, which is a function of the type, concentration and particle size and shape of the second phase present in the flow. By evaluating the scattering pattern of a laser beam (LALLS) it is possible to get information upon the morphology of the molten polymeric system in real time during the extrusion. With the interposition of a pair of crossed polarizers in the optical beam, rheo-polarimetry, it is possible to evaluate quantitatively the flow birefringence, which is a function of the degree of the polymer matrix orientation. POLYM. ENG. SCI., 54:386–395, 2014. © 2013 Society of Plastics Engineers

Flow birefringence and optical anisotropy of poly(N-vinylpyrrolidone) molecules

Concentration dependences of flow birefringence and viscosity of poly(N-vinylpyrrolidone) solutions in water and benzyl alcohol are investigated. The intrinsic anisotropy for a poly(N-vinylpyrrolidone) macromolecular segment, (α1 − α2) = −(82 ± 8) × 10−25 cm3, is determined from the results of birefringence measurements in benzyl alcohol. For aqueous solutions, a strong concentration dependence of the specific anisotropy of solution is obtained, a result that may be explained by the heterogeneity of coils. A model allowing for this heterogeneity is suggested. It makes it possible to fit the concentration dependence to a hyperbolic function, to separate contributions of heterogeneity anisotropy and form anisotropy to the birefringence of a solution, and to estimate the segment asymmetry parameter as p = 3.0 ± 0.5.

Conformational and optical properties of macromolecules of some aliphatic-substituted cellulose esters

Synthesized cellulose pelargonates, tridecanoates, valerates, and acetovalerates of various molecular weights are studied in chloroform, dioxane, and tetrachloroethane solutions by the methods of isothermal translational diffusion, sedimentation velocity method, flow birefringence (dynamooptical Maxwell effect), viscometry, and equilibrium electric birefringence (Kerr effect). The equilibrium polymer rigidities are determined and the role of the solvent and temperature in the formation of the conformational characteristics of the macromolecules under study is analyzed. The values of the intrinsic optical anisotropy of the monomeric units of the studied cellulose esters are experimentally determined. The contribution of the side chains to the optical anisotropy of the macromolecules of cellulose esters with aliphatic substituents is analyzed. The results obtained in this study are compared with the data on the cellulose esters with the aliphatic side substituents studied earlier. For the studied samples, the values of the longitudinal components of the monomeric unit dipoles in a nonpolar solvent are estimated.

0105 界面活性剤水溶液への塩添加によるゲル生成現象(OS1-1 非ニュートン流体の流動現象,OS1 非ニュートン流体の流動現象)

The gelation caused by the addition of salt to a cationic surfactant solution was experimentally studied. An aqueous solution of CTAB was used for cationic surfactant solution, and an aqueous solution of NaSal, a salt supplier, was injected into the CTAB solution. The gelation was observed by flow visualization, SALS experiments, and flow birefringence measurement. The experimental results showed that the gelation behavior depends on both the NaSal concentration and the injection rate. The flow birefringence measurement revealed that larger gel structures oriented more strongly in the flow direction appear at a higher NaSal concentration.

0111 圧力振動場における複数気泡近傍における2次元偏光計測(OS1-3 非ニュートン流体の流動現象,OS1 非ニュートン流体の流動現象)

When strong pressure-oscillation was applied to the two vertically aligned air bubbles in viscoelastic fluids from the bottom side, the lower-bubble rose faster than the upper-bubble. It is thought that a hydrodynamic interaction may be occurred in the fluid between air bubbles. To clarify the stress contribution on the interaction, we tried measuring the retardation profile near and between the vertically aligned small air bubbles under pressure-oscillating fields, by using the flow birefringence technique with CTAB / NaSal solution. In the case of near the bubbles (2μL for each), it was found that the strong retardations by the uniaxial strain between small air bubbles was observed at the time of the air bubbles shrinkage. The biaxial tensile flow was seen in vicinity of small air bubbles when the bubbles expanded.

Physical properties of a bent-core nematic liquid crystal and its mixtures with calamitic molecules

This article summarizes the results obtained by various experimental methods on the physical properties of a bent-core nematic liquid crystal 4-chloro-1,3-phenylene bis-4-[4′-(9-decenyloxy) benzoyloxy] benzoate (ClPbis10BB). The material exhibits unusual properties in all aspects tested. Its bend flexoelectric coefficient is 1000 times larger than in calamitics; it is viscoelastic with a large, shear-rate-dependent viscosity. Its bend and twist elastic constants are abnormally low; thus the nematic phase can be rendered to be a blue fog phase with a small amount of chiral dopant. It shows very high flow birefringence and unusually small leading Landau coefficient. It has two types of isotropic phases; at lower temperature it is probably tetrahedratic that can be transferred into the nematic phase with magnetic field. ClPbis10BB has a frequency-dependent conductivity anisotropy which is characterized by a double sign inversion. It exhibits various electroconvection (EC) patterns which are currently not understood in the frame of the standard theory of EC.

Instabilities in wormlike micelle systems

Shear-banding is ubiquitous in complex fluids. It is related to the organization of the flow into macroscopic bands bearing different viscosities and local shear rates and stacked along the velocity gradient direction. This flow-induced transition towards a heterogeneous flow state has been reported in a variety of systems, including wormlike micellar solutions, telechelic polymers, emulsions, clay suspensions, colloidal gels, star polymers, granular materials, or foams. In the past twenty years, shear-banding flows have been probed by various techniques, such as rheometry, velocimetry and flow birefringence. In wormlike micelle solutions, many of the data collected exhibit unexplained spatio-temporal fluctuations. Different candidates have been identified, the main ones being wall slip, interfacial instability between bands or bulk instability of one of the bands. In this review, we present experimental evidence for a purely elastic instability of the high shear rate band as the main origin for fluctuating shear-banding flows.

Flow and thermally induced birefringence in gas-assisted tubular injection moldings: Simulation and experiment

Various components of birefringence in polystyrene (PS) and polycarbonate (PC) tubular moldings, obtained by gas-assisted injection molding (GAIM), are measured and simulated considering both flow- and thermally induced stresses. The flow- and thermally induced stresses are calculated using nonlinear and linear viscoelastic theories, respectively, based on the flow and temperature histories that the polymer experiences during the GAIM cycle. Flow-induced birefringence components are calculated from flow stresses using the stress optical rule, while thermally induced birefringence components are calculated from thermal stresses using a photoviscoelastic model. The simulated total residual birefringence takes into account the contributions of both flow- and thermally induced birefringence generated during the melt injection, gas injection, and cooling stages of GAIM. The simulated results are in better agreement with the measured birefringence in PS moldings than in PC moldings. Considering both thermal and flow birefringence, simulations provides a better description of the experimental results indicating that, in GAIM moldings, the birefringence near the mold was caused mainly by flow stresses while that located towards the polymer/gas interface was caused mainly by thermal stresses. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Hydrodynamic, conformational, and optical properties of cellulose tridecanoate molecules in solutions

Cellulose tridecanoates of various molecular weights were synthesized, and their characteristics in chloroform and tetrachloroethane solutions were studied by methods of translational diffusion, velocity sedimentation, flow birefringence (Maxwell’s method), and viscometry. The effects of solvent and temperature on the conformational characteristics of the macromolecules under consideration were examined. The anisotropy of the monomeric unit of cellulose tridecanoates was studied, and the contribution of pendant chains to the optical anisotropy of macromolecules of cellulose esters with aliphatic substituents was analyzed.

Influence of the length of side substituents on optical and electro-optical properties of polydialkoxyphosphazenes

The electro-optical and dynamo-optical properties of dilute solutions of polydialkoxyphosphazenes with different lengths of side substituents are studied. Sign inversion of the specific Kerr constant and of the reduced flow birefringence for the number of carbon atoms in side aliphatic chains, m, varying from 3 to 7 is ascertained. The anisotropy of optical polarizability of a monomer unit changes in the studied series of polydialkoxyphosphazenes. It attains the minimum values and changes its sign from positive to negative at m = 5–6. The resulting data provide an explanation for the mesomorphism of these polydialkoxyphosphazenes, which is connected with the possibility of alternative orientation of monomer units.

Characterization of cellulose nanowhiskers: A comparison of two industrial bio-residues

Cellulose nanowhiskers separated from two different industrial residues, sludge from cellulose production (CNWSL) and lignin residue from ethanol production (CNWER), were compared in order to evaluate their characteristics and their potential as a source for the production of cellulose nanowhiskers (CNWs). It was found that CNWSL and CNWER suspensions exhibited flow birefringence when they were studied through cross-polarized filters. Transmission electron microscopy (TEM) study showed that the CNWSL were longer (377 nm) than CNWER (301 nm). It was also demonstrated that most CNWSL had nanowhiskers between 375-449 nm and CNWER between 300-374 nm. The UV/Vis spectroscopy showed a stronger interference in the UV and visible region for the CNWSL films. The crystallinity, obtained by X-ray analysis, was higher for CNWSL (86%) than for CNWER (78%). Finally, the thermal stability appeared to be slightly higher for the CNWER than for CNWSL. Both studied residues seem to be suitable sources for large-scale production of CNWs.

Supramolecular Structure Characterization of Cellulose II Nanowhiskers Produced by Acid Hydrolysis of Cellulose I Substrates

Cellulose II nanowhiskers (CNW-II) were produced by treatment of microcrystalline cellulose with sulfuric acid by both controlling the amount of H(2)SO(4) introduced and the time of addition during the hydrolysis process. The crystalline structure was confirmed by both XRD and (13)C CP-MAS NMR spectroscopy. When observed between crossed polarizers, the cellulose II suspension displayed flow birefringence and was stable for several months. The CNW-II nanowhiskers were significantly smaller than the cellulose I nanowhiskers (CNW-I) and had a rounded shape at the tip. The CNW-II average length and height were estimated by AFM to be 153 ± 66 and 4.2 ± 1.5 nm, respectively. An average width of 6.3 ± 1.7 nm was found by TEM, suggesting a ribbon-shape morphology for these whiskers. The average dimensions of the CNW-II elementary crystallites were estimated from the XRD data, using Scherrer's equation. A tentative cross-sectional geometry consistent with both XRD and NMR data was then proposed and compared with the geometry of the CNW-I nanowhiskers.

Rheophysical Properties of Fluorinated Nonionic Micellar Phases

Micellar phases can be used as templates for the preparation of mesoporous silica materials. Fluorinated and hydrogenated surfactants can provide a large variety of well-defined micellar structures: spherical and cylindrical micelles as well as more complex structures such as lamellar or sponge phases can be formed in various thermodynamic conditions. However, the preparation of ordered mesoporous materials from these organized media is not always successful for a reason not known at the moment. It thus seems of the highest importance to properly characterize the micellar solution prior to the addition of the silica precursor during the material synthesis. In this paper, we describe some rheophysical properties of the micellar phase L(1) prepared with a fluorinated surfactant, the formula of which is C(7)F(15)C(2)H(4)(OC(2)H(4))(8)OH, labeled as R(F)(7)(EO)(8). This surfactant forms micelles in water, and the direct micellar phases have been characterized in a wide range of temperatures and surfactant concentrations. The rheological properties of the L(1) phase have also been studied as a function of temperature and concentration. Under steady and dynamic flow conditions, the solutions behave like Newtonian or shear thinning fluids depending on the temperature and surfactant concentration. A crossover between G' and G" is observed in the solution at the concentration of 20 wt % and at the temperature of 10 °C, suggesting the presence of long entangled micelles in solution at this temperature. When subjected to the action of a shearing device, the 20 wt % solution becomes optically anisotropic and shows flow birefringence, but the average orientation of the micelles quantified by the extinction angle χ shows an unexpected behavior when the shear rate is gradually increased.

Flow birefringence property of desmin filaments.

We have investigated the flow birefringence property and assembly process of desmin, a muscle specific intermediate protein. Solution of non-polar desmin filaments showed birefringence when aligned in the sheared flow. The amount of birefringence of desmin filaments was considerably lower when compared with that of F-actin solution. Assembly of desmin from soluble state was followed by the birefringence measurements. At any desmin concentrations examined, the degree of flow birefringence increased rapidly just after the addition of the assembly buffer and reached a saturated level within 30 min. The time to reach half-maximal values of flow birefringence slightly but definitely depended on the initial soluble desmin concentrations. The plotting of the initial velocity of the assembly against the soluble desmin concentrations showed a slope of 1.4. This result suggested that the assembly process detected by flow birefringence measurements followed second-order kinetics, and the process corresponded to the second step of the three stage model for type III intermediate filament assembly proposed by Herrmann and his colleagues; the annealing of unit length filaments into filaments.

Interplay between elastic instabilities and shear-banding: three categories of Taylor–Couette flows and beyond

In the past twenty years, shear-banding flows have been probed by various techniques, such as rheometry, velocimetry and flow birefringence. In micellar solutions, many of the data collected exhibit unexplained spatiotemporal fluctuations. Recently, it has been suggested that those fluctuations originate from a purely elastic instability of the shear-banding flow. In cylindrical Couette geometry, the instability is reminiscent of the Taylor-like instability observed in viscoelastic polymer solutions. The criterion for purely elastic Taylor–Couette instability adapted to shear-banding flows suggested three categories of shear-banding depending on their stability. In the present study, we report on a large set of experimental data which demonstrates the existence of the three categories of shear-banding flows in various surfactant solutions. Consistent with theoretical predictions, increases in the surfactant concentration or in the curvature of the geometry destabilize the flow, whereas an increase in temperature stabilizes the flow. However, experiments also exhibit some interesting behaviors going beyond the purely elastic instability criterion.