Small-angle Light Scattering Patterns Research Articles

Rheo-optics of giant micelles: SALS patterns of cetyltrimethylammonium tosylate solutions in presence of sodium bromide

In this work, we present a systematic study based on Small-Angle Light Scattering (SALS) patterns of the simple shear flow response of semi-diluted solutions of cetyltrimethylammonium tosylate (CTAT; 5.5 wt.% - 0.12 M) in the presence of sodium bromide (NaBr) at different [NaBr]={0,0.12,0.19,0.25,0.3} M concentrations. We evidence a relationship between rheological and light scattering data that reveals a transition into a fast-breaking regime in the dynamics of wormlike micelles formed by the CTAT/NaBr system (Macías et al., 2011; Fierro et al., 2021). This transition into a micellar fast-breaking regime with salt addition ([NaBr]≥0) appears marked by the following features: (i) a decrease in the relaxation time of the material λ0, accompanied by (ii) a decrease of the viscosity level at low shear rates η0 (Macías et al., 2011; Fierro et al., 2021; Schubert et al., 2003; Alkschbirs et al., 2015; Bandyopadhyay et al., 2003). With these, (iii) the formation of butterfly-like patterns is recorded originating from concentration fluctuations, evolution that is accompanied by: (iv) shear banding in the form of non-monotonic flow curves and (v) slow oscillatory transient responses in start-up flow tests captured theoretically with the Bautista–Manero–Puig (BMP) model. In addition, the Cox–Merz rule is fulfilled at molar salt-to-surfactant ratios of R≥1.5. This results in shorter structure-recovery time-scales than the characteristic-time of the flow (Macías et al., 2011; Fierro et al., 2021; Manero et al., 2002). In the case of the elastic modulus G0, the variation was small, which suggests a transition from an entangled to a multiconnected network, as suggested by Kadoma & van Egmond (1997), Kadoma et al. (1997) and Fierro et al. (2021). From a theoretical perspective, we provide predictions for the shear–stress and the first normal-stress growth coefficients in transient start-up simple shear flow using the BMP model. Here, banding R=1.5 solutions display overshot responses at relatively high shear rates (γ̇=10−30s−1), in-line with experimental findings on the start-up flow of wormlike micellar solutions (Soltero et al., 1999; Lerouge et al., 2004; Hu & Lips 2005; Pipe et al., 2010; Mohammadigoushki et al., 2019). Our results are consistent with those reported in other investigations (Macías et al., 2011; Fierro et al., 2021; Schubert et al., 2003; Alkschbirs et al., 2015; Bandyopadhyay et al., 2003; Kadoma et al., 1997; Soltero et al., 1999; Lerouge et al., 2004; Hu & Lips 2005; López-Barrón et al., 2014) and reveal the influence of the Br−-ion used on the mechanical and optical response of the CTAT-NaBr system.

Rheological studies of molecular effect and processing conditions on blown film property of polyethylenes

Statistically designed blown film experiments were conducted to investigate the effects of molecular weight distribution and processing conditions on film properties of three linear low-density polyethylenes in term of their rheological characteristics. The complex interactions between molecular and processing parameters to film properties can be understood rheologically by relating the ratio of polymer largest molecular relaxation time, τmax, to a process time, tp. When represented in term of the rescaled processing time, τmax/tp, namely as Deborah Number (De), a master curve is obtained for the physical properties of these films blown under similar processing condition, while the variations of processing conditions on film properties can be characterised by families of De master-curves. The influence of complex thermo-mechanical deformation history on crystallisation during blown film processing can be highlighted with complementary pre-shear flow stress relaxation and flow-induced crystallisation experiments by Small Angle Light Scattering patterns.

Polycaprolactone/α-Alumina and Hydroxyapatite-based Micro- and Nano- Structured Hybrid Fibers

ABSTRACTThe micro- and nanostructured phase behavior of non-woven hybrid electrospun fibers of Polycaprolactone (PCL-f), Polycaprolactone/α-Alumina (PCL/AA) and Polycaprolactone/Hydroxyapatite (PCL/HA) were elucidated. Nanoparticles of Hydroxyapatite featured 7-20 nm while α-Alumina was 500 nm in average size. Analysis by Transmission Electron Microscopy (TEM), Small-Angle Light Scattering (SALS), Polarized Optical Microscopy (POM) and Differential Scanning Calorimetry (DSC) enabled us to suggest a simple structural model for the series of hybrid fibers. PCL with a molecular weight of 70,000 g/mol was dissolved in chloroform. POM exhibited qualitative birefringent regions for all samples at the microscale level. Furthermore, polarized light distinguished between amorphous and micro-ordered structures along the fibers. On the other hand, SALS patterns suggested a needle-like morphology for all fibers. The influence of both, Hydroxyapatite and α-Alumina, was apparent in the SALS patterns of the PCL semicrystalline phase. Thermal analysis by DSC showed that the crystalline phase of PCL was disrupted by the presence of the inorganic nanoparticles. TEM micrographs showed that Hydroxyapatite and α-Alumina nanoparticles were embedded along the structure of PCL microfibers.

Shear-Induced Phase Separation in Polyelectrolyte/Mixed Micelle Coacervates

A quantitative study of the shear-induced phase separation of a polycation/anionic-nonionic micelle coacervate is presented. Simultaneous rheology and small-angle light scattering (SALS) measurements allow the elucidation of micrometer-scale phase separation under flow in three coacervate solutions. Below 18 degrees C, all three of the coacervate solutions are optically clear Newtonian fluids across the entire shear rate range investigated. Once a critical temperature range and/or shear rate is achieved, phase separation is observed in the small-angle light scattering images and the fluid exhibits shear thinning. Two definitive SALS patterns demonstrate the appearance of circular droplets at low shear rates near the critical temperature and ellipsoidal droplets at higher temperatures and shear rates. The shear-induced droplets range in size from approximately 1 to 4 mum. The ellipsoidal droplets have aspect ratios as high as 4. A conceptual picture in which shear flow extends the polyelectrolyte chains of the clear coacervate liquid phase is proposed. The extended chains create interpolyelectrolyte-micelle interactions and promote expulsion of small ions from the complex, resulting in the formation of micrometer-scale phase-separated droplets.

Transient interfacial tension and morphology evolution in partially miscible polymer blends

The influence of molecular weight asymmetry across an interface on the transient behavior of the interfacial tension is investigated for two different polymer combinations, polybutadiene (PBD)/polydimethylsiloxane (PDMS) and polybutene (PB)/PDMS. This choice ensures a minor diffuse interface using the first combination and a very diffuse interface in the latter case. Measurements of the interfacial tension as a function of time are carried out using a pendent/sessile drop apparatus at different temperatures ranging from 0 °C to 80 °C. Variations in the transient interfacial tension are attributed to diffusion of the lower molecular weight components from one phase into the other and the most pronounced changes are measured for the most diffusive systems (low molecular weight and high polydispersity) when diffusion goes from the drop into the matrix. By reversing the phases, only minor changes in the transient interfacial tension are measured. This is due to a fast saturation of the drop-phase since the drop volume is much smaller than that of the continuous phase. In all cases investigated, after a sufficient time a steady value of the interfacial tension is reached. In order to estimate the characteristic diffusion times of the migrating species, a discrete solution of the diffusion equation and a kinetic model from literature are applied. Results obtained are in line with the experimental observations. The importance of a changing interfacial tension on morphology development is studied on dilute (1%) blends, using two in situ techniques: small angle light scattering (SALS) and optical microscopy (OM). The SALS patterns yield the time evolution of the drop size, which is subsequently compared with the morphology following from OM. Depending on the diffusivity of the system, the morphology development is dominated by either diffusion or coalescence. Existing sharp-interface drainage models indeed do not apply for the diffuse blends and an improved quantitative estimation of the value of the critical film thickness is needed.

小角光散乱法によるポリアミド6射出成形品の変形挙動研究

Deformation behaviors of microstructures of polyamide 6 (PA6) and elastomer-alloyed PA6 were investigated using small angle light scattering (SALS) techniques. The SALS pattern shows that PA6 has incomplete spherulitic structures. The change of SALS pattern with elongation suggests that the structures deform with external deformation up to yield strain. Then the SALS patterns discontinuously change with necking elongation and suggest that the apparent size of the spherulitic structures becomes very larger and that the degree of orientation decreases. Next lobe-streak patterns, which are considered to be due to sheaf-like structures, were observed beyond the necking elongation. These changes in SALS patterns can be explained by the reconfiguration models of adjoining spherulitic structures presented in this paper. The SALS patterns of elastomer-alloyed PA6 similarly show the existence and deformation of incomplete spherulitic structures up to yield strain. However, neither spherulitic nor sheaf-like structures were observed in the SALS patterns beyond the yield strain.

Rheology in Film Processing (1)-High-Order Structural Change of Biaxially Stretched Films during Two-Way Successive Stretching Process-

Studies on high-order structures of poly(ethylene terephtalate) films prepared by uniaxial and biaxial stretching processes were done using Small-Angle Light Scattering(SALS). On uniaxial stretching, a butterfly shape was obtained in the Hv light scattering pattern, which indicated the existence of a sheaflike crystalline high-order structure in the stretched films. Numerical calculations based on the sheaf array model were carried out for the interpretation of experimentally obtained SALS patterns. Results of the calculated patterns showed good agreement with experimental ones. In the case of biaxially stretched films, the SALS patterns changed remarkably depending on the stretching conditions and stretching systems. Higher stretching temperatures were found to be effective in the two-way successive stretching system since the high-order structure formed at the initial uniaxial stretching was not easily destroyed by the second stretching. Further, it became obvious that a three step stretching system in which machine direction stretching was divided into two steps was effective in obtaining biaxially stretched films having 8 leaf SALS patterns including the butterfly shape.

Rheo‐optical studies of the effect of shear flow on the structure of elastomer blends

AbstractThe effect of shear flow on the structure of a phase‐separated, near‐critical blend of 50/50 (w/w) poly(styrene‐ran‐butadiene) and polybutadiene was studied with two different custom‐built rheo‐optical instruments that combined polymer melt flow and small‐angle light scattering (SALS). The deformation of the phase domains during shear flow was nonaffine, and the SALS patterns evolved from a spinodal ring (SR) pattern to a squashed SR with two high‐intensity lobes, to an H‐pattern, to a butterfly pattern with a dark streak along the equator, and finally to a steady‐state, elliptical pattern. The SALS patterns were explained in terms of a network model, in which the strands of the network first orient in the flow direction, then extend in this direction, and finally break up into droplets aligned in the flow direction. According to this picture, the strands in the vorticity direction do not deform until relatively high strains, after which the periodicity of the network begins to disappear. Supporting this model was the observation that the transitions between the different SALS patterns corresponded to inflections and/or maxima in the shear stress or first normal stress difference. Increasing the shear rate changed the kinetics of the structure evolution and reduced the size of the phase‐separated droplets in the steady state. No evidence was obtained for flow‐induced miscibility. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1725–1738, 2004

STRAIN FIELD INDUCED ANISOTROPIC PHASE SEPARATION OF POLYMER BLENDS

Using a small angle light scattering (SALS) technique, we investigated the anisotropic SALS patterns formed in a phase separating polystyrene (PS) and poly (vinyl methyl ether) (PVME) blend under strain fields. We have found that, in addition to the interfacial relaxations, the stretching of the polymer chains plays an important role in the phase separation of the PS/PVME blend under a strain field. Two novel scattering patterns and the strain induced slowing down of the phase separation dynamics are observed. The experimental results are compared to a theoretical calculation based on a time-dependent Ginzburg-Landau equation incorporated with the chain stretching effect.

Rheo-optical measurement of the interfacial tension of aqueous biopolymer mixtures

Aqueous biopolymer mixtures are characterized by a very low interfacial tension, challenging most of the existing methods to measure this quantity. Here we apply a fast and accurate rheo-optical methodology, based on small angle light scattering (SALS), to obtain the interfacial tension of an aqueous gelatin–dextran biopolymer mixture. Two methods are compared. The first one is based on the analysis of the SALS patterns during fibril break-up under quiescent conditions, the second uses the anisotropy of the SALS patterns during relaxation after steady state shearing. The resulting values of the interfacial tension, obtained by the two methods, are in good agreement. In addition, the effect of temperature on the interfacial tension has been studied.

小角光散乱法によるポリエチレンテレフタレートフィルムの延伸挙動の研究

Studies on the stretching behavior of PET films were performed by small-angle light scattering (SALS). On uniaxial stretching, a butterfly shape was obtained in the Hv light scattering pattern, which indicates the existence of a sheaflike crystalline superstructure in the stretched films. In the case of biaxially stretched films, the SALS patterns change remarkably depending on the stretching conditions such as stretching temperature and stretching ratio. A three step stretching system in which machine direction stretching is divided into two steps is effective in obtaining biaxially stretched films having 8 leaf SALS patterns including the butterfly shape.Numerical calculations based on the sheaf array model were carried out for the interpretation of experimentally obtained SALS patterns. Results of the calculated patterns show good agreement with experimental ones.

Rheology and structure of isotactic polypropylene near the gel point: quiescent and shear-induced crystallization

Crystallizing isotactic polypropylene (iPP) develops large-scale spherulites and thick threads, large enough for observation by optical microscopy, and undergoes a liquid-to-solid transition as an expression of increased connectivity of the structure. In order to relate the time scales of structural and rheological changes, we measured time-resolved small-angle light scattering (SALS) and transmittance properties in a single experimental run, which then was repeated in an optical microscope for direct observation of growth of large-scale structures, and in a rheometer for mechanical spectroscopy. The results for quiescent and shear-enhanced melt crystallization of a high molar mass iPP are presented. In quiescent crystallization, iPP nuclei are only formed in the beginning (and not in later stages) and grow simultaneously at the same rate, which leads to spherulites of equal size. The critical gel point is reached close to the instant of the maximum of density fluctuations, but before spherulites impinge. Crystallinity estimates from Hv SALS (estimation method of Stein) are much higher than values from DSC. The discrepancy may be caused (in addition to the simplifying assumptions in the estimate) by the enhanced crystallization in the rheo-optical cell due to surface and sample loading effects. Shear flow induces anisotropic molecular conformations, preferably in the high molecular weight component of the iPP sample. The resulting orientation fluctuations (of highly oriented long chains and less oriented short chains) cause (1) an increase in nucleation rate, (2) possibly an increase in crystallization rate and (3) formation of highly elongated structures (threads) which are visible in the optical microscope and in anisotropic SALS patterns. The threads thicken until, at later stages, additional spherulites start to grow, presumably from the shorter chains and nucleated on by the threads.

Shear-induced band texture of side group liquid crystalline polymers

The shear-induced band texture of conventional end-on fixed side group liquid crystalline polymers (LCPs) has been investigated by using polarizing optical microscopy (POM), small angle light scattering (SALS) and infra-red dichroism techniques. The band spacing is about 1 μm, which increases very slightly on increasing the temperature of shearing and is independent of shearing rate within the range studied. The band texture is not seen to exhibit an interchange of dark and bright bands on rotation of the sample with respect to the polarizer/analyser, but a typical periodical structure is reflected by the SALS patterns of the band texture. The relaxation behaviour of the bands indicates that the band texture formed here is the result of the orderly aligning of domains exhibiting the focal-conic texture, and this is totally different from the case of main chain LCPs where the band texture is substantially an optical effect of the periodic zigzag or sinusoidal structure of parallel aligned microfibrils. Infra-red dichroism and rotating parallel-plate shearing measurements show that the axes of the backbone of the polymer tend to orient in the shearing direction and the end-on fixed mesogenic side groups tend to align perpendicular to the shearing direction.

ORIENTATION DYNAMICS OF MAGNETORHEOLOGICAL FLUIDS SUBJECT TO ROTATING EXTERNAL FIELDS

The formation and orientation of field-induced structures in magnetorheological (MR) fluids subject to rotating magnetic fields have been studied using two optical methods: scattering dichroism and small angle light scattering (SALS). The SALS patterns show how these chain-like aggregates follow the magnetic field with the same frequency but with a retarded phase angle for all the frequencies measured. Using scattering dichroism two different behaviors for both, dichroism and phase lag, are found below or above a critical frequency. Experimental results have been reproduced by a simple model considering the torques balance on the chain-like aggregates.

Crystallization Studies of LLDPE during Tubular Blown Film Processing

Abstract The final physical properties of semi-crystalline blown films are highly dependent on the crystalline morphology and orientation of polymer chains within the film. Simultaneous on-line SALS (Small Angle Light Scattering) and IR (Infrared) temperature measurements were successfully used to study crystallization during tubular blown film extrusion of LLDPE. SALS patterns were recorded at various vertical positions along the bubble. For LLDPE, an undeformed spherelulitic structure is formed if the stress level during processing is not too high. The change in average scattered intensity with axial position can be described using multiple step Avrami kinetic processes in parallel. The first step accounts for crystal growth and corresponds to the well-known temperature plateau. The later processes start with the impingement of the growing spherulites and may reflect secondary crystallization and orientation processes. Because the magnitude of the average intensity is responsive to changes in process conditions, the on-line SALS system is potentially a useful tool for monitoring process-property interactions.

Flow-Induced Anisotropy in Mixtures of Associative Polymers and Latex Particles

The effect of associative polymers on the structure and rheological behavior of colloidal suspensions is discussed. Adding associative polymer is known to increase the viscosity of the suspensions. At high shear rates the increase is close to what could be expected on the basis of the hydrodynamic effects of the added polymer. At low shear rates the viscosity increases much more. Small-angle light scattering (SALS) during flow is used here to investigate the underlying structural mechanisms. The SALS patterns indicate that the associative polymer changes the particulate structure: characteristic butterfly patterns appear even at relatively low particle volume fractions. They are not present in the suspensions without associative polymer. The patterns indicate that fluctuations in particle concentration are more pronounced in the flow direction than in the vorticity direction and that anisotropic particulate structures with an orientation along the vorticity direction develop. The evolution of their characteristic length scale during flow has been followed over time. Changing the hydrophilic part of the polymer from polyacrylamide to polyacrylic acid induces stronger associative interactions. In the suspensions this results in a reduction of the relative viscosity rather than an increase. The difference in degree of associativity between the polymers also has an effect on the SALS patterns in the suspensions both at rest and during flow. The rheology as well as the SALS suggest the presence of a strong polymer network in the second system. The competition between adsorption of the associative polymer on the particles with the intermolecular associations between the polymer chains seems to be responsible for the observed differences.

Light Scattering and Small-Angle Neutron Scattering Studies of Structures in a Semidilute Polymer Solution Induced under Oscillatory Shear Flow

Oscillatory-shear-flow-induced structures of a semidilute polymer solution of ultrahigh molecular weight deuterated polystyrene in dioctyl phthalate were investigated by using the small-angle light scattering (SALS) and the small-angle neutron scattering (SANS). Under a fixed strain amplitude of oscillatory shear flow at 4.8, we observed the shear-induced structures as a function of the angular frequency (ω) and the strain-phase. At low ω, butterfly patterns, which are the scattering patterns unique to the shear-induced structures formed in semidilute polymer solution, were observed by SALS and isotropic patterns with weak scattered intensities were obtained by SANS. At high ω, on the other hand, SANS showed butterfly patterns and SALS showed almost isotropic patterns. These results indicate that the anisotropic structures developed under oscillatory shear flow become smaller with increasing ω. From the SALS and SANS patterns, we obtained scattering profiles parallel and perpendicular to the flow directio...

Small-angle light scattering study of droplet break-up in emulsions and polymer blends

The potential of using small–angle light scattering (SALS) to probe morphological changes induced by flow in immiscible polymer blends is investigated. Well–defined flow histories are shown to result in SALS patterns that are characteristic for the morphology involved. The pertinent structural change caused by either suddenly applying flow or drastically increasing the shear rate is the stretching of inclusions into long filaments, which subsequently break up by Rayleigh instabilities. Scattering models are developed to calculate the SALS patterns resulting from a filament with a sinusoidally disturbed surface and from a series of aligned spheres. These models capture the main features of the measured SALS patterns and are used to extract quantitative morphological information of the system. This is demonstrated by comparing calculated and measured results for droplet and filament size. In this manner an in situ, time-resolved technique becomes available to follow flow-induced structural changes such as those occurring during processing of blends.

Shear induced textures of thermotropic acetoxypropylcellulose

Acetoxypropylcellulose is a thermotropic cellulose derivative which is cholesteric from below room temperature up to 170 °C. Its textures during and after shear flow were studied by optical microscopy and small-angle light scattering (SALS) light scattering. The main features are similar to those occurring in hydroxypropylcellulose solutions, i.e., a polydomain texture evolving into a striated texture, as seen by optical microscopy. Elliptical or else four lobes with a streak are seen in the SALS patterns. Defects appearing as short dark lines not aligned with the flow direction are shown to be responsible for the existence of the four lobes of the SALS patterns. In addition these defects seem to be located where the band texture develops during relaxation.

Simultaneous recording of Hv and Vv small-angle light-scattering patterns for crystallization kinetics studies

Simultaneous recording of Hv and Vv small-angle light-scattering patterns for crystallization kinetics studies