Elongational Flow Field Research Articles

Surface-Free Single-Molecule Force Spectroscopy

Mechanical forces play key roles throughout biology. Most existing methods for probing forces in/between molecules and cells, such as the AFM, optical tweezers, magnetic tweezers, traction force microscopy, etc., require molecules to be tethered to the surfaces of cover glasses or beads. However, surface tethering has a number of drawbacks. First, the conjugation chemistry for tethering can be challenging. Second, the spatial confinement and the nonspecific attraction from the surface can induce artifacts to the dynamics of the molecule. For semi-rigid objects, such as actin filaments, surface attachment could also induce bending and twisting of the filament, complicating the applied force profile. To overcome these issues, we present a surface-free force spectroscopy method that uses a high-speed cross-slot hydrodynamic trap, capable of stretching molecules and cells with hydrodynamic drag. The trap is based on a glass microfluidic cross-slot flow chamber. Buffer flows in from two opposite directions and exits via the two orthogonal outlets to create an elongational flow field with a stagnation point in the center. As a result, objects near the stagnation point are stretched by the viscous drag from the flow. In addition, the pressure in one of the outlet reservoirs is electronically controlled with a high-speed feedback algorithm to stabilize the object at the stagnation point. Thanks to the high-speed feedback, we can apply much higher flow rate and therefore much higher stretching force on the trapped object than with the cross slot alone. We demonstrate tension-dependent actin severing, extension of von Willebrand Factor (a key protein in haemostasis that changes conformation in response to hydrodynamic stress in blood stream), overstretching of double strand DNA, and stretching deformation of red blood cells. In summary, the high-speed cross-slot hydrodynamic trap can be a powerful, surface-free alternative to more commonly used force spectroscopy methods.

Process‐induced phase and crystal morphologies in water‐assisted injection molded polypropylene/polymeric β‐nucleating agent blend parts

By adding a polymeric β‐nucleating agent (acrylonitrile–styrene copolymer, SAN), in situ microfibril reinforced isotactic polypropylene (iPP)/SAN blend parts with high contents of β‐form crystals and transcrystals were molded via water‐assisted injection molding (WAIM). Thanks to the unique stress and temperature fields occurring during the WAIM, SAN microfibers formed across the whole residual wall of iPP/SAN blend parts with relatively large thickness. Numerical simulations on high‐pressure water penetration and cooling stages of the WAIM were carried out to reveal the stress and temperature fields. Comprehensive analysis of both experimental and simulated results showed that not only the shear flow field but also elongational flow field occurring during the WAIM was responsible for the formation of SAN microfibers and unique crystal morphology distribution in the WAIM iPP/SAN blend part. Moreover, during the WAIM, the high cooling rate also played an important role in the formation of both phase and crystal morphologies. The preferential formation of transcrystals in the inner layer of WAIM iPP/SAN blend part could be ascribed to the strong elongation, rather than the strong shear. It was believed that the quantification of stress and temperature fields of the WAIM via numerical simulation could provide a guidence for molding high‐performance products. POLYM. ENG. SCI., 55:1698–1705, 2015. © 2014 Society of Plastics Engineers

Effects of a flow field on amyloid fibrillogenesis in a β-lactoglobulin solution

The effects of a flow field on the amyloid fibrillogenesis of β-lactoglobulin (βLG) were investigated using a flow birefringence method and AFM imaging experiments. A 4wt% βLG aqueous solution was incubated at pH 2 and 80°C. A flow field was then applied by stirring at 250 and 474rpm. An incubation without stirring was used as a control sample. Flow birefringence measurements were taken at room temperature from the incubated sample solutions in which an elongational flow field was used. The birefringence pattern obtained indicated that the fibrils formed by the incubation were rigid rod-like molecules. Birefringence relaxation experiments revealed at least two relaxation processes, suggesting a double peaked distribution function for fibrils length. The length distribution of fibrils expected from the birefringence experiments was confirmed by the AFM images of amyloid fibrils. The order of the expected length of the resultant fibrils in both longer and shorter length distributions was those stirred at 250rpm≅474rpm>0rpm. The effects of the flow field applied during the incubation on amyloid fibrillogenesis was discussed on the basis of the rate process consideration. The present results demonstrated that the flow field should be considered as an important factor that regulates the fibrillogenesis of globular proteins.

How Do Polymer Chains with Different Topologies Pass Through a Cylindrical Pore under an Elongational Flow Field

Translocation of polymer chains through nanopores( ultrafiltration behavior) is not only a basic problem in polymer physics and biophysics,but also related to many physical and chemical processes,such as gene transfection,protein transportation,and separation of polymer chains by size exclusion chromatography.However,due to the lack of appropriate polymer model samples as well as ideal elongational flow fields,the ultrafiltration behavior of polymer chains has not been systematically explored experimentally for a long time.To deeply understand the ultrafiltration behavior of polymer chains and verify relevant theory,we have made much effort on this subject in the past decade. In this article,we'll first review the classic theory of polymer chains passing through nanopores,and then provide an overview of our recent theoretical and experimental research achievements in this field,more specifically,we have( 1) successfully observed the"coil-to-stretch"first-order transition of polymer linear chain passing through nanopores,and found that the critical flow rate( q c) is indeed independent on the chain length,but dependent on the pore size,inconsistent with de Gennes' prediction;( 2) developed a unified theoretical description of polymer chains with different topologies passing through a nanopore;( 3) systematically studied the effects of polymer chain topology and pore structure on the ultrafiltration behavior of polymer chains; and( 4) successfully applied the ultrafiltration method into the separation of polymer chain mixtures and the rapid transition between various polymeric aggregated structures.

The trend of membrane structure evolution under shear and/or elongation flow fields of immersion precipitated spun tapes

The trend of membrane structure evolution under shear and/or elongation flow fields was investigated via immersion precipitated tape spinning of a model cellulose acetate (CA)/acetone/formamide/water precursor at shear rates of 231–1005s−1 and/or draw ratios of 1–4. The effects of flow fields, tape thickness and material-based parameters were partitioned via comparing the tape structures with their corresponding cast membranes (relaxed flow fields effects), using scanning electron microscopy (SEM). The flow field application induced tape skin thinning, bulk macrovoid intensification, and microvoids size and ligament thickness increase. Nonetheless, it did not substantially change the macrovoids areal percent (MV%). In contrast, the MV% of the corresponding cast membranes was altered enormously (up to 50%) by their thickness decrease. The skin thicknesses of the cast and corresponding tape membranes were in the order of 1.1–7.2 and 0.25μm, respectively. The membrane skin thickness decrease not only intensified macrovoid formation but also changed the sponge-like structure of some cast membranes into the finger-like structures in their corresponding tape spun membranes. The membrane precursor transition toward the two phase coexistent compositions of the CA/acetone/formamide phase diagram via diminution of solvent mixture quality raised its critical thickness (LC) of macrovoid elimination and its finger-like to sponge-like structure evolution. It also changed the trend of membrane structure evolution under the applied flow fields. The increase of spun tape membrane thickness lowered the flow field׳s contribution to the macrovoid formation while omitted them after crossing 3LC.

Evaluation of flow-induced nanoclay orientation and microstructural stability in polyethylene/clay nanocomposites via melt rheological and thermal analysis

AbstractThe effects of shear rate upon the flow-induced nanoclay orientation and morphological stability in film blown polyethylene clay nanocomposites were studied by means of linear and nonlinear rheological characterization parallel with differential scanning calorimetry and X-ray diffraction (XRD) analyses. Nanocomposite samples were prepared using a modular twin screw extruder followed by film processing technique. XRD analysis performed on film samples showed that the samples exhibited intercalated/exfoliated microstructure. The 3D physical networks were formed by the clay nanolayers in the structures of undrawn samples. However, the breakdown of the clay physical networks during film processing as a result of the imposed shear field within the die area and also an elongational flow field was evidenced. Time sweep test performed at various shear rates and shearing times using a rheometric mechanical spectrometer showed that, in all samples, the time required for the restructurization of the clay nanolayers during relaxation of the melt was found to be higher than 3600 s.

Composites of sisal fiber/polypropylene based on novel vane extruder: Effect of interface and damage on mechanical properties

Sisal fibers were pretreated by alkali and maleic anhydride, and then mixed with polypropylene to fabricate sisal fiber-reinforced composites by a self-made vane extruder based on elongational flow field. Maleic anhydride-grafted polypropylene was used as compatilizer to increase the fiber/matrix interactions. The influence of treatment on the fibers structure, the damage to fibers in processing, interfaces of composites and the mechanical properties of composites were investigated. It was observed that the surface of treated fibers was improved obviously compared with that of untreated fibers, which was believed to increase the adhesion between the fibers and matrix. However, the treated fibers were more likely to be damaged during processing. In comparison to unmodified system, the incorporation of treated fibers could significantly enhance the mechanical properties of composites, especially adding the compatilizer of maleic anhydride-grafted polypropylene. The flexural and impact strengths were maximum for the sisal fiber/polypropylene and maleic anhydride-grafted polypropylene composites, and its tensile strength was also improved significantly. The major contribution of this change should be that the morphology of fibers could be well preserved in elongational flow field, which based on the vane extruder showed a good application in fiber-reinforced composites.

Polymer mechanochemistry: techniques to generate molecular force via elongational flows

Long chain polymers have a unique ability to become highly extended in elongational flow fields. The forces developed along the backbone give rise to scission of the chains near their center. Recently, this unique property of polymers has been adopted to explore new chemical transformations by embedding structural elements into the backbone designed to undergo site-specific bond cleavage, termed mechanophores. Experimental techniques to generate elongational flow fields exist in a variety of different arrangements and have been used to study polymer mechanochemistry in solution. This tutorial review will discuss progress in the field of polymer mechanochemistry as well as survey the techniques used to generate elongational flow fields. Ultrasonication will be highlighted as the technique that has been widely adopted to screen mechanophore reactivity in solution.

How Does a Hyperbranched Chain Pass through a Nanopore?

Starting from seesaw-type linear macromonomer azide∼∼alkyne∼∼azide, where “∼∼” represents polystyrene with a controllable length, we successfully obtained two series of narrowly distributed “defect-free” hyperbranched polystyrenes with an identical subchain length but different overall molar masses or with a similar overall molar mass but different subchain lengths. Our ultrafiltration study reveals that the critical flow rate (qc,b) to pull these branched chains through a small cylindrical pore under an elongational flow field depends on both polymerization degrees of the entire chain and the subchain (Nt and Nb) as qc,b ∼ NtγNbφ, where γ and φ are 1.0 and −0.4, different from those predicted values γ = 1/3 and 1/4, and φ = 1/15 and −1/4 for the weak and strong confinements, respectively. Besides the previously improper assumption of each blob as a hard sphere, such discrepancies are also attributed to (1) a smaller scaling exponent between the size and molar mass of the chain squeezed inside the pore be...

Temperature and time dependence of electrical resistivity in an anisotropically conductive polymer composite with in situ conductive microfibrils

AbstractAn anisotropically conductive polymer composite (ACPC) based on conductive carbon black (CB) and binary polymer blend of polyethylene (PE) and polyethylene terephthalate (PET) was successfully fabricated under shear and elongational flow fields. The PET phase formed in situ the aligned conductive microfibrils whose surfaces were coated by CB particles. This ACPC material exhibited a strong electrical anisotropy within a broad temperature range. When the ACPC samples were subjected to isothermal treatment (IT), they showed anomalous variations of the positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects. The PTC intensity was attenuated gradually with the increase of the IT time, and the NTC intensity was nearly eliminated after IT of 8 or 16 h. Beyond 16 h, the resistivity in the NTC region rose anomalously with the temperature after the elimination of NTC effect, which was the result of much transformation from the potential pathways to the intrinsic pathways due to the disordering of oriented conductive microfibrils. When the amount of potential pathways was very small, the effect of the intrinsic pathway separation surmounts that of the potential pathways, leading to the anomalous resistivity increase in the NTC region. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Work fluctuations in an elastic dumbbell model of polymers in planar elongational flow

We use a path-integral approach to calculate the distribution P(w,t) of the fluctuations in the work w at time t of a polymer molecule (modeled as an elastic dumbbell in a viscous solvent) that is acted on by an elongational flow field having a flow rate ̇γ. We find that P(w,t) is non-Gaussian and that, at long times, the ratio P(w,t)/P(-w,t) is equal to exp[w/(k(B)T)], independent of ̇γ. On the basis of this finding, we suggest that polymers in elongational flows satisfy a fluctuation theorem.

Globule−Stretch Transitions of Collapsed Polymers in Elongational Flow Fields

Here we present our studies on the behavior of collapsed polymer chains in elongational flow fields. In particular, we present scaling and hydrodynamic simulation results on the conformation and dynamics of these macromolecules. In the noncollapsed state, we verify via our simulations that there is a smooth transition from a coil to a stretched conformation. The introduction of self-interactions or nonsolvent effects in a polymer, however, suppresses this transition up to a well-defined threshold flow rate e* at which the chain undergoes an immediate and irreversible transition to a stretched conformation. We characterize this behavior under both freely draining and hydrodynamic interacting assumptions and develop scaling arguments to describe the globule−stretch transition in a variety of regimes. The unraveling dynamics and topologies are characterized with relation to these mechanisms, and the elongational viscosity of dilute solutions of collapsed chains is also investigated.

Kinetics of Nanotube and Microfiber Scission under Sonication

Carbon nanotubes are commonly dispersed in liquid solvents by means of sonication. This has the disadvantage, however, that it can induce the scission of the particles that are near imploding cavitation bubbles. Nanotube scission arises from the fluid friction at the surface of the nanotubes in the radial elongational flow field that forms around a cavitation bubble. An understanding of the kinetics of this phenomenon is of critical importance for controlling the length of the nantoubes in their applications yet remains elusive. We investigate this kinetics quantitatively in the present work. The strain rate of the elongational flow around a cavitation bubble is estimated experimentally using carbon microfibers of known mechanical properties. The average length L(t) of the nanotubes is measured by means of dynamic light scattering as a function of time t, and we observed that L(t) scales as t−n, with n ≅ 0.2. This scaling differs from the one predicted theoretically in the literature for the scission of f...

How Much Force Is Needed To Stretch a Coiled Chain in Solution?

to show that linear polymer chains in a good solvent couldundergo a first-order coil-to-stretch transition to pass through apore much smaller than its coiled size under an elongation flowfield with a sufficient hydrodynamic force, independent of boththe chain length and the pore size. Namely, a coiled polymerchaincanpassthroughasmallporeaslongastheflowrate(q)ishigherthanathreshold[q

Observations Regarding On-Column, Flow-Induced Degradation During SEC Analysis

The flow-induced degradation of ultra-high molar mass (M) polymers during their passage through a size-exclusion chromatography (SEC) column has been a subject of interest for several decades. Studies in this regard have been relatively few, however. Of interest is knowing whether degradation occurs in the interstitial medium, at the pore boundary, or both; whether the mechanism of degradation in the interstitial medium is the same as that at the pore boundary; and the types of flow fields involved in degradation, whether shear or extensional and, if the latter, what types of extensional flows are involved, transient or steady-state. Here, we attempt to shed some light on these topics by examining the SEC elution profiles of ultra-high M polystyrene standards. The standards have been analyzed at various flow rates, under conditions where the analyte either had access to both the interstitial volume and the pore volume or to only the interstitial volume. Results from these experiments were compared to each other, as well as to results from an ultrasonic degradation experiment where the analyte was depolymerized through the action of transient elongational flow fields. Results show that degradation occurs in both the interstitial medium and at the pore boundary and that the mechanisms of each of these are different from each other. While the degradation is almost assuredly due to extensional and not to shear flows, the former are either exclusively or predominantly steady-state, not transient.

How Are Insoluble Blocks Interacted with and Packed Inside a Micelle Made of Block Copolymers in a Selective Solvent?

It is well-known that block copolymers can form large core−shell micelles in a selective solvent. The ultrafiltration of such polymeric micelles made of polystyrene (PS) and polyisoprene (PI) block copolymers in n-hexane through small pores (20 nm) is possible only when the flow-rate-dependent hydrodynamic force in the range 10−15 to 10−12 N (i.e., 1 fN−1 pN) is sufficiently strong to pull individual copolymer chains out of the core and disintegrate each micelle. Therefore, we are able to find how strong insoluble PS blocks in the core interact with each other from such a critical flow rate. Our results reveal that the micelle retention gradually decreases as the flow rate increases, different from a sharp first-order coil-to-stretch transition of a flexible linear homopolymer chain under the same elongation flow field. As expected, the interaction strength increases as the PS block becomes longer. Each flow-rate dependence of the micelle retention can be converted to a hydrodynamic force distribution f(Fh). For PS-b-PI diblock copolymers, f(Fh) has a single peak in the range 1−200 fN, whereas for PI-b-PS-b-PI triblock copolymers, there are two separated peaks in f(Fh), respectively, in the ranges 3−20 and 30−500 fN, attributing to two kinds of packing of the PS blocks inside the core; namely, the packing of unentangled and entangled insoluble PS blocks.

Influence of Anomeric Configuration on Mechanochemical Degradation of Polysaccharides: Cellulose versus Amylose

Cellulose and amylose are (1-->4)-linked polysaccharides that are used extensively in the textiles, paper, and food and feed industries and are finding increasing use as alternative fuels and so forth. At the molecular level, cellulose and amylose differ only in their anomeric configuration: beta in cellulose, alpha in amylose. During processing and end use, these polymers experience a variety of mechanochemical stresses, many through contact with transient elongational flow fields. Here, we subject solutions of both polysaccharides to extended periods of ultrasonic irradiation, as the cavitational bubble collapse characteristic of ultrasound experiments creates flow fields strictly analogous to those encountered in other transient elongational flow scenarios. With the use of multidetector size-exclusion chromatography, the effects of anomeric configuration on both the limiting molar mass, beyond which polymers do not degrade in transient elongation flow ( M lim), and the rate of degradation have been isolated in these (1-->4)-linked polysaccharides. This effect was found to be pronounced; for example, M lim (cellulose) = 5( M lim (amylose)). Also, while extensive change was observed in molar mass averages, distribution, polydispersity, and size of the analytes during degradation, their structure was found to remain invariant. A modified "path theory" of transient elongational flow degradation was proposed, with the persistence length identified as a parameter which embodies the minimum continuous path length and flexibility requirements of the theory.

Shear and elongational rheology of polyethylenes with different molecular characteristics. II. Elongational rheology

AbstractThe elongational viscosities of polyethylenes with different molecular characteristics were measured at different Hencky strains and temperatures with a capillary rheometer by the replacement of the capillary cylindrical die with a hyperbolic converging die. The hyperbolic shape of the die established a purely elongational flow field at a constant elongational strain rate throughout the die. The effects of molecular characteristics such as the molecular weight, molecular weight distribution, and long‐chain branching and processing conditions such as the temperature and Hencky strain on the elongational rheology of the polyethylene samples were studied. Good master curves were generated for temperature and Hencky strain shifting and simultaneous shifting with respect to both the temperature and Hencky strain. Both the molecular weight distribution and long‐chain branching seemed to promote strain rate thinning and reduce the elongational viscosity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1184–1194, 2007

On the Equilibria of the Extended Nematic Polymers under Elongational Flow

We classify the equilibrium solutions of the Smoluchowski equation for dipolar (extended) rigid nematic polymers under imposed elongational flow. The Smoluchowski equation couples the Maier-Saupe short-range interaction, dipole-dipole interaction, and an external elongational flow. We show that all stable equilibria of rigid, dipolar rod dispersions under imposed uniaxial elongational flow field are axisymmetric. This finding of axisymmetry significantly simplifies any procedure of obtaining experimentally observable equilibria.

X-ray microdiffraction and micro-Raman study on an injection moulding SWCNT-polymer nanocomposite

We report the effect of a combination of shear and elongational flow fields on the structure of nanoadditive and matrix for an injection moulded SWCNT-polymer nanocomposite. Single-wall carbon nanotubes (SWCNTs) intensify the flow field effects produced during injection moulding of a PBT/SWCNT nanocomposite, templating the morphology of crystallization and providing the generation of hybrid shish-kebab superstructures. By combining X-ray diffraction and Raman Spectroscopy techniques, both working on a microfocus fashion, it has been shown that the shear flow tends to self-assemble the nanotubes into a rectangular lattice, different from that hexagonal of native SWCNT, the maximum concentration of ordered aggregates being 1 mm to the wall edge of the injection moulded bar.