A review of nonlinear oscillatory shear tests: Analysis and application of large amplitude oscillatory shear (LAOS)

The deformations and stresses during squeeze flows are evaluated for a wider class of materials than previously covered in articles on this subject. These include generalised Newtonian fluids, yield stress fluids, as well as elastic and viscoelastic materials. Wherever possible, results are given in a compact mathematical form. The effect of different boundary conditions (no slip, perfect slip and partial slip) and how these interact with different types of material behaviour to give a variety of macroscopic responses is also discussed. The significance of this in using squeeze flow as a rheometry method is highlighted and a state-of-the-art view of squeeze flow rheometry is given.

Squeeze flow theory and applications to rheometry: A review

Melt electrospinning today: An opportune time for an emerging polymer process

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An Introduction To Electrospinning And Nanofibers

The chronic nature and associated complications of nonhealing wounds have led to the emergence of nanotechnology-based therapies that aim at facilitating the healing process and ultimately repairing the injured tissue. A number of engineered nanotechnologies have been proposed demonstrating unique properties and multiple functions that address specific problems associated with wound repair mechanisms. In this outlook, we highlight the most recently developed nanotechnology-based therapeutic agents and assess the viability and efficacy of each treatment, with emphasis on chronic cutaneous wounds. Herein we explore the unmet needs and future directions of current technologies, while discussing promising strategies that can advance the wound-healing field.

http://pubs.acs.org/doi/pdf/10.1021/acscentsci.6b00371

Nanotechnology-Driven Therapeutic Interventions in Wound Healing: Potential Uses and Applications

Nonlinear response of linear and branched polymers has been investigated under medium strain amplitude oscillatory shear (strain amplitude range from 10% to 100%) with Fourier-transform rheology. A power law relationship was found between the relative third intensity (I3∕I1), which is an indicator of nonlinearity, and the strain amplitude at low and medium strain amplitudes. On a log-log plot, the intercept and slope of I3∕I1 were investigated at different excitation frequencies and temperatures. Simulation results with three different constitutive equations [Giesekus, exponential Phan-Thien Tanner (E-PTT), pom-pom model] were also compared. Experimental results show that the intercept was affected by the excitation frequency and temperature, and the slope of I3∕I1 for linear polymer remained constant regardless of molecular weight, molecular weight distribution, and excitation frequency in accordance with the predictions of the constitutive equations (Giesekus and E-PTT). It should be noted that the slop...

Fourier-transform rheology under medium amplitude oscillatory shear for linear and branched polymer melts

The effect of molecular structure of polypropylene (PP) on the melt rheological properties were investigated for electron irradiated polymer and di-2-ethylhexyl peroxy dicarbonate (EHPC)-treated polymer. The modifications were examined in terms of the rheological behaviors, molecular weight distribution, and the degree of branching. The high melt strength PP was obtained by irradiating with 50 and 80 kGy and adding EHPC. The modified PPs showed the strain hardening in the uniaxial elongational viscosity, though the linear elongational viscosity was lower than that of the unmodified PP. Low angle laser light-scattering measurements of the modified PPs showed the interesting results; high irradiation doses such as 50 and 80 kGy caused higher molecular weight chains branching. Nevertheless, the long branching chains were not detected for the EHPC modified PP, which also showed the strain hardening in uniaxial elongational flow. In this article, the relation between chain structure and rheological properties is discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1493–1500, 1999

Effect of chain structure on the melt rheology of modified polypropylene

Uniaxial extensional flow behavior was measured for the high-melt-strength polypropylene using a Meissner-type rheometer under transient extensional flow with constant tensile strain rate. The equibiaxial extensional flow behavior of the high-melt-strength polypropylene was measured via the lubricated squeezing flow method under constant strain rate. The high-melt-strength polypropylene consists of polypropylene (PP) as a main component and high-molecular-weight polyethylene (PE) component as a long relaxation time component (see part 1). This system is generally believed to be an immiscible system, at least under the quiescent state. Nevertheless, in part 1, we have found that the high-melt-strength PP with very high-molecular-weight PE shows distinctly different shear flow behaviors from conventional PP, e.g., high elasticity and two-step viscosity at low shear rates and strong and weak strain-dependent nonlinear damping functions characterizing fast and slow relaxation processes. In this study, the tra...

Melt Rheology of Polypropylene Containing Small Amounts of High-Molecular-Weight Chain. 2. Uniaxial and Biaxial Extensional Flow

In this study, linear and branched polypropylenes (PP) were compared under medium strain amplitude oscillatory shear (usually strain amplitude range from 10 to 100%) with Fourier-transform rheology (FT rheology) On a log–log diagram, the third relative intensity (I
 3/I
 1), which is a parameter to represent nonlinearity, shows a linear relationship with the strain amplitude in the range of medium strain amplitude The slope of I
 3/I
 1 of linear PP with various molecular weight and molecular weight distribution was 2 as most constitutive equations predict, while that of branched PP was 164, which is lower than that of linear PP When the linear and branch PP were blended, the slope of I
 3/I
 1 was proportional to the composition of the branch PP Therefore, it is suggested that the degree of branching can be defined in terms of the slope of I
 3/I
 1 under medium amplitude oscillatory shear

Degree of branching of polypropylene measured from Fourier-transform rheology

In this study, the effect of rheological behavior of epoxy during precuring on foaming was investigated. Dynamic time sweep test of epoxy/curing agent (100/1, w/w) was conducted. The viscosities as a function of time showed extremely rapid increase from the order of 102–103 to 106Pa · s at a certain time, followed by slow increase of the viscosities. Dynamic frequency sweep test of precured epoxy with curing agent was conducted at 90°C. The critical gelation time was obtained by using rheological criterion proposed by Winter and Chambon. We found that the slopes of G′(ω) and G″(ω) decreased with increasing precuring time. Correspondingly, tan δ showed a change from negative to positive slope at a critical time. By using the results, the critical gelation time was determined as t = 895–935 s. Samples of epoxy/curing agent/blowing agent (100/1/0.5) were precured for 960–1620 s. And then precured samples were foamed at 230°C for 300 s to decompose chemical blowing agent. The formed bubble size distribution becomes sharp with increase of the precuring time. There are roughly two sizes of bubbles when precured for relatively short time (t 100 μm) and small ones (≅30 μm). On the other hand, foams precured for long time (t > 1200 s) before foaming, large bubbles disappear, and the average diameter of the bubble becomes small while the porosity is low. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Masataka Sugimoto

Papers

Fourier-transform rheology under medium amplitude oscillatory shear for linear and branched polymer melts

Effect of chain structure on the melt rheology of modified polypropylene

Melt Rheology of Polypropylene Containing Small Amounts of High-Molecular-Weight Chain. 2. Uniaxial and Biaxial Extensional Flow

Degree of branching of polypropylene measured from Fourier-transform rheology

Effect of rheological behavior of epoxy during precuring on foaming