A novel rheometry termed ultrasonic spinning rheometry (USR) is overviewed in this paper. This methodology utilizes ultrasonic velocity profiling as a representative velocimetry for various complex fluids including multi-phase state. The USR determines optimal properties from cost function which is calculated from both equation of motion and constitutive equation of test fluids by substituting the measured velocity profiles. Various examples are explained to indicate the applicability and efficacy of USR for measuring complex fluids; silicon oil, polymer solution, clay dispersion, water-oil two-phase fluid, and more. Through these results, we discussed future prospects of USR developments regarding its applicability and efficacy.

A short review on the rheology of entangled linear wormlike micellar solutions is presented. To date, the linear and nonlinear rheological properties of wormlike micellar solutions have been extensively studied from experimental, theoretical, and numerical perspectives. For a linear response region, there are several sophisticated models, and the rheological properties have been well reproduced by these models. On the other hand, modeling the nonlinear rheological properties is still an active and challenging topic. In this review, we summarize theoretical and numerical studies on the rheological properties of wormlike micellar solutions. Furthermore, future perspectives of related topics including associative polymers are presented.

Vitrimers are a new class of sustainable cross-linked materials with an associative bond exchange mechanism. Bond exchange in vitrimers functions in an addition/elimination pathway, where bond dissociation and reassociation appear to occur simultaneously, as opposed to traditional dynamic covalent bonds that act with discrete distinct, separated steps of bond dissociation and reassociation. Because of these characteristics, network disconnection never occurs in vitrimers, and network topology alternation proceeds with maintaining the constant cross-link density at a temperature greater than the activation temperature of the bond exchange. Some unique rheological properties of vitrimers are highlighted in this review article. The first section summarizes the general relaxation features of vitrimer networks based on temperature-ramp creep test, stress-relaxation test, and temperature-sweep viscoelasticity. The applicability or inapplicability of the time-temperature superposition concept is examined in the latter section, which is vital for understanding the thermorheological simplicity (or complexity) of vitrimer materials.

Raman spectroscopy is a vibrational spectroscopic technique that is widely used for analyses of the chemical structures and morphologies of polymeric materials. The peak position and peak area of each Raman band are influenced by microscopic deformations of molecular chain e.g. load-sharing, orientation, and conformational state. In particular, Raman spectroscopic analysis has been used to investigate the structure–mechanical properties relationship of semi-crystalline polyolefins (POs) because the C–C stretching mode, which is the main chain vibration of POs, is strongly Raman-active. The present review summarizes recent Raman spectroscopic analyses of the structure–mechanical properties relationship of POs.

Amphiphilic molecules or colloids such as surfactants and Janus particles with hydrophobic and hydrophilic parts can spontaneously self-assemble in a variety of morphologies in their solutions. Coarse-grained simulations can be used to investigate the behavior of molecules inside these complex fluids and clarify the origin of rheology. However, the choice of essential degrees of freedom and kinetic equations for their dynamics must be carefully considered. Indeed, the hydrodynamic interactions play essential roles for the dynamics of solutions. This article overviews a few simulation techniques that are suitable to the problems mentioned above. The results for surfactant aqueous solutions under confinement and Janus colloid dispersions under shear are exhibited as well as typical examples.

Fracture is one of the most important topics in the polymer field. Accordingly, many insightful works about polymer fracture have been reported since the 1960s. This topical review considers polymer fracture studies of experiments, theoretical models, and simulations. These past studies have discussed craze initiation criteria, yielding mechanisms, and differences in the fracture of different chemical species. New insight into polymer fracture based on large-scale molecular simulations is also provided.

Polyelectrolytes with ionic groups are abundant in nature and essential in life. Counterions can be released into a solution and leave charges on polyelectrolyte chains, making the solution properties significantly different from those of electrically neutral polymers. A lot of scientific efforts have been made to elucidate the effect of electrostatic interactions on the conformation and material properties of polyelectrolyte solutions. However, unfortunately, our understanding is still far away from being perfect, and continuous efforts need to be provided by researchers from different aspects. This short review will highlight the research progress made in the past few years on the conformation and viscoelastic properties of polyelectrolyte solutions.

Transient polymer networks are formed by dynamic crosslinks with a finite lifetime and therefore exhibit significant viscoelasticity, including non-Newtonian behaviors. Using the combination of multiple experimental techniques, such as viscoelastic measurements and spectroscopic analyses, these properties can be understood at the molecular level. This review classified transient polymer networks as side-chain and end-chain crosslinks, and viscoelastic studies of each type were presented. A combination of linear viscoelastic and spectroscopic methods revealed deviations between the viscoelastic properties of transient polymer networks and the molecular model. These deviations are sometimes attributed to dynamic heterogeneities potentially contained in the transient polymer network. These unexpected heterogeneous structures are challenging to control and impact viscoelasticity. Controlling and discussing these heterogeneities based on multiple experimental approaches is essential for a better molecular understanding of transient networks in the future.

Ring polymers are one of the model polymers to understand the relationship between molecular architecture and the dynamics of polymers. This review summarizes the recent rheological studies on pure ring polymers, ring/linear polymer blends, and ring polymer derivatives. Pure ring polymers exhibit different linear and nonlinear rheological properties from linear polymers owing to the absence of chain ends. The presence of linear chains in ring polymers sensitively influences the rheological properties due to the occurrence of spontaneous intermolecular ring/linear threading. This effect becomes significant when a ring and linear chains are connected in a molecule for tadpole-shaped and dumbbell-shaped polymers.

Flow curves on dense suspensions exhibit highly nonlinear behaviors consisting of shear thinning, shear thickening, and multiple Newtonian regions. Moreover, it has recently been revealed that each Newtonian viscosity diverges individually with increasing density and is respectively related to the glass and jamming transitions. In this review, recent advances in physics are introduced regarding the complex flow behaviors in dense suspensions and its relation to the glass and jamming transitions. In addition, a numerical simulation model, focusing mainly on discontinuous shear thickening, is presented to provide microscopic insight into the complex flow behaviors, i.e., the role of thermal fluctuations and interparticle forces acting on the particles. Finally, a perspective on discontinuous shear thickening is presented with reviewing recent experimental and theoretical (numerical) works.

To elucidate the mechanism for flow phenomena in complex fluids, it is crucial to analyze the associated flow-induced structures both experimentally and numerically. Flow-induced birefringence (FIB) measurement is an optical measurement that is very useful for analyzing flow-induced structures in complex fluids, which is why many studies have used the FIB technique. Furthermore, various recent studies have developed new devices for measuring FIB. Reviewed briefly here are recent experimental studies that have applied the FIB technique to complex fluids such as surfactant solutions, fiber suspensions, and polymer fluids.

The current knowledge and prospects for rheological properties of nanocellulose dispersions in a dilute region are presented. It is essential to clarify the rheological properties of dilute nanocellulose dispersions because they represent the properties of nanocellulose. This study highlights intrinsic viscosity and viscoelastic relaxation, which are indicators of average size, size distribution, and flexibility. While the intrinsic viscosity and viscoelastic relaxation of rod-shaped cellulose nanocrystals (CNCs) can be explained by existing theories of polymers, those of cellulose nanofibers (CNFs) are not fully understood because of their kinks and flexibility.

Epoxy resins are an important class of thermoset resins, which are obtained by curing reactions between an epoxy compound and a curing agent. The reaction leads to the formation of a complicated three-dimensional network that extends through the entire system. Thus, as the condition of the curing reaction changes, the resultant network structure does, generally resulting in the change in the bulk glass transition temperature (T_g) of the resultant resin. In this short review, we briefly summarize how the curing condition affects the formation of the network structure and thereby alters the bulk T_g.

On the basis of the lithium electrolyte mechanism, modified glassy polymers were developed by adding lithium salts to poly(methyl methacrylate) (PMMA). This review summarizes how the rheological and mechanical properties of PMMA were changed by introducing various lithium salts: lithium perchlorate (LiClO₄), lithium trifluoroacetate (LiCOOCF₃), lithium trifluoromethanesulfonate (LiCF₃SO₃), lithium nonafluorobutanesulfonate (LiC₄F₉SO₃), and lithium bromide (LiBr). It was found that the rheological and mechanical properties of PMMA are dominated by the aggregation state of the salts in the matrix, the degree of bulkiness in anions, and anion size. This review focused on the “pinning” effect, which is attributed to the ion-dipole interaction between the lithium cations and PMMA molecular chains. This pinning effect was evaluated in the molten state during the molding, which directly affects the mechanical properties in the solid state. Therefore, the pinning, which depends on the anion species, affects not only the rheological and mechanical properties, but also the tensile properties of PMMA/Li-salts.

In this review, the author introduces a recent contribution to the development of a quantitative evaluation method of connectivity in elastomers for describing rubber elasticity. In synthetic processes, the elastomers possess a heterogeneous network structure, which affects the rheological behaviors of elastomers, such as rubber elasticity. Although the heterogeneous structure of elastomers has been evaluated using both experimental and simulation methods, it is still difficult to estimate the heterogeneous structure of elastomers in terms of connectivity. Recently, the author reported a novel evaluation method for the chain connectivity of elastomers based on network theory to describe rubber elasticity. The unified centrality, including both topological and spatial information, can describe certain parameters related to rubber elasticity. Furthermore, the behavior of extended chains is also described by centrality. This approach is expected to contribute to progress in the theory of rubber elasticity by considering complex connectivity.

A crack in a viscoelastic solid exhibits velocity jump, i.e., the propagation velocity changes abruptly in a narrow range of the applied load. However, the mechanism had been unsolved until recently. This review introduces past findings on velocity jumps in viscoelastic solids, focusing on our studies. We have developed an exactly solvable model that exhibits the velocity jump. From the mathematical solution, we have elucidated that the velocity jump is caused by a dynamic glass transition in the vicinity of the crack tip. Also, we have provided a guiding principle for toughening viscoelastic solids. Recently, the predictions of the model have been confirmed by experiments and numerical simulations.

Since the invention of atomic force microscopy (AFM), researchers have been able to study the statistical mechanical properties of individual polymer chains by using a technique known as single molecule force spectroscopy (SMFS), which stretches a single polymer chain by attaching one end of the chain to a substrate and the other end to the AFM tip. SMFS is used to obtain static information about single polymer chains, mainly through a quasistatic stretching process. With technological developments in recent years, dynamic SMFS measurements under nonequilibrium conditions have also been realized. The dynamic viscoelasticity of single molecule chains can also be measured, which will benefit our understanding of the nonequilibrium dynamic properties of polymeric materials.

Critical polymer clusters are massive randomly branched polymers formed near the gelation threshold. Because of their universal physical properties, such as the size distribution, mass fractal dimension, and viscoelastic properties, these clusters have drawn the great attention of many physicists. This review briefly introduces a few recent remarkable experimental results, which shed light on remaining questions of the critical clusters. The static structure and dynamics of these critical clusters were investigated using small angle neutron scattering (SANS), static light scattering (SLS), and dynamic light scattering (DLS). The reviewed studies primarily focused on the data analysis for the critical clusters in the intermediate concentrations between dilute and semidilute limits. An intermediate model developed by Bastide and Candau well explained the observed static scattering profiles, indicating a coexisting state of the dilute and semidilute solutions. The dilute and semidilute features were also observed in dynamic studies as a superimposed translational motion of small dilute clusters and cooperatively diffusion of large semidilute clusters. These fundamental understanding may contribute to the applications of the critical clusters and further studies for the percolation process.

Human red cell filtration using a single porous membrane is a standard technique to estimate red cell filterability (RCF) that is a surrogate of red cell deformability. However, there is still a gap between such instantaneous ex vivo red cell filtration and continuous in vivo red cell capillary flow. Therefore, two-step filtration system was designed to estimate RCF under the constant flow rate (1.29 ml/min) of red cell suspension with hematocrit of 3.0 % by monitoring pressure difference (ΔP(t)) across a couple of identical nickel mesh membranes with pore size of exactly 5.49 μm. ΔP(t) showed baseline positive pressure under the saline filtration, initial steep rise at the passage of the head of red cell suspension and the secondary linear rise during filtration of suspension in each step. The amplitude of steep rise in ΔP(t) reflects an increase in apparent viscosity of suspension (mPa·s), and the slope of secondary linear rising segment indicates the rate of plugging pores by red cells (s ^{− 1}). Comparison of RCF in each step provided us with a hint of rheologic behaviors of heterogeneous red cells showing variable deformability. Tandem filtration using two-step filtration system and our specific nickel mesh membrane is concluded to be feasible, and our prototype of this system is promising to estimate RCF with easy handling skills.

Nonlinear shear and elongational rheology of entangled poly(propylene carbonate) (PPC) melts having different molecular weights with relatively narrow molecular weight distribution are examined. In shear measurements, the PPCs exhibit a typical shear thinning behavior with stress overshoot at high shear rates. In the shear rate dependence of the steady-state viscosity, the PPCs do not violate the empirical Cox-Merz rule, which is known to be valid for many other entangled polymer melts. In uniaxial elongational measurements, the viscosity growth functions of the PPCs show a weak deviation from the linear viscoelastic (LVE) envelope to the higher side at the high Weissenberg number Wi_d (=ετ_d, where ε is the elongation rate and τ_d is the characteristic disengagement time). The steady-state viscosity of the PPCs shows an elongational thinning as a function of ε ^−0.5 within an error. These results are similar to some other polymer melts such as polystyrene (PS). In addition, the normalized elongational viscosity growth functions of PPC and PS with a similar entanglement number Z, are compared. The PPC exhibits a similar viscosity growth curve to the PS at the same Wi_d. This result suggests that the degree of the monomeric friction reduction originated from the stretch/orientation of PPC under fast elongational flow might occur at the same level as PS.

From a medical engineering point of view, dynamic properties of viscoelastic materials in high strain rate region (> 10³ s ⁻¹) are considerably important for understanding influences of recent minimally invasive surgical techniques with lasers, ultrasounds, and shock waves on biological tissues. In this article, a new rheological method via inverse analysis on laser-induced inertial micro cavitation phenomena in the viscoelastic materials is constructed to overcome limits of conventional macroscopic / microscopic rheometries in the high strain rate region. In the following, a visualization system enabling high-speed imaging of the cavitation phenomena induced by a high-energy pulsed laser is arranged, and equations of motion with specific viscoelastic constitutive laws are formulated to describe the corresponding cavitation dynamics. Furthermore, a suitable objective function for the inverse analysis is designed and numerical optimization procedures are proposed. Polyvinyl alcohol hydrogels (PVA-H) with different mass concentrations, which are well known as simulated biological tissues, are employed as test materials. As a result, it is confirmed that the present cavitation phenomena are well located in the high strain rate region, and that the dynamic properties are possible to be estimated in the PVA-H samples within moderate deviation ranges.