Entanglement Network Research Articles

Research on the influence of sodium fatty alcohol polyoxyethylene ether sulfate on the microstructure and properties of Portland cement

Sodium fatty alcohol polyoxyethylene ether sulfate (AES), an anionic surfactant, which relieves the contamination of Portland cement slurry containing mineral oil based mud (MOBM) effectively. In this paper, by testing fluidity and compressive strength firstly in 25 °C and 90 °C after 1, 3, 7, 14 and 28 days of curing respectively, Vipulanandan rheological model was applied to analyze rheological behavior. We found AES could deteriorate cement’s fluidity and compressive strength as its content increasing. Additionally, cement stone would lose about 85% of compressive strength as low as 0.05%wt AES especially. We observed microstructure of cement containing AES by Environment Scanning Electron Microscope (ESEM), which proved that AES causes cement surface to form holes, and the reduction of cement hydration products was confirmed by X-ray diffraction (XRD). Finally, by comprehensively analyzing combining Zeta Potential and Contact Angle, we used mathematical models to explain the mechanism of AES’s affecting on the structure and performance of cement: (1) In the slurry, AES deteriorates fluidity by trapping the free water. (2) AES attaches on cement particles surface, via affecting “Dynamic Potential” to decrease mutual repulsion between cement particles to accumulate them, resulting in uneven distribution of cement particles in the cement slurry with appearing holes and the dropping of density. (3) Foaming and its stability of AES makes structure of cement structure porous, forming entangled network structures and bounded air bubbles.

Direct and complete utilization of agricultural straw to fabricate all-biomass films with high-strength, high-haze and UV-shielding properties

It is of vital significance to fabricate high-value-added materials from agricultural wastes by environmentally friendly and cost-effective processes. In this work, we propose an approach to directly and completely convert agricultural straw into multifunctional all-biomass films by introducing an entanglement network of additional cellulose to enhance the strength of the regenerated straw. First, natural wheat straw is dissolved in the ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl). Then, a small amount of cellulose with a high degree of polymerization (DP) is introduced to obtain straw/cellulose/AmimCl solutions, which are subsequently soaked in water for biomass regeneration, washed and dried to obtain straw/cellulose films. Dynamic shear rheological test confirms that after adding high-DP cellulose, an enhanced entanglement network forms in the solutions, which is essential to the processing and mechanical properties of materials. Extensional rheological test indicates that straw/cellulose/AmimCl solutions exhibit excellent spinnability and film-forming properties based on a significant increase in the capillary break-up time. Therefore, after regeneration in water, straw-based all-biomass films with high mechanical strength are obtained. When the content of additional wood pulp (WP, DP = 1300) with respect to total solids is 25 wt%, the obtained straw/WP all-biomass film reaches a tensile strength of 62 MPa. More interestingly, because there is no intentional chemical pretreatment and compositional isolation involved in this process, almost all of the components in straw, such as cellulose, lignin, hemicellulose and inorganic compounds, are retained in the final films. Thus, the resultant films have a superhigh haze of 97% while preventing 97% UVA (320–400 nm) and almost 100% UVB (280–320 nm). In sum, we demonstrate the complete and value-added utilization of low-grade bioresources by a facile, green and economical process to fabricate high-strength, high-haze and UV-shielding all-biomass films, which have great potential in low-cost, biodegradable and environmentally friendly packaging.

Fabrication of highly concentrated collagens using cooled urea/HAc as novel binary solvent

It is difficult to prepare homogeneous concentrated collagen with concentration > 40 mg/mL due to its extremely high viscosity. Herein, cooled (−12 °C) urea/HAc solutions was employed as novel solvent to prepare collagen samples with concentrations varied from 40 to 120 mg/mL. Fourier transform infrared spectroscopy and sodium dodecyl sulfonate-polyacrylamide gel electrophoresis demonstrated that the concentrated collagen maintained the intact triple-helical structure. As reflected by differential scanning calorimetry, collagen with acetic acid as solvent displayed two thermal transition peaks when concentration ≥ 60 mg/mL, which could be attributed to the denaturation of dissolved collagen and un-dissolved collagen. Whereas, collagen prepared in cooled urea/HAc just exhibited one thermal denaturation peak other than samples with concentration ≥ 100 mg/mL. Images from polarizing optical microscopy displayed that the cholesteric band grew more pronounced upon increasing collagen concentration. Field-emission scanning electron microscopy exhibited more aligned topographical features of the collagen sponges when increasing concentration from 10 to 100 mg/mL, nevertheless both of the aligned structure and anomalous structure could be captured when collagen concentration further reached 120 mg/mL. Rheological properties were found to be dependent on the collagen concentration, additionally, compared with collagen in acetic acid, a weaker entanglement network and lower viscosity for collagen with the same concentration using cooled urea/HAc as solvent could be reflected by the rheological measurements. Overall, this method presents a simple mean for generating homogeneous concentrated collagens, which can be applied to wider fields such as wet spin and biomimetic mineralization.

Investigation of Dynamic Deformation of Polymer Systems in a Viscoelastic State

The process of dynamic deformation of polymer systems with a polymer concentration below the critical value is investigated. The complex viscosity and its components – viscosity and elasticity, were determined over the entire range of changes in the circular frequency, including the section of destruction of the initial structure of the polymer system. It was established that almost until the destruction of the initial structure, the constancy of the complex viscosity is maintained, within which its viscous and elastic components change. It is shown that the cause of the destruction of the initial structure of the polymer system (entanglement network) is its transition from a viscoelastic state to a forced elastic one, when the complex viscosity is almost completely determined by its elastic component. When the ultimate strength of the polymer network is reached, the initial structure is destroyed, accompanied by a decrease in the complex viscosity and its elastic component with their subsequent increase.

Strain hardening in glassy polymers: Influence of network density on elastic and viscous contributions

ABSTRACTIn this study, the rate‐ and temperature‐dependent strain hardening and the Bauschinger effect is studied for three glassy polymers. It appeared that for all materials, an equal distribution of elastic and viscous hardening was necessary to accurately predict the Bauschinger effect, as well as the rate‐ and temperature‐dependent strain hardening response. As for the elastic contribution, the viscous contribution appears to increase with an increase in entanglement network density. Investigating the effect of temperature on the Bauschinger effect revealed that at elevated temperatures the model predictions are not accurately enough. It is shown that this is caused by the magnitude of the elastic hardening contribution; to improve the predictions, a temperature‐dependent elastic contribution is necessary. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1001–1013

All-atom molecular dynamics study of impact fracture of glassy polymers. I: Molecular mechanism of brittleness of PMMA and ductility of PC

Molecular mechanism of brittle and ductile impact fractures of glassy polymers has been investigated. We performed atomistic molecular dynamics (MD) calculations for two glassy polymers, brittle poly(methyl methacrylate) (PMMA) and ductile polycarbonate (PC) using the dissociative force fields. The systems were prepared as realistic as possible such that they reproduced the experimental molecular weight distribution, tacticity, radius of gyration, and entanglement density. The calculated system simulated a small portion of the macroscopic specimen near the notch. The simulations adopted a uniaxial extension condition with the lateral pressure maintained as 1 atm. Under this condition, our atomistic models reproduced the brittle fracture of PMMA via cavitation and ductile fracture of PC via shear yielding and strain hardening. The fracture pathways were determined only by the differences in the material. A conceptual bridge between microscopic simulations and macroscopic experimental observations was provided. The brittle fracture of PMMA is found to be caused by the less flexible backbones with fewer entanglements as well as the inhomogeneity of the material. This contrasts with the finding that more flexible backbones with denser entanglement network result in ductility for PC.

Rigid nanoparticles promote the softening of rubber phase in filled vulcanizates

Enhanced mechanical softening accompanying nanoparticles reinforcement of rubber is an important source of energy dissipation and heat buildup of industrially engineered elastomers. Its mechanism previously assigned to damages in the filler network, rubber-filler interface and rubber phase remains controversial in more than 70 years. Through investigating the typical Payne effect of styrene-butadiene rubber gum and its vulcanizates as well as silica filled compounds and vulcanizates and the Mullins effect of unfilled and filled vulcanizates, we herein evidence that the filler-promoted softening of the rubber phase softens the filled elastomer nanocomposites. Especially we show that the Mullins effect is relevantly involved in the disentanglement/re-entanglement of dangling chains superposed on the entropically elastic network of the rubber phase. This paper clarifies that the mechanism of nonlinear mechanical softening for filled rubber compounds and vulcanizates should be rooted in macromolecular chains in the entanglement network (gum and filled compounds) or long dangling chain in non-ideally crosslinked network (vulcanized gum and filled vulcanizates), rather than damages involved in the “filler network” or filler-rubber interface. This suggests that adjusting the nonideally crosslinked network structure of viscoelastic rubber matrix should be able to optimize the use performance of the rubber nanocomposite products.

Unexpected Stretching of Entangled Ring Macromolecules.

In the melt state at equilibrium, entangled nonconcatenated ring macromolecules adapt more compact conformations compared to their linear analogs and do not form an entanglement network. We show here that, when subjected to uniaxial stretching, they exhibit a unique response, which sets them apart from any other polymer. Remarkably, whereas both linear and ring polymers strain-harden, the viscosity of the rings increases dramatically (the melt thickens) at very low stretch rates due to the unraveling of their conformations along the stretching direction. At high rates, stretching leads to viscosity thinning similar to that of entangled linear polymers, albeit with subtle differences.

Ultrasmall Nanoparticles Diluted Chain Entanglement in Polymer Nanocomposites

Nanoparticle-polymer composites exhibit unusual mechanical properties and chain dynamics when the nanoparticle size is smaller than the entanglement mesh size of the matrix polymer chains, corresponding to the ultrasmall regime defined by de Gennes. However, the mechanism is still ambiguous due to the lack of suitable model systems. Here, we develop an ultrasmall nanoparticle system by using a bimodal grafting strategy to graft both short alkyl chains and long polystyrene chains onto the polyoxometalate molecular nanoparticles with a tunable repulsive potential between the nanoparticles, thus facilitating their uniform dispersion in polystyrene matrices. Linear viscoelasticity of the resultant nanocomposites changes with increasing the filler content, which shows a decrease in both plateau modulus and terminal relaxation time, indicative of a dilution effect of the nanoparticles. Namely, the entanglement network becomes sparser with increasing the filler content.

A physically based visco-hyperelastic constitutive model for soft materials

Viscoelasticity is an essential mechanical property of soft materials. Many constitutive models have been proposed to capture this mechanical behavior, but few physically based models were developed due to the challenge to incorporate the micro-mechanisms of viscoelasticity into the formulation. In a previous paper, we proposed a constitutive model to characterize the hyperelastic response under different deformation states with only three parameters (Xiang et al., 2018). Based on the above work and the tube theory of polymer dynamics, we develop herein a physically based viscoelastic constitutive model in this paper. We start from a new microscopic picture at the molecular chain scale, and decompose the stress into a hyperelastic part which comes from the elastic ground network (crosslinked network and entanglement network), and a viscous part which is originated from free chains. Utilizing the same scheme from the previous work (Xiang et al., 2018), we are able to decompose the free chains into two parts, the untangled crosslinked network and the entanglement network. The contour length relaxation and disentanglement from the free chain's networks give the viscous behavior. We test VHB 4910 to validate our model. The model is applied to the mechanical behavior of the soft digital materials (DMs). In addition, the model can explain the Shore A index independent relaxation time of DMs and the asymmetry of viscoelasticity under loading and unloading. This viscoelastic model can be used to predict the mechanical response of soft materials.

Highly conductive ultra-sensitive SWCNT-coated glass fiber reinforcements for laminate composites structural health monitoring

In the present study, hierarchical single-wall carbon nanotube covered Glass fibres (GF-CNT) are developed for self-sensing Structural Health Monitoring (SHM) of epoxy laminate composites. The unidirectional (UD) CNT-modified glass fibers were fabricated by a versatile and scalable wet-chemical blade coating deposition process under ambient conditions. GF-CNT were employed to manufacture UD damage sensing composite laminates. Scanning Electron microscopy (SEM) revealed an extremely homogeneous CNT nanolayer consisting of highly entangled CNT networks covering fully the GF surfaces. A comprehensive electrical characterization of the manufactured laminate was carried out, revealing a strongly orthotropic response in terms of electrical resistivity. The damage sensing capability of the new developed “smart” reinforcement material was verified taking advantage of mode I Double Cantilever Beam (DCB) tests carried out on specimens with a pre-delamination. The electrical resistance, measured during the tests, exhibited a pronounced increase proportional to the delamination growth. The experimental data were also compared with the assessment of a predictive analytical model, showing a very satisfactory agreement.

Investigation of the Rheological Behaviors of Polymeric Materials in the Film Casting Process through Multiscale Modeling and Simulation Method

AbstractPolymeric materials show the features of different lengths and time scales. In order to achieve optimized applications in practical forming process, it is of significance to understand the evolution of integrated structure–property relationship. In the study, the rheological behaviors of polymeric materials in film casting process are investigated by means of a multiscale modeling and simulation method based on the coarse‐grained molecular dynamic (CGMD) method, the primitive path analysis, and the finite element method. The macroscopic properties of the polymeric system are predicted from the microstructure by using a bottom‐up method. Based on the entanglement network of macromolecular chains predicted with CGMD simulation, the primitive path analysis method is adopted to evaluate main conformational parameters according to the tube theory, which realizes a bridge from nano to micro scale. The viscoelastic properties of polymeric materials are characterized by using a continuum Phan‐Thien–Tanner (PTT) constitutive model, whose rheological parameters are obtained by fitting the distributions of material functions predicted from the tube model. The mathematical model of film casting process is further established based on a membrane model and the corresponding finite element model and details of numerical schemes are introduced. The characteristics of macroscopic rheological behaviors of polymeric melts can hence be investigated from the evolution of microscopic structure, and the phenomena in practical film casting process like the neck‐in and the edge bead defects in engineering are successfully predicted.

Effects of shear temperature-controlled entanglement network on the structure evolution of Poly(ethylene oxide) in shear flow

This study investigated the structure evolution of poly (ethylene oxide) (PEO) samples sheared at different temperatures above the equilibrium melting temperature followed by cooling to an isothermal temperature of 50 °C. We found that the higher shear temperature tended to decrease the number of entanglements to generate a larger network deformation, which was characterized by the deviation angle. It improved the orientation of chains and noticeably accelerated the crystallization process, however the final values of the long period, lamellae thickness and amorphous thickness remained almost similar. Based on the statistical theory of rubber elasticity, we proved that numerous entanglements, which were characterized by the longest relaxation time or the zero shear viscosity, indeed prevented the extension of chains when the concentration of the long chains was much higher than the long chain overlap concentration.

Individual Molecular Dynamics of an Entangled Polyethylene Melt Undergoing Steady Shear Flow: Steady-State and Transient Dynamics.

The startup and steady shear flow properties of an entangled, monodisperse polyethylene liquid (C1000H2002) were investigated via virtual experimentation using nonequilibrium molecular dynamics. The simulations revealed a multifaceted dynamical response of the liquid to the imposed flow field in which entanglement loss leading to individual molecular rotation plays a dominant role in dictating the bulk rheological response at intermediate and high shear rates. Under steady shear conditions, four regimes of flow behavior were evident. In the linear viscoelastic regime (), orientation of the reptation tube network dictates the rheological response. Within the second regime (), the tube segments begin to stretch mildly and the molecular entanglement network begins to relax as flow strength increases; however, the dominant relaxation mechanism in this region remains the orientation of the tube segments. In the third regime (), molecular disentangling accelerates and tube stretching dominates the response. Additionally, the rotation of molecules become a significant source of the overall dynamic response. In the fourth regime (), the entanglement network deteriorates such that some molecules become almost completely unraveled, and molecular tumbling becomes the dominant relaxation mechanism. The comparison of transient shear viscosity, , with the dynamic responses of key variables of the tube model, including the tube segmental orientation, , and tube stretch, , revealed that the stress overshoot and undershoot in steady shear flow of entangled liquids are essentially originated and dynamically controlled by the component of the tube orientation tensor, rather than the tube stretch, over a wide range of flow strengths.

Superhydrophobic Polymer Surface with Hierarchical Patterns Fabricated in Hot Imprinting Process

Superhydrophobic surfaces have been widely applied to solve environmental issues using their many functions such as drag reduction, oil–water separation and self-cleaning. It is well known that superhydrophobicity of materials can be enhanced by imparting micro/nano hierarchical patterns on its surface. Although several techniques, such as MEMS, coating, and laser ablation, have been suggested to improve superhydrophobicity, they are unsuitable for mass production. To overcome this limitation, a facile fabrication method using hot imprinting process was developed in this study. Hierarchical patterns including micro sinusoidal patterns with discharge craters were formed on the die surface obtained using wire electrical discharge machining. Thermoplastic PTFE and PC polymer surfaces with hierarchical patterns were successfully replicated from the die surface after hot imprinting. In addition, an entangled micro fibril network was observed on the PTFE surface, whereas torn shapes were developed on the PC polymer surface. As a result, the polymer surfaces were found to exhibit superhydrophobicity with a water contact angle > 150°.

Gelling mechanism and interactions of polysaccharides from Mesona blumes: Role of urea and calcium ions

In this study, the relaxation modulus was used to elucidate the gelling mechanism of polysaccharides from Mesona blumes. The pH of Mesona blumes polysaccharides (MBP) was adjusted could significantly change the relaxation modulus of MBP. The results showed that the hydrogen bonds and electrostatic interaction existed in during the formation of MBP gel. The addition of salt ions (sodium ions and calcium ions), EDTA and urea have different effects on the relaxation modulus of MBP. Result showed that the hydrogen bond was the main force maintaining the MBP gel network structure, followed was calcium ions. And electrostatic interaction was not the decisive role of gel formation. The small molecules with active hydrogen-bond donors and/or acceptors were added into MBP, which proved −COOH was involved in the hydrogen bonds formation of MBP gel. In addition, the entanglement network number (ENN) results quantitatively assessed contribution of interaction: hydrogen bonds interaction > calcium ions (calcium bridge) >electrostatic interaction.

Terphen[n]arenes and Quaterphen[n]arenes (n=3–6): One‐Pot Synthesis, Self‐Assembly into Supramolecular Gels, and Iodine Capture

AbstractHerein, two new classes of macrocyclic compounds, terphen[n]arenes (TPns) (n=3–6) and quaterphen[n]arenes (QPns) (n=3–6), were designed and synthesized by a one‐step condensation reaction in relatively high yields. They comprise 2,2′′‐dimethoxy terphenyl and 2,2′′′‐dimethoxy quaterphenyl monomers, respectively, linked by methylene bridges. Given their long and rigid monomers, TPns and QPns have much larger cavities and better self‐assembly properties than classic macrocycles. More interestingly, the cyclic pentamers and hexamers TP5, TP6, QP5, and QP6 formed supramolecular organogels, which were composed of interwoven fibers, nanosheets, or entangled macropore networks formed by multiple face‐to‐face and edge‐to‐face π⋅⋅⋅π stacking interactions. The xerogel materials effectively captured volatile iodine, not only in aqueous media but also in the gaseous state, and could be recycled multiple times without obvious loss in performance.

Terphen[n]arenes and Quaterphen[n]arenes (n=3-6): One-Pot Synthesis, Self-Assembly into Supramolecular Gels, and Iodine Capture.

Herein, two new classes of macrocyclic compounds, terphen[n]arenes (TPns) (n=3-6) and quaterphen[n]arenes (QPns) (n=3-6), were designed and synthesized by a one-step condensation reaction in relatively high yields. They comprise 2,2''-dimethoxy terphenyl and 2,2'''-dimethoxy quaterphenyl monomers, respectively, linked by methylene bridges. Given their long and rigid monomers, TPns and QPns have much larger cavities and better self-assembly properties than classic macrocycles. More interestingly, the cyclic pentamers and hexamers TP5, TP6, QP5, and QP6 formed supramolecular organogels, which were composed of interwoven fibers, nanosheets, or entangled macropore networks formed by multiple face-to-face and edge-to-face π⋅⋅⋅π stacking interactions. The xerogel materials effectively captured volatile iodine, not only in aqueous media but also in the gaseous state, and could be recycled multiple times without obvious loss in performance.

High Axial Ratio Nanochitins for Ultrastrong and Shape-Recoverable Hydrogels and Cryogels via Ice Templating.

High yield (>85%) and low-energy deconstruction of never-dried residual marine biomass is proposed following partial deacetylation and microfluidization. This process results in chitin nanofibrils (nanochitin, NCh) of ultrahigh axial size (aspect ratios of up to 500), one of the largest for bioderived nanomaterials. The nanochitins are colloidally stable in water (ζ-potential = +95 mV) and produce highly entangled networks upon pH shift. Viscoelastic and strong hydrogels are formed by ice templating upon freezing and thawing with simultaneous cross-linking. Slow supercooling and ice nucleation at −20 °C make ice crystals grow slowly and exclude nanochitin and cross-linkers, becoming spatially confined at the interface. At a nanochitin concentration as low as 0.4 wt %, highly viscoelastic hydrogels are formed, with a storage modulus of ∼16 kPa, at least an order of magnitude larger compared to those measured for the strongest chitin-derived hydrogels reported so far. Moreover, the water absorption capacity of the hydrogels reaches a value of 466 g g–1. Lyophilization is effective in producing cryogels with a density that can be tailored in a wide range of values, from 0.89 to 10.83 mg·cm–3, and corresponding porosity, between 99.24 and 99.94%. Nitrogen adsorption results indicate reversible adsorption and desorption cycles of macroporous structures. A fast shape recovery is registered from compressive stress–strain hysteresis loops. After 80% compressive strain, the cryogels recovered fast and completely upon load release. The extreme values in these and other physical properties have not been achieved before for neither chitin nor nanocellulosic cryogels. They are explained to be the result of (a) the ultrahigh axial ratio of the fibrils and strong covalent interactions; (b) the avoidance of drying before and during processing, a subtle but critical aspect in nanomanufacturing with biobased materials; and (c) ice templating, which makes the hydrogels and cryogels suitable for advanced biobased materials.

Predicting embrittlement of polymer glasses using a hydrostatic stress criterion

ABSTRACTIn this study, the aging‐induced embrittlement of three polymer glasses is investigated using a previously developed hybrid experimental–numerical method. The evolution of yield stress of unnotched tensile bars upon aging is coupled to the evolution of embrittlement of notched tensile bars using a numerical model combined with a critical hydrostatic stress criterion that determines the onset of failure. The time‐to‐embrittlement of notched tensile bars with a different notch geometry is predicted and in good agreement with the experimentally determined value. Next to that, the approach is extended to three polysulfone polymers, and it is shown that the value of the critical hydrostatic stress correlates well with the polymers entanglement density: : polymers with a denser entangled network display higher values, that is, a higher resistance against incipient cavitation. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47373.