Shape memory polymers (SMPs) are materials with a great potential for future use in smart materials and structures. When heated from cold state (below the transformation temperature, which can either be the glass transition temperature or the melting temperature of the polymer) to hot state (above the transformation temperature) they undergo transformation which can be compared with martensitic transformation of shape memory alloys. This process induces great changes of the mechanical properties and some shape memory phenomenon can be observed. This study is an experimental evaluation of the mechanical properties of SMP Veriflex under different test conditions. Veriflex was chosen because of its easy accessibility. Furthermore its properties are similar to epoxy resins which make it very suitable for usage in a wide variety of technical applications. Dynamic mechanical analysis (DMA) was used to determine evolution of the viscoelastic properties versus temperature and frequency under cyclic harmonic loading. The glass transition temperature clearly appears in a range from 45\degree C to 60\degree C depending on loading frequency. The glass transition is noticeably marked by an impressive decrease in the storage modulus of about 4 decades. The master curve of Veriflex was created and allows the time-temperature superposition to be constructed for this material. Thermo-mechanical working cycle of SMP with 100% elongation was also experimentally tested. Finally results from all these experimental investigations were used to design a demonstrator showing the possibility of application in engineering and especially for shape control.
We consider concentration dependence of rheological properties of associative telechelic polymer solutions. Experimental results for model telechelic polymer solutions show rather strong concentration dependence of rheological properties. For solutions with relatively high concentrations, linear viscoelasticity deviates from the single Maxwell behavior. The concentration dependence of characteristic relaxation time and moduli is different in high and low concentration cases. These results suggest that there are two different concentration regimes. We expect that densely connected (well percola…
We show that non-entangled polymers display an elastic-like behaviour at a macroscopic scale (probed at some 0.100 mm thickness) up to at least hundred degrees above the glass transition temperature. This observation, found under non-slippage conditions, both for side-chain liquid crystalline polymers and ordinary polymers, is in contradiction with the typically found flow behaviour of polymer melt. Our measurements were carried out with a conventional rheometer at thicknesses of several tenths millimetres. Thus, we were probing bulk properties. The observed elasticity supposedly implies that …
The rheological properties of viscoelastic materials like polymer melts are greatly affected by factors like salinity, temperature, concentration and pH of the solution. In this study, the memory of the stress affected by each of these factors is shown to be trapped in the order of the fractional derivative of the dynamical equation describing stress and strain in the material. To demonstrate this, the rheological properties of the polymer melt hydrolyzed polyacrylamide HPAM have been modeled using a two element Maxwell model. The model has successfully reproduce existing experimental data on …
A reasonably accurate representation of a polymer chain is provided by beads connected with rods, or stiff, inextensible springs that mimic a single Kuhn step. Due to high computational cost, coarse-grained bead-spring models are used in typical applications, where each spring is supposed to replace several Kuhn steps. Earlier investigations indicate that the BD simulation predictions of the steady state in different flows, with these different levels of discretization, are largely qualitatively similar. However, subtle quantitative differences exist even for the steady states. In this study, …
Tunability of Dissipative Particle Dynamics simulations for Excluded Volume and Hydrodynamic Interactions in polymer solutions and Rheological predictions
A study of the reinforcement effect of a soft polymer matrix by hard nanometric filler particles is presented. In the main part of this article, the structure of the silica filler in the matrix is studied by Small Angle Neutron Scattering (SANS), and stress-strain isotherms are measured to characterize the rheological properties of the composites. Our analysis allows us to quantify the degree of aggregation of the silica in the matrix, which is studied as a function of pH (4-10), silica volume fraction (3-15%) and silica bead size (average radius 78 A and 96 A). Rheological properties of the s…
In multi-component soft matter, interface properties often play a key role in determining the properties of the overall system. The identification of the internal dynamic structures in non-equilibrium situations requires the interface rheology to be characterized. We have developed a method to quantify the rheological contribution of soft interfaces and evaluate the dynamic modulus of the interface. This method reveals that the dynamic shear responses of interfaces in bilayer systems comprising polypropylene and three different polyethylenes can be classified as having hardening and softening …
X-ray particle tracking velocimetry for steady-state rheological characterization: Case study of a complex polymer melt flow in material extrusion additive manufacturing
University of Stuttgart（斯图加特大学）；University of Milan（米兰大学）；CNR – Consiglio Nazionale delle Ricerche, Istituto di Chimica della Materia Condensata e di Tecnologie per l’Energia（意大利国家研究委员会凝聚态材料与能源技术研究所）
The antagonistic effect of processing and thermal annealing on both the filler structure and the polymer matrix is explored in polymer nanocomposites based on natural rubber with precipitated silica incorporated by coagulation from aqueous suspension followed by roll-milling. Their structure and linear and non-linear rheology have been studied, with a particular emphasis on the effect of high temperature thermal treatment and the number of milling passes. Small-angle X-ray scattering intensities show that the silica is organized in small, unbreakable aggregates containing ca. 50 primary nanopa…
The handleability and sensory perception of hand sanitisers by consumers affect the hygiene outcome. Spillage may result in under-dosing and poor sensory properties can lead to under-utilisation. We first propose four principles (low run off, spreadability, smoothness and non-stickiness) for designing the rheology of thickened alcohol-based hand rubs with acceptable handleability and hand feel. We then evaluate a commercial hand gel and a variety of simplified formulations thickened with microgels (Carbopol 974P, Carbopol Ultrez 20 and Sepimax Zen), or linear polymers (Jaguar HP 120 COS), and …
Chocolate is known to undergo solid-liquid transition upon an increase in temperature as well as under application of deformation field. Upon sudden reduction in temperature from a molten state (or thermal rejuvenation), rheological properties of chocolate undergo evolution as a function of time under isothermal conditions, a behavior reminiscent of physical aging in polymeric glasses. Then again, subsequent to cessation of shear flow (or mechanical rejuvenation), chocolate shows temporal evolution of the rheological properties, a behavior similar to physical aging in soft glassy materials. In…
Mixtures of polymers of varying topologies and stiffnesses display complex emergent rheological properties that often cannot be predicted from their single-component counterparts. For example, entangled blends of ring and linear polymers have been shown to exhibit enhanced shear thinning and viscosity, as well as prolonged relaxation timescales, compared to pure solutions of rings or linear chains. These emergent properties arise in part from the synergistic threading of rings by linear polymers. Topology has also been shown to play an important role in composites of flexible (e.g., DNA) and s…
Fractional calculus has been proved to be very effective in representing the visco-elastic relaxation response of materials with memory such as polymers. Moreover, in modelling the temperature dependency of the material functions in thermo-visco-elasticity, the standard time-temperature superposition principle is known to be ineffective in most of the cases (thermo-rehological complexity). In this work, a novel finite element formulation and numerical implementation is proposed for the simulation of transient thermal analysis in thermo-rehologically complex materials. The parameters of the vis…
We develop computational methods that incorporate shear into fluctuating hydrodynamics methods. We are motivated by the rheological responses of complex fluids and soft materials. Our approach is based on continuum stochastic hydrodynamic equations that are subject to shear boundary conditions on the unit periodic cell in a manner similar to the Lees-Edwards conditions of molecular dynamics. Our methods take into account consistently the microstructure elastic mechanics, fluid-structure hydrodynamic coupling, and thermal fluctuations. For practical simulations, we develop numerical methods for…
We demonstrated recently that polyelectrolytes with cationic moieties along the chain and a single anionic head are able to form physical hydrogels due to the reversible nature of the head-to-body ionic bond. Here we generate a variety of such polyelectrolytes with various cationic moieties and counterion combinations starting from a common polymeric platform. We show that the rheological properties (shear modulus, critical strain) of the final hydrogels can be modulated over three orders of magnitude depending on the cation/anion pair. Our data fit remarkably well within a scaling model invol…
We propose a single chain slip-spring model, which is based on the slip-spring model by Likhtman [A. E. Likhtman, Macromolecules, 38, 6128 (2005)], for fast rheology simulations of entangled polymers on a GPU. We modify the original slip-spring model slightly for efficient calculations on a GPU. Our model is designed to satisfy the detailed balance condition, which enables us to analyze its static or linear response properties easily. We theoretically analyze several statistical properties of the model, such as the linear response, which will be useful to analyze simulation data. We show that …
Biomimetic hydrogels based on natural polymers are a promising class of biomaterial, mimicking the natural extra-cellular matrix of biological tissues and providing cues for cell attachment, proliferation and differentiation. With a view to providing an upstream method to guide subsequent experimental design, the aim of this study was to introduce a mathematical model that described the rheological properties of a hydrogel system based on covalently crosslinked collagen triple helices. In light of their organization, such gels exhibit limited collagen bundling that cannot be described by exist…
Towards the Multiscale Design of Pressure Sensitive Adhesives
Basque Center for Applied Mathematics（巴斯克应用数学中心）；University of the Basque Country UPV/EHU（巴斯克大学）；Ikerbasque, Basque Foundation for Science（伊克拉巴斯科，巴斯克科学基金会）
Polymer architecture plays critical roles in both bulk rheological properties and microscale macromolecular dynamics in entangled polymer solutions and composites. Ring polymers, in particular, have been the topic of much debate due to the inability of the celebrated reptation model to capture their observed dynamics. Macrorheology and differential dynamic microscopy (DDM) are powerful methods to determine entangled polymer dynamics across scales, yet they typically require different samples under different conditions, preventing direct coupling of bulk rheological properties to the underlying…
Blends of polymers of different topologies, such as ring and supercoiled, naturally occur in biology and often exhibit emergent viscoelastic properties coveted in industry. However, due to their complexity, along with the difficulty of producing polymers of different topologies, the dynamics of topological polymer blends remains poorly understood. We address this void by using both passive and active microrheology to characterize the linear and nonlinear rheological properties of blends of relaxed circular and supercoiled DNA. We characterize the dynamics as we vary the concentration from belo…
The synchronized molecular dynamics simulation via macroscopic heat and momentum transfer is proposed for the non-isothermal flow behaviors of complex fluids. In this method, the molecular dynamics simulations are assigned to small fluid elements to calculate the local stresses and temperatures and are synchronized at certain time intervals to satisfy the macroscopic heat- and momentum- transport equations. This method is applied to the lubrication of a polymeric liquid composed of short chains with ten beads between parallel plates. The rheological properties and conformation of polymer chain…
Analysis of the thermo-mechanical behaviour of polymers has been and still is the subject of many rheological studies both experimentally and theoretically. For small deformations, the modelling framework retained by rheologists is often of linear visco-elasticity, which led to the definition of complex modules and used to identify the glass transition temperature as the so called rule of time-temperature superposition. In this context, the effects of time are almost unanimously associated with viscous effects. It has also been observed that the dissipative effects associated with viscous effe…
We report the details of the construction and calibration of an ultra sensitive surface rheometer, inspired by the setup described in [C.F. Brooks et al Langmuir 15, 2450 (1999)], which makes use of high resolution video tracking of the motion of a floating magnetized needle and is capable of measuring the viscoelastic response of a Langmuir monolayer with an accuracy of 10^-5 N/m. This instrument is then employed for the rheological characterization of a Langmuir monolayer of a photosensitive azobenzene polymer, which can be brought out of equilibrium by a suitable photoperturbation. The comp…
We consider the simplest representative of the class of multiply branched polymer macromolecules, known as a pom-pom structure. The molecule consists of a backbone linear chain terminated by two branching points with functionalities (numbers of side chains) of $f_1$ and $f_2$, respectively. In a symmetrical case, considered in the present study, one has $f_1=f_2=f$ with the total number of chains $F=2f+1$. Whereas rheological behaviour of melts of pom-pom molecules are intensively studied so far, we turn our attention towards conformational properties of such polymers in a regime of dilute sol…
We study the influence of chain stiffness on droplet flow in a nano-channel, coated with semiflexible hydrophobic polymers by means of non-equilibrium molecular-dynamics simulations. The studied system is then a moving droplet in the slit channel, coexisting with its vapor and subjected to periodic boundary conditions in the flow direction. The polymer chains, grafted by the terminal bead to the confining walls, are described by a coarse-grained model that accounts for chain connectivity, excluded volume interactions and local chain stiffness. The rheological, frictional and dynamical properti…
We study theoretically the formation of shear bands in time-dependent flows of polymeric and wormlike micellar surfactant fluids, focussing on the protocols of step shear stress, step shear strain (or in practice a rapid strain ramp), and shear startup, which are commonly studied experimentally. For each protocol we perform a linear stability analysis to provide a fluid-universal criterion for the onset of shear banding, following our recent Letter [Phys. Rev. Lett. 110 (2013) 086001]. In each case this criterion depends only on the shape of the experimentally measured rheological response fun…
Star polymer undergoes a transformation from a group of loosely coupled chains at low number of arms to a dense hairy colloid at their high number. This change affects solubility, aggregation and rheological behavior and is of much practical interest. We study the range of size and shape properties of the star molecule and of its individual arms upon this transformation. Theoretical calculations are based on a continuous chain model and are performed in the first order in $ε=4-d$. Computer simulations are done by the dissipative particle dynamics and in part by Monte Carlo method and the resul…
Through a combination of rheological characterization and temperature-variable imaging methods, a novel gelation pathway in dilute solutions of a semiconducting polymer to achieve interconnected, crystalline networks with hierarchical porosity is reported. Upon rapid cooling, solutions of regioregular poly(3-hexylthiophene) (RR-P3HT) in ortho-dichlorobenzene formed thermoreversible gels. Temperature-variable confocal microscopy revealed cooling-induced structural rearrangement to progress through viscoelastic phase separation. The phase separation process arrested prematurely during the format…
The Synchronized Molecular-Dynamics simulation which was recently proposed by authors [Phys. Rev. X {\bf 4}, 041011 (2014)] is applied to the analysis of polymer lubrication between parallel plates. The rheological properties, conformational change of polymer chains, and temperature rise due to the viscous heating are investigated with changing the values of thermal conductivity of the polymeric liquid. It is found that at a small applied shear stress on the plate, the temperature of polymeric liquid only slightly increases in inverse proportion to the thermal conductivity and the apparent vis…
For optimal application, pressure-sensitive adhesives must have rheological properties in between those of a viscoplastic solid and those of a viscoelastic liquid. Such adhesives can be produced by emulsion polymerisation, resulting in latex particles which are dispersed in water and contain long-chain acrylic polymers. When the emulsion is dried, the latex particles coalesce and an adhesive film is formed. The rheological properties of the dried samples are believed to be dominated by the interface regions between the original latex particles, but the relation between rheology and latex parti…
This paper reports the first example of the degradable ROMP thermosetting materials catalysed by bio-derived acids and cutinase from Thermobifida cellulosilytica (Thc_Cut1). The ROMP thermosetting materials are based on norbornene dicarboximides containing acetal ester groups only in the crosslink moiety. The insoluble cross-linked materials were subjected to acid-catalysed hydrolysis using bio-derived acetic and citric acids as well as enzymatic degradation using Thc_Cut1, resulting in the materials becoming completely soluble in dichloromethane. 1H NMR and rheological analysis performed on m…
Cellulose nanocrystals (CNC) are naturally-derived nanostructures of growing importance for the production of composites having attractive mechanical properties, and offer improved sustainability over purely petroleum-based alternatives. Fabrication of CNC composites typically involves extrusion of CNC suspensions and gels in a variety of solvents, in the presence of additives such as polymers and curing agents. However, most studies so far have focused on aqueous CNC gels, yet the behavior of CNC-polymer gels in organic solvents is important to their wider processability. Here, we study the r…
