Search results for "viscoelasticity"
showing 10 items of 224 documents
Non linear viscoelasticity of polymeric liquids interpreted by means of a stress dependence of free volume
1977
Several existing data of non-linear viscoelasticity of amorphous polymers aboveT g are here interpreted by assuming that the free volume changes during the motion. Equations of a stress-temperature equivalence are suggested which favorably compare with the data. It is also shown that the volume variations are sufficiently small to have escaped observation.
New Viscoelastic Materials Obtained by Insertion of anα-Olefin in atrans-Polyisoprene Chain with a Single-Component Organolanthanide Catalyst
2001
Copolymerisation of isoprene with C 6 -C 18 a-olefins by a single component organolanthanide catalyst affords poly(trans-1,4-isoprene) containing 6-10% of inserted olefin. The mechanical properties of highly crystalline transpolyisoprene are dratically modified after insertion of the alkyl chains, leading to quasi-amorphous viscoelastic materials.
Rheological Consequences of Hydrogen Bonding: Linear Viscoelastic Response of Linear Polyglycerol and Its Permethylated Analogues as a General Model …
2014
Viscoelastic properties of linear, hydroxyl-functional polymers are only little understood with respect to the effect of functional group interactions. Melt rheology and thermal phase transitions of linear polyethers (polyglycerol, linPG-OH) and their methylated analogues (linPG-OMe) in a broad molecular weight range (Mn = 1–100 kg/mol) with low polydispersities (PDI) have been investigated as a general model for hydroxyl-functional polymers with respect to their functionality and hydrogen bond interactions. We provide detailed insight into the rheodynamics of nonentangled and well-entangled polyethers bearing one functional group per monomer unit. Booij–Palmen plots (BBP) revealed failure …
Local dynamics in supramolecular polymer networks probed by magnetic particle nanorheology
2019
Transient supramolecular polymer networks are promising candidates as soft self-healing or stimuli-sensitive materials. In this paper, we employ a novel nanorheological approach, magnetic particle nanorheology (MPN), in order to better understand the local dynamic properties of model supramolecular networks from a molecular point of view. Hence, the bond strength between four-arm star-shaped polyethylene glycol (PEG) functionalized at the four extremities with terpyridine ligands is tuned by implementing different metal ions with variable complexation affinities for the ligand. We show that MNP allows for the evaluation of the strength and connectivity of the polymer networks by the estimat…
High energy radiation cure of resin systems for structural adhesives and composite applications
2002
Abstract Radiation cure polymerisation of a commercial diglycidyl ether of bisphenol F epoxy resin has been achieved using a 60Co irradiation source, compounding the monomer with few percentage of an onium salt catalyst. The cure process has been monitored by a gamma-calorimetric technique and systems irradiated at doses corresponding to different positions in the gamma-calorimetric curve have been characterised via solubility tests and dynamic mechanical torsion analysis. Changes in both the measured gel fractions and tan δ values were associated with the progress of polymerisation and crosslinking reactions and these were dose dependent. Furthermore, systems irradiated at lower doses exhi…
Structure and Yielding of Colloidal Silica Gels Varying the Range of Interparticle Interactions.
2016
The relationship between interaction range, structure, fluid-gel transition, and viscoelastic properties of silica dispersions at intermediate volume fraction, Φv ≈ 0.1 and in alkaline conditions, pH = 9 was investigated. For this purpose, rheological, physicochemical, and structural (synchrotron-SAXS) analyses were combined. The range of interaction and the aggregation state of the dispersions were tuned by adding either divalent counterions (Ca(2+)) or polycounterions (PDDA). With increasing calcium chloride concentration, a progressive aggregation was observed which precludes a fluid-gel transition at above 75 mM of calcium chloride. In this case, the aggregation mechanism is driven by s…
Transient birefringence of polymer melts in intermittent shear flow: Model analysis of the non-linear viscoelastic behaviour
1977
A non-linear viscoelastic model has been used to interpret transient flow birefringence in changing shear flow for a polymer melt. It is shown how the new model is consistent with the basic hypothesis of the linear stress-optical law. Stress growth in shear flow and relaxation after different amounts of shearing are compared with the predictions of the non-linear model. A good agreement between experimental data and theoretical predictions is found.
Viscoelastic recovery behavior following Atomic Force Microscope nanoindentation of semi-crystalline poly(ethylene)
2007
The residual imprint left behind by the AFM nanoindentation of polymers has been seldom studied in the past. In this work, the evolution of indentations at room temperature performed on a semicrystalline poly- (ethylene) in a broad range of experimental conditions is presented. The study shows that the recovery after 24 h is substantial, although not complete. Moreover, the dynamics of the recovery process is not seen to depend on the magnitude of the applied load for the nanoindentation, but instead on the rate of the indentation used. This points out that viscoelastic processes are minimized when performing fast nanoindentations, while at low loading rates there seems to be a residual vis…
Linear ViscoElastic (LVE) Behaviour of Pure Bitumen via Fractional Model
2012
AbstractBy fitting experimental data from static creep/recovery carried out on pure bitumen, it is shown that the fractional model proposed enables the description of both creep and recovery behaviour with fewer parameters than those needed by other models in the literature. In particular, the model is fitted to experimental data of complex modulus |G*| and phase angle δ° obtained from Dynamic Mechanical Analysis. Lastly, it is demonstrated that when the fractional model is used, complex modulus isotherms for a range of frequencies can be created simply starting from isochronals at f = 1Hz.
Viscoelastic properties of acid milk gel as affected by fat nature at low level
2005
International audience; The viscoelastic properties of acid milk gels containing small amounts of different fats were investigated. Skim milk was reconstituted from ultra low-heat skim milk powder and emulsions made with 2% (v/v) sunflower oil, olive oil, groundnut oil, or anhydrous milk fat using a pressure homogenizer. Acidification at 20 °C for 14 h to pH ∼4.6 was achieved by adding glucono-δ-lactone to the emulsion. Stress relaxation testing enabled determination of the firmness and the solid-like properties, i.e., elasticity. Regardless of the physical state of the fat, emulsion gels exhibited higher firmness than fat-free gels, despite the low fat level used. The firmness of the gels …