Search results for "Viscosity."

Thermo-Mechanical Degradation of LDPE-Based Nanocomposites

2007

Thermo-mechanical degradation of LDPE-based nanocomposites was studied by mainly investigating the rheological properties. For all of the investigated processing conditions, the viscosity of the nanocomposites was higher than that of the pure-LDPE matrix, but on increasing the severity of the mixing conditions, the difference between the viscosity of the nano-filled polymer and that of the pure LDPE decreased. The X-ray traces of the nanocomposites suggest that intercalation has been achieved during the melt, when less-severe processing conditions were used. At severe processing conditions (longer mixing time, high temperature and shear stress) the thermo-mechanical degradation was accelera…

Influence of polymer flexibility on nanoparticle dynamics in semidilute solutions

2018

The hierarchical structure and dynamics of polymer solutions control the transport of nanoparticles (NPs) through them. Here, we perform multi-particle collision dynamics simulations of solutions of semiflexible polymer chains with tunable persistence length lp to investigate the effect of chain stiffness on NP transport. The NPs exhibit two distinct dynamical regimes - subdiffusion on short time scales and diffusion on long time scales. The long-time NP diffusivities are compared with predictions from the Stokes-Einstein relation (SER), mode-coupling theory (MCT), and a recent polymer coupling theory (PCT). Increasing deviations from the SER as the polymer chains become more rigid (i.e. as…

Composite soy lecithin–decylpolyglucoside vesicles: A theoretical and experimental study

2008

In the present work, vesicles made with soy lecithin and a commercial mixture of alkyl polyglucosides were prepared and characterized. Vesicles with a constant amount of soy lecithin and an increasing amount of a decylpolyglucoside surfactant, (OrNS10), were formulated and their physicochemical properties were studied with the aim to design a drug delivery system suitable for different applications. To this purpose, morphology, size distribution, ζ-potential and apparent viscosity of the prepared vesicles were studied. Vesicles were also characterized by using optical and light polarized microscopy, transmission electron microscopy and photon correlation spectroscopy. A stability study was …

Are polymers suitable rock analogs?

2002

To evaluate if a polymer is suitable for analog modeling, it is essential to know the rheological properties of the material. Polymers used in analog modeling exhibit a complex rheological behavior; only part of which has been taken into account in most modeling studies. The mechanical behavior is strongly dependent on strain rate and temperature, and is characterized by specific dependencies of the storage and loss moduli, related to the elasticity and viscosity, on the deformation rate (frequency). We have measured the storage and loss moduli at a broad range of strain rates and strains, using an oscillatory parallel-disk rheometer. Investigated materials are polydimethylsiloxane (PDMS), …

Intrinsic viscosities of polyelectrolytes in the absence and in the presence of extra salt: Consequences of the stepwise conversion of dextran into a…

2011

Abstract Viscosities of dilute polymer solutions were measured in capillary viscometers for samples varying in their fraction f of charged units from 0.00 to 0.90. The dependence of the logarithm of the relative viscosity on polymer concentration c is in all cases reproduced quantitatively by three characteristic parameters: [ η ], the intrinsic viscosity; B , a viscometric interaction parameter (related to the Huggins constant); [ η ] , a parameter required only for polyelectrolytes at low concentrations of extra salt. In pure water [ η ] increases more than 80 times as the fraction f rises from zero to 0.90 and [ η ] starts from zero and goes up to ≈71 mL/g. Upon the addition of NaCl [ η …

Gamma-radiation ageing of a low density polyethylene. Effects of irradiation temperature and dose rate

1993

Abstract Ageing due to gamma radiation of a low density polyethylene at various dose rates and temperatures is studied; the effect of thermal treatment only is also considered. The modifications induced in the molecular and crystallinity behaviour of the polymer are investigated by means of gel extraction, measurements of intrinsic viscosity and thermal analysis. Results indicate the occurrence of both crosslinking and oxidative degradation; the extent of the latter increases on decreasing the irradiation dose rate and on increasing the irradiation temperature. Some exceptions are found because of the increase in the mobility of free radicals at high temperature. These effects modify also t…

1996

Developing an artificial oxygen carrier for use in humans, we polymerize native haemoglobin and myoglobin, using bifunctional, amino group specific cross-linkers, to soluble, so-called hyperpolymers. These polymers, like other polymerized globular proteins, are members of a new class of macromolecues which consist of macromolecular base units. They all have, due to the mechanisms of the chemical reaction, broad distributions of molecular weights. Fractions of hyperpolymers of human haemoglobin were obtained by employing preparative gel-permeation (size-exclusion) chromatography. The calibration curve of analytical gel-permeation chromatography (GPC) for haemoglobin hyperpolymers was determi…

On the viscosity of moderately concentrated solutions of poly(ether imide) in a mixed solvent of marginal quality

2000

Abstract Viscosities η were measured for moderately concentrated (15.5 wt%) solutions of poly(ether imide) (PEI) as a function of the composition of the cosolvent tetrahydrofuran (THF) plus γ-butyrolactone (γ-BL). The solutions are almost by a factor of four less viscous when THF predominates than when γ-BL is the major component of the solvent mixture. Furthermore, the viscosity passes a minimum as the composition of the mixed solvent is varied. Both observations can be well understood in terms of the viscosities of the mixed solvents and the hydrodynamic interaction between the polymer molecules. The pronounced dissymmetry of η as a function of the composition of the mixed solvent η resul…

Aqueous Laponite Clay Dispersions in the Presence of Poly(ethylene oxide) or Poly(propylene oxide) Oligomers and their Triblock Copolymers

2008

The effect of polyethylene oxide (PEO) or polypropylene oxide (PPO) oligomers of various molecular weight (Mw) as well as of triblock copolymers, based on PEO and PPO blocks, on aqueous laponite RD suspensions was studied with small-angle neutron scattering (SANS). The radius of gyration (RG) increases for low Mw whereas the opposite occurs for larger Mw. This behavior is explained on the-basis that an effective RG is given by two contributions: (1) the size of the particles coated with the polymer and (2) the interactions between the laponite RD particles which are attractive for small and repulsive for large polymers. The SANS curves in the whole Q-range are well described by a model of n…

1991

A new rotational viscometer is presented which can be operated up to 2 000 bar and a maximum shear stress of 420 Pa. It allows, for the first time, to investigate the non-Newtonian flow behaviour of moderately concentrated polymer solutions. Results of measurements with two representatives of the system 2-propanol/poly(butyl methacrylate) with weight-average molecular weights Mw = 520 000 and Mw = 2 050 000, and ratios of weight- to number-average molecular weights Mw/Mn = 1,08 and Mw/Mw = 1,23, resp. in the region of moderate polymer concentrations are reported. For a ca. 7 wt.-% solution of the higher-molecular-weight polymer one obtains viscometric relaxation times τ0 varying from 1 to 1…