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Rheological Experiments (rheological + experiment)

Distribution by Scientific Domains

Polymers and Materials Science	80%

Selected Abstracts

Gel-to-Sol and Sol-to-Gel Transitions Utilizing the Interaction of , -Cyclodextrin with Dodecyl Side Chains Attached to a Poly(acrylic acid) Backbone

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 10 2005
Itsuro Tomatsu
Abstract Summary: By utilizing the interaction of , -cyclodextrin (, -CD) with dodecyl side chains in polymers of x mol-% dodecyl-modified poly(acrylic acid) (p(AA/C12(x))), systems that undergo gel-to-sol and sol-to-gel transitions were successfully constructed. Rheological experiments indicated that addition of , -CD to the hydrogel of p(AA/C12(5)) caused a drastic decrease in the viscosity, while addition of oligo(, -CD) to the solution of p(AA/C12(2)) led to a remarkable increase in the viscosity. Photographs for a gel-to-sol transition upon addition of , -CD to 5.0 g,·,L,1 p(AA/C12(5)). [source]

Preparation and characterization of a customized cellulose acetate butyrate dispersion for controlled drug delivery

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2002
Siva Vaithiyalingam
Abstract The purpose of the present experiment was to prepare and characterize the aqueous-based pseudolatex system of cellulose acetate butyrate (CAB) for controlled drug delivery. Aqueous pseudolatex systems are advantageous over organic-based coating systems because these systems are devoid of criteria pollutants such as carbon monoxide, nitrogen oxides, nonmethane volatile organic compounds, and sulfur dioxide. Pseudolatex was prepared with CAB and polyvinyl alcohol (stabilizer) by a polymer emulsification technique. The stability of pseudolatex was evaluated. Particle size was measured and rheological experiments were conducted. The glass transition temperature, microscopic free volume, permeation coefficient, and mechanical properties of plasticized pseudolatex films were estimated. Surface roughness of coating on inert Nu-Pareil® beads (Ingredient Technology Corp., Mahwah, NJ) was measured as a function of coating weight gain. The CAB Pseudolatex was found to be stabilized by steric forces. From intrinsic viscosity, the thickness of the stabilization layer was estimated. An increase in polymeric particles proportionately decreased the thickness of the stabilization layer. All the essential properties of a coating membrane such as microscopic free-volume fraction, permeability coefficient, mechanical properties, and glass transition temperature were fairly controllable as a function of plasticizer concentration. The pseudolatex dispersion of CAB was stable with negligible sedimentation volume and a particle size of 300 nm. Because CAB is water insoluble and non-ionizable, this pseudolatex can be used for pH-independent coating. The films obtained were strong and flexible for controlled drug delivery applications. Coating with the CAB dispersion reduced the surface roughness of beads but it remained stable as a function of increase in coating weight gain. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:1512,1522, 2002 [source]

Influence of composition and phase morphology on rheological properties of polypropylene/poly(ethylene- co -octene) blends

POLYMER COMPOSITES, Issue 1 2010
Lin Zhu
In this article, the phase morphology and rheological properties of polypropylene (PP)/poly(ethylene- co -octene) (POE) blends with a droplet-matrix microstructure were studied by scanning electron microscopy and rheological experiments. The data were analyzed to yield the variations of rheological behavior with blend composition and insight into the microstructure of PP/POE blends. The Palierne's emulsion type model was used to extract information on rheological properties, and the interfacial tensions between the PP and POE were determined by fitting the experimental data with this model. The results indicated that the interfacial tensions were shown to depend on blend composition and temperature. Rheological properties of PP/POE blends were investigated in a systemic way with varying shear histories. The results showed that shear history had an important effect on the rheological properties of the blends due to the dispersed phase (POE) domains refined with increasing preshear rate and preshear time. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers [source]

Influence of melt-blending conditions on structural, rheological, and interfacial properties of polyamide-12 layered silicate nanocomposites

POLYMER ENGINEERING & SCIENCE, Issue 8 2006
Pascal Médéric
The influence of the melt-blending conditions on the structural, rheological, and interfacial properties of modified montmorillonite/Polyamide-12 nanocomposites has been studied performing transmission electron microscopy observation combined with X-Ray diffraction and rheological experiments. In the dilute regime, for short mixing times, the apparent aspect ratio of primary clay entities, determined from intrinsic viscosity measurements, is shown to increase with rotational speed. At high blade rotational speeds, the viscometric results suggest an almost achieved exfoliation, as confirmed by transmission electron microscopy micrographs. For longer mixing times, a significant drop of viscous dissipation is observed, which is very marked at high blade rotational speeds and attributed to a modification of the particle/matrix interface. In the concentrated regime, the rheological behavior of nanocomposites is attributed to the formation of a network of mesoscopic domains, composed of correlated clay entities. Upon increasing strain during mixing, the clay aggregates within these domains break into intercalated stacks and finally exfoliated layers, as shown by transmission electron microscopy micrographs and wide-angle X-ray diffraction patterns. The melt state elastic and viscous properties of the nanocomposites are mainly governed by the networked domains, and not by the nature and properties of the structure within the domains. POLYM. ENG. SCI. 46:986,994, 2006. © 2006 Society of Plastics Engineers. [source]

Morphology and rheological properties of polypropylene/reactive elastomer blends

POLYMER ENGINEERING & SCIENCE, Issue 10 2002
Frédérique Marguerat
The relation of morphology to the linear viscoelastic properties for polymer blends consisting of an inert polypropylene and an elastomeric dispersed phase, made of two miscible copolymers, EVA and EMA, was investigated. The rheological properties of the elastomeric phase were modified by crosslinking in presence of an organometallic catalyst. The activation energy for the transesterification reaction taking place between EVA and EMA has been determined by following the increases of the complex viscosity with time and temperature. The Palierne model has been used to describe the linear viscoelastic behavior of the blends, and to estimate the interfacial tension between the immiscible components. The model was shown to describe relatively well the linear viscoelastic properties of reactive and nonreactive blends containing 30% or less elastomer. In parallel, the morphology of reactive and nonreactive blends (i.e. without catalyst in the elastomeric phase), before and after rheological experiments, has been determined using scanning electron microscopy. The size of the dispersed elastomeric particles for reactive blends prepared using an internal mixer was found to be, in most cases, much smaller than that for nonreactive blends. [source]