Baltasar Mena

A note on the translation of a thin rod inside a cylinder

The problem of a thin rod moving longitudinally along the axis of symmetry of a cylindrical vessel is examined for Newtonian and non-Newtonian liquids.For non-Newtonian fluids, the inelastic power-law type solution predicts the experimental results particularly well. On account of wall effects, the induced pressure gradients are much greater for a Newtonian fluid than for a viscoelastic fluid. In fact, in the latter case, they may be considered negligible when the radius of the inner cylinder is small compared to the one of the outer cylinder.

Instrumentation and start up of a new elongational rheometer with a preshearing history

This article describes the design, start up, and some preliminary results of a rheometer that preshears the test fluid and measures its elongational viscosities. Preshearing takes place within a concentric cylinders arrangement. Fluid goes out from the lower part of the cylinders arrangement where an elongational flow is produced, by means of a vacuum chamber, which draws out the fluid filament. The influence of the preshearing history upon the elongational properties is analyzed. Data of elongational stress, uniaxial stretch rate, elongational normal stress difference, and apparent elongational viscosity are obtained. The rheometer design is based on a previous work by Sridhar and Gupta [Rheological Act 24, 207 (1985)]. Glycerin was used as the test fluid. Stretch rates up to 1250 s−1 were found. Troutons ratios ranging from 2.6 to 3.6 were obtained.

Characterization of hybrid microparticles/Montmorillonite composite with raspberry-like morphology for Atorvastatin controlled release

In this work, we prepared a novel composite based on hybrid gelatin carriers and montmorillonite clay (MMT) to analyze its viability as controlled drug delivery system. The objective of this research involves the characterization of composites formed by structured lipid-gelatin micro-particles (MP) and MMT clay. This analysis included the evaluation of the composite according to its rheological properties, morphology (SEM), particle size, XRD, FT-IR, and in vitro drug release. The effect of pH in the properties of the composite is evaluated. A novel raspberry-like or armor MP/MMT clay composite is reported, in which the pH has an important effect on the final structure of the composite for ad-hoc drug delivery systems. For pH values below the isoelectric point, we obtained defined morphologies with entrapment efficiencies up to 67%. The pH level controls the MP/MMT composite release mechanism, restringing drug release in the stomach-like environment. Intended for oral administration, these results evidence that the MP/MMT composite represents an attractive alternative for intestinal-colonic controlled drug delivery systems.

On the motion of a rod along the axis of a cylinder

The problem of a thin rod moving logitudinally along the axis of symmetry of a cylindrical vessel is examined for Newtonian and non‐Newtonian liquids. The influence of each rheological property of the fluid upon the total drag force on the rod is analyzed separately. It is shown that for very thin rods, viscoelasticity may be approximated with great accuracy by an inelastic (power‐law type) solution and that effects may be neglected entirely. The induced pressure gradients due to wall effects are much greater for a Newtonian fluid than for a viscoelastic liquid so that for the latter they may be considered negligible when the inner cylinder radius is small compared to the radius of the outer cylinder.