Polymeric materials

Summary The Polymer Section of the Santa Barbara Workshop on Modeling of Materials is briefly reviewed. Motivation and need for modeling in polymer-based materials are outlined and the recommendations resulting from the workshop reported.     

The Influence of Water-soluble Polymers and pH on Hydroxypropyl-β-Cyclodextrin Complexation of Drugs

The effect of water-soluble polymers and ionization of the drug molecules on the cyclodextrin, mainly 2-hydroxypropyl-β-cyclodextrin (HPβCD), solubilization of drugs was investigated. HPβCD has significant solubilizing effect on acetazolamide, prazepam, and sulfamethoxazole in aqueous solutions. All three polymers tested-i.e., hydroxypropyl methylcellulose (HPMC), polyvinylpyrrolidone (PVP), and carboxymethylcellulose-increase the solubilizing effect of HPβCD. The polymers increase the solubilization by increasing the apparent stability constant (K_c of the drug-HPβCD complex. Thus, addition of 0.10% (w/v) HPMC to the aqueous complexation medium results in a 56% increase in K, for the acetazolamide-HPβCD complex and a 200% increase in K_c for the prazepam-HPβCD complex. Addition of 0.25% (w/v) PVP to the complexation medium results in a 138% increase in K for the sulfamethoxazole-HPβCD complex. The HPβCD solubilization of the drugs can also be improved by ionization of the drug molecule through pH adjustments. However, larger improvements of the HPβCD solubilization are obtained when both methods are used simultaneously compared to when either method is used separately.     

The molecular mechanisms of actin-based intracellular motility by Listeria monocytogenes

A rapid, sensitive method was developed for the quantification of the R- and S-enantiomers of ketoprofen and their acyl glucuronide conjugates in the plasma and dialysate of hemodialysis-dependent anephric patients. Unconjugated R- and S-ketoprofen plasma concentrations were determined directly by liquid chromatography using a S,S-Whelk-O1 chiral stationary phase. R- and S-Ketoprofen glucuronide for use as standard were resolved using a C18 reversed-phase HPLC column with a mobile phase containing the ion-pair reagent tetrabutylammonium hydrogen sulfate. Plasma glucuronides, however, could not be directly quantified due to matrix interference. Therefore, the glucuronides were isolated using reversed-phase HPLC and quantified after alkaline hydrolysis using the S,S-Whelk-O1 chiral stationary phase column.     

Computer optimization of transducer transfer functions usingconstraints on bandwidth, ripple, and loss

Transducers, having one piezoelectric layer near its half-wave resonance and N quarter-wave layers, are designed using computer optimization to adjust the thicknesses and impedances of the various layers so as to fit the resulting transfer function to a target function. An augmented Mason model is used to evaluate the transducer. Optimization of fit is by a steepest descent algorithm. Essentially error-free fits are achieved for target functions that match the underlying dynamics. By applying classical filter theory to a lumped-element transducer model, the transducers dynamics are identified as all-pole filters, which are characterized by polynomials of order N to N+1. The design methodology is tested by designing a series of low-loss transducers that explore fractional bandwidths from 45 to 116%. From these studies there appears to be constraints on the minimum Q of the poles, and other properties. Typical power transfer efficiencies of -1 dB are achieved by impedance scale matching. Using a second-order Fano bound, it is shown that the matching layers function as an optimal compensation network for low-loss flat bandpass transducers. Finally, by the inclusion of loss, lower Q poles are demonstrated with a Bessel transducer     

Effect of rotation on the structure of a convecting mushy layer

Summary Nonlinear natural convection in a mushy layer during solidification of a binary alloy is investigated under a high gravity environment where the rotation axis is inclined to the high gravity vector. Asymptotic and scaling analyses are applied to convective flow within the mushy layer and in vertical chimneys. The main result is that, for some particular moderate rotation range, vertical velocity in the chimneys decreases rapidly with increasing rotation rate and appears to have opposite signs across some rotation dependent vertical level.     

Vitamin C Spray Drying: Study of the Thermal Constraint

Temperature variation in the spray drying method has no effect on the ascorbic acid molecule. No chemical interaction between the colloidal silica and the ascorbic acid could be determined, but a physicochemical interaction “absorption” was determined. Colloidal silica improved the final yield of spray drying in proportion to its concentration. No polymorphic forms could be determined in the spray-dried ascorbic acid. Drug release from the ascorbic acid spray dried was found to be dependent on the Aerosil content: highest release rates were obtained with Aerosil.     

On stability of stationary motions of the body with viscous filler on the rod

In the problem of motion of the dynamically symmetrical body-shell with cavity completely filled with fluid and suspended by the rod to the fixed point, stationary motions are studied by Routh’s technique. To describe the interaction between the filler and shell walls, a phenomenological model of “internal friction” is used.     

Effect of chromium and binder on diamond-matrix contact strength

The vacuum production of diamond drill bits is considered. The effect from the concentration of an adhesive-active element (chromium) on the diamond-tool contact strength is analyzed. It is examined how the binder affects the dependence of diamond-retaining force on the chromium content.