Raviteja Kurapati

Bio: Raviteja Kurapati is an academic researcher from Indian Institutes of Technology. The author has contributed to research in topics: Adsorption & Chemistry. The author has an hindex of 1, co-authored 1 publications receiving 1 citations.

Factors Responsible for the Aggregation of Poly(vinyl alcohol) in Aqueous Solution as Revealed by Molecular Dynamics Simulations

Abstract: Molecular dynamics simulations are used to study structure and dynamics of poly(vinyl alcohol) and water in aqueous solution as a function ofconcentration at different temperatures in the range 278...

A Systematic Approach to the Development of Cilostazol Nanosuspension by Liquid Antisolvent Precipitation (LASP) and Its Combination with Ultrasound.

Abstract: Nanosizing is an approach to improve the dissolution rate of poorly soluble drugs. The first aim of this work was to develop nanosuspension of cilostazol with liquid antisolvent precipitation (LASP) and its combination with ultrasound. Second, to systematically study the effect of bottom-up processing factors on precipitated particles' size and identify the optimal settings for the best reduction. After solvent and stabilizer screening, in-depth process characterization and optimization was performed using Design of Experiments. The work discusses the influence of critical factors found with statistical analysis: feed concentration, stabilizer amount, stirring speed and ultrasound energy governed by time and amplitude. LASP alone only generated particle size of a few microns, but combination with ultrasound was successful in nanosizing (d10 = 0.06, d50 = 0.33, d90 = 1.45 µm). Micro- and nanosuspension's stability, particle morphology and solid state were studied. Nanosuspension displayed higher apparent solubility than equilibrium and superior dissolution rate over coarse cilostazol and microsuspension. A bottom-up method of precipitation-sonication was demonstrated to be a successful approach to improve the dissolution characteristics of poorly soluble, BCS class II drug cilostazol by reducing its particle size below micron scale, while retaining nanosuspension stability and unchanged crystalline form.

Rheological investigation on the associative properties of poly(vinyl alcohol) solutions

Abstract: We report intrinsic viscosity and flow curve measurements on a set of five industrial poly(vinyl alcohol) (PVOH) samples, with varying degree of hydrolysis, molecular weight, and concentration in two solvents: water and dimethyl sulfoxide (DMSO). Aqueous poly(vinyl alcohol) solutions exhibit clear features of associative polymers, and the hydroxyl-carbonyl hydrogen bonds seem to dominate polymer chain associations. We propose a “sticky-blob” model, applicable to any associating polymer solution with many stickers inside each correlation blob, which predicts the concentration dependence of the specific viscosity and the chain relaxation time in the entanglement regime. When PVOH polymers are dissolved in DMSO, a strong hydrogen bond acceptor, chain-chain associations are fully prevented for all relevant degrees of hydrolysis. The specific viscosity and the relaxation time of the chain recover the expected concentration dependences for nonassociating flexible polymers in DMSO. The same concentration dependences are exhibited by literature data on 100% hydrolyzed PVOH in water, as the acetate content, dominating interchain associations, is zero. Comparing entangled aqueous and DMSO solutions at the same concentration enables the experimental measure of the time delay due to associations as the ratio between the terminal relaxation time of solutions in water and DMSO. The concentration dependence of such a time delay was also captured by the simple sticky-blob model introduced in this work.

Parisi et al.: Rheological investigation on the associative properties of poly(vinyl alcohol) solutions

Abstract: We report intrinsic viscosity and flow curve measurements on a set of five industrial poly(vinyl alcohol) (PVOH) samples, with varying degree of hydrolysis, molecular weight, and concentration in two solvents: water and dimethyl sulfoxide (DMSO). Aqueous poly(vinyl alcohol) solutions exhibit clear features of associative polymers, and the hydroxyl-carbonyl hydrogen bonds seem to dominate polymer chain associations. We propose a “sticky-blob” model, applicable to any associating polymer solution with many stickers inside each correlation blob, which predicts the concentration dependence of the specific viscosity and the chain relaxation time in the entanglement regime. When PVOH polymers are dissolved in DMSO, a strong hydrogen bond acceptor, chain-chain associations are fully prevented for all relevant degrees of hydrolysis. The specific viscosity and the relaxation time of the chain recover the expected concentration dependences for nonassociating flexible polymers in DMSO. The same concentration dependences are exhibited by literature data on 100% hydrolyzed PVOH in water, as the acetate content, dominating interchain associations, is zero. Comparing entangled aqueous and DMSO solutions at the same concentration enables the experimental measure of the time delay due to associations as the ratio between the terminal relaxation time of solutions in water and DMSO. The concentration dependence of such a time delay was also captured by the simple sticky-blob model introduced in this work.

Froth stability and entrainment evaluation of a novel frother for KCl / NaCl flotation

Abstract: The rate of KCl recovery by froth flotation using low-grade carnallite is 70%–85%. Herein, a novel frother, dipropylene glycol butyl ether (DPNB), was prepared to increase the flotation efficiency of KCl recovery systems. DPNB could be applied at only half the dosage of the conventional frother methyl isobutyl carbinol (MIBC) and achieve a KCl recovery rate of 94.8%–98.6% with a high KCl grade (63.2%–66.5%). To date, these results are the best reported for pneumatic flotation. DPNB had a 10% higher maximum dynamic stability factor compared with MIBC; moreover, the apparent entrainment velocity of DPNB was half that of MIBC. The molecular structure of DPNB had hydroxyl and ether groups, which promoted interactions with water, thereby contributing to its excellent froth stability. DPNB is environment friendly owing to its low volatility and, thus, a promising frother for the green and highly efficient flotation of KCl/NaCl.