Steady Flow Properties of Monodisperse Polymer Solutions. Molecular Weight and Polymer Concentration Dependences of Steady Shear Compliance at Zero and Finite Shear Rates

1972 ◽  
Vol 5 (6) ◽  
pp. 786-792 ◽  
Author(s):  
Mototsugu Sakai ◽  
Teruo Fujimoto ◽  
Mitsuru Nagasawa
Keyword(s):  
Molecular Weight ◽  
Steady Flow ◽  
Polymer Solutions ◽  
Polymer Concentration ◽  
Steady Shear ◽  
Flow Properties ◽  
Shear Rates ◽  
Finite Shear ◽  
Concentration Dependences ◽  
Shear Compliance

scholarly journals Evaporation-induced Rayleigh–Taylor instabilities in polymer solutions

2020 ◽  
Vol 378 (2174) ◽  
pp. 20190533 ◽  
Author(s):  
E. J. Mossige ◽  
V. Chandran Suja ◽  
M. Islamov ◽  
S. F. Wheeler ◽  
Gerald. G. Fuller
Keyword(s):  
Molecular Weight ◽  
Time Scales ◽  
Polymer Solutions ◽  
Critical Concentration ◽  
Polymer Concentration ◽  
Onset Time ◽  
Dense Layer ◽  
Strong Concentration ◽  
Aqueous Polymer ◽  
Gravitational Instabilities

Understanding the mechanics of detrimental convective instabilities in drying polymer solutions is crucial in many applications such as the production of film coatings. It is well known that solvent evaporation in polymer solutions can lead to Rayleigh-Bénard or Marangoni-type instabilities. Here, we reveal another mechanism, namely that evaporation can cause the interface to display Rayleigh–Taylor instabilities due to the build-up of a dense layer at the air–liquid interface. We study experimentally the onset time ( t p ) of the instability as a function of the macroscopic properties of aqueous polymer solutions, which we tune by varying the polymer concentration ( c 0 ), molecular weight and polymer type. In dilute solutions, t p shows two limiting behaviours depending on the polymer diffusivity. For high diffusivity polymers (low molecular weight), the pluming time scales as c 0 − 2 / 3 . This result agrees with previous studies on gravitational instabilities in miscible systems where diffusion stabilizes the system. On the other hand, in low diffusivity polymers the pluming time scales as c 0 − 1 . The stabilizing effect of an effective interfacial tension, similar to those in immiscible systems, explains this strong concentration dependence. Above a critical concentration, c ^ , viscosity delays the growth of the instability, allowing time for diffusion to act as the dominant stabilizing mechanism. This results in t p scaling as ( ν / c 0 ) 2/3 . This article is part of the theme issue ‘Stokes at 200 (Part 1)’.

Effects of molecular weight and concentration on flow properties of concentrated polymer solutions

2007 ◽  
Vol 15 (1) ◽  
pp. 381-406 ◽  
Author(s):  
Shigeharu Onogi ◽  
Shigezo Kimura ◽  
Takashi Kato ◽  
Toshiro Masuda ◽  
Nobuyuki Miyanaga
Keyword(s):  
Molecular Weight ◽  
Polymer Solutions ◽  
Flow Properties

Creep Behavior of Polymer Solutions. II. Steady-Shear Compliance of Concentrated Polystyrene Solutions

1971 ◽  
Vol 4 (1) ◽  
pp. 87-92 ◽  
Author(s):  
Yoshiyuki Einaga ◽  
Kunihiro Osaki ◽  
Michio Kurata ◽  
Mikio Tamura
Keyword(s):  
Creep Behavior ◽  
Polymer Solutions ◽  
Steady Shear ◽  
Shear Compliance

scholarly journals Influence of PVA Molecular Weight and Concentration on Electrospinnability of Birch Bark Extract-Loaded Nanofibrous Scaffolds Intended for Enhanced Wound Healing

Molecules ◽  
2020 ◽  
Vol 25 (20) ◽  
pp. 4799
Author(s):  
Francis Kamau Mwiiri ◽  
Rolf Daniels
Keyword(s):  
Molecular Weight ◽  
Wound Healing ◽  
Drug Release ◽  
Polymer Solutions ◽  
Ex Vivo ◽  
Polymer Concentration ◽  
Weight Ratio ◽  
Bark Extract ◽  
Birch Bark ◽  
Fiber Morphology

Triterpenes from the outer bark of birch (TE) are known for various pharmacological effects including enhanced wound healing. Apart from an already authorized oleogel, electrospun nanofiber mats containing these triterpenes in a polyvinyl alcohol (PVA) matrix appear to be an advantageous application form. The effects of PVA molecular weight and concentration on the fiber morphology have been investigated. Three different molecular weights of PVA ranging from 67 to 186 kDa were used. The concentration of PVA was varied from 5 to 20 wt%. Polymer solutions were blended with colloidal dispersions of birch bark extract at a weight ratio of 60:40 (wt.%). The estimated viscosity of polymer solutions was directly linked to their concentration and molecular weight. In addition, both pure and blended solutions showed viscoelastic properties with a dominant viscous response in the bulk. Fiber morphology was confirmed using scanning electron microscopy (SEM). Both polymer concentration and molecular weight were found to be significant factors affecting the diameter of the fibers. Fiber diameter increased with a higher molecular weight and polymer concentration as more uniform fibers were obtained using PVA of higher molecular weight (146–186 kDa). In vitro drug release and ex vivo permeation studies indicated a faster drug release of betulin from electrospun scaffolds with lower PVA molecular weight. Our research suggests that the fabricated TE-loaded PVA electrospun dressings represent potential delivery systems of TE for wound care applications.

scholarly journals Flow Properties of Polymer Solutions. II. Phenomenological Relation for the Stress Following Sudden Start of Steady Shear Flow

1974 ◽  
Vol 6 (2) ◽  
pp. 165-169 ◽  
Author(s):  
Kunihiro Osaki ◽  
Yoshiyuki Einaga ◽  
Nobuhiro Yamada ◽  
Shin-ichi Ohta ◽  
Michio Kurata
Keyword(s):  
Shear Flow ◽  
Polymer Solutions ◽  
Steady Shear ◽  
Flow Properties ◽  
Steady Shear Flow

Shear Dependence of Viscosity and Molecular Weight Transitions. A Study of Entanglement Effects

1967 ◽  
Vol 40 (2) ◽  
pp. 522-531
Author(s):  
Suresh N. Chinai ◽  
William C. Schneider
Keyword(s):  
Molecular Weight ◽  
Shear Rate ◽  
Polymer Solutions ◽  
Shear Rates ◽  
Molecular Weights ◽  
Critical Molecular Weight

Abstract Flow of concentrated polymer solutions covering molecular weights up to 150,000 was examined at shear rates up to 200,000 sec−1. The viscosity, molecular weight, and shear rate results of previous workers recognizing only single critical molecular weight M*, above which ordinary Bueche entanglements dominated the flow, were compared with our findings in which two distinct critical molecular weights, upper M* and lower M** exist. These results are compared with the theory, and new interpretations are presented.

Sign in / Sign up

Export Citation Format

Share Document