Dynamic Light Scattering and Dynamic Viscoelasticity of Poly(vinyl alcohol) in Aqueous Borax Solutions. 4. Further Investigation on Polymer Concentration and Molecular Weight Dependencies

Abstract

Viscosity measurements are made on aqueous borax solutions of poly(vinyl alcohol) (PVA) samples over a wide range of PVA concentration, C, to examine the hydrodynamic properties of associated polymers compared to those of neutral polymers. The dynamic viscoelastic data are reanalyzed using a statistical−mechanical theory for elastically effective chains in transient gels developed by Tanaka and Ishida. The viscosity data are not superposed in the plot of viscosity against C[η] using the Huggins relationship, especially around and over a critical concentration, C N, at which the dynamical behaviors drastically change and an inflection point of a curve in the plot of the viscosity against C is located. On the other hand, when we assume that the chain dimension around C N is the unperturbed one, the viscosity data around C N is well-superposed on a curve in the plot of viscosity against C/C*up, where C*up is the overlapping concentration of the unperturbed chain. The inflection point of this composite curve is located at C/C*up = 1, which infers that C N corresponds to the overlapping concentration. All data of the density of elastically effective chains, νeff, are superposed on a curve in the plot of νeff/ν against (C − C N)/C N where ν is the density of polymer chains, which implies that C N should be regarded as a kind of gel point. Some discrepancies between the experimental data and the theoretical curve were observed, some of which cannot be explained using the pairwise association of PVA chains.

Experimental Evidence for an Intrinsic Route to Polymer Melt Fracture Phenomena: A Nonlinear Instability of Viscoelastic Poiseuille Flow

“…In this Letter we present qualitative as well as quantitative experimental evidence for this scenario: (i) for our experimental model system other common instability mechanisms such as those described above are not present but nevertheless the onset of irregular flow behavior occurs at values comparable to those listed in the engineering literature for a whole range of polymer solutions and melts [11]; (ii) the difference in threshold value in between a cylindrical and slit die is in good agreement with the theoretical calculations; (iii) we observe a hysteresis that one expects near such a ''firstorder-like'' subcritical transition; (iv) without adjustable parameters our experimental results compare well with our theoretical predictions [12] for the frequency of the surface distortions and with recent numerical simulations published after submission of this paper [16]. We study extrusion experimentally for a polymer/ crosslinker system (polyvinyl alcohol/sodium tetraborate) for which changing the crosslinker concentration allows variation of the viscoelastic properties of the system: the relative importance of the viscous and elastic stresses can be changed in a continuous fashion [17]. The aqueous polymer solution contained in a cylindrical reservoir is forced to flow through a cylindrical glass die by a piston driven by a step motor.…”

Structure and dynamics of poly(vinyl alcohol) gels in mixtures of dimethyl sulfoxide and water

“…The viscosity began to abruptly increase with the polymer concentration at BC p ¼3.0 wt%; the viscosity is B4Â10 2 Pa s À1 at C p ¼4.8 wt%, which is more than five orders of magnitude greater than that of C p ¼2.4%. 46,47 We designated the aqueous borax solutions of PVA with concentrations less than and greater than 3.0 wt% as PVA-borax sol and PVA-borax gel, respectively. In the aqueous borax solutions of PVA, the gelation process occurs through intermolecular hydrogen bonds between hydroxyl groups on PVA chains because of the intervention of a borate anion.…”

Dynamic and static fluctuations in polymer gels studied by neutron spin-echo

“…The viscosity of the aqueous solution with the PVA concentration C p ¼ 2.4 wt% is about 2 Â 10 À3 Pa s, this abruptly begins to increase with the polymer concentration at around C p ¼ 3.0 wt%, and the viscosity is about 4 Â 10 2 Pa s at C p ¼ 4.8 wt%, being more than 5 orders of magnitude larger than that of C p ¼ 2.4% [14,15]. In this paper, we will refer to the aqueous borax solutions of PVA with the concentration below and above 3.0 wt% as PVA-borax sol and gel, respectively.…”