Werner-Michael Kulicke

Preparation, characterization, solution properties and rheological behaviour of polyacrylamide

In this report a survey is given on structure and properties of polyacrylamide homopolymers (PAAm) in solution. However the review is restricted to all those papers, where a molecular characterization of the polymers has been achieved as a basis to correlate this fundamental information with applicational properties. Different polymerization methods are summarised in brief, the preparation and solution structure of long chain branched polyacrylamides as well as chemical modification reactions of linear PAAm are also mentioned. A number of experimental characterization methods (GPC, ultracentrifugation, intrinsic viscosity, and light scattering measurements) are described with special emphasis on the difficulties of the different procedures including some proposals for properly designed experimental techniques. The state of solution is discussed in view of experimental data obtained with different solvents. Moreover viscosity constant o is calculated for aqueous solution and the unperturbed dimensions are estimated. All available data on cross correlations (e.g. [η] - M, S0 - M, 12 - M) are collected with the intention to give a survey of established relations and, comparing the given relationships, to suggest the reliable ones of them. The phenomenon of long-term viscosity decrease of aqueous PAAm solutions has been investigated and discussed with regard to its molecular origin. The viscoelastic properties are discussed in dependence on molecular weight, concentration, solvent quality, and shear rate (⩽106 · s−1). Based on these data a simple equation was developed oped for the η0-c-M relationship, which can be applied to other polymer systems as well. It is further described that the elastic nature (first normal stress difference) may overwhelm the viscous nature (shear stress) at relatively low shear rates. This high elasticity can cause deviation from laminar flow conditions. Moreover, it can be demonstrated — based on instationary measurements as well as the comparison of steady shear flow with dynamic rheology — that energetic interactions (H-bonds) strongly influence the rheological behaviour.

Correlation between immunological activity, molar mass, and molecular structure of different (1→3)-β-d-glucans

(1-->3)-beta-D-Glucans are said to be potential biomedical drugs against bacterial or viral infections and also show antitumour activity. These substances seem to enhance the activity of the immune system, but today there is no accepted mechanism, and not even any agreement on the parameters which influence the activity. Therefore, glucans with different structures and/or varying molar mass were characterized by multi-angle laser-light scattering coupled with size-exclusion chromatography in order to obtain the molar mass distribution and to gain an idea of the structure in solution. After ensuring that all samples were free of pyrogens, the Tumour-necrosis-factor-alpha release activity and the superoxide-anion released from human blood monocytes were measured in groups of samples with comparable polydispersity and degree of substitution. All glucans investigated, regardless of molar mass and solution structure, stimulate the investigated immunological measures more than a commercially available biomedical drug used for comparison. The greatest magnitude of molar mass was found to be about 550,000 g/mol for all the glucans investigated. Contrary to the cited literature, helical structures were not essential, and not even advantageous, for immunological activity.

How Dilute are Dilute Solutions in Extensional Flows

We investigate the concentration dependence of the characteristic relaxation time of dilute polymer solutions in transient uniaxial elongational flow. A series of monodisperse polystyrene solutions of five different molecular weights (1.8×106⩽M⩽8.3×106g∕mol) with concentrations spanning five orders of magnitude were dissolved in two solvents of differing solvent quality (diethylphthalate and oligomeric styrene). Optical measurements with a capillary breakup extensional rheometer of the rate of filament thinning and the time to breakup in each fluid are used to determine the characteristic relaxation time. A criterion for a lower sensitivity limit is introduced, in the form of a minimum concentration cmin necessary for experimental resolution of the effects of polymeric viscoelasticity. This criterion is validated by experiment and comparison to numerical calculations with a multimode bead-spring dumbbell model. These calculations also rationalize previous paradoxical observations of extensional thinning i...

Rheological studies of barley (1→3)(1→4)-β-glucan in concentrated solution: mechanistic and kinetic investigation of the gel formation

Abstract The gelation of concentrated barley (1→3)(1→4)-β-glucan solutions was investigated. The gelation rate was quantified by a novel parameter called the elasticity increment I E , accessible via oscillatory time experiments. Decreasing molar mass and increasing concentration proved to raise the gelation rate. Despite a very similar plateau storage modulus G ′ p of the final gels for a given concentration, the mechanical stability increases with increasing molar mass. Oat β-glucan and lichenan, both (1→3)(1→4)-β-glucans, are also able to form solid gels. The turbidity, syneresis, melting temperature of the gels and the gelation rate increase in the order oat β-glucan, barley β-glucan and lichenan, indicating an increasing extent of the junction zones. Examination of the fine structure revealed the most regular chain structure for lichenan, with cellotriose units linked by β-(1→3) bonds as the main structural feature. From this it was deduced that sections of consecutive cellotriose units constitute the cross-links. A gelation model based on sporadic nucleation similar to crystallization of polymer melts is proposed.

Viscosimetry of Polymers and Polyelectrolytes

1 Introduction and Objective.- 2 Basic Concepts.- 3 Execution of Viscosity Measurements.- 4 The Intrinsic Viscosity.- 5 Parameters Affecting the Intrinsic Viscosity.- 6 Viscosimetric Determination of the Molar Mass.- 7 Determination of the Polymer Coil Dimensions from the Intrinsic Viscosity.- 8 A Deeper Insight Into Viscosimetry.- 9 List of References.- 10 Subject Index.

Characterization of aqueous car☐ymethylcellulose solutions in terms of their molecular structure and its influence on rheological behaviour

A set of car☐ymethylcellulose (CMC) samples was varied in degree of substitution (DS) from 0.71 to 2.95, with the partial degree of substitution being raised uniformly at positions C2, C3 and C6, so that a homologous series of CMC was made available. A further set of samples varied in molar mass from 200 000 to 2 000 000 g mol−1 at a constant DS of ∼ 1. The chemical structural parameters were determined by n.m.r. spectroscopy, showing that quantification of the degree of substitution at position C6 may be distorted by impurities of glycolic acid. The mean molar masses, for establishing the [η]-M relationship, were determined by multiangle laser light scattering preceded by size exclusion chromatography. The influence of concentration on zero-shear viscosity was given by η0 ∝ c4.3, whereas the influence of the molar mass was determined by η0 ∝ M3.9. An increasing DS within a homologous series influences the viscosity in different solvents (H2O 0.01 M NaCl, 0.1 M NaCl) at low polyelectrolytic concentrations. Surprisingly, the viscosity for all the CMC samples can be predicted by the single equation: η0[Pas]=8.91×10−4+1.30×10−5cMW0.9+5.33×10−8c2MW1.8+4.60×10−15c4.34MW3.91 at T = 298 K in 0.01 M NaCl. Increasing the DS up to a value of ∼ 1 improves the solubility characteristics (increases the viscosity), whereas above DS ≈ 1 this effect is overlapped by degradation of the molar mass. It was also possible to quantitatively determine the viscoelasticity as a function of frequency and molecular parameters.

The shear viscosity dependence on concentration, molecular weight, and shear rate of polystyrene solutions

AbstractThe solution viscosity of narrow molecular weight distribution polystyrene samples dissolved in toluene and trans-decalin was investigated. The effect of polymer concentration, molecular weight and shear rate on viscosity was determined. The molecular weights lay between 5 ⋅ 104 and 24 ⋅ 106 and the concentrations covered a range of values below and above the critical valuec*, at which the macromolecular coils begin to overlap. Flow curves were generated for the solutions studied by plotting logη versus log

Relation between steady shear flow and dynamic rheology

\dot \gamma