Otakar Quadrat

Influence of the electroviscous effect and particle swelling on the hydrodynamic behavior of acrylate copolymer latices

Abstract We have demonstrated that the dissociation of carboxylic groups on the polymer particle surface induces changes in the effective hydrodynamic volume due to an increased electroviscous effect and swelling. The influence of the former effect on the hydrodynamic properties of dispersions predominates, so that even a small amount of acrylic acid (1 and 2%) in copolymers with ethyl acrylate caused a strong increase in the hydrodynamic volume of polymer particles after their alkalinization, while the swelling of these particles under the same conditions was negligibly small, as shown by light scattering measurements. The presence of styrene in acrylate copolymers resulted in the suppression of both these effects.

Swelling and dissolution of latex dispersions of the ethyl acrylate-methacrylic acid copolymers during alkalization

By using non-Newtonian viscometry and the static light-scattering method, changes in the structure of particles of latex dispersions of ethyl acrylate-methacrylic acid copolymer during alkalization with ammonium hydroxide were investigated. It was found that in dispersions with an acid content up to 20 wt% the particles only swell; at acid content between 20 and 40 wt% they decompose to smaller units represented by supermolecular aggregates of macromolecules, and only when approximately starting from 40 wt% of acid does the copolymer become molecularly dissolved. This means that even if dispersions with an acid content from c. 20 wt% are clarified by alkalization, no complete dissolution takes place.

Aggregation behaviour of stereoregular poly(methyl methacrylates) in dilute solution: light scattering and proton n.m.r. study

Abstract The aggregation behaviour of syndiotactic and isotactic poly(methyl methacrylate) in methyl ethyl ketone, n-butyl acetate, and 2-ethoxyethanol was investigated by light scattering and 1 H n.m.r. spectroscopy. Syndiotactic poly(methyl methacrylate) remains in its molecular form in solution at temperatures above 60°–70°C; on cooling it undergoes aggregation followed by macroscopic separation (precipitation) of the polymer from solution. The rate of these processes depends on temperature, concentration of the polymer, and solvent. Molecular solutions of isotactic poly(methyl methacrylate) can be prepared only by long-term heating at temperatures above 100°–130°C. During cooling, isotactic macromolecules prior to separation form stable associates in the region limited by discrete temperatures, and below this region polymer precipitates. The individual stereo forms of poly(methyl methacrylate) are separated from solution at different temperatures which are above the θ-temperatures of the atactic polymer.

An anomalous electrorheological behavior of magnesium hydroxide suspensions in silicone oil

In contrast to the usual electrorheological behavior manifesting in an increase in viscosity of suspensions of various materials in electrical field, a negative electrorheological effect, i.e., a decrease in viscosity of suspensions of magnesium hydroxide particles in silicone oil was observed.

Stereo complexes in solutions of syndio- and isotactic poly(methyl methacrylate) mixtures: 2. Mutual interaction constant of stereo polymers

Abstract The coefficient of interaction between syndiotactic and isotactic poly(methyl methacrylate) was determined at 25°C in solutions of a mixture of these two polymers in dioxan and chlorobenzene by using the method of instrinsic viscosity measurement in a ‘polymer solvent’. In these systems where stereocomplexes are formed the coefficient is unusually high and depends on the solvent used.

An investigation of aging aqueous poly(vinyl alcohol) solutions by the light scattering method

Aqueous poly(vinyl alcohol) solutions of various concentrations were investigated. The aged solutions were diluted and then analyzed by the light scattering method, size exclusion chromatography, and viscometry. It was found that a relatively small quantity of supermolecular formations arise during aging; they are dispersed in the molecular solution of the predominant part of the polymeric material present. The amount of these aggregated structures and their formation rate increase with concentration of the aging solution.

The effect of (2-hydroxypropyl)-β-cyclodextrin on rheology of hydrophobically end-capped poly(ethylene glycol) aqueous solutions

(2-Hydroxypropyl)-β-cyclodextrin (HPBCD), a modified cyclic oligosaccharide, changes the flow behavior of aqueous solutions of a model telechelic associative polymer, hydrophobically end-capped poly(ethylene glycol) (ODU-12), because the inclusion complexation of HPBCD and octadecyl end-capping groups interferes with aggregation of the polymer end groups. The HPBCD-induced decrease in the high-frequency modulus can be well described assuming a 1:1 binding isotherm, but cannot fully explain the decrease in the low shear rate Newtonian viscosity, because HPBCD also strongly decreases the relaxation time. Consequently, besides decreasing low shear rate Newtonian viscosity, HPBCD also extends the Newtonian behavior to higher shear rates as predicted by the free-path version of the transient network theory [Marrucci et al., Macromolecules 26, 6483–6488 (1993)].(2-Hydroxypropyl)-β-cyclodextrin (HPBCD), a modified cyclic oligosaccharide, changes the flow behavior of aqueous solutions of a model telechelic associative polymer, hydrophobically end-capped poly(ethylene glycol) (ODU-12), because the inclusion complexation of HPBCD and octadecyl end-capping groups interferes with aggregation of the polymer end groups. The HPBCD-induced decrease in the high-frequency modulus can be well described assuming a 1:1 binding isotherm, but cannot fully explain the decrease in the low shear rate Newtonian viscosity, because HPBCD also strongly decreases the relaxation time. Consequently, besides decreasing low shear rate Newtonian viscosity, HPBCD also extends the Newtonian behavior to higher shear rates as predicted by the free-path version of the transient network theory [Marrucci et al., Macromolecules 26, 6483–6488 (1993)].

Rheological behavior of poly(methyl methacrylate) dispersions stabilized by a diblock copolymer: An anomalous viscosity–particle concentration dependence

The rheological study of dispersions of poly(methyl methacrylate) particles stabilized in decane by a steric stabilizer, polystyrene-block-poly(ethylene-co-propylene) diblock copolymer, revealed an extremely high apparent viscosity at low shear rates or even the yield stress at a relatively low volume fraction of particles (∼0.1). This behavior is due to highly interacting stabilizer macromolecules anchored to the particle surface. As the concentration of poly(methyl methacrylate) is further increased, the volume fraction of particles also increases, the particle diameter grows, the number of particles is reduced and the viscosity of the dispersion falls.

Negtive thixotropy of solutions of partially hydrolyzed polyacrylamide. Part I: The influence of shear rate on time changes of flow characteristics

A strongly negative thixotropic behavior of solutions of partially hydrolyzed polyacrylamide in a glycerol-water mixture has been observed at high dilution. Using a Couette viscometer, time changes of viscosity at various shear rates were studied in detail.

Light scattering characterization of constituent copolymers from polyacrylate latices

Abstract The method described is based on static light scattering measurement of solutions obtained by the direct dissolution of latex in a suitable organic solvent without intermediate isolation of solids. In the case of latices of acrylate copolymers with acrylic or methacrylic acid, often used in the paint industry, 2-ethoxyethanol proved to be the best solvent for this purpose. Static light scattering can also be used to estimate the mass and size of the dispersion particles prior to their dissolution.