Biomedical subjects

R Pelton

Publications and source records attributed to R Pelton.

4 recordsLinked to original sources

PubMed2000

Properties of Poly(N-isopropylacrylamide)-Grafted Colloidal Silica.

Poly(N-isopropylacrylamide-co-3-trimethoxysilylpropyl methacrylate) was prepared by radical polymerization and was grafted onto the surface of spherical colloidal silica. The copolymer, which had on average 1 silyl group per chain, condensed on the silica dispersed in THF at 60 degrees C. The resulting particles had a critical coagulation concentration of calcium chloride of 500 mM at room temperature, indicating robust colloidal stability. By contrast, heating the suspension to 50 degrees C lowered the critical coagulation concentration by more than three orders of magnitude, giving a value of 0.1 mM. Thus, the PNIPAM shell induced temperature-sensitive colloidal stability in the silica dispersion. The coated silica particles were also surface active. However, the surface tension of 50 mJ/m(2) at 25 degrees C is 15% higher than the corresponding value for PNIPAM solutions. Copyright 2000 Academic Press.

Journal Article↗

PubMed2000

Temperature-sensitive aqueous microgels.

An account of the preparation and characterization of temperature-sensitive aqueous microgels based on poly(N-isopropylacrylamide) was first published in 1986. Since then there has been a steady increase in the number of publications describing preparation, characterization and applications of temperature-sensitive microgels. This paper reviews the important developments in the area of temperature-sensitive aqueous microgels over the last decade. Although most of the work involves gels based on poly(N-isopropylacrylamide), other polymers are also considered. Core-shell latex particles exhibiting temperature-sensitive properties are also described.

Acrylic Resins↗

PubMed1997

Effect of Shear on the Strength of Polymer-Induced Flocs

Micromechanics was used to show that the rupture strength of polymer-induced flocs varied with the hydrodynamic conditions at which the flocs were formed. A maximum floc strength at an intermediate shear rate was observed. The overall performance of the polymeric flocculants, as determined by two independent methods, showed that the conditions for optimal flocculation did not coincide with those for maximum floc strength. The amount of flocculation was explained in terms of the competing effects of the particle collision frequency and the destructive hydrodynamic forces. The contributing forces to the floc strength are, however, more likely to be densification of the floc by shear and the weakening of reattachment strengths. The evidence presented here may be useful for explaining flocculation data that depart from the constant yield stress theory. Thus, the notion of the floc strength varying with shear rate may offer an alternative to multilevel floc structure models in the description of flocculation kinetics. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗

PubMed1996

Micromechanics: A New Approach to Studying the Strength and Breakup of Flocs

Micromechanical techniques were developed to pull apart single floc particles 6 to 40 μm in size in order to measure floc strengths and fractal dimensions. Flocs were formed by aggregating aqueous precipitated calcium carbonate sols with two water-soluble polymers. The tensile strengths ranged from 20 to 200 nN and showed no correlation with floc sizes when plotted on logarithmic scales. Flocs created by the two flocculant systems were found to have fractal dimensions of 1.8 and 2.4 based on analysis of fragment sizes. The compact flocs favored breakup by surface erosion, whereas flocs characterized by the lower fractal dimension tended to undergo large scale fragmentation. Comparison of the two polymeric flocculants revealed that both the fractal dimension and the tendency for ruptured fragments to reflocculate were sensitive to the polymer used.

Journal Article↗