Two species of sea anemones, Metridium senile and Anthopleura xanthogrammica , illustrate the sorts of compromises made by sessile organisms between maximizing the transport done and minimizing the mechanical forces caused by flow. 

1. 1. M. senile occur in calm areas, but because they are tall, they are exposed to mainstream current velocities. Although A. xanthogrammica occur in areas exposed to wave action, they are short and effectively hidden from mainstream velocities.

2. 2. Measurements of drag forces on anemones and models in a flow tank and in the field indicate that the shapes, sizes, flexibilities, and behaviours of anemones affect the flow forces they encounter.

3. 3. Although M. senile and A. xanthogrammica occur in different flow habitats, the drag force on an individual of either species is about 1 N.

4. 4. The water currents encountered by these anemones and their mechanical responses to the currents can be related to the manner in which the anemones harvest food from flowing water.

Effects of Sea Anemones on the Flow Forces They Encounter

POLYETHYLENE oxide (PEO) is one of the most extensively studied of all water-soluble synthetic polymers, both for its wide range of applications1–4 and from the fundamental standpoint of understanding the behaviour of polymer solutions The aggregation behaviour of PEO in water and its consequences have been a matter of concern in many studies5–11 of this system It is not clear, however, whether PEO aggregation is an inherent property of these aqueous solutions, although this knowledge can have important and widespread consequences for both industry and polymer science Here we use dynamic light scattering from high-molecular-weight PEO in carefully purified water and in methanol to show unambiguously that both are good solvents in the sense that PEO behaves like a typical random coil in both, with no evidence of aggregation

Polyethylene oxide does not necessarily aggregate in water

Dilute aqueous solutions of broad and narrow distribution poly(ethylene oxide) fractions were studied using dynamic (DLS) and static (SLS) light scattering, as well as gel permeation chromatography (GPC). It was found that above a critical self-association concentration, which depends on the molecular weight of the PEO, polymer clusters and free polymer coils coexist in a thermodynamic equilibrium. The polymer clusters can be removed by filtration and begin to reform spontaneously in solution within 30 min after filtration. A steady-state amount of PEO in clusters is attained within about 24 h. At steady-state the narrow-distribution and broad-distribution PEO samples have 7−10% wt/wt and 12−18% wt/wt of the polymer present as clusters in solution, respectively, at PEO concentrations of about 250 mg/L. It was found that the PEO clusters were composed of a few hundred polymer chains per cluster. From DLS the polymer cluster diameters were found to be independent of molecular weight and to decrease, with ti...

Dilute Aqueous Poly(ethylene oxide) Solutions: Clusters and Single Molecules in Thermodynamic Equilibrium

Effect of drag reducing polymers on oil-water flow in a horizontal pipe

Drag reduction with polymers in gas-liquid/liquid-liquid flows in pipes: A literature review

SMALL quantities of certain polymers dissolved in a liquid can reduce considerably the frictional drag exerted by the liquid when it flows over a surface. This effect has been observed with various solvent/polymer combinations, but most investigations involve polyethyleneoxide (PEO), polyacrylamide or guar gum in water, where the concentrations required are of the order of a few parts per million.

A. M. North

Papers

Role of molecular aggregates in liquid drag reduction by polymers