Roger S. Porter and D. H. Condit California Research Corporation Richmond, California
Streams of Bouncing Liquid
The pouring of polymer systems is normally uneventful. A small heaping-up effect can be generally observed, as noted by Ilaye, at the point of entry where viscous fluids are poured into themselves.1 Poured fluids can, however, jump entirely out of the intended receptacle. Streams of bouncing or jumping liquid can be visually observed for a variety of systems. Such systems observed here include the polymer solutions listed in Table 1. Polyisobutenes are popular commercially, and demonstration samples are available from commercial sources. Fluid bouncing is due to electrostatic effects. This hypothesis has been verified and demonstmted by use of a spark source. A common inexpensive commercial leak tester, when sparked against a flowing polymer stream, produces continuous "bouncing." Eliminating the spark immediately reduces "bouncing" by about a factor of ten in both frequency and distance jumped. Sparked polymer streams bounce off the liquid surface to such an extent that they are difficult to collect in containers. This simple procedure provides a dramatic demonstration of the effect of electrostatics in fluid flow. Table 1. Polymer Solutions for Which "Bouncing" Has Been Observed Molecular weight Wt % Polymer type Mu X in cetane 2.0 loa Atactie Polypropylene Polyisobutene 5.1 49.0 Polyisobutene 4.0 51.0 Polyisobutene 141.0 5.0 In cis-decslin.
The figures show a polymer stream houncing out under the influence of an electrostatic charge. The photographs are enlarged and air-brushed frames from 16-mm movie film. The photographs show the onset and the finishing stages of two differentbouncing streams. A bouncing event takes about one second and is easily seen. The leak tester was sparked against the stream just above the photographic field. Bouncing is sporadically observable with most fluid polymer systems without sparking, a t ambient conditions. The degree of houncing appears to vary with laboratory conditions such as humidity. Bouncing is virtually unobservable on rainy days. The effect of adding a commercial electrostatic agent to a polymer solution lends support to the electrostatic explanation for houncing or jumping. One such agent, Socal Electrostatic Additive, Standard Oil Company of California, 'KATE,A., Nalu~e197,1001(1963).
is known to increase electrical conductivity and thus effect charge distributions in liquids. Emulsifying 10% of this agent with the polymer solutions eliminated totally the effect of bouncing even in the presence of sparking. Simple pouring tests with fluids such as water, nhexadecane, and low molecular weight polybutenes produced no houncing. The effect of sparking in these cases is only to break the poured stream into heads rather than to produce bouncing. Viscous and elastic effectsare thus helpful in providing cohesion in a poured polymer stream.' Konetheless,the basic effect in bouncing liquids is essentially electrostatic and related to streaming potential, the electrical potential generated by a liquid flowing past a surface. A general rclatiouship indicates that streaming potential should increase with decreasing fluid electrical conductivity and viscosity.*
Bouncing of o polymer rtreorn under the influence of on eleetro~fatie charge.
It has long been known that pouriqg and transferring of commercial amounts of polymers such as polybutenes involves severe problems due to accumulated electrostatic charge. If for example, a polybutene (kinematic viscosity 6.5 stokes a t 210°F) is pumped through metal lines and a filter into an empty metal drum, the static charge often causes the product to creep up the sides and over the lip onto the floor. Bonding the line to the drum, putting sharp points on the pipe outlet, and other devices, reduce but do not remove problems. The demonstration developed here thus illustrates the importance of electrostatics in the handling of many common, commercial systems. The experiment is dramatic and, importantly, reproducible. In general, electrokinetic effectfi and shaming potentials are difficult to measure with precision.' The contribution of Mr. A. R. Bruzzone and helpful discussions with Dr. D. W. Criddle are acknowlcdged. ADAMSON, A. W., "Physical Chemistry of Surfaces," Interscience Publishers, New York, 1960,p. 194.
Vol. 42, Number I , January 1965
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