NEILLWEBERAND WALTERH. BAUER
270
Vol. 60
FLOW PROPERTIES OF ALUMISUM DILATIRATE-TOLUENE GELS BY NEILL WEBERA N D WALTERH. BAUER Department os Chemistry, Walker Laboratory, Rensselaer Polytechnic Instilule, Troy, N . Y . Received August 2, 1966
Flow properties of aluminum dilaurate in toluene gels a t 25" have been studied in a pressure capillary viscometer over a rmge of mean rate of shear from to l o f a cm. -I. Flow curves, mean rate of shear versus wall shearing stress, obtained for gels of 1, 2,3, 5% weight per cent. soap in toluene, showed three types of flow. A region of Newtonian flow with high viscosity was found at shear rates below loW2set.-'. When a critical shear stress range was exceeded, the shear rate rapidly increased with small increase in shear stress. A t shear rates above 100 set.-', a third regime of flow was found, in which a plot of log shear rate oerst(s log shear stress approached a constant slope, always greater than unity, and the flow curve was a very marked fuirctioii of the length to radius ratio of the capillary used. The shear modulus of elasticity and the viscosity were measured for 2, 3 and 5% weight per cent. soap in toluene gels at shear rates below 10-2 sec.-I.
Systems of aluminum soaps dispersed in hydrocarbon solvents exhibit a wide variety of rheological properties, ranging from those characteristic of inelastic fluids in dilute dispersions to those typical of plastic solids in gels of high soap concentration. Studying the flow properties of aluminum soap dissolved in gasoline, Carver and Van Wazerl showed the presence of a structure affecting flow which was partially destroyed under shea.r and restored after rest. They interpreted their results to show a yield value for extension, but there was no Bingham yield value. Goldberg and Sandvik12 measuring elastic constanbs for alumilium soap gels in Varsol, found that the dynamic visc,osity and the elastic shear modulus were functions of the rate of shear. Complete recovery of the original elastic properties was found after a period of rest. Dilute solutions of aluminum soaps in benzene were found by Alexander and Gray3to show streaming birefringence under low rates of shear. The viscosity, double refraction, and extinction angle were measured at various rates of shear. Garner, Nissan and Wood,4 studying gels of aluminum stearate in petrol, found that the apparent viscosity at different ra.tes of shear was at first constant. Above a value of one for the rate of shear, the viscosity began to decrease, reaching another approximately constant value a t very high rates of shear in a capillary JTiscometer. Unusually large inlet end effects were found ivhen the flow of the gels iii pipes was studied. It is thus apparent that various regions of flow are exhibited by hydrocarbon gels of aluminum soaps, according to the range of rate of shear, the applied shearing stress, and the concentmtion of the soap used. I n any attempt to correlate the structure of the aluminum soap polymers and t'he nature of the parent fatty acid wit>hthe flow properties of soap-hydrocarbon gels, it is thus iiccwaary to study the flow properties i i i ilistrument.s i l l which rates of shear may be varied o1.w very wide ranges. For the purposes of this i i 1 \.estigatioti , t heitef ore, a vapi Ilary viscometer was constru(!ted, so t'hat a \ w y \vide raiige of floiv rate might, bc stmudiedi n a siliglc vapillary if desired. I I I order to provide a I&s for cwmparison, a study of the flow properties of tdumiiiiim hydrosydilaurate gels in t.oluene was undertaken. Although this (1) E. I
