SYNOPSISThe stability of vinyl acetate miniemulsions employing polyvinyl alcohol (PVOH) as the surfactant, and hexadecane and/or various polymers as the cosurfactant, were studied. Shelf lives (to phase separation) and monomer droplet sizes were measured. The results indicate that it is possible to prepare stable miniemulsions using a nonionic surfactant (PVOH) and hexadecane as the cosurfactant. Polymeric cosurfactants do not create stable miniemulsions but retard Ostwald ripening to an extent that allows predominant droplet nucleation. The polymerization behavior of these miniemulsion systems was investigated using on-line conductance measurements to differentiate droplet versus micellar/homogeneous nucleation. The effect of cosurfactant concentration on the reaction rate was compared for hexadecane and polymeric cosurfactants.
Time-resolved resonance fluorescence detection of atomic chlorine following 266-nm laser flash photolysis of ClZCO/RSR'/N2 mixtures has been employed to study the kinetics of C1 reactions with HzS(kl), CH3SH(kz), DzS(k3), and CDsSD (k4)
A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the Cl( 2 P J ) + C 2 Cl 4 association reaction as a function of temperature (231-390 K) and pressure (3-700 Torr) in nitrogen buffer gas. The reaction is found to be in the falloff regime between third and second order over the range of conditions investigated, although the second-order limit is approached at the highest pressures and lowest temperatures. At temperatures below 300 K, the association reaction is found to be irreversible on the experimental time scale of ∼20 ms. The kinetic data at T < 300 K have been employed to obtain falloff parameters in a convenient format for atmospheric modeling. At temperatures above 330 K, reversible addition is observed, thus allowing equilibrium constants for C 2 Cl 5 formation and dissociation to be determined. Second-and third-law analyses of the equilibrium data lead to the following thermochemical parameters for the association reaction: ∆H°2 98 ) -18.1 ( 1.3 kcal mol -1 , ∆H°0 ) -17.6 ( 1.3 kcal mol -1 , and ∆S°2 98 ) -27.7 ( 3.0 cal mol -1 K -1 . In conjunction with the well-known heats of formation of Cl( 2 P J ) and C 2 Cl 4 , the above ∆H values lead to the following heats of formation for C 2 Cl 5 at 298 and 0 K: ∆H°f ,298 ) 8.0 ( 1.3 kcal mol -1 and ∆H°f ,0 ) 8.1 ( 1.5 kcal mol -1 . The kinetic and thermochemical parameters reported above are compared with other reported values, and the significance of reported association rate coefficients for understanding tropospheric chlorine chemistry is discussed. † Present address: Cl 2 + hν (355 nm) f nCl( 2 P 3/2 ) + (2n)Cl( 2 P 1/2 ) (2) ln{[Cl( 2 P J )] 0 /[Cl( 2 P J )] t } ) (k 1 [C 2 Cl 4 ] + k 3 )t ) k′t (I)
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