performed with DBP in a radioactively contaminated electrodynamic balance yielded similar results except that mass losses as large as 75% and charge losses as large as 63% occurred. The mean value of q-/qRL was 0.73 for these data, which is not statistically different from the previous result. It is likely that the electric fields used to suspend the droplets affect the stability phenomenon, that random thermal fluctuations in local surface charge density can contribute only in a minor way to the instability, and that surface contamination can alter the fragmentation of the exploding droplet.Differential scanning calorimetry (DSC) and 'H NMR spectroscopy were used to study various lyotropic liquid crystalline phases of sodium bis(2-ethylhexyl)sulfosuccinate (Aerosol OT or AOT) and water. At 25 "C the lamellar liquid crystalline phase contains between surfactant bilayers bulklike water ("water l"), which has a melting point Tlm = 0 "C and an enthalpy of melting AHlm = 80 cal/g. Close to the bilayers, the lamellar liquid crystalline phase contains interfacial water, "water 2", which melts at TZm = -4 f 2 "C and has AH2" = 35 f 8 cal/g of water. After most of water 1 and 2 freezes, the surfactant and the remaining liquid water undergo a phase transition to a nonlamellar liquid crystalline phase. In this phase, "water 3" melts at T3"' = -9 1 "C and has AH3m = 12 f 5 cal/g of water. When water is in ultrathin (510 A) films in lamellar liquid crystal, then water 1 is absent and water 2 can be supercooled to -45 "C or lower. The surfactant has substantial rotational mobility even when the water is frozen at temperatures from -35 to -10 "C. Similar phase and thermal behavior is observed when initially isotropic aqueous micellar solutions of AOT are frozen or melted.
No abstract
We report a conformational change observed in poly-n-butyl isocyanate (PBIC) dissolved in carbon tetrachloride (CC14) with temperature. This change was detected by measuring the reduced viscosity of the polymer solution with a Zimm-Crothers type viscometer of very low shear rate; we found a reversible jump in reduced viscosity whose amplitude depends on concentration, but its position is only molecular weight dependent. This jump goes from lower to higher values of reduced viscosity when we increase the temperature, corresponding to an increase in the hydrodynamic volume of the chain. The largest size of the jump we found was about 3.5% of the viscosity value, and the jump decreased when the concentration approached the overlap concentration c*.
The translational self-diffusion coefficient of a solvent (D) in two rodlike polymer/solvent systems, poly(benzy1 glutamate) in dimethylformamide (PBLG/DMF) and poly(n-butyl isocyanate) in benzene (PBIC/benzene), was measured by pulsed gradient spin echo nuclear magnetic resonance. D decreases monotonically with polymer concentration at all temperatures and polymer rod lengths studied. DMF diffusion was independent of PBLG molecular weight and dropped more than a factor of 5 as 50 vol 7% polymer was approached. Using known properties of PBLG, including the mixing of its sidechains with solvent, the obstruction of DMF diffusion by the presence of PBLG could be accounted for using the solvent penetrable prolate ellipsoid model of Jonsson et al. (Colloid Polym. Sci. 1986, 264, 77). Benzene diffusion in the presence of PBIC can also be understood using the same model. The obstruction to solvent diffusion by 'fuzzy rods" was compared to that observed for random coil polymers. We show that in the dilute and semidilute regions this approach can also model experimental results with only a modest reduction of solvent diffusion coefficient within the domain of the polymer molecule. IntroductionThe translational diffusion of small molecules in simple liquids has been studied for many years. Self-diffusion measurements, those not involving a concentration gradient, are typically made by isotopic tracer1 or pulsed gradient spin echo nuclear magnetic r e s o n a n~e~,~ measurements. When a second component becomes of colloidal dimensions and is impenetrable, it is effectively stationary with respect to the motion of the solvent and presents simply an obstruction about which the solvent must diffuse. If the solvent diffusion is followed for distances that are long compared to the dimensions of the obstruction, the observed diffusion coefficient will be reduced, dependent on the volume fraction and geometry of the obstruction. In addition to obstruction, dispersed particles may have specific interactions with the solvent, e.g., hydration of ionic groups or hydrogen bonding, or the solvent may have a limited though finite solubility in the particle. Each of these will have an effect on the solvent diffusion and frequently is the reason for solvent self-diffusion ~tudies.l.~-~ A number of models have been presented which may be used to correlate the concentration and temperature dependence of the diffusion coefficient of the s o l~e n t .~-'~ One of the most clear-cut experimental systems is that of charge-stabilized spheroidal latex particles, which may be produced with diameters ranging from hundreds of angstroms to tens of microns. In aqueous dispersions of poly(methy1 methacrylate) latex, agreement with predictions is achieved up to 20 vol % latex, with solvent diffusion falling off more rapidly than predicted at higher concentrations.1° Deviations are considered to be the result of solvent interaction with the latex. With polystyrene latex, where solvent uptake should be minimal, both latexI3 and solvent14J5 diffusion have be...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.