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In this paper we present the results of model calculations on the rotational motion of linear molecules in dense systems. To this end we have developed a matrix description for the rotational diffusion, which is extended in this article to the J-diffusion limit. Closed expressions are obtained for the orientational, angular momentum, and rotational energy autocorrelation functions. The precise time dependence of these correlation functions is determined by the time distribution of collisions and the magnitude of energy and momentum transfer during a collision. A systematic analysis of the role of these two effects on the rotational relaxation is presented
Starting with an m-diffusion model a matrix description is given of the rotational motion of a dipole molecule undergoing frequent collisions. This treatment gives rise to an analytical expression for the dipole correlation function and for the angular momentum correlation function in which a limited number of parameters from the model appear. It is argued that the collision distribution which determines the rotational diffusion process need not necessarily be a Poisson distribution. In liquids with strong interactions the distribution is governed by the frequency distribution of the medium. This leads to the inclusion of a librational motion in the rotational diffusion model. A comparison of simulations with different collision distributions and experimental data is given
The dipole correlation functions determined from far infra-red absorption measurements of a variety of liquids are compared with correlation functions calculated with different models for the motion of the molecules. These models vary from simple rotational diffusion models to models derived from solid state theory. Experimental results are presented of far infra-red measurements of HCl dissolved in liquid argon and of solutions of CH3CN in some organic solvents. For these liquid systems good agreement can be obtained between experiment and model calculations. It is pointed out that the description of these systems in terms of a model has a strong phenomenological character.
De verhouding tussen grote en kleine druppels in een regenbui of in een emulsie (mayonaise, dagcrème, boorvloeistoffen voor de olie-industrie) wordt onder andere bepaald door het samenvloeien, ofwel de coalescentie van druppels [1]. De grootte van de druppels en de verdeling hiervan heeft weer een grote invloed op bijvoorbeeld het stromingsgedrag van emulsies. Het is dus belangrijk het coalescentieproces in detail te begrijpen. Coalescentie speelt ook een rol in bijvoorbeeld inkjetprinters, het aanbrengen van coatings, en het gedrag van meerfasestromingen (ook weer belangrijk voor de oliewinning). De hydrodynamica van het samenvloeien van druppels is echter tot nu toe niet of nauwelijks experimenteel bestudeerd, om de simpele reden dat het proces te snel gaat: de meeste beschikbare experimentele technieken zijn te langzaam om de coales...
We present experimental evidence that drop breakup is caused by thermal noise in a system with a surface tension that is more than 106 times smaller than that of water.We observe that at very small scales classical hydrodynamics breaks down and the characteristic signatures of pinch-off due to thermal noise are observed. Surprisingly, the noise makes the drop size distribution more uniform, by suppressing the formation of satellite droplets of the smallest sizes. The crossover between deterministic hydrodynamic motion and stochastic thermally driven motion has repercussions for our understanding of small-scale hydrodynamics, important in many problems such as micro- or nanofluidics and interfacial singularities.
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