Dipolar soft-sphere fluid

Dipolar spheres have often been used as a first approximation for a model molecular fluid [1,2,11]. Here we will use a dipolar soft sphere fluid as our first example of a SDF and the additional information (not present in a radial... 

Figure 1 (a) Radial distribution functions for soft sphere (solid line) and dipolar soft-sphere fluids at the same temperature and density, (b) The spatial distribution function g(r,0), where 0 is the angle between the dipole and separation vectors, for the dipolar soft-sphere in (a). 

At larger values of the dipole moments orientational ordering occurs even at low shear rates [207]. If a dipolar soft sphere fluid T = 1.35, p = 0.80 and p. = 2.5) is subjected to a moderate shear force (y 0.5), the dipole moments orient parallel to the xy plane at an angle of approximately 118°, i.e. in the direction where the coordination sphere is most compressed, forming a ferroelectric state. As there is no preference for the net dipole moment to point... 

Increasing the dipole coupling shifts the transition densities to lower densities. For instance, in dipolar soft spheres (256 particles) magnetic ordering sets in at a density p pa 0.85 for 7, 4 [103], p pa 0.65 for X 6.25 [102,103] and p pa 0.55 - 0.60 at A, 9 [102,103]. Transition densities are similar in DHS [113,135], but are much higher in Stockmayer fluids where a ferroelectric transition exists only for A, > 4 [127,136] at densities generally larger than the liquid densities at 1-g coexistence. MC simulations by Gao and... 

The structure formation in an ER fluid was simulated [99]. The characteristic parameter is the ratio of the Brownian force to the dipolar force. Over a wide range of this ratio there is rapid chain formation followed by aggregation of chains into thick columns with a body-centered tetragonal structure observed. Above a threshold of the intensity of an external ahgn-ing field, condensation of the particles happens [100]. This effect has also been studied for MR fluids [101]. The rheological behavior of ER fluids [102] depends on the structure formed chainlike, shear-string, or liquid. Coexistence in dipolar fluids in a field [103], for a Stockmayer fluid in an applied field [104], and the structure of soft-sphere dipolar fluids were investigated [105], and ferroelectric phases were found [106]. An island of vapor-liquid coexistence was found for dipolar hard spherocylinders [107]. It exists between a phase where the particles form chains of dipoles in a nose-to-tail... 

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