Suspensions, monodisperse, particle

Flard spherocylinders (cylinders witli hemispherical end caps) were studied using computer simulations [118]. In addition to a nematic phase, such particles also display a smectic-A phase, in which tire particles are arranged in liquid-like layers. To observe tliis transition, ratlier monodisperse particles are needed. The smectic-A phase was indeed observed in suspensions of TMV particles [17]. 

Recently it has been reported that even colloidal particle suspensions themselves, without added polymers, can form dissipative structures. Periodic stripes of colloidal particles (monodisperse particles of diameter 30 nm and 100 nm, respectively) and polystyrene particles (monodisperse diameters from 0.5 to 3 pm) can be formed from dilute aqueous suspensions. The stripes are parallel to the receding direction of the edge of the suspension droplet and thus indicate that a fingering instability... 

Increasing the radius of the suspended particles, Brownian motion becomes less important and sedimentation becomes more dominant. These larger particles therefore settle gradually under gravitational forces. The basic equation describing the sedimentation of spherical, monodisperse particles in a suspension is Stokes law. It states that the velocity of sedimentation, v, can be calculated as follows ... 

Many synthetic methods for the preparation of nanodispersed material have been reported, several routes applying conventional colloidal chemistry, with others involving the kinetically controlled precipitation of nanocrystallites using organometallic compounds.3 6-343 Controlled precipitation reactions yield dilute suspensions of quasi-monodispersed particles. This synthetic method sometimes involves the use of seeds of very small particles for the subsequent growth of larger ones.359 360... 

Photon Correlation. Particles suspended in a fluid undergo Brownian motion due to collisions with the liquid molecules. This random motion results in scattering and Doppler broadening of the frequency of the scattered light. Experimentally, it is more accurate to measure the autocorrelation function in the time domain than measuring the power spectrum in the frequency domain. The normalized electric field autocorrelation function g(t) for a suspension of monodisperse particles or droplets is given by ... 

In the absence of interactions, particles of differing sizes and shapes are statistically independent. For this reason, we can treat the statistical properties of light scattered from a dilute polydisperse suspension as the sum of contributions of many dilute monodisperse suspensions of particles with characteristic shape and size. Suppose that each characteristic shape/size combination is labeled with the index v. Let (V represent the number of particles having a particular shape and size. Clearly, we require N = Ns. All sums over the (V particles in a suspension can be expressed in terms of sums over the shape/size distribution. Thus we have... 

Monodisperse particles may also be produced with a cross-linked structure, and monodisperse porous particles may be obtained (Ugelstad et aL, 1980a) by applying methods known from suspension polymerization. Particles with functional surface groups have been prepared by chemical modification of the surface of cross-linked monodisperse particles of styrene-divinylbenzene or by copolymerization with monomers containing the desired functional groups. 

Other problems in deriving a priori equations result from the polydisperse namre of pharmaceutical suspensions. The particle size distribution will determine rj. A polydisperse suspension of spheres has a lower viscosity than a similar monodisperse suspension. 

With solid-in-liquid dispersions, such a highly ordered structure - which is close to the maximum packing fraction (q> = 0.74 for hexagonally closed packed array of monodisperse particles) - is referred to as a soHd suspension. In such a system, any particle in the system interacts with many neighbours and the vibrational amplitude is small relative to particle size thus, the properties of the system are essentially time-independent [30-32]. In between the random arrangement of particles in dilute suspensions and the highly ordered structure of solid suspensions, concentrated suspensions may be easily defined. In this case, the particle interactions occur by many body collisions and the translational motion of the particles is restricted. However, this reduced translational motion is less than with solid suspensions - that is, the vibrational motion of the particles is large compared to the particle size. Consequently, a time-dependent system arises in which there will be both spatial and temporal correlation. 

Polydispersity Effect. In the previous sections, we discussed the rheology of monodispersed particles, that is, all of the solids have the same particle size and shape. In this section, we consider the case where the suspension is made up of solids having different sizes. 

Using the formulas (8.147) and (8.148), it is possible to determine experimentally the properties of infinite diluted suspensions containing same-sized particles (a monodisperse suspension), for example, the mass concentration and size of particles. If the suspension contains particles of different sizes (a polydisperse suspension), then dividing the entire spectrum of particle sizes from amin to amax into a finite number of fractions, it is possible to carry out the argumentation stated above for each fraction, and to determine the laws of motion for the corresponding discontinuity surfaces. Measuring the velocities of discontinuity surfaces in an experiment, it is possible to determine the characteristics of each fraction and thereby the size distribution of particles. 

This effect is not exclusive of monodispersed particles and has also been found in polydisperse, poly modal suspensions and emulsions (16.24). Figure 30 shows the viscosity of oil-in-waler emulsitnis having the same overall internal... 

Although these PANI-coated monodispersed particles are ideal for use as model ER materials, the particle size is micrometer-size and large particle settling problem is needed to overcome. Recently, using nanoparticles as the dispersal phase or filler has attracted considerable interest in the development of a non-conventional ER fluids [ 12-15,48-52]. In particular, significant attention has been paid to one-dimensional (ID) nanofiber suspensions because it has been foxmd that the nanofiber suspensions exhibit not only higher ER or MR effect, but also reduced particle sedimentation... 

A convenient way to express /(< ) is to introduce the differential scattering cross section dcrftjj/dn, since it is independent of transmission and form of the sample. For a suspension of monodisperse particles with spherical symmetry, the differential scattering cross section is given by... 

Numerical calculations by Mic s theory for model gamma distribution of particles and experiments with bimodal latex suspensions have shown (Khlebtsov and Mel nikov, 1992) the mean particle size determined by the turbidity spectrum method from n(r) calibrations for monodisperse particles to correspond to the relationship... 

It should be noted that the QELS intensity for PMS was less by order than that for the suspensions of nanosilica with the same eoneentration. This is due to the differences in the morphology of secondary PMS particles and in the nature of primary particles because 3D network in 2D/3D PMS particles is looser and elose to the 2D network due to CH3 groups attached to each Si atom and residual silanols. For maximum diluted PMS suspensions, the presence of monodisperse particle... 

Monodisperse particles based on fluorinated, crosslinked poly-(meth)acrylates are preferably used for the inkjet ink composition. Pol5miers of this t q)e may be produced by suspension pol mieriza-tion of the monomers. 

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