Particle-cluster mechanism

At the synthesis beginning solution contains only monomer, which within the frameworks of irreversible aggregation models can be considered as particles, uniting later in a cluster (macromolecular coil). As it is known [21], within the frameworks of the indicated models such mechanism is called mechanism particle-cluster and aggregates with fractal dimension 2.5 is the result of its action. Besides, the value Cj was calculated according to the Eq. (18) with the following parameters using t = 0.5 min, i3r=4.8 mol/l s and Q=8.3><10-3. 

In Fig. 29, the dependences of D on reaction duration t for DMDAACh polymerization at both indicated above conditions are adduced. As one can see, the two dependences Dj(t) are similar qualitatively and their distinction consists of only in more slow reaction realization for DMDAACh-1 (the kinetic parameters for DMDAACh synthesis adduced conditions differ on about two orders [1]). Let us note, that for DMDAACh-2 the aggregation mechanism change is observed twice within the range of t < 2 min mechanism particle-cluster is changed by diffusion-limited mechanism cluster-cluster and within the range of t = 5-10 min opposite change occurs [21]. It is important to note, that the last mechanisms change occitrs at constant initial monomers concentration c and practically constant value MM [1]. 

In Fig. 6.1, the images of the studied nanocomposites, obtained in the force modulation regime, and corresponding to them nanoparticles aggregates fractal dimension distributions are adduced. As it follows from the adduced values particles aggregates in the studied nanocomposites are formed by a mechanism particle-cluster (P-Cl), that is, they are Witten-Sander clusters [7]. The variant A, was chosen which according to mobile particles are added to the lattice, consisting of... 

Hence, the stated above results allow to give the following interpretation of critical temperatures and T of amorphous glassy polymers structure within the frameworks of solid body synergetics. These temperatures correspond to governing parameter (nanocluster contents) cp j critical values, at which reaching one of the main principles of synergetics is realized-sub-ordination principle, when a variables set is controlled by one (or several) variable, which is an order parameter. Let us also note reformations number m = 1 corresponds to structure formation mechanism particle-cluster [4, 5]. 

The underlying questions with these clusters are What is the mechanism for their existence Where are the clusters formed and How do clusters affect entrainment rates Based on evidence from pilot and commercial scale plants along with highspeed video of a cold-flow fluidized bed, the mechanism of particle clustering in and above fluidized beds and its effect on entrainment were examined. 

The results from placing baffles in a fluidized bed, as shown in Figures 11.10 and 11.11, also support this mechanism. The addition of baffles may not only serve as a mechanism to break up clusters (especially at low superficial gas velocities), but to disrupt the larger recirculation zones in the fluidized bed and reduce the time a cluster spends in this cycle. Instead of one large recirculation zone, several recirculation zones may develop with only the top recirculation zone contributing to the particle clusters that can be entrained. 

Voids can be formed by either entrapment of air mechanically or by one of two nucleation processes. Mechanical entrapment could include (1) entrained gas bubbles from the resinmixing operation, (2) bridging voids from large particles or particle clusters (quenched DDS curing agent, airborne particles, or paper release agent), (3) voids from wandering tows, fuzz... 

It is noted that a cluster as referred to here is a lump of solid particles over which flow properties such as voidage do not vary substantially. It is formed mainly as a result of hydrodynamic effects. The mechanism of particle clustering is different from that of agglomeration, in which particles adhere to one another mainly by surface attraction (e.g., van der Waals force and electrostatic forces), and mechanical or chemical interaction [Horio and Clift, 1992],... 

The suspension-to-wall surface heat transfer mechanism in a circulating fluidized bed (see Chapter 10) comprises various modes, including conduction due to particle clusters on the surface or particles falling along the walls, thermal radiation, and convection due to... 

---