The Coagulation Theory

Blood coagulation might well be the chemical transformation in the blood known to physicians for the longest time. Still, little is known of the process except for some steps in fibrinogen conversion to fibrin. Therefore, blood coagulation continues to be described in mysterious terms, reminiscent more of a secret code than of chemical nomenclature. 

Distortion of this delicate homeostatic balance may lead to either hemorrhagic disease or thrombi formation. The white thrombi result from interaction between platelets and abnormal vessel walls. Red thrombi are caused by the cooperative effect of hypercoagulability and stasis. 

Thromboplastin is present in tissue juices and in platelets. In experimental studies on blood coagulation, thromboplastin is usually obtained by extracting it with saline from brain or lung. In the blood vessels, the thromboplastin that starts the coagulation process is generated by the disintegration of the blood platelets (which will be discussed in more detail later), but thromboplastin release coincides with the release of vasconstricting substances. 

The antihemophilic globulin, the factor absent from the blood in the best-known hemophilia, combines stoichiometrically with a platelet thromboplastic factor, and the two compounds act like precursors, yielding a product itself a precursor. For thromboplastin, the product is prothromboplastin. The platelet thromboplastin component acts like a catalyst consequently, its concentration does not change during the reaction. The prothromboplastin combines with another compound called the plasma-accelerating globulin to yield a new product, namely, thromboplastin. 

The next series of transformations leads to thrombin formation. A precursor of thrombin, the familiar prothrombin whose synthesis in the liver requires vitamin K, combines with thromboplastin stoichiometrically. The reaction requires calcium and a platelet factor referred to as platelet factor 1. The product of the reaction is thrombin but prothrombin production by the mechanism just described is so slow that the process must be activated for efficient coagulation, and thrombin catalyzes its own production. Thus, thrombin converts a plasma component, factor 1, or the plasma AC globulin into an active catalyst capable of accelerating prothrombin conversion to thrombin. 

---

With the coagulation theory of morphine action and drug addiction substantiated, there appears to be no reason why certain morphine addicts should not be cured efficiently and completely by the use of sodium thiocyanate. 

Interstitial aerosol particles collide with cloud droplets and are removed from cloud interstitial air. The coagulation theory of Chapter 13 can be used to quantify the rate and effects of such removal. If n(Dp,t) is the aerosol number distribution and nd(Dp,t) the droplet number distribution at time r, the loss rate of aerosol particles per unit volume of air due to scavenging by cloud drops is governed by... 

The coagulation theory of colloidal particles is based on a balance of repulsive and attractive forces between particles. When attractive forces dominate, particle aggregation (coagulation or flocculation) can take place. Flocculation is reversible aggregation, whereas coagulation and coalescence are irreversible processes. 

The debate as to which mechanism controls particle nucleation continues. There is strong evidence the HUFT and coagulation theories hold tme for the more water-soluble monomers. What remains at issue are the relative rates of micellar entry, homogeneous particle nucleation, and coagulative nucleation when surfactant is present at concentrations above its CMC. It is reasonable to assume each mechanism plays a role, depending on the nature and conditions of the polymerization (26). 

There are two general theories of the stabUity of lyophobic coUoids, or, more precisely, two general mechanisms controlling the dispersion and flocculation of these coUoids. Both theories regard adsorption of dissolved species as a key process in stabilization. However, one theory is based on a consideration of ionic forces near the interface, whereas the other is based on steric forces. The two theories complement each other and are in no sense contradictory. In some systems, one mechanism may be predominant, and in others both mechanisms may operate simultaneously. The fundamental kinetic considerations common to both theories are based on Smoluchowski s classical theory of the coagulation of coUoids. 

Nomura and Fujita (12), Dougherty (13-14), and Storti et al. (12). Space does not permit a review of each of these papers. This paper presents the development of a more extensive model in terms of particle formation mechanism, copolymer kinetic mechanism, applicability to intervals I, II and III, and the capability to simulate batch, semibatch, or continuous stirred tank reactors (CSTR). Our aim has been to combine into a single coherent model the best aspects of previous models together with the coagulative nucleation theory of Feeney et al. (8-9) in order to enhance our understanding of... 

Broze GJ Tissue factor pathway inhibitor and the revised theory of coagulation. Annu Rev Med 1995 46 103. 

The original theory of diffusional coagulation of spherical aerosol particles was developed by von Smoluchowski (1916,1917). The underlying hypothesis in this theory is that every aerosol particle acts as a sink for the diffusing species. The concentration of the diffusing species at the surface of the aerosol particle is assumed to be zero. At some distance away, the concentration is the bulk concentration. 

The most complete theory for aerosol coagulation is that of Fuchs (1964). Since the attachment of radon progeny to aerosols can be considered as the coagulation of radon progeny (small diameter particle) to aerosols (large diameter particle), it is reasonable to use Fuchs theory to describe this process. The hybrid theory is an approximation to Fuchs theory and thus can be used to describe the attachment of radon progeny to aerosols over the entire aerosol size spectrum. 

In a number of recent publications (1, 2) microcrystailine cellulose dispersions (MCC) have been used as models to study different aspects of the papermaking process, especially with regard to its stability. One of the central points in the well established DLVO theory of colloidal stability is the critical coagulation concentration (CCC). In practice, it represents the minimum salt concentration that causes rapid coagulation of a dispersion and is an intimate part of the theoretical framework of the DLVO theory (3). Kratohvil et al (A) have studied this aspect of the DLVO theory with MCC and given values for the CCC for many salts, cationic... 

The coagulation, flocculation, and adsorption processes were modeled mathematically using classical coagulation theory as a starting point. The Smoluchowski equation for orthokinetic coagulation in laminar flow is written (18)... 

The presence of polymers or polyelectrolytes have important effects on the Van der Waal interaction and on the electrostatic interaction. Bacterial adhesion, as discussed in Chapter 7.9 may be interpreted in terms of DLVO theory. Since the interaction in bacterial adhesion occurs at larger distances, this interaction may be looked at as occurring in the secondary minimum of the net interaction energy (Fig. 7.4). Particle Size. The DLVO theory predicts an increase of the total interaction energy with an increase in particle size. This effect cannot be verified in coagulation studies. 

In summary, the DLVO theory seems to break down at very close separation where interfacial phenomena such as particle-particle interaction (coagulation) and particle-surface interaction (deposition) are important. 

M. V. Smoluchowski, Mathematical theory of the kinetics of the coagulation of colloidal solutions, Z. Phys. Chem. 92, 129-168 (1917). 

The coagulation process can now be considered in perspective of a ternary polymer-solvent-nonsolvent system, A schematic ternary phase diagram, at constant temperature, is shown in Figure 8. The boundaries of the isotropic and narrow biphasic (isotropic-nematic) regions are based on an extension of Flory s theory ( ) to a polymer-solvent-nonsolvent system, due to Russo and Miller (7). These boundaries are calculated for a polymer having an axial ratio of 100, and the following... 

W is the stability ratio, i. e. the factor by which the coagulation velocity is reduced due to interparticle repulsion. It is related to the height of the energy barrier. When coagulation is fast, W = 1. Various aspects of slow coagulation are still not fully understood (O Melia, 1987). Several theories of the kinetics of coagulation are discussed by Grand et al. (2001). 

Now let us see how this result is to be understood in terms of the DLVO theory. At first glance, it seems remarkable that any consistency at all can be found in tests as arbitrary as the CCC determination. It is not difficult, however, to show that these results are quite close to the values predicted in terms of the DLVO model for interacting blocks with flat faces. From an inspection of Figure 13.8, we concluded that the system at k = 108 m l would be stable with respect to coagulation, whereas the one at k = 3 108 m l would coagulate. Furthermore, we examined the energy barrier to draw these conclusions. Next we must ask how the qualitative criteria we used in discussing the curves can be translated into an analytical expression. 

---