tailieunhanh - Particles in Water Properties and Processes - Chpater 4

Keo tương tác và keo ổn định 4,1 tương tác keo - khái niệm chung Giữa các hạt trong nước có các loại tương tác khác nhau, tùy thuộc vào các thuộc tính, đặc biệt là các thuộc tính bề mặt của các hạt. Những tương tác này có thể cung cấp cho lực lượng thu hút hoặc lực đẩy. Nếu lực hấp dẫn chiếm ưu thế, sau đó các hạt sẽ dính với nhau trong liên lạc và hình thành các cụm, tập hợp. Khi các hạt đẩy nhau, chúng được lưu giữ ngoài và ngăn chặn từ tập hợp. Trong. | chapter four Colloid interactions and colloid stability Colloid interactions general concepts Between particles in water there are various kinds of interaction depending on the properties especially surface properties of the particles. These interactions can give forces of attraction or repulsion. If attractive forces dominate then the particles will stick together on contact and form clusters or aggregates. When particles repel each other they are kept apart and prevented from aggregating. In the latter case the particles are said to be stable whereas when aggregates can form the particles are unstable or destabilized. Because these concepts are mainly relevant to particles in the colloidal size range the subject is known as colloid stability and the interactions are known as colloid interactions. These topics are dealt with in this chapter. Importance of particle size Before dealing with the different types of colloid interactions it is worth pointing out some important general features. The first point is that colloid interactions are usually of rather short range usually much less than the particle size. Thus they do not come into play until particles are nearly in contact and so do not have much influence on the transport of particles which is still governed by mechanisms discussed in Chapter 2 . diffusion sedimentation and convection . When particles do approach very close then colloid interactions are crucial in determining whether attachment occurs. The other important feature is the dependence of the interactions on particle size. As we shall see in most cases the strength of interaction is roughly proportional to the first power of the particle size. There are other important forces acting on particles which were discussed in Chapter 2 . fluid drag and gravitational attraction . Fluid drag is proportional to the projected area of the particle and thus roughly to the square of the particle size. The gravitational force is proportional to .