Interactions between Colloidal Particles83If our materials are produced by techniques such as milling or high-speed dispersion, the particles may be small compact aggregates of primary crystallites or fragments of crystals. Specialist texts are often left on the shelf as we search for attempts to solve a particular problem. These materials are widely used as stabilizers and cleaning agents. Particles of a micron or two in size will be satisfactory. The second problem of equilibrium is, however, that at low concentrations of surfactant a signicant time passes before the molecules in solution diffuse to the surface and equilibrium becomes established. Although the process appears a little complicated, it is relatively easy to program a computer to carry this out. The author should be congratulated for his clarity.
This is that the low-frequency contributions i. The considered mechanisms indicate the factors for control of foaminess. Using the relationships from the lattice model, Equation 2. Category: Science Author : Bernard P. After an introduction to the basic concepts and principles, the book divides into two sections. However, the points that we need to keep in mind here arise from the usual condition in thermodynamic calculations that at some point we have required the system to be at equilibrium. If there are dissolved species present, we must consider the presence of such species at the surface or interface as we shall see when we explore surfactants.
The London constant shown in Equations 3. Here, we use the algebra to separate the elastic storage of work done from that dissipated by viscous ow. In both cases, there is a 12-carbon parafn chain with a polar head group. The cause of this motion is, in turn, the motion of the molecules making up the suspending uid. For example, the surfactants present in our lungs are vital for their operation, as are the bile salts produced by the pancreas, and act to disperse dietary fat into colloidal size droplets or chylomicra which pass into the blood stream where they are utilized by the body. The range of the interaction is no greater than the dimension of the solution species which is causing the effect, and so we can consider it to be a short-range interaction.
This material is known as a latex and is manufactured by the emulsion polymerization of vinyl monomers. Hence, using this text, the user will always have the fundamentals readily to hand. The transition from a dilute to a condensed phase can be very sharp and is a function of the range of the forces, as noted above. These have particular relevance to many colloidal systems as many of our surfactant systems have a linear aliphatic chain as one element of their composition. It will also help researchers, policymakers, industry personnel, journalists and the general public to understand food nanotechnology in great detail.
The conformation of a polymer chain in solution is a spheroidal coil which can be characterized by the root-mean-square end-toend chain dimension, as follows:r2 0:5 c1 N 0:5 l cIdeal solution r2 0:5 cGood solvent c1 N l 0:6 2:6 We may also characterize the coil dimension in terms of its radius of gyration, Rg. Furthermore, we have only considered pairs of atoms or molecules interacting in the absence of any intervening medium. The circuits are printed by using inks with metallic colloidal particles dispersed in organic media. The rst thing to note is that the trimethylammonium head group is a larger group than a carboxylic acid group, but twice as big? The attachment and detachment of particles from surfaces require an understanding of the interparticle forces and how we can manipulate them, whether by chemical environment or surfactant type. Lyklema is coauthor of two chapters and general editor.
Characterization of molecular weight needs to be carried out in a solvent system which will suppress such aggregation. That is, the extensional viscosity is high and applications such as spraying become difcult. Water-soluble polymers contain polar groups such as hydroxyl, carboxylic acid or ether groups which can take part in the hydrogen H -bonding structure of water. After drying, the circuits are completed by sintering the particles to give optimum conductivity. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. When we look at a colloidal sol in the microscope, we observe the particles to move around with a random motion. Recent results on fabricating two-dimensional 2D arrays from micrometer and sub-micrometer latex particles, as well as 2D crystals from proteins and protein complexes, are reviewed.
Consider some typical anionic surfactants such as sodium dodecanoate or sodium dodecyl sulfate. They have been used as stabilizers for inorganic particles in paints, inks and photographic lm, for example. Light scattered from the white pigment particles usually titanium dioxide hides the underlying surface. The equilibrium constant for this reaction is given by the following: Ki xi x1 i 2:27 where x1 and xi are the mole fractions of the monomers and micelles, respectively. The latter moieties are strongly hydrated and the rst two or three carbon atoms of the tail near to the head group are close enough to be inuenced by the head group hydration. They are the London dispersion forces which are due to the coupling of the uctuations of the charge density of the electron clouds of one atom with its neighbours. Synthesizing the polymer as colloidal particles dispersed in water can efciently produce this.
This is achieved by having a small mole percentage of lyophobic polymer material on the backbone of the polymer, which results in a weak assembly of these regions so that all of the polymer molecules are associated with each other. This leaves the rest which is solvated to expand away from the interface and prevent other particles from close approach. Such structures can vary from simple linear block structures to sophisticated branched structures resembling brushes or combs. This is then viewed with a polarizing microscope. Solid particles may be spherical but are often non-spherical. When molecular weights 106 are utilized, however, problems in rheological behaviour become apparent.
As this is a model, we may choose the location of the Gds to be the most convenient, i. At this point, it is worthwhile to briey review the methods most frequently used. The processing and delivery of the correct properties is often dependent on the material being in the colloid state and yet few courses cover the subject in depth, if at all. The key feature of this lattice is that the solvent molecules are assumed to be the same size as the segments of the polymer chain. The behaviour of the dispersion can be thought of as analogous to that of a gas except that the motion is Brownian and not ballistic, i.
A dissolved polymer molecule is one such region and each molecule will scatter light. Water, for example, has a value for g1 of 72 mN m1. To obtain a uniform polymer concentration right up to the interface, the conformations in the different parts of the polymer would have to be reduced as that part of the coil close to the surface becomes more concentrated. The oil phase here is tetradecane which represents a light fuel oil and has a chain length commonly found in nature. The Nature of Colloids Table 1.