Foam formation fundamentals

Foam destabilization is also a factor in the packing and orientation of mixed films, which can be determined from monolayer studies. It is worth mentioning that foam formation from monolayers of amphiphiles constitutes the most fundamental process in everyday life. The other assemblies, such as vesicles and BLM, are somewhat more complicated systems, which are also found to be in equilibrium with monolayers. 

Introduction to Foams and Foam Formation 5 FUNDAMENTALS OF FOAM FORMATION... 

This two-part series is an excellent source prepared by authors expert in their fields. Part 1 has an overview of the entire field of plastic foams in the introductory chapter, an extensive treatment of the fundamental principals of foam formation of nearly all types in Chapter 2, followed by specific chapters on foam varieties which are predominantly flexible. A chapter on testing of all types is included. Part 2 covers primarily rigid foam types and has a series of chapters on applications of foams. 

Foam Formation. Three fundamental pore-level generation mechanisms exist snap-off, division, and leave-behind. 

The fundamentals of foam formation have been reviewed in detail by a number of authors [17-19]. Therefore, only the main concepts will be reviewed in this chapter. Cellular plastics are produced through several methods, irrespective of cell structure (open or closed). However, the most commonly used methods for cellular PLA are the following ... 

In this chapter, we first consider the nature of surface activity in gas-hydrocarbon interfaces in general and in gas-crude oil systems in particular. That represents an issue fundamental to understanding the causes of foam formation in gas-oil separators and has relevance for the mode of action of antifoams in that context. In a separate section, we consider the possible causes of foam formation in gas-crude oil systems. There we review the observations of foam behavior in gas-crude oil systems and make the limited comparison with theory which that permits. Finally we consider foam control in gas-oil separators, which usually involves the use of antifoams. Therefore, we describe the design criteria for suitable antifoams and the evidence available concerning their mode of action in a non-aqneons medium such as crude oil. 

This book focuses on emulsions, foams, and suspensions their fundamentals and applications. The variety of systems represented or suggested by Tables 1.1 and 1.2 underscores the fact that the problems associated with colloids are usually interdisciplinary in nature and that a broad scientific base is required to understand them completely. A wealth of literature exists on the topic of colloidal dispersions, including a range of basic colloid reference texts [12-28], dictionaries [9-11,29], and treatises on the myriad of applied aspects, of which only a few are cited here [1-5,30-36], The widespread importance of emulsions, foams, and suspensions in particular, and scientific interest in their formation, stability and properties, have precipitated a wealth of specialized publications dedicated to each of emulsions [37-42], foams [43-47], and suspensions [48-51],... 

Foams may be prepared by either one of two fundamental methods. In one method, a gas such as air or nitrogen is dispersed in a continuous liquid phase (e.g. an aqueous latex) to yield a colloidal system with the gas as the dispersed phase. In the second method, the gas is generated within the liquid phase and appears as separate bubbles dispersed in the liquid phase. The gas can be the result of a specific gasgenerating reaction such as the formation of carbon dioxide when isocyanate reacts with water in the formation of water-blown flexible or rigid urethane foams. Gas can also be generated by volatilization of a low-boiling solvent (e.g. trichlorofluoromethane, F-11, or methylene chloride) in the dispersed phase when an exothermic reaction takes places, (e.g. the formation of F-11 or methylene chloride-blown foams). 

Abstract. The lecture will review the recent advances in the techniques for formation of bubbles of gas and droplets of liquid in two-phase microfluidic systems. Systems comprising ducts that have widths of the order of 100 pm produce suspensions of bubbles and droplets characterized by very narrow size distributions. These systems provide control over all the important parameters of the foams or emulsions, from the volumes of the individual bubbles and droplets, through the volume fraction that they occupy, the frequency of their formation, and the distribution of sizes, including monodisperse, multimodal and non-Gaussian distributions. The lecture will review the fundamental forces at play, and the mechanism of formation of bubbles and droplets that is responsible for the observed monodispersity. 

This book provides an introduction to the nature and occurrence, properties and uses, and formation and breaking of foams in the petroleum industry. It is aimed at scientists and engineers who may encounter foams or apply foams, whether in process design, petroleum production, or research and development. Primarily the focus is on the introduction and subsequent application of foam principles, and includes attention to practical foam problems. Books available up to now are either principally theoretical (such as the colloid chemistry texts) or focus on foams in general (like Bikerman s classic books). A significant gap in this coverage concerns foams in the petroleum industry, a topic that is not only of great practical importance but also presents many problems of fundamental interest. 

The tendency of surfactants to adsorb at interfaces and self-assemble results in unique physical properties and behavior. Formation of micelles, liquid crystals, macroemulsions, microemulsions, and foams, as well as surface tension reduction and improving wettabiUty of aqueous solutions, are just a few phenomena exhibited by surfactants. This behavior is of both fundamental interest as a unique subset of physical chemistry as weU as leading to many practical applications. 

Aerosols, like foams, emulsions, and dispersions, may be either advantageous or detrimental, depending on the situation. The previous discussion introduced some of the fundamental aspects of aerosol formation. Of equal or perhaps greater practical importance is the question of the suppression of aerosol formation, the destruction of unavoidable aerosols, or the controlled deposition of aerosols onto surfaces. Perhaps the best approach to solving such problems is through an understanding of some of the general principles involved in their stabilization and destruction. In that context, some of the mechanisms of destruction involved will be essentially the same as those for other colloidal systems flocculation and coalescence. 

Food emulsions and foams are complex dispersions that constitute a major part of the food products that are consumed daily. The correct elaboration of such colloidal systems determines the functional properties of the final product such as texture or long-term stability. Accordingly, the optimization of the food product depends fundamentally on the comprehension of the structural characteristics of its components. Foams and emulsions are dispersions of air and liquid in another immiscible liquid, respectively. Formation of these dispersions is subject to the presence of amphiphilic molecules, which tend to place themselves at the air-water interface (foams) or the oil-water interface (emulsion). Thus, they constitute molecular barriers that stabilize the dispersion. The composition and structure of these molecular barriers determine ultimately the behavior of foams and emulsions. 

---