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Fundamentals of Latex Film Formation

Processes and Properties

verfasst von: Joseph L. Keddie, Alexander F. Routh

Verlag: Springer Netherlands

Buchreihe : Springer Laboratory

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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Über dieses Buch

This book has emerged out of our long-time research interests on the topic of latex film formation. Over the years we have built up a repertoire of slides used in conference presentations, short courses and tutorials on the topic. The story presented in this book has thereby taken shape as it has been told and re-told to a mix of academic and industrial audiences. The book presents a wide body of work accumulated by the polymer colloids community over the past five decades, but the selection of examples has been flavoured by our particular experimental interests and development of mathematical models. We intend the book to be a starting point for academic and industrial scientists beginning research on latex film formation. The emphasis is on fundam- tal mechanisms, however, and not on applications nor on specific effects of formu- tions. We hope that the book consolidates the understanding that has been achieved to-date in the literature in a more comprehensive way than is possible in a review article. We trust that the reader will appreciate the fascination of the topic.

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Inhaltsverzeichnis

Frontmatter

1. An Introduction to Latex and the Principles of Colloidal Stability

Abstract

Latex is an example of a colloidal dispersion. It consists of polymeric particles, which are usually a few hundred nanometres in diameter, dispersed in water. The particles typically comprise about 50 percent by weight of the dispersion. Depending on the particular application, there will also be a complex mixture of pigments, surfactants, plasticising aids and rheological modifiers. The whole dispersion is colloidally stable, meaning that it can sit on a shelf for years and remain dispersed, without sedimentation of particles making ‘sludge’ at the bottom. In this book, the word ‘latex’ will be used as shorthand for a wet dispersion. Sometimes, however, latex is used as an adjective, as in ‘latex film’. The plural of ‘latex’ is ‘latices’, not to be confused with ‘lattices’! (An alternative is to say ‘latexes’, but ‘latices’ will be used through this book.)

Joseph L. Keddie, Alexander F. Routh

2. Established and Emerging Techniques of Studying Latex Film Formation

Abstract

The study of the processes of latex film formation presents many challenges to the experimentalist. Each stage of film formation has specific requirements for any analytical technique.

In the drying stage, there is a need to measure water concentration at various positions laterally and through the depth of a wet film. Latex in the wet state precludes the use of techniques that require the sample to be held in a high vacuum, such as Auger spectroscopy or secondary ion mass spectrometry. Electron microscopy conventionally has a high vacuum in the sample chamber, and so it cannot be used in the standard way.

Joseph L. Keddie, Alexander F. Routh

3. Drying of Latex Films

Abstract

Drying is an important operation in a manufacturing process. An example is film formation which requires the removal of water to allow the particles to pack and to form a coherent film. This water removal is achieved by evaporation. In addition to film formation, there are a number of other examples where it is desirable to reduce the amount of water (or indeed any solvent) from a product:

To reduce transport costs for products, such as washing powder, which— although used and manufactured in the wet state—are shipped in a dry form.
To maintain suitable handling properties. For example, sand will flow easily when dry yet will be difficult to handle if wet.
To stop corrosion and the growth of microorganisms.

Joseph L. Keddie, Alexander F. Routh

4. Particle Deformation

Abstract

When soft particles come into close packing, they will usually start to deform. The ideal result is a structure without voids—although with the individual particles still distinguishable, prior to interdiffusion. For such a deformation there must be a driving force for compaction, and there will be a mechanical response from the particles to balance it. The primary driving force is essentially a reduction in the surface free energy and hence the surface area. Depending on the controlling mechanism, there are three interfacial areas in a latex film that can be reduced: polymer/air; polymer/water; and water/air. For polymeric materials, the rheological response is complex and is crucially dependent on temperature. It is possible to have an instantaneous elastic response or a time-dependent viscous creep.

Joseph L. Keddie, Alexander F. Routh

5. Molecular Diffusion Across Particle Boundaries

Abstract

In the previous chapters, we have reviewed how particles pack together during the drying process and why they become deformed from their initial spherical shape. Yet, the film formation process does not stop there: an important third stage follows.

In 1958, only a few years after the theories of particle deformation were first proposed (as outlined in Chapter 4), Voyutskiĭ published his reaction to this previous work. His short paper contained some impressive insights but did not have quantitative experiments to support them. His ideas foreshadowed many of the future experimental developments that will be presented in this chapter.

Joseph L. Keddie, Alexander F. Routh

6. Surfactant Distribution in Latex Films

Abstract

Colloidal polymer particles are made by techniques of emulsion polymerisation, as described in Chapter 1. To emulsify the monomer phase in conventional emulsion polymerisation, and to create micelles that serve as seed particles, one or more surfactants are used. Surfactants are amphiphilic molecules that have a hydrophilic head group and a hydrophobic tail, causing them to adsorb at interfaces and to self-assemble. They impart colloidal stability (through steric or charge effects) and encourage monodispersity of particle size. Although it is possible to perform surfactant-free emulsion polymerisation (Goodwin 1971), which avoids the complications of surfactant migration and segregation, it is difficult to obtain high volume fraction latices with this method. Hence, industrial latices typically contain a large amount of surfactant (on the order of 2 wt. % of the polymer). Surfactants are usually classified as either non-ionic, cationic or anionic, depending on the charge on the hydrophilic head of the molecule.

Joseph L. Keddie, Alexander F. Routh

7. Nanocomposite Latex Films and Control of Their Properties

Abstract

We have seen in previous chapters how identical, homogeneous particles may be used as the ‘building blocks’ of a homogeneous film. Within the past decade, there has been enhanced interest in using colloidal particles in water to create nanocomposite films, which are defined as materials made of two or more phases blended at nanometre length scales. A key advantage of the colloidal approach is that it offers control of structure at the nanoscale (within particles) and at the meso- and even macroscale through the creation of ordered assemblies of particles via film formation. The fabrication of nanocomposites offers exciting new challenges and opportunities for the science and technology of latex film formation. The film formation process offers a way of tailoring the properties of nanocomposite films through the control of the assembly of particles, just as is the case for conventional latex films.

Joseph L. Keddie, Alexander F. Routh

8. Future Directions and Challenges

Abstract

This book has aimed to provide a comprehensive introduction to the main topics relevant to film formation. It is interesting to note some of the topics that were considered as future challenges and new directions in 1997 in a review of latex film formation (Keddie 1997):

Film formation from latex blends;
Film formation from core-shell and composite particles;
Using reactive surfactants.

Progress on these topics during the intervening years is easily charted. Developments in the creation of nanocomposite films through latex blends and two-phase particles were summarised in Chapter 7. Achievements in the use of reactive surfactants were highlighted in Section 6 of Chapter 6.

Joseph L. Keddie, Alexander F. Routh

Backmatter

Titel: Fundamentals of Latex Film Formation
verfasst von: Joseph L. Keddie
Alexander F. Routh
Copyright-Jahr: 2010
Verlag: Springer Netherlands
Electronic ISBN: 978-90-481-2845-7
Print ISBN: 978-90-481-2844-0
DOI: https://doi.org/10.1007/978-90-481-2845-7

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