Poring over membranes
A new book on membrane science and technology focuses on the use of atomic force microscopy in the study and characterization of polymer membranes and also provides practical tips on how to undertake an experiment.
April 22, 2008
Peter A. Williams, Materials Science Research Centre, North East Wales Institute, UK
 |
|
Kailash C. Khulbe et al. |
This latest addition to the Springer Laboratory series provides a good overview of membrane technology and the application of atomic force microscopy (AFM) in membrane characterization. It is easy to read and provides a significant number of AFM images from recent research papers so that the reader is quickly brought up to date with the latest developments.
The initial section of the book is a concise review of the procedures used in the preparation of symmetric and asymmetric polymeric membranes, covering areas such as track etching, precipitation from the vapor phase, and phase inversion. It also briefly describes methods for the preparation of composite membranes and includes procedures used for membrane surface modification. Also incorporated into this section is a summary of membrane types used in various separation processes, such as reverse osmosis, nano-, ultra-, and microfiltration, gas separation, dialysis, and various other examples.
A special feature of the book is a chapter that provides a detailed introduction to the principles of AFM. This section will be of particular interest to experimentalists since it gives details, not only of the various modes of AFM operation (i.e. contact, noncontact, tapping), but also provides practical instructions on how to undertake an experiment. These include tips on sample preparation techniques, how to introduce a sample into the instrument, and hints on laser and photodiode alignment.
The remaining sections of the book are concerned predominantly with the application of AFM in the characterization of polymeric membranes. One chapter notes the various theories that have been reported for the formation of the nodular structure observed in flat sheet and hollow fiber membranes. The authors present AFM images from a number of recent research studies involving different membrane chemistries that provide details of the size of the supermodular aggregates that give rise to this nodular structure.
A further chapter deals with the determination of pore size, pore size distribution, and surface roughness of membranes using AFM. It points out the importance of the geometry of the tip used in AFM experiments and presents pore size results from recent publications that differ significantly from those obtained by other microscopic techniques such as scanning electron microscopy (SEM) and solute transport measurements.
It is noted that AFM provides much better resolution than SEM and is by far superior for measurement of pore size. The fact that AFM always gives larger pore size values than those obtained by solvent transport techniques is highlighted and discussed in the light of conclusions drawn in recent articles. Details of work on the determination of membrane surface roughness and cross-sectional structure are also included with supporting AFM images.
The book also demonstrates the versatility of AFM by including a chapter on its use for the measurement of adhesive forces, which play an important role in predicting membrane fouling. A description of the modes of operation of AFM is also included and some of the discussion presented earlier in the book is repeated once more for clarification.
In summary, this book presents a good introduction to the field of membrane science and technology. It will be of interest to both academics and industrialists involved in the use of membranes in separation processes and will be particularly welcomed by experimentalists who wish to become involved in AFM.