Analytical Ultracentrifugation of Polymers and Nanoparticles
Description
Analytical ultracentrifugation (AUC) is a powerful method for the characterization of polymers, biopolymers, polyelectrolytes, nanoparticles, dispersions, and other colloidal systems. The method is able to determine the molar mass, the particle size, the particle density and interaction parameters like virial coefficients and association constants. Because AUC is also a fractionation method, the determination of the molar mass distribution, the particle size distribution, and the particle density distribution is possible. A special technique, the density gradient method, allows fractionating heterogeneous samples according to their chemical nature that means being able to detect chemical heterogeneity. The book is divided into chapters concerning instrumentation, sedimentation velocity runs, density gradient runs, application examples and future developments. In particular, the detailed application chapter demonstrates the versatility and power of AUC by means of many interesting and important industrial examples. Thus the book concentrates on practical aspects rather than details of centrifugation theory.
Both authors have many years of experience in an industrial AUC research laboratory of a world leading chemical company.
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7 Recent Developments and Future Outlook (p. 215-216)
In 1991, one of the authors of this bookwrote a paper about the future requirements formodern analytical ultracentrifuges [1]. The four most important requirements proposed in this paper were:
(i) multi-hole rotors,
(ii) multiple detecting systems,
(iii) automatic online data analysis, and
(iv) a new running technique with a variable rotor speed ?(t) during a run.
In a recent feature article about analytical ultracentrifugation of nanoparticles, Cölfen [2] wrote "it is amazing that small parts of these requirements were understood in only a few specialized laboratories, although their potential benefit is obvious".
Nevertheless, some of these proposed requirements are realized: eighthole rotors are standard, the Optima XL-A/I now has two simultaneous online detectors (absorption and interference), Laue [3] recently presented a powerful new fluorescence detector inside an XL-A/I, and the authors of this book together with coworkers presented a Schlieren optics detector (needed for density gradients, [4]).Additionally, there has been a dramatic improvement of data analysis due to new, fast and powerful computer programs described by Philo [5], Demeler [6], Schuck [7, 8], Stafford [9], Lechner [10], and Behlke [25], which are partly mentioned in the foregoing chapters.
To date, however, no 50-hole rotors, nor any triple or quadruple detectors have been developed. Nearly all detectors are still not fast enough, and the quality of their primary measuring data should be higher. Thus, the full power of the new data analysis cannot be used fully today. Furthermore, the benefits of the variable rotor speed ?(t) technique are used only rarely, although recent efforts are dedicated to using variable rotor speeds on the Optima XL-A/I [26, 27].
The authors of this book are optimistic that in the next two decades, the requirements proposed in 1991, but not yet developed, will be realized. Especially,we appeal to themanufacturers of analytical ultracentrifuges to attend to this business. Each laboratory working with GPC, liquid and size exclusion chromatography or field flow fractionation, i.e., each laboratory analyzing polymers, polyelectrolytes, colloids, emulsions or nanoparticles (and there are a lot of them!) is a potential user of AUC technology.
It has to be stressed here that a more user-friendly design of the AUC, especially of the measuring cells, is believed to directly increase the number of potential users. It is one major drawback of AUC technology that a relatively high expertise is needed to run an apparatus. In the following three sections, some details of the requirements remaining to be realized are repeated briefly. Additionally, some new ideas and possible improvements of the AUC technique are proposed. In Sect. 7.1, new instrumentation and detectors will be discussed, whereas Sect. 7.2 will deal with new AUC methods, and Sect. 7.3 with new data analysis.
7.1 New AUC Instrumentation and Detectors
The present standard AUC, the Optima XL-A/I of Beckman-Coulter, is a good basis for further improvements of the AUC technique. We hope Beckman-Coulter, or other manufacturers will carry this out, but it could also be a task for specialized scientific laboratories, because the XL-A/I is a compact modular instrument that has enough space inside the rotor chamber to introduce new detectors and other modifications. However, it is not easy to make use of this type of modularity, as well as of the space inside and below the rotor chamber, because of the associated safety and warranty loss aspects.
