What is a Polyelectolyte Multilayer (PEM)?
Self-assembly processes of charged polymers known as polyelectrolytes (PE1, PE2 ) can be used to build-up multilayered materials (PEM) with unique properties. In the early 90's Decher et al  demonstrated the feasibility of the self-assembly of polyelectrolyte multilayers (PEMs) using the so-called Layer-by-Layer (LbL) technique(animation,schematic plot). If you want to know more about PEM´s generalities you can for instance visiti PEM´s web page at Florida State University.
Why Polyelectrolyte multilayers are interesting?
The versatility of the LbL process has allowed the fabrication of thin multilayer films made of synthetic polyelectrolytes, DNA, lipids and proteins, which has resulted in a boost of novel applications in recent years. For instance, PEMs are used as matrix materials for enzymes and proteins in sensor applications , and also as a matrix for active components in solar cells. PEMs are used as a coating for protecting and control the healing process of damaged arteries . In addition PEM's can be used as permeable membranes for nanofiltration , gas separation, and fuel cells. Furthermore, PEM's are also used in the fabrication of non-linear optical materials , coloured electrochromic electrodes (future display devices), and to tailor the properties of photonic crystalls . Other uses of PEM's include analyte separation processes (chromatography) , and the fabrication of thin-walled hollow micro- and nanocapsules (see , and ref. therein). These capsules have great potential for drug carrier and nanoreactors.
Status of the PEM´s research at a glance
Since the pionering work of Decher et al in the 90´s, many scientists have been studying and characterizing the properties of Polyelectrolyte Multilayers. The research done about PEMs has been summarized in a few reviews [9-13]. But, just to mention a few relevant contributions to the field of PEM´s:
Nonetheless, despite the amount of work done during the last 15 years, the understanding of the multilayer formation process and the knowledge about how slight differences during the growth process are able to strongly modify the properties of the multilayer materials is still in its infancy. The complex nature of PEMs possesses a challenge when one tries to choose a PEM system for a particular application. Therefore, one must first try to learn more about the fundamental properties of PEMs before it is possible to understand how to use these films for specific applications without a large and exhausting process of trial and error. Doubtless, the understanding of such issues is of paramount importance to improve current building-up methods and devices, tune finely the properties of such materials for specific purposes, and in turn devise new potential applications for such materials. Such knowledge will not be only of benefit for the Scientific Community but also for industry as well as society due to the huge potentiality of such materials for new devices and applications.
Our current reserach on Polyelectrolyte Multilayers (PEM´s) is aimed to help to shed light on some still not clearly understood aspects governing multilayer formation and the control of their properties. At this stage, numerical simulations that use the state-of-the-art algorithms to deal with charged soft matter offer a very valuable and useful tool in order to elucidate the mechanisms governing multilayering assembly and the properties of PEMs. These numerical simulations can build a bridge between the detailed experimental results and the relatively coarse grained analytical models. Our currents aims in the area of PEM research are:
- Clarify which factors contribute to stabilize multilayer films with special reference to weak polyelectrolytes.
- Explain the mechanisms and the causes that induce the formation of exponential growing films instead of linear films.
- Study how the stability and the properties of PEMs, as well as the kinetics of both linear and exponential buildup regimes as a function of the several factors which have been observed to be of relevance in experiments.
- Study of hollow spherical PEM nanocapsules as drug carriers and chemical nanoreactors.
- Refine current electrostatic methods in order to allow faster and more detailed simulations of large PEM systems.
- Investigate, in close collaboration with simultaneous experimental investigations (Specially groups of von Klitzing, T. Hugel, Helm), the inner structure and dynamics of a well defined, but small number of multilayer polymers on various substrates.
 Decher G, Hong JD, and Schmitt J, Thin Solid Films, 210, 831, (1992).
 Tran D, and Renneberg R, Biosensors and Bioelectronics, 18, 1491, (2003).
 Thierry B, Winnik FM, Merhi Y, and Tabrizian M, J. Am. Chem. Soc., 125, 7494, (2003).
 Malaismy R, and Bruening M, Langmuir, 21, 10587, (2005)
 Jiang L, Lu F, Chang Q, Liu Y, Liu H, Li Y, et al., Chem. Phys. Chem., 6, 481,(2005).
 Arsenault AC, Halfyard J, Wang Z, Kitaev V, Ozin GA, et al., Langmuir, 21, 499, (2005).
 Kamande MW, Fletcher KA, Lowry M, and Warner IM, J. Sep. Sci., 28, 710, (2005).
 Khopade AJ, Arulsudar N, Khopade SA, Hartmann J, Biomacromolecules, 6, 229, (2005).
 Messina R, Holm C, Kremer K, J. Poly. Sci. B, 42, 3557, (2004).  Klitzing RV, Wong JE, Jaeger W, and Steiz R, Current Op. Coll. Interf. Sci., 9, 158,(2004).
 Schönhoff M, Current Op. Coll. Interf. Sci., 8, 86, (2003).  Hammond PT, Current Op. Coll. Interf. Sci., 4, 430, (2000).
 Decher G, Science, 277, 1232, (1997).
 Kharlampieva E, and Sukhishvili SA, Langmuir, 19, 1235, (2003).
 Schoeler B, Kumaraswamy G, and Caruso F, Macromolecules, 35, 889, (2002).
 Kujawa P, Moraille P, Sanchez J, Badia A, Winnik FM, J.Am.Chem.Soc, 127, 9224, (2005) .
 Salomäki M, Vinokurov IA, Kankare J, Langmuir, 21, 11232, (2005).  Guyomard A, Muller G, Glinel K, Macromolecules, 38, 5737, (2005).
 Netz RR, Joanny JF, Macromolecules, 32, 9013, (1999).
 Park SY, Rubner MF, and Mayes AM, Langmuir, 18, 9600, (2002).
 Castlenovo M, and Joanny JF, Langmuir, 16, 7524, (2000).  Messina R, Holm C, Kremer K, Langmuir, 19, (10), 4473, (2003).
 D. Kovacevic, S. van~der Burgh, M.A. Cohen-Stuart, Langmuir 18, 5607 (2002).
 Patel PA, Jeon J, Mather PT, and Dobrynin AV, Langmuir, 21, 6113, (2005).
 Panchagnula V, Jean J, Rusling JF, and Dobrynin AV, Langmuir, 21, 1118, (2005).
 Abu-Sharkh B, J. Chem Phys., 123, 114907, (2005).
Polyelectrolyte Multilayers page is under construction ... --Jcerda 20:58, 4 January 2008 (CET)