Difference between revisions of "Polyelectrolyte Multilayers"

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'''Polyelectrolyte Multilayers page is under construction ...'''
 
 
  
 
== What is a Polyelectolyte Multilayer (PEM)? ==
 
== What is a Polyelectolyte Multilayer (PEM)? ==
  
Self-assembly processes of charged polymers (polyelectrolytes, see for instance [http://en.wikipedia.org/wiki/Polyelectrolyte
+
<onlyinclude>PEMs are composed of '''alternating layers of oppositely charged polyelectrolytes''' (PEs) (synthetic PEs or biomolecules), which are generally built up based on the Layer-by-Layer technique. [1,2] Due to their potential applications as membrane, encapsulation and matrix materials, and for enzymes and proteins in sensor applications, PEMs have stimulated great interests from both academic researchers and industries.[3] See also a [http://www.chem.fsu.edu/multilayers/ PEM website]Despite the large number of experimental works, '''theoretical and computational studies''' toward understanding the microscopic structure of PEMs '''are scarce'''.[4]
, the Wikipedia]) involving electrostatic interactions can be used to build-up multilayered materials(PEM) with unique properties. In the early 90's Decher et al [1] demonstrated the feasibility of the self-assembly of polyelectrolyte multilayers (PEMs) using the so-called [http://www.chem.fsu.edu/multilayers/Multilayer%20Animation%20Slow.swf Layer-by-Layer (LbL) technique] (see also the following [http://www.chem.fsu.edu/multilayers/Schematic_of_the_LayerbyLayer_files/slide0002.htm schematic plot]). To know more about PEM´s, see the web page of [http://www.chem.fsu.edu/multilayers/ PEM´s] at Florida State University.
+
</onlyinclude>
 +
== Our Research ==
  
== Why Polyelectrolyte multilayers are interesting? ==
+
In close collaboration with experimental investigations from groups of Prof. [http://www.chemie.tu-berlin.de/klitzing/menue/home/ von Klitzing] and Prof. [http://www.bio.ph.tum.de/index.php?id=69 Hugel], we are currently working to investigate the inner structure and dynamics of a small layer number of PEMs via '''all-atom''' (AA) and '''coarse-grained''' (CG) simulations. The project is funded by the [http://www.dfg-spp1369.de/front/joomla/ '''DFG SPP 1369''': Polymer-Solid Contacts: Interfaces and Interphases]
 +
[[Image:spp1369_logo_small.jpg|100px|]]
  
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 [2], 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 [3]. In addition  PEM's can be used as permeable membranes for nanofiltration [4], gas separation, and fuel cells. Furthermore, PEM's are also used in the fabrication of non-linear optical materials [5], coloured electrochromic electrodes (future display devices), and to tailor the properties of photonic crystalls [6]. Other uses of PEM's include analyte separation processes (chromatography) [7], and the fabrication of thin-walled hollow micro- and nanocapsules (see [8], and ref. therein). These capsules have  great potential for drug carrier and nanoreactors.
 
  
== Status of the PEM´s research at a glance ==
+
[[Image:scheme_PSS-PDADMA.png|200px|right|thumb|Schematic representation of PSS and PDADMA.]]
  
Since the pionering work of Decher et al in the 90´s, many scientists have been studying and characterizing the properties of Polyelectrolyte Multilayers, just to mention a few relevant contributions in the field of PEM´s:
+
The AA level simulations proved to be '''consistent''' with existing experimental data on '''chain conformation''' of adsorbed poly(styrene sulfonate) (PSS) in PSS monolayer systems, '''dielectric permittivity''' and '''diffusion constant''' of water in PSS/PDADMA polyelectrolyte complexes (PDADMA stand for poly(diallyldimethylammonium)).
  
* [[PEM experimental studies]].
+
So far, we are building the PSS/PDADMA bilayers based on the previously obtained PSS monolayers and we are expecting to extract exciting information from these studies. The simulation of a bilayer represents our final goal for atomistic simulations of PMEs so far, due to the high requirement of computer resources (ca. 1000 000 cpu hours in total).
* [[PEM theoretical studies]].
 
* [[Numerical simulations about 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.  
+
Due to the limitations of atomistic simulations, further insight into structure and dynamics of PEMs can be achieved only with simulations at CG level. Qualitative understanding and agreement with experiments has been obtained by us using the already existing generic bead-spring PE model. However, a refined CG PE model is needed in order to be quantitatively predictive. This is part of our next working program.  
  
== Our Research ==
+
Some selected results obtained during the last 2.5 years are:
  
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:
+
'''a) Bilayer thermodynamical instability'''
  
* Clarify which factors contribute to stabilize multilayer films with special reference to weak polyelectrolytes.
+
[[Image:thermodynamic_stability_bilayer_vs_trilayer.png|200px|right|thumb|Thermodynamic instability of the bilayer and the stability of the fast deposited tri-layer.]]
* 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.
 
  
== References ==
+
Our CG level simulations have shown that depending on the relative strength of the monomer-monomer and monomer-surface interaction energies, a '''progressive redissolution''' of the first bilayer or a '''partial dewetting''' resulting in a disordered melt can happen.
  
[1] Decher G, Hong JD, and Schmitt J, Thin Solid Films, 210, 831, (1992).
+
We have shown that a '''fast enough deposition of the third layer''' -- before the aging process  --  can '''prevent such redissolution or partial dewetting''' and provide the stability
 +
needed to form a PEM. We have checked that the deposition of further layers is a stable process. This suggests that the first PE bilayer is not thermodynamically stable, while tri-layers and higher layers are stable, at least within the long run time of our simulations.
  
[2] Tran D, and Renneberg R, Biosensors and Bioelectronics, 18, 1491, (2003).
+
'''b) Charge compensation mechanism'''
  
[3] Thierry B, Winnik FM, Merhi Y, and Tabrizian M, J. Am. Chem. Soc., 125, 7494, (2003).  
+
[[Image:intrinsic_vs_extrinsic_result_in_PEC.png|200px|right|thumb|Possibilities of sulfurs from PSS and nitrogens from PDADMA which are intrinsically and extrinsically charge compensated.]]
  
[4] Malaismy R, and Bruening M, Langmuir, 21, 10587, (2005)
+
In our AA level simulations on PSS/PDADMA complexes, intrinsic (polyanions pair with polycations) and extrinsic (polyions pair with salt ions) charge compensation mechanisms have been found to co-exist, although '''the intrinsic one is predominant''' in the investigated salt (NaCl) concentration range from 0.17 to 1.00 mol/L.
  
[5] Jiang L, Lu F, Chang Q, Liu Y, Liu H, Li Y, et al., Chem. Phys. Chem., 6, 481,(2005).  
+
Furthermore, the relative scale of the interaction energy of the ion-pairs in such PSS/PDADMA mixture is calculated to follow (in kJ/mol): Na-Cl (-520) > PSS-Na (-420) > PDADMA-Cl (-280) ~ PSS-PDADMA (-270). The relative scale of the interaction energy can be very useful to explain some experimental finding, such as PSS is found to be in a higher concentration than PDADMA in PSS/ PDADMA complexes [5]. This information is also valuable to properly model the interactions between ion-pairs in the upcoming refined CG model.
  
[6] Arsenault AC, Halfyard J, Wang Z, Kitaev V, Ozin GA, et al., Langmuir, 21, 499, (2005).
+
'''c) PSS adsorption monolayer'''
 +
[[Image:PSS_momolayer.png|200px|right|thumb|PSS adsorption monolayer]]
  
[7] Kamande MW, Fletcher KA, Lowry M, and Warner IM, J. Sep. Sci., 28, 710, (2005).
+
The PSS monolayer is diposited from a PSS solution via atomistic simulations. Our results demonstrate that short-range interactions of van der Waals origin from the adsorbing substrate play a significant role in the layer structure of the adsorbed PSS, and they alone are already sufficient to induce a stable PSS adsorption layer. The PSS chains are found to behave as hydrophilic PEs, two kinds of conformations of which are observed: flat PSS adsorption layer dominates with some adsorbed PSS chains dangling into the above PSS solution.
  
[8] Khopade AJ, Arulsudar N, Khopade SA, Hartmann J, Biomacromolecules, 6, 229, (2005).
 
  
[9] Messina R, Holm C, Kremer K, J. Poly. Sci. B, 42, 3557, (2004). [10] Klitzing RV, Wong JE, Jaeger W, and Steiz R, Current Op. Coll. Interf. Sci., 9, 158,(2004).
+
'''d) PE chain pulling experiment'''
  
[11] Schönhoff M, Current Op. Coll. Interf. Sci., 8, 86, (2003). [12] Hammond PT, Current Op. Coll. Interf. Sci., 4, 430, (2000).
+
[[Image:PE_pulling_experiment.png|200px|thumb|Results from our CG simulations]]
 +
[[Image:PE_pulling_experiment_Hugel.png|200px|thumb|Exp. data from Hugel's group]]
  
[13] Decher G, Science, 277, 1232, (1997).
+
The present, non-refined CG model yields a qualitative agreement with the experiments by the Hugel group. This makes us confident that maybe even a quantitative comparison might be obtainable once the refined coarse-grained model will be ready.
  
[14] Kharlampieva E, and Sukhishvili SA, Langmuir, 19, 1235, (2003).
+
In the computer simulations on PE pulling experiments, a PE chain, which is similar to the PE chains of the capping layer, is introduced with the corresponding counterions. The averaged force, that is needed to keep one of the chain ends fixed at a given point Z_{tip}, is measured by performing several independent runs. The position of the chain tip is slowly increased to a new value where a new measurement was performed.
  
[15] Schoeler B, Kumaraswamy G, and Caruso F, Macromolecules, 35, 889, (2002).
+
== Scientists ==
  
[16] Kujawa P, Moraille P, Sanchez J, Badia A, Winnik FM, J.Am.Chem.Soc, 127, 9224, (2005) .
+
* ''[[Christian Holm]]''
 +
* ''[[Baofu Qiao]]''
 +
* ''[[Joan Josep Cerdà]]''
 +
* ''[[Marcello Sega]]''
  
[17] Salomäki M, Vinokurov IA, Kankare J, Langmuir, 21, 11232, (2005). [18] Guyomard A, Muller G, Glinel K, Macromolecules, 38, 5737, (2005).
+
== Publications ==
 +
<bibentry> messina03a, messina04b, cerda09b,cerda09c, qiao10a, qiao11a</bibentry>
  
[19] Netz RR, Joanny JF, Macromolecules, 32, 9013, (1999).
+
== References ==
 
+
[1] J. Schmitt, G. Decher and G. Hong. ''Thin Solid Films'', '''1992''', ''210/211'', 831.[http://www.sciencedirect.com/science/article/B6TW0-47X13HN-47/2/e56caa8317193804cc1863ce3db4a32b URL]
[20] Park SY, Rubner MF, and Mayes AM, Langmuir, 18, 9600, (2002).
 
 
 
[21] Castlenovo M, and Joanny JF, Langmuir, 16, 7524, (2000).   [22] Messina R, Holm C, Kremer K, Langmuir, 19, (10), 4473, (2003).  
 
 
 
[23] D. Kovacevic, S. van~der Burgh, M.A. Cohen-Stuart, Langmuir 18, 5607 (2002).
 
  
[24] Patel PA, Jeon J, Mather PT, and Dobrynin AV, Langmuir, 21, 6113, (2005).  
+
[2] G. Decher, ''Science'','''1997''', ''277'', 1232. [http://www.sciencemag.org/cgi/content/abstract/277/5330/1232 URL]
  
[25] Panchagnula V, Jean J, Rusling JF, and Dobrynin AV, Langmuir, 21, 1118, (2005).
+
[3] J. B. Schlenoff, ''Langmuir'', '''2009''', ''25'', 14007.[http://pubs.acs.org/doi/abs/10.1021/ja802054k URL]
  
[26] Abu-Sharkh B, J. Chem Phys., 123, 114907, (2005).
+
[4] A. V. Dobrynin. ''Curr. Opin. Colloid Interface Sci'', '''2008''', ''13'', 376.[http://www.sciencedirect.com/science/article/B6VRY-4S7JFXX-2/2/fd13c66c913bca456ed80d11acd1da39 URL]
  
== Scientists ==
+
[5] H. H. Hariri, and J. B. Schlenoff, ''Macromolecules'', '''2010''', DOI: 10.1021/ma1012978. [http://dx.doi.org/10.1021/ma1012978 URL]
* ''[[Joan Josep Cerdà]]''  
+
[[Category:Research]]
* ''[[Christian Holm]]''
 

Latest revision as of 20:21, 5 September 2011


What is a Polyelectolyte Multilayer (PEM)?

PEMs are composed of alternating layers of oppositely charged polyelectrolytes (PEs) (synthetic PEs or biomolecules), which are generally built up based on the Layer-by-Layer technique. [1,2] Due to their potential applications as membrane, encapsulation and matrix materials, and for enzymes and proteins in sensor applications, PEMs have stimulated great interests from both academic researchers and industries.[3] See also a PEM website. Despite the large number of experimental works, theoretical and computational studies toward understanding the microscopic structure of PEMs are scarce.[4]

Our Research

In close collaboration with experimental investigations from groups of Prof. von Klitzing and Prof. Hugel, we are currently working to investigate the inner structure and dynamics of a small layer number of PEMs via all-atom (AA) and coarse-grained (CG) simulations. The project is funded by the DFG SPP 1369: Polymer-Solid Contacts: Interfaces and Interphases Spp1369 logo small.jpg


Schematic representation of PSS and PDADMA.

The AA level simulations proved to be consistent with existing experimental data on chain conformation of adsorbed poly(styrene sulfonate) (PSS) in PSS monolayer systems, dielectric permittivity and diffusion constant of water in PSS/PDADMA polyelectrolyte complexes (PDADMA stand for poly(diallyldimethylammonium)).

So far, we are building the PSS/PDADMA bilayers based on the previously obtained PSS monolayers and we are expecting to extract exciting information from these studies. The simulation of a bilayer represents our final goal for atomistic simulations of PMEs so far, due to the high requirement of computer resources (ca. 1000 000 cpu hours in total).

Due to the limitations of atomistic simulations, further insight into structure and dynamics of PEMs can be achieved only with simulations at CG level. Qualitative understanding and agreement with experiments has been obtained by us using the already existing generic bead-spring PE model. However, a refined CG PE model is needed in order to be quantitatively predictive. This is part of our next working program.

Some selected results obtained during the last 2.5 years are:

a) Bilayer thermodynamical instability

Thermodynamic instability of the bilayer and the stability of the fast deposited tri-layer.

Our CG level simulations have shown that depending on the relative strength of the monomer-monomer and monomer-surface interaction energies, a progressive redissolution of the first bilayer or a partial dewetting resulting in a disordered melt can happen.

We have shown that a fast enough deposition of the third layer -- before the aging process -- can prevent such redissolution or partial dewetting and provide the stability needed to form a PEM. We have checked that the deposition of further layers is a stable process. This suggests that the first PE bilayer is not thermodynamically stable, while tri-layers and higher layers are stable, at least within the long run time of our simulations.

b) Charge compensation mechanism

Possibilities of sulfurs from PSS and nitrogens from PDADMA which are intrinsically and extrinsically charge compensated.

In our AA level simulations on PSS/PDADMA complexes, intrinsic (polyanions pair with polycations) and extrinsic (polyions pair with salt ions) charge compensation mechanisms have been found to co-exist, although the intrinsic one is predominant in the investigated salt (NaCl) concentration range from 0.17 to 1.00 mol/L.

Furthermore, the relative scale of the interaction energy of the ion-pairs in such PSS/PDADMA mixture is calculated to follow (in kJ/mol): Na-Cl (-520) > PSS-Na (-420) > PDADMA-Cl (-280) ~ PSS-PDADMA (-270). The relative scale of the interaction energy can be very useful to explain some experimental finding, such as PSS is found to be in a higher concentration than PDADMA in PSS/ PDADMA complexes [5]. This information is also valuable to properly model the interactions between ion-pairs in the upcoming refined CG model.

c) PSS adsorption monolayer

PSS adsorption monolayer

The PSS monolayer is diposited from a PSS solution via atomistic simulations. Our results demonstrate that short-range interactions of van der Waals origin from the adsorbing substrate play a significant role in the layer structure of the adsorbed PSS, and they alone are already sufficient to induce a stable PSS adsorption layer. The PSS chains are found to behave as hydrophilic PEs, two kinds of conformations of which are observed: flat PSS adsorption layer dominates with some adsorbed PSS chains dangling into the above PSS solution.


d) PE chain pulling experiment

Results from our CG simulations
Exp. data from Hugel's group

The present, non-refined CG model yields a qualitative agreement with the experiments by the Hugel group. This makes us confident that maybe even a quantitative comparison might be obtainable once the refined coarse-grained model will be ready.

In the computer simulations on PE pulling experiments, a PE chain, which is similar to the PE chains of the capping layer, is introduced with the corresponding counterions. The averaged force, that is needed to keep one of the chain ends fixed at a given point Z_{tip}, is measured by performing several independent runs. The position of the chain tip is slowly increased to a new value where a new measurement was performed.

Scientists

Publications


References

[1] J. Schmitt, G. Decher and G. Hong. Thin Solid Films, 1992, 210/211, 831.URL

[2] G. Decher, Science,1997, 277, 1232. URL

[3] J. B. Schlenoff, Langmuir, 2009, 25, 14007.URL

[4] A. V. Dobrynin. Curr. Opin. Colloid Interface Sci, 2008, 13, 376.URL

[5] H. H. Hariri, and J. B. Schlenoff, Macromolecules, 2010, DOI: 10.1021/ma1012978. URL