Polyelectrolyte self-assembly

The adsorption of organic molecules to interfaces is offering a variety of possibilities for the design of novel materials with structures defined on a nanometer scale.

So-called "self-assembly"-processes, employing the self-organization of molecules at interfaces as a result of for example hydrophobic or electrostatic interactions can be employed to produce layered materials.

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  Multilayer formation

  In this context we are employing polyelectrolyte adsorption, driven by electrostatic interaction. Multiple adsorption steps, alternating between polycations and polyanions yield so-called polyelectrolyte multilayers. Applying a large number of repetitions is a simple way of forming a material with a large variability concerning different molecular constituents.

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  PARTICLE COATING

  PEMs can even be formed on colloidal particles as templates instead of planar substrates. In this case, the excess polyelectrolyte has to be removed by centrifugation or ultrafiltration.

  The development of PEM- coating procedures for particles is a major achievement, since it allows to prepare dispersions with a large surface area. In such samples, PEMs can be studied by volume techniques which require a sufficient amount of compound, such as for example NMR or DSC.

  

  After coating of colloidal particles the template itself can be removed employing suitable chemical procedures (for example a dissolution or degradation in acidic conditions). Provided that the PEM shell is stable against that treatment, a hollow polymeric capsule is remaining. Such hollow containers are interesting objects for applications such as encapsulation and the controlled release of active compounds. Therefore, the permeability and mechanisms to control it are of great interest.

• Why are we interested in these materials?

  A number of potential applications make PEMs very interesting. Apart from pure charged homopolymers, a variety of additional components with defined functionalities can be employed in the layer formation, such as for example proteins, enzymes, inorganic nanoparticles, or functional polymers sensitive to external stimuli (pH, temperature). This leads to new possibilities of controlled material design on the smallest possible length scale available with molecular arrangements.

  In our group, we employ functional components such as for example gold nanoparticles or guest-host systems in polyelectrolyte multilayers. We employ synthetic or bio-polymers, and we optimize our systems towards applications such as molecular imprinting, pH triggered release or ion conduction.

  For any kind of application, however, a basic understanding of the principles of self-organized layer formation is essential. Therefore we also investigate fundamental mechanisms of layer formation, for example interdiffusion processes, which may change the growth law from a linear to an exponential one.

  
  Selected publications:

  Movilli, J.; Choudhury, S.S.; Schönhoff, M.; Huskens, J.
  Enhancement of Probe Density in DNA Sensing by Tuning the Exponential Growth Regime of Polyelectrolyte Multilayers
  Chem. Mater. 2020, 32, 9155-9166.
  https://dx.doi.org/10.1021/acs.chemmater.0c02454

  Schlicke, J.; Hoffmann, K.; Lorenz, M.; Schönhoff, M.; Cramer, C.
  Ionic Conductivity Enhancement of Polyelectrolyte Multilayers by Variation of Charge Balance
  J. Phys. Chem. C 2020, 124 (31), 16773–16783.
  https://doi.org/10.1021/acs.jpcc.0c03043

  Parveen, N.; Jana, P. K.; Schönhoff, M.
  Viscoelastic Properties of Polyelectrolyte Multilayers Swollen with Ionic Liquid Solutions
  Polymers 2019, 11(8), 1285.
  https://doi.org/10.3390/polym11081285

  Ostendorf, A.; Schönhoff, M.; Cramer, C.
  Ionic conductivity of solid polyelectrolyte complexes with varying water content: application of the dynamic structure model
  Phys. Chem. Chem. Phys. 2019, 21(14), 7321-7329.
  https://doi.org/10.1039/c8cp05853a

  Bütergerds, D., Cramer, C., Schönhoff, M.
  pH-dependent growth laws and vicoelastic parameters of poly-L-lysine/ hyaluronic acid multilayers
  Adv. Mat. Interf. 2017, 4(1), 1600592
  https://doi.org/10.1002/admi.201600592

  
  Nicolas, H., Yuan, B., Zhang, X., Schönhoff, M.
  Cucurbit[8]uril-Containing Multilayer Films for the Photocontrolled Binding and Release of a guest Molecule
  Langmuir 2016, 32, 2410-2418
  Ostendorf, A., Cramer, C., Decher, G., Schönhoff, M.
  https://pubs.acs.org/doi/abs/10.1021/acs.langmuir.6b00128

  
  Humidity-Tunable Electronic Conductivity of Polyelectrolyte Multilayers Containing Gold Nanoparticles
  J. Phys. Chem. C 2015, 119(17), 9543-9549
  https://doi.org/10.1021/jp5127706

  
  

• Further reading about Polyelectrolyte multilayers:

  Schönhoff, M.
  Self-Assembled Polyelectrolyte Multilayers
  Current Opinion in Coll. Interf. Sci. 2003 , 8(1), 86-95.

  Schönhoff, M.
  Layered Polyelectrolyte Complexes: Physics of Formation and Molecular Properties
  J. Phys.: Cond. Matter 2003, 15(49), R1781-R1808.