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Modification and functionalization of interfaces

The surface properties of solids, such as the wettability by liquids, are important for many technological processes. and often they are directly related to adhesion phenomena. They are primarily determined by the chemical and morphological characteristics of the interfaces and less by the bulk characteristics.  Specific surface modification and functionalization allow the variation of surface properties in a large scale and for different applications. The surfaces are patterned in the µm- and nm-scale and can be provided with chemical functionalities for further chemical reactions.

These functional layers are obtained by plasma processes, by using self-assembly prosesses and/or by coating of thin polymer films.

In this context, weak polyelectrolytes are interesting and advantageous. Because of their ionic properties they can adsorb from aqueous solutions onto solid surfaces. Dependending on the pH value of the aqueous solution, an equilibrium between ionic and noncharged functional groups is available in the films. Thus, these functional groups can be used for intramolecular cross-linking reactions to stabilize the layer. But they can also be used as a reactive anchor for a subsequent functionalization. In this way, it is not only possible to control the surface characteristics. There is also the chance to design the interface between the inorganic under layer and the polymer matrix. This strategy gives the possibility to optimize not only the adhesive but also the mechanical properties in this area. The idea for using weak polyelectrolytes for surface modification has the advantage that  it is largely independent on the (surface) properties of the substrate materials.










Illustration of the self-assembly by molecules of ω-mercaptoalkyl phosphonic acids and ω-mercaptoalkyl phosphoric acids respectively on a titanium substrate (the phosphonic acid and the phosphate groups respectively are symbolized by An)

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Illustration to the chemical structure of a superhydrophobic film on anodicly roughened aluminium oxide surfaces. Chitosan was incorporated in the porous structure of the oxidic under ground as a hydrophilic polymer. The following reaction of chitosan amino groups with a maleic anhydride copolymer forms a network and by using copolymers with long alkyl chains a hydrophic surface is created.













Scheme of chemical anchoring of end-functionalised homopolymers onto curved surfaces. “Grafting from” approach is also used for surface modification.










Concept of modification of micropatterned surface by two oppositely charged polyelectrolytes. Depending on the surrounding conditions, one polymer is swollen (charged and hydrophilic) while the other is collapsed (uncharged and hydrophobic), thereby demonstrating the inverse switching of surface topography, wettability, and charge.

Another field of work is the surface modification of inorganic nanometer, sub-micrometer and micrometer-sized particles with symmetrical and asymmetrical chemical composition in order to design functional core-shell composite materials. Different polyelectrolytes with positive / negative charges, polymers with hydrophilic / hydrophobic properties or self-assembled monolayers (SAM's) from silanes are used for the surface modification of curved and planar surfaces as well. The obtained materials are of special interest for the design of  protective coatings with improved mechanical properties, fabrication of nano- and microporous materials, colloidal crystals, modification of textiles etc.

On the other hand, fabrication of micropatterned polymer surfaces and their modification by grafting oppositely charged polyelectrolytes allows to design surfaces with the reversible inversion of surface wettability, topography and charge. Depending on the pH value of the surroundings one kind of the polymer chains is swollen (charged and hydrophilic) while the other is collapsed (uncharged and hydrophobic). The main advantage of such surfaces is their capability of inverse switching, for example hydrophilic patterns can be reversibly converted into hydrophobic ones and vice versa, via external stimuli.

 

Co-workers

Relevant publikations

  1. Höhne, S.; Frenzel, R.; Heppe, A.; Simon, F.
    Hydrophobic chitosan micro-particles: Heterogeneous-phase-reaction of chitosan with hydrophobic carbonyl reagents more
    Biomacromolecules 8 (2007) 2051-2058

  2. Synytska, A.; Stamm, M.; Diez, S.; Ionov, L.
    Simple and fast method for the fabrication of switchable bicomponent micropatterned polymer surfaces more
    Langmuir 23 (2007) 5205-5209

  3. Roth, I.; Simon, F.; Bellmann, C.; Spange, St.
    Functionalization of silica Particles Functionalized with Chromophores and Amino Groups Using Synergism of Poly(vinylamine) Adsorption and Nucleophilic Aromatic Substitution with Fluoroaromatics more
    Chemistry of Materials 18 (2006) 4730-4739

  4. Synytska, A.; Ionov, L.; Dutschk, V.; Minko, S.; Eichhorn, K.-J.; Stamm, M.; Grundke, K.
    Regular Patterned Surfaces from Core-Shell Particles. Preparation and Characterization more
    Progress in Colloid and Polymer Science (2006) 72-81

  5. Hahn, M.; Pleul, D.; Nitschke, M.; Frens, G.; Bundel, G.; Prause, S.; Simon,
    Plasma modification of diamond surfaces more
    Journal of Adhesion Science and Technology 19 (2005) 1039-1052

  6. Eschner, M.; Frenzel, R.; Simon, F.; Pleul, D.Pleul; Uhlmann, P.; Adler, H. J.
    w-Substituted Long Chain Alkylphosphonic Acids - Their Synthesis and Deposition on Metal Oxides and Subsequent Functional Group Conversion on the Deposited Compounds more
    Macromolecular Symposia 210 (2004) 77-84

 
Modification and functionalization of interfaces
Modifizierung und Funktionalisierung von Grenzflächen

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Polymer Interfaces

Fields of Work