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Forschungsarbeit

Controlling the Morphology of Supramolecular Nanofibers by Self-Assembly and Melt Electrospinning

Von Julia Singer (21.10.2013)

Self-assembly of molecules is a promising technology for the controlled build-up of defined nanostructured geometries from small units. Recently, 1,3,5-benzene- and 1,3,5-cyclohexane-trisamides gained interest as buildings blocks in supramolecular chemistry due the formation of self-assembled aggregates in melt and solution; also some exhibit thermotropic liquid-crystalline behavior. [1]

Figure 1: Self-assembled trisamide nanofiber, supported on a glass specimen with defined channels for AFM bending tests[Bildunterschrift / Subline]: Figure 1: Self-assembled trisamide nanofiber, supported on a glass specimen with defined channels for AFM bending tests

In the context of my dissertation several questions will be tackled to promote the better understanding of the self-assembly mechanism of 1,3,5-benzene- and 1,3,5-cyclohexane-trisamides on different length scales. My work focuses especially on two methods to obtain supramolecular fibers: self-assembly/controlled crystallization from solution (bottom-up approach) and melt electrospinning (top-down approach).

We could show that molecular structure, solvent polarity, concentration and cooling rate have to be chosen carefully to obtain reproducible thin supramolecular trisamide nanofibers (diameters around 200 nm). The mechanical properties of these fibers were determined by AFM bending measurements in cooperation with Daniel Kluge, Physical Chemistry I, University of Bayreuth (Figure 1). The normalized Young’s moduli E are almost the same and in the range of 3-5 GPa. [2]

Moreover, for the first time, we successfully conducted melt electrospinning in the range of 150 to 330 °C from the isotropic state of benzene-1,3,5-trisamides, as well as cyclohexane-1,3,5-trisamides (Figure 2). Latter can also be electrospun from their nematic phase. Depending on the settings, long and homogenous fibers with a immense aspect ratio of more than 1000:1, as well as spheres, short thick fragments, or fiber connected beads have been observed with SEM. [3]

[Bildunterschrift / Subline]: Figure 2: left: scheme of the electrospin set-up; right: melt electrospun 1,3,5-benzene-trisamide fibers at 250 °C (isotropic phase).3 Reproduced by permission of The Royal Society of Chemistry

Additionally, we compared the properties of melt electrospun trisamide fibers in comparison to self-assembled ones on different length scales. X-ray investigations revealed that the crystal structure of both fiber types is the same and independent from the preparation method. The morphology of both fiber types shows significant differences, however, the fiber diameters are comparable with values around 1 µm. Self-assembled fibers show a hierarchical structure with bundles of individual strands (diameter around 

100 nm). In contrast, electrospun fibers exhibit a homogenous, smooth surface without defects or pronounced surface features. In spite of these differences, AFM tensile tests revealed that the mechanical properties are similar and the Young’s modulus E is still around 3-5 GPa. [4]

 

References:

(1) Timme, A., Kress, R., Albuquerque, R.Q., Schmidt, H.-W., Phase behaviour and mesophase structure of benzene- and cyclohexane-1,3,5-tricarboxamides: Towards an understanding of loosing order at the transition into the isotropic phase, Chem. Eur. J., 2012, 18, 8329-8339.

(2) Kluge, D., Singer, J.C., Neubauer, J.W., Abraham, F., Schmidt, H.-W., Fery, A., Influence of the molecular structure and morphology of self-assembled 1,3,5-benzenetrisamide nanofibers on their mechanical properties, Small, 2012, 8, 2563-2570.

(3) Singer, J.C., Giesa, R., Schmidt, H.-W., Shaping self-assembling small molecules into fibres by melt electrospinning, Soft Matter, 2012, 8, 9972-9976.

(4) Kluge, D., Singer, J.C., Neugirg, B., Neubauer, J.W., Schmidt, H.-W., Fery, A., Top-down meets bottom-up: A comparison of the mechanical properties of melt electrospun and self-assembled 1,3,5-benzenetrisamide fibers, Polymer, 2012, 53, 5754-5759.


mailto: Julia Singer
Julia Singer
* 1986

Wissenschaftlicher Werdegang
  • 2005-2008
  • Bachelorstudiengang Chemie (Bachelor of Science), Universität Bayreuth
  • 2008-2010
  • Masterstudiengang Materialchemie und Katalyse (Master of Science), Universität Bayreuth
  • seit 2010
  • Promotion am Lehrstuhl „Makromolekulare Chemie I“ bei Professor Dr. Hans-Werner Schmidt an der Universität Bayreuth im Promotionsprogramm „Polymer Science“ der Bayreuther Graduierten¬schule für Mathematik und Naturwissenschaften (BayNAT)

Publikationen
  • * Kluge, D., Singer, J. C., Neubauer, J. W., Abraham, F., Schmidt, H.-W., Fery, A., Influence of the Molecular Structure and Morphology of Self-Assembled 1,3,5-Benzenetrisamide Nanofibers on their Mechanical Properties, Small, 2012, 8, 2563-2570
  • * Singer, J.C., Giesa, R., Schmidt, H.-W., Shaping self-assembling small molecules into fibres by melt electrospinning, Soft Matter, 2012, 8, 9972-9976.
  • * Kluge, D., Singer, J.C., Neugirg, B., Neubauer, J.W., Schmidt, H.-W., Fery, A., Top-down meets bottom-up: A comparison of the mechanical properties of melt electrospun and self-assembled 1,3,5-benzenetrisamide fibers, Polymer, 2012, 53, 5754-5759.