Thin films from pH and thermoresponsive triblock copolymers: from network dynamics to defect-free films
Final Report Abstract
The goal of the project was to investigate the self-assembly behavior of multi-responsive multiblock polymers in solution and in thin films. At this, two pentablock polymers having pH-responsive and/or thermoresponsive blocks were studied. A pentablock terpolymer, which features short thermoresponsive endblocks and a pH- responsive middle block, was designed for applications as a tunable hydrogel. While the formation, mechanical properties and responsive behavior of the hydrogels were investigated by our collaborator, small-angle neutron scattering revealed the structural properties on a large range of length scales. Changes of the pH value and the temperature alter the tendency for bridging and the network functionality. A pentablock quaterpolymer, similar to the terpolymer with the exception of an additional hydrophilic middle block, was investigated in dilute aqueous solution in dependence on pH and temperature. The micellar structures with respect to the fraction of dangling ends or loops and the aggregation number and micellar size are found to depend strongly on pH and temperature. Thin films were prepared from solutions having different pH values and were investigated using grazing-incidence small-angle X-ray scattering (GISAXS), also during swelling in water or toluene vapor. Films prepared at low pH values, where the middle blocks are charged, are microphase-separated with two types of spherical nanodomains, while films prepared at high pH values, where the middle blocks are uncharged, are disordered. Swelling the films in the vapor of the polar solvent water favors disordering, while swelling the films in the non-polar solvent toluene induces microphase separation. The results are explained by the role of electrostatic interactions for microphase separation, as suggested in recent theoretical work on charged diblock copolymers. To carry out the envisaged heating and cooling protocols on the thin films in the swollen state, we improved our setup for solvent vapor swelling with respect to thermal control and stability, in situ humidity measurements and a more compact design, optimizing it for experiments at large scale facilities. Furthermore, a strategy to simulate and fit 2D GISAXS patterns was developed which may be used as a guideline for the analysis of GISAXS data of a wide range of systems, increasing the amount of information obtained from such experiments. In addition, a doubly pH-responsive pentablock terpolymer was studied, which features two different types of weak polyelectrolytes as mid blocks, end-capped by hydrophobic blocks. The pH value was found to govern the self-assembly behavior in aqueous solution. Using dynamic light scattering and synchrotron small-angle X-ray scattering, with increasing pH value, molecularly dissolved chains, loose clusters, spherical micelles and worm-like micelles were observed. The self-assembly is mainly driven by the pH-dependent solubility of the central block and the chain flexibility of the middle blocks. Atomic force microscopy and GISAXS showed that the films are disordered or feature standing cylinders. Mixing of the blocks and thus the formation of common nanodomains was found to be dependent on their degree of ionization in the solution as well as the ability of the polyelectrolyte to form bridges or loops. This interplay leads to a remarkably strong dependence of the cylinder distance on the pH value. Our investigations show that multiblock polymers consisting of pH- and thermoresponsive blocks offer novel possibilities for tuning the nanostructures in thin film geometry.
Publications
- Thermoresponsive Hydrogels Based on Telechelic Polyelectrolytes: From Dynamic to “Frozen” Networks, Macromolecules 51 (2018) 2169-2179
C. Tsitsilianis, G. Serras, C.-H. Ko, F. Jung, C. M. Papadakis, M. Rikkou-Kalourkoti, C. S. Patrickios, R. Schweins, C. Chassenieux
(See online at https://doi.org/10.1021/acs.macromol.8b00193) - Crosstalk Between Responsivities to Various Stimuli in Multiresponsive Polymers: Change in Polymer Chain and External Environment Polarity as the Key Factor. Colloid Polym. Sci. 297 (2019) 1383-1401
M. Hruby, P. Štěpánek, J. Pánek, C. M. Papadakis
(See online at https://doi.org/10.1007/s00396-019-04576-5) - Structural Properties of Micelles Formed by Telechelic Pentablock Quaterpolymers with pH-Responsive Midblocks and Thermoresponsive End Blocks in Aqueous Solution, Macromolecules 52 (2019) 9746-9758
F. A. Jung, P. A. Panteli, C.-C. Ko, J.-J. Kang, L. C. Barnsley, C. Tsitsilianis, C. S. Patrickios, C. M. Papadakis
(See online at https://doi.org/10.1021/acs.macromol.9b01775) - Charge-Dependent Microphase Separation in Thin Films from a Multiresponsive Pentablock Quaterpolymer: A GISAXS Investigation, Macromolecules 53 (2020) 6255-6266
F. A. Jung, D. Posselt, D.-M. Smilgies, P. A. Panteli, C. Tsitsilianis, C. S. Patrickios, C. M. Papadakis
(See online at https://doi.org/10.1021/acs.macromol.0c01151) - Effect of pH on the Dynamics and Structure of Thermoresponsive Telechelic Polyelectrolyte Networks: Impact on Hydrogel Injectability, ACS Appl. Polym. Mater. 3 (2021) 819-829
M. M. Soledad Lencina, C.-H. Ko, F. A. Jung, R. Schweins, M. Rikkou-Kalourkoti, C. S. Patrickios, C. M. Papadakis, C. Tsitsilianis
(See online at https://doi.org/10.1021/acsapm.0c01159) - Highly Tunable Nanostructures in a Doubly pH-Responsive Pentablock Terpolymer in Solution and in Thin Films. Adv. Funct. Mater.
F. A. Jung, M. Schart, L. Bührend, E. Meidinger, J.-J. Kang, B.-J. Niebuur, S. Ariaee, D. D. Molodenskiy, D. Posselt, H. Amenitsch, C. Tsitsilianis, C. M. Papadakis
(See online at https://doi.org/10.1002/adfm.202102905)
