Dynamic surface coatings through the hierarchical self-assembly of responsive colloidal building blocks
Final Report Abstract
In this project a UV light driven and pH responsive colloid coating system based on TiO2 and weak polyelectrolytes (PE) was developed. As PE polyampholyte systems derived from poly(dehydroalanine) (PDha) were synthesized und modified by grafted phosphonate moieties (P(Dha-g-PAA)), resulting in an improved solubility and strong coordinative and electrostatically attractive linkages to nanoparticular TiO2. Beside P(Dha-g-PAA) also weak poly(acrylic acid) (PAA) and poly(allylamine) were utilized. We further established a synthetic route to amphiphilic block copolymers containing a PDha segment and – in addition – a functional endgroup stemming from the employed SG1 initiator for NMP. pKa values of these PE were determined via conventional potentiometric titration and less known FTIR Titration. For PAA and PAH+ solutions values of pKa = 5.42 (MW = 50.000 g/mol, 0.2 M) and pKa = 9.55 (MW = 50.000 g/mol, 0.2 M) and for 0.1 M P(Dha-g-PAA) solutions pKa1 = 2.34 and pKa2 = 10.50 were determined. Mixing TiO2 suspensions (anatase, rutile) and PE solutions (PDHAG, PAA, PAH) resulted in colloidally stable dispersions with particle radii between 187-367 nm. PDHAG/TiO2 dispersions showed best temporal colloidal stability. Illumination (1h) of these PE/TiO2 dispersions at the initial pH = 6.00 with UV light at 365 nm resulted in significant decrease of pH down to 5.27 for the anatase modification, while fo rutile no such pH drop was obtained. Largest pH decrease was obtained for P(Dha-g-PAA)/TiO2. FTIR spectra at these dispersions revealed chemical alterations, which suggest degradation. Explanations of these findings base on different band gaps for anatase and rutile as well as particle sizes i.e surface areas. Graded PE/TiO2 coatings were obtained by casting and drying for various concentrations (cSUSP). FTIR spectra at these coatings show a higher retention of the TiO2 component and a lower one of the PE component. PAA/TiO2 coatings reveal highest surface integrity at cSUSP = 1 mg/ml and higher PAA and TiO2 retention for smaller PAA/TiO2 ratios. PE/anatase coatings show significant photodegradation of PE component upon UV illumination, where for PAA/anatas highest degradation and for PAH/TiO2 and P(Dha-g-PAA)/TiO2 a similar but lower degradation of PE was observed. With increasing TiO2/PE ratio PE degradation increased. For PAA/rutile no significant PE degradation was obtained. By alternate treatment of PAA/TiO2 coatings with UV light and NH3 ambient atmosphere periodic dynamic changes of the dissociation degree of PAA were found. In general, photodegradation of PE was more pronounced for PE/TiO2 coatings compared to PE/TiO2 dispersions, while photoacidity was more pronounced for PE/TiO2 dispersions compared to PE/TiO2 coatings. Presumably, for dispersions rather the reaction of the TiO2 photocatalytic sites (e.g. at electron hole) with water, while for the coatings rather the reaction of these cartalytic sites with the organic material (PE) is dominating. Finally, significant photodegradations of acetate and the model drug flufenamic acid (Mobilat®) loaded at PAA/TiO2 coatings could be observed. From this observation interesting applications might result for personalised water treatment, where antiinflammatory drugs from respective ointments contaminating waste water can be first separated by filter material and afterwards illuminated with UV-Licht at 365 nm under elimination of the pollutant drug.
Publications
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Determination of the Carboxyl Dissociation Degree and pKa Value of Mono and Polyacid Solutions by FTIR Titration. Macromolecular Chemistry and Physics, 222(4).
Müller, Martin; Wirth, Luise & Urban, Birgit
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Polyampholytic Graft Copolymers as Matrix for TiO2/Eosin Y/[Mo3S13]2− Hybrid Materials and Light‐Driven Catalysis. Chemistry – A European Journal, 27(68), 16924-16929.
Nabiyan, Afshin; Max, Johannes Bernhard; Neumann, Christof; Heiland, Magdalena; Turchanin, Andrey; Streb, Carsten & Schacher, Felix Helmut
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Photoacidity and Photodegradation within Polyelectrolyte/TiO2 Suspensions and Coatings. ACS Applied Polymer Materials, 4(12), 9430-9440.
Müller, Martin; Všivcev, Dmitrij; Urban, Birgit; Wendler, Felix; Schacher, Felix H. & Fery, Andreas
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Determination of the pKa Value of Protonated Mono and Polyamine in Solution Using Fourier Transform Infrared Titration. Applied Spectroscopy, 78(1), 56-66.
Müller, Martin; Wirth, Luise & Urban, Birgit
