Journal Article

PreJuSER-10528

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Thermoresponsive copolymer hydrogels based on n-isopropylacrylamide and cationic surfactant monomers prepared from micellar solution and microemulsion in a one-step reaction

Friedrich, T. ; Tieke, B. ; Meyer, M.FZJ* ; Pyckhout-Hintzen, W.FZJ* ; Pipich, V.FZJ*

2010
Soc. Washington, DC

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Please use a persistent id in citations: doi:10.1021/jp911358z

Abstract: Thermoresponsive hydrogels were prepared upon radiation-induced copolymerization of aqueous micellar solutions containing N-isopropylacrylamide (NiPAAm) and a cationic surfactant monomer (surfmer), and of microemulsions containing NiPAAm, surfmer, and styrene. Three surfmer compounds were used: (11-(acryloyloxy)undecyl)trimethylammonium bromide (AUTMAB), (11-(methacryloyloxy)undecyl)trimethylammonium bromide (MUTMAB), and (2-(methacryloyloxy)ethyl)dodecyldimethylammonium bromide (MEDDAB). Comonomer solutions were studied on their phase behavior and structure using small-angle neutron scattering (SANS). The presence of surfmers increased the solubility of NiPAAm in the aqueous phase. SANS studies indicate that the surfmers form spherical micelles, which in the presence of styrene are increased and in the presence of NiPAAm are decreased in size. Styrene is incorporated in the core, and NiPAAm is incorporated in the shell of the micelles. If styrene and NiPAAm are present, the effects of both compensate each other, the micelle size remains unchanged, and only small amounts of styrene are solubilized. Evaluation of scattering curves indicated remarkable changes in headgroup dissociation of surfmers in the presence of NiPAAm in the micellar solutions. If exposed to (60)Co-gamma irradiation (dose: 80 kGy), stable, transparent, and thermoresponsive hydrogels were directly obtained. The lower critical solution temperature (LCST) of gels containing surfmer in low concentration was higher than that for pure NiPAAm gels, whereas in gels with high surfmer concentration it was lower. The lowest LCST was observed if MEDDAB was present in the gel. 1 % (w/w) was already sufficient to lower the LCST from 33.2 to 28.5 degrees C. Gels with low surfmer concentration (< or = 1 wt %) exhibited a strong, rapid swelling in water at 20 degrees C and a rapid and reversible shrinking at 50 degrees C. For a gel containing 1% AUTMAB, the swelling ratio was 2.4 times higher (MUTMAB, 2.8; MEDDAB, 1.5) than that for a pure NiPAAm gel. Copolymer gels containing more than 1 wt % surfmer exhibited a strong and rapid swelling below and above the LCST, because the copolymerized ionic surfmer induced an osmotic pressure in the gel. The effects of a variation of NiPAAm and surfmer concentration were studied, and the origins of the thermoresponsive properties are discussed.

Keyword(s): J

Note: This research project has been supported by the European Commission under the seventh Framework Programme through the Key Action: Strengthening the European Research Area, Research Infrastructures. Contract No.: 226507 (NMI3). The DFG is thanked for financial support (project TI 219/10-1 and 10-2, priority program 1256 "Intelligent hydrogels"). Prof. Dr. K. Meerholz is thanked for providing the scanning electron microscope and Ruth Broker for taking the SEM images.

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Contributing Institute(s):

1. Neutronenstreuung (IFF-5)
2. Streumethoden (IFF-4)
3. JCNS (Jülich Centre for Neutron Science JCNS (JCNS) ; JCNS)

Research Program(s):

1. BioSoft: Makromolekulare Systeme und biologische Informationsverarbeitung (P45)
2. Großgeräte für die Forschung mit Photonen, Neutronen und Ionen (PNI) (P55)
3. NMI3 - Integrated Infrastructure Initiative for Neutron Scattering and Muon Spectroscopy (226507) (226507)

Experiment(s):

1. KWS-2: Small angle scattering diffractometer (NL3ao)

Appears in the scientific report 2010

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