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    E/Z reversible photoisomerization of methyl orange doped polyacrylic acid-based polyelectrolyte brush films
    (Hoboken, NJ [u.a.] : Wiley InterScience, 2022) Al‐Bataineh, Qais M.; Telfah, Ahmad D.; Ahmad, Ahmad A.; Bani‐Salameh, Areen A.; Abu‐Zurayk, Rund; Hergenröder, Roland
    The photoswitching behavior of the polyacrylic acid (PAA) doped by methyl orange (MO) brush film was investigated using spectral analysis of UV-Vis absorbance, Fourier Transformation Infrared spectroscopy, 2D electrical conductivity mapping and Atomic Force Microscopy. The kinetics and time evolution of the photoisomerization of the PAA-MO PEBs film from E-state to Z-state by UV-light irradiation, and reverse thermal relaxation to E-state was explored. The results confirm that the photoisomerization kinetics of the overall peak is the superposition of the photoisomerization kinetics of (Formula presented.) transition, low- and high-frequency of the (Formula presented.) transition bands. The E–Z transformation led to transforming the azobenzene from flat with no dipole moment to 3.0 D dipole moment. Hence, the electrical conductivity escalated accordingly. The transformation of E-state to Z-state led to the collapse of the formed brushes because of the angular rotational momentum consequent to E–Z isomerization.
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    Reconfigurable assembly of charged polymer-modified Janus and non-Janus particles: From half-raspberries to colloidal clusters and chains
    (Cambridge : Royal Society of Chemistry, 2019) Marschelke, Claudia; Diring, Olga; Synytska, Alla
    Understanding the dynamic and reversible assembly of colloids and particles into complex constructs, inspired by natural phenomena, is of fundamental significance for the fabrication of multi-scale responsive and reconfigurable materials. In this work, we investigate the pH-triggered and reconfigurable assembly of structures composed of binary mixtures of oppositely charged polyacrylic acid (PAA)-modified non-Janus and poly(2-dimethylamino)ethyl methacrylate (PDMAEMA)/poly(N-isopropylacrylamide) (PNIPAM)-modified Janus particles driven by electrostatic interactions. Three different target structures are visible both in dispersions and in dry state: half-raspberry structures, colloidal clusters and colloidal chains depending on the mass, numerical and particle size ratio. All formed structures are well-defined and stable in a certain pH range. Half-raspberry-like structures are obtained at pH 6 and numerical ratios NJP/PAA-HP of 1 : 500 (for 200-PAA-HP), 1 : 44 (for 450-PAA-HP) and 1 : 15 (for 650-PAA-HP), respectively, due to electrostatic interactions between the central JP and the excessive PAA-HP. Colloidal chains and cluster-like structures are generated at numerical ratios NJP/PAA-HP of 4 : 5 (for 200-PAA-HP), 4 : 3 (for 450-PAA-HP), and 4 : 1 (for 650-PAA-HP). Moreover, the smaller the size of a "connecting" PAA colloid, the larger is the average length of a colloidal chain. Depending on the particle size ratio SJP/PAA-HP, some of the observed structures can be disassembled on demand by changing the pH value either close to the IEP of the PDMAEMA (for half-raspberries) or PAA (for colloidal clusters and chains) and then reassembled into new stable structures many times. The obtained results open a pathway to pH-controlled reconfigurable assembly of a binary mixture composed of polymeric-modified non-Janus and Janus particles, which allow the reuse of particle building blocks. © 2019 The Royal Society of Chemistry.