TY  - JOUR
A1  - Papadakis, Christine M.
A1  - Müller-Buschbaum, Peter
A1  - Laschewsky, Andre
T1  - Switch It Inside-Out: "Schizophrenic" Behavior of All Thermoresponsive UCST-LCST Diblock Copolymers
JF  - Langmuir
N2  - This feature article reviews our recent advancements on the synthesis, phase behavior, and micellar structures of diblock copolymers consisting of oppositely thermoresponsive blocks in aqueous environments. These copolymers combine a nonionic block, which shows lower critical solution temperature (LCST) behavior, with a zwitterionic block that exhibits an upper critical solution temperature (UCST). The transition temperature of the latter class of polymers is strongly controlled by its molar mass and by the salt concentration, in contrast to the rather invariant transition of nonionic polymers with type II LCST behavior such as poly(N-isopropylacrylamide) or poly(N-isopropyl methacrylamide). This allows for implementing the sequence of the UCST and LCST transitions of the polymers at will by adjusting either molecular or, alternatively, physical parameters. Depending on the location of the transition temperatures of both blocks, different switching scenarios are realized from micelles to inverse micelles, namely via the molecularly dissolved state, the aggregated state, or directly. In addition to studies of (semi)dilute aqueous solutions, highly concentrated systems have also been explored, namely water-swollen thin films. Concerning applications, we discuss the possible use of the diblock copolymers as "smart" nanocarriers.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.langmuir.9b01444
SN  - 0743-7463
VL  - 35
IS  - 30
SP  - 9660
EP  - 9676
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Zhong, Qi
A1  - Wang, Weinan
A1  - Adelsberger, Joseph
A1  - Golosova, Anastasia
A1  - Koumba, Achille M. Bivigou
A1  - Laschewsky, André
A1  - Funari, Sergio S.
A1  - Perlich, Jan
A1  - Roth, Stephan V.
A1  - Papadakis, Christine M.
A1  - Müller-Buschbaum, Peter
T1  - Collapse transition in thin films of poly(methoxydiethylenglycol acrylate)
JF  - Colloid and polymer science : official journal of the Kolloid-Gesellschaft
N2  - The thermal behavior of poly(methoxydiethylenglycol acrylate) (PMDEGA) is studied in thin hydrogel films on solid supports and is compared with the behavior in aqueous solution. The PMDEGA hydrogel film thickness is varied from 2 to 422 nm. Initially, these films are homogenous, as measured with optical microscopy, atomic force microscopy, X-ray reflectivity, and grazing-incidence small-angle X-ray scattering (GISAXS). However, they tend to de-wet when stored under ambient conditions. Along the surface normal, no long-ranged correlations between substrate and film surface are detected with GISAXS, due to the high mobility of the polymer at room temperature. The swelling of the hydrogel films as a function of the water vapor pressure and the temperature are probed for saturated water vapor pressures between 2,380 and 3,170 Pa. While the swelling capability is found to increase with water vapor pressure, swelling in dependence on the temperature revealed a collapse phase transition of a lower critical solution temperature type. The transition temperature decreases from 40.6 A degrees C to 36.6 A degrees C with increasing film thickness, but is independent of the thickness for very thin films below a thickness of 40 nm. The observed transition temperature range compares well with the cloud points observed in dilute (0.1 wt.%) and semi-dilute (5 wt.%) solution which decrease from 45 A degrees C to 39 A degrees C with increasing concentration.
KW  - Hydrogel
KW  - Thin film
KW  - Thermoresponsive
KW  - LCST behavior
KW  - GISAXS
KW  - AFM
Y1  - 2011
U6  - https://doi.org/10.1007/s00396-011-2384-1
SN  - 0303-402X
VL  - 289
IS  - 5-6
SP  - 569
EP  - 581
PB  - Springer
CY  - New York
ER  -