PMID- 20882241
OWN - NLM
STAT- PubMed-not-MEDLINE
DCOM- 20110531
LR  - 20110208
IS  - 1463-9084 (Electronic)
IS  - 1463-9076 (Linking)
VI  - 13
IP  - 8
DP  - 2011 Feb 28
TI  - Composite hydrogels with temperature sensitive heterogeneities: influence of gel 
      matrix on the volume phase transition of embedded poly-(N-isopropylacrylamide) 
      microgels.
PG  - 3039-47
LID - 10.1039/c0cp01135e [doi]
AB  - The thermo-responsive behaviour of poly-(N-isopropylacrylamide) (PNiPAM) 
      microgels embedded in covalently cross-linked non-temperature-sensitive 
      polyacrylamide (PAam) hydrogel matrixes with different compositions was 
      investigated by using small angle neutron scattering (SANS). The composition of 
      the composite hydrogel was varied by (a) increasing the cross-linker and 
      acrylamide concentration leading to strong hydrogel matrixes and (b) by 
      increasing the microgel concentration to obtain composite gels with an internal 
      structure. Additionally we synthesized composite hydrogels by using gamma-irradiation 
      as initiation for the polymerisation. This leads to the formation of chemical 
      bonds between the PNiPAM microgels and the surrounding polyacrylamide matrix. 
      Thus it is possible to synthesize hydrogels without an additional cross-linker, 
      as well as pure particle networks. Some samples were prepared at two different 
      temperatures, below and above the volume phase transition temperature of PNiPAM, 
      resulting in highly swollen or totally collapsed microgels during the 
      incorporation step. The volume phase transition of microgels is not influenced by 
      a hydrogel matrix with high acrylamide concentration independent of the 
      preparation temperature. However, an increased cross-linker concentration leads 
      to a corset like constraint on microgel swelling. Microgels, which are embedded 
      in the collapsed state (at 50  degrees C), are not able to swell upon cooling, whereas 
      microgels embedded in the swollen state can collapse upon heating. For samples 
      with an increased microgel concentration, the close microgel packing was 
      disturbed by the formation of the polyacrylamide matrix. The hydrogel matrix 
      squeezes the microgels together and leads to partial aggregation. The experiments 
      demonstrate how composite hydrogels with stimuli-sensitive heterogeneities can be 
      prepared such that the full responsiveness of the embedded microgels is retained 
      while the macroscopic dimensions of the gel are not affected by the volume phase 
      transition of the microgels.
FAU - Meid, Judith
AU  - Meid J
AD  - Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, D-52074 
      Aachen, Germany. Richtering@rwth-aachen.de.
FAU - Friedrich, Tatjana
AU  - Friedrich T
FAU - Tieke, Bernd
AU  - Tieke B
FAU - Lindner, Peter
AU  - Lindner P
FAU - Richtering, Walter
AU  - Richtering W
LA  - eng
PT  - Journal Article
DEP - 20100930
PL  - England
TA  - Phys Chem Chem Phys
JT  - Physical chemistry chemical physics : PCCP
JID - 100888160
EDAT- 2010/10/01 06:00
MHDA- 2010/10/01 06:01
CRDT- 2010/10/01 06:00
PHST- 2010/10/01 06:00 [entrez]
PHST- 2010/10/01 06:00 [pubmed]
PHST- 2010/10/01 06:01 [medline]
AID - 10.1039/c0cp01135e [doi]
PST - ppublish
SO  - Phys Chem Chem Phys. 2011 Feb 28;13(8):3039-47. doi: 10.1039/c0cp01135e. Epub 
      2010 Sep 30.