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@ARTICLE{Schneider:186324,
      author       = {Schneider, Florian and Balaceanu, Andreea and Feoktystov,
                      Artem and Pipich, Vitaliy and Wu, Yaodong and Allgaier, J.
                      and Pyckhout-Hintzen, Wim and Pich, Andrij and Schneider,
                      Gerald J.},
      title        = {{M}onitoring the {I}nternal {S}tructure of {P}oly( {N}
                      -vinylcaprolactam) {M}icrogels with {V}ariable
                      {C}ross-{L}ink {C}oncentration},
      journal      = {Langmuir},
      volume       = {30},
      number       = {50},
      issn         = {1520-5827},
      address      = {Washington, DC},
      publisher    = {ACS Publ.},
      reportid     = {FZJ-2015-00400},
      pages        = {15317 - 15326},
      year         = {2014},
      abstract     = {The combination of a set of complementary techniques allows
                      us to construct an unprecedented and comprehensive picture
                      of the internal structure, temperature dependent swelling
                      behavior, and the dependence of these properties on the
                      cross-linker concentration of microgel particles based on
                      N-vinylcaprolactam (VCL). The microgels were synthesized by
                      precipitation polymerization using different amounts of
                      cross-linking agent. Characterization was performed by
                      small-angle neutron scattering (SANS) using two
                      complementary neutron instruments to cover a uniquely broad
                      Q-range with one probe. Additionally we used dynamic light
                      scattering (DLS), atomic force microscopy (AFM), and
                      differential scanning calorimetry (DSC). Previously obtained
                      nuclear magnetic resonance spectroscopy (NMR) results on the
                      same PVCL particles are utilized to round the picture off.
                      Our study shows that both the particle radius and the
                      cross-link density and therefore also the stiffness of the
                      microgels rises with increasing cross-linker content. Hence,
                      more cross-linker reduces the swelling capability
                      distinctly. These findings are supported by SANS and AFM
                      measurements. Independent DLS experiments also found the
                      increase in particle size but suggest an unchanged
                      cross-link density. The reason for the apparent
                      contradiction is the indirect extraction of the parameters
                      via a model in the evaluation of DLS measurements. The more
                      direct approach in AFM by evaluating the cross section
                      profiles of observed microgel particles gives evidence of
                      significantly softer and more deformable particles at lower
                      cross-linker concentrations and therefore verifies the
                      change in cross-link density. DSC data indicate a minor but
                      unexpected shift of the volume phase transition temperature
                      (VPTT) to higher temperatures and exposes a more
                      heterogeneous internal structure of the microgels with
                      increasing cross-link density. Moreover, a change in the
                      total energy transfer during the VPT gives evidence that the
                      strength of hydrogen bonds is significantly affected by the
                      cross-link density. A strong and reproducible deviation of
                      the material density of the cross-linked microgel polymer
                      chains toward a higher value compared to the respective
                      linear chains has yet to be explained.},
      cin          = {ICS-1 / Neutronenstreuung ; JCNS-1 / JCNS (München) ;
                      Jülich Centre for Neutron Science JCNS (München) ;
                      JCNS-FRM-II},
      ddc          = {670},
      cid          = {I:(DE-Juel1)ICS-1-20110106 / I:(DE-Juel1)JCNS-1-20110106 /
                      I:(DE-Juel1)JCNS-FRM-II-20110218},
      pnm          = {451 - Soft Matter Composites (POF2-451) / 54G - JCNS
                      (POF2-54G24)},
      pid          = {G:(DE-HGF)POF2-451 / G:(DE-HGF)POF2-54G24},
      experiment   = {EXP:(DE-MLZ)KWS1-20140101 / EXP:(DE-MLZ)KWS3-20140101},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000347140000033},
      doi          = {10.1021/la503830w},
      url          = {https://juser.fz-juelich.de/record/186324},
}