Decisive test of the ideal behavior of tetra-PEG gels

The objective of this work is to investigate the thermodynamic and scattering behavior of tetra-poly(ethylene glycol) (PEG) gels. Complementary measurements, including osmotic swelling pressure, elastic modulus, and small angle neutron scattering (SANS), are reported for a series of tetra-PEG gels m...

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Bibliographic Details
Published in:The Journal of chemical physics 2017-04, Vol.146 (16), p.164905-164905
Main Authors: Horkay, Ferenc, Nishi, Kengo, Shibayama, Mitsuhiro
Format: Article
Language:English
Subjects:
Crosslinking
Dependence
Elastic scattering
Free energy
Gels
Inhomogeneity
Mechanical measurement
Modulus of elasticity
Molecular chains
Molecular weight
Neutron scattering
Physics
Polyethylene glycol
Polymers
Shear modulus
Swelling pressure
Variation
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Summary:The objective of this work is to investigate the thermodynamic and scattering behavior of tetra-poly(ethylene glycol) (PEG) gels. Complementary measurements, including osmotic swelling pressure, elastic modulus, and small angle neutron scattering (SANS), are reported for a series of tetra-PEG gels made from different molecular weight precursor chains at different concentrations. Analysis of the osmotic swelling pressure vs polymer volume fraction curves makes it possible to separate the elastic and mixing contributions of the network free energy. It is shown that in tetra-PEG gels these free energy components are additive. The elastic term varies with the one-third power of the polymer volume fraction and its numerical value is equal to the shear modulus obtained from independent mechanical measurements. The mixing pressure of the cross-linked polymer is slightly smaller than that of the corresponding solution of the uncross-linked polymer of infinite molecular weight but it exhibits similar dependence on the polymer concentration. The observed deviation between the osmotic mixing pressures of the gel and the solution can be attributed to the presence of small amount of structural inhomogeneities frozen-in by the cross-links. SANS reveals that the scattering response of tetra-PEG gel is mainly governed by the thermodynamic concentration fluctuations of the network, i.e., the contribution from static inhomogeneities to the SANS signal is small.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.4982253