title: Nonlinear Behavior of Gelatin Networks Reveals a Hierarchical Structure.
abstract: We investigate the strain hardening behavior of various gelatin networks-namely physical gelatin gel, chemically cross-linked gelatin gel, and a hybrid gel made of a combination of the former two-under large shear deformations using the pre-stress, strain ramp, and large amplitude oscillations shear protocols. Further, the internal structures of physical gelatin gels and chemically cross-linked gelatin gels were characterized by small angle neutron scattering (SANS) to enable their internal structures to be correlated with their nonlinear rheology. The Kratky plots of SANS data demonstrate the presence of small cross-linked aggregates within the chemically cross-linked network whereas, in the physical gelatin gels, a relatively homogeneous structure is observed. Through model fitting to the scattering data, we were able to obtain structural parameters, such as the correlation length (ξ), the cross-sectional polymer chain radius (R(c)) and the fractal dimension (d(f)) of the gel networks. The fractal dimension d(f) obtained from the SANS data of the physical and chemically cross-linked gels is 1.31 and 1.53, respectively. These values are in excellent agreement with the ones obtained from a generalized nonlinear elastic theory that has been used to fit the stress-strain curves. The chemical cross-linking that generates coils and aggregates hinders the free stretching of the triple helix bundles in the physical gels.
authors.affiliation: School of Chemical Sciences, The University of Auckland , Private Bag 92019, Auckland 1142, New Zealand.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Yang
authors.affiliation: School of Chemical Sciences, The University of Auckland , Private Bag 92019, Auckland 1142, New Zealand.|Institute of Fundamental Sciences, Massey University , Palmerston North 4442, New Zealand.|The Riddet Institute , Palmerston North 4442, New Zealand.
authors.forename: Yacine
authors.initials: Y
authors.lastname: Hemar
authors.affiliation: Institute for Polymers and Composites/I3N, University of Minho , Campus de Azurém, 4800-058 Guimarães, Portugal.
authors.forename: Loic
authors.initials: L
authors.lastname: Hilliou
authors.affiliation: Bragg Institute, Australian Nuclear Science and Technology Organisation , Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
authors.forename: Elliot P
authors.initials: EP
authors.lastname: Gilbert
authors.affiliation: School of Chemical Sciences, The University of Auckland , Private Bag 92019, Auckland 1142, New Zealand.|Institute of Fundamental Sciences, Massey University , Palmerston North 4442, New Zealand.|The MacDiarmid Institute , Palmerston North 4442, New Zealand.
authors.forename: Duncan J
authors.initials: DJ
authors.lastname: McGillivray
authors.affiliation: Institute of Fundamental Sciences, Massey University , Palmerston North 4442, New Zealand.|The Riddet Institute , Palmerston North 4442, New Zealand.|The MacDiarmid Institute , Palmerston North 4442, New Zealand.
authors.forename: Martin A K
authors.initials: MA
authors.lastname: Williams
authors.affiliation: Division of Physical Sciences and Engineering, King Abdullah University of Sciences and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Sahraoui
authors.initials: S
authors.lastname: Chaieb
mesh_terms: D000818:Animals; D055119:Elastic Modulus; D005780:Gelatin / Q000737:chemistry*; D008958:Models, Molecular; D033363:Neutron Diffraction; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D053838:Scattering, Small Angle; D033081:Shear Strength; D034421:Sus scrofa
chemical_list: D005780:Gelatin