Kinetic Analysis of Cryotropic Gelation
of Poly(Vinyl Alcohol)/Water Solutions
by Small-Angle Neutron Scattering
Claudio De Rosa, Finizia Auriemma, and Rocco Di Girolamo
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
2 General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
2.1 Physical Gels in the Preparative Ensemble: Main Processes Creating Networks . . 164
2.2 Metastability and Sol–Gel Transitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
2.3 Role of Phase Separations in Gel Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
3 Poly(Vinyl Alcohol) Hydrogels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
3.1 Crystal Structure of PVA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
3.2 PVA Physical Hydrogels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
3.3 PVA Cryogels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
3.4 Structure of PVA Cryogels at Different Length Scales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
3.5 Influence of Addition of Other Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
3.6 Mechanism of Formation of PVA Cryogels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
3.7 Kinetic Analysis of SANS Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
4 Concluding Remarks and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
Abstract Aqueous poly(vinyl alcohol) (PVA) solutions subjected to cryogenic
treatment form strong physical gels. The cryogenic treatment basically consists of
freezing an initially homogeneous polymer solution at low temperatures, storing in
the frozen state for a definite time, and defrosting. These gels are of great interest
for biotechnology, medicine, the food industry, and many other applications. The
outstanding properties of these systems depend on a complex macroporous architecture, whereby PVA chains and water molecules are organized over different
hierarchical length scales. The structure and the principal processes subtending the
formation of these systems are discussed in the framework of our current understanding of polymer gels. These processes involve formation of ice crystals, PVA
C. De Rosa • F. Auriemma (*) • R. Di Girolamo
Dipartimento di Scienze Chimiche, Universita ` di Napoli Federico II, Complesso Monte Sant’
Angelo, via Cintia, 80126 Napoli, Italy
e-mail: finizia.auriemma@unina.it
O. Okay (ed.), Polymeric Cryogels, Advances in Polymer Science 263,
DOI 10.1007/978-3-319-05846-7_4, © Springer International Publishing Switzerland 2014
159
of Poly(Vinyl Alcohol)/Water Solutions
by Small-Angle Neutron Scattering
Claudio De Rosa, Finizia Auriemma, and Rocco Di Girolamo
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
2 General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
2.1 Physical Gels in the Preparative Ensemble: Main Processes Creating Networks . . 164
2.2 Metastability and Sol–Gel Transitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
2.3 Role of Phase Separations in Gel Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
3 Poly(Vinyl Alcohol) Hydrogels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
3.1 Crystal Structure of PVA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
3.2 PVA Physical Hydrogels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
3.3 PVA Cryogels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
3.4 Structure of PVA Cryogels at Different Length Scales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
3.5 Influence of Addition of Other Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
3.6 Mechanism of Formation of PVA Cryogels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
3.7 Kinetic Analysis of SANS Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
4 Concluding Remarks and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
Abstract Aqueous poly(vinyl alcohol) (PVA) solutions subjected to cryogenic
treatment form strong physical gels. The cryogenic treatment basically consists of
freezing an initially homogeneous polymer solution at low temperatures, storing in
the frozen state for a definite time, and defrosting. These gels are of great interest
for biotechnology, medicine, the food industry, and many other applications. The
outstanding properties of these systems depend on a complex macroporous architecture, whereby PVA chains and water molecules are organized over different
hierarchical length scales. The structure and the principal processes subtending the
formation of these systems are discussed in the framework of our current understanding of polymer gels. These processes involve formation of ice crystals, PVA
C. De Rosa • F. Auriemma (*) • R. Di Girolamo
Dipartimento di Scienze Chimiche, Universita ` di Napoli Federico II, Complesso Monte Sant’
Angelo, via Cintia, 80126 Napoli, Italy
e-mail: finizia.auriemma@unina.it
O. Okay (ed.), Polymeric Cryogels, Advances in Polymer Science 263,
DOI 10.1007/978-3-319-05846-7_4, © Springer International Publishing Switzerland 2014
159