Open Access
Guo, Liang
Graduate Program:
Materials Science and Engineering
Doctor of Philosophy
Document Type:
Date of Defense:
January 06, 2003
Committee Members:
  • Ralph H Colby, Committee Chair
  • James Patrick Runt, Committee Member
  • Qing Wang, Committee Member
  • Gregory Ray Ziegler, Committee Member
  • gelatin
  • gelation
  • rheology
  • percolation
  • micelle
  • SANS
Two topics of aqueous polymer solutions are covered in this thesis. The first addresses gelation kinetics and dynamics of aqueous gelatin solutions. The second deals with micelle structure changes in aqueous nonionic surfactant mixtures. Triple helix reversion kinetics of aqueous gelatin solutions is studied with optical rotation. A combination of first- and second-order concentration dependence of the reversion rate is observed and, based on this observation, a new two-step mechanism of helix formation distinct from the Flory and Weaver theory is proposed. The rate limiting step is formation of a two-stranded nucleus, either intramolecular (first-order) or intermolecular (second-order). The triple helix is formed by subsequent wrapping of a third strand onto the nucleus. Gelation dynamics of gelatin solutions is monitored with optical rotation and rheology. Viscosity data below the gel point are used to evaluate the gel point and the viscosity exponent, assuming dynamic scaling theory applies. Shear modulus data above the gel point are used to determine the dynamic scaling modulus exponent. As observed in the time-dependent optical rotation, an initial rapid growth region where new helices are formed is followed by a slower growth region involving helix lengthening. The viscosity and modulus exponents depend on concentration, but not on temperature for cases where the gel point occurs before the helix reversion slows down appreciably. However, anomalous exponents are measured at higher temperatures, where the helix reversion slows down appreciably before the gel point is reached. The observed concentration dependences of the dynamic scaling exponents are discussed in terms of chain overlap and entanglement. The structure of nonionic surfactant mixtures in water are probed by rheology and small-angle neutron scattering. Small amounts of a C14 diol (Surfynol® 104) cause enormous structural and rheological changes when added to aqueous solutions of an ethylene oxide-propylene oxide-ethylene oxide triblock copolymer (Pluronic® P105). The hydrophobic diol incorporates into the existing copolymer micelles and causes a cascade of changes in micelle structure, with resultant changes in rheology. Particularly striking is the spherical to wormlike micelle transition, where the viscosity changes by a factor of more than 10^4.