USAXS Studies on Homogeneous and Mesoscopically Heterogeneous Hydroxypropyl Cellulose Gel

1. USAXS Studies on Homogeneous and Mesoscopically Heterogeneous Hydroxypropyl Cellulose Gel Tingtai Guo; Dale W. Schaefer Department of Chemical and Materials Engineering University of Cincinnati Sponsor: Givaudan Flavors Corporation Background and Objective USAXS  Heterogeneous Gel Lower Critical Solution temperature (LCST) Synthesized 2oC above LCST • Background • Thermo-responsive gels (TRG) undergo volume transition at a critical temperature. Membranes made from TRG change their transport properties at the critical temperature. Hydroxypropyl cellulose gel is TRG made from cellulose derivatives. It aroused interests in drug and food industry because cellulose derivatives are generally regarded as safe materials. • Applications • Controlled drug or flavor release induced by temperature change. • Objective • Study the physics of volume transition of TRG Heterogeneous gel above LCST Temp. 2 phases LCST 1 Phase H2O Polymer Modified TIPS Stevin H.Gehrke Reaction Time Homogeneous gel below LCST Phase separation occurs on two length scales Cross linking HPC below and above critical temperature m scale out of range Thermo Responsive Gel (TRG) HPC Gels Synthesized at Different Temperatures USAXS  Heterogeneous Gel Synthesized 3oC above LCST Volume Transition of TRG Critical Temperature 38oC T High T Collapsed Two Phases LCST Volume Transition One Phase H2O Polymer Low T Swollen Phase diagram of polymer with Lower Critical Solution Temperature(LCST). TRG prepared by cross linking polymer showing LCST Environmental SEM photographs Phase separation on m scale for heterogeneous gel Thermo Responsive Behavior Conclusions Release Controlled by TRG • For homogeneous gel, micro-phase separation occurs on 100 Å level at high temperature above LCST. This is probably caused by association of hydrophilic and hydrophobic chains respectively • For heterogeneous gel, besides micro-phase separation on 100 Å level, the other phase separation occurs on m level caused by different cross-linking density in separated phases during cross-linking reaction High T barrier, low T release Temp. Dense film Hi T Barrier 25oC 40oC 50oC Critical Temp. Volume transition of homogeneous gel at enhanced temperatures Volume transition of HPC gels synthesized below and above LCST Loose film Low T Permeable Flavor/Drug core TRG wall USAXS  Homogeneous Gel This project is funded by: Membrane Applied Science and Technology Center (MAST) University of Colorado at Boulder and University of Cincinnati A National Science Foundation Industry/University Cooperative Research Center since 1990 Synthesized below LCST www.mastcenter.org Low T. Swollen High T. Collapsed The UNICAT facility at the Advanced Photon Source (APS) is supported by the Univ. of Illinois at Urbana-Champaign, Materials Research Laboratory (U.S. DOE, the State of Illinois-IBHE-HECA, and the NSF), the Oak Ridge National Laboratory (U.S. DOE under contract with UT-Battelle LLC), the National Institute of Standards and Technology (U.S. Department of Commerce) and UOP LLC. The APS is supported by the U.S. DOE, Basic Energy Sciences, Office of Science under contract No. W-31-109-ENG-38. Hydrophilic main chain Hydrophobic side chain Cross linkage Phase separation occurs on the scale distance between crosslinks 1 5 9 Homogeneous and Heterogeneous Gel 2 6 10 3 7 11 Acknowledgements 4 8 12 Synthesis of Hydroxypropyl Cellulose (HPC) Gel Graft vinyl group to HPC 2. Gelation of HPC in water