title: Role of viscosity in influencing the glass-forming ability of organic molecules from the undercooled melt state.
abstract: OBJECTIVE
  Understanding the critical factors governing the crystallization tendency of organic compounds is vital when assessing the feasibility of an amorphous formulation to improve oral bioavailability. The objective of this study was to investigate potential links between viscosity and crystallization tendency for organic compounds from the undercooled melt state.
  
  
  METHODS
  Steady shear rate viscosities of numerous compounds were measured using standard rheometry as a function of temperature through the undercooled melt regime. Data for each compound were fit to the Vogel-Tamman-Fulcher (VTF) equation; kinetic fragility via strength parameter (D) was determined.
  
  
  RESULTS
  Compounds with high crystallization tendencies exhibited lower melt viscosities than compounds with low crystallization tendencies. A correlation was observed between rate of change in viscosity with temperature and crystallization tendency, with slowly crystallizing compounds exhibiting larger increases in viscosity as temperature decreased below T(m). Calculated strength parameters indicated all compounds were kinetically fragile liquids; thus, kinetic fragility may not accurately assess glass-forming ability from undercooled melt state.
  
  
  CONCLUSIONS
  A link was observed between the viscosity of a compound through the undercooled melt regime and its resultant crystallization tendency, indicating viscosity is a critical parameter to fully understand crystallization tendency of organic compounds.
authors.affiliation: Department of Industrial and Physical Pharmacy, College of Pharmacy, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Jared A
authors.initials: JA
authors.lastname: Baird
authors.forename: Darlene
authors.initials: D
authors.lastname: Santiago-Quinonez
authors.forename: Carlos
authors.initials: C
authors.lastname: Rinaldi
authors.forename: Lynne S
authors.initials: LS
authors.lastname: Taylor
mesh_terms: D001566:Benzocaine / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D003992:Dibucaine / Q000737:chemistry; D008012:Lidocaine / Q000737:chemistry; D008825:Miconazole / Q000737:chemistry; D009930:Organic Chemicals / Q000737:chemistry*; D011343:Procaine / Q000737:chemistry; D012212:Rheology; D013816:Thermodynamics; D014044:Tolbutamide / Q000737:chemistry; D044366:Transition Temperature; D014783:Viscosity
chemical_list: D009930:Organic Chemicals; D011343:Procaine; D008825:Miconazole; D014044:Tolbutamide; D008012:Lidocaine; D003992:Dibucaine; D001566:Benzocaine