Food Physics_Chapter 2.ppt

* * 随机游动模型（Random Walk model） b Rf Random walk chain comprises n steps of length b Chain dimensions described in terms of statistical parameter - Rf Rf - r.m.s. end to end distance. b ? Kuhn segment length ? 4 or 5 repeat units for a typical “vinyl” addition polymer Chain with fixed valance angles - ? 分子构象 Sphere（球形） Branched（支化） Random coil（无规线团） Semi-rigid rod（半刚性棒） Rigid rod（刚性棒） 分子构象的表征 1.0 0.5?0.6 0.333 c 1.8 0.5?0.8 0 a rigid rod random coil compact sphere coefficients Mark - Houwink Equation 构象转变 （conformational Transition） 线团-螺旋转变（Coil-helix transition） 单螺旋（single helix）；双螺旋（double helix）；三螺旋（triple helix） 多糖的三级结构：分子聚集、凝胶结构、液晶结构 分子凝聚（molecular association）：海藻酸钠蛋壳结构的形成 分子聚集 （molecular aggregation）：阿拉伯胶溶液中聚集体 三维凝胶网络结构：海藻酸钠凝胶 液晶结构 向列液晶 碟状液晶 胆甾型液晶 液晶结构的生成可引起粘度的降低 第二节 溶液性质 Solution property Concentration regime (浓度分区) ?0 Polymer concentration, c c* c** ?0 ~ c3-5.1 ?0 ~ c1.1-1.4 dilute Semi-dilute unentangled Semi-dilute entangled c c* c = c* c c* Dilute Coil overlap Non-dilute Dilute Solution-intrinsic viscosity Huggins Eqn: Kraemer Eqn: Huggins Kraemer c [?] 固有粘度单位：ml/g Semi-dilute region: macromolecular entanglement, and viscoelasticity Power law model (幂律模型） Newtonian Shear thickening Shear thinning Plastic fluid Polymer coil in absence of shear flow field Chain segments and associated solvent define a spherical “molecular envelope” Polymer coil in shear flow field Shear Recovery Thermodynamic driving force favouring return to random coil conformation Elastic storage of energy during flow Molecular dynamics in semi-dilute regime Dilute solution Semi-dilute solution Gel Zimm Behaviour (Non-Free Draining) Rouse Behaviour (Free Draining) Reptation Behaviour (Entangled) Increasing c, M 第三节 相变 Phase transition Gelation (凝胶化） According to a rheological definition given by Kramer, gel is a soft, solid or liquid-like material of two or more components, one of which is a liquid, present in substantial quant