3.1 Interactions in Polymer System 3.7 Thermodynamics of Gels 3.4 Thermodynamics and Conformations of Polymers in Dilute Solution 3.6 Conformations of Polymer in Semi-dilute Solution 3.3 Thermodynamics of Polymer Solutions: Flory-Huggins Theory 3.8 Polyelectrolytes Solution 3.9 Hydrodynamics of Polymer Solutions 3.5 Scaling Law(ḷᓖᖻ) of Polymers 3.2 Criteria of Polymer Solubility 4.1 Thermodynamics of Polymer Mixtures 4.2 Properties of Polymer Interface 4.3 Thermodynamics of Block Copolymers