The structural and dynamical properties of flexible polymer chains confined under a geometrical constraint are relevant to a number of problems in biology and material sciences. Whereas there have been a plethora of experimental and theoretical studies on the effects of various geometrical constraints on self-avoiding polymer, relatively less attention has been paid to a single chain in tri-critical Θ-point upon confinement.
After giving an overview of basic concept of polymer physics for general audiences, I will discuss some problems arising from the compression of a Θ-chain in a slit or cylindrical confinement. If time allows, I will further present our on-going work on 2D polymer solution in Θ-solvent (many Θ-polymer chains confined in two dimensions), and discuss the origin of its characteristic scaling relation Π ∼ c8 between  the osmotic pressure (Π) and concentration (c).