What Is the Structure of a Polymer in Solution?

Abstract

We have developed a guided-inquiry laboratory exercise in which students perform viscosity measurements to infer the structure of poly­(vinyl alcohol) (PVA) in aqueous solution. The activity combines both experiments and modeling. In the experimental portion of the exercise, students measure the viscosity of several solutions of PVA with differing molar masses. They discover that the size of molecules does not increase with the cube root of molar mass, as expected for objects with uniform density, but rather with the square root of molar mass. In the modeling part of the experiment, students use random numbers to create two-dimensional “random walk” objects on paper or on a computer. They discovered that the size of a random-walk object increases with the square root of the walk length. Combining what they discovered through the random walk models with what they learned from the viscosity measurement, they conclude that the structure of PVA dissolved in water (a theta solvent for PVA) is consistent with a random walk structure.

Interactive Learning of Diffusion and the Diffusion Equation with Mathematical Software

“…Also, in a recent paper published in this Journal , students can see how the structure of a polymer in solution (its effective radius) can be simulated through a random walk process. The authors provide the structures generated by a random walk code to avoid the computational load to the students.…”

Particle simulations for inquiry-based teaching of polymer shape and entropic elasticity using computational thinking

“…The various routes to the code described above allow differentiation and individualisation in teaching a scientific subject and lead to several occasions for discussing the topic. (5) The model can then be explored by running the program and varying the parameters or other suitable parts in the code. The obtained results can be compared with experimental observations.…”

“…The structure of molecules with flexible bonds can be coiled in the solid state and is always coiled to some extent in solution depending on solvent molecular interactions. A guided-inquiry experimental approach for realising the structure of polymers in solution based on viscosity measurements has recently been proposed by Everest et al [5]. Their approach also includes an activity on paper to simulate the random walk (RW) model, but does not focus on computer simulations to a big extent.…”