Lecture 7

Question 1

Entropy of mixing equation

Answer 1

= k ln(omega)

Question 2

define X(chi)

Answer 2

dimensionless, empirical, characterizes change in local free energy upon mixing

Question 3

when X = 0

Answer 3

system is a thermal

Question 4

when X> 0

Answer 4

system is endothermal, favors demixing

Question 5

when X<0

Answer 5

system is exothermal, favors mixing

Question 6

spinodal decomposition

Answer 6

region where spontaneous phase separation occurs and a system minimizes its energy

Question 7

metastable region

Answer 7

where phase separation occurs via homogeneous nucleation and growth

Question 8

Two types of techniques to determine MW

Answer 8

absolute and relative

Question 9

absolute

Answer 9

• no calibration, only procedure
  -osmometry
  -light scattering

Question 10

relative

Answer 10

-requires calibration
-SEC/GPC
-viscometry

Question 11

most MW determination techniques require

Answer 11

polymers to be dissolved in solution

Question 12

Techniques sensitive to number of polymer molecules determine _____ average MW

Answer 12

number

Question 13

Techniques sensitive to mass of polymer molecules determines _____ average MW

Answer 13

weight

Question 14

GPC and viscometry do not measure MW directly… why?

Answer 14

they probe hydrodynamic properties

Question 15

Rh vs Rg

Answer 15

objects of different shapes can be approximated through a sphere with Rh

Question 16

Rg for infinitely thin disk

Answer 16

Rg^2 = R^2 / 2

Question 17

Rg for solid sphere

Answer 17

Rg^2 = 3/5 R^2

Question 18

translation from Rh to Rg for gaussian coil

Answer 18

Rh = 0.66Rg

Question 19

Static Light Scattering (SLS):

Answer 19

• Rg or RMS radius
• mass averaged distance from each point in a molecule from the center of gravity

Question 20

Dynamic Light Scattering (DLS)

Answer 20

• Rh or hydrodynamic radius
• radius of a sphere with the same diffusion coefficient as the sample

Question 21

Chain Expansion/Contraction and Solvent quality relationship

Answer 21

Rg ~ N^v

Question 22

when v>0

Answer 22

good solvent

Question 23

when v<0

Answer 23

poor solvent

Question 24

when v = 0

Answer 24

theta solvent

Question 25

T/F expanded chains in good solvents are Gaussian.

Answer 25

FALSE, they are not

Question 26

For 2nd virial coeff, A>0, X<1/2

Answer 26

good solvent

Question 27

For 2nd virial coeff, A<0, X>1/2

Answer 27

bad solvent

Question 28

For 2nd virial coeff, A=0, X=1/2

Answer 28

theta conditions

Question 29

A2 ~

Answer 29

(1-2X)