Part 1 Flashcards
What is soft condensed matter?
The term describes materials that are neither simple liquids nor crystalline solids.
What is a colloidal dispersion?
sub micrometre particles or liquid are dispersed within another liquid
Give examples of SCM
- colloidal dispersions
- polymer melts
- liquid crystals
- surfactants
How are the properties of SCM determined?
by chemistry and general structure connectivity of the material
- small changes in shear force, temp and pH cause the properties of SCM to change dramatically
What are SCM materials composed of?
- mesoscopic particles with complex internal structure
Describe Colloidal Crystal polymerisation
- structure made of hydrogel monomers
- at low temperatures chains are long and hydrophilic
- as temp is increased chains shorten and become hydrophobic
How is globule coil transition connectivity affected by temperature?
- Hydrodynamic radius is heavily dependent on temperature
- At low temperatures the polymer is coiled
- At high temperatures it becomes more linear, and able to bind with the solvent.
- sharp transition
What is the most important property in SCM?
Self-Assembly
What causes self assembly?
- driven by entropy, due to weak intermolecular interactions
- no external intervention required
- some ordering can be heirarchial with structures such as micelles forming
- strongly modifies mechanical properties
How are SCM and Brownian motion connected?
- drives the transitions between phases with different degrees of order
- gives SCM constant random motion
- polymer chains constantly turn and planar structures can bend and flex
Define hydrodynamic radius
The radius of an equivalent hard sphere diffusing at the same rate as the molecule under observation.
What are the practical applications of SCM?
- polymers: heat and flame resistant materials and packaging
- Colloidal dispersions: food industry, personal care products, nano fluids, paints, glues and soaps
- self organised structures: pcp, agrochemicals, pesticides, drugs, templates for nano reactors and nanoparticles, liquid crystals
What is the main form of repulsion in SCM?
- caused by Pauli Exclusion Principle
- short ranged
- occurs when the orbitals of neighbouring atoms begin to interact
- no simple mathematical explanation
What is the hard sphere model?
- used to explain repulsion in SCM
- as soon as orbitals interact their repulsion is infinite
- other than this repulsion is zero
- provided evidence for a fluid solid transition, where the only driving force is entropy
- entropy of solid»_space; entropy of gas!!!
What are the 7 types of attractive force in SCM?
- van der Waals
- dipole dipole
- coulombic
- hydrogen bonds
- hydrophobic interaction
- metallic
- covelant
Describe the van der Waals forces in SCM
- between uncharged and weakly interacting molecules
- not strongly directional
- on the order of 10^-20
Describe the dipole-dipole interactions in SCM
- directional
- long ranged
- magnitude of 10^-19
Describe the coulombic forces in SCM
- non directional
- magnitude of 10^ -19
- screening means effects on test ion are not as strong as expected
- strength and range vary with ionic strength
- weak above the Bjerrum length
Describe hydrogen bonding in SCM
- no simple mathematical form
- 4-20 kT
- short ranged
Describe metallic and covelant forces in SCM
- not a significant contribution
Describe the hydrophobic interaction in SCM
- Molecules perturb the 3D structure of the water molecules around them, causing a decrease in entropy and increase in free energy.
- If two or more of the non water molecules are brought together, the overall increase in the free energy is minimised, therefore overall there is an attraction between the two molecules.
- Strength of around 1-10 kbT
- very short ranged
- Strength increases with temperature therefore there is an entropic point of origin.
What can the hydrophobic interaction cause?
- formation of clathrates/ cages but only for small molecules
How does the hydrophobic effect change the solubility of molecules?
- In water solubility of gas decreases and then increases which is a signature of the hydrophobic effect
- In organic solvents solubility increases with temperature, at low temps entropy is very negative
What affects SCM phase diagrams?
- strongly dependent on the range of a potential
- for a narrow potential, no liquid phase can form
- there is also a critical nucleation temperature
- plotted against temperature and density
How does mechanical response change in SCM?
- depends on the way the stress has applied
- quantified through sheer stress and shear strain
What is a hookean solid?
- shear strain proportional to shear stress
- constant shear modulus
What is a newtonian liquid?
- flows with constant shear strain rate when shear stress is applied
- depends on the viscosity of a liquid
How does the time of the strain affect the response in SCM?
- viscoelastic response
- fast strain gives an elastic response
- slow strain gives a viscous response
- relaxation time is the barrier between the two schemes
What is a non-newtonian fluid?
- when viscosity depends on sheer rate
- shear thinning occurs when fluid flows better with stress
- shear thickening occurs when fluid flows worse under stress
What does young modulus measure?
- measures the stiffness of an elastic material
- related to potential and interatomic interactions
What is relaxation time?
- The relaxation time is connected to the microscopic structure of the soft material
- The time for one atom to jump out of its ‘cage’ caused by the applied strain, vibrational relaxation time
- Activation energy is about ½ the latent heat of vaporisation of the molecule
- There are deviations from this model which occur at the single molecule level
- Characteristic Arrhenius dependence of viscosity
Give some characteristic relaxation times
- Liquids : 10-12 texp» Relaxation Time leading to viscous flow
- Soft matter: 10-3 -1s texp=Relaxation Time leading to visoelastic behaviour
- Liquids : more than 1s texp«_space;Relaxation Time leading to elastic behaviour
- Glasses have long relaxation times (millions of years)
- Macroscopic behaviour can be tuned using relaxation time
