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SOFT CONDENSED MATTER > Part 1 > Flashcards

Part 1 Flashcards

1
Q

What is soft condensed matter?

A

The term describes materials that are neither simple liquids nor crystalline solids.

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2
Q

What is a colloidal dispersion?

A

sub micrometre particles or liquid are dispersed within another liquid

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3
Q

Give examples of SCM

A
  • colloidal dispersions
  • polymer melts
  • liquid crystals
  • surfactants
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4
Q

How are the properties of SCM determined?

A

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

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5
Q

What are SCM materials composed of?

A
  • mesoscopic particles with complex internal structure
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6
Q

Describe Colloidal Crystal polymerisation

A
  • structure made of hydrogel monomers
  • at low temperatures chains are long and hydrophilic
  • as temp is increased chains shorten and become hydrophobic
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7
Q

How is globule coil transition connectivity affected by temperature?

A
  • 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
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8
Q

What is the most important property in SCM?

A

Self-Assembly

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9
Q

What causes self assembly?

A
  • 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
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10
Q

How are SCM and Brownian motion connected?

A
  • 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
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11
Q

Define hydrodynamic radius

A

The radius of an equivalent hard sphere diffusing at the same rate as the molecule under observation.

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12
Q

What are the practical applications of SCM?

A
  • 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
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13
Q

What is the main form of repulsion in SCM?

A
  • caused by Pauli Exclusion Principle
  • short ranged
  • occurs when the orbitals of neighbouring atoms begin to interact
  • no simple mathematical explanation
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14
Q

What is the hard sphere model?

A
  • 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&raquo_space; entropy of gas!!!
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15
Q

What are the 7 types of attractive force in SCM?

A
  • van der Waals
  • dipole dipole
  • coulombic
  • hydrogen bonds
  • hydrophobic interaction
  • metallic
  • covelant
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16
Q

Describe the van der Waals forces in SCM

A
  • between uncharged and weakly interacting molecules
  • not strongly directional
  • on the order of 10^-20
17
Q

Describe the dipole-dipole interactions in SCM

A
  • directional
  • long ranged
  • magnitude of 10^-19
18
Q

Describe the coulombic forces in SCM

A
  • 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
19
Q

Describe hydrogen bonding in SCM

A
  • no simple mathematical form
  • 4-20 kT
  • short ranged
20
Q

Describe metallic and covelant forces in SCM

A
  • not a significant contribution
21
Q

Describe the hydrophobic interaction in SCM

A
  • 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.
22
Q

What can the hydrophobic interaction cause?

A
  • formation of clathrates/ cages but only for small molecules
23
Q

How does the hydrophobic effect change the solubility of molecules?

A
  • 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
24
Q

What affects SCM phase diagrams?

A
  • 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
25
Q

How does mechanical response change in SCM?

A
  • depends on the way the stress has applied

- quantified through sheer stress and shear strain

26
Q

What is a hookean solid?

A
  • shear strain proportional to shear stress

- constant shear modulus

27
Q

What is a newtonian liquid?

A
  • flows with constant shear strain rate when shear stress is applied
  • depends on the viscosity of a liquid
28
Q

How does the time of the strain affect the response in SCM?

A
  • viscoelastic response
  • fast strain gives an elastic response
  • slow strain gives a viscous response
  • relaxation time is the barrier between the two schemes
29
Q

What is a non-newtonian fluid?

A
  • when viscosity depends on sheer rate
  • shear thinning occurs when fluid flows better with stress
  • shear thickening occurs when fluid flows worse under stress
30
Q

What does young modulus measure?

A
  • measures the stiffness of an elastic material

- related to potential and interatomic interactions

31
Q

What is relaxation time?

A
  • 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
32
Q

Give some characteristic relaxation times

A
  • 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&laquo_space;Relaxation Time leading to elastic behaviour
  • Glasses have long relaxation times (millions of years)
  • Macroscopic behaviour can be tuned using relaxation time

SOFT CONDENSED MATTER (5 decks)

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