Quiz 2 Flashcards
What is the difference between PEG and PEO? $$
- Low molecular weight polymers, 200 to 20,000 average molecular weight, are poly(ethylene glycols) (PEG) polymerized using base catalysis
- Poly(ethylene oxide)s (PEO) have molecular weights between 100,000 and 5,000,000, and are free-flowing white powders
What does the 400 represents in PEG 400? $$
9 repeting units of PEG:
PEG MW = 44gr/mol
400/44 = 9 units of PEG
Types of biosurfactants ($$test)
Fatty acids
Glycolipids
Lipopeptides, Lipoproteins
Polymeric surfactants
Phospholipids
Particulate biosurfactants
The main advantages of biosurfactants $$
- lower toxicity,
- biodegradable nature, and
- effectiveness at low as well as high temperatures.
Froces in self-assembly $$
Attractive Driving Force: Brings Self-Assembly building units together. (Hydrophobic tails)
Repulsive Opposition Force: Balances Self-Assembly building units at a certain point. (hydorphilic heads)
Directional/functional Force: Guides the direction of self-assembly/ Provides functionality (such as Magnetic fields, geometry, gravity )
Case A: Describe the self-assembly when only arractive driving and repulsive opposition forces are present, $$
- self-assembly is a random and usually one-step process.
- aggregates show nonhierarchical structure.
Case B: Describe the self-assembly when third class of force is involved $$
- the self-assembly processes are now directional
- in many cases they occur as multi-stepwise processes
- show hierarchical structure.
Is self-assembly always a single step process? $$
- Self-assembly is not always a single-step process;
- it can occur in a double-, triple-, and multi-step patern
- show hierarchical structure.
Force balance: $$
Total net potential can be described as the net total of all of the arractive and repulsive potentials Involved in each step of the self-assembly as follows:
Utotal (x) = fp | UA,P (x)+UR,P (x) | + fS ⋅| UA,S (x)+UR,S (x) | + fT ⋅| UA,T (x)+UR,T (x) | +Uext (x)
£ fp + fs + f3 + … = 1 ==> Are the fractional coefficients of the contribution of the net potential of each self-assembly step to the total net potential
fp | UA,P (x)+UR,P (x) | = Arractive & repulsive potentals for self-assembly of **primary building units **
fS ⋅| UA,S (x)+UR,S (x) | = Arractive & repulsive potentals for self-assembly of **secondary building units **
fT ⋅| UA,T (x)+UR,T (x) | = Arractive & repulsive potentals for self-assembly of **tertiary building units **
Self-assembly is the force balance process between three classes of forces:
- Attractive Driving Force: Brings Self-Assembly building units together.
- Repulsive Opposition Force: Balances Self-Assembly building units at a certain point.
- Directional/functional Force: Guides the direction of self-assembly/ Provides functionality
Force Balance Approach for Sufactant Micelles
Attractive Driving Force: Brings Self-Assembly building units together. (Driving force:** hydrophobic arraction** )
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Repulsive Opposition Force: Balances Self-Assembly building units at a certain point. (
Opposition force electrostatic repulsion and/or solvation force, Steric, hydration and electric double-layer)
self-assembly is a _______ and usually ________ process.
- aggregates show ______________ structure.
it can occur in a __________, _______________, _________-_______ patern
random
one-step
nonhierarchical
double-, triple-, and multi-step
Force Balance Approach for Colloids
Attractive Driving Force: Brings Self-Assembly building units together (Van der Waals force)
<=====>
Repulsive Opposition Force: Balances Self-Assembly building units at a certain point. (Electric double-layer)
Case A: Describe sefl-assembly when onlly attractive driving and repulsive opposition forces are present:
- Sefl-assembly is a random and usually one-step process
- Aggregates show non-heriarchical structure
Formation of surfactant or polymer mesophases (i.e. liquid crystals) When:
- fp > fs
- fp = fs
- fp < fs
- fp > fs the primary self-aggregate will be dominate over the secondary aggregate
- fp = fs coexistance of primary self-aggregate and secondary aggregate
- fp < fs favors assembly proceeding to the secondary aggregate
Total net potential in self-assembly can be described as:
the net total of all of the arractive and repulsive potentials Involved in each step of the self-assembly:
Utotal = |Arractive & repulsive potentials for self-assembly of primary building units| + |Arractive & repulsive potentials for self-assembly of secondary building units | + |Arractive & repulsive potentials for self-assembly of tertiary building units|
Type I: Self-Assembly and examples $$
occurs through only the primary self-assembly step (fp = 1)
- The interplay between the arractive and repulsive forces between the primary building units solely determines the self-assembly process.
- Examples:
- micelle forma^on of surfactants or amphiphilic polymers at low concentration
- Formation of vesicles or microemulsions
- Stable colloidal suspensions
Type II: Self-Assembly and examples $$
Assembly occurs through both primary and secondary self-assembly steps (fp +fs= 1)
- Examples: FormaTion of surfactant or polymer mesophases (i.e. liquid crystals)
Type III: Self-Assembly and examples $$
Assembly occurs through primary, secondary, and tertiary and above steps ∑fp + fS + fT +⋅⋅⋅=1
- Examples: quaternary formation of proteins.
Type IV: Self-Assembly and examples $$
Type IV: Assembly involving external forces and primary, secondary, and or tertiary steps
external forces = magnetic force, electric force, flow stress, capillary force, gravity, substrate interactions
When Utotal >0 Uext(X)= 0
The self-assembly is
Not possible
When Utotal (X) < 0 Uext (X) = 0
The self-assembly is ___________ driven $$
kinetically driven.
- self-assembly continues until most of the building units are exhausted - self-aggregates have indefinite sizes and less-defined shapes.
- Examples: coagulated colloidal precipitates, bilayers, gels, macroemulsions
When Utotal (X) = 0 with Uext (X) = 0
The self-assembly is ___________ driven $$
Thermodinamically
- the building units are in equilibrium with the self-aggregates
- self-aggregates have finite sizes and defined shapes.
- Examples: polymer or surfactant micelles, vesicles, microemulsions
Forces involved in Self-Assembly
Weak and long-ragne forces play an important role in self-assembly
Attractive Forces
- Van der Waals
- Solvation
- Depletion
- Bridging
- Hydrophobic
- π-π Stacking
- Hydrogen bond
- Coordination Bond
Van der Waals Forces $$
Types of Van der Waals
are transient, weak electrical attraction of one atom for another. They originate from dipole or induced-dipole interactions at the atomic and molecular level.
- Keesom: permanent dipole-permanent dipole interaction
- Deby: permanent dipole-induced dipole interaction
- London: (or dispersion) interaction: induced dipole-induced dipole interaction
Forces involved in self-Assembly
Describe the movement of ions during electric ion layer formation. $$$$
- negatively charged ions from solution will be attracted to the positively charged surface
- While the counterions (anions) will be strongly concentrated near the surface the co-ins (cations) will deplete the vicinity of that surface.
- At a distance farther from the surface, positively charged ions will build up
- Far away from the surface both concentrations approach the bulk concentration
The electric double layer is made up of the Stern layer, where cations are adsorbthe surface and the diffuse layer, where the number of counterions exceeds the number of anions
At pH above the isoelectric point, the cations are adsorbed within the Stern layer; there is an excess of cations in the diffuse layer.
Electric Double Layer between 2 surfaces with the same type of charge. $$
When two surfaces with the same type of charge are approaching together, the first contact area is the outermost region of the diffuse layers.
As two surface are coming closer, the diffuse layers (the potentials) from each surface come to overlap. This generates excess pressure that originates the repulsive force between the two surfaces: electrostatic double - layer repulsion.
The potential in the diffuse layer is mainly changed by
- the geometry of the surface, and
- the concentration and type of electrolyte.
DLVO theory
(Derjaguin, Landau, Vervey, and Overbeek (DLVO)
The total force acting on the colloidal objects in solution is the sum of the electrostatic Double layer force and the van der Waals force.
U(x) = Electric double layer forces - Van der Waals Forces
One forces has to be cancelled to allow self-assembly.
Attractive forces arise when:
- Solvent is a poor solvent..
- The polymer chain has enough affinity with the surfaces.
- When the colloidal objects are interacting in the solution with nonadsorbing polymer, attractive depletion interaction can occur.
Bridging Flocculation
When a high molecular weight (i.e. very long chain) polymer is present in a very Small amount (parts per million, ppm), and adsorbs onto the colloidal particles.
Parts of the polymer may adsorb onto different colloidal particles and draw them together.
- One theory suggests that the polymer attaches to two particles simultaneously by both ends
- Another theory assumes that the polymer attaches at several points leaving loops projecting which attach to other particles
Depletion Flocculation
The polymer is not adsorbed to the particle, but remains free in solution.
polymer chains are distributed event between colloidal particles when the distance between the colloids is large enough.
When the distance between the approaching colloids becomes smaller, polymer chains in the intercolloidal region are squeezed out, thus depleting this region.
When individual polymers or nanoparticles cannot enter the space between the two surfaces, they tend to ‘‘deplete’’ between the colloidal surfaces to gain more conformational conformational entropy, which results in an osmotic pressure imbalance (P) inside and outside the gap and leads to a depletion attraction between the two surfaces.
Hydrogen bonding:
1) Donor groups,
2) Accpetor groups
An interaction between a covalently bonded hydrogen atom o_n a donor group_ and a pair of non-bonded electrons on an acceptor group.
1) Donor: N-H, O-H
2) Acceptor: O, S, N
The aggregation number (N)
- N < CMC
- N = CMC
- N > CMC
- The value of N depends on
is the number of surfactant or polymer molecules within a micelle once the critcal micelle concentration (CMC) has been reached.
- N < M. Too small micelles have too large area per head group.
- N=M
- N > M. Too large micelles have head groups too closely packed together. Difficulties also in packing hydrocarbons chains. Some head groups forced inside the hydrophobic core.
- the type of surfactant, temperature and electrolyte concentration
Sketch describe how the monomer and micelle concentration change vs. the total amphiphile
At low surfactant (amphiphile) concentration there is only monomer, and the concentration of monomer in solution increases.
The amount of the monomers adsorbed at the air – liquid interface and liquid – solid interface (for some of the systems) typically ranges below 10− 8 mole/liter.
At the cmc micelles begin to form. Since the monomers and micelles are at equilibrium, the additonal amount of surfactants forms the micelles after the cmc .
Addition of more monomer above the cmc makes the micelle concentration increase linearly with the total concentration, while the monomer concentration in solution remains almost constant.
The concentration of micelles is corrected at the point where the spherically shaped micelles are transformed into higher - order structures such as rod - shape or wormlike micelles.
