Surfactants, Intermolecular Forces, and Surface Tension

Flashcards generated from lecture notes on surfactants, intermolecular forces, and surface tension.

What industrial and commercial importance do characterization methods have in chemistry?

Characterization methods are important industrially and commercially and it is worth knowing a bit about them and their chemistry.

Why are intermolecular forces important concerning surfactants?

Intermolecular forces are a backbone for surfactants, but it is also very applicable to just about anything else, especially when you start to think about how molecules are going to come together.

When calculating dispersion forces between two benzene units, what should one focus on?

Focus on the benzene units themselves, not the charges or the alcohol chain. These could be done separately in a different calculation.

In the dispersion forces equation, what must you do if calculating the interaction between benzene and another molecule?

You have to use the specific values for that second molecule instead of using the benzene values twice.

What conversion is needed when provided ionization energy (IE) values in electron volts (eV) for dispersion force calculations?

Convert eV to Joules by multiplying the eV value by 1.609 x 10^-19.

What is the strongest intermolecular attractive interaction?

Hydrogen bonding.

What is critical for effective hydrogen bonding?

The correct arrangement and alignment of the molecules.

Why is the arrangement of molecules particularly important in polymers regarding hydrogen bonding?

Because misalignment can readily lead to repulsive forces.

How do surfactant and water molecules typically maximize hydrogen bonding?

They arrange themselves to optimize hydrogen bonding because they are small and can move easily.

What happens to the potential energy as the angle deviates from the peak for hydrogen bonds?

The potential energy becomes positive, indicating repulsion.

In non-covalent interactions, besides covalent and ionic bonds, what has the potential to be the strongest?

Hydrogen bonds.

Why can pi-pi interactions be quite strong?

Because pi-pi interactions are included in dispersion forces and they are really very strong.

What key property of surfactants changes the surface tension of a solution?

The presence of surfactants changes the surface tension.

What is interfacial tension?

The higher energy state at the interface between two substances compared to within their bulks.

What makes molecules at an interface want to return to the bulk?

Molecules at the surface really want to get back into the bulk because they are in a much happier, much lower energy state.

What counteracts the tendency of molecules at the surface to return to the bulk?

Surface tension.

Why are water droplets spherical?

Because a sphere is the smallest surface area to volume ratio.

Why does salad dressing separate?

The oil-water interfacial tension is high, leading to separation to minimize the interface.

What is the basic principle behind measuring surface tension involving pulling something through the surface?

You measure how much force you're having to apply to take it off the surface.

What is the relationship between the shape of a drop and surface tension in the pendant drop method?

The more spherical the drop, the higher the surface tension.

How does surface tension relate to the ability of a paperclip to float?

For the paperclip to float, the forces going up (interfacial tension and buoyancy) need to be bigger than the forces going down (weight).

What happens when a surfactant is added to the water and a paperclip sinks?

Molecules of the surfactant come in and form an oriented monolayer, and that reduces the surface tension.

By how much does adding surfactants drop the surface tension of pure water and why is this important?

It drops surface tension roughly by half. The surfactants is effectively making the surface water seem to be organic.

What is the main difference between surface tension and interfacial tension?

Surface tension is generally referring to air to liquid or liquid to solid in space, while interfacial tension generally refers to two liquids.

What happens when surfactants are added to water regarding surface tension?

When you put them in water they form these oriented monolayers, and the surface tension gets reduced.

What is surface pressure?

It is basically the amount to which someone actually wants to go and stand at the interface.

What is the surface pressure of water with a high surface tension?

The surface pressure is zero.

How does the addition of surfactants affect surface pressure?

Surfactant molecules,tend to want to go to the interface, occupying a space that water molecules don’t have to occupy anymore.

Why do surfactants move towards the interface?

Because the energy of the surfactants is lower at the interface than it is in the actual bulk.

What kind of interactions occur at the interface between the head groups and the water?

Hydrogen bonding interactions.

Can the repulsion between charged head groups and counterions at the interface drive the process?

No, overall, because it looks like the interaction strength between the molecules, it is not the thing that's driving this process.

What is the hydrophobic effect in surfactant solutions?

The entropic drive for nonpolar molecules to aggregate in water, minimizing their disruption of hydrogen bonds.

What happens to water molecules around the alcohol chain?

The alcohol chain is driving the water that surrounds it into a crystalline state.

Why are surfactants not very soluble in water?

Adding surfactants into the fold is something that is really not good for entropy.

Where does the driving force come from when a surfactant is removed from the water?

The removal of hydrophobic cavities gives a lot of disorder back into the water structure.

What drives molecules to absorb and increase surface pressure?

The hydrophobic effect.

What is the general relationship between surface tension and surfactant concentration?

As the surfactant concentration increases, the surface tension decreases until the CMC is reached.

At what point during interface filling, is there a pseudo linear region where the most change occurs?

The pseudo linear region is due to the interface filling up.

What is the critical micellar concentration (CMC)?

The breakpoint in the surface tension vs. concentration curve where micelles begin to form.

What is present in the solution at the CMC regarding surfactants?

At the CMC, my cells haven’t quite formed yet. There is an equilibrium of a few micelles kicking around.

Why do micelles form above the CMC (critical Micelle concentration)?

They form because we’ve run out of space at the interface. You have an entropic drive that is not supported with additional monomers.

Where do hydrophobic tails and heads stay at the center of micelles?

Hydrophobic tails get sequestered into the centre of micelles while hydrophobic heads stay on the outside.

What is the relationship between aggregation number and micelle formation.

The more surfactant molecules you have, the more the micelles will start to form.

What are the different considerations to predict the area of the head group to help predict a possible solution

Changing concentrations and how we’re changing our solution.

What can be used in this context to realize changing concentrations and how it is changing the solution concentration wise?

A phase diagram.

Define what the L1 area represents on the liquid crystals diagram.

The L1 area is presence of my cells.

What does is mean to be below a certain temperature on the phase diagrams?

We end up actually with crystals that could have water with each other.

What does it mean to measure the CMC?

The point that is basically an idea of the maximum solubility of stocks of molecules

What needs to happen in order for my cells to occur?

My cells need to form above the CMC and above the cross temperature.

What are some ways of detecting CMC?

Physical properties changing such as measuring it using surface tension or by using conductivity.

As conductivity changes when detecting CMC why is it subtle

In myself, the counter runs are not fully dissociated.

What process accomplished using Deep Blue and use of GPU as an important factor

The modeling of much more complicated systems such as self-assembly.

What concept needs to happen in order to get from A to A?

The two moleces, the fact that we'll find each other to make a diamond and then that diamond will make a drama until you get to N where N is the aggregation number

What is the close association model?

You take a number of surfactant molecules, you have a single equilibrium constant, and that forms the mice cell

In calculations with closed association model, what form of concentration must be used?

Mole fraction.

What is used to find change in G of my civilization based on a CMC?

R T log X CMC.

How can the change in concentration be proven in a water system?

If we set the volume of B in a litre.

What happens if you use log concentration of surfactant in molar quantities?

Those that include log of a, and that is wrong because you get the wrong G from oilisation by about ten of alls per amount.

Where is most of how we solve equations accurate to and what happens when we need a tune up

Non-icfact, add a two factor mostly.

How dissociation occurs is by.

How charged the voice cell is divided by the much that I can remember.

If you increase the salt concentration you get to.

Push the cations back towards SDF because there’s just more of them and they going to get closer.

What factors affect the CMC?

Temperature, Tell and Solvent utility.

When we look at chain chemistry what should we be calculating to get a perspective on the solution.

You actually see a calculation that gives you how much it’s going to change by.