It's a fairly niche area, I'm not surprised that you didn't cover it in Undergrad.

I had a class on Interfacial Thermodynamics that covered the theory relevant to this (that I remember almost nothing about other than it having 80 or so 'essential' equations to comprehend in a 10 lecture course), surfactants weren't discussed explicitly in the class but thermo is thermo and applies to all systems equally.

I came across this particular area of knowledge doing some post-doctoral work for an excellent physical chemist who specialised in surfactants.

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The answer that was removed kind of boiled down to 'if it forms micelles it forms foam' with some very vague statements in support. It was poorly written, didn't use scientific language, mixed up cause and effect. Most of the facts weren't wrong, but they weren't factors in foaming behaviour. It actually made it pretty difficult to dispute, which is why I didn't bother to explicitly address it. Didn't want to get drawn into a potential pedantry showdown!

The bit I remember was a dubious claim that seemed to suggest that the air partitions into the core of the micelle, which is completely untrue (but was hard to understand exactly what he meant because of the lack of technical language). FYI when you bubble air into a surfactant solution you are in fact creating a new area of air/water interface along which the surfactant forms a typical monolayer.

Anyhoo! Not a problem anymore.

Sadly the current top answer is quite wrong.

Foaming behaviour and micelle formation are not linked in any meaningful way. I won't address why, I'll just answer your question, by rephrasing it just a tiny bit:

>Why do some surfactants form stable foams while others don't?

Because if you blow air through a suitably concentrated solution of almost every surfactant you can generate 'bubbles'. The question is really whether or not they are stable.

The stability of a foam depends on the interfacial tension of the hydrophobic/air interface and on the ability of the hydrophilic side to trap water.

The foam is basically air/detergent/water/detergent/air. They are quite similar to lamellar sheets that many detergents form, which are water/detergent/detergent/water. I don't know if forming lamellar phases in solution is a predictor of forming stable foams or not.

If the interfacial tension is low, the bubbles are extremely metastable, they'll pop and merge and generally fall apart fairly quickly. Conceptually the interfacial tension (if you can hold everything else constant) is covarient with how densely the hydrophobic tails pack, like if you could make a model system where you could arbitrarily vary the density of the hydrophobic bit, the denser one would also have higher interfacial tension.

But this can lead you to the false conclusion that less curved foams must be more stable, which is indeed a false conclusion. Because of course it's actually a free energy property so there's a series of enthalpic and entropic terms to consider.

If the hydrophilic side can't trap water sufficiently well then they will 'drain'. That is to say, the water in the detergent sandwich will be pulled back by gravity into the bulk solution.

The size of the air bubble in the foam is determined by the aspect ratio of the detergent which is not particularly correlated with either of the other two properties (this is why I included the spurious conclusion about less curved foams being more stable) and the initial size of the bubble is also affected by how you prepare the foam which is a confounding variable.

There are additives you can add to detergents to stabilize or destabilize a foam.

ELI5: Almost everything is more soluble in hot water than cold water. Including Soaps. The soap is what cleans the germs off. More soap in the water = better germ cleaning.

Soaps help water remove things that don't usually mix with water - like oils, fats and germs. The soap has one end that like water and one end that likes fat/oil/"not water". The soap surrounds the germs and the water surrounds the soap

Beyond ELI5:

A few interesting examples occur of things are NOT more soluble in hot water than cold water: triethylamine is soluble in water below 19C only. Nicotine is soluble in water below 61C and insoluble above that (weirdly, it becomes soluble again above 210C in pressurised containers). Some polymers show similar behaviour. It's called a lower critical solution temperature

The explanation for this comes down to a Gibbs Free Energy change which is too advanced for this sub.

My experience using this exact method, although I tend to use parts boxes is:

1. Number the bags (or sections in a parts box) in Chronological Order that you removed them, name each bag. You can even section name them for big projects, which makes this method scale well. e.g. 'Engine #1 Chassis hanger bolts'

2. It doesn't really matter what you name most bags/sections: 'Flange Bolts' is not particularly specific but will usually be apparent when it comes at the correct time in your build order.

3. This method allows for several bags of screws labelled '?????' as long as they are sufficiently separated in the Chronological Order.

>Does the cerebral spinal fluid of people with Alzheimer's have a notably different pH from 'normal' people's?

Probably not, but not for the reasons others have stated (which are true).

Excess Tau Protein in the CSF is the only reliable assay test we have for Alzheimers, because the Tau protein escapes into the CSF, but Alzheimers isn't a disease of the CSF. Alzheimers is a disease of Neuron Cells in the Brain.

The better question might be - is the Neuronal pH of Alzheimers disease patients different from nominally health people?

I also don't know the answer to this question either, but you might be able to find out. I wouldn't expect there to be a global difference in pH - homeostatis is very effective and long term pH changes are make for very unhappy cells (i.e. necrosis and death), but whether the pH changes during acute stress events enough to make a difference is an interesting thought that someone may have pursued.