# Preface! ✨

It’s your favorite material science & nanotechnology enthusiast! Today, we will cover the pH gelation time for a silica aerogel (sol-gel chemistry)!

There is no article to prepare you this time! Let’s jump into today’s topic! 😄

# pH Value Explained! 💡

## What is pH? 🔑

pH is actually a scale that determines how acidic or basic something is by the number of hydrogen ions in a substance/solution. pH is the scale where we can measure the power/strength of acids and bases.

While this is not completely true, you could remember pH as “Power (p) of Hydrogen (H) → pH.”

For today’s purposes, solutions/substances that are acidic tend to have a LOT of hydrogen ions (H+) { sometimes it can also be mentioned as H3O+), while solutions/substances that are basic tend to have a LOT of hydroxyl ions. (OH-)

If you’re still confused by this, this is why you should never play with acids or bases: the concentration of hydrogen or hydroxyl ions is out of balance.

Acids want hydroxyl ions to neutralize themselves, and basics/alkalines want hydrogen ions to neutralize themselves back to a special number: 7.

## Calculation! 🔑

You can use this logarithm to explain/calculate the pH in a solution:

## pH = -log10¹[H+]

For example, the number of hydrogen ions in water is 1 x 10^-7 molar (moles/liter). “1 x 10^-7” will replace the symbol “H+” in the logarithmic equation. The equation now looks like this:

## pH = -log10¹[1 x 10^-7] → pH = -log10¹[10^-7]

To calculate this, all we do is ask about the 10 attached to “log”, and ask: “What power should I raise [10¹/10] to get to [10^-7]? The answer is -7.

The reason why it is 7 is that the “10” outside of the brackets is the same as writing 10¹. Since the bases (10) is the same inside and outside of the brackets, we could just look at the exponents (1*? = -7) The answer to the question mark is (-7).

That means our equation is left like this:

## pH = -[-7] or pH =(-1)(-7)

The answer is 7. That means the pH of water is 7.

# What about the pH Gellation Time For Aerogels? 💡

## Polycondensation! 🔑

To explain the gelation time for the aerogels, I need to explain two concepts: hydrolysis and polycondensation.

Hydrolysis is the chemical breakdown of a compound/molecule due to a water reaction with the compound.

Polycondensation is the contraction/compression of smaller molecules that get closer to each other (condense) to form a compound with high molecular weight (aka increased fluid friction/viscosity). Water is released from the condensation of these smaller molecules.

A liquid with low fluid friction/viscosity is water. A liquid with high fluid friction/viscosity is honey.

Viscosity can be simply defined as the fluid’s resistance to flow (against a force/intermolecular force).

But Carlos, why does viscosity have to do with the molecular weight?

With a higher viscosity, there is a higher molecular weight because there are longer polymer chains and there is more strength between the intermolecular forces. High molecular weight polymer chains are long enough to temporarily become entangled with each other, thereby forming physical crosslinks. These crosslinks prevent molecular flow and lead to rubber-like behavior.

# Closing Thoughts! 💭

The behavior of polycondensation can directly impact how fast hydrolysis can occur since hydrolysis is just the chemical breakdown of a compound because it interacted with water molecules, and in polycondensation, water is released from the contraction of smaller molecules!

However, the hydrogen atoms in a water molecule could lose their electrons, which creates hydrogen ions, and decreases their pH level!

All of these concepts (pH, hydrolysis, polycondensation) are related to one another!

Summary:

pH is the scale where we can measure the power/strength of acids and bases. The pH of water is 7, so water is neutral, anything lower than 7 has a LOT of hydrogen ions, and anything above than 7 has a LOT of hydroxyl ions.

Hydrolysis is the chemical breakdown of a compound/molecule due to a water reaction with the compound.

Polycondensation is the contraction/compression of smaller molecules that get closer to each other (condense) to form a compound with high molecular weight (aka increased fluid friction/viscosity). Water is released from the condensation of these smaller molecules.

Viscosity is the fluid’s resistance to flow. This is either because of the intermolecular forces or the polymers cross-linked with each other to prevent molecular flow.

See you tomorrow on some results from a research paper discussing gelation time for aerogels using pH, polycondensation, and hydrolysis!

# Vocabulary! 📓

pH → The scale where we can measure the power/strength of acids and bases.

Acids → Tend to have a LOT of hydrogen ions (H+/H3O+)

Bases/Alkalines → Tend to have a LOT of hydroxyl ions (OH-)

Hydrolysis → The chemical breakdown of a compound/molecule due to a water reaction with the compound.

Polycondensation The contraction/compression of smaller molecules that get closer to each other (condense) to form a compound with high molecular weight (aka increased fluid friction/viscosity). Water is released from the condensation of these smaller molecules.

Viscosity → The fluid’s resistance to flow (against a force/intermolecular force).

PolymersA chain of many repeating/identical large molecules that make up a material.