PURE ZETA: PART ONE. For those interested, breaking things down to "street level" will be attempted, but a bunch of science/math is involved.
PURE ZETA: PART ONE. For those interested, breaking things down to "street level" will be attempted, but a bunch of science/math is involved.
History:
The Smoluchowski Equation is named after physicist Marian Smoluchowski, who made significant contributions to the field
2/ of colloidal science and statistical physics.
Colloidal physical chemistry focuses on the study of colloids and colloidal systems. Colloids are a type of mixture in which tiny particles are dispersed or suspended in a different medium. These particles are typically larger than
3/ individual molecules but smaller than what we consider macroscopic particles. For those of you who drink orange juice, or are familiar, imagine you have a glass of orange juice with some "pulp" in it. The pulp, as it exists in these tiny pieces, are too small for you to pick
4/out of it, individually in pieces. They are not as small as dust or as grains of sugar (not to be taken literally, we are going into LNP which is nano size, this is for imagery.) The tiny pulp bits could be referred to as "colloids". Colloidal science is the study of how these
5/ bits or colloids, behave in different mediums (liquids or other substances) with other colloids, molecules, pH--there are many factors (we'll get there). In simplest terms, colloids are the mixtures where one substance is split into minute particles which are dispersed
6/throughout a another substance, such as liquid soap, milk, and human blood.
There are some key components when speaking to colloids. Particle Size: Ranging from nanometers to micrometers. They are larger than individual molecules but still small enough to remain suspended in
7/a liquid or gas without settling to the bottom. Colloids are usually dispersed in a liquid phase. The surface properties of colloidal particles play a crucial role in their behavior. They have a high surface area relative to their volume, leading to unique surface qualities.
8/ It's like taking PlayDoh, and making tiny little balls with it, rolling it around with your fingers on top of a table. If you made it really small, like the size of a pin head, the whole outside of that little ball, would take up more space, than the little thing itself.
8/ Back to Smoluchowski. Smoluchowski developed the theory for the motion of charged colloidal particles under the influence of an applied electric field. He derived the equation that relates electrophoretic mobility to zeta potential, which is known as the Smoluchowski equation
9/ Imagine you have those same orange pulp particles 9although not charged) floating around in a glass of orange juice. Electrophoretic mobility measures how fast the pieces of orange pulp move when an electric field is applied to the orange juice (if they could). It's like
10/ you are pushing them to move around--some move faster than others. Zeta potential is a way to measure electric charges if they could exist on pieces of orange pulp. Of course oranges cannot have a charge, but this is the road we are on now. Zeta potential is a measure
11/ what the charge is, and how strong it is, in what direction.
This equation was a gargantuan breakthrough in understanding the electrophoretic behavior of charged particles, and became a cornerstone in the study of colloidal stability.
12/ The HENRY EQUATION. The Henry equation is based on the work of the American chemist and physicist Donald L. Henry. He focused on how these little bits of orange pulp would behave in liquids, based on their shape and size (for anyone paying attention, now you understand a bit)
13/ He could see that if particles are NOT little perfect balls, little spheres, that the Smoluchowski equation, would not be accurate. He looked at ones that were oblong, or a bit different in shape. Also, size matters. He looked at particles that varied in size, looking at
14/ particles that might be above 50 nm, perhaps 50 nm to 100? Larger?
He was not just looking at oblong or unique shapes, he knew the Smoluchowski equation would not assist, when trying to measure polydiverse particles. Poly diverse particles means there are a difference in
15/ the size of particles. This is where you could have, say, lipid nanoparticles that vary in size, shape, but also, if they have a charge, and zeta potential, then which equation do you use?
Also, what else do you account for in the calculation of zeta potential?
Next: Debye.