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Brownian motion of sol particles

Brownian motion is the random, or zig zag motion of particles of any system due to the random motion of atoms which causes collisions with one another which further creates movement in the system,The movement never ceases.A sol is a type of colloid made when solid particles are immersed  in liquid particles,Brownian motion in sols  is a basically observing Brownian motion in a very specific system where the dispersed phase is solid and the dispersion medium is liquid .Brownian motion was discovered by Scottish botanist Robert Brown in 1827 while observing motion of pollen grain particles in water under a microscope,therefore the first time brownian motion was observed under a sol system as pollen grains are solid and the water is liquid. The Brownian motion is only observable under a  visible light microscope and not visible to the naked eye because ,even though the particle size that exhibits Brownian motion is much bigger than that of an atom it is still small enough to be seen by the naked eye .Particles of a particular size only exhibit brownian motion as with size of particles increases the kinetic energy of the system particles decreases therefore the size of the particle must be small enough to be moved by brownian motion.Brownian motion never ceases because when the particles collide with one another energy is transferred from one particle to another particle hence the energy of the total system remains conserved ,which explains random movement of particles for an indefinite period of time.

In sols Brownian motion plays a huge role in the formation of the sol as if there was no Brownian motion in the system the solid particles would eventually settle down and therefore, we can say that Brownian motion plays a huge role in formation as well as stability of sol particles. In a homogeneous mixture Brownian motion is caused by random bombardment between particles of similar kind but in sols it is caused due to collision between particles of dispersed phase and dispersion medium, which in sols is solid and liquid. It can be difficult to distinguish between movement caused by brownian motion and movement caused by other factors.In biology for example ,sometimes an observer needs to tell whether a specimen is moving because it is just motile(can move on its own) or because it is a subject to brownian motion.Most of the times it is extremely easy to differentiate between difference between any other motion and brownian motion because brownian motion is extremely zig-zag and random while a particle which is motile is observed to be moving in a specific direction.Anything that affects the movement of particles in the system affects the rate of brownian motion.For example, Size of particles,Temperature of The surroundings,Number of particles in the system,The viscosity of the solution and so on. With increase in size of particles the rate of brownian motion of the system decreases,similarly is the case with viscosity as it increases the rate of brownian motion decreases.While on the other hand with increase of temperature and and number of particles the rate of brownian motion increases.

Brownian motion also has many applications in physics ,chemistry ,maths and Biology.It is due to brownian motion we are able to explain some of the very key concepts of the subjects mentioned above and Mathematical model of brownian motion is Used in stock markets as it explains randomness which becomes very important concept for describing stocks as their is a randomness in stock markets as well.

Titles of Section


 * History and Definition
 * Brownian motion and coagulation of sols
 * Factors affecting Brownian motion in a sol
 * Brownian motion and size of particles in sols
 * Applications of Brownian motion

History and Definition

Brownian motion, also known as pedesis(means leaping in Greek) in sols is defined as when the particles of dispersed phase and particles of the dispersed medium collide and cause random Zig Zag motion in the whole system, this random motion of sol particles is said to be Brownian motion. Brownian motion is named after Robert Brown who discovered it, initially it was first observed in a colloidal solution of pollen grains and water but still it remained a mystery on the fact how this motion occurred and under what kind of systems we can observe this motion, since we discovered the motion it gave us the above two questions which lasted 68 years. It was Leon Gouy demonstrated convincingly that the irregular motion of suspended particles was not a result of external vibration, temperature, incident light, surface tension, etc: in other words that Brownian motion was indeed a fundamental physical property of fluid otherwise till 1898 it was still being claimed that Brownian movement is caused due to temperature differences between liquid and surroundings in other words till late 1890 Brownian was believed to be caused by an external phenomenon rather than being a fundamental property of a liquid .In the year 1905 Albert Einstein published the solution to a 68-year-old mystery and gave us the explanation of how Brownian motion behaves over time which further opened doors for many other discoveries on this topic .Another great historical importance of this phenomenon was that its explanation and experimental verification could prove that atom exists Einstein assumed that brownian particles are no different from atoms, except that the particles are much bigger in size and display random thermal behaviour which atoms were believed to have.He developed an equation representing the distance wandered by a particle over a time t .This distance depended on a number of factors such as temperature of fluid in which particles are suspended, viscous drag and many other things.Einstein's predictions of wandering distances was verified in a series of experiments by Jean perrin ,which was published in 1912 after which no seriously doubted the existence of atoms.

Brownian motion and coagulation of sols

We can classify colloids on the basis of the phase of  dispersed substance and the dispersion medium, Sols are a type of colloids in which the dispersion phase is solid and the dispersion medium is liquid, For example blood, paint, pigmented ink and so on .For sol particles in colloids are continuously bombarded by the molecules of the dispersion medium which results in the zig-zag random brownian movement, the particle size should be between 1 nanometer to 1 micrometer for it to exhibit Brownian movement. Which in return becomes a key factor to be classified as a sol for examples if we take dispersed medium particle size extremely large the particles might settle down at bottom separating the dispersed phase from dispersed medium that is not the case with sols dispersed phase particles never settle down and thus Brownian motion becomes one of the key properties in identifying a sol.We can further say that brownian motion is a fundamental physical property of the given system rather than being caused by some external factor such as vibration,temperature etc.We can forcefully cause the particles to settle down or in turn seize the random motion by using external factors such as temperature, electricity etc. If we pass electricity through the sol it leads to aggregation of dispersed phase particles hence seizing the random motion causing particles to in turn coagulate the sol causing a forced settlement of the particles of the dispersed phase this technique is highly used for sewage treatments .Brownian motion in sols has a lot of applications in day to day life.For Example in Blood which is type of sol we have RBC cells which transport oxygen through the entire human body using the process of diffusion which is nothing but but brownian motion at macroscopic leve l. Consider two adjacent regions, Region X  and Region Y now region X has twice as many particles as region Y, The probability that the particle will leave region X and enter region Y is twice as much as the probability of particle leaving Y and entering X , due to the completely random nature of brownian motion.This above scenario is the same used by red blood cells to transport oxygen all over the human body using diffusion or Brownian motion at macroscopic level.

Factors affecting Brownian motion in a sol

Any factor that affects movement of particles in the sol would affect Brownian motion. For example, temperature, number of particles, size of particles, viscosity and so on. With increased temperature the rate of Brownian motion also increases as the particles have more kinetic energy than usual as temperature is directly proportional to the kinetic energy of particles which in turn causes more collisions and more random movement in the system hence increasing the rate of Brownian motion. Temperature is also related to the viscosity of the liquid so with increase in temperature the viscosity of the sols decreases and hence as the viscosity of the liquid decreases the kinetic energy of the overall system increases therefore increasing the rate of brownian motion in the sol . It has a similar relationship with the number of particles in the system as the number of particles increase the collision between dispersed phase medium particles increases hence increasing the rate of  Brownian movement in the system. It has an inverse relationship with the size of particles though as we increase the size of particles Brownian motion in the system decreases as the kinetic energy of the system decreases with increase in the mass therefore causing an overall less collision within the system hence decreasing the rate of brownian motion in the overall system. It also shares an inverse relationship with viscosity as increasing the viscosity of the liquid basically means that we are increasing the particle size and hence decreasing the kinetic energy of the overall system causing  a decrease in the rate of brownian movement.

Brownian motion and size of particles in sols

As we already known that Brownian motion decreases when we increase the size of sol particles as the velocity of the atoms decrease due to the increase in particle size and weight hence resulting in a decrease in kinetic energy of the overall system causing a decrease in Brownian motion hence particle size of the dispersed medium has a very large effect on Brownian motion as well as formation of sols .So basically particles of the dispersed medium are larger than the simple molecules you will find but less than what can be seen with the naked eye .The size range of diameter of the particles of the dispersed medium lie from 1 nanometer to 1 micrometer while the size range of diameter of dispersed phase particles lies from 1 nanometer to a 100 nanometer .As we know that brownian motion is an intrinsic property of sols we can say in the above given particle range brownian motion occurs.So for Brownian motion to occur in a particular system the size of particles must be in such a range that motion could be caused due to brownian movement therefore we can say that particle size is very important and is one of the major key factors affecting brownian motion.

Applications  of Brownian motion

Brownian motion is a very simple and significant concept that has applications in many fields and its initial importance was that it supported the modern atomic theory which was a stepping stone for today's modern day science.Mathematical models which described the randomness of brownian motion now apply in many aspects of our daily life though we may not be aware of it .Not only the movement of atoms but anything which has an irregularly movement such as stock markets,identification of images, fingerprint testing,tracking animal genes,computer simulations and the list goes on .Many significant concepts of chemistry, maths and so on are based on brownian motion so it is a very important topic and has a huge number applications in every field.