Colloids

On the basis of the diffusion rate of liquid and solution through the animal membrane, they can be two types; Crystalloid and colloids.  Those substances which can obtained in the crystalline form are easily dissolved and diffuse through the membrane are termed as crystalloid. For example; sugar, urea and salt.
While substances like starch, gum etc cannot diffused through the membrane easily are termed known as colloids.
It is well known, that solutions are homogenous systems while suspensions are heterogeneous systems, i.e., they consist of more than one phase. In between the extremes of suspensions and solutions lies the colloidal system.
Colloids appear homogenous like a solution, but they consist of comparatively large particles of one substance dispersed throughout another substance (dispersion medium). The essential difference between a solution and a colloid is one of particle size.
1) In a solution, the particles are ions or small molecules.
2) In a colloidal system, the dispersed phase may consist of particles of a single macromolecule or an aggregate of many atoms, ions or molecules. Although colloidal particles are larger than simple molecules, they are small enough to remain suspended. Colloidal particle sizes range from about 10Ao to about 1000 Ao i.e., 1nm to 1000 nm.It is well known, that solutions are homogenous systems while suspensions are heterogeneous systems, i.e., they consist of more than one phase. In between the extremes of suspensions and solutions lies the colloidal system.

Colloids appear homogenous like a solution, but they consist of comparatively large particles of one substance dispersed throughout another substance (dispersion medium). The essential difference between a solution and a colloid is one of particle size.

1) In a solution, the particles are ions or small molecules.

2) In a colloidal system, the dispersed phase may consist of particles of a single macromolecule or an aggregate of many atoms, ions or molecules. Although colloidal particles are larger than simple molecules, they are small enough to remain suspended. Colloidal particle sizes range from about 10A^o to about 1000 A^o i.e., 1nm to 1000 nm.

Colloidal state is the state of matter in which the size of constituent particles is in between 1 to 1000 nm, because of that they can pass through a normal filter paper but cannot pass through the animal or vegetable member.
The non-diffusibility of colloids compare to true solution is due to difference in particle size. Since the constituent particles are bigger compare to true solution, hence they cannot pass through membrane.
On the hand the particles in colloids are smaller than the particle present in a suspension; hence they cannot precipitate like suspension. The main difference between true solution, colloids and suspension is as follow;








 Table: Difference between true solution, colloids and suspension The colloids can be differentiating from true solution and suspension by using their different properties. But the difference in properties is because of their constituent particles only. If the particles present in any solution are very small, they can easily pass through filter paper as well as any membrane just like true solution. But if the particles are big enough, they cannot pass through any membrane and filter paper as in suspension. If the particle size in intermediate in between these two extremes, they make colloids. The colloidal particles size is in the range of 1-1000 nm, so they can pass through the filter paper and but cannot pass through the animal membrane or vegetable membrane. While the particles size of true solution is less than 10^-9 meter or 1 nm so particles can be pass through filter paper as well as any membrane.
In case of suspension, the particles are bigger than 10^-9 m, hence they settle down at the bottom of beaker and separate as a residue on filter paper. As we know, in a normal solution, there is a substance dissolved in another substance. The substance which present in small amount is known as solute and another is termed as solvent. Hence a solute dissolved in solvent to make a
solution. In the same way in colloids, the solute term represented by dispersed phase and solvent by dispersion medium. Hence colloids are also termed as colloidal solution or colloidal suspension.
There are different ways to classify colloids. Colloids can be classified on the basis of;
a.    Based on physical state of dispersed phase and dispersion medium.
b.    Based on the nature of interaction between both phases.
c.    Based on the type of particles of the dispersed phase.
 
a. Based on physical state of dispersed phase and dispersion medium:  Out of three physical states, dispersed phase
and dispersion can be any one. Hence there are eight possible combinations of these three states of matter and each type of colloid named as a certain type of colloid.





 b. Based on the nature of interaction between both phases:
On the basis of interaction between both phase and medium, colloids can be two types;
(i) Lyophilic colloids: In such type of colloids there is an affinity between dispersion phase and dispersion medium. For example; gum, starch etc when mixed with dispersion medium like water, they directly form colloidal sol. This sol is also called as colloidal sol or lyophilic sol. If water is present as a dispersion medium it termed as
hydrophilic sol. Lyophilic sol are reversible on nature i.e. precipitate can remix and convert to colloidal again. For such type of sol the viscosity is very high and surface tension is low. Lyophilic sols are quite stable due to affinity between dispersion phase and dispersion medium, hence not easily coagulated.
(ii) Lyophobic colloids: when there is no affinity between dispersion phase and dispersion medium, we cannot prepare sol by simple mixing but certain preparation methods required for that. Such type of colloids
are termed as lyophobic colloids and if the medium is water than called as hydrophobic colloids.
Since they do not have affinity between phase and medium, hence they are unstable and easily coagulated. They
are irreversible in nature and cannot reform after precipitation. When a dispersion phase added to dispersion medium to form lyophobic colloid, there will be no change in viscosity as well as surface tension. For example; when substance like metal sulphide mixed with dispersion medium, they form lyophobic colloids. If the dispersion medium is water, they called as hydrophobic colloids.
c) Based on the type of particles of the dispersed phase:
Third type of classification based on the range of [particle size of dispersed phase in given colloids. On the
basis of particle size, colloids can be three types;
 (i) Multimolecular colloids: When a large number of small particles (dispersion phase) aggregate to form a large
size molecule or particle having the size in the colloidal range, it known as  Multimolecular colloids. Here the atoms or particles are held together by weak van der walls force of attraction.  For example; gold sol contains particles of various sizes having several atoms. Another example is sulpher sol.
(ii)Macromolecular colloids:   In such type of colloid there are macromolecules like polymers acts as dispersion medium. These macromolecules when dissolved in suitable dispersion medium, they form a solution in which the molecules of substances i.e. the dispersion phase have size in the colloidal range. Polymers like starch, proteins, cellulose are formed such type of colloids. These colloidal solutions are quite stable and resemble to the true solutions in many respects.
(iii) Associated colloids: These colloidal solutions are also known as Micelles. In these colloids, when a dispersion
phase dissolved in dispersion medium at low concentration, they behave as normal strong electrolyte. But as the concentration increases, they show colloidal state properties due to the formation of large particles which are
aggregates of small particles present in solution. At high concentration, the van der wall force of attraction is strong between dispersion phase and dispersion medium. These aggregate particles called as micelles and the temperature associated with the formation of micelles is called as kraft temperature (Tk). The concentration at which the micelles formation starts is called as critical micelle concentration (CMC). The best example of associated
colloids is soap and synthetic detergents in water. Different examples of colloids are as follow;


Purest colloids are the finest colloidal products with the highest level of effectiveness by using colloidal silver or other colloidal metals. Purest colloids are called as mesocolloids.
These colloids consist mesoparticles in which have a large surface area compare to that colloids produced by other method. The process to develop mesoparticles is known as mesoprocess. In meso process; at constant concentration of metal particles, as the particles decreases, the particle surface area increases. With increasing the surface
area, the chemical reactivity of particles increases as more surface will be included in reactions. Hence with increasing the surface area of particles, the effectiveness of colloidal solution increases.  The surface area of particles is written as cm²/mL and expressed in cm² /mL. The colloids with high purity are produced by using mesoprocess. In this process
the metal is converting into a form of its individual atoms which further convert in particles consisting of nine atoms each.
These particles dissolved uniformly in pure deionized water to produce a colloidal suspension. Due to small negative electric charge imparted to each particle which is known as zeta potential, particles remain suspended in water
indefinitely. Hence there is no need to add any binder or additive to maintain the stability of mesocolloids. They are simply pure water and pure metal.
For example; a colloidal solution of silver =contains two different forms; silver nanoparticles and silver ions.
In meso silver there is 80% mesoparticles and 20% silver ions, hence the total silver concentration becomes 20%.






                                                            
                                                                              Fig: Purest Colloids: Meso silver
There are many types of purest colloids produced by using mesoprocess, like;
a)   Meso silver
b)   Meso gold
c)   Meso copper
d)   Meso platinum
e)   Meso palladium
f)    Meso iridium
g)   Meso titanium
h)   Meso zinc The main difference between crystalloid and colloids is their ability to diffuse through the membrane. Crystalloids passed
through the filter paper as well as through the animal membrane while colloids cannot pass through animal and vegetable membrane due to large particle size. The same concept is applicable in intravenous fluid also which exists in between venous. This fluid can be classified on the basis of their ability to cross the membrane or barriers which separate
different body fluid compartments like between intravascular and extravascular (interstitial) fluid compartments. 
Since colloidal particles are large enough for passing the diffusion barrier , they infused in to the vascular space and show
a great tendency to stay in intravascular space to enhance the plasma volume compare to any crystalloid.
For example; with 5% albulmin which is a colloid fluid, the plasma expansion is nearly twice compare to the equivalent
volume of isotonic saline. The large solute particles which cannot move freely across barriers between fluid compartments can create a force which draws water into the large solute compartment.  This force which works opposite to the hydrostatic pressure is known as the colloid osmotic pressure (COP) or oncotic pressure.  The ability of each colloid fluid to expand the plasma volume is directly proportional to the colloid osmotic pressure COP. Hence the higher magnitude of colloid osmotic pressure, the volume expansion will be high. The colloid osmotic pressure of plasma is 25 mm Hg. If the oncotic pressure of a colloid fluid is greater
than the oncotic pressure of plasma, the plasma volume expansion exceeds the infused volume.
For example;25% albumin solution has oncotic pressure of 70 mm Hg and a plasma volume expansion is 4 to 5 times than the infused volume. The other examples of colloid fluids are hetastarch (A synthetic colloid available as a 6% solution in isotonic saline) , pentastarch ( Low-molecular-weight-derivative of hetastarch) and dextrans ( Glucose polymers produced by a bacterium incubated in a sucrose medium).