Biophysics II: Colloids, Properties, and States

Biophysics II

Colloids

Colloids are suspensions of very small particles (micelles), even much larger than the dispersed molecules within a liquid. They are also called pseudo-solutions or colloidal solutions.

State of Sol and Gel

Protoplasmic colloids undergo sol-gel processing, also called reversal or phase change. Colloids present an intermediate state between solid, liquid, and gas. States in the protoplasm of sol and gel usually alternate due to changes in concentration. The most important sols in biology are protein dispersions in water.

Types of Colloids According to the Physical State of the Phases

The dispersant phase can be a solid, liquid, or gas, just as the dispersed phase may be liquid, solid, or gaseous. The passage from a sol to a gel is called peptization, and passing from a sol to a gel is called gelation or flocculation.

Properties of Colloids in the Sol State

• Tyndall Effect: The passage of a light ray beam through a solution. The beam is visible in a colloidal solution.
• Brownian Movement: The continuous, irregular movement in all directions seen under the impact or shock of the dispersing phase, which is in continuous stirring.
• Dialysis: The diffusion of solute through a differentially permeable membrane.
• Electrophoresis: A physical phenomenon by which one can identify the electrical charges of the colloid micelles. Electrodes are introduced into the solution, some will be directed to a cathode and others to an anode.

Protoplasmic Colloids

These are divided into two types:

• Lyophilic: Named for their affinity for the dispersing phase. In the protoplasm, this is water, so they are also called hydrophilic. Carbohydrates, lipids, and proteins belong to this group and are reversible.
• Lyophobic: Also called hydrophobic, their micelles have no affinity for water as a solvent and are irreversible.

Properties in the Area

The surface presents a lot of living matter because of the division of body cells and the subsequent division of cellular substances into formations that also have a surface.

a) Surface Tension: When two substances in contact cannot be mixed, they have surfaces, and each one is a separate phase.

b) Adsorption: This is the accumulation of one class of molecules on the particle surface of another class. We must distinguish adsorption from absorption because while adsorption refers to the forces of the surface, absorption is related to capillary forces. Example: Water is absorbed by a sponge.