Surfactants and Their Properties

SURFACTANTS

• Surfactants are molecules that reduce the surface tension of liquids. This is also known as a surface active agent.
• Common surfactants have a water-soluble (hydrophilic) end and a water-insoluble (hydrophobic) end.
• The hydrophilic end is strongly attracted to water, while the hydrophobic end is attracted to oily liquids.
• Many surfactants appear in nature and are generated in laboratories.

EFFECT OF SURFACTANTS IN WATER

• When surfactants are added to water, they align with the hydrophobic end pointing outward away from the water.
• This alignment disrupts the surface structure of water, decreasing surface tension.
• A small concentration of surfactant can reduce water's surface tension from 73 dyn/cm to 30 dyn/cm.

TYPES OF SURFACTANTS

• Surfactants can be categorized as non-ionic, anionic, cationic, or amphoteric.
• These categories differ in the chemical makeup of their hydrophilic end.

SURFACTANTS IN OILY LIQUIDS

• In oily liquids, surfactants align with the hydrophilic end pointing outward away from the oil.
• This alignment leads to a reduction in the oil's surface tension.
• Soaps and detergents use surfactants. The hydrophobic end dissolves into oily substances and the hydrophilic end is exposed to water, cleaning the oily substance.

REFRACTION (OPTICS)

• Refraction is the bending of a wave as it passes from one medium to another where its speed is different.
• Light bends towards the normal when crossing from a fast medium to a slow medium. The amount of bending depends on the index of refraction of both media.
• Snell's Law governs the relationship between refractive index and angles of incidence and refraction.

LAWS OF REFRACTION

• Incident ray, refracted ray, and the normal at the point of incidence all lie in the same plane.
• Snell's Law: n₁ sin θ₁ = n₂ sin θ₂ , where n₁ and n₂ are the refractive indices of the first and second media, respectively, and θ₁ and θ₂ are the angles of incidence and refraction.

INDEX OF REFRACTION

• The index of refraction (n) is the ratio of the speed of light in a vacuum to the speed of light in a medium.
• Air, water, glass, and diamond have different values for their refractive index.
• The higher the index of refraction, the more light bends entering the medium.

CRITICAL ANGLE AND TOTAL INTERNAL REFLECTION

• The critical angle is the minimum angle of incidence at which light, travelling from a higher refractive index medium to a lower one, is refracted along the boundary instead of passing into the second medium.
• Total internal reflection occurs when the angle of incidence exceeds the critical angle, resulting in all light reflecting back into the first medium.

BRIX REFRACTOMETERS

• Brix refractometers measure sugar concentration in a sucrose solution, often provided as percent by mass.
• Specific gravity is also a way to quantify the amount of sugar in a liquid.

FUNDAMENTALS OF OPTICS IN BIOPHYSICS

• Optics is the branch of physics investigating light behavior and properties.
• Light exhibits wave-particle duality (both wave-like and particle-like behavior).
• Lenses are optical devices that manipulate light to create images.

TYPES OF LENSES

• Convex lenses converge light rays to a focal point, used to magnify small objects.
• Concave lenses diverge light rays, creating virtual images that appear smaller than the object, often used in eyeglasses.

IMAGE FORMATION BY THIN LENSES

• Object distance (d₀), image distance (dᵢ), focal length (f), and height of object (h₀) and height of image (hᵢ) are important variables in image formation analysis. Equations relating these variables exist ( Thin Lens Equations ).
• Converging lenses can produce real or virtual images depending on the object's position relative to the focal point.
• The image formed is farther away on the same side of the lens as the object. It is called a virtual image and cannot be projected.

MAGNIFICATION

• Magnification is the ratio of image size to object size. A magnification greater than 1 means the image is larger than the object.
• Linear magnification (M) is given by M = hᵢ/h₀ = dᵢ/d₀.

MICROSCOPY TECHNIQUES IN BIOPHYSICS

• Microscopy is a crucial technique in biophysics for visualizing biological samples.
• Different microscopy techniques including brightfield, phase contrast, fluorescence, and confocal microscopy are used to visualize samples at various levels, including cellular and molecular.

APPLICATIONS OF OPTICS IN BIOPHYSICS

• Optic principles, lenses, and microscopes are essential in biophysics to investigate diverse processes such as cell biology, medical diagnostics, or biological research involving particles and dynamics.