semipermeabeli

Semipermeabeli, typically written semipermeable, describes a barrier that allows certain substances to diffuse through while blocking others. In physiology and materials science, semipermeable membranes enable selective transport. The concept is essential to osmosis and dialysis and to many filtration processes. The term combines Latin semi- "half" and permeare "to pass through". In practice, a semipermeable membrane might be more permeable to solvent molecules such as water than to solute particles such as ions or polymers.

Mechanisms: Permeability depends on molecular size, charge, polarity, and the chemical nature of the membrane. Small, nonpolar molecules often pass readily by passive diffusion, while larger or charged solutes require channels, carriers, or pores. Water can move through membranes via diffusion or via specialized channels called aquaporins. The movement of solvent across a semipermeable membrane toward higher solute concentration is osmosis; the diffusion of solute through pores is filtration/diffusion depending on gradient and membrane properties.

Biological examples: Cell membranes are inherently semipermeable, balancing ion homeostasis and nutrient uptake. In plant cells, turgor pressure relies on water movement across semipermeable membranes. In medicine, dialysis membranes selectively remove waste solutes from blood.

Artificial membranes: In water treatment, reverse osmosis and nanofiltration use dense semipermeable barriers to block salts while letting water through. In medical devices, dialysis machines use semipermeable membranes to separate small molecules from larger proteins. Material types include cellulose derivatives, polyamides, polysulfones, and thin-film composites; pore size, surface charge, and fouling resistance govern performance.

Limitations and considerations: Trade-offs exist between permeability and selectivity. Fouling, concentration polarization, and energy requirements affect efficiency. Advances focus on improving selectivity and longevity while reducing cost and energy use.