Hydrofiliisyyttä

Hydrofiliisyyttä, or hydrophilicity, refers to the affinity of a substance for water. Compounds or surfaces that are hydrophilic can attract and absorb water molecules through various interactions such as hydrogen bonding, dipole–dipole interactions, or Van der Waals forces. This property is distinct from hydrofobicity, where materials repel water.

In chemistry, hydrophilic molecules are typically polar or ionic. Common examples include sugars, alcohols, and many salts. Their solubility in water is often high, which is crucial in biological systems where solutes must remain in aqueous environments. Hydrophilic surfaces, such as those coated with polyethylene glycol or treated with plasma, exhibit low water contact angles—generally below 90 degrees—indicating strong wetting behavior. These surfaces are widely employed to reduce protein adsorption in medical implants or to enhance adhesion in adhesives.

Measurement of hydrophilicity commonly involves the contact angle goniometer, which assesses how a water droplet spreads on a surface. The contact angle coefficient is derived from the Young equation, accounting for the solid–liquid, liquid–vapor, and solid–vapor interfacial tensions. In bulk materials, water uptake or swelling tests provide quantitative data about the degree of water absorption.

Applications that rely on hydrophilic characteristics include filtration membranes, where hydrophilic pores allow selective passage of water while rejecting oils; coatings for anti-fogging surfaces; and in agriculture, where hydrophilic fertilizers promote efficient water delivery to plant roots. Hydrophilicity also plays a role in environmental remediation, enabling the capture of hydrophilic contaminants by polymeric sorbents.