This activates the ionic functionality of the polymer, causing
the polymer to swell through charge repulsion (hydrodynamic
volume expansion). Controlled hydrophobic association occurs
via the combination of semi-hydrophobic and hydrophobic side
chains at specific sites. Acidic ingredients used in personal care
products (such as lactic, glycolic, salicylic, fruit acids and low pH
salts) can serve both as active agents and acid swelling agents
for the polymer to achieve the desired viscosity.