p H -adaptive microlenses using pinned liquid-liquid interfaces actuated by pH-responsive hydrogel

The authors report on variable-focus liquid microlenses self-adaptive to environmental pH. The microlens is formed via a water-oil interface stably pinned at a hydrophobic-hydrophilic contact line along an aperture in a flexible slip. A set of hydrogel microposts is photopatterned in a microfluidic chamber around the aperture; the microposts autonomously respond to the environmental pH variation by expanding or contracting, thus deforming the aperture slip and tuning the curvature of the water-oil interface and the focal length of the microlens. A single microlens has a tunable focal length from −7.6mm to −∞ (divergent) and from 8.5mm to +∞ (convergent).