•Process: electrospraying in carbon dioxide-expanded antisolvent.•Phenomenon: product morphology change with pressure.•Mechanism: interplay of solvent extraction with polymer plasticization.•Calculation: Peclet number.To prepare polymer particle and microporous membrane, for the first time carbon dioxide-expanded antisolvent is proposed as a new atmosphere with tunable properties for electrospraying, which offers an opportunity of control over the product morphology by manipulating the operating pressure. The electrospraying of PLGA solution in acetone was conducted in different atmospheres including ambient air, ambient hexane, high-pressure carbon dioxide, and in carbon dioxide-expanded hexane, respectively. The product morphology is characterized by scanning electron microscope (SEM) and the morphological evolution mechanisms upon interplay of solvent extraction and polymer plasticization are presented. Finally, the Peclet number of the electrospraying in different atmospheres were estimated and related to product morphology.