Polymerization in Droplet of Aqueous Solution of PEGDA/Irgacure at Various Concentrations of Components

The authors experimentally studied the behavior of evaporation, convection in the liquid, and temperature of the free surface of a pendant droplet of aqueous solution of PEGDA/Irgacure 2959 before and after the onset of polymerization under UV radiation. Data on the temperature of the free surface of droplet were obtained for a wide range of the initial concentration of the polymer base \(C_{0}\). For \(C_{0}= 35\)% and less, no polymerization area was observed (according to thermal images). The temperature gradients observed over the droplet surface were very low (less than 0.3°C). At \(C_{0}= 65\)% and \(C_{0}= 90\)%, the average temperature \(T_{\rm S}\) on the free surface of droplet changed during polymerization by 2.8C° and 3.7°C, respectively. After polymerization, \(T_{\rm S}\) for the hydrogel became higher than \(T_{\rm S }\) of droplet of pure water. The average velocity of motion of polyamide particles \(U_{C}\) for water was 2.2–2.4 times higher than that for the PEGDA solution with the initial concentration \(C_{0} = 65\)%, which is associated with the higher viscosity of the solution. At the onset of polymerization, the velocity \(U_{C}\)dropped to 0 mm/s in a very short time. With increase in the concentration \(C_{0}\) in the pre-polymer, the time of polymerization reaction start decreased significantly, which shortened the time in which the particles stopped completely. Different limiting factors govern evaporation of a water droplet and a hydrogel droplet. The evaporation rate of droplet of hydrogel decreased with time due to the porous structure of the hydrogel.