(140c) Accurate Nucleation Rate Measurement of Pnipam Colloidal Crystals

Even though the nucleation of crystalline materials is extensively studied, partly due to the limitations of experimental evidence, many aspects such as the kinetics of nucleation and the discrepancy between simulations and experimental data remain under hot debate. Colloidal suspensions, are not only very good model systems for atomic matters, but will also contribute to a better understanding of important biological materials, such as DNA or proteins, and help advance bioengineering, food sciences and medical fields.

In this project, emulsion droplets containing gel particles of a thermo-responsive polymer, poly-N-isopropylacrylamide (PNIPAM), were used as an experimental model system for the study of nucleation. The colloidal suspensions are injected into a microfluidic flow-focusing device to fabricate suspension droplets in oil. Using independent droplets, we can isolate the interactions between crystallites. Also, emulsion crystallization is proved to be capable of eliminating heterogeneous crystallization in atomic systems. Therefore, we are able to carry accurate measurements of the nucleation rate of colloidal crystals. Temperature was used to fine-tune the volume fraction of the PNIPAM suspensions. The droplet sizes were varied with flow rates in microfluidic emulsification to tune the nucleation volume. Measurements of UV-Vis spectroscopy, light scattering and polarized microscopy offer complimentary information of crystallization from reciprocal space (UV-Vis and light scattering) and real space (polarized microscopy).