| Colloidal crystals are typical soft matter systems, which are often used as modelsystems for the study of crystal nucleation and growth process. The Ostwald’s steprule, as a classic rule for the crystalization process, has been confirmed in numerousexperiments in atomic and molecular systems. However, its applicability in colloidalcrystallization has not been confirmed until recently in dilute solution. The study ofthe crystallization process of the colloidals particles at higher concentrations will behelpful for further investigating the universality of the rule, and for deepening theunderstanding of crystallization process, which will provide a theoretical basis forcontrolling the growth of colloidal crystals. Besides, the shear modulus which is oneof the very important properties of colloidal crystals, has also attracted much attention.However, the influences of internal voids, interparticle distance, etc. on shear modulusare still not very clear. Aiming at these problems, we focused on the crystallizationprocess at high concentrations and factors influencing the shear modulus of colloidalcrystals in this paper. And the main works are summarized in the following aspects:(1) Synthesized a series of polystyrene (PS) microspheres, by one-step and two-stageemulsion polymerization method respectively, and made a detail preliminarycharacterization of the size and surface charge.(2) Investigated the crystallization process of colloidal particles at highconcentrations, in order to verify the universality of the Ostwald’s step rule.Reflection spectra were used to monitor the crystallization process. The peak intensity,the crystal growth rate, and crystal parameters, etc. were analyzed from the measuredreflection spectra. We found that the proportion and lifetime of metastable statedecreases with volume fraction increased, until the metastable state becomes notobservable. In addition, a theoretical model was proposed to explain the experimentalphenomena. Experimental and analytical results show that, Ostwald’s step rule isuniversal for the crystallization process of colloidal crystals, the relative transitionspeed of liquid-metastable and metastable-stable determines whether the metastablestate is measurable. For those systems in which the metastable state in crystallization process have not been observed, it is probably because the transition of metastable–stable is too fast.(3) Torsional resonance spectroscopy was used to measure the shear modulus ofcolloidal crystals formed by different particles. By this means, we analyzed the affectof particle size, internal voids, etc. on shear modulus of colloidal crystals. It wasfound that, the shear modulus increases with volume fraction for crystal formed by thesame colloidal particles. For crystals formed by different colloidal particles, eventhough the parameters are different, the shear moduli are roughly the same if theirnearest interparticle distance is close. Further analysis shows that the main factorinfluencing the shear modulus is the nearest interparticle distance, which is consistentwith the experimental results. This finding is of great significance for understandingthe microscopic mechanism of macroscopic shear modulus. |
