Research On The Formation Mechanism And Application Of Organic Small Molecule Spherulites

Spherulite is radially polycrystalline aggregates with an outer spherical envelope.Many kinds of crystalline material can form spherulites.The crystalline products of organic small molecule materials play very important roles in human society,and it is known to all that the morphology of crystals can have significate effect on the properties of materials.However,currently,there are only few studies on the spherulites of small organic molecules.Therefore,systematic study on the formation process and mechanism of organic small molecular spherulites is meaningful because it can not only improve the understanding on this unique morphology,but also can be helpful to find the application potential of spherulites in the field of industrial crystallization.Systematic study on the microstructure,growth and formation mechanism spherulites of several kinds of organic small molecule materials,especially L-tryptophan,was carried out in this work.In this study,optical microscope,scanning electron microscope(SEM)and atomic force microscope(AFM)were used to characterize the morphology and microstructure of spherulites of six different kinds of organic small molecule materials.Based on the qualitative analysis on the characteristic of spherulitic growth,it seems that the materials which normally form small size plate-like or needle-like crystals would be easier to be prepared as spherulites,and it is reasonable to conclude that there is a relationship between the spherulitic pattern of material and its crystal structure.Compact spherulites of L-tryptophan were produced in droplet system in the presence of trace amount of additive which plays a significate role in the formation of spherulites.Hot stage polarizing optical microscopy(POM)was used for the in situ observation and collection of the spherulitic growth kinetics data in droplet system.A new population-based model was proposed to model the spherulitic growth of Ltryptophan.It was revealed that the spherulitic growth of L-tryptophan is interface kinetics controlled.The influence of the additives on the solid-liquid equilibrium of L-tryptophan in water was investigated by static method.Focused beam reflectance measurement(FBRM)technology was used to measure the induction period of L-tryptophan under different condition.It was found that trace amount of additives have strong inhibition effect on the nucleation process of L-tryptophan.The characteristic parameters of nucleation process were calculated based on classical nucleation theory.L-tryptophan took on continuous growth in all the situations discussed in this work.According to the experimental results,the “Side Faces Nucleation” hypothesis was proposed to explain the formation mechanism of spherulites.PVP and gelatin were found to be very effective in terms of introducing the spherulitic growth of L-tryptophan.The influence of 11 different kinds of additives on the morphology of L-tryptophan was investigated in lab scale cooling crystallization system.Besides,the effect of operation conditions on the morphology,particle size,size distribution of the spherulitic products were investigated in detail.The experimental results could fit very well with the prediction of the “Side Faces Nucleation” hypothesis.Based on the experimental data and theoretical hypothesis,the spherulitic crystallization technology for L-tryptophan was developed,and spherulitic particles with controllable size and better powder propertied were produced by this new technology.Furthermore,the spherulitic crystallization technology was generalized to L-malic acid which was formed as spherulitic particles with better flowability.Since different crystal structures of the same material can result in different spherulitic pattern,a new form of DDT,Form II,was discovered.At the same time,optical microscope and AFM were used to study the transformation process of Form II by tracking the change in the spherulitic pattern.New polymorph of resorcinol,? form,was discovered right after the observation of appearance of new spherulitic pattern.Through a combination of high-resolution synchrotron powder diffraction data and by computational crystal structure prediction algorithms,the crystal structure was solved and the stability of this form was analyzed.According to these two cases,it can be suggested that it's a simple,convenient,high sensitive way to discover the new polymorph of important organic small molecule materials by the polymorph dependent spherulitic pattern.