Research On The Non-classical Crystallization Of Inorganic Substances And The Effect Of Oligomer Additives

Crystallization of inorganic substances has always occupied an important position in many research fields such as geochemistry,biology,chemical industry,and materials.Alt-hough there is a relatively complete classical theoretical system for the study of crystal nu-cleation and growth processes,more and more studies have observed inorganic crystalliza-tion phenomena that are difficult to be explained by classical crystallization theories.The study of the non-classical crystallization process of inorganic materials is of great signifi-cance for optimizing the physicochemical properties of inorganic products by regulating the size,morphology,crystallinity and aggregation state of inorganic particles.Oligomer addi-tives have the advantages of both small（simple structure,easy to dissolve）and polymer（synergistic effect between adjacent groups,the ability to self-assemble into hierarchical structures）molecules,which have shown a significant impact on the crystallization of inor-ganic substances.Therefore,it is of great significance to study the mechanism of non-clas-sical crystallization of inorganic substances and the effect of oligomer additives.In this paper,Li₂CO₃ and Si O₂ with typical amorphous nucleation behavior,Na₂CO₃?1.5H₂O₂ with typical non-crystallographic branching growth behavior,and ZnO with typical particle attachment growth behavior were selected as model substances.The effects of external environmental factors and sodium hexametaphosphate or oligomeric pep-toids on their non-classical crystallization processes and morphologies were investigated.The main contents of this paper are as follows:（1）For the non-classical nucleation behavior of amorphous homogeneous nucleation,Li₂CO₃ was selected as a model material.For the first time,in situ experiment showed a morphological evolution from aggregate of amorphous precursors to pseudo-3-fold hexa-gram morphology during the early stage of Li₂CO₃ nucleation.Based on the result,it was proposed that the crystal agglomeration of Li₂CO₃mainly resulted from the formation of amorphous precursors during nucleation.The spherulites and needle-like crystals in the product were separated by knocking experiments that were designed for the first time as far as we know,and the mass percentage of spherulites in the product was used to quantify the degree of agglomeration.The effects of supersaturation,stirring rate,seed crystals and so-dium hexametaphosphate on the degree of product agglomeration were further investigated.The Li₂CO₃ amorphous precursor was suppressed by reducing supersaturation or adding seeds to obtain a product that was substantially free of coalescence.A 100%agglomerated product was obtained by adding sodium hexametaphosphate.（2）A series of oligomer peptoid fibers were designed according to the characteristics of non-classical nucleation of amorphous Si O₂,and the mechanism of amorphous heteroge-neous nucleation of Si O₂ on the surface of these fibers was studied.These peptoid fibers were self-assembled from the amphiphilic peptoids with the same hydroohobic but different hydrophilic dimains.The peptoid-peptoid and peptoid-silica interactions could be pro-grammed by changing the arrangement and number of amino and carboxyl groups in the peptoid hydrophilic domains,which further influenced the peptoid self-assembly and silic-ification on the fiber surface.The alternate arrangement of carboxyl and amino groups could effectively improve the self-assembly efficiency of peptoid fibers in neutral aqueous solu-tion.The results from silica mineralization experiment and molecular dynamics simulation indicate that amino groups on the fiber surface play a key role in inducing the heterogeneous nucleation of amorphous Si O₂.（3）Non-crystallographic branching growth often occurred during the growth of Na₂CO₃?1.5H₂O₂ crystals.For the first time,the results from process analysis of particle size and morphology during the crystallization of Na₂CO₃?1.5H₂O₂demonstrated that the crystal agglomeration of Na₂CO₃?1.5H₂O₂ primarily resulted from non-crystallographic branching growth.The results from growth kinetics analysis indicated a critical growth rate during the growth of Na₂CO₃?1.5H₂O₂and the crystal with growth rate higher than the crit-ical growth rate could show non-crystallographic branching behavior.Moreover,It was found that sodium hexametaphosphate could promote the branching of Na₂CO₃?1.5H₂O₂which makes it possible to produce compact SPC spherulite product.（4）For the non-classical growth behavior of particle attachment,ZnO was shosen as a model material.ZnO mesocrystal composed of ZnO nanoflakes could be observed in the blank control experiment.The size of ZnO particles increased with higher initial Zn²⁺con-centration,which is a typical characteristic of growth by particle attachment.Four kinds of ZnO one or two-dimensional nanostructures with different thicknesses were induced by the oligomeric peptoids with different hydrophilic/hydrophobic arrangements and monomer types.The relationship between the hydrophobicity of the peptoids and the thickness of resultant ZnO nanomaterials was investigated,which shows a positive correlation.