Introduction to raw materials
Intraocular lens is an important type of material. The research of intraocular lens includes crystal structure, crystal growth, crystal performance and its characterization, crystal material application, etc. Crystal growth research is the foundation of artificial crystal research. Since this century, crystal growth research has made great progress. It has gradually developed from a pure process research into two main directions: crystal preparation technology research and crystal growth theory research. The two mutually infiltrate and promote each other. The research of crystal preparation technology provides a wealth of research objects for the theoretical research of crystal growth, and the research of crystal growth theory tries to reveal the basic laws of crystal growth in essence, and then guide the research of crystal preparation technology.
In recent decades, with the continuous advancement of basic disciplines such as physics, chemistry and preparation technology, the theoretical research of crystal growth has been rapidly developed in terms of research methods, research objects, and research levels. , Has become an independent branch subject. It has developed from the initial study of crystal structure and growth morphology, classical thermodynamic analysis, to the study of the growth interface and additional area melt structure, mass, heat transport and interface reaction at the atomic and molecular level, and has formed many theories or theoretical models. . Of course, due to the diversity of crystal growth technologies and methods and the complexity of the growth process, there is still a considerable distance between the current theoretical research of crystal growth and the practice of crystal growth. People's understanding of the crystal growth process needs to be further deepened. It can be predicted that the future crystals The research on growth theory is bound to have greater development.
The research object of crystal growth theory is the complex objective process of crystal growth. The basic scientific problems of crystal growth theory research can be summarized into the following two aspects: crystal structure, crystal defect, crystal growth morphology, crystal Growth conditions, the relationship between the four. In essence, the study of crystal growth theory is to fully understand the relationship between the internal structure, defects, growth conditions and crystal morphology of different crystals. To understand the relationship between these four, you can predict the growth morphology of crystals with specific crystal structures under different growth conditions in the preparation experiment, and control the generation of internal defects in the crystal by changing the growth conditions, and improve and improve the quality of the crystal. And performance.
Basic process
From a macroscopic point of view, the crystal growth process is a process in which the crystal-environment phase vapor, solution, and melt interface continue to move into the environment phase, which is composed of inclusions The parent phase of the crystal unit changes from a low-order phase to a highly-ordered crystal phase. From a microscopic point of view, the crystal growth process can be regarded as a "primitive" process. The so-called "primitive" refers to the most basic structural unit in the crystallization process. In a broad sense, the "primitive" can be atoms, molecules, or It can be an aggregate of atoms and molecules with a certain geometric configuration. The so-called "primitive" process includes the following main steps:
1. Primitive formation: Under certain growth conditions, substances in the environmental phase interact to dynamically form different structures.
2. Primitives of form: These primitives are constantly moving and transforming into each other, and they appear or disappear at any time.
3. Adsorption of primitives on the growth interface: Due to convection, irregular thermodynamic motion or attraction between atoms, primitives move to the interface and are adsorbed.
4. The movement of primitives on the interface: the primitives migrate and move on the interface due to thermodynamics. The primitives crystallize on the interface or detach from the primitives attached to the interface and undergo a certain movement. , It may crystallize at an appropriate position on the interface and grow into the solid phase, or desorb and return to the environmental phase.
The internal structure of the crystal, environmental phase state and growth conditions will directly affect the "primitive" process of crystal growth. The influence of environmental phases and growth conditions is concentrated in the formation of primitives. The process of adsorption, movement, crystallization or desorption of growth elements with different structures on different crystal plane families is mainly related to the internal structure of the crystal. Crystals with different structures have different growth morphologies. For the same crystal, different growth conditions may produce growth primitives with different structures, and ultimately form crystals of different shapes. The same kind of crystals may have phases with multiple structures, that is, homogenous and heterogeneous bodies. This is also the result of different growth conditions and different "primitive" processes. The formation of defects in the crystal is related to the disturbance of the "primitive" process. Therefore, the establishment of the concept of "primitive" process can describe the relationship between the internal structure, defects, growth conditions and growth morphology of the crystal on a macro or micro level.
Real-time observation
Using advanced technical means, real-time observation of the changes in the crystal surface micro-morphology and overall morphology as well as the fluid movement during the crystal growth process to obtain information about crystal growth. It is another basic way to study crystal growth theory. As early as 1992, optical interferometry was used to observe the lateral movement of the crystal surface layer grown by the vapor phase method. Subsequently, phase contrast and interference phase contrast microscopy were also applied to improve the accuracy of observation. In 1983, using a computer to process images and control the growth conditions, combined with TV video technology, using an optical microscope to observe and record a step movement as small as 10A. In addition, he also observed the crystal growth and dissolution of high-temperature melt and high-temperature solution systems. Recently, Yu Xiling reported the use of holographic phase contrast interference microscopy and laser diffraction techniques to study the growth rate of metastable phase crystals and the mass transport process of the boundary layer. Among them, the hologram record of the boundary layer transport process and the real-time measurement of crystal growth rate by laser diffraction technology. Generally speaking, the scope of real-time observation is limited to certain crystal growth systems under specific conditions, and the application is not extensive.
Development direction
1. Strengthen in-depth research on the environmental structure. A review of the existing theories found that the main reason that the existing theories cannot explain the actual growth process well is the superficial understanding of the environmental phase structure. Without understanding the structure of the environmental phase and the structure of the growth element, it is impossible to have a correct understanding of the influence of external conditions and the structure of the interface. This aspect requires more researchers to explore, such as solutions including room temperature solutions and high temperature solutions. The study of melt structure. Through the study of environmental phase structure,
relevant information about growth primitives can be obtained.
2. Establish a theoretical model that includes external conditions. Based on the study of environmental phase structure, it is very necessary to establish a growth model that can organically include external conditions, because only such a model can describe the influence of crystal structure, environmental phases and growth conditions on the growth primitive process at a micro level. , Thereby revealing the relationship between the internal structure of the crystal, growth conditions and growth morphology, and crystal defects. Anion coordination polyhedral growth primitive model has made a good attempt in this respect, and it needs to be further developed and perfected.
3. Strengthen the intersection and penetration of various disciplines. The development of non-equilibrium growth theory and crystal growth theory require the crossover, penetration and cooperation of various disciplines such as crystallography, physical chemistry, statistical physics, fluid mechanics, heat transfer, solid physics, crystal chemistry and so on. Because the crystal growth process is a non-equilibrium process, the application of non-equilibrium thermodynamics and statistical physics will be a very promising development direction method, and it has a good application prospect in this respect.
4. Develop experimental technology to realize the visualization of crystal growth process. No matter what kind of growth theory, it needs experimental verification in the end. The development of experimental observation technology to visualize the growth process is the ultimate goal of crystal growth experimental technology and an inevitable development direction. At present, efforts should be made to expand the observable growth system and improve the accuracy of observation.