What is nanomaterial?
Introduction: The nano concept is 1959, and the Nobel Prize was presented by Richard Feynman in a speech. In his “There is plenty of room at the bottom” speech, he mentioned that humans can make machines smaller than their size with macroscopic machines, and this smaller machine can make smaller machines, thus achieving molecular scale step by step. That is, the production equipment is reduced step by step, and finally the atoms are arranged directly according to the wishes, and the products are manufactured. He predicted that chemistry would become a technical problem of accurately placing atoms one by one according to the wishes of human beings. This is the earliest idea with modern nano concepts. In the late 1980s and early 1990s, an important tool for characterizing nanometer scales, scanning tunneling microscopy (STM), and atomic force microscopy (AFM), a direct tool for understanding nanoscale and nanoworld materials, has greatly facilitated On the scale of understanding the structure of matter and the relationship between structure and nature, nanotechnology terminology emerged and nanotechnology was formed.
In fact, nano is just a unit of length, 1 nanometer (nm) = 10 and negative 3 times square micron = 10 and negative 6th power millimeter (mm) = 10 and minus 9 times square meters (m) = l0A. Nanoscience and Technology (Nano-ST) is a science and technology that studies the laws and interactions of systems consisting of substances between 1-100 nm in size and possible technical problems in practical applications.
1 nanometer material characteristics
Nano is a unit of measurement, 1 nm is a millionth of a millimeter, that is, 1 nanometer, that is, a billionth of a meter, and an atom is about 0 1 nm. Nanomaterials are a new type of ultra-fine solid material composed of nanoparticles, which are from 1 to 100 nm in size. Nanotechnology is the study and study of substances and materials on tiny structures below 100 nm, that is, the science and technology of making substances with a single atom or molecule.
Nanoparticles are atomic groups or groups of molecules consisting of a small number of atoms and molecules. The surface of a large proportion is originally an amorphous layer with neither long procedures nor short procedures: inside the particles, there is a well-crystallized layer. Periodically arranged atoms, but their structure is different from the completely long program structure of the crystal sample. It is this special structure of nanoparticles that leads to the singular surface effects, small size effects, quantum size effects, quantum tunneling effects of nanoparticles, and thus the physical and chemical properties of many nanomaterials different from conventional materials.
1.1 Surface and interface effects
The surface effect of the nanomaterial, that is, the ratio of the atomic to total atomic number of the nanoparticle increases with the decrease of the size of the nanoparticle, and the surface energy and surface tension of the particle also increase, which causes the change of the properties of the nanometer. For example, the specific surface area of SiC with a particle size of 5 nm is as high as 300 /12/g; while the surface area of nano-tin oxide varies more with particle size, and the specific surface area at 10 lltlfl is 90.3 m2/g, compared with 5 nm. The surface area increased to 181 m2/g, and when the particle size was less than 2 nm, the specific surface area jumped to 450 m2/g. Such a large specific surface area greatly increases the number of atoms at the surface. The crystal field environment and binding energy of these attacking atoms are different from those of internal atoms. There are a large number of defects and many dangling bonds, which have high unsaturated properties, which makes these atoms easy to combine with other atoms. It is stable and has a high chemical reactivity.
In addition, the surface energy of the highly activated nanoparticles is also high, and the specific surface area and surface area can make the nanoparticles have strong chemical reactivity. For example, metal nanoparticles can burn in the air. Some oxide nanoparticles are exposed to the atmosphere and adsorb gases and react with gases. In addition, nanomaterials have new optical and electrical properties due to the original malformation of the surface of the nanoparticles, which also causes changes in surface electron spin conformation and electron energy potential. For example, some oxide and nitride nanoparticles have a good absorption and emission effect on infrared rays and have a good shielding effect on ultraviolet rays.
1.2 small size effect
When the size of the ultrafine particles is equal to or smaller than the physical feature size such as the wavelength of the light wave, the wavelength of De Broglie, and the coherence length or transmission depth of the superconducting state, the periodic boundary conditions will be destroyed, sound, light, electromagnetic, thermodynamics, etc. Features will present a new size effect. For example, the light absorption significantly increases and produces a plasmon resonance frequency shift of the absorption peak; the magnetic ordered state is in a magnetic disordered state, and the superconducting phase is converted to a normal phase; the phonon spectrum is changed. These small size effects of nanoparticles are practical
Expanded new areas. For example, silver has a melting point of 900’C, and the melting point of nanosilver can be reduced to 100, C, which provides a new process for the powder metallurgy industry. By utilizing the properties of particle size change of plasmon resonance frequency, the displacement of the absorption edge can be controlled by changing the particle size, and a microwave absorption nano material having a certain bandwidth can be manufactured for electromagnetic wave shielding, stealth aircraft and the like.
1. 3 quantum size effect
When the particle size drops to a certain value, the electron energy level near the Fermi level changes from quasi-continuous to discrete energy level. The relationship is:
Where: £ is the energy level spacing; E is the Fermi level; N is the total electron number. Macroscopic objects contain an infinite number of atoms (ie, the number of electrons contained, N), so 0, that is, the energy level spacing of large particles or macroscopic objects is almost zero; while the nanoparticles contain a limited number of atoms, and the value of N is small, resulting in a certain The value of the energy level is split. The electron energy spectrum of a bulk metal is a quasi-continuous energy band. When the energy level spacing is greater than the thermal energy, magnetic energy, magnetostatic energy, electrostatic energy, photon energy or superconducting condensed energy, the quantum effect must be considered, which leads to the nanoparticle. Magnetic, optical, acoustic, thermal, electrical, and superconducting properties are significantly different from macroscopic properties, known as quantum size effects.
1.4 Physical characteristics
The physical effects of nanomaterials include magnetic and optical properties.
The diameter of the nanomaterial is small, and the material is mainly composed of ionic bonds and covalent bonds. Compared with crystals, the absorption capacity of light is enhanced, showing the characteristics of wide frequency band, strong absorption, and low reflectance. For example, although various block metals have different colors, all metals appear black when they are refined to nano-sized particles; some objects also exhibit new luminescence phenomena, such as silicon itself, which is not illuminating, However, nano-silicon has a phenomenon of luminescence.
Due to the small diameter of the nanomaterials, the atoms and molecules are more exposed, the magnetic rows are more random and more irregular, and therefore, the nanomaterials are superparamagnetic.
1.5 chemical characteristics
The chemical effects of nanomaterials include adsorption and catalysis.
Nanomaterials have a large specific surface area. It makes it have stronger adsorption properties for other substances.
Nanomaterials can be used as high education catalysts. Due to the small size of the nanoparticles, the volume percentage of the surface is large, the bond state and the electronic state of the surface are different from the inside of the particles, and the surface atomic coordination is incomplete, which leads to an increase in the active position of the surface, which makes it have the basic conditions as a catalyst. . There are three main aspects of the role of nanomaterials as catalysts:
(1) changing the reaction rate and improving the reaction efficiency;
(2) Determine the reaction route and have excellent selectivity, such as hydrogenation and dehydrogenation only, without hydrogenation decomposition and dehydration;
(3) Lower the reaction temperature. For example, a catalyst prepared by using ultrafine particles of Ni and Cu-mon alloy having a particle diameter of less than 0.3 nm as a main component can make the hydrogenation efficiency of organic matter 10 times that of a conventional nickel catalyst; ultrafine PL powder and WC powder. It is a highly efficient hydrogenation catalyst; ultrafine Fe, Ni and Fe02, mixed light sintered body can replace precious metal as automobile exhaust gas purifying agent; ultrafine Aug powder can be used as catalyst for acetylene oxidation.
2. Preparation of nanometer materials
There are many ways to prepare nanomaterials. According to whether there is obvious chemical reaction during the preparation process, it can be divided into physical preparation methods and chemical preparation methods. The physical preparation methods include a mechanical grinding method, a dry impact method, a blending method, and a high temperature evaporation method; and the chemical preparation method includes a sol-gel method, a precipitation method, and a solvent evaporation method.
3. Application of nanometer materials in textile field
It is precisely because of these peculiar properties of nanoparticles that it lays the foundation for its wide application. For example, nanoparticles have special UV resistance, absorption of visible light and infrared rays, anti-aging, high strength and toughness, good electrical and electrostatic shielding effects, strong antibacterial deodorizing function and adsorption capacity, and the like. Therefore, by combining nanoparticles having these special functions with textile raw materials, it is possible to manufacture new textile raw materials, nano-pastes, and to improve fabric functions.
3.1 anti-ultraviolet, anti-sun and anti-aging fiber
The so-called anti-ultraviolet fiber refers to the fiber which has strong absorption and reflection properties to ultraviolet light. The principle of preparation and processing is usually to add ultraviolet shielding material to the fiber to be mixed and treated to improve the absorption and reflection of ultraviolet rays by the fiber. ability. The substances that can block ultraviolet rays here refer to two types, that is, substances that reflect ultraviolet rays, which are customarily called ultraviolet shielding agents, and have strong selective absorption of ultraviolet rays, and can perform energy conversion to reduce the amount of permeation thereof. Substance, customarily known as UV absorbers. Ultraviolet shielding agents usually use some metal oxide powders, and there are many varieties of UV absorbers at home and abroad. Commonly used are salicylate compounds, metal ion chelate compounds, benzophenones and benzotriazoles. . A small amount of nano-TiO 2 is added to the synthetic fiber by using the excellent light absorption characteristics of the nanoparticles. Because it can shield a large amount of ultraviolet rays, the garments and articles made of the same have the effect of blocking ultraviolet rays, and have an auxiliary effect on preventing skin diseases and skin diseases caused by ultraviolet absorption.
3.2 antibacterial fiber
Some metal particles (such as nano-silver particles, nano-copper particles) have certain bactericidal properties, and they are combined with chemical fiber to produce anti-bacterial fibers, which have stronger antibacterial effect and more washability than general antibacterial fabrics. frequency. For example, the ultra-fine antibacterial powder developed by the National Ultrafine Powder Engineering Center can impart antibacterial ability to resin products and inhibit various bacteria, fungi and molds. The core of the antibacterial powder may be a nanoparticle of barium sulfate or zinc oxide, coated with silver for antibacterial, and surrounded by copper oxide and zinc silicate to resist fungus. By adding 1% of this powder to the Taiwanese fiber, an antibacterial fiber having good spinnability can be obtained.
3.3 far infrared fiber
Some nano-scale ceramic powders (such as zirconia single crystals, far-infrared negative oxygen ion ceramic powders) are dispersed into a melt spinning solution and then spun into fibers. This fiber can effectively absorb external energy and radiate far infrared rays that are the same as the human body’s biological spectrum. This far-infrared radiation wave is not only easily absorbed by the human body, but also has a strong penetrating power. It can penetrate deep into the skin and cause deep resonance of the skin to produce a resonance effect. It activates biological cells, promotes blood circulation, strengthens metabolism, and enhances.
Health care such as tissue regeneration.
3.4 High-strength wear-resistant new materials
The nanomaterial itself has the characteristics of super strong, high hardness and high toughness. When it is integrated with chemical fiber, the chemical fiber will have high strength, high hardness and high toughness. For example, carbon nanotubes are used as composite additives, and have great development prospects in aerospace textile materials, automotive tire cords and other engineering textile materials.
3.5 stealth textile materials
Some nano-materials (such as carbon nanotubes) have good absorbing properties, and they can be used to add light to the textile fiber. The nano-materials have the characteristics of wide band, strong absorption and low reflectivity of light waves, so that the fibers do not reflect light. It is used to make special-purpose anti-reflective fabrics (such as military invisible fabrics).
3. 6 antistatic fiber
Adding metal nano-materials or carbon nano-materials in the process of chemical fiber spinning can make the spun filaments have antistatic and microwave-proof properties. For example, carbon nanotubes are a very excellent electrical conductor. Their conductivity is better than that of copper. It is used as a functional additive to stably disperse in chemical fiber spinning solution. It can be made at different molar concentrations. Fiber and fabric with good electrical conductivity or antistatic properties.
3.7 anti-electromagnetic fiber
High dielectric insulating fibers can be obtained by adding nano-SiO 2 to the synthetic fiber. In recent years, with the continuous development of communication and household appliances, the use of mobile phones, televisions, computers, microwave ovens, etc. is becoming more and more common. Electromagnetic fields exist around all electrical equipment and wires, and electromagnetic waves are on the human heart, nerves, and pregnant women. The impact of the fetus has a clear conclusion. According to reports, the United States, Japan, South Korea and other anti-electromagnetic wave clothing has been listed, and domestic research on the use of nano-materials to prepare anti-electromagnetic wave fibers is also underway.
3.8 other functional fiber piles
The different properties of nanoscale or ultrafine materials are used in individual functional fibers. Develop ultra-suspension fibers using high-specific gravity materials such as tungsten carbide, such as “XY-E” from Toray Industries, “July” from Asahi Kasei Corporation, and “Pyramidal” from Toyobo Co., Ltd.; and develop opaque fibers using the refractive properties of Ti02. Japan’s Unijica uses a sheath-core composite spinning method. The cortex and core layer contain different amounts of TiO2 to obtain a polyester fiber with good opacity. The fluorescent fiber is developed by using the luminosity of barium aluminate and calcium aluminate. Japan’s fundamental special chemical company has developed a light-storing material with barium aluminate and calcium aluminate as the main components, and the rest time can reach more than 10 h; some metal double salts, transition metal compounds undergo crystal transformation due to temperature changes. Or the color change of the ligand geometry or the crystallization of water “water”, the use of its reversible thermochromic characteristics to develop color-changing fibers; Mitsubishi Rayon Company uses the addition of colloidal calcium carbonate in the polyester to make hollow The fibers are treated with alkali reduction to form micropores on the fibers, and the fibers have good hygroscopic properties.
Nanomaterial science is a new discipline growth point that emerges from the intersection of atomic physics, condensed matter physics, colloid chemistry, solid chemistry, coordination chemistry, chemical reaction kinetics, surface and interface science. There are many unknown processes and novel phenomena involved in nanomaterials, which are difficult to explain with traditional physical chemistry theory. In a sense, the advancement of nanomaterials research will push many disciplines in the field of physics and chemistry to a new level. In recent years, by adding certain ultrafine or nano-scale inorganic material powders to the Taiwanese fiber-forming polymer, it has become a popular functional fiber manufacturing method, such as far-infrared fiber and anti-wear, by spinning to obtain fibers having a certain special function. Ultraviolet fibers, magnetic fibers, super-overhanging fibers, fluorescent fibers, color-changing fibers, antistatic fibers, conductive fibers, and highly hygroscopic fibers. With the continuous progress in the synthesis of nanomaterials and the improvement of basic theories, nanomaterials will develop more rapidly, and the application will cover many fields in the world.