What is soft matter? The softest substance in the world is what is the softest substance in the worl

Soft matter", which was the title of a presentation given by the French scientist Pg de Gennes at the 1991 Nobel Prize in Physics, although he was awarded for his work in "superconductors, liquid crystals and polymers". Is it too much for some scientists to call Derener the modern-day Newton? Then please read "Soft Matter and Hard Science" carefully, and you may come to the same opinion.

After winning the Nobel Prize in Physics in 1991, De Gener was enthusiastic about popular science, giving lectures at various schools about the new subject he had pioneered called "soft matter......"., introducing the theme of science, and introducing the marginal disciplines across the three major disciplines of physics, chemistry and biology to the audience. And his assistant, Dr. Barbie, compiled this contemporary popular science masterpiece "Soft Matter and Hard Science" based on his lectures and recordings in various places.

Degena started with rubber boots from the Indians, who applied the milk of a white rubber tree to their feet, which solidified into a pair of boots after 20 minutes, an invention 2,500 years ago. The solidification of milk is due to the action of oxygen, and the discovery of the vulcanization of rubber has brought the application of rubber to a new stage. The vulcanization of rubber is an extremely weak chemical reaction, but it is sufficient to change the substance from a liquid state to a solid state, and from a fluid to rubber.

Degena says that this proves that the state of matter can be changed by a faint external action, just as a sculptor can change the shape of clay with a gentle press of his thumb. This is the core and basic definition of soft matter. ”

De Gerna's favorite example is Chinese ink, the carbon black can be used for writing when it is mixed with water, but the carbon black will settle after being placed, and the solution is to add a little glue in the water to stabilize the ink. Why? Because the long-chain sugar molecule in the glue, polyhyaluronic acid, adheres to several points of the carbon particles, thus blocking the carbon particles from approaching each other, and the carbon particles cannot agglutinate together.

"It took more than 4,000 years for Chinese ink to be fully explained, and it was only ten years ago when we understood the mechanism of polymer stabilization that we got the explanation, and there was a gap of thousands of years between the invention and the explanation," De Genne said. This shows that invention predates the emergence of explanations long before they occur.

Moreover, the production of explanations, like inventions, is a long and rugged road, with people trying and failing along the way until the correct explanation is finally found. ”

The book does cover a lot of interesting topics that we encounter in our daily lives, all of which show that in the second half of the 20th century, the discipline of soft matter has quietly emerged and will become one of the mainstream of science in the 21st century.

1. The world's softest things are water, soy products, human hair, newborns' sweaters and sweaters after professional washing, these things are the softest things in the world, and the spring cover Chang's hands can give people a very comfortable feeling, especially for newborns. Stuffy wide.

2. Water is the softest thing in the world, the general liquid water does not even have a fixed shape, there is no way for people to touch the state of water, the shape of water is determined according to the shape of the container, so many people who believe in Taoism and Buddhism are particularly fond of water, thinking that water is the most good divine object, and water is also the cleanest and most holy liquid.

Soft matter refers to matter that sits between a solid and an ideal fluid. Also known as soft condensed matter. It is generally composed of macromolecules or groups, including liquid crystals, polymers, colloids, membranes, foams, particulate matter, and living system substances (such as DNA, cells, body fluids, proteins), etc.

It can be a solid-liquid mixture, a liquid-liquid mixture, a gas-liquid mixture, etc. It is widely found in nature, living organisms, daily life and production. Rubber, glue, ink, detergent, paint, cosmetics, food, etc., which can be found everywhere, are all soft substances.

The basic properties of soft matter are sensitivity and nonlinear response to small external effects, self-organizing behavior, spatial scaling symmetry, etc. The coexistence of fluid thermal fluctuations and the confinement of the solid state leads to a new behavior of soft matter, which reflects its complexity and particularity. The composition, structure, interactions, and macroscopic properties of soft matter are very different from those of ordinary solids, liquids, and gases.

The sensitivity of soft matter to small external effects is the meaning of "soft" in soft matter**. The "softness" of soft matter refers to the property of a small external action that can cause large changes. This external action varies from system to system and can be mechanical, electrical, magnetic, thermal, chemical perturbation and doping.

For example, adding a little brine can turn soy milk into tofu; Add some bone glue to stabilize the ink without precipitation; A very small electric field can easily change the state of the liquid crystal molecule display; Vulcanized rubber is transformed from a liquid into an elastic solid by adding trace amounts of sulfur (the ratio of sulfur atoms to carbon atoms is 1 200). However, almost all soft matter is indeed soft in terms of mechanical properties. Soft matter can be compared with simple fluids and solids to see the difference in composition and configuration between them.

Molecules in a simple fluid can change positions freely, and their properties do not change after position exchange. Whereas, the position of the molecules of an ideal solid is fixed. Soft matter, on the other hand, has complex situations, some of which are confined and not freely interchangeable by macromolecules or molecules within groups.

Macromolecules or groups are weakly linked to each other, such as polymer solutions, liquid crystals, colloids, and particulate matter; Some are fluid molecules that are interchangeable inside and outside the group, while they are not interchangeable inside and outside the group, such as liquid-liquid mixtures and gas-liquid mixtures. Take jelly and ice as an example to compare the differences between soft and hard substances. Jelly is composed of gelatin molecules and water, and the gelatin molecules are weakly linked together by water, so they are soft and elastic.

The hardness and strength of ice results from its molecular composition. The H2O molecules in the ice are tightly packed together, and there is a strong interaction between the molecules, which requires a lot of force to change the ice. Strong extrusion can disrupt the bonds between atoms in the ice, resulting in brittle rupture.

Ice is a hard substance, and jelly is a soft substance. Water is a substance that has a certain volume and cannot maintain its own form, and any shear force will cause it to flow. Jelly, on the other hand, retains its shape and does not flow freely, or takes a long time to slowly deform or flow.

The reason why soft matter is "soft" is also related to the complexity of the aggregate states of its constituent molecules. Taking liquid crystals as an example, the centroid of a nematic phase molecule reflects the liquid phase, while the orientation of its long axis reflects the crystalline phase. The center of mass of the molecule of the near-crystalline liquid crystal reflects the liquid phase in one plane and the crystalline phase in the vertical direction. Rubber molecules, on the other hand, are liquids in the microscopic localized state, but macroscopic in solids. Therefore, solids in general belong to hard substances, while liquids and solutions consisting of small molecules in general are not soft substances.

Some people refer to ordinary liquids (such as water) and solutions as ultra-soft substances.

Self-organization is the basic property of soft matter, which does not have rotational symmetry or translational symmetry, but forms a special coherent order, with spatial expansion symmetry, or scaling symmetry. Each fragment of the polymer molecule in the solution will expand randomly in the form of random walking relative to its previous fragment, and the association between random walking steps and steps is random, while the spatial distribution of steps is not random, showing self-organizing behavior. The same is true for the agglomeration of particles in the colloid, where adjacent particles are randomly connected while the whole is regularly distributed.

However, its density is not uniformly distributed like ordinary solids or liquids, but is distributed regularly with decreasing distance, showing fractal behavior. Observe the aggregation of particles in the polymer molecular solution and colloid at different magnifications, as long as the molecular components are not magnified to the point where the molecular components can be seen, the images at different magnifications will look the same, that is, they have spatial scale symmetry. Almost all soft substances obey this law.

Some forms of self-organization occur within a single molecule, such as the DNA molecule, which can withstand twisting and bending, and mechanical twisting at one point in the molecule will change the morphology of the molecule as a whole. The internal energy of the interaction between atoms in hard matter contributes much more to the free energy than the entropy, and the structure of the matter is mainly determined by the internal energy, and the thermal fluctuation only plays a perturbative role. However, for soft matter, the interaction between the constituent units is weak, and the internal energy hardly changes when the configuration changes.

This means that small external perturbations are prone to complex deformations and flows, and thermal fluctuations have a great impact on the structure and behavior of the system, i.e., the characteristics of the system depend largely on the entropy of the system. The restoring force of a stretch spring is determined by the interaction between atoms and is a property of hard matter. The situation of soft substances such as erasers before and after stretching is very different:

The polymer molecules in the unstretched eraser are in a coiled state, with high entropy and low total energy; In the stretched eraser, the polymer molecules are straightened, the entropy decreases, and the energy increases. Therefore, the restoring force of stretching the eraser is driven by the "entropy force". Under the effect of "entropy force", there will be many novel behaviors in soft matter systems, such as the originally chaotic microscopic system will become orderly, and complex protein molecules will fold into special structures on their own.

Using these properties, many soft materials with special properties can be manufactured, which are difficult to replace with hard materials.

Softening, as the name suggests, is the reduction of the hardness of water.

Methods: (1) Heating method, hard water is heated or distilled to remove calcium salt, magnesium salt, etc.; (2) Lime and Su wide beating methods can reduce the hardness of carbonate and non-carbonate respectively; (3) Ion exchange method, using ion exchanger to remove calcium, magnesium and other ions.

The softened water system consists of three parts, namely the ion exchange part, the salt regeneration part, and the control part. Ion exchange technology is the working principle of the softening system, its main body is ion exchange resin, because the hardness of water is mainly formed and represented by calcium and magnesium, so cation exchange resin is generally used to replace Ca2+ and Mg2+ (the main component of the formation of scale) in the water, and with the increase of Ca2+ and Mg2+ in the resin, the efficiency of resin to remove Ca2+ and Mg2+ is gradually reduced. Therefore, when the water softener equipment is used for a period of time, the resin needs to be regenerated with the salt regeneration part to restore the efficiency of the resin and improve the service life of the resin.

The control part can realize the automatic operation of the whole system, and the salt regeneration is carried out automatically according to the operating time of the system or the amount of water passed.

Refers to the softening of the bare skin, also known as enzyme softness or enzyme softness. A process in the preparation stage of tanning. The bare skin after de-ashing is adjusted to weak alkalinity (pH value is about 38) and warm conditions (about 38) with ammonium salt, and treated with trypsin and/or protease preparation solution, which can remove the residual hair root decomposition products, oils, lipids and other substances and some non-collagen substances and their degradants in the skin, and further eliminate the expansion cavity skin of the skin, and at the same time make the skin fibers loose after light dispersion.

The softened bare leather has good air permeability, and the leather made is relatively soft and delicate, rich in elasticity and extensibility. Generally, light leather must be softened by enzymes.