Physical properties and properties of silicone oil
Physical properties and performance of silicone oil
With Si-O-Si as the main chain, the linear chain of methyl groups connected to the silicon atomsDimethicone, due to the small intermolecular force, the molecule has a helical structure, the methyl groups are arranged outward and can rotate freely, so it has different characteristics from A series of properties of other polymers, such as colorless and transparent, wide viscosity range, small viscosity-temperature coefficient, large expansion coefficient, low vapor pressure, high flash point, high and low temperature resistance, weather resistance, radiation resistance, etc., low surface tension, High compressibility, oxygen-resistant plasma, high insulation, shear resistance, good film-forming properties, hydrophobic, defoaming, high gloss, inert to materials, such as chemical inertness, non-corrosion and physiological inertness, etc. It is these properties that determine its wide range of uses.
Silicone oils used as fabric finishing aids are all based on the molecular structure of dimethyl silicone oil, with active functional groups replacing a certain amount of side chain methyl groups to obtain relatively low-cost functionality. Silicone oil. The product combines the advantages of dimethicone and can provide reactivity or other functions after substitution. For example, early hydrogen-based silicone oils prepared by partially replacing methyl groups with hydrogen groups can provide durability when used in waterproof finishing of fabrics.
For other types of linear silicone oils, including hydroxyl silicone oil, alkoxy silicone oil, acetoxy silicone oil, vinyl silicone oil and amino intrinsic silicone oil, their main special features are also chemically active. During the fabric finishing process, it can chemically react with the active functional groups on the side chains of fiber macromolecules, thereby providing durability. However, most of the substituents in the molecular structure of functional silicone oils are still methyl groups, and all of these silicone oils retain some of the physical properties of dimethyl silicone oil.
Viscosity characteristics
Dimethicone remains in a liquid state within a wide range of molar masses (162 ~ 500000g/mol), and its viscosity can range from 0.65mm2/s to 1X1000000mm2/s, which is the case with other polymer systems. incomparable.
Viscosity-temperature properties. Dimethicone has the smallest change in viscosity with temperature (viscosity-temperature coefficient) of all polymers. In this regard, two theories have been proposed. The first is that dimethyl silicone oil has intramolecular forces due to dipolar attraction and low steric hindrance of the methyl group, causing the molecular chains to tightly entangle themselves at low temperatures. Therefore, the viscosity is lower than expected at low temperatures. When the temperature rises, the molecular chains stretch out, which leads to increased entanglement with neighboring molecules.��offsets part of the viscosity reduction effect due to temperature increase.
Therefore, if the intermolecular forces remain unchanged, increasing the temperature will not cause a significant decrease in viscosity. A second theoretical explanation for the viscosity-temperature changes is that the intermolecular forces of dimethicone are generally very low, allowing temperature changes to have little effect on these interactions. This is because there are no strong polar interactions between molecules, and the main chain bonds of the molecules are easily rotated, allowing each polymer molecule to occupy a relatively large volume, thereby hindering the extensive entanglement of the molecular chain.
Preparation of viscosity. Dimethyl silicone oil of a certain viscosity can be obtained by adjusting the amount of chain stopper during synthesis, but it can also be obtained by mixing two dimethyl silicone oils of different viscosities. In principle, any two viscosity silicone oils can be mixed, but if the viscosity difference is too large, it will affect the shear resistance of the final product.
Shear resistance. The relationship between the shear rate and viscosity of dimethyl silicone oil is related to the control of process parameters during application. Shear force can break the bonds of polymer molecules and reduce their viscosity. Under the same circumstances, the viscosity of silicone oil decreases very little, indicating that it has excellent shear resistance. The viscosity of dimethyl silicone oil with a viscosity of 1000mm2/s (25°C) does not change significantly at a shear rate of 5000s^(-1). The viscosity of dimethyl silicone oil with a higher viscosity changes slightly under high shear force. It decreases, and it is a temporary change, but it can recover when the shear is eliminated, indicating that the decrease in viscosity is not caused by the molecules being cut off, but due to the change in the Si-O-Si bond angle.
Interface features
Surface tension. Dimethicone has very Low surface tension and high surface activity make it easy to spread on the surface of the material to form a film, so it can be used as an efficient hydrophobic agent, defoaming agent and foam stabilizer. The surface tension of silicone oil is related to its viscosity. In Me3SiO (MeSiO) nSiMe, when n=0, Me3SiOSiMe3 has the lowest surface tension (15.9mN/m). As the viscosity increases, the surface tension stabilizes at 20 ~ 21mN/m.
(Source: Global Silicone NetworkAuthor: Zhiran)
Silicone oils used as fabric finishing aids are all based on the molecular structure of dimethyl silicone oil, with active functional groups replacing a certain amount of side chain methyl groups to obtain relatively low-cost functionality. Silicone oil. The product combines the advantages of dimethicone and can provide reactivity or other functions after substitution. For example, early hydrogen-based silicone oils prepared by partially replacing methyl groups with hydrogen groups can provide durability when used in waterproof finishing of fabrics.
For other types of linear silicone oils, including hydroxyl silicone oil, alkoxy silicone oil, acetoxy silicone oil, vinyl silicone oil and amino intrinsic silicone oil, their main special features are also chemically active. During the fabric finishing process, it can chemically react with the active functional groups on the side chains of fiber macromolecules, thereby providing durability. However, most of the substituents in the molecular structure of functional silicone oils are still methyl groups, and all of these silicone oils retain some of the physical properties of dimethyl silicone oil.
Viscosity characteristics
Dimethicone remains in a liquid state within a wide range of molar masses (162 ~ 500000g/mol), and its viscosity can range from 0.65mm2/s to 1X1000000mm2/s, which is the case with other polymer systems. incomparable.
Viscosity-temperature properties. Dimethicone has the smallest change in viscosity with temperature (viscosity-temperature coefficient) of all polymers. In this regard, two theories have been proposed. The first is that dimethyl silicone oil has intramolecular forces due to dipolar attraction and low steric hindrance of the methyl group, causing the molecular chains to tightly entangle themselves at low temperatures. Therefore, the viscosity is lower than expected at low temperatures. When the temperature rises, the molecular chains stretch out, which leads to increased entanglement with neighboring molecules.��offsets part of the viscosity reduction effect due to temperature increase.
Therefore, if the intermolecular forces remain unchanged, increasing the temperature will not cause a significant decrease in viscosity. A second theoretical explanation for the viscosity-temperature changes is that the intermolecular forces of dimethicone are generally very low, allowing temperature changes to have little effect on these interactions. This is because there are no strong polar interactions between molecules, and the main chain bonds of the molecules are easily rotated, allowing each polymer molecule to occupy a relatively large volume, thereby hindering the extensive entanglement of the molecular chain.
Preparation of viscosity. Dimethyl silicone oil of a certain viscosity can be obtained by adjusting the amount of chain stopper during synthesis, but it can also be obtained by mixing two dimethyl silicone oils of different viscosities. In principle, any two viscosity silicone oils can be mixed, but if the viscosity difference is too large, it will affect the shear resistance of the final product.
Shear resistance. The relationship between the shear rate and viscosity of dimethyl silicone oil is related to the control of process parameters during application. Shear force can break the bonds of polymer molecules and reduce their viscosity. Under the same circumstances, the viscosity of silicone oil decreases very little, indicating that it has excellent shear resistance. The viscosity of dimethyl silicone oil with a viscosity of 1000mm2/s (25°C) does not change significantly at a shear rate of 5000s^(-1). The viscosity of dimethyl silicone oil with a higher viscosity changes slightly under high shear force. It decreases, and it is a temporary change, but it can recover when the shear is eliminated, indicating that the decrease in viscosity is not caused by the molecules being cut off, but due to the change in the Si-O-Si bond angle.
Interface features
Surface tension. Dimethicone has very Low surface tension and high surface activity make it easy to spread on the surface of the material to form a film, so it can be used as an efficient hydrophobic agent, defoaming agent and foam stabilizer. The surface tension of silicone oil is related to its viscosity. In Me3SiO (MeSiO) nSiMe, when n=0, Me3SiOSiMe3 has the lowest surface tension (15.9mN/m). As the viscosity increases, the surface tension stabilizes at 20 ~ 21mN/m.
(Source: Global Silicone NetworkAuthor: Zhiran)
