Isotonic specific volume is used to measure the molar volume of substances, and has been widely used in the estimation of physical properties of pure substances and mixtures. The more common method is to calculate the surface tension of pure substances and mixtures.The measured surface tension of many compounds and the density of their liquid and gas phases were used to calculate the isotonic specific volume of these compounds, and then the isotonic specific volume was linked with the group in the compound to obtain the group contribution value of the isotonic specific volume, which was used to calculate the isotonic specific volume of other known structures.
Isotonic specific volume is used to measure the molar volume of substances, and has been widely used in the estimation of physical properties of pure substances and mixtures. The more common method is to calculate the surface tension of pure substances and mixtures.Actual measurement of many compounds usedsurfaceThe isotonic specific volume of these compounds is calculated by the tension and the density of its liquid and gas phases, and then the isotonic specific volume is linked with the group in the compound to obtain the group contribution value of the isotonic specific volume, which is used to calculate the isotonic specific volume of other known structures[1]。
Infer the surface tension of known structural agents
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The foaming process of aqueous solution is the process of increasing the gas water interface, so it is easy to bubble when the surface tension (i.e. surface energy) of the solution decreases.Therefore, the surface tension of foaming agent is directly related to its foaming performance.Generally speaking, the lower the surface tension of the foaming agent, the stronger the foaming ability may be.However, the surface tension is measured when the solution is still, and the foam formation process also includes the evaporation, compression, expansion of the holding film and the flow of water on the foam wall. Therefore, the reduction of the surface tension is not completely parallel to the improvement of the foaming performance.Nevertheless, the surface tension is still an important basis for judging the foaming performance of the medicament.
It is not difficult to measure the surface tension value of liquid with ordinary precision. The problem is to calculate their surface tension value according to the pharmaceutical structure and find new foaming agents without obtaining the actual pharmaceutical products[2]。
Inferring the structure of medicament according to the calculation of surface tension
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Due to the variety of organic compounds and the complexity of organic synthesis reaction, it is often difficult to determine the product structure when developing new drugs.There are many methods to determine the structure of the agent, and it is also one of the methods to deduce the structure of the agent from the calculation of the isotonic specific volume.Only the density and surface tension of the agent are needed for calculation, which is not difficult to measure[2]。
Analyze the relationship between structure and performance of foaming agent
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The relationship between the structure of the foaming agent and its foaming capacity is quantitatively revealed to inspire us how to improve the performance of the agent.
Size of polar and non-polar groups of foaming agent
The fourth power of molecular weight is inversely proportional to the surface tension.Therefore, in homologues, namely a group of agents with the same polar group but different non-polar groups, with the increase of the molecular weight of the non-polar group, the surface tension decreases within a certain range and the foaming ability increases.It can be seen that this is the relationship stipulated by the famous Traubedine rule.At the same time, we can see that when the molecular weight of polar groups is large, their foaming ability may also increase.
Foaming agent heteroatom type
Where there are atoms with large values in the molecule, such as sulfur, nickel, chlorine, iodine, phosphorus and other elements, their values must be high so that the foaming ability is not strong or does not have foaming ability.To make compounds containing such atoms have foaming properties, the molecular weight of the non-polar radical must be large enough, while still maintaining a certain solubility.For example, although the alkyl sulfonate mentioned above has sulfur, sodium and other elements, it still has good foaming property when the alkyl group is large enough[3]。
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The surface tension of foaming agent is discussed. The foaming performance of foaming agent is not completely parallel to the numerical value.For example, in order to make the foam have good stability, it is necessary to keep the water in the foam wall from flowing away and evaporating. When the foaming agent molecules are directionally arranged and adsorbed at the liquid gas interface, if the non-polar groups of the agent molecules are arranged too tightly or the hydrophobicity is too strong, it is not conducive to retaining the water molecules in the foam wall and making the bubbles easy to break.At this time, if the non-polar group of the agent is isomeric (so that the molecules cannot close together closely) or some hydrophilic groups or bonds are introduced, the safety of the foam can be increased, thus improving the foaming property of the agent[3]。
