| Message: | Factors affecting the properties of carbomer gel
The effect of pH
As the carbomer polymer has a large number of free carboxyl groups, its pKa value is usually small. When the pH of the medium is less than 4, the carboxyl groups hardly dissociate, and when the pH>4, the carboxyl groups begin to dissociate, the polymer swells, and the viscosity increases. , When the pH value is 8, the dissociation is almost complete and the viscosity is the largest. When carbomer is used as a carrier for basic drugs, after the drug is dissolved, the pH of the medium increases, the degree of carbomer dissociation increases, the gel layer thickens, and the drug release rate decreases, so as to achieve the control of drug release purpose. The pH value of the medium also affects the adhesion of the carbomer gel. When the pH value is lower than its pKa, the gel has a stronger bonding ability and increased adhesion. At the same time, the ionic strength of the medium can change the sensitivity of the carbomer gel to pH. When the ionic strength is high, the carbomer is easier to release protons, and its pKa value decreases, so it can dissociate and dissolve at a lower pH. rise. |
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