Abstract
Hydrogels are polymeric materials which can swell in water and retain a significant fraction of water within their structure without dissolving in water. Swelling rate is one of the most important properties of hydrogels. To measure the swelling rate, the profile of swelling capacity versus time of a hydrogel sample is obtained by performing free-absorbency capacity measurements at consecutive time intervals. Traditionally, either the tea-bag method, the sieve method, or the filtration method is used for the free-absorbency capacity measurements depending on the amount of the available sample and the desired precision. However, each method has its own systematic drawbacks. In this paper, a novel method called sieve filtration method is proposed for the measurement of the swelling rate of hydrogels. A protocol for this method is described in detail. The measurement results obtained from the proposed method and the traditional methods are compared. The proposed method has the following advantages over the traditional methods:•It is more efficient than the traditional methods due to full contact of the hydrogel powders with water or aqueous solution as well as fast and complete removal of excessive fluid from the water-absorbed gel.•It enables repeatable and reproducible measurement of the swelling rate of hydrogels.•It is easy to implement, suitable for various types of hydrogels and aqueous solutions; and it requires small amounts of sample, minimal technical skill, and inexpensive equipment.
Highlights
Hydrogels are polymeric materials which exhibit the ability of swelling in water and retaining a significant fraction of water within their structure without dissolving in water [1]
Either the tea-bag method, the sieve method, or the filtration method is used for the free-absorbency capacity measurements depending on the amount of the available sample and the desired precision
When the tea-bag method is used, we found that a vigorous shaking of the bag during the time it is dipped in water or aqueous solution can significantly improve the contact between the hydrogel powders and the liquid, making the measured swelling capacity dramatically increased
Summary
Hydrogels are polymeric materials which exhibit the ability of swelling in water and retaining a significant fraction of water within their structure without dissolving in water [1]. The sieve method is often used to address this drawback, i.e., using the sieve method, the hydrogel powders can swell freely in the liquid This method is still far from being perfect, i.e., the excessive fluid is removed from the water-absorbed gel by repeated rubbing the gauze bottom using a piece of a soft polyurethane foam, which usually takes an extensive amount of time, resulting in inaccurate measurements. When the tea-bag method is used, we found that a vigorous shaking of the bag during the time it is dipped in water or aqueous solution can significantly improve the contact between the hydrogel powders and the liquid, making the measured swelling capacity dramatically increased. The amount cannot be too little, either – the water-absorbed gel should be large enough to cover the meshes of the sieve right above the hole of the size 7 rubber stopper, so that the vacuum can be effectively created to suck the excessive fluid out
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