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Comparatively Speaking: Hysteresis vs. Syneresis
By: Anthony J. O'Lenick Jr., Siltech LLC; and Thomas O'Lenick, SurfaTech Corp.
Posted: April 12, 2011
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Syneresis in chemistry is the extraction or expulsion of a liquid from a gel.2 Typically, when a gel is formed, little pockets of liquid are trapped in a solid matrix. If this matrix packs tightly enough, or the components of the gel are not compatible, the liquid can be forced out of the network. This occurs when dealing with natural waxes or blends of two waxes with different melting points.
Natural waxes are blends of many different components. Typically these waxes have mixtures of hydrocarbons (high molecular weight/high melt point and low molecular weight/low melt point alkyl chains), esters, fatty acids and alcohols. When the wax solidifies, the high melt point components start to arrange themselves into a solid matrix. During this solidification, small molecular weight components (low melt point or liquid) are forced out of the matrix to allow maximum overlap of the high molecular weight components.
For example, during cheese making, syneresis is the formation of the curd due to the sudden removal of the hydrophilic macropeptides, which causes an imbalance in intermolecular forces. Bonds between hydrophobic sites start to develop and are enforced by calcium bonds, which form as the water molecules in the micelles start to leave the structure. This process is usually referred to as the phase of coagulation and syneresis.
Another example of this phenomenon is starch in water. When starch is mixed with water, a free flowing “gel” network is obtained. If a rapid force is applied to this starch solution, water will be forced out of the starch network and the gel will act as a solid. When the force is released, the water returns and the solution flows again. If a pool is filled with the starch solution, a person can walk rapidly across the pool as if they were walking on solid ground. When the person stops walking, they sink into the solution as if they were standing in water. There are videos online showing off this phenomenon.
It is important for a formulator to understand both syneresis and hysteresis when designing a product. When designing a product with a specific melt point or cloud point, it is important for a formulator to know what that melt point is and whether it will change depending on if the system is heated or cooled.