Gel Products2nd Installment

Gel Products2nd Installment

That wondrous substance called gels.

We all learned in school about the 3 states of matter - that is, "gas", "liquid", and "solid" and that an existing state or phase may change to another under certain conditions. However there also exists a somewhat curious state which is neither solid nor liquid. A typical substance in this category are gels. Gels are colloid solutions which have lost their ability to flow but retain water or other solvents in liquid form. As such they are completely different from solids such as ice. Colloid solutions which are in the flow able state are referred to as sols. Typical examples of sol-gels are agar and jellied fish and as you know, these substances liquefy (sols) when heated and solidify (gels) when cooled.
You may be surprised at the extent to which gels are part of our daily lives. The paper diaper is an example where the properties of gels are employed to create a hit product. The paper diaper incorporates a substance which traps (gels) urine enabling the diaper to maintain dryness, thus making them much more comfortable than cloth diapers. There are other such interesting products. There is a device which injects resins into bicycle and wheelchair tires and induces a gel state to create puncture-proof tires. This is an ingenious application of the properties of gels. The device warms the resin to a liquid state in order to allow it to be injected into the tire through the air vent after which the resin is naturally cooled to a suitable hardness. As resin is used in place of air to fill the tire there is no leakage of air.

What practical uses do gels have in our daily lives?

In the manufacture of products which exploit the properties of gels, finely calculated control of viscosity is required. Let us look, for example, at the properties of thixotropic gels. Thixotropicity involves a phenomena where a substance changes to a sol when a high viscosity liquid (gel) is subjected to stress such as vibration, etc., but reverts to the highly viscous state (gels) when left unattended. It may not be apparent to the reader how close an association we have with such substances. But in fact, in the world of viscosity they play a hidden, ninja-like role. Consider a ball point pen and the relationship of ink with the tip (ball) of the pen. The pen may write smoother if the ink is thin but inks that are water-based of low viscosity are apt to run and smear when wet. Conversely, high viscosity oil-based inks may not write well and are further hampered by slow paper absorption.
This is where viscosity control comes into play in the creation of an optimum type of thixotropic ink (gel ink). While the ink is in the pen it is at high viscosity for stability, but when the ink is involved in writing the rotation of the ball tip induces stress which lowers the inks viscosity to the consistency of water-based ink permitting smoother writing. Further, as this ink penetrates the paper, it reverts to its gel state for run-free writing.
As we understand how sol-gels behave, there are probably other examples which may be called to mind. For example, paints which are applied to walls. A free-flowing paint would permit easier spreading but on the other hand is likely to drip or run. For the do-it-yourself er, it would be ideal if the paint could be spread easily when applying it with a brush but hardens as soon as it is applied. Women may rightly think of cosmetics in this context. For lotions and lipstick, etc., ease of application is important as well as their stability. Examples are many. Tomato ketchup on the dining table is normally quite difficult to get out of the bottle but, by giving it a shake to lower its viscosity, it becomes easier to pour.

The important implications of viscosity control

Thickening agents, in addition to providing a simple means of viscosity control are also used to induce thixotropic properties. Although we have touched on examples in our daily lives, the control of viscosity in industry has further important implications. Take for example, control of a mixed solution. If a solution which includes oil & fat content can be imbued with thixotropic attributes, it can be stored in a stasis, gel state which would prevent the separation of the oil & fat and precipitation of other components. When this substance is being utilized however, the sol state can be induced by the application of shear allowing it to be transported via pipelines, for example.
In addition to purposes of such major system utilizations, ongoing competition is keen in the development of thickening agents which induce high viscosity states of various base solutions. Thus the need is critical for precise viscosity measurement-based control in order to achieve the viscosities (viscous characteristics) demanded by food products and cosmetics for enhanced textures as well as to meet the exacting performance requirements of industrial products.

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