Water preservation through smart materials (hydrogel)
Expt No. Date:
Principle:
Hydrogels are polymeric cross-linked network structures obtained from a class of
synthetic and/or natural polymers which can absorb and retain significant amount of water
due to the presence of hydrophilic groups or domains (Scheme 1). Water is brought into the
network through the process of osmosis and quickly is absorbed into the central part of the
polymer network. This is mainly due to the affinity of these functional groups towards water
(e.g., due to the protonation/deprotonation as a result of changes in pH and temperature) and
leading to a reversible change in the swelling degree as shown in Scheme 1.
O OH O O
+ H2O + H3O
n n
eg. Polyacrylic acid
Scheme 1: Absorption of water by the polymer chain of a hydrogel
Figure 1: Bulk hydrogels with specific functional groups (FG) – the different solvation water depending on
environmental conditions (e.g., pH, or temperature) leads to large reversible changes in the degree of swelling.
Hydrogels find applications mainly in tissue engineering, pharmaceutical, and
biomedical and agricultural fields. Due to their high water absorption capacity and
biocompatibility they are now being used in wound dressing, drug delivery, sanitary pads as
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well as trans-dermal systems, dental materials, implants, injectable polymeric systems,
ophthalmic applications, hybrid-type organs.
Table-1
Sl. No. Wt. of polymer taken, g Wt. of polymer Amount of
after swelling, g water absorbed,
mL
1 Wd1 Ws1
2 Wd2 Ws2
3 Wd3 Ws3
Average
Swelling index of the polymer material with deionized water =
Table-2
Sl. No. Wt. of polymer Amount of Wt. of polymer Amount of
taken, g ionic after swelling, water
compound g absorbed, mL
added
1 Wd1 Ws1
2 Wd2 Ws2
3 Wd3 Ws3
Average
Swelling index of the polymer material with ionic impurities =
Table-3
Sl. No. Wt. of polymer Amount of Wt. of polymer Amount of
taken, g neutral after swelling, water
compounds g absorbed, mL
added
1 Wd1 1.0 Ws1
2 Wd2 1.0 Ws2
3 Wd3 1.0 Ws3
Average
Swelling index of the polymer material with neutral impurities =
Required apparatus and chemicals
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250 mL beakers -3, Glass rods-3, Filter papers -3, Funnels -2
Deionized water, Polymer material, NaCl, Sucrose, Acetone, Methanol, Ethanol, Butanol,
and Urea.
Procedure
Part-A:
A small amount of superabsorbent polymer material is placed in the beaker (0.5 g, note down
the exact weight of the polymer) and then 100 mL of deionized water is poured into the
beaker. After 5 min the swollen polymer was separated by using a filter paper and note down
the weight of the gel. By weighing the gel, one can find the swollen capacity of the polymer
taken.
The swelling percentage of hydrogels was calculated based on Eq-1, which consists of the
difference between the initial and the final weight of the sample divided by the initial weight.
Here Ws corresponds to the weight of the swollen gels and Wd is the weight of dry polymer
before immersion into the water.
----Eq.1
Part-B
The swelling behavior of polymers is determined by ionic and neutral impurities in water. A
small amount of dry polymer material is placed in the beaker (0.5 g, note down the exact
weight of the polymer) and then 0.1% NaCl solution (prepared by adding 0.1 g of NaCl in
100 mL of deionized water) is poured into the beaker. After 5 min the swollen polymer was
separated by using a filter paper and note down the weight of the gel. By weighing the gel,
one can find the swollen capacity of the polymer taken as per the following equation.
Part-C
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A small amount of dry polymer material is placed in the beaker (0.5 g, note down the exact
weight of the polymer taken) and then 1 % sucrose solution (prepared by adding 1 g of
sucrose in 100 mL of deionized water) is poured into the beaker. After 5 min the swollen
polymer was separated by using a filter paper and note down the weight of the gel. By
weighing the gel, one can find the swollen capacity of the polymer using the given equation.
Swelling index of the polymer material with neutral impurities =
OBSERVATION AND CALCULATIONS
Result
Swelling index of the polymer material with deionized water = _____________
Swelling index of the polymer material with ionic impurities = _____________
Swelling index of the polymer material with neutral impurities = _____________
Important questions to be answered:
1. How is water absorption affected by ionic and neutral compounds? Is it possible to
increase the efficiency of absorption process?
2. How do we separate the polymer material from water?
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Students are informed to bring their choice of materials (any neutral or ionic) to carry out the
experiments on their own to answer the above questions. Answers for these questions are
very important to use these hydrogel materials in an efficient way with recoverability.
