Chitosan Hydrogels: Swelling and Synthesis

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Questions and Answers

Which pH condition resulted in the highest R2 value for the first order kinetics of CS1Glut0.4?

pH 10.5

Temp. 40°C

pH 7 (correct)

pH 2.5

What parameter corresponds to the lowest K2 value in the second order kinetics for CS1Glut0.2?

Temp. 20°C (correct)

0.1M NaCl

Temp. 40°C

pH 10.5

Which ion concentration exhibited the highest Seq(obtained) value for CS1Glut0.4 at pH 7?

0.001M NaCl

0.01M NaCl

0.1M CaCl2

0.1M NaCl (correct)

In the context of chitosan hydrogels, which temperature condition demonstrated the highest R2 value for the second order kinetics?

Temp. 40°C Signup and view all the answers

Which of the following showed a significant increase in Seq(calculated) for the second order kinetics of CS1Glut0.2?

0.1M CaCl2 Signup and view all the answers

What is the first model described in relation to solvent distribution into the gel matrix?

Swelling fraction model Signup and view all the answers

What type of behavior do sigmoidal swelling curves often describe?

Non-Fickian diffusion behavior Signup and view all the answers

In the synthesis of uncrosslinked CS beads, what is used as a precipitation bath?

0.1N NaOH solution Signup and view all the answers

What differentiates the synthesis of uncrosslinked CS films from CS beads?

The method of pouring the mixture Signup and view all the answers

What is a notable characteristic of the swelling curve according to the models discussed?

It tends to fail in situations of large volume changes. Signup and view all the answers

What aspect of CS hydrogels has seen limited literature availability?

Mathematical modeling of their properties Signup and view all the answers

During the synthesis of CS hydrogels, what is mixed with chitosan to create a uniform solution?

Distilled water and acetic acid Signup and view all the answers

What is the primary reason for the interest in shape-changing hydrogels?

Their response to external stimuli Signup and view all the answers

What is the role of 'n' in diffusion analysis?

To identify the type of diffusion. Signup and view all the answers

How can the diffusion coefficient 'D' for cylindrical hydrogels be calculated according to Fick's second law?

Through the relationship $D = \frac{k}{\pi r^2 (4) n}$. Signup and view all the answers

At what solvent entry percentage should the ln F versus ln t graph be plotted for data collection?

60% Signup and view all the answers

What type of atmosphere is used during the thermogravimetric analysis of crosslinked CS hydrogels?

Nitrogen flow Signup and view all the answers

At what temperature range is the maximum weight loss of about 43% observed in the polymeric network?

225°C to 298°C Signup and view all the answers

Which thermal analysis method assesses the thermal properties of the hydrogels?

Differential Scanning Calorimetry Q-200 Signup and view all the answers

What is the temperature range maintained during the thermogravimetric analysis?

30°C to 500°C Signup and view all the answers

What is the primary cause of weight loss in the first stage of polymer decomposition?

Evaporation of bound water Signup and view all the answers

Peleg's empirical equation is used for what purpose in material research?

To model water absorption. Signup and view all the answers

Which of the following modifications generally leads to decreased thermal stability of chitosan (CS)?

Modification with glutaraldehyde Signup and view all the answers

What weight loss percentage is approximately observed at 160°C?

12% Signup and view all the answers

What concentration of glutaraldehyde is used in synthesizing the disc shaped hydrogels?

Low concentration Signup and view all the answers

What significant changes occur to the molecules between 225°C and 298°C?

Decomposition to simpler molecules Signup and view all the answers

What is the maximum heating rate used during the DSC analysis of hydrogels?

10°C/min Signup and view all the answers

What effect does chemical modification with glutaraldehyde and sulfuric acid have on chitosan (CS)?

Improves mechanical strength Signup and view all the answers

Which type of hydrogel shapes are mentioned as part of the study?

Disc shaped and bead shaped Signup and view all the answers

Which factors influence the amount of weight loss during polymer decomposition?

Hydrophilicity, crystallinity, and molecular weight Signup and view all the answers

Which of the following acids were mentioned as modifying agents for chitosan (CS)?

Sulfuric acid and glutaraldehyde Signup and view all the answers

What would be the consequence of a chemical modification that decreases thermal stability in chitosan (CS)?

Enhanced degradation at lower temperatures Signup and view all the answers

What is the effective pKa of chitosan (CS) as mentioned in the content?

6.0-6.5 Signup and view all the answers

How does the swelling value of uncrosslinked CS beads at pH 7 compare to other studies?

It exceeds 100%-200%. Signup and view all the answers

What happens to the swelling behavior of CS when the pH is alkaline?

Swelling decreases. Signup and view all the answers

Which equation represents the exponential association model for swelling?

S = [1−exp(−kR2t)] Signup and view all the answers

What is the best swelling percentage reported for a flat 2D shaped film at pH 7?

3000% Signup and view all the answers

What occurs during absorption according to the equations provided?

The equation uses '+' for swelling. Signup and view all the answers

What describes the behavior of chitosan in acidic solutions?

It dissolves, affecting swelling data. Signup and view all the answers

When converting the exponential model equation to a straight-line equation, what is the main purpose?

To estimate the correlation coefficient R2. Signup and view all the answers

What is the observed swelling behavior of CS beads at pH 7 referenced from another study?

More than 80% swelling. Signup and view all the answers

What is indicated by the k1 and k2 constants in the swelling equations?

The kinetics of swelling and its characteristics. Signup and view all the answers

Study Notes

Swelling

Two models describe the swelling of chitosan hydrogels.
The first model describes the swelling fraction increasing linearly with the square root of time.
This model is only valid for smaller swelling fractions.
The second model focuses on the relationship between stress gradient and swelling/network expansion.
These models lack the ability to describe sigmoidal swelling curves.
Sigmoidal swelling curves often represent non-Fickian diffusion behavior.
Fickian diffusion correctly describes sigmoidal swelling behavior when considering the movement of the gel surface.

Chitosan Hydrogels Synthesis

Chitosan hydrogels can exist in different shapes including beads, films, and discs.
Uncrosslinked chitosan hydrogels are synthesized by precipitating chitosan (CS) in sodium hydroxide (NaOH).
The chitosan and acetic acid mixture forms beads in a precipitation bath.
In a petridish, the mixture dries to form a film.
Glutaraldehyde is used as a crosslinker for CS in disc shaped hydrogels.
CS can be crosslinked using other methodologies such as irradiation techniques.

Chitosan Hydrogel Swelling Ability

Chitosan beads display a swelling of 100-200% at pH 7.
Chitosan beads show lower swelling in alkaline pH.
Chitosan is soluble below its pKa of 6-6.5 and insoluble above it.
Chitosan films exhibit higher swelling than beads.
Uncrosslinked chitosan film swelling is about 3000% at pH 7.
This film is susceptible to dissolution in acidic conditions, resulting in a 3D tubular shape in neutral condition.

Modeling of Water Absorption in Hydrogels

Peleg's absorption model is used to describe water absorption.
This model is expressed using the following equation:
```
S = So ± k1/(1 + k2*t)
```
This equation uses two parameters, k1 and k2 which represent kinetic and characteristic constants.
The "+" sign is used for water absorption and "-" is used for desorption.
The Exponential association model is used for describing exponential growth and decay.
This model is expressed by the following equation:
```
S = [1−exp(-kR2t)]
```
The kinetic constant in this model is kR2.

Diffusion Coefficient Equation

The diffusion coefficient for cylindrical hydrogels can be calculated using the following equation:
```
D = k1/πr^2 (4/n)
```
The equation is derived from Fick's second law of diffusion.
D represents the diffusion coefficient (m^2/s)
r represents the radius of the swollen hydrogel (meter)
k1 is kinetic constant and n is the diffusion exponent.

Thermogravimetric Analysis of CS hydrogels

Thermal properties of CS hydrogels are assessed using thermogravimetric analysis (TGA).
Three stages of weight loss are observed during thermal decomposition.
The first stage mainly consists of water evaporation from the hydrogels network.
The second stage involves decomposition of CS and conversion of complex molecules into simpler ones like acetic acid and lower fatty acids.
The third stage continues the decomposition of remaining fragments.
Chemical modification generally leads to a decrease in thermal stability of CS.

Kinetics of Water Absorption

Two kinetic models are used to describe water absorption: First order and second order kinetics.
The R2 values (correlation coefficient) for both models are given in Tables 2 and 3.
The kinetic constants k1, k2 and R2 values are presented for hydrogels at different pH values, temperatures, and in the presence of different salts.

Diffusion Exponent

The diffusion exponents values are given in Table 4.
These values provide insights into the diffusion mechanism of water in the hydrogels.

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Description

Explore the fascinating world of chitosan hydrogels, focusing on their swelling behavior and synthesis methods. This quiz covers two models that describe swelling, including the linear increase with time and the implications of stress gradients. Additionally, learn about the formation of various hydrogel shapes and the role of crosslinking in their structure.