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Questions and Answers
What happens to the hydrodynamic diameter (Dh) of particles as the temperature increases up to 38 °C?
What happens to the hydrodynamic diameter (Dh) of particles as the temperature increases up to 38 °C?
How does the chemical composition of the chitosan-PNIPAM hydrogel systems affect their properties?
How does the chemical composition of the chitosan-PNIPAM hydrogel systems affect their properties?
What technique is mentioned in the analysis of hydrogels that shows particle size changes due to temperature?
What technique is mentioned in the analysis of hydrogels that shows particle size changes due to temperature?
What effect does increasing temperature beyond 50 °C have on the hydrogels?
What effect does increasing temperature beyond 50 °C have on the hydrogels?
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What relationship is important to consider when altering the NIPAM/chitosan ratio in the hydrogel systems?
What relationship is important to consider when altering the NIPAM/chitosan ratio in the hydrogel systems?
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At what temperature range does gelation behavior begin to appear in the hydrogels?
At what temperature range does gelation behavior begin to appear in the hydrogels?
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What occurs to the particles in hydrogels at temperatures higher than 40 °C?
What occurs to the particles in hydrogels at temperatures higher than 40 °C?
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How do the hydrogels respond to changes in pH in terms of maintaining their stability?
How do the hydrogels respond to changes in pH in terms of maintaining their stability?
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What effect does a higher pH (> 11) have on the zeta potential of the selected hydrogels?
What effect does a higher pH (> 11) have on the zeta potential of the selected hydrogels?
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At what temperature does the viscosity of the hydrogels start to increase significantly?
At what temperature does the viscosity of the hydrogels start to increase significantly?
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How does the composition of microgels affect their zeta potential at pH ≈ 6 and T = 25 °C?
How does the composition of microgels affect their zeta potential at pH ≈ 6 and T = 25 °C?
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What phenomenon occurs as a result of swollen particles exceeding the LCST of PNIPAM?
What phenomenon occurs as a result of swollen particles exceeding the LCST of PNIPAM?
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What is the observed trend of viscosity with increasing temperature after reaching a peak point?
What is the observed trend of viscosity with increasing temperature after reaching a peak point?
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What effect does the charge density of microgels have on their behaviour?
What effect does the charge density of microgels have on their behaviour?
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What causes the viscosity of microgels to remain stable over a wide range of pH?
What causes the viscosity of microgels to remain stable over a wide range of pH?
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Which process contributes to the increase in viscosity at low shear rates in microgels?
Which process contributes to the increase in viscosity at low shear rates in microgels?
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What effect does increasing the NIPAM/chitosan ratio have on the size of hydrogel particles?
What effect does increasing the NIPAM/chitosan ratio have on the size of hydrogel particles?
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What is the phenomenon that occurs when the temperature rises above the lower critical solution temperature (LCST) for PNIPAM?
What is the phenomenon that occurs when the temperature rises above the lower critical solution temperature (LCST) for PNIPAM?
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How does the temperature of the solution beyond the critical temperature affect the microgels?
How does the temperature of the solution beyond the critical temperature affect the microgels?
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What role does crosslinking density play in the behavior of microgels?
What role does crosslinking density play in the behavior of microgels?
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What is the primary measurement technique mentioned for assessing the hydrodynamic diameter of microgels?
What is the primary measurement technique mentioned for assessing the hydrodynamic diameter of microgels?
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What characteristic of the chitosan-PNIPAM hydrogels is highlighted in relation to temperature?
What characteristic of the chitosan-PNIPAM hydrogels is highlighted in relation to temperature?
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What can be inferred about the interaction of PNIPAM with water at temperatures below the LCST?
What can be inferred about the interaction of PNIPAM with water at temperatures below the LCST?
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Which alteration in properties is suggested when NIPAM content is higher in the polymeric network?
Which alteration in properties is suggested when NIPAM content is higher in the polymeric network?
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Study Notes
Hydrogels and Temperature
- Increasing temperatures (above 50°C) can cause dehydration in hydrogels.
- This dehydration weakens the association between collapsed particles, leading to decreased viscosity (indirect shear thinning effect).
- At temperatures higher than the Volume Phase Transition Temperature (VPTT), hydrogels experience shrinkage due to the deswelling of particles.
- This shrinkage was observed in dynamic light scattering (DLS) results, with the hydrodynamic diameter (Dh) decreasing with increasing temperature up to 38°C.
- Visual analysis using the tube inversion method also confirmed gelation behavior above the VPTT.
- These hydrogels demonstrate potential for drug delivery applications as the deswelling occurs near human body temperature (36-39°C).
Compositional Effects on Hydrogels
- Varying the chemical composition of microgels, like changing the NIPAM/chitosan ratio or cross-linker (MBA) content, affects their rheological behavior.
- This variation directly impacts the hydrophilicity/hydrophobicity balance of the network.
- The size and VPTT of the microgels are influenced by these chemical adaptations.
- Microgel stability is observed over a wide range of pH (pH ≈ 2–8) at room temperature for at least 3 months.
- The zeta potential values are less than four, indicating stability at a wide range of pH for a given temperature.
- Alterations in zeta potential with varying chemical composition reflect changes in the hydrophilic–hydrophobic balance, influencing interactions with the solvent and charge density on the particles.
Viscosity Changes and Temperature
- For the investigated hydrogels, there is a minimal change in viscosity with temperature up to 28–29 °C.
- Beyond this temperature range, viscosity increases gradually until reaching the VPTT, at which point a sharp rise occurs.
- The abrupt increase in viscosity at/above VPTT signifies a gelation/association process.
- Viscosity then decreases with further increases in temperature, potentially due to dehydration and shear thinning effects.
- At temperatures above 50°C, minor fluctuations in viscosity-temperature profiles are observed.
Microgel Behavior and LCST
- When swollen particles are exposed to temperatures exceeding the lower critical solution temperature (LCST) of PNIPAM, they shrink.
- This shrinkage arises from the disruption of hydrogen bonding with water molecules and the formation of hydrophobic associations between isopropyl moieties of PNIPAM.
- The resulting compact particles contribute to increased viscosity at low shear rates.
- The critical temperature for this transition varies with changes in microgel composition, indicating a delicate balance between hydrophobic and hydrophilic interactions within the polymer network.
- Changes in solution temperature near the critical temperature trigger chain transitions between extended and compacted coil states, leading to changes in the hydrophobic and hydrophilic interactions within the polymer chain.
PNIPAM Behavior
- Below its LCST (approximately 32 °C), PNIPAM is hydrophilic and exists in water as individual random coil chains.
- When the temperature exceeds the LCST, PNIPAM adopts hydrophobic characteristics and collapses depending on solution conditions.
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Description
Explore the impacts of temperature on hydrogels, including dehydration effects and viscosity changes as temperature approaches the Volume Phase Transition Temperature (VPTT). Learn about their applications in drug delivery and how varying chemical compositions can influence their properties and behavior.
