Let's answer each question step-by-step, as requested. --- ### **1. pH-responsive hydrogels and swelling of anionic hydrogels** #### **Step-by-step Solution:** **a) What are pH-responsive hydrogels?** - pH-responsive hydrogels are cross-linked polymer networks that can absorb a large amount of water and swell or shrink in response to changes in the pH of their environment. **b) What are anionic hydrogels?** - Anionic hydrogels contain negatively charged groups (e.g., –COO⁻ from acrylic acid) attached to the polymer backbone. **c) pH Condition that Promotes Swelling:** - At high pH (basic conditions), the acidic groups (e.g., –COOH) on the polymer deprotonate to form –COO⁻. - The negative charges repel each other, causing the polymer network to expand and absorb more water (swelling). **d) Underlying Mechanism:** - **Low pH:** The carboxylic acid groups (–COOH) are protonated. There is little electrostatic repulsion, so the hydrogel remains collapsed. - **High pH:** The –COOH groups ionize to –COO⁻. Electrostatic repulsion between these negative charges causes the network to swell. **e) Sketch (for illustration):** ``` Low pH (collapsed) High pH (swollen) | | | | | | --COOH--COOH-- --COO⁻ COO⁻-- | | | | | | ``` --- ### **2. Shear-thinning properties of polymers** #### **Step-by-step Solution:** **a) What is shear-thinning?** - Shear-thinning (pseudoplasticity) is when a material’s viscosity decreases as the shear rate increases. **b) Shear properties of polymers:** - At rest or low shear, polymer chains are entangled, leading to high viscosity. - With increasing shear, chains align in the direction of flow, reducing entanglement and viscosity. **c) Reasons for shear-thinning:** - Alignment of polymer chains under shear. - Disruption of temporary intermolecular associations. **d) Sketch (for illustration):** ``` Before shear: During shear: tangled chains aligned chains ~~~~~~ ||||||| ``` --- ### **3. 3D Printing vs. Traditional Manufacturing** #### **Step-by-step Solution:** **a) Advantages of 3D Printing:** - Enables complex geometries and customization. - Reduces material waste (additive process). - Rapid prototyping and shorter lead times. - Lower initial setup cost for small production runs. **b) Disadvantages of 3D Printing:** - Slower for mass production. - Limited material choices and sometimes lower mechanical strength. - Surface finish may require post-processing. - Higher cost per part for large volumes. **c) Traditional Manufacturing (e.g., Injection Moulding, Subtractive Manufacturing):** - **Advantages:** High production speed and consistency, good surface finish, suited for mass production. - **Disadvantages:** High initial tooling costs, less flexibility for design changes, more material waste in subtractive processes. --- ### **4. Absorbent materials in diapers** #### **Step-by-step Solution:** **a) Function:** - Diapers use superabsorbent polymers (SAPs), mainly sodium polyacrylate, to absorb and retain large amounts of liquid. **b) Absorption Mechanism:** - The SAP network contains hydrophilic groups (e.g., –COO⁻Na⁺). - On contact with water, Na⁺ ions dissociate, and water is drawn into the polymer by osmosis. - The polymer swells, trapping water within its network. **c) Capacity:** - These materials can absorb water up to 300 times their weight due to their high affinity for water and ability to form gel-like structures. **d) Sketch (for illustration):** ``` Dry SAP beads: After absorbing water: • • • (swollen beads) ( •••••• ) ``` --- ## **Summary of Final Answers:** 1. **Anionic hydrogels swell at high pH due to ionization of acidic groups, leading to electrostatic repulsion and water uptake.** 2. **Polymers show shear-thinning as their chains align under shear, reducing viscosity due to decreased entanglement.** 3. **3D printing allows for complex, customized parts with less waste, but is slower and costlier for mass production compared to traditional methods.** 4. **Diapers use superabsorbent polymers like sodium polyacrylate, which can absorb over 300 times their weight in water by forming a gel network.** Let me know if you'd like a more detailed explanation for any specific question!