The water repelling characteristic of silicones is due to

Options

A. the presence of alkyl group pointed towards surface.
B. strong Si-O-Si-bonds.
C. low surface area.
D. high van der Waal's forces.

Answer

To determine the water-repelling characteristic of silicones, we can follow these steps:

### Step 1: Understand the Structure of Silicones
Silicones are polymers that contain a backbone of alternating silicon (Si) and oxygen (O) atoms. They often have organic groups (like methyl groups, -CH₃) attached to the silicon atoms.

### Step 2: Identify the Functional Groups
In silicones, the presence of alkyl groups (such as methyl groups) is significant. These groups are hydrophobic, meaning they repel water.

### Step 3: Analyze the Water Repelling Characteristic
The water-repelling characteristic of silicones is primarily due to the presence of these hydrophobic alkyl groups (methyl groups) that point towards the surface. This arrangement prevents water molecules from interacting with the silicone surface effectively.

### Step 4: Evaluate the Options
Given the options:
1. Strong Si-O-Si bond
2. Low surface energy
3. High van der Waals forces
4. Presence of alkyl groups pointing towards the surface

The correct option is **4. Presence of alkyl groups pointing towards the surface**. This is because these groups create a hydrophobic barrier that repels water.

### Final Answer
The water-repelling characteristic of silicones is due to the presence of alkyl groups (like methyl groups) pointing towards the surface.

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