The molecular structure of silicone oil, as a fabric softener, is primarily determined by the flexibility of the silicon-oxygen (Si-O) bond backbone, the low interaction of the side-chain organic groups, and the free rotational capability of the molecular chain. These characteristics enable it to effectively reduce inter-fiber friction and impart excellent softness to fabrics. A detailed analysis follows:

I. Flexibility of the Si-O Bond Backbone
The silicone oil molecular backbone is composed of alternating silicon-oxygen (Si-O) bonds. These bonds have relatively long bond lengths and large bond angles (approximately 143°), giving the molecular chain excellent flexibility. Compared to carbon-carbon (C-C) bonds, Si-O bonds have lower rotational resistance, allowing the silicone oil molecular chain to bend and stretch freely in space. This flexibility allows the silicone oil to dynamically adjust its conformation according to the bending and friction of the fiber when forming a lubricating film on the fiber surface, continuously reducing direct contact between fibers and thus lowering the coefficient of friction.

II. Low Interactions of Side-Chain Organic Groups
Silicon atoms in silicone oil molecules are typically linked to non-polar organic groups such as methyl (-CH₃) and phenyl groups. These groups are oriented on the outer side of the molecular chain, forming a hydrophobic layer that prevents water molecules and other polar substances from penetrating the interior. Simultaneously, the interactions between non-polar groups are weak (e.g., van der Waals forces), making it difficult for surface molecules to form strong attractive forces with other substances, further reducing surface tension. This low-interaction characteristic makes the lubricating film formed by silicone oil on the fiber surface more stable and less susceptible to damage from washing or friction, thus prolonging the softening effect.

III. Free Rotation of Molecular Chains and Low Viscosity
The side-chain groups (such as methyl groups) in silicone oil molecules can rotate freely, allowing the molecular chain to more easily change its structure during flow, reducing intermolecular resistance. This characteristic results in low viscosity and good flowability of silicone oil, enabling it to penetrate evenly into fiber gaps, filling tiny surface pits and making the fiber surface smoother. For example, methyl silicone oil, with all its side chains consisting of methyl groups, has excellent low viscosity and lubricating properties, allowing it to spread quickly on the fiber surface to form a protective film.

IV. Performance Optimization of Modified Silicone Oils
The softening properties of silicone oils can be further optimized by introducing specific functional groups through chemical modification.
For example:
Amino-modified silicone oils: After introducing amino groups into the side chains or end groups, the amino groups can bind with functional groups such as hydroxyl and carboxyl groups on the fiber surface through hydrogen bonds or chemical bonds, promoting the directional adsorption of the siloxane backbone on the fiber surface. This directional adsorption reduces the coefficient of friction between fibers, giving textiles excellent softness and smoothness.
Epoxy-modified silicone oils: After introducing epoxy groups, silicone oils become reactive and cross-linkable, improving the wrinkle resistance and sewingability of fabrics.
Polyether-modified silicone oils: Combining the water solubility of polyethers and the low surface tension of silicone oils, they can be used as emulsifiers and conditioning agents in daily chemical products, making products more uniform and stable, while giving hair and skin a good smoothness and moisturizing properties.