Question:
Select the statement of Smectic liquid crystal
Select the statement of Smectic liquid crystal
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Liquid crystals are crucial in pharmaceutical applications, especially in transdermal and controlled drug delivery systems, due to their unique alignment and mobility characteristics.
Updated On: Jul 14, 2026
- Mobility in two directions or no rotation
- Three directions or no rotation
- Mobility in two directions or rotation in one axis
- Mobility in three directions or rotation in one axis
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The Correct Option is C
Approach Solution - 1
Liquid crystals are a state of matter that possess properties between those of conventional liquids and solid crystals. The smectic phase is one of the most ordered liquid crystalline phases.
- Smectic liquid crystals are characterized by their molecules being arranged in distinct layers. Within each layer, the molecules are free to move (flow) in two directions (within the layer), and they exhibit rotational motion around their long axis.
- This contrasts with nematic liquid crystals, where molecules are oriented in the same direction but do not form layers.
- In smectic phases, molecular mobility is restricted compared to nematic phases but still allows some fluidity. The molecular arrangement leads to anisotropic properties, which are crucial for their applications in display technologies and drug delivery systems.
Thus, smectic liquid crystals show mobility in two directions and rotation around one axis, which corresponds to option (c).
- This contrasts with nematic liquid crystals, where molecules are oriented in the same direction but do not form layers.
- In smectic phases, molecular mobility is restricted compared to nematic phases but still allows some fluidity. The molecular arrangement leads to anisotropic properties, which are crucial for their applications in display technologies and drug delivery systems.
Thus, smectic liquid crystals show mobility in two directions and rotation around one axis, which corresponds to option (c).
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Approach Solution -2
This question asks how molecules move within a smectic liquid crystal phase. Comparing the layered structure of the smectic phase against what mobility in two directions and rotation actually mean physically sorts out the right description.
- Mobility in two directions or no rotation: This description captures the layered sliding motion correctly but leaves out the rotational freedom molecules retain around their own long axis within a layer, so it is only half right.
- Three directions or no rotation: Smectic molecules are confined to move within their layer rather than moving freely in all three dimensions, since the layered structure restricts motion perpendicular to the layers. This overstates the translational freedom while also denying rotation, which does not fit either.
- Mobility in two directions or rotation in one axis: In the smectic phase, molecules are arranged in stacked layers. Within a layer, a molecule can slide sideways and forwards and backwards, which is motion in the two directions that make up the plane of the layer, and it can also spin around its own long molecular axis. This combination of restricted sliding plus rotation about one axis matches how the smectic phase is described.
- Mobility in three directions or rotation in one axis: Free movement in three directions would mean the molecules are not confined to layers at all, which describes a liquid rather than the layered smectic structure.
The layered arrangement of the smectic phase restricts molecules to sliding within their own layer while still letting them rotate about their long axis, matching the two-directions-plus-one-axis-rotation description.
So the correct answer is mobility in two directions or rotation in one axis.
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