Institute of Physical Chemistry of the Polish Academy of Sciences, 44/52 Kasprzaka Street, 01-224 Warsaw, Poland.
Nanoscale. 2013 Oct 21;5(20):9732-8. doi: 10.1039/c3nr03496h.
We measure the frequency of collective molecular precession as a function of temperature in the ferroelectric liquid crystalline monolayer at the water-air interface. This movement is driven by the unidirectional flux of evaporating water molecules. The collective rotation in the monolayer with angular velocities ω ~ 1 s(-1) (at T = 312 K) to 10(-2) s(-1) (at T = 285.8 K) is 9 to 14 orders of magnitude slower than rotation of a single molecule (typically ω ~ 10(9) to 10(12) s(-1)). The angular velocity reaches 0 upon approach to the two dimensional liquid-to-solid transition in the monolayer at T = 285.8 K. We estimate the rotational viscosity, γ1, in the monolayer and the torque, Γ, driving this rotation. The torque per molecule equals Γ = 5.7 × 10(-8) pN nm at 310 K (γ1 = 0.081 Pa s, ω = 0.87 s(-1)). The energy generated during one turn of the molecule at the same temperature is W = 3.5 × 10(-28) J. Surprisingly, although this energy is 7 orders of magnitude smaller than the thermal energy, kBT (310 K) = 4.3 × 10(-21) J, the rotation is very stable. The potential of the studied effect lies in the collective motion of many (>10(12)) "nano-windmills" acting "in concerto" at the scale of millimetres. Therefore, such systems are candidates for construction of artificial molecular engines, despite the small energy density per molecular volume (5 orders of magnitude smaller than for a single ATPase).
我们测量了在水-空气界面处铁电液晶单层中的集体分子进动频率作为温度的函数。这种运动是由蒸发水分子的单向流动驱动的。在单层中，集体旋转的角速度ω1 s(-1)（在 T = 312 K 时）到 10(-2) s(-1)（在 T = 285.8 K 时）比单个分子的旋转慢 9 到 14 个数量级（通常ω10(9)到 10(12) s(-1)）。当接近单层中的二维液-固转变时，角速度在 T = 285.8 K 时降至 0。我们估计了单层中的旋转粘度γ1和驱动这种旋转的扭矩Γ。在 310 K 时，每个分子的扭矩等于Γ= 5.7 × 10(-8) pN nm（γ1 = 0.081 Pa s，ω = 0.87 s(-1)）。在相同温度下，分子旋转一圈产生的能量为 W = 3.5 × 10(-28) J。令人惊讶的是，尽管这种能量比热能 kBT（310 K）= 4.3 × 10(-21) J 小 7 个数量级，但旋转非常稳定。这种效应的潜力在于许多（>10(12)）“纳米风车”的集体运动，它们在毫米级的范围内“协同”作用。因此，尽管每个分子体积的能量密度（比单个 ATPase 小 5 个数量级）很小，但这些系统仍然是构建人工分子发动机的候选者。
