Diffusion cannot be a major water transport mechanism in osmotic membranes because of the lack of true water concentration gradient within the membrane. Due to the semipermeable property of osmotic membranes, water concentration in the membrane is virtually constant because of the absence of salts. The recently confirmed porous structure of the skin layer of osmotic membranes cannot support the basis to exclude bulk water flow in the membrane as assumed in the classic solution-diffusion model. Herein we demonstrate that the concentration difference of water at the membrane-solution interface manifests itself as a negative hydraulic pressure in the membrane. Hence, the only possible driving force for water movement in osmotic membranes is hydraulic pressure gradient. Osmotically driven membrane processes are characterized with negative pressure within the membrane below the water vapor pressure, inevitable leading to the formation of vapor or small bubbles within the membrane matrix. This phenomenon is expected to markedly reduce the effectiveness of osmotic pressure as a driving force for water transport. Delineation of the breakdown and possible restoration of water continuity under negative pressure is essential for proper understanding of the principles governing water transport in osmotic membranes.

由于膜内缺乏真实的水浓度梯度，扩散不能成为渗透膜中的主要水传输机制。由于渗透膜的半透性，由于不含盐，膜中的水浓度实际上是恒定的。最近证实的渗透膜表层的多孔结构不能支持排除在经典溶液扩散模型中假设的膜中大量水流的基础。在这里，我们证明了膜 - 溶液界面处水的浓度差异本身表现为膜中的负液压。因此，渗透膜中水运动的唯一可能驱动力是水压梯度。渗透驱动的膜过程的特点是膜内的负压低于水蒸气压，不可避免地导致膜基质内形成蒸汽或小气泡。预计这种现象将显着降低渗透压作为水运输驱动力的有效性。描述负压下水的连续性分解和可能的恢复对于正确理解渗透膜中水传输的原理至关重要。