Study On The Mechanism Of Osmosis At Nano Scale

In the field of engineering and materials,the artificial membrane technology,which already has huge commercial market,still maintains a rapid development momentum:reverse osmosis(RO).Nanofiltration(NF)and other mature and proven membrane technologies are widely used in many fields including wastewater treatment,seawater desalination and continue to be optimized;new membrane technologies including forward osmosis(FO),pressure retarded osmosis(PRO)advance constantly and have begun commercialization attempt.The fast-evolving nanotechnology captivates researchers in many areas including membrane desalination technology.Nano-materials such as carbon nanotubes and graphene are introduced into the field of membranes manufacturing in order to improve their performance.In the biological field,as the origin of life,water plays important physiological roles by acting as both the carrier of material transport and the environment of various biochemical reactions.In recent years,many natural nano-scale water channels including aquaporin(AQP)and UT-B(a urea transporter,which also has water permeability)were discovered and studied.Understanding the function and the physiological significance of these nano channels at the levels of cell,tissue and organism to develop new medical methods and drugs has been an important research project at present and in the future.The core issue of the subjects discussed above is the osmosis at nanoscale.The existing theories that describe this problem are mainly phenomenological models represented by K-K equations.The defects and shortcomings of such models are exposed by both new experimental data and application requirements.Overcoming these shortcomings and searching a deeper understanding of the nano-scale mass transfer become increasingly urgent.Therefore,the mechanism of nano-scale osmosis process was studied by combining theories and experiment.The main contents are as follows:1.Theoretical and Experimental Study on the Kinetics of Nanoscale Osmosis.On the basis of McMillan-Mayer solution theory,the effect of solute size on the osmosis process at the nanometer scale was analyzed using molecular dynamics method.The kinetic description was introduced into the thermodynamic analysis of permeation and diffusion.The kinetic osmotic pressure coefficient and the solute transport rate are introduced to modify the K-K equation.The former one is mainly influenced by the entrance effect of the nanochannel,while the latter is determined by both the entrance effect and the internal structure of the channel.The new model was found to be highly accurate by compareing with the AQP permeation experiments in the literature and able to solve the long-troubled puzzle in membrane physiology that the reflection coefficients(actually the kinetic osmotic pressure coefficient)of the completely impermeable solutes are less than 1 and are positively correlated with the molecular sizes,the Solomon-Hill effect.In order to rule out the possible interference of UT-B in red blood cell(RBC)osmosis experiments,we conducted a nano-scale mass transfer experiment using red cells from UT-B knockout mice.As a natural nano-channel,AQP1 is rich expressed in RBCs and makes RBCs an ideal material for nanoscale mass transfer experiments.Using stopped-flow,the fast non-equilibrium osmosis process through AQP1 can be recorded.The difference in the kinetic osmotic pressure between two completely impermeable solutes(larger glucose molecules and smaller urea molecules)to AQP1 was measured more precisely.The influence of UT-B on the kinetic osmotic pressure of small molecules to RBC was found to be limited.2.Study on the Non-equilibrium Thermodynamics of Nano-scale Mass Transfer.In the study of non-equilibrium thermodynamics of AQP1 osmosis.Solomon-Hill effect was found to bring new question:in some cases,it allows water molecules to transport through the AQP1 against the chemical potential difference:an entropy reduction process that violates the second law of thermodynamics.Due to its hourglass shape,AQP1 can sense the information of solute molecules in osmosis.AQP1 move water against its chemical potential gradient at the cost of consuming this information,which will cause additional entropy production according to Landauer’s principle.By adding this entropy increase,the whole entropy change will also be greater than 0.Taken together,AQP1 in fact can work as one kind of Maxwell’s Demon in the body:it can move water against its chemical potential gradient at the cost of consuming information in same case.Subsequently,possible physiological and theoretical significance of the AQP1-Demon mechanism is discussed.On the basis of this work,the concept of "information availability" was introduced.By taking into account the information at the boundary of the system and the information about the system’s microscopic reversibility,entropy increasing principle for isolated system was extended to available information attenuation principle for any system.From the view of available information,the cycle processes of the classical Carnot engine were analyzed.A result consistent with the conventional thermodynamics was got as well as the deep connectiones among Szilard engine,and Carnot’s theorem.Then,from the perspective of information,the Gibbs paradox,spooky action at a distance in quantum entanglement,the thermodynamics of PRO system,urea transport against its concentration gradient in the kidney,and the black hole information paradox were analyzed.Some new conclusions that may contribute to the development of related fields were obtained.