CN105223123B - A kind of theoretical modeling research method of polyvinylidene fluoride film nano surface hole working mechanism - Google Patents
A kind of theoretical modeling research method of polyvinylidene fluoride film nano surface hole working mechanism Download PDFInfo
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- CN105223123B CN105223123B CN201510800323.3A CN201510800323A CN105223123B CN 105223123 B CN105223123 B CN 105223123B CN 201510800323 A CN201510800323 A CN 201510800323A CN 105223123 B CN105223123 B CN 105223123B
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Abstract
The present invention relates to the prediction techniques that a kind of brine composition passes through polyvinylidene fluoride film nano surface hole.The structure of VMD constructive system is specially first passed through, hydrone is then calculated separately by Adaptive biasing force method in NAMD, sodium ion and chloride ion pass through the free energy curve of nano aperture.By obtaining passing through rate in response path upper integral free energy curve.It combines corresponding structural analysis to obtain by the decomposition to free energy curve and passes through mechanism, and provide theoretical direction to the structure optimization of sea water desalination membrane.By calculating hydrone, sodium ion and chloride ion pass through rate in different size holes, obtain the full-size hole that can be used to desalinize seawater.By the change to hole configurations and modification group, influence of the different chemical environments to the hole working efficiency is obtained.It is accurate using the resulting calculated result of this method, significantly improve design efficiency.Therefore, theoretical method of the present invention can be used for the exploration of the working efficiency prediction and working mechanism of sea water desalination membrane.
Description
Technical field
The invention belongs to the theoretical prediction technology in water treatment field, it is involved in the problems, such as evaluating reverse osmosis membrane working mechanism.
Background technique
China's economy achieves huge achievement in the past more than 20 years reform and opening-up.In rapid industrial development and people
While people's living standard improves rapidly, along with the generation of a large amount of industrial and life contaminated waters.The many sheets of these contaminated wastewaters
With regard to nervous freshwater resources.And the more water resources of continuation development need social from now on.Therefore existing water resource is not enough to
Support the further demand of society.Shortage of water resources becomes the root problem of limitation social development.
Membrane separation technique is using film to the difference of component selection permeability each in solution, realizing to component solute and
The separation of solvent.This method is efficient, energy conservation, environmental protection, and molecular level filtering and filter process are simple, easily controllable etc..Therefore, extensively
Applied to fields such as food, medicine, biology, environmental protection, chemical industry, metallurgy, the energy, petroleum, electronics, be in current separation science most
One of important means.It is the current prefered method for solving shortage of water resources simultaneously.In coastal area, Membrane seawater desalination is slow
Solve the main means of these regional waters shortage.Embrane method sewage recycling is current solution water pollution problems, realizes sewage money
The one preferred technique that source utilizes.Membrane separation technique becomes guarantee drink also by the purification techniques as waterworks of new generation simultaneously
The core technology of water safety.
Film is the core element in membrane separation technique.According to the material of component film, film can be divided into inoranic membrane and organic film.
According to the size in film surface aperture, film can successively be divided into microfiltration membranes, ultrafiltration membrane, nanofiltration membrane, reverse osmosis membrane.Wherein reverse osmosis membrane
Aperture there was only several nanometers, the dissolved salts that can be effectively removed in water.Reverse osmosis membrane is based on high molecular material preparation, example
Such as cellulose acetate, aromatic polyamide, polyether sulfone, fluoropolymer.Kynoar (PVDF) is that a kind of crystallinity is fluorine-containing
Polymer, there is preferable heat resistance and thermostabilization is high, not degradable, and has its extremely strong hydrophobicity.It therefore is ideal film
Material.In recent years, people have furtherd investigate the preparating mechanism and the relevant technologies of various pvdf membranes, based on the anti-of material preparation
Permeable membrane has reached its maturity, and is widely used in coastal major seawater desalting plant.Pvdf membrane relies primarily on the desalination effect of seawater
The micropore of its surface nanoscale, selective permission hydrone passes through, while stopping passing through for ion.Existing research is main
It concentrates on improving pvdf membrane by chemical modification method, the pure water flux of pvdf membrane after testing improvement.Also have simultaneously few
The research of theoretical side is measured, these researchs have focused largely on the structure feature for inquiring into polymeric membrane, between macromolecule surface and solvent
The property at interface.And directly research pvdf membrane from microcosmic angle and process is filtered out to salt in solution, especially hydrone passes through
The process and hole of film surface hole then rarely have and are related to the repulsion process of ion.
Molecular dynamics simulation is a kind of common theoretical modeling method.It is widely used in studying biology from microcosmic angle
Film, nanotube, the nano aperture in ionophorous protein.It especially studies hydrone and ion passes through the mistake of these holes
Journey.By simulation, people largely have studied the forming process of phospholipid bilayer surface hole defect.And different external rings
Border, for example, voltage, ion concentration, ultrasonic wave, polypeptide micromolecular etc., the influence to Void Formation.And to sodium ion,
Medicine small molecule etc. passes through these holes and has done detailed simulation and analysis.Hummer of NIH et al. by theoretical method find,
There is a stable water chain structure in nanotube, wherein the dipole of each hydrone is towards unanimously, this arrangement enhances hydrophobicitys
The stability of hydrone in cavity, and greatly improve the movement speed of hydrone.The formation for illustrating water chain in nano aperture is water
Molecule efficiently passes through the structure basis of nano aperture.Former Cornell University Roux professor et al. by simulation discovery, potassium from
There are several carbonylic oxygen atoms for enclosing and periodically occurring in subchannel.Each group of carbonylic oxygen atom stablizes one by electrostatic interaction
Potassium ion.This several groups of carbonylic oxygen atoms can make to will form stable KwK (potassium ion-hydrone-potassium ion) structure in channel.When
A new potassium ion arrives, and understands and a hydrone be incorporated in channel side together, entire KwK structure moves one to the other side
Lattice, while the potassium ion of the other side and a hydrone can be discharged into environment together, the move mechanism substantially increase potassium from
The movement speed of son, and in same channel sodium ion cannot be formed with carbonylic oxygen atom NwN (sodium ion-hydrone-sodium from
Son) structure, the movement speed of sodium ion is with regard to much lower.Similarly (adulterated at equal intervals in cavity inside several with the carbon nanotube that N is adulterated
Group N atom) also show height passability to a certain specific ion.Therefore the specific structure inside hole and its with ion it
Between interaction significantly control the speed that ion passes through hole.
Conjugated free energy calculation method on the basis of molecular dynamics simulation, such as adaptive-biased power method, umbrella shape are adopted
Sample, elementary reaction dynamics (metadynamics) etc. determine quantifier elimination ion and pass through various interactions during hole
Contribution.This method is widely used in research ion channel, calculates free energy curve when ion passage lanes, finds crossing process
In some metastable states, analyze these metastable structures.The position of free energy highest point is obtained, is locked crucial residual in crossing process
The position of base.And the energy barrier height of crossing process is obtained, it calculates pass through rate on this basis.The side that ion passes through in the channel
Formula is uncertain, it may be possible to excessively complete second ion of an ion after, it is also possible to two or three ions cooperate withs lead to together
It crosses, can be indicated at this time with Two Dimensional Free energy curved surface or 3 D auto energy flow pattern.It is passed through additionally by calculating ion not of the same race logical
The Gibbs free situation in road can compare the complexity that these ions pass through hole.This method has been widely used in
Study of various ion, small molecule pass through the hole inside a variety of channel proteins.
This project exactly based on this, studies nano aperture in pvdf membrane by application molecular dynamics simulation
Rock-steady structure and the factor for influencing the structure.Water chain structure in primary study pvdf membrane hole discloses hydrone in hole
Pass through mechanism.Secondly Conjugated free energy calculation method, studies sodium ion and chloride ion passes through pvdf membrane nano surface hole
Process.Aim to solve the problem that following three problems: the rock-steady structure of nano aperture in pvdf membrane, hydrone passes through mechanism in the hole
And the hole is to the filtration mechanism of sodium ion and chloride ion.It is desirable that nano aperture in pvdf membrane is calculated by simulation
Middle hydrone refuses salt mechanism by mechanism and hole.It is desalinized seawater the understanding of mechanism with expanding us to pvdf membrane.For with
It designs and more efficiently provides fundamental basis with durable PVDF class sea water desalination membrane afterwards.
Summary of the invention
The purpose of the present invention is in view of the above problems, provide a kind of theoretical prediction ultrafiltration membrane and small molecule contaminants
The method of bond strength, so that the working efficiency of assessment ultrafiltration membrane.
The technical scheme comprises the following steps provided by realize the present invention:
1) Kynoar chain is chosen for constructing pvdf membrane, chooses sodium ion and chloride ion passes through polymeric membrane surface
Nano-void is modeled by ChemDraw and VMD.
2) movement of molecular dynamics simulation software NAMD simulated system in a solvent is used.It uses in this procedure
Interaction in CHARMM position description system between each molecule.Using periodic boundary condition.It is dynamic using Langevin
Mechanics and the control of Langevin piston pressure, are maintained at 298K and 1bar for temperature and pressure.It is calculated using Verlet r-RESPA
Method integrates the equation of motion.All covalent bonds comprising hydrogen atom are limited using SHAKE algorithm.For nonbonding phase
Interaction uses application truncation, and electrostatic interaction is handled using PME method.
3) reaction coordinate is chosen, ion is calculated using Adaptive biasing force method method and passes through high score
Gibbs free when sub- film surface nano aperture.
4) it is calculated by the following formula out the Conjugated free energy constant of two small molecules.
The theoretical modeling method used in the present invention can predict that sodium ion and chloride ion pass through pvdf membrane nano surface hole
Rate constant when hole is a kind of green safe prediction technique without handling actual sample.Utilize existing simulation
Software can be predicted directly, and component each in reverse osmosis membrane can be optimized and be improved according to calculated result.Therefore, originally
Invention provides a kind of quick material function appraisal procedure.
Detailed description of the invention
Fig. 1 for (A) pvdf membrane studied and film surface hole.(B) vertical view of the sectional view of hole and (C) hole
Figure.
Specific embodiment
To be best understood from the present invention, the present invention will be further described in detail below with reference to the embodiments, but of the invention
Claimed range is not limited to the range of embodiment expression.
Embodiment:
1) this project selects Kynoar chain (containing 20 repetitive units) to prepare polymeric membrane first.Pass through ChemDraw
Construct the pdb structure of vinylidene chain, sodium ion and chloride ion.The psf of these three molecules is constructed by psfgen plug-in unit in VMD
File, and changed three kinds of molecule difference solvent (water) using VMD software.
2) the molecular dynamics simulation software NAMD write using Klaus Schulten seminar of U.S. UIUC university.?
The charmm general force field description system developed in the program using Maryland university professor Mackerell
Middle Kynoar chain, sodium ion and chloride ion.Hydrone is described using TIP3P model.Under NVT assemblage, service life
Boundary condition.It is controlled respectively using Langevin dynamics and Langevin piston pressure, temperature and pressure is maintained at 298K
And 1bar.The equation of motion is integrated using the Verlet r-RESPA algorithm of multi-time-step, time step 2fs.It adopts
All covalent bonds comprising hydrogen atom are limited with SHAKE algorithm.Every 10 step updates primary non-key table.It is mutual for nonbonding
Effect usesCutoff value, electrostatic interaction using particle mesh Ewald method handle.PVDF chain is carried out
Energy, which minimizes, to be calculated, and simulation is then balanced.Using the chain of balance as the array of building unit 5 × 6 × 2.To the structure into
Row energy minimizes and balance simulation.At least 200ns simulation is carried out, the size of whole system is counted.After the dimensionally stable, both
It can determine that the film is stable.
The energy for carrying out 20ps to moisture film system minimizes.The balance simulation of 20ns.Obtain the balanced structure of moisture film system.
Secondly by the tclBC functional module in NAMD, hole is generated in film surface.Based on the script provided in study course, from Z axisIn range, applying a force constant to all PVDF molecules is 5.With the power gradually to decay that becomes larger with a distance from Z axis.It carries out
The simulation of 20ns.Determine that the hole configurations has been balanced.TclBC functional module is closed, simulation is balanced, by calculating hole
The aperture in hole.And observation aperture is changed with time situation.Balance simulation stops when aperture no longer changes.Then change poly-
The degree of polymerization and film thickness of vinylidene chain study influence of these factors to hole configurations.Finally research aperture is to hole knot
The influence of structure.
It is observed by VMD, the conformation of hydrone in hole.In the carbon nanotube hole of similar water transport property, Ren Menfa
The existing molecular chain structure of one and only one moisture.The movement speed of hydrone is moisture in ontology phase in the water chain structure
1.7 times or so of sub- diffusion velocity.Therefore the water chain structure is the structure basis that hydrone high speed passes through in hole.Therefore, originally
Partial emphasis is the presence for confirming water chain structure in hole.And when film pressure at both sides is 1 atmospheric pressure, hydrone is calculated
Pass through the flux of the hole.The pressure for then changing film two sides water phase, calculates the hydrone flux in hole.In aforementioned research
On the basis of, consider influence of the hole aperture to water chain structure and hydrone flux.Final estimation is being kept existing for water chain structure
On the basis of, the maximum value of fenestra hole diameter.
3) proposed free energy calculation method Adaptive is taught in conjunction with the Eric Darve of Stanford university
Biasing force method (ABF), studies sodium ion and chloride ion passes through the free energy curve of pvdf membrane surface hole defect.Choosing
Take ion to the distance distanceZ of center membrane plane as reaction coordinate, by following formula quantify the energy of counting system along
The first differential of the reaction coordinate.
Then this first derivative is integrated along reaction coordinate and just obtains free energy curve, be shown below.
After obtaining free energy curve, the legitimacy of confirmatory reaction coordinate is needed.At the energy barrier of free energy curve, selection
The conformation of certain amount (such as saying 100).20 balance simulations are carried out to each conformation.It is required that the temperature phase simulated every time
Together, but the initial velocity of each atom is different.The transient equilibrium simulation of 20ps is carried out, system falls in energy barrier one after statistical simulation
The probability of side.And count the distribution situation of corresponding 100 probability of 100 conformations.If the distribution is gaussian-shape and with 0.5 is
Center, the then reaction coordinate selected are correct.
4) free energy curve is further decomposed by the pair interaction calculation module in NAMD
At multiple interaction items.Which entire adsorption process is analyzed to be controlled by interaction.These phases of integrated structure analysis and summary
Contribution of the interaction term in different phase to ion crossing process, is specifically passed through mechanism, and obtains the main tribute of energy barrier
Offer factor.At the same time, the reaction rate of entire crossing process is calculated in integral free energy curve.It can be estimated by the rate
Calculate the flux of pvdf membrane surface hole defect.Above-mentioned calculating then carried out to the hole of different pore size, research aperture and ionic flux it
Between relationship, finally estimate ion can be stopped to pass through maximum diameter of hole.
Claims (2)
1. a kind of method of Fast Evaluation sea water desalination membrane working efficiency, it is characterised in that: hydrone is calculated using theoretical method,
What sodium ion and chloride ion passed through sea water desalination membrane nano surface hole passes through rate；Steps are as follows:
Step 1: choosing Kynoar chain for constructing pvdf membrane, choose sodium ion and chloride ion passes through PVDF polymeric membrane table
The nano aperture in face is modeled by ChemDraw and VMD；
Step 2: using the movement of molecular dynamics simulation software NAMD simulated system in a solvent, using Langevin dynamics
It is controlled with Langevin piston pressure, keeps the temperature at 298K, pressure is maintained at 1bar, it is minimum to carry out energy to PVDF chain
Change and calculate, simulation is then balanced, using the PVDF chain of balance as the array of building unit 5 × 6 × 2, to the PVDF chain of balance
The array of building carries out energy minimum and balance simulation, after whole system dimensionally stable, that is, can determine that pvdf membrane is steady
It is fixed；
Step 3: by the tclBC functional module in NAMD, in pvdf membrane Surface Creation hole, water in hole being observed by VMD
Molecular conformation confirms that water chain structure whether there is in hole, calculate hydrone flux in hole, obtains hole aperture and chain to water
The influence of structure and hydrone flux；Change the pressure of film two sides water phase, calculate the hydrone flux in hole, keeps water link
On the basis of structure is existing, the maximum value of fenestra hole diameter is determined；
Step 4: choosing ion to the distance Z of center membrane plane as reaction coordinate, using Adaptive biasing force
Method method calculates Gibbs free when ion passes through polymeric membrane nano surface hole, after obtaining free energy curve, tests
Demonstrate,prove the legitimacy of reaction coordinate；Free energy curve is further decomposed into multiple interaction items, is summarized in conjunction with Analysis of Membrane Structures
Interact contribution of the item in different phase to ion crossing process, is specifically passed through mechanism；Integrate free energy curve meter
Calculation obtains the reaction rate of entire ion crossing process；The calculating for obtain to the hole of different pore size reaction rate, obtains
Relationship between hole aperture and ionic flux.
2. a kind of method of Fast Evaluation sea water desalination membrane working efficiency according to claim 1, it is characterised in that: use
The pre- measured ion of molecular dynamics simulation Conjugated free energy calculation method passes through the rate of sea water desalination membrane, and the result is applied to sea
Water desalinates field.
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| CN107563146A (en) * | 2017-10-17 | 2018-01-09 | 天津工业大学 | It is a kind of to evaluate milipore filter and the method for small molecule organic pollution bond strength |
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| CN103558348A (en) * | 2013-11-18 | 2014-02-05 | 天津工业大学 | Method for rapidly evaluating binding strength of ultrafiltration membrane and small organic molecular pollutant |
| WO2014155894A1 (en) * | 2013-03-28 | 2014-10-02 | 株式会社日立製作所 | Reverse osmosis equipment performance calculation method, reverse osmosis equipment performance calculation device and program |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2014155894A1 (en) * | 2013-03-28 | 2014-10-02 | 株式会社日立製作所 | Reverse osmosis equipment performance calculation method, reverse osmosis equipment performance calculation device and program |
| CN103558348A (en) * | 2013-11-18 | 2014-02-05 | 天津工业大学 | Method for rapidly evaluating binding strength of ultrafiltration membrane and small organic molecular pollutant |
Non-Patent Citations (2)
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Inventor after: Liu Peng Inventor after: Tan Xiaoyao Inventor after: Yu Pengfei Inventor after: Yang Jingjing Inventor after: Yang Kun Inventor before: Liu Peng Inventor before: Yang Jingjing Inventor before: Tan Xiaoyao Inventor before: Yang Kun |
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