Hyper-crosslinked Isoporous Block Copolymer Membranes with Robust Solvent Resistance and Customized Pore Sizes for Precise Separation.

Isoporous block copolymer membranes are viewed as the next-generation separation membranes for their unique structures and urgent application in precise separation. However, an obvious weakness for such membranes is their poor solvent-resistance which limits their applications to aqueous solution, and isoporous membranes with superior solvent-resistance and tunable pore size have been rarely prepared before. Herein, self-supporting isoporous membranes with excellent solvent resistance are prepared by the facile yet robust hyper-crosslinking approach which is able to create a rigid network in whole membranes. The hyper-crosslinking is found to be a novel and non-destructive approach that does not change pore size and isoporous structure during the reaction, and the resulting hyper-crosslinked isoporous membranes display superior structural and separation stability to a broad range of solvents with varied polarities for months to years. More importantly, hyper-crosslinking has proved to be a universal strategy that is applicable to isoporous membranes with varied pore size and pore chemistry, offering an important opportunity to prepare solvent-resistant isoporous membranes with customizable pore size and pore functionality that are important to realize their accurate separations in organic solvents. This concept is demonstrated finally by precise and on-demand separation of nanoparticles with the prepared membranes.

Structure-controlled zwitterionic nanocapsules with thermal-responsiveness.

A facile approach is established to prepare zwitterionic nanocapsules (ZN C s) with controlled diameters and core/shell structures based on an inverse reversible addition-fragmentation transfer (RAFT) miniemulsion interfacial polymerization method. The diameters and core volume fractions of ZNCs can be tuned finely from 61 to 220 nm and from 0.22 to 0.61, respectively. Furthermore, the thermal-responsive property of the prepared zwitterionic nanocapsules was systematically studied relating to core/shell ratios and cross-linking degrees. These ZNCs could be particularly useful in constructing polymeric materials with well-defined nanoporous structures for nano-void membranes, drug delivery devices and catalytic carriers.

Intrinsic Nanoscale Structure of Thin Film Composite Polyamide Membranes: Connectivity, Defects, and Structure-Property Correlation.

Transport of water, solutes, and contaminants through a thin film composite (TFC) membrane is governed by the intrinsic structure of its polyamide separation layer. In this work, we systematically characterized the nanoscale polyamide structure of four commercial TFC membranes to reveal the underlying structure-property relationship. For all the membranes, their polyamide layers have an intrinsic thickness in the range of 10-20 nm, which is an order of magnitude smaller than the more frequently reported apparent thickness of the roughness protuberances due to the ubiquitous presence of nanovoids within the rejection layers. Tracer filtration tests confirmed that these nanovoids are well connected to the pores in the substrates via the honeycomb-like opening of the backside of the polyamide layers such that the actual separation takes place at the frontside of the polyamide layer. Compared to SW30HR and BW30, loose membranes XLE and NF90 have thinner intrinsic thickness and greater effective filtration area (e.g., by the creation of secondary roughness features) for their polyamide layers, which correlates well to their significantly higher water permeability and lower salt rejection. With the aid of scanning electron microscopy, transmission electron microscopy, and tracer tests, the current study reveals the presence of nanosized defects in a polyamide film, which is possibly promoted by excessive interfacial degassing. The presence of such defects not only impairs the salt rejection but also has major implications for the removal of pathogens and micropollutants.

Nanovoid Membranes Embedded with Hollow Zwitterionic Nanocapsules for a Superior Desalination Performance.

In order to lower the capital and operational cost of desalination and wastewater treatment processes, nanofiltration (NF) membranes need to have a high water permeation and ionic rejection, while also maintaining a stable performance through antifouling resistance. Recently, Turing-type reaction conditions [ Science 2018, 360, 518-521] and sacrificed metal organic frame (MOF) nanoparticles [ Nat. Commun. 2018, 9, 2004] have been reported to introduce nanovoids into thin-film composite (TFC) polyamide (PA) NF membranes for an improved performance. Herein, we report a one-step fabrication of thin-film nanocomposite membranes (TFNM) with controllable nanovoids in the polyamide layer by introducing hollow zwitterionic nanocapsules (HZNCs) during interfacial polymerization. It was found that embedding HZNCs increases the membrane internal free volume, external surface area, and hydrophilicity, thus enhancing the water permeation and antifouling resistance without trading off the rejection of multivalent ions. For example, water permeation of the NF membranes embedded with about 19.0 wt % of HZNCs (73 L m-2 h-1) increased by 70% relative to the value of the control TFC NF membrane without HZNCs (43 L m-2 h-1). This increase comes while also maintaining 95% rejection of Na2SO4. Further, we also determined the effect of the mass loading of HZNCs on the top surface of the TFC NF membranes on the membrane performance. This work provided a direct and simple route to fabricate advanced desalination membranes with a superior separation performance.

Antibiofouling polysulfone ultrafiltration membranes via surface grafting of capsaicin derivatives.

Biofouling is a critical issue in the membrane separation process as it can increase the operational cost by lower down membrane permeability. Covalent binding of an antibacterial agent on the membrane surface to kill microorganisms to hinder biofouling formation process draws great attention. In this study, we used three kinds of capsaicin derivatives, MBHBA, HMBA, and HMOBA, to fabricate antibiofouling membrane via UV-assisted photo grafting method. The influence of these capsaicin derivatives on membrane properties was investigated and compared. The results suggest that HMBA showed the best UV activity, followed by HMOBA and MBHBA successively. Due to the difference of functional groups among capsaicin derivatives, there is an increase in membrane wettability of HMBA and HMOBA-modified membranes, while there is a decrease for MBHBA-modified membrane. MBHBA-modified membrane showed enhanced irreversible fouling, which is in contrast to that of HMBA- and HMOBA-modified membranes. The modified membranes showed similar antibacterial activity against Escherichia coli. The practicability of the modified membranes was examined by dipping them into tap water and seawater for 30 days, and the results displayed the modified surfaces have the potential to relieve biofouling for separation membranes.

Enhanced flux performance of polyamide composite membranes prepared via interfacial polymerization assisted with ethyl formate.

A novel thin film composite (TFC) polyamide reverse osmosis membrane was prepared via the interfacial polymerization of m-phenylene diamine (MPD) in aqueous phase and 1,3,5-trimesoyl chloride (TMC) in organic phase on a polysulfone ultrafiltration support by assisting with ethyl formate as a co-solvent added in the organic phase. The ethyl formate added in the organic phase is intended to form a narrow miscibility zone, which leads to the thicker reaction zone. The multi-layered loose polyamide structure with larger pore size was formed due to the thicker reaction zone and lower content of MPD. The enhanced hydrophilicity of the membrane was proved by the decreased water contact angle. Water flux was measured at 1.6 MPa with 2,000 ppm NaCl aqueous solution. Compared to the TFC membrane prepared without ethyl formate, the water flux across the TFC membrane with ethyl formate in the organic phase increased with the increased ethyl formate content (from 23 to 45 L/(m2 h)) and the salt rejection remained at a high level (>90%). The ethyl formate can be used as a co-solvent to effectively enhance the performance of the TFC membrane.

Layer-by-layer assembly of aquaporin Z-incorporated biomimetic membranes for water purification.

We fabricated a biomimetic nanofiltration (NF) membrane by immobilizing an Aquaporin Z (AqpZ)-incorporated supported lipid bilayer (SLB) on a layer-by-layer (LbL) complex polyelectrolyte membrane to achieve excellent permeability and salt rejection with a high stability. The polyelectrolyte membranes were prepared by LbL assembly of poly(ethylenimine) (PEI) with positive charges and poly(sodium 4-styrenesulfonate) (PSS) with negative charges alternately on a porous hydrolyzed polyacrylonitrile (H-PAN) substrate. AqpZ-incorporated 1,2-dioleloyl-sn-glycero-3-phosphocholine (DOPC)/1,2-dioleoyl-3-trimethylammo-nium-propane (chloride salt) (DOTAP) vesicles with positive charges were deposited on the H-PAN/PEI/PSS polyelectrolytes membrane surface. The resulting biomimetic membrane exhibited a high flux of 22 L·m(-2)·h(-1) (LMH), excellent MgCl2 rejection of ∼97% and NaCl rejection of ∼75% under an operation pressure of 0.4 MPa. Due to the attractive electrostatic interaction between SLB and the polyelectrolyte membrane, the biomimetic membrane showed satisfactory stability and durability as well as stable NF flux and rejection for at least 36 h. In addition, the AqpZ-containing biomimetic membrane was immersed in a 0.24 mM (critical micellar concentration, CMC) Triton X-100 solution for 5 min. The flux and rejection were slightly influenced by the Triton X-100 treatment. The current investigation demonstrated that the AqpZ-incorporated biomimetic membranes fabricated by the LbL method led to excellent separation performances and robust structures that withstand a high operation pressure for a relatively long time.

Impact of monoolein on aquaporin1-based supported lipid bilayer membranes.

Aquaporin (AQP) based biomimetic membranes have attracted considerable attention for their potential water purification applications. In this paper, AQP1 incorporated biomimetic membranes were prepared and characterized. The morphology and structure of the biomimetic membranes were characterized by in situ atomic force microscopy (AFM), infrared absorption spectroscopy, fluorescence microscopy, and contact angle measurements. The nanofiltration performance of the AQP1 incorporated membranes was investigated at 4 bar by using 2 g l-1 NaCl as feed solution. Lipid mobility plays an important role in the performance of the AQP1 incorporated supported lipid bilayer (SLB) membranes. We demonstrated that the lipid mobility is successfully tuned by the addition of monoolein (MO). Through in situ AFM and fluorescence recovery after photo-bleaching (FRAP) measurements, the membrane morphology and the molecular mobility were studied. The lipid mobility increased in the sequence DPPC < DPPC/MO (RMO = 5/5) < DOPC/MO (RMO = 5/5) < DOPC, which is consistent with the flux increment and salt rejection. This study may provide some useful insights for improving the water purification performance of biomimetic membranes.

Reversibly Cross-Linked Isoporous Membranes Fabricated by the Recyclable Block Copolymer with Pendent Dithiolane Groups.

The reversible formation and cleavage of disulfide bonds under physical/chemical stimuli make it a valuable motif in constructing dynamically cross-linked materials. In the present work, the block copolymer bearing pendent dithiolanes was synthesized and fabricated into isoporous membranes by the combination of self-assembly and nonsolvent-induced phase separation strategy. The cross-linking within the membrane was realized by the thiol-initiated ring-opening cascades of cyclic disulfides. Successful formation of disulfide bond networks within the isoporous membranes was proved by the Raman spectra, UV-vis diffuse reflectance spectroscopy, differential scanning calorimetry, and rheological analysis. The cross-linking in membranes was further demonstrated by the notably improved toughness and obviously enhanced swelling resistance to acid/alkaline solution as well as organic solvents. Importantly, the cross-linked isoporous membranes were fully dissolvable in solution containing dithiothreitol, which enabled the complete cleavage of disulfide bonds and successful recovery of the block copolymer that was able to be repeatedly fabricated into isoporous membranes with pore sizes identical to membranes prepared from the freshly synthesized copolymer. Our results indicate that dynamically cross-linked isoporous membranes with improved durability and good recyclability can be custom-made by simply incorporating active dithiolane moieties into self-assembling block copolymers.

Enhancing the water permeability of composite NF membranes through the incorporation of organic ions in the aqueous phase.

Composite nanofiltration (NF) membranes prepared using interfacial polymerization (IP) have gained significant attention in the field of wastewater treatment. In this study, sodium camphor sulfonate (CSA-Na) and tetraethylammonium chloride (TEAC) were employed as aqueous phase additives to regulate the diffusion of piperazine (PIP) molecules through electrostatic interactions. The dissociated CSA-Na and TEAC in the aqueous solution formed an organic structure at a certain concentration, restricting the interfacial transport behavior of PIP monomers. The results show that when the content of CSA-Na is 2% w/v, TEAC is 3.9% w/v, that is, the material dosage ratio is 1 : 3, and the NF membrane shows the best performance, with a water flux of 55.61 L m-2 h-1 (test pressure is 0.5 MPa), and MgSO4 rejection rate of more than 98%.

Construction of PDA-PEI/ZIF-L@PE tight ultra-filtration (TUF) membranes on porous polyethylene (PE) substrates for efficient dye/salt separation.

Tight ultra-filtration (TUF) membranes were constructed by in situ growing zinc imidazole frameworks micro-crystalline leaves (ZIF-L) in polyethylene imine (PEI) and polydopamine (PDA) deposit layers on porous polyethylene (PE) substrates. The effects of preparation conditions on the surface physical and chemical structures as well as on the dye/salt separation performance of the formed TUF membranes were systematically investigated. By inserting selective water permeation channels and increasing contacting surface areas, in situ-grown ZIF-L arrays tightly cross-linked in the coating matrix greatly increased water permeation without trading off dye/salt retention selectivity. The morphology of the included ZIF-L particles could be varied by adjusting the ligand/Zn molar ratio (α) in the preparation processes. Optimized PDA-PEI/ZIF-L@PE TUF membranes containing ZIF-L of cross-cross block morphology showed very high pure water permeability of 180 ± 20 L·m-2·h-1·bar-1 (LMHB) and retention selectivity (SCR/Na2SO4 and SMB/Na2SO4) of 267 and 43, respectively, as well as excellent stability and anti-fouling properties.

Double cross-linked 3D layered PBI proton exchange membranes for stable fuel cell performance above 200 °C.

Phosphoric acid doped proton exchange membranes often experience performance degradation above 200 °C due to membrane creeping and phosphoric acid evaporation, migration, dehydration, and condensation. To address these issues, here we present gel-state polybenzimidazole membranes with double cross-linked three-dimensional layered structures via a polyphosphoric acid sol-gel process, enabling stable operation above 200 °C. These membranes, featuring proton-conducting cross-linking phosphate bridges and branched polybenzimidazole networks, effectively anchor and retain phosphoric acid molecules, prevent 96% of its dehydration and condensation, improve creep resistance, and maintain excellent proton conductivity stability. The resulting membrane, with superior through-plane proton conductivity of 0.348 S cm-1, delivers outstanding peak power densities ranging from 1.20-1.48 W cm-2 in fuel cells operated at 200-240 °C and a low voltage decay rate of only 0.27 mV h-1 over a 250-hour period at 220 °C, opening up possibilities for their direct integration with methanol steam reforming systems.

Ligand Substitution: An Effective Way for Tuning Structures of ZIF-7 Nanoparticles (NPs) and Improving Energy Recovery Performance of ZIF/PA TFN Membranes.

It is an important initiative to reduce the building energy consumption using energy recovering ventilation (ERV) systems. The application of ERV systems is hindered by the low CO2 barrier performance of commercial total heat exchange membranes (THEMs) that lead to unsatisfactory indoor air refreshing rate, and there is an urgent need for THEMs that have improved CO2 barrier properties and effective energy recovery efficiencies. Here, we report the formation of novel ZIF/PA TFN THEMs based on ZIF-7-X nanoparticles (NPs) with "core-shell" structures and tunable particle sizes, formed from benzimidazole (BIM) ligands and BIM substituted by -NH2, -CH3, -C2H5, and -C3H7 functional groups. The NPs were mixed with pyr omellitic triformyl chloride (TMC) in the organic phase during the interface polymerization process to form ZIF/PA TFN membranes. The total heat exchange performance of ZIF/PA TFN membranes could be effectively modified by the type and quantity of ZIF-7-X NPs added. The CO2 barrier properties and water vapor permeability of ZIF/PA TFN membranes could be improved by the addition of optimal levels of ZIF-7-X NPs, showing low CO2 permeance of 7.76 GPU, high H2O permeance of 663.8 GPU, and excellent enthalpy exchange efficiency of 72.1%. This work provided an effective strategy for tuning not only the nanostructures of ZIF-7 fillers but also the CO2 barrier properties of the formed ZIF/PA TFN membranes.

Generation of Nano-Bubbles by NaHCO3 for Improving the FO Membrane Performance.

Thin-film composite (TFC) polyamide membranes have a wide range of applications in forward osmosis, but tuning the water flux remains a significant challenge due to concentration polarization. The generation of nano-sized voids within the polyamide rejection layer can change the roughness of the membrane. In this experiment, the micro-nano structure of the PA rejection layer was adjusted by adding sodium bicarbonate to the aqueous phase to generate nano-bubbles, and the changes of its roughness with the addition of sodium bicarbonate were systematically demonstrated. With the enhanced nano-bubbles, more and more blade-like and band-like features appeared on the PA layer, which could effectively reduce the reverse solute flux of the PA layer and improve the salt rejection of the FO membrane. The increase in roughness raised the area of the membrane surface, which led to a larger area for concentration polarization and reduced the water flux. This experiment demonstrated the variation of roughness and water flux, providing an effective idea for the preparation of high-performance FO membranes.

C-shaped porous polypropylene fibers for rapid oil absorption and effective on-line oil spillage monitoring.

Development of efficient absorbent materials for detection and treatment of offshore oil spillages remained a challenge. In this work, C-shaped polypropylene oil-absorbent fibers with sub-micron internal pores were prepared by combining spun-bonding technique and thermally induced phase separation (TIPS). The effect of drawing speed on the phase separation and the porous morphology of the shaped fiber non-woven fabric (NWF) was investigated. C-shaped NWF with porous morphology had large water contact angle, higher porosity, larger specific surface area, and increased oil absorption speed and capacity. An online oil spillage detection system was developed using porous C-shaped NWF and an oxygen sensing probe, showing shorter response time and higher signal-to-noise (STN) ratio. The response time for detecting the spillage of soybean oil and diluted crude oil (0.5 mL/0.8 L) in water were only 24 s and 10 s, respectively. The reliable oil detection low detection limit (RLDL) of the oxygen sensing probe was reduced 173 times (from 36.5 g/L to 0.21 g/L) when combined with C-shaped porous fiber NWF.

Incorporating Ag@RF core-shell nanomaterials into the thin film nanocomposite membrane to improve permeability and long-term antibacterial properties for nanofiltration.

Ag@resorcinol-formaldehyde resin (Ag@RF) core-shell nanomaterials were prepared by Stöber method, and introduced into polyamide (PA) selective layer of thin-film nanocomposite (TFN) membranes through the interfacial polymerization (IP) process. Due to the abundant hydroxyl groups on the surface and suitable particle size, Ag@RF nanoparticles (Ag@RFs) could be uniformly dispersed in the piperazine aqueous solution and participate in the IP process to precisely regulate the microstructure of the PA selective layer. The resulting "crater structure" and irregular granular structure enlarged the permeable area and contributed to the surface hydrophilicity. For the nanofiltration application, the water flux of TFN membrane modified by Ag@RFs to Na2SO4 solution reached 150 L·m-2·h-1 which was 87.5% greater than TFC, and salt rejection was maintained. The antibacterial efficiency of the prepared TFN membrane on E. coli reached 99.6% in the antibacterial experiment. In addition, due to the special structure of Ag@RFs, the TFN membrane also showed an expected slow-release capability of Ag+, allowing for long-term anti-biofouling properties. This work demonstrates that Ag@RF core-shell nanoparticles with high compatibility of organic nanoparticles and antibacterial properties of Ag nanoparticles could be used as promising nanofillers for designing functional nanofiltration TFN membranes.

Functionalized MOF-Derived Nanoporous Carbon as Compatible Nanofiller to Fabricate Defect-Free PDMS-Based Mixed Matrix Pervaporation Membranes.

Metal-organic framework (MOF)-based polydimethylsiloxane mixed matrix membranes applied for alcohol recovery with high permeability and selectivity are drawing more and more attention. However, the design and fabrication of high-quality and stable MOF-based mixed matrix membrane for pervaporation are still a big challenge. Herein, PDMS functionalized MOF-derived nanoporous carbon (P-ZNC) was first explored as compatible nanofiller to mutually blend with polydimethylsiloxane on PVDF substrate to fabricate defect-free mixed matrix membranes via dip-coating and thermal cross-linkng. Induced by UV illumination, hydrophobic modification of MOF-derived nanoporous carbon was successfully realized under mild conditions within one step, simplifying the operation step. By using this facile strategy, we can not only solve the existing problem of agglomeration, but also covalently cross-link MOF derivative with polymeric matrix and effectively eliminate the interface defect between polymer and nanoparticles without any extra steps. The method also gives a good level of generality for the synthesis of versatile stable nanoporous MOF-derived carbon-based mixed matrix membranes on various supports. The prepared PDMS/P-ZNC with commendable structures possessed excellent separation performance in low concentration n-butanol recovery and had a good balance between permeance, selectivity, and stability.

The Intrinsic Parameters of the Polyamide Nanofilm in Thin-Film Composite Reverse Osmosis (TFC-RO) Membranes: The Impact of Monomer Concentration.

The realistic resistance zone of water and salt molecules to transport across a TFC-RO membrane is the topmost polyamide nanofilm. The existence of hollow voids in the fully aromatic polyamide (PA) film gives its surface ridge-and-valley morphologies, which confuses the comprehensions of the definition of the PA thickness. The hollow voids, however, neither participate in salt-water separation nor hinder water penetrating. In this paper, the influence of intrinsic thickness (single wall thickness) of the PA layer on water permeability was studied by adjusting the concentration of reacting monomers. It confirms that the true permeation resistance of water molecules originates from the intrinsic thickness portion of the membrane. The experimental results show that the water permeability constant decreases from 3.15 ± 0.02 to 2.74 ± 0.10 L·m-2·h-1·bar-1 when the intrinsic thickness of the membrane increases by 9 nm. The defects on the film surface generate when the higher concentration of MPD is matched with the relatively low concentration of TMC. In addition, the role of MPD and TMC in the micro-structure of the PA membrane was discussed, which may provide a new way for the preparation of high permeability and high selectivity composite reverse osmosis membranes.

Ultra-low pressure PES ultrafiltration membrane with high-flux and enhanced anti-oil-fouling properties prepared via in-situ polycondensation of polyamic acid.

Polyamic acid (PAA) is a flexible polymer and has abundant valuable hydrophilic groups. Herein, we developed an ultra-low pressure ultrafiltration (UF) membrane by integrating PAA into the polyethersulfone (PES) matrix via the "in-situ polycondensation" method. PAA was well compatible with PES and distributed uniformly in the membrane. The introduction of PAA improved membrane hydrophilicity. Meanwhile, the membrane pore structures were also refined. The membrane exhibited an excellent permeability under ultra-low pressure due to its improvement of hydrophilicity and pore structures. Under 0.3 bar, compare with the water flux of PES membrane, PES/PAA membrane improved nearly 2 times (571.05 L/(m2·h)), with a high BSA rejection (≥90%). Even under a lower pressure, 0.1 bar, >300 L/(m2·h) still can be achieved. Interestingly, the membrane we developed could maintain a high performance after drying, and then is very suitable for dry preservation. PES/PAA membrane showed a high oil removal (≥92%) and could remove oil from water effectively. Besides, the membrane exhibited excellent anti-oil-fouling properties. The flux recovery rate of PES/PAA (70.0%) far exceeds that of PES (37.9%) after three filtration and cleaning cycles. The membrane we developed is very valuable in oily wastewater treatment.

Antibacterial polyvinyl alcohol nanofiltration membrane incorporated with Cu(OH)2 nanowires for dye/salt wastewater treatment.

In many important industries, such as the textile printing industry, a large amount of dye/salt wastewater is often discharged, which can destroy the ecological environment of the water body. Membrane technology has a great potential in the treatment of environmental problems caused by dye/salt wastewater. Polyvinyl alcohol (PVA) nanofiltration (NF) membrane has a bright future in dye/salt wastewater treatment, however, works on this are rare. Herein, antibacterial PVA NF membrane incorporated with Cu(OH)2 nanowires for the dye/salt wastewater treatment is reported. The membrane was prepared via coating the solutions containing PVA, glutaraldehyde and Cu(OH)2 nanowires on the polyethersulfone ultrafiltration membrane. Cu(OH)2 nanowires has a diameter of 60 nm and was successfully introduced into the membrane. The introduction of nanowires improved the membrane hydrophilicity and roughness, which is conducive to the improvement of membrane flux. Membrane separation performance for one component solution and dye/salt solution were investigated. The introduction of Cu(OH)2 increases the flux of the membrane obviously (the highest increase is 178.78% (from 21.49 to 38.42 L·m-2·h-1·bar-1, for NaCl solution as the feed). Besides, the membrane doped with nanowires also possessed a high dye/salt selectivity. For one component solution, the dye removal rate was over 97.00% while the salt rejection was low (the lowest was 13.18% (NaCl)). For the dye/salt solution, the dye (Congo Red) rejection kept at a high level (98.91%) and the salt (NaCl) rejection was still low (13.71%), while the flux was also high (37.56 L·m-2·h-1·bar-1). The performance is superior to that of many membranes reported in previous works. Moreover, the Cu(OH)2 nanowires endowed the membrane with an improved and high antibacterial property. The sterilization rate of Escherichia coli and Staphylococcus aureus reached more than 99.99%.