A method for preparing a highly oriented layered composite thin film

Abstract

This invention belongs to the field of composite film preparation and discloses a method for preparing a highly oriented layered composite film. A self-made preparation apparatus is used, including a rectangular base, a horizontal cylindrical mold, and a heating control system. Left-right oriented strip guide rails are provided on the top surfaces of the front and rear sides of the base, and an adjustable-speed motor is fixedly mounted on the top surface of the right side of the base. A slider is provided on the outer side of each guide rail, and a limiting block is provided at the upper end of the slider. A mounting plate is fixed between the two limiting blocks, and a mounting seat is provided on the mounting plate. The mold is located directly above the base, and both ends of the mold are detachably equipped with end caps. Ventilation holes are provided on the end caps, and a horizontal support shaft is fixed at the center of each end cap, rotatably connected to the mounting seat and respectively connected to the output shaft of the adjustable-speed motor. This invention can produce highly oriented, densely stacked layered composite films.

Description

Technical Field

[0001] This invention belongs to the field of composite film preparation technology, and specifically relates to a method for preparing a highly oriented layered composite film. Background Technology

[0002] In recent years, biomimetic layered composite films derived from the layered structure of seashells have become an important research direction in multiple disciplines such as materials science, chemistry, and life sciences. Among them, lightweight, high-strength, and high-toughness layered composite films based on seashell biomimetic fabrication exhibit excellent mechanical properties with their multi-scale, multi-level "brick-and-mortar" stacked structure. Highly oriented and densely stacked low-dimensional functional fillers also enable biomimetic layered composite films to possess excellent electron / phonon transport characteristics. However, composite films prepared by traditional film-forming processes, such as vacuum-assisted filtration, evaporation-induced self-assembly, blade coating, and hot pressing, often suffer from low orientation and non-dense stacking. Therefore, there is an urgent need to develop a method for preparing highly oriented, densely stacked layered composite films. Summary of the Invention

[0003] In view of the problems of low orientation and non-dense stacking in the preparation process of layered composite films in the prior art, the purpose of this invention is to provide a method for preparing highly oriented and densely stacked layered composite films.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for preparing a highly oriented layered composite thin film, characterized in that: a self-made preparation device is used, the preparation device including a rectangular base, a horizontal cylindrical mold and a heating control system;

[0006] A left-right strip guide rail is fixed on each of the top surfaces of the front and rear sides of the base, and an adjustable speed motor is fixed in the middle of the top surface of the right side of the base.

[0007] Each of the two guide rails has a slider slidably connected to its outer side. A limit block is fixedly connected to the upper end of the slider. A mounting plate is fixedly connected between the two limit blocks in a front-back direction. A mounting seat is fixedly connected to the middle position of the mounting plate.

[0008] The mold is located directly above the base between two guide rails. The mold has detachable end caps at both ends, and several ventilation holes are evenly distributed on the end caps. A horizontal support shaft is fixed at the center of each end cap, and the right horizontal support shaft is connected to the output shaft of the adjustable speed motor, while the left horizontal support shaft is rotatably connected to the mounting base.

[0009] The heating control system includes a heating device, a thermocouple, and a temperature controller. The heating device is located directly above, below, in front of, or behind the mold. The working end of the thermocouple probe is located near the heated surface of the outer wall of the mold. The thermocouple and the heating device are respectively connected to the temperature controller, which is placed in an unoccupied position on the outer periphery of the base.

[0010] The preparation steps are as follows:

[0011] (1) Loosen the limiting bolts on the two limiting blocks and pull them out of the limiting holes. Then, remove the connection between the left horizontal support shaft and the mounting base. Slide the two sliders to the left so that the left horizontal support shaft comes off the mounting base.

[0012] (2) Remove the left end cap of the mold and attach a layer of polymer release film to the inner wall of the mold;

[0013] (3) Weigh the polymer and layered filler according to the required ratio of the target product layered composite film, add solvent to prepare a polymer / filler dispersion system to ensure that the polymer concentration is 1~10 wt%, and add the polymer / filler dispersion system into the mold;

[0014] (4) Install the left end cover of the mold, slide the two sliders to the right, insert the limit bolts on the two limit blocks into the limit holes and tighten them, and at the same time rotate the left horizontal support shaft to the mounting base.

[0015] (5) Start the adjustable speed motor and adjust the speed to 1000~6000 rpm. At the same time, start the temperature controller and set the temperature that can evaporate the solvent in the polymer / filler dispersion system. The heating device starts to heat the rotating mold.

[0016] (6) After the mold has rotated for 1 to 6 hours and no more gas is being released from the vent holes on the end cap, turn off the temperature controller and the adjustable speed motor.

[0017] (7) After the temperature of the outer wall of the mold has cooled down to room temperature, repeat the operation of step (1), remove the left end cap of the mold, take out the polymer release film, and peel the layered composite film off the polymer release film.

[0018] Preferably, the polymer is one or more of polyvinyl alcohol, polyethylene, polypropylene, chitosan, cellulose and its derivatives, aramid nanofibers, and polyvinylidene fluoride.

[0019] Preferably, the layered filler is one or more of MXene, graphene, boron nitride, molybdenum sulfide, montmorillonite, kaolin, and mica.

[0020] Preferably, the polymer release film is one of polycarbonate, PPSU, and PI.

[0021] Furthermore, the heating device is an electric heating tube, an infrared radiation lamp, a warm air blower, or an electric furnace. When the heating device is an infrared radiation lamp, a warm air blower, or an electric furnace, the heating device is fixed to the top, front side, or rear side of the mold by a fixing device. When the heating device is an electric heating tube, the heating device is fixed to the top or bottom of the mold by a fixing device.

[0022] Preferably, when the heating device is an electric heating tube, the corresponding fixing device is an arc plate. The arc of the arc plate is the same as that of the mold. Several electric heating tubes are fixedly mounted on the inner arc surface of the arc plate parallel to the central axis of the mold. An installation groove is opened on the base directly below the mold, and the arc plate is fixed in the installation groove.

[0023] Furthermore, the mounting groove is a through groove, and a strip plate is fixedly provided at the bottom center of the arc plate along its axis. U-shaped fasteners are fixed on the left and right sides of the strip plate at intervals. The opening of the fastener faces the bottom of the arc plate and its middle part is vertically fixed on the strip plate. The two ends of the fastener are bent outward and fixed to the bottom of the base on both sides of the through groove.

[0024] Furthermore, a first insert is rotatably connected to the top surface of the base on the front side of the through groove. The first insert has a first insertion hole, and the probe of the thermocouple is inserted into the first insertion hole with its working end close to the heated surface of the outer wall of the mold.

[0025] Preferably, a number of limiting holes are provided at intervals on the top surface of both guide rails, and bolt holes are provided on the left or right end of the limiting block. Limiting bolts are provided in the bolt holes, and the limiting bolts are threadedly connected to the limiting holes on the guide rails. This design makes it convenient to limit the position of the slider when it slides to the expected position.

[0026] Preferably, an inverted T-shaped limiting plate is fixed on the top surface of the base at least on the left side of the two guide rails; this design can prevent the slider from sliding out of the guide rail.

[0027] Preferably, the outer side of the cylindrical body of the mold is provided with a safety cover that is adapted to the size of the mold. The rear end of the safety cover is hinged to the outer side of the rear end of the base. The front end of the safety cover is respectively fixed with a handle and rotatably connected with a second insert plate. The second insert plate is provided with a second insertion hole. The outer side of the front end of the base is provided with a fixing hole, and the fixing hole and the second insertion hole are fixedly connected by bolts. This design can improve the safety of the device.

[0028] Furthermore, the safety shield is shaped like an arc or a polygon that is adapted to the size of the mold.

[0029] Furthermore, the safety cover is evenly equipped with several heat dissipation holes; this design facilitates the dissipation of mold temperature and increases the safety of the device.

[0030] Furthermore, the left and right ends of the mold are provided with two end covers that are adapted to the size of the two ends of the mold. The two end covers are adapted to the shape of the left and right end faces of the safety cover and are integrally formed with them. The bottom of the two end covers is reserved with space for the guide rail to extend.

[0031] Beneficial effects: The present invention has a simple structure, is easy to operate, and is highly efficient. The high-speed centrifugal motion of the mold can make the liquid or colloidal polymer / filler dispersion system evenly spread on the inner wall of the mold. Due to the density difference of the components of the dispersion system, the filler and polymer molecular chains inside are subjected to outward centrifugal force, which promotes the orderly arrangement and dense stacking of the filler and polymer molecular chains. Attached Figure Description

[0032] Figure 1 : A three-dimensional structural schematic diagram of one embodiment of the preparation device of the present invention (without safety cover, and omitting the heating control system);

[0033] Figure 2 : A schematic diagram of the main structure of one embodiment of the preparation device of the present invention;

[0034] Figure 3 : A top view of one embodiment of the preparation device of the present invention;

[0035] Figure 4 A three-dimensional structural diagram of the arc-shaped plate and the electric heating element in combination;

[0036] Figure 5 A bottom view of the structure where the curved plate is fixed to the base;

[0037] Figure 6 : A three-dimensional structural schematic diagram of the second embodiment of the preparation device of the present invention (with a safety cover, omitting the heating control system).

[0038] Figure 7 : WAXD azimuth integral curves (a, c) and statistical values ​​of FWHM and Hermann orientation factor f for each sample obtained in Examples 1-9 and Comparative Example 1 (b, d).

[0039] The attached figures are labeled as follows: 1-base; 2-mold; 3-guide rail; 4-motor; 5-slider; 6-limiting block; 7-mounting plate; 8-mounting seat; 9-limiting plate; 10-bolt hole; 11-limiting hole; 12-end cover; 13-horizontal support shaft; 14-mounting groove; 15-safety cover; 16-end cover; 17-heat dissipation hole; 18-arc plate; 19-electric heating tube; 20-strip plate; 21-fixing component; 22-first insert; 23-first insertion hole. Detailed Implementation

[0040] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0041] Example 1

[0042] A method for preparing a highly oriented layered composite thin film, using a self-made preparation apparatus, such as... Figures 1-5As shown, the preparation device includes a rectangular base 1, a horizontal cylindrical mold 2, and a heating control system. A left-right oriented strip guide rail 3 is fixedly mounted on each of the front and rear top surfaces of the base 1. An adjustable speed motor 4 is fixedly mounted in the middle of the right top surface of the base 1. Several limiting holes 11 are spaced apart on the top surfaces of the two guide rails 3. A slider 5 is slidably connected to the outer side of each guide rail 3. A limiting block 6 is fixedly connected to the upper end of the slider 5. A bolt hole 10 is opened on the left side of the limiting block 6, and a limiting bolt (not shown) is installed in the bolt hole 10. The limiting bolt is threadedly connected to the limiting hole 11 on the guide rail 3. A mounting plate 7 is fixedly connected between the two limiting blocks 6 in a front-to-back direction, and a mounting base 8 is fixedly connected to the middle position of the mounting plate 7; an inverted T-shaped limiting plate 9 is fixed to the top surface of the base 1 at the left and right ends of the two guide rails 3; the mold 2 is located directly above the base 1 between the two guide rails 3, and the mold 2 is provided with detachable end caps 12 at both ends, with several vent holes (not shown) on the end caps 12. A horizontal support shaft 13 is fixedly provided at the center of each end cap 12, and the right horizontal support shaft 13 is connected to the output shaft of the adjustable speed motor 4, while the left horizontal support shaft 13 is connected to the mounting base 8. Rotary connection; the heating control system includes a heating device, a thermocouple (not shown), and a temperature controller (not shown). The heating device is located directly below the mold 2, and the working end of the thermocouple probe is located near the heated surface of the outer wall of the mold 2. The thermocouple and the heating device are respectively connected to the temperature controller, which is placed in an unoccupied position on the outer periphery of the base 1. The heating device consists of several electric heating tubes 19. An installation groove 14 is provided on the base 1 directly below the mold 2. The installation groove 14 is a through groove, and an arc-shaped plate 18 is fixed in the through groove. The arc of the arc plate 18 is the same as that of the mold 2. The several electric heating tubes 19 are parallel to the mold. The central axis of 2 is fixed on the inner arc surface of the arc plate 18; a strip plate 20 is fixed along its axis at the middle position of the bottom of the arc plate 18, and U-shaped fasteners 21 are fixed on the left and right sides of the strip plate 20 at intervals. The opening of the fastener 21 faces the bottom of the arc plate 18 and its middle part is vertically fixed on the strip plate 20. The two ends of the fastener 21 are bent outward and fixed to the bottom of the base 1 on both sides of the through groove; a first insert 22 is rotatably connected to the top surface of the base 1 on the front side of the through groove. The first insert 22 is provided with a first insertion hole 23. The probe of the thermocouple is inserted into the first insertion hole 23 and its working end is close to the heated surface of the outer wall of the mold 2.

[0043] The preparation steps are as follows:

[0044] (1) Loosen the limiting bolts on the two limiting blocks 6 and pull them out of the limiting hole 11. Then, remove the connection between the left horizontal support shaft 13 and the mounting base 8, and slide the two sliders 5 to the left so that the left horizontal support shaft 13 is removed from the mounting base 8.

[0045] (2) Remove the left end cap 12 of mold 2 and attach a layer of polycarbonate release film to the inner wall of mold 2;

[0046] (3) Weigh 1 g of PVA particles and 1.5 g of Mxene according to the required ratio of the layered composite film of the target product, add water to prepare a polymer / filler dispersion system (PVA concentration is 1 wt%), and add the polymer / filler dispersion system into mold 2;

[0047] (4) Install the left end cover 12 of the upper mold 2, slide the two sliders 5 to the right, insert the limit bolts on the two limit blocks 6 into the limit holes 11 and tighten them, and at the same time rotate the left horizontal support shaft 13 to the mounting base 8.

[0048] (5) Start the adjustable speed motor 4, adjust the speed to 4000 rpm, and start the temperature controller at the same time, set the temperature to 100℃, and the heating device starts to heat the rotating mold 2.

[0049] (6) Under the action of high-speed centrifugal force of mold 2, the polymer / filler dispersion system forms a film on the inner wall of mold 2. While the polymer / filler dispersion system forms a film, the solvent is gradually evaporated due to heat. After mold 2 rotates for 1 hour and the solvent is completely evaporated (no more gas is released from the vent on end cap 12), the temperature controller and adjustable speed motor 4 are turned off.

[0050] (7) After the temperature of the outer wall of mold 2 naturally cools down to room temperature, repeat the operation of step (1), remove the left end cap 12 of mold 2, take out the polymer release film (at this time, the layered composite film is attached to it), peel the layered composite film off the polymer release film, and the sample is recorded as M6P4(1)-4000.

[0051] Example 2

[0052] The difference from Example 1 is that in step (3), the concentration of PVA in the prepared polymer / filler dispersion system is 1.5 wt%; all other aspects are the same as in Example 1.

[0053] The sample obtained in this embodiment is denoted as M6P4(1.5)-4000.

[0054] Example 3

[0055] The difference from Example 1 is that in step (3), the concentration of PVA in the prepared polymer / filler dispersion system is 2 wt%; all other aspects are the same as in Example 1.

[0056] The sample obtained in this embodiment is denoted as M6P4(2)-4000.

[0057] Example 4

[0058] The difference from Example 1 is that in step (3), the concentration of PVA in the prepared polymer / filler dispersion system is 2.5 wt%; all other aspects are the same as in Example 1.

[0059] The sample obtained in this embodiment is denoted as M6P4(2.5)-4000.

[0060] Example 5

[0061] The difference from Example 1 is that in step (3), the concentration of PVA in the prepared polymer / filler dispersion system is 3 wt%; all other aspects are the same as in Example 1.

[0062] The sample obtained in this embodiment is denoted as M6P4(3)-4000.

[0063] Example 6

[0064] The difference from Example 1 is that in step (3), the concentration of PVA in the prepared polymer / filler dispersion system is 2 wt%, and in step (5), the rotation speed is adjusted to 3000 rpm; all other aspects are the same as in Example 1.

[0065] The sample obtained in this embodiment is denoted as M6P4(2)-3000.

[0066] Example 7

[0067] The difference from Example 1 is that in step (3), the concentration of PVA in the prepared polymer / filler dispersion system is 2 wt%, and in step (5), the rotation speed is adjusted to 2000 rpm; all other aspects are the same as in Example 1.

[0068] The sample obtained in this embodiment is denoted as M6P4(2)-2000.

[0069] Example 8

[0070] The difference from Example 1 is that in step (3), the concentration of PVA in the prepared polymer / filler dispersion system is 2 wt%, and in step (5), the rotation speed is adjusted to 1000 rpm; all other aspects are the same as in Example 1.

[0071] The sample obtained in this embodiment is denoted as M6P4(2)-1000.

[0072] Example 9

[0073] The difference from Example 1 is as follows: Figure 6As shown, the outer side of the cylinder of mold 2 is provided with a polygonal safety cover 15 that is adapted to the size of mold 2. The left and right ends of mold 2 are provided with two end covers 16 that are adapted to the size of the two ends of mold 2. The two end covers 16 are adapted to the shape of the left and right end faces of the safety cover 15 and are integrally formed with it. The bottom of the two end covers 16 is reserved with space for the guide rail 3 to extend. Several heat dissipation holes 17 are evenly provided on the safety cover 15. The rear end of the safety cover 15 is hinged to the outer side of the rear end of the base 1. The front end of the safety cover 15 is respectively fixed with a handle (not shown) and rotatably connected with a second insert (not shown). The second insert is provided with a second insertion hole (not shown). The outer side of the front end of the base 1 is provided with a fixing hole (not shown). The fixing hole and the second insertion hole are fixedly connected by bolts.

[0074] Everything else is the same as in Example 1.

[0075] Note: When it is necessary to close the safety cover 15, the operator holds the handle and pushes the safety cover 15 forward to close it. Then, rotate the second insert to align the second socket with the fixing hole and insert the bolt. When it is necessary to open the safety cover 15, remove the bolt and pull it out of the fixing hole and the second socket. Rotate the second insert away from the fixing hole. The operator holds the handle and rotates the safety cover 15 backward until it is fully open.

[0076] Comparative Example 1

[0077] Weigh 1 g of PVA particles and 1.5 g of Mxene, add water to prepare a polymer / filler dispersion system (PVA concentration of 2wt%), and then use a single-pass coating process with a blade height of 800 μm to prepare a composite film with a thickness similar to that of Example 1 as a control sample. The sample is denoted as M6P4(2)-0.

[0078] To evaluate the distribution and arrangement of MXene filler in the composite films obtained in Examples 1-8 and Comparative Example 1, statistical analysis was performed on the WAXD azimuth integral curves, FWHM, and Hermann orientation factor f values ​​for each sample. The results are as follows: Figure 7 As shown. By Figure 7 It can be seen that the f values ​​of the samples obtained in Examples 1-8 are all significantly higher than those of Comparative Example 1, and the f value of Example 3 can reach 0.794, while the f value of Comparative Example 1 is only 0.681. At the same time, the integral curves of the films obtained in Examples 1-8 are all sharper than those of Comparative Example 1, and the FWHM is narrower, indicating that the orientation degree of the layered filler in the composite film obtained by the preparation method provided by the present invention is significantly higher than that of the composite film obtained by the traditional blade coating method, and the filler arrangement is more compact.

Claims

1. A method for preparing a highly oriented layered structure composite film, characterized by: The preparation device comprises a rectangular base, a horizontal cylinder-shaped mold and a heating control system; A left-right strip-shaped guide rail is fixedly arranged on the top surface of each of the front and rear sides of the base, and an adjustable speed motor is fixedly arranged at the middle position of the top surface of the right side of the base; A plurality of limiting holes are arranged on the top surfaces of the two guide rails, and a sliding block is slidably connected to the outer side of each of the two guide rails, a limiting block is fixedly connected to the upper end of the sliding block, a bolt hole is formed in the left side end or the right side end of the limiting block, and a limiting bolt is arranged in the bolt hole and is in threaded connection with the limiting hole on the guide rail; a mounting plate is fixedly connected between the two limiting blocks in the front-rear direction, and a mounting seat is fixedly connected to the middle position of the mounting plate; The mold is located directly above the base between the two guide rails, and end covers are detachably arranged at the two ends of the mold, a plurality of air holes are uniformly arranged on the two end covers, a horizontal support shaft is fixedly arranged at the center position of each of the two end covers, and the right side horizontal support shaft is connected with the output shaft of the adjustable speed motor, and the left side horizontal support shaft is rotatably connected with the mounting seat; The heating control system comprises a heating device, a thermocouple and a temperature controller, the heating device is located directly above, directly below, on the front side or on the rear side of the mold, the working end of the probe of the thermocouple is located at the heated surface close to the outer wall of the mold, and the thermocouple and the heating device are respectively connected to the temperature controller, and the temperature controller is arranged at the idle position of the outer periphery of the base; The preparation steps are as follows: (1) unscrew the limiting bolts on the two limiting blocks and pull them out of the limiting holes, then detach the connection between the left side horizontal support shaft and the mounting seat, slide the two sliding blocks to the left, and make the left side horizontal support shaft come off the mounting seat; (2) detach the left end cover of the mold, and attach a layer of polymeric release film to the inner wall of the mold; (3) according to the required proportion of the layered structure composite film of the target product, the polymer and the layered filler are weighed, a solvent is added to prepare a polymer / filler dispersion system to ensure that the concentration of the polymer is 2 wt%, and the polymer / filler dispersion system is added to the mold; wherein the mass ratio of the polymer and the layered filler is 2:3, the polymer is polyvinyl alcohol, and the layered filler is Mxene; (4) install the left end cover of the mold, slide the two sliding blocks to the right, insert the limiting bolts on the two limiting blocks into the limiting holes and tighten them, and rotatably connect the left side horizontal support shaft to the mounting seat; (5) start the adjustable speed motor, adjust the speed to 4000 rpm, start the temperature controller, set the temperature at which the solvent in the polymer / filler dispersion system can be evaporated, and start heating the rotating mold by the heating device; (6) after the mold rotates for 1-6 hours and it is observed that no gas is volatilized from the air holes on the end cover, the temperature controller and the adjustable speed motor are turned off; (7) after the temperature of the outer wall of the mold decreases to room temperature, repeat the operation of step (1), detach the left end cover of the mold, take out the polymeric release film, and peel off the layered structure composite film from the polymeric release film.

2. The method for preparing a highly oriented layered composite thin film as described in claim 1, characterized in that: The polymeric release film is one of polycarbonate, PPSU and PI.

3. The method for preparing a highly oriented layered composite thin film as described in claim 1, characterized in that: The heating device is an electric heating tube, an infrared radiation baking lamp, a warm air blower or an electric furnace, and when the heating device is an infrared radiation baking lamp, a warm air blower or an electric furnace, the heating device is fixed above, on the front side or on the rear side of the mold by the fixing device, and when the heating device is an electric heating tube, the heating device is fixed above or below the mold by the fixing device.

4. The method for preparing a highly oriented layered composite thin film as described in claim 3, characterized in that: When the heating device is an electric heating tube, the corresponding fixing device is an arc-shaped plate, the arc-shaped plate has an arc corresponding to the mold, and a plurality of electric heating tubes are fixed on the inner arc surface of the arc-shaped plate in parallel to the central axis of the mold; an installation groove is formed in the bottom of the base below the mold, and the arc-shaped plate is fixed in the installation groove.

5. The method for preparing a highly oriented layered composite thin film as described in claim 4, characterized in that: The installation groove is a through groove, a strip-shaped plate is fixed on the bottom of the arc-shaped plate at the middle position along the axis of the arc-shaped plate, U-shaped fixing members are fixed on the left and right sides of the strip-shaped plate, the openings of the fixing members face the bottom of the arc-shaped plate, and the middle portions of the fixing members are fixed perpendicularly on the strip-shaped plate, and the two side ends of the fixing members are bent and fixed on the bottom of the base on the left and right sides of the through groove.

6. The method for preparing a highly oriented layered composite thin film as described in claim 1, characterized in that: The top surface of the base at at least the left side end of the two guide rails is fixed with an inverted T-shaped limiting plate.

7. The method for preparing a highly oriented layered composite thin film as described in claim 1, characterized in that: The cylindrical body of the mold is provided with a safety cover matching the size of the mold, the rear end of the safety cover is hingedly connected to the outer side surface of the rear end of the base, the front end of the safety cover is fixed with a handle and rotatably connected with a second insertion piece, and the second insertion piece is provided with a second insertion hole; a fixing hole is formed in the outer side surface of the front end of the base, and the fixing hole and the second insertion hole are fixedly connected by a bolt.

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